Electronic Proportioning Valve: Doing More With Less Hardware

Electronic Proportioning Valve: Doing More With Less Hardware

Anti-lock brake systems (ABS) and the HCU are replacing proportioning, combination and other valves to change the braking forces in the front and rear. This is called Electronic Brake Distribution (EBD) and it can dynamically change the proportioning to take into account if the vehicle is turning or is loaded.

Anti-lock brake systems (ABS) and the HCU are replacing proportioning, combination and other valves to change the braking forces in the front and rear. This is called Electronic Brake Distribution (EBD) and it can dynamically change the proportioning to take into account if the vehicle is turning or is loaded.

The system can also use EBD to perform a “soft stop.” This routine is performed when a vehicle is slowing at low speeds and the brake force is varied in the front and rear so the vehicle’s attitude is controlled and weight is evenly transferred. This means a flatter and more stable stop.

If the ABS light it on, the system may go into a default setting with a static braking force distribution level. The customer may notice lock-up or difficulty modulating pedal force.

The software running the EBD system is calibrated by engineers to the vehicle in computer simulations and on test tracks. Most of the time they get it right. But, sometimes problems are not discovered until the vehicle is on the road being driven by the public.

Sometimes the program/calibration for the ESC system needs a little “tweaking” due to changes in the vehicle, like a new tire size, vehicle weight or unforeseen driver behaviors. This is where SAE J2534 reflashing comes into play. Some OEMs like Honda and Chrysler have released updates to enhance pad wear and other braking behaviors.

This is why checking TSBs on a vehicle is critical if the customer or technician notices abnormal wear problems like the rear brakes wearing out before the fronts.

Most OEMs are very protective of their reflash programs. The growing trend is that the new program does not reside on the hard drive or memory of the reflash tool. Instead, the program is directly burned onto the module from the internet. Most of the OEMs site piracy and intellectual property concerns, which is valid since the cost to write the code and test the calibrations is very expensive.

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Ford issued TSB 11-7-14 in 2011 concerning premature front brake pad wear on 2010 and certain 2011 Transit models. When the engineers at Ford “Americanized” the Transit, they left the brake calibrations alone, but changed to a non-asbestos organic (NAO) pad that had less noise. The solution was new front brake pads and a reprogramming of the ABS module on the AdvanceTrac vehicle.

If there is a DTC in the ABS module specifically for the HCU, or if there are two or more wheel speed sensor DTCs, the EBD will be disabled. When the EBD is disabled, the ABS warning indicator, the red brake warning indicator and the sliding car icon will be illuminated.

The number one complaint by Transit Connect drivers is brake pad and shoe life. Most of these complaints can be traced back to two sources. First, ABS system problems that disable the EBD and cause the system to go into a failsafe mode that does not adjust brake bias like it should. Second, inexpensive pads and shoes that do not work well together. This can cause either the front or rear to work harder.

Honda Accord

Electronic brake proportioning (also called Electronic Brake Distribution or EBD) was introduced on some Honda models in 2006, and all 2011 Honda vehicles, except the S2000, now have EBD. With electronic brake proportioning, pressure from the master cylinder is routed equally to the front and rear brakes. There is no mechanical proportioning valve in the brake system. Instead, the anti-lock brake system (ABS) controls what happens at the brakes.

On some 2008-‘09 Honda Accords, the stock programming for the EBD system caused premature rear pad wear. Typically, the rear pads would only last 12,000 to 20,000 miles. The fix for this problem is a reflash of the ABS system and improved brake pads.

VW

2The rear pads and rotors on a 2005-2011 VW Jetta or Golf will typically wear out faster than the front brakes. The Volkswagens of this generation have electronic brake distribution, and under normal stopping conditions, the system will use the rear brakes more than the front. This prevents nosedive and makes for a more pleasant braking event. There is no cure for this. According to the repair information, Volkswagen has not released an updated calibration for the system. The front pads have electronic wear sensors, but the rear pads do not on most models.

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