DYNAMIC BRAKING SYSTEM
The dynamic braking system is designed to enhance the braking control of the DSC for the driver of the vehicle. The dynamic braking control and maximum braking control are functions that are programmed into the control electronics of the DSC with no additional hardware changes.
Dynamic Braking Control (DBC)
The DBC function is designed to provide the maximum braking force available during rapid (panic) braking situations. The DSC control module looks at the inputs from the brake pedal switch and the signal from the brake pressure sensor on the master cylinder. The criteria for activation of DBC is how rapidly is the brake pressure built up with the brake pedal depressed. The total criteria required for DBC activation includes
- Brake switch ON
- Brake pressure build up > threshold value
- Vehicle road speed > 5MPH
- Vehicle not in reverse
- Not all wheels in ABS regulation
If the threshold for DBC activation is achieved, the DSC control module will activate a pressure build up regulation phase through the hydraulic unit. The pressure at all wheels is increased up to the ABS regulation point. This occurs even if the driver does not achieve the ABS regulation point with the pedal.
The rear axle brakes are controlled with select-low regulation and the front axle brakes are controlled individually. ABS regulation will continue until the driver releases the pedal and the pressure in the master cylinder drops below the threshold value stored in the DSC control module.
Maximum Brake Control
The MBC function is also designed to enhance a driver initiated braking procedure. The MBC will build up the pressure in the rear brake circuit when the front brakes are already in an ABS regulation cycle. The additional braking pressure at the rear wheels will shorten the stopping distance. The following criteria must be met before the DSC control module will activate MBC
- Both front wheel brakes in ABS regulation
- Vehicle speed > 5 MPH
- Vehicle not in reverse
- DBC and pressure sensor initialization test OK
- Rear wheels not in ABS regulation
BOSCH DSC III - 5.7 COMPONENTS
With the exception of the following, all components of the DSC - 5.3 are carried over and their functional operation remains the same.
- Control Module/Hydraulic Unit
- Rotational Rate/Lateral Acceleration Sensor
- Master Cylinder Pressure Sensor
Control Module Hydraulic Unit
The control module is now integrated into the hydraulic unit as one compact unit. This reduces the size and wiring required for DSC operation. Additionally the motor relay and valve relay have been replaced by solid state final stages in the control module. The hydraulic unit continues to use
- Two Pre-Charge Solenoid Valves
- Two Changeover Solenoid Valves
- Four Intake Solenoid Valves
- Four Outlet Solenoid Valves
- One Return Pump
Rotation Rate/Transverse Acceleration Sensor
Located under the driver's seat, the rotation rate and transverse acceleration sensor have been combined into one unit. The new sensor is smaller in size and weight and is isolated from chassis vibrations through its rubber mounting.
The sensor provides the same information as the two separate sensors used on the DSC 5.3 version. It receives power and ground from the DSC control module.
For rotational speed, the sensor produces a reference signal of 2.5 volts and a linear voltage signal from 0.7 to 4.3 volts. This linear voltage input signal is used by the DSC control module as the degree of rotational rate (yaw).
The sensor also produces a linear voltage signal for the lateral acceleration (G-force) that ranges from 0.5 to 4.5 volts. The DCS control module uses this input to determine the side forces acting on the vehicle for DSC regulation.
Rotation Rate/Transverse Acceleration Sensor Operational Diagram. Scheme 35
Brake Pressure Sensor
A brake pressure sensor is installed in the master cylinder to determine the degree of pressure build-up for Dynamic Brake Control. It is installed in the front axle brake circuit.
The sensor receives its power supply from the DSC control module and produces a linear voltage input signal ranging from 0.5 to 4.5 volts depending on how hard the brakes are applied.
Identifying Brake Pressure Sensor. Scheme 36
Brake Pressure Sensor Hydraulic System Diagram. Scheme 37
Brake Pressure Sensor System Circuit Diagram. Scheme 38
Control Module/Hydraulic Unit
The control module is installed in the engine compartment on the right side next to the strut tower.
Both the control module and the hydraulic unit are replaceable as separate components.
All processing functions for ABS/ASC or DSC regulating functions are carried out in the one control module. The module is linked to the CAN bus for communication with the DME and AGS control modules. Additionally the CAN bus is used for communication with the steering angle sensor and for illumination of the ABS and DSC indicator lamps in the instrument cluster.
