Sudden Acceleration in Vehicles with Mechanical Throttles and Idle
Contents
1. On the other hand once a higher than normal engine speed has occurred in either DRIVE or REVERSE the higher than normal engine speed persists when shifting back into PARK or NEUTRAL and may get even higher when the load on the engine is removed The only way to stop the higher than normal engine speed is to turn off the ignition This leads one to believe that the closed loop idle controller is probably not at fault in causing sudden acceleration However the open loop idle controller requires further consideration The idle speed actuator start up control function is an open loop controller mode which causes the idle speed actuator to go to its maximum open position while the engine is being cranked during engine start up This position provides the air that the engine needs for starting since the mechanically controlled throttle valve is normally closed during engine start up The idle speed actuator opening is then reduced to a smaller value while the controller is in the open loop mode prior to entering the closed loop idle control mode Since this function is used only during engine start up it is unlikely that it could produce a higher than normal engine speed during subsequent engine operation unless the idle actuator happened to stick in the fully open position In this case it would produce a higher than normal idle speed while the vehicle was in PARK which would alert the driver of a dangerous situation For this reason the idle spe2. a The iteration of the control map acts as an incrementer b The load coordinate acts as an accumulator c The two together act as an incrementer accumulator This increment accumulate function will cause an increase in engine speed and engine torque with each iteration leading to a runaway of the engine speed to a speed determined by the maximum IAC opening or sudden acceleration This will happen even though the driver does not have his foot on the accelerator pedal Actual operating point changes every iteration Actual operating point after one controller cycle MAP pressure MAF air flow Engine torque Actual idle speed after one controller cyde Ww 2 g g To e Q one controller cycle Expected air opening at idle Expected operating point at idle p Engine Speed Figure 5 For an engine idling in DRIVE or REVERSE in the open loop idle mode if the gain of the idle air control valve is higher than the gain assumed by the control map and if the idle speed control map has a load coordinate that increases with increasing idle air valve opening then the operating point of the engine changes with each iteration of the control map causing the engine to run away to a speed determined by the maximum IAC opening Looking back at Figure 4 one might conclude that the maximum engine speed achievable during a runaway condition is the speed at which the idle actuator reaches its fully open state or about 300
3. July 2015 caused by a higher gain of the IAC valve due to an incorrect battery voltage compensation coefficient The IAC controller doesn t know the difference between these two sources of increased air flow It only responds to the measured air flow sensed by the MAP or MAF sensor and the engine speed Therefore no diagnostic code is set because there is no way for the MAP or MAF sensor to tell the difference about whether the increased air flow is caused by the mechanically actuated throttle opening or by an increased idle actuator gain 3 Even if a fail safe routine in the ECM were to detect a functional error during sudden acceleration OBD II regulations say that it is not necessary to post a diagnostic code unless the same error occurs a second time This is to eliminate false errors which can occur on a transient basis If the same error does not occur a second time then the pending code is erased Turning the ignition off and then back on again is considered to be the second sample But turning off the ignition off and then back on again causes the ECM to re sample the battery voltage Since the occurrence of a negative voltage spike during A D sampling is a Statistically rare event the likelihood of this same rare event occurring a second time immediately after a first event is practically negligible Therefore a diagnostic code is never set and a pending code is erased whenever the ignition is turned off and then back on again The ignit
4. but showed a high air flow the IAC was at maximum open and the fuel trims went to the maximum rich condition i He thought the cause of the problem was a bad TPS sensor but this would not explain the symptoms he saw in the data logs of a longer pulse width and the trims maxed out It would also not account for the ISC changing randomly or going back to normal after turning the engine off and then back on again 5 Comments by brian1703 remarking on a car accelerating on its own He states a J am aware of at least one reported instance of a faulty idle air control valve causing the vehicle to accelerate on its own The specific case I recall involved a Ford Taurus and it happened after the idle air control valve was cleaned Ford doesn t recommend cleaning them maybe that s why b It the IAC valve definitely is not cut out of the circuit above idle Above idle on Ford vehicles it is fully open so that the computer can gradually close it so as to provide smoother deceleration if the driver lifts completely off the gas pedal 6 Volkswagen recall No 24M9 R7 dated May 22 2008 NHTSA Campaign ID Number 08V235000 which states Summary Volkswagen is recalling 4079 MY 2008 Passat and 2500 Tiguan passenger vehicles equipped with 2 0T FSI ULEV II engines These vehicles have an engine control module ECM containing software that may not properly control engine idle with the air conditioning turned on In rare cases
5. impact performance For example if the actual IAC position is greater than expected based on the perceived number of steps then engine run on can be an issue as well as making parking maneuvers more difficult 4 The experiences of a hobbiest engine tuner who reports on a problem with his IAC actuator randomly raising the idle speed to 2K RPM and holding it there He found a It happened intermittently usually when stopped at a light when the RPM s all of a sudden raise up to 2K and never go down b Turning off the engine and turning it back on again caused the problem to go away for a few minutes but then the idle went back up on its own again when the engine is restarted Swapping IAC motors with two new ones did not solve the problem d Tapping on the IAC s while at high idle to see if they were stuck open did not cause the idle to go down e Unplugging the IAC while at high idle caused the engine to stall immediately f Replacing the electronic control module that controls the IAC and its dashpot function did not solve the problem Sudden Acceleration in Vehicles with 10 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 g The normal idle speed is 864 RPM during which the IAC duty cycle was 49 When the idle speed jumped to 2K RPM the IAC duty cycle jumped to 100 h When the idle speed was at 100 data logs showed that the fuel injection pulse width was maxed out the MAF voltage was good
6. the ECM may unexpectedly increase engine RPM Consequence An engine surge caused by an unexpected increase in engine RPM may surprise the vehicle operator and can result in a crash without warning Remedy Dealers will inspect and update the ECM software free of charge We shall now consider what can cause the IAC gain to change D How the IAC Gain Can Exceed the Value Assumed by the IAC Control Map To understand how the IAC gain can exceed the value assumed by the IAC control map one must first understand how an IAC actuator works IAC actuators come in three major types as shown in Figure 7 1 a DC stepper motor 2 a linear solenoid and 3 rotary slide valve type The DC stepper motor type is the most common and is used on most GM and Chrysler vehicles The linear solenoid type is used on most Ford motor company vehicles The rotary slide valve type is used on many Asian and European vehicles but has largely been superseded by the stepper motor type All three types are powered by the 12V DC battery voltage using pulse width modulation PWM to vary the actuator current which causes the IAC valve opening to change in proportion to the PWM duty cycle The proportionality constant between the IAC opening and the PWM duty cycle is called the IAC actuator gain Sudden Acceleration in Vehicles with 11 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 Ignition Battery switch To Extend Valve Reduce Air Bypass T
