Suppliers are adding greater functionality to electronic stability control systems to improve safety and entice car buyers to check the ESC option box.
Automotive Design & Production
, Christopher A. Sawyer
Ever since the first Mercedes A-Class flipped over an imaginary moose during testing in the late 1990s, electronic stability control (ESC) systems have moved from a quick fix to a commonplace new vehicle offering. Supplier studies show 61% of car buyers have a strong interest in the system if the option price is no higher than $600. Yet fewer than 25% of 2007 passenger vehicles are expected to offer the technology for the simple reason that new car buyers don’t expect to ever find themselves in a situation where ESC is needed.
“It’s tough trying to sell a safety system like ESC to the end consumer,” says Scott Dahl, marketing director, Chassis System Management at Bosch. “They can see the value of an entertainment system, but can’t justify the expense of ESC.” Perhaps buyers need to be introduced to Critical Sliding Velocity (CSV), the lateral velocity at which a trip (hitting a curb, sliding onto a soft shoulder) can induce a rollover. For cars, the speed range is 11 mph to 18 mph. For light trucks and SUVs, the speed range is 9 mph to 13 mph. Of course, it takes more work to get a car–which has a higher effective track width–into this situation, thus the real world rollover disparity between cars and light trucks and the reason many OEMs will offer ESC across their SUV lines by the end of the decade.
Another way to entice OEMs and buyers alike is to expand the capabilities of ESC systems through value-added functions that answer specific needs, thereby moving the sales focus away from an extreme condition safety system toward one with more everyday utility. Many are based on adding functionality to the brake units used in the ESC systems. Others add software to existing hardware. Bosch, Continental, and Delphi each have added variations on the ESC theme to their portfolios.
Hydraulic Brake Assist from Robert Bosch Corp. (Farmington Hills, MI) looks at the rate of brake application, compares it to a set of deceleration parameters, and increases brake pressure to meet requirements. This includes initiation of ABS braking. Hydraulic Fade Compensation increases braking pressure when fade is detected. It looks at the pressure in the brake master cylinder, compares this to what is happening at the wheel, and uses the ESC pump to actively build pressure in the system up to ABS initiation levels. Bosch sees it as an advantage for vehicles towing trailers or carrying a big load on hills. Hydraulic Rear Wheel Boost increases rear brake pressure when the front axle is in ABS mode. By boosting the rear brakes to ABS levels, the rears do more work which reduces stopping distances, especially when the vehicle is loaded. Roll Over Mitigation uses ESC sensors to determine when a vehicle is in danger of rolling over due to extreme lateral forces, and initiates outside front wheel braking. It’s claimed this system reacts quicker than those that rely on roll angle sensors. Trailer Sway Mitigation works in combination with ESC to apply the tow vehicle’s brakes in a proprietary sequence that prevents side-to-side trailer oscillations.
Active Rollover Protection from Continental Teves (Auburn Hills, MI) applies a high burst of brake pressure to the appropriate wheels to counteract excessive body roll and keep the wheels on the ground. ESC II combines electronic brake force distribution, ABS, yaw control and traction control with active steering intervention that adds or subtracts steering as needed to keep the vehicle heading along the intended path. Active Passive Integration Approach (APIA) combines current production subsystems to avoid accidents and reduce injuries. If an accident is unavoidable, the “danger control module” initiates a staged response that closes the sunroof, puts the front seats in their optimal position, raises the windows, and locks the doors while pre-filling the braking system, pre-tensioning the seatbelts, and readying the airbags for deployment. For vehicles already fitted with ESC and Adaptive Cruise Control, moving up to a complete APIA system would add approximately $300. Electronic Park Assist may not avoid accidents, but it shows how you can expand functionality of basic systems. It adds a side sensor to Continental’s Mk. 60 electronic brake system that measures the parking gap and relative vehicle position while passing a parked vehicle. It computes the optimal parallel parking path, and assists the driver in following that path through controlled steering. Like Bosch, Continental also has a trailer sway system.
Quadrasteer with Handling Enhancement from Delphi Corp. (Troy, MI) shows what a little (1.0ºº to 1.5º) in-phase steering at the rear axle can do for stability, especially when it’s fitted to a large SUV. The system adds next-generation software to a production Quadrasteer system, requires no additional hardware or sensors, and gives it functionality that goes well beyond increased maneuverability. Advanced ESC refines the brake controller software to better detect excessive yaw and roll, and apply the brakes individually in order to counteract the unwanted motion earlier in the process.