Understanding the ESP (Electronic Stability Program) System

Here are some articles I found on line that do a wonderful job of describing the ESP system in Mercedes Benz vehicles. This first one is written by Scott Memmer of Autotrader.com.

"Stability control is actually the latest in a series of braking-related developments that began appearing in production vehicles in the 1980s. As with many high-tech advances, the original designs debuted in German vehicles, typically Mercedes S-Class and BMW 7 Series sedans. There's a good reason for the German connection. Robert Bosch GmbH, headquartered in Stuttgart, Germany, is one of the largest original equipment manufacturers (OEMs) in the world. The company, a world leader in safety development, works extensively with German automakers. Laying the groundwork for stability control, in the mid-80s Bosch brought the antilock braking system (ABS) to market through Mercedes and BMW. As most consumers probably know by now, ABS has become a standard feature on many new cars. It works by sensing and preventing wheel lock-up, thereby improving the vehicle's traction and enhancing steerability during hard braking.

According to Eric Kosmider, spokesman for Robert Bosch Corp., the American subsidiary of Robert Bosch GmbH, "ABS was the first 'building block' in the chain of components that eventually led to stability control." After Bosch perfected ABS, the company moved on to the second "building block" — traction control. Sometimes referred to as ASR traction control (the ASR stands for "Acceleration Slip Regulation" and typically referees to systems appearing in German cars), the technology works in a similar fashion to ABS, but at the opposite end of the performance spectrum. Whereas ABS focuses on eliminating lock-up in braking situations, traction control regulates wheelspin during acceleration. In other words, when speeding from a standing stop or while in motion, a driver may give too much accelerator input, causing the wheels to spin freely. In such cases, traction control monitors wheel speed, cuts engine power or even applies the brakes to optimize contact between the tires and the road surface.

This brings us to our present topic: stability control. The third "building block" in modern braking systems, stability control incorporates everything ABS and traction control do plus a yaw-sensing feature that works to increase traction during potential side-skidding situations. In other words, whereas both ABS and traction control work on the longitudinal (front-to-back) axis of the vehicle, stability control operates on the lateral (side-to-side) axis. Bosch's Electronic Stability Program (ESP), the first such system on the market, began appearing in 1995 Mercedes-Benz S-Class sedans. It has since become a popular feature on many upscale vehicles.

According to Bosch's Kosmider, "The platform for ABS, traction control and stability control is essentially the same. We simply add sensors to get the desired effect." In addition to discrete electrical components, ceramic sensors and solenoid valves, stability control systems typically utilize wheel-speed sensors, steering-angle sensors and a hydraulic modulator. The key component is, however, something called a rotational speed sensor (also known as a yaw-rate sensor). Yaw can be described as "the movement of an object turning on its vertical axis." Picture an aircraft instrument panel with that "airplane" symbol tipping right and left and this will perhaps give you a better image of the concept of yaw.

The yaw-rate sensor determines how far off-axis a car is "tilting" in a turn. This information is then fed into a microcomputer that correlates the data with wheel speed, steering angle and accelerator position, and, if the system senses too much yaw, the appropriate braking force is applied. As you can imagine, stability control systems are particularly effective in inclement driving conditions, where the roadway may be covered with rain, ice or snow and the normal friction between the tires and the road is reduced.

There are a couple of things you may want to know about stability control. First, the system will do most of the "thinking" for you. Depending on the particular driving situation, the system may activate an individual wheel brake or any combination of the four, as well as control the throttle, until the vehicle is once again stable. Second, the system is fully independent of the driver's actions. Even if the car is free-rolling (no acceleration or braking input from the driver), the stability control system will kick in and perform its duty. All you need to do is steer. Remember, though, that stability control, like any technology, is not fool-proof. All vehicles must ultimately obey the laws of physics. Members of our road test staff report spinning sedans with activated stability control systems on dry pavement. Be sure to make your driving decisions based on the appropriate criteria — visibility, road conditions, speed, the condition of the tires and brakes — and not to rely on any technology to correct for unsafe driving."

Full article here.

This article was found on the DaimlerChrysler Australia Pacific site. The author is unknown.

ESP® works according to the principle of a "permanent monitor", whereby sensors observe the driver’s and the vehicle’s behaviour and then send their data to a high-performance control unit loaded with a mathematical model. As a result, the actual condition of the vehicle is continuously compared to a reference value provided by the driver. The system is thus able to sense when the vehicle is in danger of skidding.

When the ESP® computer registers a discrepancy between the two values, it engages at lightning speed according to a specially developed logic system on the basis of which it applies precise dosages of braking power to the front or rear wheels, and also adjusts the engine torque. If, for example, the vehicle’s rear axle swings too far outwards when taking a curve, ESP® will lower the drive torque, thereby increasing the lateral guidance force of the rear wheels. If this action fails to produce the desired result, the system will apply precise brake pressure to the front wheel on the outside of the curve in order to stabilise the vehicle. The braking impulses counteract the critical rotary movement, while the simultaneous deceleration provides an additional safety effect.

Unlike the acceleration skid control system, which assists the driver when he or she accelerates the vehicle, ESP® is available to go into action at any time — during braking, acceleration, or cruising along. ESP® immediately adapts to the vehicle’s movements and continues to engage until there is no longer any danger of skidding.

Full article here.

Was this info helpful? to help keep this site up.

I found all the diagrams I needed with my Alldatadiy.com subscription. If you sign up for the service using the link below, I receive a small commission which helps me cover the costs of administrating my site. Thanks!

If you can't see the Alldata image above, click here.