7. the air fuel ratio becomes too low or too rich thereby causing misfiring and delivery of a large amount of un combusted components into the exhaust system This causes the problem of air contamination Furthermore when secondary air is injected into the exhaust system for the purpose of purifying the exhaust gases combustion of this un combusted component occurs in the exhaust system and causes so called after fire In order to avoid high emission of un combusted components or occurrence of afterfire during deceleration in high speed running it has been proposed to incorporate a throttle control means such as a throttle positioner throttle opener dashpot etc which temporarily increases the idle opening when the throttle valve has been abruptly closed after a long lasting full open condition Again in US patent 4569803 Toyota teaches the following It is generally known the upon engine deceleration a great quantity of hydrocarbon HC and or carbon oxidide sic CO gases are discharged owing to imperfect combustion and misfiring which are caused by a rich air fuel ratio and a lowering of volumetric efficiency Accordingly there have been introduced several kinds of engine deceleration control devices which prevent HC and CO gases from being discharged from the engine In a dashpot device such being one of such devices when a carburetor throttle valve returns to an engine idle speed position upon engine deceleration the return actio
8. your foot on the brake nothing happens besides feeling the normal idle creep of the vehicle in gear Your car is working normally and you are happy Once in a blue moon however something can go wrong Assume for example that you have started your vehicle in PARK or NETURAL The engine speed stays high for a minute or two and then slowly dies down to about 800 RPM Again while the engine is idling normally in PARK or NEUTRAL an Sudden Acceleration in Vehicles with 14 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 A D converter in the ECM takes a 50 microsecond sample of the battery voltage to form a compensation coefficient for actuators which depend on the battery voltage But this time a negative voltage spike occurs during the 50 microsecond sampling time The negative voltage spike is caused by some electric motor turning on like the air conditioner compressor or a radiator fan which causes practically a dead short across the battery for a very short time like 100 microseconds The chance of this negative voltage spike occurring during the 50 microsecond A D sampling time is about one in a million which seems like it might never occur But the chance is not zero The magnitude of the negative voltage spike may be anywhere between one half a volt to several volts depending on the state of charge of your battery after starting your car Therefore the negative voltage spike makes the A D sample voltage read lower than 12
9. 0 6 3 E 3 4 8 100 3 2 1 6 0 o 20 40 60 80 100 Iterations Fig 6 A small IAC gain increase of X can cause a large change in the IAC air opening after many iterations At 10 msec per iteration 100 iterations take only one second It is interesting to consider what would happen if the IAC gain is less than what the IAC control map assumes In this case a lower IAC gain will decrease the manifold pressure or the air mass over what the throttle requests at each iteration causing a progressive movement of the IAC opening to smaller values leading the IAC valve to close completely This will cause the engine to stall The fact that this happens rarely if at all gives us a clue to what can cause the IAC gain to change namely a negative voltage spike Before delving into what can cause the IAC gain to change it is worth citing some references which support the previous discussion These references include 1 The author s previous paper which explains that a higher throttle gain is responsible for sudden acceleration in vehicles with electronic throttles 2 The author s previous paper which explains that a higher electric motor gain is responsible for sudden acceleration in a passenger vehicle with electric traction motors 3 Visteon patent no 7191755 which states Other modes such as dashpot mode operate entirely using an open loop where any error in the IAC position will significantly
10. 0 RPM However engine speeds of 6000 to 7000 RPM have been reported by some drivers during sudden acceleration incidents It is not known at this time how such high engine speeds can be achieved with the throttle closed It is known however that in some turbocharged engines the boost pressure can continue to increase while the throttle opening is fixed at its maximum opening as a result of changes in the opening of the wastegate valve Since the wastegate valve is powered from the 12V battery supply by a PWM signal it is likely that this PWM voltage must be compensated for changes in battery voltage If Sudden Acceleration in Vehicles with 8 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 so then the wastegate PWM control input might be increased by the same A D sample of the battery voltage that that increases the gain of the IAC valve which could explain the higher engine speeds One should not dismiss these reports of higher engine speeds until all possibilities for explanation have been exhausted One more thing happens as the IAC control map is being stepped through on each iteration It is known that the engine torque increases with engine speed as the throttle opening gets larger until some maximum is reached and then the torque begins to decrease at still higher engine speeds This produces a negative slope on the torque versus engine speed characteristic which causes an engine at a high engine speed to increase its torq
11. 6 volts say 12 0 volts instead of the normal DC voltage of 12 6 volts In this case the compensation coefficient that results is larger than unity Normally if this compensation coefficient results from a low DC voltage without a spike and is applied to the idle actuator valve when the DC battery voltage is at the same low voltage then the gain of the IAC valve which decreases with a lower DC battery voltage is brought back up to the normal gain once more However in this case when the lower A D sample voltage is caused by a negative voltage spike then the larger than unity compensation coefficient is applied to the normal idle actuator gain associated with the normal DC voltage of 12 6 volts This causes the gain of the IAC valve to become higher than normal While the engine continues to idle in the PARK or NEUTRAL state this causes no observable change in the engine speed because the idle controller in the PARK or NEUTRAL state is a closed loop idle controller which merely re adjusts itself to maintain the normal idle speed of 800 RPM However the engine is running in a non equililbrium state The snowball has been placed on top of the hill Assume now that you place your foot on the brake and shift the car into either DRIVE or REVERSE This changes the idle speed controller from a closed loop controller to an open loop controller that is much more sensitive to the gain of the idle actuator Unbeknownst to you this gives the snowba
12. AF sensor provided a much more accurate load sensor but one which had a relatively slow response Therefore a manifold air pressure sensor MAP was retained along with the MAF sensor because the MAP sensor is faster although not as accurate More recently torque based engine management systems have become commonplace with either engine torque Te or wheel torque Tw used to represent the engine load The use of torque as a load indicator simplifies the design of the engine management system But the torque is still computed from the air charge which is a function of either the MAF or MAP sensors Therefore the idle valve control operation in torque based engine management systems is very similar to idle valve control operation in speed density engine management systems and air mass engine management systems Table 1 shows that a All the maps for an engine management system have load on one axis and engine speed on the other axis b Ifa vehicle has an idle air control actuator and no MAP sensor or MAF sensor then the vehicle has an alpha N engine control system and the map that controls the idle actuator has coordinates of TPS vs Ne c Ifa vehicle has an idle air control actuator and MAP sensor then the vehicle has a speed density engine control system and the map that controls the idle actuator has coordinates of MAP vs Ne d Ifa vehicle has an idle air control actuator and MAF sensor then the vehicle has a mass air flow engine co
13. Actuator current control Motor current controlled by PWM Motor current controlled by PWM Actuator position sensor Most IAC s have no position sensor Redundant throttle position sensors Parasitic effects Motor current proportional to 1 Battery voltage 2 Actuator resistance and temperature Motor current proportional to 1 Battery voltage 2 Actuator resistance and temperature Elimination of parasitic effects Controller compensates for 1 Battery voltage variation 2 Actuator temperature variation Controller compensates for 1 Battery voltage variation 2 Actuator temperature variation Control approach Two levels of control 1 PID closed loop controller for inner loop actuator control 2 Feed forward function based controller for outer loop Two levels of control 1 PID closed loop controller for inner loop actuator control 2 Feed forward function based controller for outer loop Feed forward controller functions Feed forward controller iteration time Start up air control Fast warm up idle Closed loop curb idle Open loop running idle Idle ups on load change Throttle follower opening dashpot return 7 Idle speed changes with engine and vehicle speed Digital controller adjusts air opening approx every 10 msec NNnNBWN Start up air control Fast warm up idle Closed loop curb idle Open loop running idle Idle ups on load change Throttle opening da