The hydraulic unit consists of the following
- Four Inlet Solenoids
- Four Outlet Solenoids
- Two Changeover Solenoids
- Two Charge Solenoids
Identifying Control Module/Hydraulic Unit. Scheme 39
Wheel Speed Sensors
The E46 DSC III system uses the wheel speed sensors from the ASC system.
Wheel Speed Sensor Circuit Diagram. Scheme 40
Brake Light Switch
The brake light input signal is used by the control module to interrupt an ASC regulation control if the driver steps on the brakes during its operation.
This interruption does not take place during DSC regulation.
The DSC system comes on every time the vehicle is switched on. The DSC button can be used to switch the system off. The warning indicator lamp comes on when the system is manually switched off
Steering Angle Sensor
The steering angle sensor is mounted at the bottom of the steering column, in front of the flexible coupling. It utilizes two potentiometers to determine steering angle and the rate of steering change. These signals are processed in the steering angle sensor and a digital output signal is passed over the CAN bus to the DSC control module.
The sensor requires calibration after repairs to the steering or suspension system. The sensor is calibrated using the DIS or MoDiC. Once calibrated, the sensor sends an ID number to the DSC control module. The ID provides confirmation to the module that the angle sensor is properly calibrated.
Installing a new sensor or exchanging sensors with another vehicle will require that this calibration procedure is carried out.
Identifying Steering Angle Sensor. Scheme 42
CAN Interface
The DSC control module communicates over the CAN line for the following
- Steering angle from the steering angle sensor
- Engine control module for engine intervention
- Transmission control module for shift intervention
- Instrument cluster for illumination of the warning indicator lamps see scheme 13: CAN Interface System Diagram
Rotation Rate Sensor
The rotational rate sensor is mounted under the driver's seat. It provides a signal to the DSC control module that corresponds to the vehicle's rotational speed around its axis (yaw speed).
The sensor receives its operating power (5 volts) from the DSC control module and provides an output voltage of approx. 0.25 to 4.65 volts depending on the amount of yaw exerted on the vehicle.
The sensor operates on the Coriolis effect to produce the output voltage. The element of the sensor is a micromechanical double quartz tuning fork. A frequency of 11 Hertz is applied to one side of the fork and as the vehicle turns on its axis, vibrations are induced into the tips at the other end.
The sensor processes the signals produced by the fork and produces an analog voltage signal that is proportional to the amount of yaw.
Based on the control module's programming parameters, the DSC will activate a DSC regulation cycle to ensure that the vehicle remains stable under all driving conditions.
Rotation Rate Sensor Circuit Diagram. Scheme 43
Lateral Acceleration Sensor
The lateral acceleration sensor is mounted in the left "A" pillar. The sensor provides the DSC control module with an input signal that corresponds to the degree of lateral acceleration ("G" forces) acting on the vehicle.
The sensor is a capacitive type with two capacitive plates (one fixed and one moving). Under the effect of lateral acceleration, the one plate moves in relation to the fixed plate. This results in a voltage signal being produced in proportion to the degree of lateral acceleration.
The voltage signal output of the sensor to the DSC control module ranges from 0.5 to 4.5 volts. When the vehicle is stationary, The standing voltage from the sensor is approximately 1.8 volts.
This signal is used in conjunction with the yaw sensor input to determine the degree of DSC regulation required to maintain the vehicle's stability.
Identifying Lateral Acceleration Sensor. Scheme 44
DSC System Component Flow Diagram. Scheme 45
Charge Pump
The charge pump is installed between the master cylinder and the brake fluid reservoir. During DSC controlled regulations that involve brake intervention, the charge pump ensures that the required volume of fluid is available for the hydraulic unit.
When activated, the charge pump draws fluid from the reservoir and delivers it to the master cylinder at a pressure of 10 Bar.
Identifying Charge Pump. Scheme 46
Pressure Sensors
Two pressure sensors are installed on the master cylinder in the outlet ports for the front and rear brake circuits. The sensors provide the DSC control module with an analog voltage signal in proportion to the brake pressure in the master cylinder.
