BENDIX SD-13-4793 User's Manual
Contents
1. EXHAUST SOLENOID 2 po EH BRAKE VALVE SUPPLY SOLENOID SUPPLY CHAMBER DIAPHRAGM SPRING FIGURE 6 M 21 M 22 MODULATOR NON ANTILOCK EXHAUST OF SERVICE BRAKES RAPID ANTILOCK EXHAUST FIGURE 7 When wheel lock is detected or imminent the antilock controller simultaneously energizes both the supply and exhaust solenoids in the modulator Energizing the supply solenoid causes its exhaust to close and inlet to open With the inlet of the supply solenoid open application air is permitted to flow to the control side of the supply diaphragm Air pressure acting on the supply diaphragm causes it to close the supply and prevent further delivery of air to the brake chamber Energizing the exhaust solenoid closes its inlet and opens its exhaust By closing the exhaust solenoid inlet application airis prevented from flowing to the control side ofthe exhaust diaphragm Air pressure which was present on the control side of the exhaust diaphragm flows out the exhaust port of the modulator With control air pressure removed from the exhaust diaphragm brake application air forces the exhaust diaphragm to unseat which allows it to flow out the modulator exhaust port The modulator will remain in the antilock exhaust mode until the antilock controller senses that wheel speed has increased The modulator can enter the antilock hold or re apply mode from the antilock exhaust mode ANTILOCK2. ms gt BRAKE VALVE SUPPLY SOLENOID KE BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING SPRING FIGURE 5 M 21 M 22 MODULATOR NON ANTILOCK EXHAUST OF SERVICE BRAKES NORMAL NON ANTILOCK EXHAUST The manner in which air exhausts through the modulator differs depending upon how rapidly the brake application is released by the driver Normal Exhaust Figure 5 During a normal relatively slow brake release air moves back through the modulator in the reverse direction as it flowed during application The internal components of the modulator will remain in the same position as they assumed during application until air pressure decreases to approximately one half psi at which time the supply diaphragm will seat on the supply passage Air will generally not be expelled from the modulator exhaust port during normal brake release Rapid Exhaust Figure 6 The rapid exhaust operation described in the following text only occurs when the modulator is controlling two type 30 or larger service chambers During a very rapid brake release the modulator will exhaust air in a different manner An example of this would be the case if the driver made a severe brake application then lifted his foot from the foot valve During a rapid brake release air from the exhaust diaphragm flows back through the open exhaust solenoid and to the application device s exhaust With pressure removed from the control side
3. HOLD The antilock controller will place the modulator in the hold position when it senses that the correct wheel speed braking force has been attained The antilock controller will also place the modulator in the hold position prior to entering the re apply when it detects recovery from a locked wheel condition In this mode of operation the modulator supply solenoid remains energized while the exhaust solenoid is de energized De energizing the exhaust solenoid opens its inlet and closes its exhaust Opening the exhaust solenoid inlet allows application air to flow to the control side of the exhaust diaphragm which then seals the exhaust passage With the exhaust diaphragm seated further exhaust of brake chamber air pressure is prevented Because the supply solenoid remains energized the supply diaphragm remains seated thus preventing application air from flowing to the delivery port and out to the brake chamber The modulator can enter the antilock exhaust or re apply mode from the antilock hold mode EXHAUST DIAPHRAGM EXHAUST SOLENOID YY EXHAUST e Il milli 2 IL Ss ae BRAKE VALVE SUPPLY SOLENOID O BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING SPRING FIGURE 7 M 21 M 22 MODULATOR ANTILOCK EXHAUST OF BRAKES ANTILOCK RE APPLY If the antilock controller senses that wheel speed has increased sufficiently to