14. M7 System without ETC To create this Sudden Acceleration in Vehicles with 20 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 conventional or basic system without ETC the cylinder charge control has to be limited to the operating range of the idle speed actuator Due to the fact that there is a fixed mechanical link between the pedal and the throttle position the throttle position represents the driver s request With the help of these major supplements the M7 system for vehicles with idle speed actuators was derived from the ME7 system for vehicles with electronic throttles very easily and in a very short development time Words in parentheses have been added to clarify the meaning Sudden Acceleration in Vehicles with 21 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015
15. PH when the accelerator has been released and the engine speed is back down to idle This means that the same battery voltage compensation coefficient is used for a prolonged time on the order of minutes to hours N 3 Once in a while a negative voltage spike can occur while the battery voltage is being sampled causing an incorrect battery voltage coefficient that increases the IAC gain This precipitates a sudden acceleration Once in a while something can go wrong with the A D converter sampling operation This is because there are negative voltage spikes on the battery supply line and if one of these spikes occurs during the A D sampling operation then the A D converter will read a voltage that is lower than the true DC supply voltage If this happens the resulting compensation coefficient will be larger than unity causing the AC Note3 The torque converter on a vehicle with an automatic transmission always transmits torque while the gears are engaged in either DRIVE or REVERSE The only time it does not transmit torque is when the transmission is in either PARK or NEUTRAL http www off road com atv tech hondas torque converter how it works 2003 honda rincon 21514 html This means that creep is caused by the engine idle speed and raising the engine idle speed while in either DRIVE or REVERSE will increase the engine torque and cause the vehicle to creep faster without pressing on the accelerator pedal Creep is merely slow acc
16. Sudden Acceleration in Vehicles with Mechanical Throttles and Idle Speed Actuators by Ronald A Belt Plymouth MN 55447 1 July 2015 Abstract Between 1983 and 1986 automobile engine designs transitioned from carburetors with mechanical idle and dashpot controls to fuel injection systems with electronic idle and dashpot controls In this same time frame the occasional phenomenon of stuck throttles known to occur with mechanical throttles was accompanied by the new phenomenon of sudden acceleration incidents even though both engine designs used mechanical throttles Auto manufacturers dismissed the new sudden acceleration incidents as being caused by drivers hitting the gas pedal instead of the brake and they were supported by a controversial 1989 NHTSA study The NHTSA study however looked only at idle actuator operation and did not consider the control functions associated with this actuator In this paper it is shown that a problem can occur in the idle controller operation which causes the idle actuator to suddenly open to its maximum position while the mechanically actuated throttle valve remains closed causing the engine to suddenly operate at about 3000 RPM or more This behavior can explain a large number of observed sudden acceleration incidents occurring between 1983 and 2003 in vehicles having mechanical throttles with digitally controlled idle speed actuators I Introduction When fuel injection systems replaced carburetors in t
17. You claim that it was not your fault but the car s fault and submit a report to the NHTSA If you are fortunate enough to have NHTSA investigate your accident they finally conclude that you put your foot on the accelerator instead of the brake because there is no mechanical defect to explain the accident And if you sue the auto manufacturer in court their defense is that you put your foot on the accelerator instead of the brake The jury nearly always agrees One reason why it is difficult to convince the NHTSA or a jury that the driver is not at fault is that no one has offered a plausible explanation for how the engine can rev up on its own while the driver s foot is on the brake and yet leave no evidence for investigators to find This paper for the first time offers such an explanation It is the same explanation that causes sudden acceleration in vehicles having electronic throttles which was discussed by this author in an earlier paper Clearly if NHTSA and the auto manufacturers would have investigated sudden acceleration more carefully thirty years ago in vehicles with mechanical throttles and idle control valves they would have found this cause and would have avoided the problems we are having today in vehicles with electronic throttles However thirty years ago they chose to blame the driver for the problem and continue to blame the driver yet today And if they do not fix the problem soon we will continue to have the same problem f
18. ators come in three basic types All are powered from the 12 volt supply and all are PWM controlled b Some idle actuators have a return spring which closes the throttle opening on loss of supply voltage but this is intended to simplify control of the actuator rather than to be a fail safe control IV Conclusion It has been shown that the idle speed actuators in 1983 2003 model year cars with sudden acceleration are controlled by a map of idle valve position as a function of intake manifold pressure or intake manifold air flow versus engine speed This means that if the actual the idle valve opening for a given manifold pressure and engine speed is larger than the value contained in the map then a higher manifold pressure and engine speed will result This creates an incrementing function whereby the idle opening is incremented to a larger value each 10 millisecond iteration of the engine control system And since opening the idle valve further increases the manifold pressure and engine speed each increment of manifold pressure and engine speed is accumulated causing the manifold pressure and engine speed to be incremented and accumulated with each iteration of the control system The result is that the manifold pressure and engine speed reach the maximum value in the control map in less than 100 iterations or less than one second which results in a sudden acceleration The reason that the idle valve opening can be larger than ex
19. battery voltage compensation can cause a large change in the AIC air flow after many iterations of the control map At 10 msec per iteration 100 iterations take only one second II Summary of the Complete Mechanism for Sudden Acceleration A Complete mechanism for sudden acceleration in vehicles with mechanical throttles and idle speed actuators This section explains the complete mechanism for sudden acceleration in vehicles with mechanical throttles and idle speed actuators The explanation is provided in the time order that the events occur using a scenario format to make the description more understandable to non technical readers Assume that you have a vehicle with a mechanical throttle and an idle speed actuator or IAC valve Normally after starting your car in PARK or NETURAL the engine speed stays high for a minute or two and then slowly dies down to about 800 RPM While the engine is idling normally in PARK or NEUTRAL an A D converter in the ECM takes a 50 microsecond sample of the battery voltage to form a compensation coefficient for actuators which depend on the battery voltage like the IAC the fuel injectors and the spark dwell Normally this 50 microsecond sample turns out to read 12 6 volts which is the DC voltage of a healthy battery In this case the compensation coefficient becomes unity which means it makes no change to the gain of the idle actuator control valve When you shift the vehicle into DRIVE or REVERSE with
