Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2001-09-24
2003-11-04
Graham, Matthew C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S116200, C303S119200, C303S900000
Reexamination Certificate
active
06641230
ABSTRACT:
BACKGROUND
The invention relates to an anti-locking brake system for a land vehicle, which is set up in particular for traction control and vehicle dynamics control in such a way that a pump for actuating a wheel brake removes brake fluid in a controlled manner from a brake pressure generating unit and supplies it to the wheel brake.
From DE 40 35 527 A1 it is known to provide a 2-setting/2-position valve between the input side of the pump and the brake pressure generating unit. Said valve arrangement has only one actuation and/or connection setting. In said case, the flow cross section of said one actuation and/or connection setting has to be very large so that, upon entry into the directional stability control system, a rapid pressure build-up in the wheel brake is achieved via the pump, especially in order at low temperatures to achieve a good intake performance (high pumping capacity) of the pump. A large flow cross section however entails the drawbacks of loud hydraulic flow noises and severe pedal reactions, which is perceived as intrusive and far from comfortable.
Such a valve arrangement is known as a so-called “normal-closed” (NC) valve. In the non-actuated state, i.e. the basic or normal position, the flow connection between the fluid connections of the valve arrangement is blocked, whereas in the actuated state the flow connection between the fluid connections is established. So that in the non-actuated state the flow connection between the fluid connections is blocked, a valve element under the action of a spring arrangement is biased so as to come sealingly into abutment with a sealing seat. In order in the actuated state to establish the flow connection between the fluid connections, it is necessary for the actuating device to summon up a force which is capable of surmounting at least the bias force of the spring arrangement so that the valve element lifts off the sealing seat.
However, in most applications it is not enough for the actuating device to summon up a force which is only slightly greater than the bias force of the spring arrangement because during operation different fluid pressures arise at the fluid connections of the valve arrangement, so that the valve element is additionally acted upon by a pressure differential force which, depending on the effective direction, is in the opposite direction to the force summoned up by the actuating device. The actuating device accordingly has to be designed in such a way that the actuating force is greater than the sum of the bias force of the spring arrangement and the maximum anticipated pressure differential force in order to guarantee reliable functioning of the valve arrangement. One drawback of this is that the actuating device has to be over dimensioned for many situations, particularly when, as in the majority of applications, in the actuated state of the valve arrangement a large flow cross section is required to prevent a throttling effect of the valve arrangement. A large flow cross section however additionally entails a very high pressure differential force, as a consequence of which a high actuating force has to be summoned up. The result is high costs and a high outlay when designing the valve arrangement. The size of the valve arrangement is also relatively large as a result.
In such a brake system which is set up for traction control and vehicle dynamics control it should be possible to generate, independently of a brake pedal actuation, brake pressure in the wheel brake/s to prevent by active brake engagement slipping of the driven wheels or skidding of the vehicle, especially when driving through curves. Such a brake systems is in a known manner bassed on a conventional brake system already adapted for anti lock control.
To be able to use the pump anyway provided in the anti lock control for returning brake fluid also for generating brake pressure in traction control and vehicle dynamics control, it is known from DE 38 32 023 C2 to additionally use a 3-setting/2-position valve which in a non-enabled condition, for a normal braking or anti lock control, establishes connection between the master cylinder and the output side of the pump and severs the connection to the input side of the pump. In the enabled condition the 3-setting/2-position valve severs for traction control the connection between master brake cylinder and output side of the pump and establishes the connection to the input side of the pump so that for generating brake pressure the pump can on the input side suck brake fluid from the master brake cylinder and at the output side feed it into the wheel brake/s. During traction control the brake pressure modulation is effected in a known manner by means of the valves provided for the anti-lock control.
There is the problem that brake pressure modulation results in considerably varying pressure levels between the output side of the pump and the wheel brake/s which causes intrusive hydraulic flow noises.
According to the above discussed DE 40 35 527 A1, now a valve combination is used which comprises two 2-connection/2-position valves instead of the additional 3-setting/2-position valve known from DE 38 32 023 C2, and which in an enabled condition severs both the connection between master cylinder and output side of the pump and the connection to the input side of the pump for the traction control.
Since the valve positions known from DE 38 32 023 C2 already allow pressure build-up and pressure reduction, this further valve position allows also to maintain the pressure as the input side of the pump is blocked so that no brake fluid can be taken. This is to make it possible to perform brake modulation during traction control exclusively via the two 2-setting/2-position valves, i.e. without switching the valves provided for the anti-lock control. Hydraulic flow noises as mentioned above are thus reduced.
However, it is a drawback in this connection that a precise brake pressure modulation is not possible during traction control. Even if the input side of the pump is blocked in order to maintain the pressure, there is always a small fluid volume at the input side of the pump which effects a minor pressure build-up rather than the desired maintenance of the pressure which as a whole renders pressure modulation inaccurate. Though the accuracy of the pressure modulation described in DE 40 35 527 A1 may be sufficient for traction control, it cannot at all or only by tolerating a restricted efficiency of the brake system be transferred onto a traction control because when driving through curves, an active brake intervention requires a precise brake pressure modulation to compensate for the vehicle's tendency to oversteer or understeer. Too rough a brake pressure modulation would be impossible first of all for reasons of the brake system's safety.
SUMMARY OF THE INVENTION
An object of the invention is to provide an anti-locking brake system while avoiding the previously described drawbacks. The brake system according to the invention is to meet the high demands made on a vehicle dynamics control and has at the same time to be applicable for the traction control.
To achieve the object, according to the invention an anti-locking brake system is further developed in that during the operating phase “maintain pressure”, contrary to the position of the electromagnetic valve described in DE 40 35 527 A1, the third electromagnetic valve is in the actuated position. Accordingly, connection between the output connection of the pump and the wheel brake is blocked and a small fluid volume at the input side of the pump can not, as is possible with the brake system described in DE 40 35 527, be fed to the wheel brake through the pump. Due to this actually simple change of the position of the electromagnetic valve, surprisingly accuracy of the pressure modulation is considerably improved. This high accuracy is of importance especially for the vehicle dynamics control.
In addition, according to the invention, the anti-lock brake system described in DE 40 35 527 A1 has been developed further particular
Bach Thomas
Gegalski Helmut
Heller Frank
Knechtgens Josef
Marx Andreas
Graham Matthew C.
Lucas Industries plc
MacMillan Sobanski & Todd LLC
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