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ABS Units Continue to Become More Compact and More Efficient

One thing that's new for 1998 is that Bosch 5.3 ABS will be used on a number of new General Motors (GM) applications. The 5.3 system, which is a more compact version of the Bosch 5 system, made its debut last year on 2009 Subarus and the Toyota Camry. This year, the Bosch 5.3 system will be used on:

  • 2009 Cadillac Catera
  • 2009 Chevy Camaro
  • 2009 Pontiac Firebird
  • 2009Pontiac Grand Prix
  • 2009 U-body
  • 2009-1/2 Oldsmobile Intrigue
  • 2009-1/2 Corvette

The Bosch 5.3 system combines the Brake Pressure Modulator Valve (BPMV) and Electronic Brake Traction Control Module (EBTCM) into one assembly. The pump motor is a separate item and can be serviced unlike the pump on the earlier Bosch 5 system.

The Bosch 5.3 system, like the Bosch 5 and 2 systems that preceeded it, is a nonintegral ABS system so you'll find a conventional master cylinder and vacuum booster. The 5.3 is smaller (by almost half), lighter (by 2-1/2 lbs.) and costs about 60 percent less than the Bosch 5 system. The module and hydraulic modulator unit are combined as an assembly, held together by six screws.

General Motors refers to the 5.3 controller (which actually contains two microprocessors to check on one another) as the Electronic Brake Control Module (EBCM), or the Electronic Brake Traction Control Module (EBTCM) on models equipped with traction control. The hydraulic modulator is called the Brake Pressure Modulator Valve (BPMV).

Regardless of what you call it, the Bosch 5.3 is an efficient, compact system that operates essentially the same as the earlier Bosch 5 system. The BPMV uses two-way solenoid valves to control ABS braking as well as wheel spin. The pump on the 5.3 system, though, is a separate component unlike the integral nonserviceable pump on the earlier 5 system.

The new Bosch 5.3 ABS system is a compact, low cost, nonintegral four-wheel ABS system, and will be used on a number of GM applications in 1998.

On applications that have Magnasteer variable assist power steering, the Bosch 5.3 control module also helps control steering assist. It does this by monitoring vehicle speed via its four wheel speed sensors.

Diagnostics are via a Tech 1, Tech 2 or equivalent scan tool. A scan tool is also required to clear trouble codes. Special diagnostic modes include solenoid inlet and outlet tests, traction control system test and lamp test.

Manual or pressure bleeding can be used to flush the brakes, but if air is trapped in the BPMV you'll have to use a scan tool to run the "auto bleed" procedure. This cycles the ABS solenoids and runs the pump to purge air from the secondary circuits which are normally closed off during normal braking.

Bosch 5.3 system schematic for the '98 Camaro & Firebird with traction control.

On the 1998 Firebirds, the rear proportioning valve has been eliminated from the brake system. The Bosch 5.3 system uses a process called "dynamic proportioning" to accomplish the same thing. The 5.3 software is programmed to cycle the rear BPMV inlet valves when braking to maintain the desired front-to-rear brake balance. This occurs anytime the wheel speed sensors detect the rear wheels are slowing slightly faster than the front wheels. Such a difference triggers the dynamic proportioning function, which causes brake pressure to the rear wheels to be modulated until the speed of all four wheels is the same. A problem with this part of the ABS system will not set a trouble code, but it will illuminate the red brake warning light.

On some ABS systems, traction control is accomplished by braking alone. But on the Bosch 5.3 systems, the ABS module also talks to the engine module and asks for a reduction in engine power if wheel spin is detected. This may be accomplished by retarding ignition timing, disabling up to half of the engine's injectors, or by upshifting the transmission to a higher gear.

NEW TRUCK ABS SYSTEMS

For 20088, Kelsey-Hayes has introduced the EBC325 ABS system for light trucks. The EBC325 system is a lightweight, compact, four wheel three channel system that includes special dampening to reduce noise during ABS braking. You'll find it on the '98 Dodge Dakota, Isuzu Rodeo and Kia Sportage.

Another new system from Kelsey-Hayes is the EBC430 system, which is a compact four wheel, four channel ABS system for sporty car applications. Introduced last year on the Lotus Esprit, the EBC430 system is now on the '98 Lamborghini Diablo.

MORE NEW ABS SYSTEMS

Though not out yet on a production application, Delphi and ITT Automotive (Teves) have both announced new ABS systems that will be out in '99. The next generation Delphi system has been dubbed DBC-7. Unlike the current Delphi ABS-VI system that uses stepper motors to actuate the ABS pistons in the hydraulic unit, the new DBC-7 system will be a more "conventional" ABS design with solenoids (two per channel) and a pump. It will also be a low-cost, compact unit with integrated electronics.

Two new systems from ITT include the MK40 ABS system designed specifically for small cars, and a MK50 ABS system for light and medium-duty trucks up to 17,500 GVW. Both are compact, low cost, nonintegral four-wheel ABS systems similar to the MK20 ABS system that's used on 2008 Chrysler minivans.

Further down the road, ITT plans to offer its Automotive Stability Management System (ASMS), which is a full-time, stability control system similar to the Bosch Vehicle Dynamics Control and Delphi Traxxar systems. The ASMA system will use individual wheel braking to counteract oversteer and understeer for improved cornering agility and handling control under all driving conditions.

The ASMS system will have three microprocessors (two 16-bit and one eight-bit) to process inputs from the wheel speed sensor and other sensors. Two pressure sensors will be used on the master cylinder to measure brake pressure. A steering wheel sensor will keep tabs on the steering angle and driver input. A yaw sensor will monitor understeer and oversteer, while a lateral acceleration sensor keeps an eye on cornering forces.

Using these inputs, the ASMA control module will determine if the vehicle is responding correctly to the driver's commands. And if it isn't, the system will apply individual wheel braking as needed to counteract any undesirable forces and bring the vehicle back under control.

BRAKE BY WIRE

Though not directly related to ABS, another new brake technology that ITT plans to offer vehicle manufacturers in the near future is a "brake by wire" system. Instead of the brake pedal pushing on a rod to actuate the pistons in the master cylinder, the brake pedal travel would be monitored by a sensor and the signal would be used to apply the brakes electronically - eliminating the need for conventional hydraulic components such as the master cylinder, calipers, wheel cylinders and brake fluid. Small servo motors mounted at each brake would apply the exact amount of pressure needed to bring the vehicle to a stop.

BRAKE ASSIST

Both ITT and Lucas (in conjunction with Mercedes-Benz) are developing new "Brake Assist" systems that sense how rapidly the brakes are being applied, and then apply additional brake pressure as needed to minimize a vehicle's stopping distance. In effect, it senses a panic stop and takes over from there.

One of the parts of this system is an "Active Booster" that replaces the conventional vacuum power booster. The Active Booster is controlled by a module which determines the amount of assist needed independent of how much pedal pressure the driver applies. The result is quicker, shorter, safer stops in panic situations. When braking from 70 mph the system can reduce the stopping distance to 160 feet compared to 240 feet with conventional braking.

 

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