20. created then during the next iteration through the map the same operating point for the idle speed actuator will be selected However if the actuator gain differs from the gain assumed when the map was created then a different map location will be selected on the next iteration This difference in gain is not a problem when a TPS sensor is used as the load sensor because a larger idle actuator gain cannot change the TPS sensor value which is determined only by the accelerator pedal and its linkage Therefore with each map iteration only a small offset of the idle actuator opening relative Sudden Acceleration in Vehicles with 7 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 to the values in the map is produced at all map coordinates and the offsets will not accumulate Such a behavior will not lead to a runaway condition or sudden acceleration with the alpha N control system However if a MAP or MAF sensor is used as the load sensor then a larger idle actuator gain will change the load coordinate by increasing the manifold pressure or the air mass slightly more than what the throttle requests In this case with each map iteration a small offset of the idle actuator response relative to the values in the map is produced at all map coordinates and the offsets will accumulate with successive iterations This will cause a progressive movement of the operating point through the map as shown in Figure 5 In this case we find
21. ed actuator start up function has little potential to be a cause of sudden acceleration The idle speed actuator high idle control function is an open loop controller mode which causes the idle speed actuator to go to its maximum open position while the engine temperature is below its normal operating temperature This causes the engine to heat up faster allowing the engine to stabilize faster at its normal idle As the operating temperature rises to its normal level the idle actuator opening is reduced to a smaller value while still in the open loop mode Once the engine temperature stabilizes near the normal value control enters the closed loop idle control mode This function is normally used only after engine start up while the vehicle is in PARK Therefore it is unlikely that it could produce a higher than normal engine speed during subsequent engine operation unless the idle actuator happens to stick in the fully open position In this case it would produce a higher than normal idle speed while the vehicle was in PARK which would alert the driver of a dangerous situation For this reason the idle speed actuator high idle function has little potential to be a cause of sudden acceleration The idle speed actuator cracker control function is an open loop controller mode which causes the throttle to be cracked open slightly by small amounts as a function of vehicle speed above some fixed actuation speed in the range of 2 to 4 MPH Below this
22. eleration with the accelerator pedal released Note4 Auto manufacturers prefer not to reveal that battery voltage compensation of the IAC valve gain is performed or the details of when the battery voltage is sampled and how often it is sampled However the manufacturers of several after market engine management systems or ECM s have mentioned that their products incorporate this function 7 Sudden Acceleration in Vehicles with 13 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 gain to increase The probability that a negative voltage spike occurs during A D sampling of the DC battery voltage determines the probability that sudden acceleration occurs because once this happens sudden acceleration is sure to follow as a result of the actuator gain being larger than the IAC gain assumed by the control map It doesn t take much of a voltage spike to cause a sudden acceleration Figure 8 shows how a small negative voltage spike can change the IAC air flow in a short amount of time IAC Air Flow Increase vs Iterations When a Negative Voltage Spike is Sampled During A D Conversion 100 000 Vesrr A D 4 11 4V 10 000 11 6V 1 000 11 8V Multiplier 12 0V 100 12 2V mer 12 4V m 12 6V o 20 40 60 80 100 Iterations Fig 8 A small negative voltage spike occurring during A D sampling of the DC battery voltage to get a Vsarr A D value for
23. essure sensor MAP MAP vs Ne Air mass Manifold mass air sensor MAF MAF vs Ne Engine torque Te Torque Te computed from air charge as a Te vs Ne function of either MAF or MAP Wheel torque Tw Torque Tw computed from air charge as a Tw vs Ne function of either MAF or MAP a Control maps are used for computing all critical engine parameters including fuel injection charge spark angle variable valve timing angle idle actuator position turbo boost pressure etc b All control maps use the same two coordinates with the table values at each coordinate denoting the commands for the critical parameter being controlled c Commands at coordinates lying in between the coordinate values in the map are obtained by 2 dimensional interpolation of the command values at the nearest coordinates The earliest fuel injection engine control systems used alpha N systems with a throttle position sensor TPS serving as the load sensor This system had problems with load estimation at low loads and low engine speeds because the engine load is a function of both throttle opening and manifold pressure After a few years engine management systems were improved to the speed density type with a manifold pressure sensor MAP as the load sensor This system was much better although it was still not ideal Eventually engine management systems were improved again to the mass air flow type with a mass air flow sensor MAF as the load sensor The M
24. he early eighties several functions were changed along with the carburetor 1 Fuel injectors took over the fuel metering function from the Venturi based carburetor 2 An idle speed control function replaced the idle set screw on the carburetor 3 An idle speed actuator idle up control function replaced several discrete air control valves each meant to increase the idle when the engine load increased due to the activation of an accessory such as the air conditioner 4 An idle speed actuator start up control function replaced the mechanically actuated engine start up throttle setting on the carburetor 5 An idle speed actuator high idle control function replaced the wax controlled or bimetallic strip controlled fast idle air bypass valve FITV used to create a high idle for fast engine warm up after starting 6 An idle speed actuator throttle cracker control function replaced the cam operated cracker control function on some vehicles 7 An idle speed actuator throttle follower dashpot control function replaced the mechanical dashpot on the carburetor and 8 An idle speed actuator calibration function was included to reset the actuator to a known state during each ignition on drive cycle While the fuel injector function idle speed control function and idle up functions are often discussed the remaining five idle speed actuator control functions are rarely mentioned The idle speed control function is used to
25. he result is that pushing on the brake seems to increase the acceleration i e torque just like a car in cruise control going up a hill seems to increase the engine acceleration torque because the hill is putting a higher load on the engine The only thing that stops this runaway engine behavior is to turn off the ignition shift into neutral or to crash into some object which puts such high load on the engine that the engine speed is reduced to zero causing the engine to stall But you attention is so consumed by steering the car away from danger that you have little time to turn off the ignition or shift into neutral This explains the high number of parking lot crashes as well as crashes into store fronts houses trees pools lakes rivers and even from high rise parking lots The crash happens while your foot remains the brake The snowball has finished rolling down the hill It has crashed The crash is only the beginning of your nightmare however The police come to investigate and you tell them everything that happened as accurately as you can All you can say is that the engine revved up suddenly while your foot was on the brake Maybe you even explain to the policeman that the engine accelerated a little bit more as you pressed on the brake pedal The policeman smiles kindly and then turns to a reporter and says He she put his her foot on the accelerator instead of the brake However he does not cite you for the accident
26. in normal operation i e without faults in the ACS return to idle must occur within 1 second after release of the accelerator pedal for light vehicles p90 states Response Time When tested in accordance with S6 3 and S6 4 the maximum time to return to idle as indicated by the throttle position or other selected idle state indicant shall be a Not greater than 1 second for vehicles of 4536 kilograms 10 000 pounds or less gross vehicle weight rating GVWR p89 states Idle or idle state means the normal running condition of a vehicle s engine or motor with no faults or malfunctions affecting engine or motor output when there is no input to the driver operated accelerator control Idle state conditions are conditions which influence idle state during normal operation of a vehicle including but not limited to engine temperature air conditioner load emission control state and the use of speed setting devices such as cruise control Idle state indicant means a vehicle operating parameter which varies directly with engine or motor output including throttle position fuel delivery rate air intake rate electric power delivery and creep speed J Gerhardt H Honninger and H Bischof A New Approach to Functional and Software Structure for Engine Management Systems International Congress and Exposition Detroit Michigan February 23 26 1998 SAE Technical Paper No 980801 p 11 This reference states on p11
