Originally Posted by REDNAX
The negative to this controller (which I otherwise desire) is the lack of a direct reading of the brake pressure as with the MAXBRAKE or earlier SMARTBRAKE (and the several decade standard KELSEY-HAYES controller) in favor of some computations; a sort of after-the-fact way versus the more preferable "reading" of the drivers foot, so to speak, as hydraulic brake pressures rise.
I desire the unit as I assume that the TT anti-lock system module compatibility with the TV will give some superior performance. Anti-lock trumps what we have now, on the one hand, but on the other we have taken away a distinct advantage.
Were it not for the anti-lock I wonder how much this controller differs, from, say, a P3. Any thoughts on this Mexray, Bab (or others)?
I'll take a stab at this...but...I am sure DirecLink's datastream read and application is proprietary. I'll use my knowledge of GM products only, although otheres are similar, I'm sure. I am making logical educated assumptions here...OK?
Here is a system operation overview for a 2012 Escalade. (All GM products are similar).
ABS Description and Operation
This vehicle is equipped with a Bosch ABS/EBD/TCS/VSES brake system. The electronic brake control module (EBCM) and the brake pressure modulator valve is serviced separately. The brake pressure modulator valve uses a 4 circuit configuration to control hydraulic pressure to each wheel independently.
The following vehicle performance enhancement systems are provided.
• Antilock Brake System (ABS)Antilock Brake System
• Electronic Brake Distribution (EBD)
• Hill Start Assist
• Power Brake Booster Solenoid Vacuum Supply
• Traction Control System (TCS)
• Vehicle Stability Enhancement System (VSES)
Solid Line – Hard Wire I/O
Dash Line – Serial Data
Electronic Brake Control Module (EBCM)
Steering Angle Sensor
Yaw and Lateral Accelerometer Sensor
Brake Booster Vacuum Sensor
Instrument Panel Cluster (IPC)
Body Control Module
Wheel Speed Sensor (WSS)- LF
Wheel Speed Sensor (WSS)- RF
Wheel Speed Sensor (WSS)- LR
Wheel Speed Sensor (WSS)- RR
The following components are involved in the operation of the above systems.
• ABS pump motor—The ABS pump motor is part of the brake pressure modulator valve. The ABS pump motor is active during ABS, VSES and base brake power assist functions.
- System relays—There are two system relays internal to the EBCM. The solenoid relay is energized when the ignition is ON. The ABS pump motor relay supplies a ground path to the ABS pump motor when the EBCM commands the ABS pump motor on. The system relays are non serviceable.
- Solenoids—The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the brake pressure modulator valve (BPMV).
• Brake booster vacuum sensor—The Brake Booster Vacuum Sensor is a input to EBCM, and operates the ABS pump motor to precharge the brake system.
• Brake pressure modulator valve (BPMV)—The BPMV uses a 4-circuit configuration to control hydraulic pressure to each wheel independently.
The BPMV contains the following components:
- ABS pump motor and pump
- Four inlet valves
- Four outlet valves
- Two TC isolation valves
- Two TC supply valves
- A master cylinder pressure sensor
- A front low-pressure accumulator
- A rear low-pressure accumulator
• Master cylinder pressure sensor—The master cylinder pressure sensor is located within the BPMV. The master cylinder pressure sensor uses a 5-volt reference and generates an output signal proportionate to the hydraulic fluid pressure which is present in the front brake circuit at the master cylinder.
• Steering wheel position sensor—The EBCM receives several inputs from the steering wheel position sensor. Three digital square wave signal inputs and one analog signal input are wired directly to the EBCM harness connector. The EBCM uses the signals A and B for determining position movement and uses the analog and index signals to determine absolute center. All signals are monitored for plausibility to each other. The sensor is provided ground and 5-volt power directly from the EBCM.
• Traction control switch—VSES and the engine torque reduction function of TCS are manually disabled or enabled by pressing the traction control switch.
• Wheel speed sensors (WSS)—EBCM sends a 12-volt reference voltage signal to each wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed increases, but does not increase the signal amplitude.
• Yaw/lateral accelerometer sensor--The yaw rate, lateral acceleration and longitudinal acceleration sensors are combined into one yaw/lateral accelerometer sensor, external to the EBCM. The EBCM receives serial data message inputs from the yaw rate, lateral acceleration and longitudinal acceleration sensor and activates stability control and hill start assist function depending on multi-axis acceleration sensor input
All of these items communicate on the bus. So, you can see, there are decelerometers, pressure sensors, speed sensors, etc. It is pretty easy to develop an algorythm for the brake controller for it to know very accurately, electronically, what is going on in real time.