4. SOLENOID CONNECTOR DELIVERY SUPPLY CAST IN ID 1 MOUNTING HOLES DELIVERY CAST IN ID 2 EXHAUST CAST IN ID 3 SUPPLY DELIVERY CAST IN ID 1 SOLENOID CONNECTOR MOUNTING HOLES EXHAUST CAST IN ID 3 M 21 MODULATOR FIGURE 1 M 21 AND M 22 MODULATOR DESCRIPTION There are two Bendix antilock modulators available from Bendix Commercial Vehicle Systems LLC the older M 21 modulator and the newer M 22 modulator Both are functionally the same The M 21 and M 22 antilock system modulators Figure 1 are essentially high capacity on off air valves that incorporate a pair of electrical solenoids for control The solenoids provide the electro pneumatic interface or link between the antilock controller electronics and the air brake system The modulator can be used to control the braking function on an individual wheel or two service actuators When used to control both service chambers on an axle or two chambers on the same side of a tandem axle the modulator is sometimes mounted ahead of a quick release M 22 MODULATOR valve which provides quick exhaust of service applications during normal braking Figure 2 In the case of individual wheel control applications the modulator is always the last control valve through which air passes on its way to the service brake actuator and a solenoid assembly which contains one normally open solenoid NOS one normally closed sole
5. lve to facilitate ease of installation 4 Disconnect both air lines and the electrical connector 5 Remove the valve from the vehicle VALVE INSTALLATION 1 Install all air line fittings and plugs making certain thread sealing material does not enter the valve Install the assembled valve on the vehicle 3 Reconnect both air lines to the valve using the identification made during VALVE REMOVAL step 3 4 Reconnect the electrical connector to the modulator 5 After installing the valve test all air fittings for excessive leakage and tighten as needed M 21 MODULATOR TECHNICAL INFORMATION Porting 1 Supply Port from brake relay or quick release valve 1 Delivery Port brake actuator Solenoid Voltage 12 Volts DC Nominal Maximum Operating Pressure 150 psi Gauge Operating Temp Range 40 to 185 Fahrenheit Pressure Differential 1 psi maximum EXHAUST EXHAUST DIAPHRAGM SOLENOID EXHAUST PORT 22 7 ZZ D gt BRAKE VALVE D H I 7 SUPPLY 77000000 N SCH l SOLENOID Al ALA A Ei y SPRING BRAKE SUPPLY CHAMBER DIAPHRAGM SPRING FIGURE 8 M 21 M 22 MODULATOR ANTILOCK APPLICATION HELD POSITION CONNECTOR M 21 MODULATOR M 22 MODULATOR FIGURE 9 M 21 M 22 MODULATOR CONNECTOR VIEW 1 GENERAL SAFETY GUIDELINES WARNING PLEASE READ AND FOLLOW THESE INSTRUCTIONS TO AVOID PERSONAL INJURY OR DEATH When working o
6. n or around a vehicle the following general precautions should be observed at all times Park the vehicle on a level surface apply the parking brakes and always block the wheels Always wear safety glasses Stop the engine and remove ignition key when working under or around the vehicle When working in the engine compartment the engine should be shut off and the ignition key should be removed Where circumstances require that the engine be in operation EXTREME CAUTION should be used to prevent personal injury resulting from contact with moving rotating leaking heated or electrically charged components Do not attempt to install remove disassemble or assemble a component until you have read and thoroughly understand the recommended procedures Use only the proper tools and observe all precautions pertaining to use of those tools If the work is being performed on the vehicle s air brake system or any auxiliary pressurized air systems make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle If the vehicle is equipped with a Bendix AD IS air dryer system or a dryer reservoir module be sure to drain the purge reservoir Following the vehicle manufacturer s recommended procedures deactivate the electrical system in a manner that safely removes all electrical power from the vehicle 6 7 10 11 Never exceed manufacturer s recommended pressures Never connect