27. ion is turned off and then back on again after nearly every sudden acceleration incident NHTSA appears to be unfamiliar about how the dashpot function works in vehicles with either idle speed actuators or electronic throttles In their Notice of Proposed Rule Making on brake throttle override dated March 28 2012 they propose maintaining the existing requirement of one second for the idle to return to normal operation after release of the accelerator pedal in light vehicles They define normal idle operation as the normal running condition of a vehicle s engine or motor with no faults or malfunctions affecting engine or motor output when there is no input to the driver operated accelerator control This requirement appears to exclude any dashpot operation which may take longer than one second to return the engine speed to curb idle from any higher engine speed Yet the normal dashpot function in most vehicles takes longer than one second to return the engine to curb idle from a high engine speed This longer settling time results from the auto manufacturer s desire to make deceleration more gradual and to reduce engine emissions Auto manufacturers seemed reluctant to point this out to NHTSA in their responses to NHTSA s proposed rule Apparently they are more concerned about passing the emissions tests in most states than they are about passing the proposed federal regulation on idle speed return Perhaps this is because the federal govern
28. ll a little nudge down the hill What happens next is completely beyond the control of the driver The AC valve is controlled by commands contained in a map or table While your foot is still on the brake on the first iteration through the control map the higher than normal IAC gain causes more air to flow into the engine than the control map expects increasing the engine speed slightly Ten milliseconds later on the second iteration through the control map the higher air flow and higher engine speed cause a different map location to be selected resulting in a command to the IAC valve to increase the air opening just a little bit more But again the higher than normal IAC gain causes more air to flow into the engine than the map expects increasing the engine speed even more With each successive map iteration the IAC valve opens further and the engine speed increases This causes a runaway engine condition which results in the engine revving up suddenly to approximately 3000 RPM or more The time it takes for this to happen is less than one second because each map iteration takes only about 10 milliseconds Therefore in one second about 100 map interations occur which is more than enough to cause the map to be completely traversed The snowball is now rolling down the hill While this takes place your foot remains on the brake You know it is there because you had to put it there to shift out of PARK Now with the engine revving suddenly at it
29. ment i e NHTSA is not aggressive enough in testing new cars for this standard B Comparison of Idle Speed Actuators and Electronic Throttle Actuators The sudden acceleration mechanism for vehicles with mechanical throttles and idle speed actuators is identical to the sudden acceleration mechanism vehicles with electronic throttles This is because idle speed actuators and electronic throttle actuators are similar in many respects Table 2 lists these many similarities A negative voltage spike affects both types of actuators in exactly the same way to cause sudden acceleration The two types of actuators and associated controllers are so similar that Bosch needed to make only minor changes in their ME7 engine management system for vehicles with electronic throttles to derive their M7 engine management system for vehicles with idle actuators Table 2 Idle speed actuators and electronic throttle actuators are very similar in many respects Electronic Idle Speed Actuator Electronic Throttle Actuator Air opening controlled Throttle bypass opening Throttle opening Actuator type Electric motor or solenoid Electric motor Actuator torque multiplier Gears not used on most IAC s Gears Sudden Acceleration in Vehicles with 17 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 Actuator control approach Motor torque proportional to motor current Motor torque proportional to motor current
30. n of the throttle valve is delayed by means of a buffer action of a dashpot Thus the throttle valve gradually returns to the idle position to thereby prevent the occurrence of a rich air fuel ratio and misfiring Operation of the engine without a dashpot function is shown schematically in Figure 1 Manifold pressure increases with engine load as the vehicle accelerates by opening the throttle When the driver releases the accelerator pedal to slow down the throttle opening closes abruptly without a dashpot function causing rapid deceleration due to the abrupt load change vertical transition and high emissions due to running the engine with the throttle closed while fuel is still present on the manifold walls horizontal transition Sudden Acceleration in Vehicles with 3 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 Emissions are increased even further if fuel continues to be injected into the engine cylinders while the throttle is closed Operation of a fuel injected engine with an idle valve dashpot function is shown conceptually in Figure 2 In this case an idle valve controls the air flow in a channel which bypasses the normal throttle opening When the throttle opening increases in response to the driver stepping on the accelerator pedal the idle valve opens in proportion to the increased load on the engine as sensed by the manifold pressure until the idle valve is fully open at some throttle position Above this thr
31. ntrol system and the map that controls the idle actuator has coordinates of MAF vs Ne e Furthermore a speed density engine management system is used whenever an engine has a turbocharger i e whenever the manifold air is under pressure Sudden Acceleration in Vehicles with 6 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 Based on these observations we can deduce that the idle air control actuators in vehicles with MAP or MAF sensors are controlled by a map that has MAP or MAF sensor values on one axis and engine speed on the other axis like the one shown in Figure 4 Maps for all the other critical engine parameters such as fuel injection charge spark angle variable valve timing angle and turbo boost pressure will have the same MAP MAF vs engine speed coordinates but will contain the control positions for those actuators e idleacthator oppnings afeaconstant_ mx mazimumvdluein this region J mew O e ee T ee eee eee r o o o aximumdpening oo Soo Ee ee Em e l o o d a ee E o o doa d E H teactyetoroppunes cp iff o joo engine pad spetedinthif region J J AL S E NT E LLL E kee AEE aE eee Engine Speed RPM Engine Load MAP MAF Figure 4 Map characteristics for the idle air actuator control map in a speed density or mass air engine control system The absolute values of the coordinates may vary from one vehicle to the next Each map location contains the c
32. o Retract Valve Increase Air Bypass Fig 7a1 Stepper motor IAC valve used on many Fig 7a2 Stepper motor drive circuitry GM and Chrysler vehicles Microsteppers commonly use 256 total microsteps gt IAC Valve Ez Vent Filter RSO JL ny n nim IIE Spring ECM Ja Solenoid AIRFLOW AIRFLOW OUTLET INLET Fig 7b1 Linear solenoid IAC valve used on many Fig 7b2 Linear solenoid drive circuitry The Ford motor company vehicles opening force is opposed by a closing spring X 2 S ISC valve LA NAN 4 Su i 5 6 T MP 520400 Fig 7c1 Rotary slide type IAC valve used on Fig 7c2 Rotary slide valve drive circuitry One coil many Asian and European vehicles opens the valve while the second coil closes it Figure 7 IAC valves are of three different types All three are powered from the 12 volt battery supply and all three use PWM to control the air opening 1 IAC gain varies with the battery supply voltage The torques in the stepper motor type IAC valve and the rotary slide type IAC valve and the force in the linear solenoid type IAC valve are proportional to the currents in the coils These currents are controlled by the PWM duty cycle of the waveforms applied to the actuator inputs i e the coil inputs which switch between the 12 volt battery voltage and ground This makes the actuator coil cu
