Dynamic Stability Control Systems: Introduction

Dynamic Stability Control (DSC III version 5.3) was introduced on the 1998 Model Year E38 and E39 - 540 vehicles. For Model Year 1999, the system is enhanced with additional control functions and a new combined rotational rate/lateral acceleration sensor as version 5.7. It continues to be offered as standard equipment in the E38 and E39 - 540 models. The new functions are titled as the Dynamic Braking System and include the:

• Dynamic Brake Control (DBC)
• Maximum Brake Control (MBC)

DSC III adds a further dimension to the dynamic stability control system. DSC II has the ability to mildly correct for lateral instability and only at the rear brakes when braking control is necessary. DSC III has the ability to brake any wheel during cornering maneuvers where the control module's programmed limits for vehicle oversteer and understeer are exceeded.

New sensors are added to the DSC III system to monitor the rotational rate of the vehicle around its vertical axis and a lateral acceleration sensor to monitor the side to side forces on the vehicle.

The hydraulic system of the DSC II has also been modified to allow brake regulation on the front wheels and to ensure that the supply of brake fluid for DSC II regulation is maintained.

Two different hydraulic systems are used on the Bosch 5.3 DSC system as follows:

• 740i/iL & 540iA use a charge pump for the front brake circuit.
• 750iL uses a boost pump and separate charge piston for both the front and rear brake circuits.

The hydraulic system used on the Bosch DSC III 5.7 has changed on the E38 and E39. The 750iL now uses a similar hydraulic system to the 740i/iL and 540i. The charge piston and pre-boost pump have been eliminated. The brake pressure sensor is now located in the hydraulic unit on all Bosch 5.7 systems.