7. noid NCS and two inlet and exhaust diaphragm valves A Packard three pin 280 series weather resistant electrical connector is an integral part of the modulator solenoid assembly and serves to carry control commands from the antilock controller to the modulator Two 35 inch diameter mounting holes are provided for frame or cross member mounting The single supply delivery and exhaust port on both modulators is identified with a cast embossed numeral for positive identification FRONT AXLE SYSTEMS WHEEL CONTROL AXLE CONTROL ANTILOCK ANTILOCK CONTROLLER CONTROLLER M 21 OR M 22 MODULATOR TO ANTILOCK CONTROLLER SERVICE BRAKE CHAMBER SERVICE BRAKE CHAMBER FIGURE 2 WHEEL AND AXLE CONTROL SYSTEMS They are as follows Identification Air Line Connection 1 Supply incoming air from foot valve or relay 2 Delivery air delivery to service actuators 3 Exhaust air exhaust during antilock control OPERATION NON ANTILOCK APPLICATION FIGURE 3 During normal non antilock braking both solenoids are de energized no electrical power Brake application air enters the supply port of the modulator and flows to and through the open exhaust solenoid then to the exhaust diaphragm Air pressure along with spring force seats the exhaust diaphragm on the exhaust passage thus preventing the escape of service air Simultaneously application air flows to the supply diaphragm and forces it away from i
8. of the exhaust diaphragm air returning to the modulator from the service chambers lifts the exhaust diaphragm from its seat Returning air flows past the open exhaust and out the modulator exhaust port Air will also 4 flow past the open supply diaphragm and back to the application device s exhaust ANTILOCK OPERATION GENERAL If a service brake application is made and the antilock system detects an impending wheel lockup the antilock controller will immediately begin modification of the brake application using the modulator In order to modify the brake application the coils of the two solenoid valves contained in the modulator are energized or de energized in a pre programmed sequence by the antilock controller When a solenoid coil is energized a shuttle within the solenoid moves and depending upon the function of the specific solenoid it either opens or closes thereby causing the exhaust or re application of air pressure to the brake actuator The solenoids in the modulator are controlled independently by the antilock controller By opening and closing the solenoid valves in the modulator the antilock controller is able to simulate what the driver does when he pumps the brakes It must be remembered however that unlike the driver the antilock controller is able to pump each modulator along with the brakes connected to it independently and with far greater speed and accuracy EXHAUST DIAPHRAGM UU EXHAUST PORT
9. or disconnect a hose or line containing pressure it may whip Never remove a component or plug unless you are certain all system pressure has been depleted Use only genuine Bendix brand replacement parts components and kits Replacement hardware tubing hose fittings etc must be of equivalent size type and strength as original equipment and be designed specifically for such applications and systems Components with stripped threads or damaged parts should be replaced rather than repaired Do not attempt repairs requiring machining or welding unless specifically stated and approved by the vehicle and component manufacturer Prior to returning the vehicle to service make certain all components and systems are restored to their proper operating condition For vehicles with Automatic Traction Control ATC the ATC function must be disabled ATC indicator lamp should be ON prior to performing any vehicle maintenance where one or more wheels on a drive axle are lifted off the ground and moving 10 11 12 BW1664 O 2010 Bendix Commercial Vehicle Systems LLC All rights reserved 6 2010 Printed in U S A
10. require reapplication of braking pressure it de energizes the supply and exhaust solenoids With both solenoids de energized the modulator re applies air to the brakes in the same manner it did during a non antilock application PREVENTIVE MAINTENANCE GENERAL Perform the tests and inspections presented at the prescribed intervals If the modulator fails to function as described or leakage is excessive it should be replaced with a new or genuine Bendix remanufactured unit available at any authorized parts outlet EVERY 3 MONTHS 25 000 MILES OR 900 OPERATING HOURS 1 Remove any accumulated contaminates and visually inspect the exterior for excessive corrosion and physical damage Inspect all air lines and wire harnesses connected to the modulator for signs of wear or physical damage Replace as necessary Test air line fittings for excessive leakage and tighten or replace as necessary Perform the ROUTINE OPERATION AND LEAKAGE TESTING described in this manual OPERATION amp LEAKAGE TESTS LEAKAGE TESTING 1 Park the vehicle on a level surface and block or chock the wheels Release the parking brakes and build the air system to full pressure 2 Turn the engine OFF and make 4 or 5 brake applica tions and note that the service brakes apply and release promptly 3 Build system pressure to governor cut out and turn the engine OFF 4 Make and hold a full service brake application A Apply a soap solution to