33. olts causing it to creep more while in gear or it will idle slower with a voltage less than 12 volts causing it to possibly stall Since the IAC gain is voltage dependent maintaining this creep rate idle adjustment requires voltage compensation Similarly the idle up needed for maintaining idle speed when the air conditioner turns on thereby increasing the load on the engine also requires voltage compensation Bosch patent number 4580220 shows that battery voltage compensation is used for the idle speed actuator Hewlett Packard patent 6441579 shows that stepper motors must allow for variation of the power supply Battery voltage compensation requires sampling the battery voltage with an A D converter This is done within a minute or so after starting on most vehicles when the battery voltage is at its lowest and the idle speed has stabilized The compensation coefficient is formed by dividing the nominal battery voltage of 12 6 volts by the sampled battery voltage Vg where Vx is the ignition switched value of the DC battery voltage In vehicles with IAC valves this same Vx voltage sample is used to compensate other actuators as well such as the fuel injection pulse width and the spark dwell time It is usually assumed that the battery voltage does not change rapidly with time so the battery voltage is sampled only occasionally such as each time the ignition switch is turned on or after an elapsed time at a higher engine speed such as 30 M
34. ommand for opening the idle speed actuator at those coordinates Commands for coordinates lying in between the coordinate values on the axes are obtained by 2 dimensional interpolation of the parameter values at the four nearest coordinates C How the Idle Speed Actuator Dashpot Function Can Fail to Operate Correctly Now that we have seen how the idle speed actuator is controlled by a map like the one shown in Figure 4 we can determine how the idle speed actuator dashpot control function can fail to operate correctly We are aided in this analysis by the author s previous papers and a 2007 Visteon patent which states Other modes such as dashpot mode operate entirely using an open loop where any error in the IAC position will significantly impact performance For example if the actual IAC position is greater than expected based on the perceived number of steps then engine run on can be an issue as well as making parking maneuvers more difficult With these references as a hint let us look at what can happen if the IAC gain is larger than expected by the idle speed actuator control map Let s assume for example that the vehicle is stationary with the engine at curb idle and the transmission in either DRIVE or REVERSE In this case the idle speed actuator is controlled by an open loop controller with a map like the one shown in Figure 4 If the gain of the idle speed actuator agrees with the gain assumed by the map when the map was
35. on emissions We will see later in this paper that the fuel injector voltage compensation coefficient is also higher than normal because this coefficient is based on the same voltage sample as the IAC compensation coefficient creating an even larger fuel charge and causing the engine to run even richer This rich engine condition explains the observations of some drivers that they could smell gasoline after sudden acceleration The gasoline smell comes from the unburned hydrocarbon emissions produced because there wasn t enough air to burn all the fuel All of these changes take place as a result of the IAC opening i e IAC gain being larger than expected by the IAC control map Figure 6 shows that it does not take much of an IAC gain increase for this to happen because the increase in air flow accumulates with each map iteration For example after 100 iterations the air flow can increase by over 10x with an IAC gain increase of less than 3 Assuming a typical map iteration time of 10 milliseconds this change in engine speed can take place in less than one second This explains why drivers often state that the engine revved up suddenly or that the tachometer jumped suddenly to several thousand RPM Sudden Acceleration in Vehicles with 9 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 IAC Opening Change after N Iterations when IAC IAC Gain Increases by X Gain 100 000 Increase I5 10 000 r 7 9 g 100
36. or another thirty years or more Another reason why it is difficult to convince the NHTSA or a jury that the driver is not at fault is that no diagnostic code is set during a sudden acceleration incident The reason why a diagnostic code is not set during a sudden acceleration by this mechanism is as follows 1 Sudden acceleration is essentially caused by an increase of the curb idle speed while in gear which normally causes a vehicle with an automatic transmission to creep while in either DRIVE or REVERSE If this creep idle speed is increased slightly no diagnostic code will be set Creep is merely slow acceleration Therefore increasing this same idle speed to the engine speed determined by the maximum IAC opening will cause no diagnostic code to be set One company has even stated that it does not check the accelerator pedal position sensor APS or the throttle position sensor TPS while at idle 2 More specifically sudden acceleration is caused by the normal idle actuator dashpot function operating with an increased air flow and engine speed Normally the dashpot function causes the IAC valve to open more as the air flow and engine speed increase as a result of the accelerator pedal opening the throttle valve by a mechanical linkage During sudden acceleration however the air flow and engine speed increase as a result of additional air flow Sudden Acceleration in Vehicles with 16 R Belt Mechanical Throttles and Idle Speed Actuators 1
37. oth engine speed and manifold air flow And while this patent appears to show the idle valve closing only with time some later idle valves close as a function of engine speed while others close as a function of time Since we are most interested in sudden acceleration we will look now into how the IAC valve dashpot opening is actually achieved in most vehicles TPS IAC Ne Figure 3 A Honda patent shows that at low acceleration left the IAC opening follows the throttle opening TPS while at high acceleration right the AC opening follows the engine speed Ne In both cases when the throttle is released the IAC opening decreases slowly with time to zero or to a lower value set by the engine speed This figure shows the general concept of how the IAC dashpot function operates but later IAC designs open as a function of engine speed and manifold pressure or manifold air flow B How the Idle Air Actuator Dashpot Opening Is Controlled In order to assess whether the idle valve dashpot function can cause sudden acceleration we need to know how the idle valve control system works Unfortunately information about the idle air actuator dashpot function and how it is controlled in vehicles with fuel injection systems is rarely discussed by auto manufacturers in their training publications service manuals or the patent literature The dearth of information about this function suggests that auto manufacturers have made a determined effort to kee
38. ottle position an increase in the idle air flow is no longer possible When the driver releases the accelerator pedal to slow down the throttle opening still closes abruptly but the idle valve controlling the bypass air closes more slowly creating a dashpot function which smoothes deceleration and reduces engine emissions Throttle Throttle Open Open High Load High Load o5 v Throttle 5 l 5 Released a a Pas ana Idle Valve 2 g a OF Pre Position a a 25 v Throttle W gr Released 2 Idle Valve E cC zZ Dashpot Function l gt 7 a ee l Throttle ge Throttle ERD 0 E Closed Gin 0 SE Ae Closed Idle No Load Idle No Load Engine Speed Engine Speed Figure 1 With no dashpot the manifold pressure is Figure 2 With a dashpot function in an idle valve high during acceleration but drops abruptly when controller the idle valve opens during acceleration the throttle is released causing rapid deceleration and closes slowly after the throttle is released and high emissions smoothing deceleration and reducing emissions Figure 3 shows idle valve dashpot operation as a function of time as described by a Honda patent The left hand diagram shows the case for low acceleration where the IAC opening increases with throttle opening as sensed by a throttle position sensor TPS When the driver reduces the acceleration level at time t a lower value at time tz the IAC valve closes more slowly
