Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1990-07-06
1992-03-17
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303DIG5, 303DIG6, B60T 850
Patent
active
050962698
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an antilock brake system comprising a master cylinder in which a hydraulic fluid can be subjected to pressure, a connecting conduit between the master cylinder and a brake cylinder at the brake of an antilock brakable wheel, and a vent valve which is arranged in a further connecting conduit between the brake cylinder and a reservoir for hydraulic fluid and opens in an antilock control operation for reducing the pressure of the hydraulic fluid in the brake cylinder.
The structure and function of such antilock systems for four-wheeled and two-wheeled vehicles are known to the person skilled in the art. In them, the rotational behaviour of the wheels is continuously monitored by means of sensors and when the slip and/or the angular deceleration of the wheel exceeds a predetermined threshold value and thus indicates a danger of the wheel locking the normally open shutoff valve between the master cylinder and the brake cylinder is closed and the vent valve opened so that momentarily the pressure of the hydraulic fluid in the brake cylinder can be reduced to accelerate the wheel again into a favourable range of the friction coefficient-slip curve.
On starting a braking, i.e. when the driver via the brake pedal increases the pressure of the hydraulic fluid in the master cylinder, a pressure buildup as far as possible without delay is desirable in the brake cylinder to ensure that immediately on brake actuation a brake action also starts. For this purpose, the flow resistance in the hydraulic connecting line between the master cylinder and the brake cylinder must be as small as possible.
In an antilock control, that is a braking with pressure increases and pressure reductions following each other at very small time intervals in the brake cylinder, it is in contrast desirable to increase the pressure in the brake cylinder in retarded manner. A too rapid buildup of the pressure, i.e. a pressure buildup with too steep a time gradient, has among others the disadvantage that during an antilock control operation the pressure in the brake cylinder oscillates upwardly and downwardly about the optimum pressure value with excessive deviations, thus impairing the control and finally wasting braking distance. In contrast, with a throttled pressure buildup in the brake cylinder it is possible in an antilock control to adapt the profile of the brake pressure in optimum manner to the desired curve profile without the undesired "overshoot".
Antilock brake systems are already known in which an antilock control of a change of the pressure buildup gradient takes place. For this purpose, however, in the prior art complicated and/or trouble-prone means are proposed.
The invention is based on the problem of further developing an antilock brake system of the type mentioned at the beginning in such a manner that in simple economic and reliable manner on braking with antilock control a throttled pressure buildup takes place whilst on braking without antilock control a rapid unthrottled pressure buildup at the brake cylinder is possible.
According to the invention this problem is solved in that in the connecting conduit between the master cylinder and the brake cylinder a valve is arranged which in an antilock control operation has a larger flow resistance for the hydraulic fluid than in a braking without antilock control.
An advantageous further development of the invention provides that the valve generating a different flow resistance functions in purely mechanical manner. For this purpose, it comprises a floating piston which is subjected on one side to pressure of the hydraulic fluid in the master cylinder and on the other side to the pressure of the hydraulic fluid in the brake cylinder. The floating piston is arranged displaceably in the valve and the pressure of the hydraulic fluid in the master cylinder, if it is large enough, can cause a valve body to be pressed against a valve seat, the flow resistance for the hydraulic fluid between the master cylinder and the brake cylinder thereby being increased.
This
REFERENCES:
patent: 4099793 (1978-07-01), Iio
patent: 4116495 (1978-09-01), Belart
patent: 4752104 (1988-06-01), Miyake
patent: 4765692 (1988-08-01), Miyake
patent: 4941712 (1990-07-01), Hirobe
patent: 4957330 (1990-09-01), Morikawa et al.
patent: 4988148 (1991-01-01), Farr et al.
Graham Matthew C.
Lucas Industries Public Limited Company
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