Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1997-01-07
1999-07-27
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031132, B60T 842
Patent
active
059278269
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydraulic brake system and more particularly relates to brake systems having brake slip control and traction slip control. DE-A 41 08 756 discloses a brake system of this type which operates pursuant the return principle during brake slip control operations. Pressure fluid is discharged into the low-pressure accumulator due to the outlet valves opening, when the change-over valve is closed. The pressure fluid is returned by the return pump through the pressure line into the brake line. A suction line branches off from the brake line between the master cylinder and the point where the pressure line terminates into the brake line.
When the brake is not operated (hence, also during traction slip control operations), the change-over valve in the suction line is open so that the return pump, which is of the self-priming type, can aspirate pressure fluid from the pressure fluid reservoir by way of the master cylinder to feed the pressure fluid into the brake line. To prevent the pressure fluid from flowing back into the master brake cylinder, the separating valve, arranged between the port of the pressure line into the brake line and the point where the suction line branches from the brake line, is closed. There is uninterrupted operation of the pump during the entire traction slip control period. When the supply pressure required for traction slip control operations is reached, a pressure-relief valve connected in parallel to the separating valve will open towards the master cylinder. Due to the power losses of the pump motor caused by the permanent fluid supply to the master cylinder by way of the pressure-relief valve, the pump motor overheats and can only be used for a smaller number of pressure-increase phases during traction slip control.
Therefore, a brake system of the previously mentioned type was proposed in DE-A 40 25 859, wherein the pump is not a self-priming pump but is supplemented by a charging pump connected to the supply reservoir. In order to prevent power losses of the non-self-priming return pump, a shut-off valve is inserted into the connection between the charging pump and the return pump. The shut-off valve includes a control line having its pressure act upon the shut-off valve in the closing direction. The control line of the shut-off valve is connected to a pressure-relief line in which a pressure-relief valve is inserted which opens when the supply pressure of the return pump exceeds a certain extent. Thus, the control line of the shut-off valve is mostly disconnected from the pressure line of the pump and is connected with the pressure side of the pump only when the pressure-relief valve discharges a too high pump pressure. The pressure-relief valve is acted upon by the master cylinder pressure in the closing direction so that it can open only when the master cylinder is not operated. If the pump produces an excessively high pressure and tends to overheating during a traction slip control operation, the pressure-relief valve will open and conduct the supply pressure of the pump into the control line of the shut-off valve. The shut-off valve closes, as does the pressure-relief valve, because a second pressure-relief valve with a lower opening pressure provides another connection between the pressure-relief line and the pressure fluid supply reservoir, thereby causing pressure reduction in the pressure line of the pump. Because the closing pressure of the shut-off valve is lower than the opening pressure of the second pressure-relief valve, however, the shut-off valve may re-open only after the pressure in the control line has been reduced by way of a throttle connected in parallel to the second pressure-relief valve. Thus, the point of time of opening of the shut-off valve depends only on whether the pressure in the valve's control line, which pressure is irrespective of the pressure side of the pump when the first pressure-relief valve is closed, has been reduced by way of the throttle. On the one hand, this implies that at a point of time where the
REFERENCES:
patent: 4892362 (1990-01-01), Takata
patent: 5330258 (1994-07-01), Hoshoya et al.
patent: 5374112 (1994-12-01), Takata et al.
Search Report of the German Patent Office for Application P4409911.8.
Graham Matthew C.
ITT Automotive Europe GmbH
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