39. p knowledge of this function a closely guarded secret out of the hands of the general public The only reference the author has found to idle air actuator control is from a Toyota training course which states The idle air control program is based on an ECM stored look up table which lists pintle step positions in relation to specific engine RPM values One might think that the only way to learn how the idle air control dashpot function really works is to look at the ECM software of a specific vehicle However it is possible to learn how idle valve control functions work from other sources such as vendors of after market engine management systems and the web sites of engine tuning enthusiasts Based on information learned from these two sources it is possible to deduce how the idle air control valve dashpot function works based on only some very general considerations These considerations are summarized in Table 1 Table 1 shows that engine management systems for fuel injected vehicles come in only a few different types distinguished by how they represent the engine load Sudden Acceleration in Vehicles with 5 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 Table 1 Engine Management Systems for Fuel Injection Systems and Their Characteristics Engine Management Load vs Engine Speed i Sie Poad Sensor Map A TERU ne Alpha N Throttle position sensor TPS TPS vs Ne Speed density Manifold absolute pr
40. pected by the control map is that the battery voltage compensation coefficient used to make the idle opening independent of battery voltage can occasionally become incorrect as a result of a negative voltage spike occurring during the sampling of the DC battery voltage by an A D converter in the ECM This sampling occurs soon after the engine is started and occasionally when the engine has been running above a given engine speed for some elapsed time but has been then returned to idle This means that the same negative voltage spike hypothesis advanced by the author in several earlier papers can explain sudden acceleration not only in all vehicles with electronic throttles from about year 2000 to the present but also in all vehicles with idle air control valves from about 1983 to about 2003 The root cause of sudden acceleration is the same in both types of vehicles This same negative voltage spike hypothesis can also explain all of the observed symptoms that drivers have observed during sudden acceleration incidents The consequences of such a simple hypothesis are so comprehensive that they testify to the validity of the hypothesis in the real world The validity of this hypothesis means that thousands of sudden acceleration incidents occurring after 1983 could have been prevented if the automobile manufacturers and NHTSA had looked more closely into the cause of these incidents when they were first reported instead of brushing aside the complaint
41. r2 20spyder References Technical 20Training 01 20 20Engine 20and 20Engine 20Control 07 pdf 6 R Belt Simulation of Sudden Acceleration in a Torque Based Electronic Throttle Controller January 30 2015 http www autosafety org dr ronald belt 7 E2 80 99s sudden acceleration papers 7R Belt Sudden Unintended Acceleration in an All Electric Vehicle February 27 2015 http www autosafety org dr ronald belt 7 E2 80 99s sudden acceleration papers M K Vint US patent 7191755 Idle Air Control Valve Stepper Motor Initialization Technique Visteon Global Technologies March 20 2007 PoweredByAFR185 on the EEC tuning forum at http eectuning org forums viewtopic php t 20208 amp p 112612 p112313 1 brian 1703 http ths gardenweb com discussions 2265770 car accelerating on its own 5 Volkswagen recall No 24M9 R7 dated May 22 2008 as quoted by Mickey in a comment on February 26 2010 to the article Toyota Unintended Acceleration Hearings Summary http www tundraheadquarters com blog toyota unintended acceleration hearings summar Toyota Engine Control Systems I Course 852 Section 6 p 6 3 Toyota Engine Control Systems I Course 852 Section 6 p 6 8 Gunter Braun Wolfgang Kosak and Alfred Kratt US patent 4580220 Failsafe Emergency Operation Device for Idling Operation in Motor Vehicles Robert Bosch GmbH April 1 1986 columns 2 3 4 C Van Lydegraf S Gothard S Kranz and G Brown C
42. rrents sensitive to Sudden Acceleration in Vehicles with 12 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 variations in the 12 volt battery voltage which changes the applied torques in the stepper motor valve or the rotary slide type valve or the applied force in the linear solenoid type valve Since these applied torques or force cause the valves to open to their desired positions in response to a duty cycle input thereby determining the normal gain of the actuator then changes in these torques or force brought about by changes in the 12 volt battery voltage cause changes in the normal gain of all the actuators Therefore the IAC gain of all three actuators varies with the battery supply voltage 2 IAC gain must be stabilized by compensating the PWM duty cycle for changes in battery voltage Because the IAC gain of all three actuators varies with battery voltage one must compensate the AC gain for voltage changes to maintain a proper idle speed while operating in either DRIVE or REVERSE The in gear idle speed is a fine adjustment which trades off using less air flow to minimize idle creep while using more air flow to reduce the chances of a stall Since this idle function is a feed forward controller function it is adjusted a priori and assumes a specific gain for the idle actuator If the IAC actuator gain changes with battery supply voltage the engine will either idle faster at a voltage higher than 12 v
43. s maximum RPM the vehicle begins to move because it is in either DRIVE or REVERSE Normally when the car is in either DRIVE or REVERSE the car would be creeping slightly But with the engine revving at its maximum RPM the creep becomes a high acceleration The acceleration is high because the engine torque is multiplied by a Note 5 The closed loop idle controller can reduce the engine speed if it gets too high or increase it if it gets too low The open loop idle controller gets no feedback of the engine speed so it does not know if the engine speed gets too high or too low It merely issues an idle command and assumes that the result is what was expected by the design engineer Note6 This sensitivity is why an IAC gain compensation coefficient is needed in the first place because if the IAC gain becomes higher then the engine speed will be made higher than the control map expects causing a higher creep rate at idle If the IAC gain becomes lower then the engine speed will be made lower than the control map expects causing the engine to possibly stall Sudden Acceleration in Vehicles with 15 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 factor of 4 to 5 in either first gear or reverse gear and by another factor of 2 in the torque converter And as you apply the brake harder to control the car the brake puts a higher load on the engine which slows down the engine speed and increases the torque that the engine puts out T
44. s of hundreds of drivers involved in these incidents as being the result of driver confusion by stepping on the accelerator instead of the brake This clearly shows what can happen when an entire industry fails to listen to the voice of the customer and is motivated instead by saving their corporate reputations and profits NHTSA is encouraged to step up to its mandate of making cars safer by testing this hypothesis in vehicles with idle air control valves and electronic throttles Only by such testing and fixing the vehicles if they prove faulty can we prevent another 30 years of sudden acceleration incidents V References K Shinoda US patent 4181104 Idle Speed Controller for Internal Combustion Engines Toyota Jidosha Kogyo Kabushiki January 1 1980 Y Takakura Toyota and K Kitamura US patent 4569803 Dash Pot Device Aisin Seiki Kabushiki Kaisha February 11 1986 Sudden Acceleration in Vehicles with 19 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 gt Y Otobe S Fujimoto and A Kato US Patent 4788954 Method for Controlling By Pass Air Flow on Deceleration of Internal Combustion Engine Honda Giken Kabushiki Kaisha December 6 1988 Figures 1 and 2 are adopted from Figure 6 in this patent to further clarify the concepts Ibid Figure 3 comes from Figure 7 in Honda patent 4788954 Toyota Engine Control Systems I Course 852 Section 6 p 6 7 http www testroete com car Toyota m
45. set the engine idle speed when the accelerator pedal is released It is used in two different ways When the engine is first started idle speed control is done by an open loop or feed forward controller using predetermined ISC actuator openings until the engine is warmed up and the idle speed has stabilized close to the desired idle set point for a fixed amount of time Then if Sudden Acceleration in Vehicles with 1 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 the accelerator pedal is released and the vehicle is in either PARK or NEUTRAL idle speed control is transferred to a closed loop controller which controls the idle speed based on the deviation of the engine speed from a desired idle speed set point e g 8300 RPM This closed loop controller is much more robust When the transmission later is shifted into either DRIVE or REVERSE idle speed control changes from the closed loop controller back to the open loop controller In the open loop case the idle speed control is less precise and idle speed can vary as pre determined adjustments are made in response to changes in the engine load from accessories turning on such as air conditioner compressor clutch engagement or radiator cooling fan turn on It is interesting to note that sudden acceleration incidents frequently occur when shifting the transmission from PARK into either DRIVE or REVERSE but are never associated with high engine speed prior to shifting out of PARK
