Anti-locking brake system

Details Anti-locking brake system Anti-locking brake system

2001-09-24

2003-01-21

Lavinder, Jack (Department: 3613)

Fluid-pressure and analogous brake systems

Speed-controlled

And traction control

C303S139000

Reexamination Certificate

active

06508521

ABSTRACT:

BACKGROUND
The invention relates to an anti-locking brake system, 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 overdimensioned 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.
SUMMARY OF THE INVENTION
An object of the invention is to provide an anti-locking brake system while avoiding the previously described drawbacks.
To achieve the object, according to the invention the initially mentioned anti-locking brake system is further developed in that disposed between the brake pressure generating unit and an input connection of the pump is a valve arrangement in the form of a 2-connection/3-position valve, which in a non-actuated (normal) position blocks the connection between the brake pressure generating unit and the input connection of the pump, in a first actuating position establishes a secondary flow connection between the brake pressure generating unit and the input connection of the pump, and in a second actuating position establishes a primary flow connection between the brake pressure generating unit and the input connection of the pump, wherein the primary flow connection has a larger flow cross section than the secondary flow connection.
All of the drawbacks of the previously described known arrangement (DE 40 35 527 A1) may be avoided by the solution according to the invention, which additionally provides a further actuating position with a reduced flow cross section. For, by said means, the volumetric flow from the brake pressure generating unit to the pump may be precisely metered. This applies particularly when the volumetric flow is modulated by a purposeful temporary switch between the normal position (1.1) and the first actuating position (1.2). Thus, during regulation of the brake pressure in the wheel brake the pressure level at the output side of the pump may be adapted almost to the pressure level in the wheel brake, with the added result that hydraulic noises are reduced.
Particularly suitable for use as the two/three-way valve (
1
) inserted between the brake pressure generating unit
31
and input side
42
c
of the pump
42
is the valve arrangement, which is shown in the non-actuated state in FIG.
2
and in the actuated state in FIG.
3
. For the present application the valve arrangement is then energized in such a way
that given a first current for producing the first actuating position (1.1) only the further valve element
11
is actuated (secondary flow connection B),
and that given a second current for producing the second actuating position (1.2) the valve element
3
is moreover actuated (primary flow connection A).
A crucial advantage of the anti-locking brake system according to the invention is that, before the primary flow connection is established, a secondary flow connection is first established. Because of the secondary flow connection, in the situation where different fluid pressures at the fluid connections additionally exert a pressure differential force upon the valve element a pressure-equalizing process between the fluid connections is first initiated, thereby eliminating the pressure differential force so that during establishment of the primary flow connection the pressure differential force is no longer effective and may no longer have disadvantageous consequences. Thus, only a relatively low actuating force is required, with the result that the actuating device may be of an inexpensive, simple design which takes up little installation space. As a result, the flow cross section determined mainly by the primary flow connection may be relatively generous in order to rule out an undesirable throttling effect in the flow behaviour of the valve arrangement. As the secondary flow connection has only a small flow cross section compared to the primary flow connection, the pressure differential force to be surmounted during the establishment of the second flow connection is negligibly low.
The actuating device and/or the further actuating device may preferably be electromagnetically and/or hydraulically controlled. Thus, in particular, the actuating device, which actuates the valve element to establish the primary flow connection, may be electromagnetically controlled and the further actuating device, which actuates the further valve element to establish the secondary flow connection, may be hydraulically controlled. In said case, the further hydraulically actuated actuating device may be controlled by means of the pressure difference existing between the fluid connections in order to establish the secondary flow connection for the purpose of initiating the pressure-equalizing process between the fluid connections. When after elimination of the pressure differential force the primary flow connection is established by the electromagnetically actuated actuating device, the actuating force to be summoned up is likewise only relatively low. This has a particularly advantageous effect upon the design of the electromagnetic arrangement of the actuating device, because the fact that the

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