AIR COMPRESSOR CONTROL
Air Compressor Controlis an optional DDEC feature that allows DDEC to regulate engine speed and load/unload a valve in order to maintain a requested compressor outlet air pressure for air compressor applications.
The DDEC Air Compressor Control Feature is available with the following software releases:
DDEC III - Release 4.0 (only)
DDEC IV - all software versions (Release 20.0 or later)
The ECM monitors the air outlet pressure while varying the engine speed and operating load/unload a valve. The valve will be opened or closed. The desired operating pressure may be varied by the operator, within limits preset by the OEM.
The ECM will activate the Air Compressor Governor Controls when the digital input “Air Compressor Load Switch” is grounded. Engine speed is governed based on the actual air compressor outlet pressure versus the desired output pressure. The Air Compressor Pressure Sensor provides a pressure signal to the ECM.
Engine Operation with Air Compressor Controls
Each horsepower rating has an associated pressure range. Horsepower ratings are defined at time of order entry. The minimum and maximum pressure setting for each of the horsepower curves is set with the DDDL/DDR, Vehicle Electronic Programming System (VEPS), or DRS. The initial pressure set point is saved between ignition cycles.
Increase (Resume/Acceleration On)
Momentarily toggling and releasing the Increase Switch (grounding the "Resume/Acceleration On" digital input) increases set point pressure by 4% of the pressure range. Holding the switch in the increase position (grounding the digital input), will increase the set point pressure at a rate of two increments per second. Releasing the switch sets the compressor controls to the higher setting.
ANTI-LOCK BRAKE SYSTEMS
Anti-lock Brake Systems (ABS) are electronic systems that monitor and control wheel speed during braking. The systems are compatible with standard air brake systems.The system monitors wheel speed at all times, and controls braking during emergency situations. Vehicle stability and control are improved by reducing wheel lock during braking.
The ECM transmits engine data via SAE J1587, SAE J1922, or SAE J1939. Anti-lock brake systems monitor data on one or more of these communication links. In the event that an excessive wheel spin is detected, the ECM receives a message from the ABS requesting a 0% output torque limit. The message is transmitted on SAE J1922 or SAE J1939.
SAE J1922 and SAE J1939 both implement the same message set. The difference being hardware and performance. SAE J1922 transmits and receives data at 9.6 K baud while SAE J1939 transmits/receives data at 250 K baud. SAE J1939 has a much higher bit rate so messages reach their destination very quickly nearly eliminating the latency found with SAE J1922.
SAE J1922 is enabled on all DDEC IV ECMs. SAE J1939 is enabled on all DDEC IV ECMs (Release 24.0 or later). ECMs prior to Release 24.0 must be configured if SAE J1939 is required.
See Figure 5-2 and Figure 5-3 for interface with Meritor/WABCO and Bosch respectively.
Managing the Vehicle Damage Repair Process
In the event that your vehicle requires damage repairs, GM recommends that you take an active role in its repair. If you have a pre-determined repair facility of choice, take your vehicle there, or have it towed there. Specify to the facility that any required replacement collision parts be original equipment parts, either new Genuine GM parts or recycled original GM parts. Remember, recycled parts will not be covered by your GM vehicle warranty.
Insurance pays the bill for the repair, but you must live with the repair. Depending on your policy limits, your insurance company may initially value the repair using aftermarket parts. Discuss this with your repair professional, and insist on Genuine GM parts. Remember if your vehicle is leased you may be obligated to have the vehicle repaired with Genuine GM parts, even if your insurance coverage does not pay the full cost.
If another party’s insurance company is paying for the repairs, you are not obligated to accept a repair valuation based on that insurance company’s collision policy repair limits, as you have no contractual limits with that company. In such cases, you can have control of the repair and parts choices as long as cost stays within reasonable limits.
Decrease (Set/Coast On)
Momentarily toggling and releasing the decrease switch decreases set point pressure by 4% of the pressure range. See Figure 5-1. Holding the switch in the decrease position (grounding the digital input), will decrease the set point pressure at a rate of two increments per second. Releasing the switch sets the compressor controls to the lower setting.
Air Compressor Load Switch
Closing (grounding) the air compressor load switch digital input activates the air compressor control system. See Figure 5-1. Opening the air compressor load switch digital input deactivates the air compressor control system.
Air Compressor Solenoid
When the pressure reaches a programmable limit above the pressure set point the DDEC digital output will be grounded. This output may be used to either open an air compressor vent or close the air inlet. Once the air pressure has dropped to a lower programmable limit, the digital output will be open circuited which will either close the vent or open the air inlet.
Air Compressor Shutdown
DDEC will respond to a proprietary immediate engine shut down message sent over the SAE J1587/J1708 data link by the Electronic Display Module (EDM). This feature requires both an EDM and an Auxiliary Information Module (AIM); refer to section 5.6 for addition information on EDM and AIM.
Multiple Pressure Ratings
The pressure ranges are linked to the engine ratings. A pressure range can be associated with each rating. The maximum number of engine ratings and pressure ranges is three. Choosing the rating, with the DDR/DDDL or rating switches will automatically select the associated pressure range. The proper 6N4D group with multiple 6N4M groups must be specified. For additional information, contact your DDC Applications Engineer.
ROGRAMMING REQUIREMENTS AND FLEXIBILITY
Air Compressor Controls must be specified at the time of engine order or added to the ECM calibration by Detroit Diesel Technical Service. An Application Code (6N4C)Group must be selected that is configured for Air Compressor Control at order entry or by contacting Detroit Diesel Technical Service.
The digital outputs and inputs listed in Table 5-2 are required for Air Compressor Controls and must be configured by order entry, VEPS, or the DRS.