46. shpot return 7 Idle speed changes with engine and vehicle speed Digital controller adjusts air opening approx every 10 msec Potential defect operation Iteration of IAC actuator gain larger than the calibrated actuator gain causes runaway to engine speed determined by the maximum IAC opening Iteration of ETC actuator gain larger than the calibrated actuator gain causes runaway to the fully open throttle position Control authority Limited authority of bypass air limits engine speed to lt 3000 RPM and vehicle speed to lt 40 mph Full authority of throttle air allows engine speed gt 6000 RPM amp vehicle speed gt 90 mph Fail safe controls Fail safes on idle function 1 Return spring closes idle opening on loss of supply voltage No limits on idle speed Numerous fail safes on throttle function 1 Two springs produce a limp home opening on loss of supply voltage 2 Redundant accelerator and throttle position sensors 3 Limits on throttle torque reduce throttle functionality No limits on idle speed Electronic defects Intermittent shorts in PWM driver 1 Opens in potentiometer type reported transistors produce high idle TPS sensors produce high condition throttle condition 2 Tin whisker shorts in APS Sudden Acceleration in Vehicles with 18 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 sensors produce elevated throttle condition a Idle actu
47. than the throttle closes reaching a new level at time t2 and smoothing the deceleration Later when the driver releases the throttle completely at time ts the throttle drops to zero at time t4 but the IAC valve closes again more slowly reaching curb idle at the later time t In this way deceleration is smoothed and emissions are reduced The right hand diagram of Figure 3 shows the case for high acceleration where the IAC opening increases with throttle opening TPS at first and then increases with engine speed after t until the maximum IAC opening is reached at time t The IAC opening then stays at its maximum until the driver releases the throttle completely at time t7 after which the throttle drops to zero at time tg But the IAC valve closes more slowly than the throttle reaching curb idle at the later time ts Again deceleration is smoothed and emissions are reduced While this Honda figure is good for explaining how a dashpot works in general not all IAC valves operate in exactly the same fashion This Honda patent shows that the IAC opening increases with throttle opening at low acceleration or with throttle opening and engine speed at high acceleration Sudden Acceleration in Vehicles with 4 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 However only the earliest IAC valves opened as a function of the throttle opening Later IAC valves open as a function of both engine speed and manifold pressure or b
48. ue as the engine speed decreases when a load is placed on the engine by the driver applying the brakes This explains why many drivers have complained that stepping on the brakes actually increased the vehicle s acceleration which is a layman s way of saying that the engine torque increased as the engine speed was reduced by the load placed on the engine by the brakes Something else happens during a runaway condition while the IAC control map is being stepped through with each iteration Since the MAP MAF vs Ne coordinates on the IAC map are changing with each iteration this means that the same MAP MAF vs Ne coordinates on all the other engine control maps are also changing causing all the other control maps to be stepped through with each iteration This means a The fuel injection and spark advance maps are being stepped through simultaneously supporting the increase of engine speed and torque caused by the increase of IAC air flow The engine doesn t know that the throttle has not been opened but only that it sees a larger air flow Therefore the engine thinks this larger air flow is caused by the throttle being open and supports the larger air flow with more fuel and an advanced spark b The engine is running richer than normal because it has less air than normal to support the higher engine speed This means that the engine is running in a high speed state but with an air to fuel ratio AFR lower than normal causing higher hydrocarb
49. urrent Magnitude Variation Correction for Operating Stepper Motor Drive Circuit US patent 6441579 August 27 2002 Euro 1EFI Engine Management System User Manual Ole Buhl Racing UK Ltd par 3 15 17 p30 http www obr uk com support_pages Eurol 430 20handboook pdf 7 MegaSquirt Tuner Studio MS Lite Reference MegaSquirt MS2 Extra Firmware Version 3 3 3 Release 2015 04 08 p 124 which states in paragraph 11 13 PWM Idle Voltage Compensation Some 2 wire PWM idle valves will operate differently depending on the system voltage This slows a compensation to be applied for that difference Typically at lower voltages the valve will need slightly more duty positive number and at higher voltages it will need less duty negative number S Volkswagen Audi Vehicle Communication Software Manual EAZ0031B01E Rev A August 2013 p 72 Available from https www1 snapon com Files Diagnostics UserManuals VolkswagenAudi VehicleCommunicationSoftwareManual_EAZ0031B01D pdf 1 Notice of proposed rulemaking NPRM on electronic throttle ETC failure modes and test procedures and on brake throttle override BTO as part of 49 CFR Part 571 Docket No NHTSA 2012 0038 Federal Motor Vehicle Safety Standards Accelerator Control Systems published in the Federal Register Vol 77 No 73 Monday April 16 2012 Proposed Rules p 22638 P59 states Response Time for Normal Operation This proposal maintains the existing requirement that
50. vehicle speed the vehicle is assumed to be stationary and the cracker throttle opening is set to zero Since the cracker openings are so small at any given vehicle speed the cracker function has little potential to be a cause of sudden acceleration An idle speed actuator dashpot control function is an open loop controller mode which causes the engine speed to return slowly to the curb idle position when the driver s foot is removed from the accelerator Notel If the engine RPM was abnormally high while in PARK most drivers would recognize the unusual mode of engine operation and would avoid shifting out of PARK Note2 The idle speed actuator opening controls the amount of air that is bypassed around the mechanical throttle valve Sudden Acceleration in Vehicles with 2 R Belt Mechanical Throttles and Idle Speed Actuators 1 July 2015 while driving at any higher engine speed This function is required because removing one s foot from the accelerator pedal causes the mechanically controlled throttle valve to close immediately producing an abrupt deceleration that is very disturbing to the vehicle s occupants The sudden loss of air through the throttle also causes the engine to run richer than normal which increases hydrocarbon emissions Therefore a dashpot function is required not only to slow down the rate of deceleration but also to satisfy OBD I emission regulations And because it must operate to slow down vehicle deceleration from an
51. y higher engine speed the idle speed actuator opening must increase with engine speed before deceleration occurs In fact the idle speed actuator opens all the way from nearly zero at curb idle to fully open at normal engine cruising speeds This capability of the idle speed actuator to open further with increasing engine speed gives it a high potential for causing sudden acceleration It is interesting that the idle speed actuator dashpot function is rarely discussed by automobile manufacturers and was never discussed in NHTSA s 1989 Silver Book report Further discussion of this function is provided in the following section II Idle Speed Actuator Dashpot Operation First we will explain how the idle speed actuator is supposed to work during dashpot operation Then we will explain how it can fail to operate like it is supposed to A How the Dashpot is Supposed to Work In US patent 4181104 Toyota teaches why a dashpot is needed In automobile engines if the throttle valve is abruptly closed to the idle position by full release of the accelerator pedal while the engine is running at relatively high speed a high manifold vacuum is caused in the intake system of the engine whereby liquid fuel droplets attached to the inner wall of the intake passage violently evaporate and a large amount of fuel is drawn into the cylinders of the engine On the other hand since the flow of intake air is reduced by the closing of the throttle valve
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