Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-05-19
2000-11-21
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303900, 3031132, B60T 840, B60T 842, B60T 848
Patent
active
061492507
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is based on a hydraulic automotive vehicle brake system with a return pump and a precharging pump. Concepts of this type are frequently used where the objective is to retrofit a device for automatic braking to brake systems operating according to the return principle for anti-lock control. Automatic braking, on the one hand, refers to traction slip control operations where brake management is only performed by the wheel brakes of the driven wheels or, on the other hand, to a control of the yaw torque of the vehicle by brake management on individual vehicle wheels. In addition, automatic braking refers to a retardation of a vehicle for defined reasons, for example, in the event of a sensor triggering an alarm signal which indicates a too small distance from a vehicle ahead, and like events.
In brake systems operating according to the return principle for anti-lock control, the return pump used is frequently of the self-priming type in order to permit automatic aspiration of pressure fluid from the pressure fluid supply reservoir for automatic braking operations. At low temperatures, however, the viscosity of the pressure fluid used, i.e., brake fluid, is high so that it is very difficult for the return pump to provide the necessary suction capacity.
Sharp throttling effects are caused by the master cylinder when fluid is aspirated from the supply reservoir by way of the brake line and the master cylinder. In addition, a pressure gradient is involved with long pipe lines and bores.
Therefore, it has frequently been disclosed to use a precharging pump. Partly, the return pumps in brake systems of the above type are not of the self-priming type. Partly, however, the precharging pump has only a supporting effect, and the return pump remains the self-priming type.
There are different proposals how to connect the pressure side of the precharging pump to the suction side of the return pump. It must be ensured in any case that the pilot pressure generated by the precharging pump will propagate to the suction side of the return pump and is prevented from discharging into an unpressurized reservoir. Also, the reduction of residual pressure must be ensured when the pumps are disconnected. A frequent problem encountered is that the precharging pump continues running even after its disconnection, with the result that additional valves are required which are opened to discharge the developing residual pressure.
An object of the present invention is to provide a brake system of the type mentioned hereinabove having a precharging concept which is simple and inexpensive, but operates effectively.
SUMMARY OF THE INVENTION
This object is achieved by connecting the pressure line of a precharging pump to the brake line with a flow connection to the master cylinder at a junction point that is so remote from the master cylinder that a sufficient pilot pressure for the return pump develops due to throttling effects which are caused in the brake line between the junction point and the master cylinder. No valves are required for the reduction of residual pressure by arranging the pressure line so that it opens into the brake line directly before or within the hydraulic control unit. This is because the pressure side of the precharging pump, by way of the brake line, is permanently connected to the supply reservoir when the master cylinder is not operated. On the other hand, the pipe connection from the master cylinder to the hydraulic control unit is so long that this line alone is sufficient to throttle the pressure fluid flow from the pressure side of the precharging pump to such an extent that the largest portion is conducted to the suction side of the return pump.
A separating valve in the brake line to disconnect a pressure fluid flow to the master cylinder is only necessary between the pressure side of the return pump and the master cylinder. The pressure line of the precharging pump can open into the brake line between the separating valve and the master cylinder.
In order
REFERENCES:
patent: 4773715 (1988-09-01), Farr
patent: 4787684 (1988-11-01), Schonlau et al.
patent: 5255962 (1993-10-01), Newhaus et al.
patent: 5342120 (1994-08-01), Zimmer et al.
patent: 5429425 (1995-07-01), Drott
Dehio Gottfried
Steffes Helmut
Volz Peter
Butler Douglas C.
ITT Manufacturing Enterprises Inc.
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