ESP, what does it do exactly?

[MCPaudiTT - DEFCON 1]

the systems.

First the acronyms:

TLA(Three Letter Acronym) = German Term = English Term = AKA

ABS = Antiblockiersystem = Anti-lock Braking System
ASR = Antriebsschlupfregelung = Automatic Slip Reduction = Traction Control, several other terms by other manufacturers
ESP = Elektronisches Stabilitaets-Programm = Electronic Stability Program = Vehicle Dynamic Control (VDC), several other terms by other manufacturers

These systems were developed in this order (ABS/ASR/ESP), as they each built on the other's technologies and needed new developments in order to be implemented.

The first system was ABS. By measuring wheel speed sensors at each wheel, the ABS system can tell when a wheel starts to lock up in a braking event. The first action is to close off the pressure to the locking wheel, so that the pressure does not build further. If it still is locked, the pressure to that wheel is reduced by pumping the brake fluid back to the master cylinder (this is the pulsation you feel in the pedal). Back in 1996 when I was at Bosch, the processor could perform this operation over 100 times per second on the newer ABS5.3 model. It is likely in the 200-300 times per second range by now. There are no other pieces to an ABS system - just wheel speed sensors and the hydraulic unit (which contains solenoid valves and an electric motor driven pump). The motor only runs the pumps during an ABS event. If your ABS system completely fails, your normal braking system should continue to function correctly (an external leak is an exception to this rule).

ASR adds integration to the engine management system. ASR only comes on cars with ABS, as it builds on the groudwork of the hydraulic unit. ASR (also known as Traction Control), monitors the wheel speed sensors under acceleration (ABS is a deceleration-only system). If wheel spin is detected under acceleration, the first line of defence is to cut engine power through timing or other means. If that is not sufficient, the hydraulic unit motor is turned on, generating pressure in the braking system, and solenoid valves are switched to apply brake pressure to the spinning wheel. The hydraulic unit for an ASR system has more solenoid valves, more complicated programming, and costs more $$$ than an ABS-only system, but is not really too much more complicated.

ESP is on another performance level completely. ESP is used to straighten out a car that is experiencing excessive under- or over-steer. This is determined through the additional sensors needed for an ESP system: yaw sensor (measures the degree the car is actually pivoting about the center axis of the car), steering position sensor (measures where the driver is intending to steer the car), and lateral accelerometer (measures how much side load the car is in). ESP, as you may have guessed, is only built on a car that already has the ABS/ASR system (if you have ESP, you have ABS and ASR as well). So what ESP does is detect what direction you are steering (where you want to go as indicated by the steering wheel position sensor), and compares that with where you are actually going (using the yaw sensor and accelerometers). If your intended trajectory does not match your actual trajectory, it applies brakes at opposing corners of the car in order to straighten it out. So, if you are turning left, and are in an oversteer condition (the car is actually going WAY left), the system will apply brakes to the passenger front and driver rear wheels. This will tend to pivot the car to the right, more in line with the intended direction. If you are turning left, and are in an understeer condition (the car is not turning left enough), the system will apply brakes to the driver front and passenger rear wheels. This will tend to pivot the car to the left, more in line with the intended direction. Again, this happens MANY times per second. Also, it will only intervene past a certain threshold programmed by the manufacturer. In addition to the brake application, engine power is also modulated to control the spin. Systems can be "obtrusive" and not allow any fun driving, or much less obtrusive allowing for the tail end to slide out some before the system kicks in. As mentioned, the ESP system adds several sensors on to an existing ABS/ASR system, namely the yaw sensor, steering wheel position sensor, and lateral accelerometer.

Anecdote: I don't know if this is true or not, but I believe it. It was told to me that Bosch was trying to sell Ford on the ESP system. They put three Ford execs in to a Taurus with an ESP system and let them play on a test track, so they could see how impressive the system was. After a few fun laps, the execs were put in to an identical car that was non-ESP equipped. They promptly slid off the track and rolled the car in a sharp turn. Two lessons were learned.

1. ESP Works!
2. Learn the limits of the car with ESP off. Driving a car without ESP as if it has ESP will lead to disaster.

To my knowledge, the Taurus product line never received an ESP system...

Also of note, GM put their own Delco developed and manufactured ABS/ASR/ESP systems in to almost all of their cars. The exceptions? Cadillac and Corvette - those were Bosch systems (this was '94-'96, I don't now what they use now)... Which would you rather have?

[Seneb]

[XCLR8TT]

no matter how hard you try to throw it into an oversteer, ESP kept catching it.

Interestly enough, the cars that Audi had for the school had switches inside the drivers door to turn ESP and ABS completly off. Apparently the ESP button doesn't completely disable the ESP.