11. rt sharp and well defined perform the Electrical Tests ELECTRICAL TESTS 1 90 m gt Before testing the solenoid assembly of a suspect modulator its location on the vehicle should be confirmed using the Trouble Shooting or Start Up Procedure for the specific antilock controller in use See the Service Data Sheet for the antilock controller for this procedure Proceed to the modulator in question and inspect its wiring connector Disconnect the connector and test the resistance between the pins ON THE MODULATOR Refer to figure 9 HOLD to SOURCE Read 3 5 to 5 OHMS EXHAUST to SOURCE Read 3 5 to 5 OHMS EXHAUST to HOLD Read 7 to 10 OHMS Individually test the resistance of each pin to vehicle ground and note there is NO CONTINUIT Y If the resistance readings are as shown the wire harness leading to the modulator may require repair or replacement Before attempting repair or replacement of the wire harness refer to the test procedures specified for the antilock controller in use for possible further testing that may be required to substantiate the wire harness problem If the resistance values are NOT AS SHOWN ABOVE replace the modulator VALVE REMOVAL 1 Park the vehicle on a level surface and block the wheels and or hold the vehicle by means other than the air brakes 2 Drain the air pressure from all vehicle reservoirs Identify and mark or label all air lines and their respective connections on the va
12. the exhaust port of the modulator Leakage should not exceed a 1 bubble in less than 3 seconds If leakage exceeds the specified maximum replace the modulator B Apply a soap solution around the solenoid assembly top and bottom Leakage should not exceed a 1 bubble in less than 3 seconds If leakage exceeds the specified maximum tighten the solenoid cap screws and re test If the leakage remains excessive after re testing replace the modulator C Apply a soap solution around each diaphragm cover Leakage should not exceed a 1 bubble in less than 3 seconds If leakage exceeds the specified maximum tighten the diaphragm cap screws and re test If the leakage remains excessive after re testing replace the modulator OPERATION TESTING To properly test the function of the modulator will require 2 service technicians 1 Park the vehicle on a level surface and block or chock the wheels Release the parking brakes and build the air system to governor cut out Turn the engine ignition key to the OFF position then make and hold a full brake application With the brake application held and a service technicians posted at one of the modulators turn the vehicle ignition key to the ON position ONE OR TWO SHORT bursts of air pressure should be noted at the modulator exhaust Repeat the test for each modulator on the vehicle If at least a single burst of exhaust is not noted or the exhaust of air is prolonged and not sho
13. ts seat Air flows past the open supply and out the modulator delivery port to the service brake chambers M 21 OR M 22 MODULATOR QUICK RELEASE VALVE REAR AXLE SYSTEM WHEEL CONTROL TO ANTILOCK CONTROLLER M 21 OR M 22 MODULATOR CONTROLLER RELAY ASSEMBLY M 21 OR M 22 MODULATOR ANTILOCK CONTROLLER SERVICE amp SPRING BRAKE CHAMBER NON ANTILOCK HOLD FIGURE 4 When the desired air pressure is attained in the service brake chambers the brake system is in the holding position In the holding position both solenoids in the modulator remain de energized and the balance of the internal components remain in the same position as they assumed during application EXHAUST EXHAUST r DIAPHRAGM SOLENOID Z Var ebe EXHAUST PORT 2 2 Sege SUPPLY cken as Z cht U Ga SOLENOID O BRAKE SPRING SUPPLY CHAMBER DIAPHRAGM SPRING duch y Cl fe a BRAKE VALVE FIGURE 3 M 21 M 22 MODULATOR NON ANTILOCK APPLICATION OF SERVICE BRAKES EXHAUST EXHAUST DIAPHRAGM SOLENOID EXHAUST PORT REG Z x O ER Z BRAKE VALVE d e Y 7 SUPPLY d E zeen GEN Z lla SOLENOID BRAKE SUPPLY CHAMBER DIAPHRAGM FIGURE 4 M 21 M 22 MODULATOR NON ANTILOCK APPLICATION HELD POSITION EXHAUST DIAPHRAGM EXHAUST SOLENOID EXHAUST PORT ec Ce
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