Hydraulic Charge

Hydraulic Charge
Existing ASC+T and DSC II systems already perform hydraulic control regulation but do not require the additional charge pump systems. Why? The reason being those systems only actuate the rear axle circuits. Obviously, the DSC III system has the capability to actuate front and rear axle circuits together which requires additional hydraulic fluid supply.

For this reason, during an ASC or DSC regulation function requiring hydraulic intervention, the DSC III control module switches the electrical charge pump on to provide this additional fluid.






740i/iL & 540iA Vehicles:
When activated, the Charge Pump delivers a brake pressure of 10 - 15 bar to the front axle circuit of the hydraulic unit and into the front axle circuit pressure chamber of of the master cylinder. The master cylinder piston for the front axle circuit contains a notched restricter forward of the central valve which allows excess fluid to return to the reservoir under a restriction.

The pressurized fluid also acts on the rear axle circuit of the master cylinder. This provides the hydraulic charge to the rear axle circuit of the hydraulic unit as needed.






75OiL Vehicles:
The electric Pre-boost pump delivers a brake fluid pressure of 7-15 bar to the isolated chamber of the charge piston. The pre-boost pump incorporates an integral pressure relief valve which opens at 15 bar.

From the isolated chamber the fluid returns to the reservoir through a restriction. The restriction causes pressure to build in the chamber which pushes the pistons outward. This immediately acts on two valves which block the normal braking circuits that flow through the charge piston ports.

The pressure in the isolated chamber continues to push the pistons outward delivering the required charge pressure.

For ABS and CBC operation, the pump systems are not switched on, only during ASC/DSC regulation requiring hydraulic intervention are the pre-boost pump or the charge pump switched on. The balance of the hydraulic system functions operate in the same familiar manor of all previous systems. The individual brake circuits can be isolated as needed to restore lateral locating forces through pressure build, hold and release phases of operation. During an ASC hydraulic intervention requiring only rear wheel brake application, the inlet valves for the front wheels are closed preventing any pressure influence from the charge pump systems.