Vehicles with M57, M62 and N62 engines are equipped with a dynamic stability control system – DSC, which includes all the functions of the ABS/ASC+T system.
Failure of any of these systems allows the vehicle to move, but requires greater attention to speed and traffic conditions, as the efficiency of vehicle control is sharply reduced.
Attention! All work on the "ABS" system must be carried out with the ignition off and the "-" terminal of the battery removed. Before work using electric welding equipment, it is necessary to disconnect the ECU "ABS/ASC+T" ("DSC") loop.
When painting a car, the maximum permissible drying temperature is no more than +80°C, for two hours.
The "ABS/ASC+T" and "DSC" systems installed on the car increase the active safety of the car and prevent wheel locking during sudden braking and skidding in turns. At the same time, the car maintains control until it comes to a complete stop, without skidding. The system is automatically switched on at a speed of about 8 km/h and switched off at a speed below 3 km/h.
The "ABS" braking subsystem works most effectively at maximum friction of the tire with the road surface. To brake, the tire must transmit a certain friction force to the surface, causing it to slide along the road surface. Thus, the circumferential speed of the wheel becomes less than the speed of the car. At a certain braking mode, the braking force transmitted by the wheel is of the greatest importance. However, when going beyond its limits, the wheel locks and the friction force with the ground decreases.
The role of "ABS" is to immediately limit and maintain the braking effect of each wheel within the optimal braking mode when the road surface condition changes. "ABS" includes - a standard braking system, wheel pulse generators (wheel speed sensors), hydraulic unit, electronic control unit and electrical wiring harness.
The pulse generator consists of a toothed ring mounted on the wheel hub, which interacts with the Hall sensor. The frequency of the generated pulses corresponds to the wheel rotation frequency and is sent to the electronic control unit of the ABS system (ECU-ABS), where it is processed. By comparing the rotation speed of each wheel with the average speed of all wheels, the ECU-ABS determines the degree of slippage of an individual wheel and can thus determine the moment when one of them is close to blocking.
And based on this information, it issues control pulses to the electromagnetic valves of the hydraulic unit (hydraulic unit). As soon as one of the wheels approaches locking, the brake fluid pressure in its caliper increases in relation to the tire's grip on the road. The hydraulic system, under the influence of control signals, maintains the brake fluid pressure stable. This means that the pressure in the caliper does not increase even if the brake pedal is pressed further. If the risk of locking remains, the pressure decreases by opening the release valve, but only to the point where the wheel begins to accelerate slightly again, after which the pressure is again maintained constant.
If the wheel starts to rotate faster, the ABS ECU issues a signal to increase the pressure, but not higher than the total pressure in the brake system. The process of braking and releasing the wheel, when the brake pedal is pressed sharply, will be repeated until the brake pedal is released or the vehicle speed drops to 2-3 km/h. The driver feels the action of the ABS by the pulsation of the brake pedal and the characteristic sound of the hydraulic unit in the engine compartment, which signals him about driving in boundary conditions. This reminds him of the need to reduce the speed of movement.
The hydraulic unit of the system is installed on the brake line after the main brake cylinder. Each of the four pipelines approaching the hydraulic unit has an electromagnetic valve that diverts the brake fluid to an electric pump that provides brake pressure in the line of a specific wheel. The operability of the ABS system is checked using the indicator in the instrument cluster. The lamp lights up when the ignition is turned on and goes out after 3 seconds. If the indicator continues to light or lights up while driving, then it is necessary to:
- stop the car, turn off the engine and start it again;
- check the battery voltage, it should be at least 10.5 V;
- check the reliability of the battery contact connections;
- raise the vehicle, remove the wheels, check the integrity of the wheel speed sensor harness.
If the ABS system malfunctions, its ECU stops generating control pulses, and the car's braking occurs according to the standard scheme (without regulation). The "ABS" control lamp in the instrument cluster is constantly lit. The "ASC+T" subsystem is a system for regulating the load on the drive wheels, which reduces the torque of both drive wheels when they slip by reducing engine power. The system simultaneously acts on the brakes and additionally reduces engine power through the ECU of the power unit.
If the rear wheel tends to slip, the electronic engine management system (DME – digital engine electronics) receives this information from the ABS/ASC+T ECU. A short-term reduction in engine power is achieved by reducing the amount of fuel supplied, and on a cold engine, additionally by changing the ignition timing. This action of the system is equivalent to releasing the gas pedal.
If this is not enough, the "T" function intervenes in the braking process (traction control), which carries out metered braking of the drive wheels.
The "ASC+T" subsystem eliminates wheel slip during acceleration and cornering across the entire speed range, as it integrates traction control. By braking the engine, it prevents short-term locking of the drive wheels when driving on slippery roads. Up to a speed of 40 km/h, traction control ("T") can create the effect of a locking differential. Since the left and right wheels are braked independently of each other, the "ASC+T" system acts as a locking differential with an almost 100% locking effect.
The "ASC+T" system is linked to the "ABS" system via a single "ABS/ASC+T" ECU, which in turn is linked to the KSUD ECU (DME-Motronic). The operation of the "ASC+T" system is indicated by the flashing of the "ABS" indicator lamp on the instrument panel.
The "ASC+T" system is automatically switched on after each engine start. When the ignition is switched on, the system performs self-diagnostics, and the "ABS" indicator lights up briefly. The system can be switched off by pressing the key "ASC" ("DSC") on the center console (see fig. 1.56), the control indicator also lights up (14, see Fig. 1.12). Pressing the button again turns the system back on and the indicator lamp goes out. Flashing of the lamp means that the system is adjusting the traction force based on the actual driving mode and conditions.
If the control lamp does not go out after starting the engine or lights up continuously while driving, then a malfunction of the "ASC+T" system is signaled, with the braking system functions preserved, but without regulation. The car can continue driving, but at a properly selected speed and it is necessary to contact a service station.
Attention! When driving in deep snow, with anti-skid chains or when driving out of deep mud, it is advisable to switch off the "ASC+T" / "DSC" system.
"DSC" system
The "DSC" (Driving Stability Control) system is installed in combination with the "M62" and "N62" engines. It recognizes the car's tendency to lose stability at the very beginning and stabilizes its position on the road within milliseconds.
The original text of the article is available on the resource: «BMWMAN.RU»