Motors: expansible chamber type – Working member position feedback to motive fluid control – Plural input signal means for single motor valve
Reexamination Certificate
2002-02-08
2003-02-18
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Plural input signal means for single motor valve
C091S37600A
Reexamination Certificate
active
06520063
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to vacuum brake boosters.
Vacuum brake boosters as such have been known for some time and millions of them are in use for boosting the actuating forces of a vehicle hydraulic brake system and hence keeping said forces at a comfortably low level for the driver of a vehicle.
Recently, there has been a growing tendency to equip vacuum brake boosters with so-called brake assist. By said term is usually meant a system, which in an emergency braking situation, given substantially the same actuating force, may provide the driver with increased braking power. Systems of said type were developed because investigations revealed that the majority of vehicle users in an emergency braking situation do not press as hard on the brake pedal as is necessary to achieve the maximum braking power. The stopping distance of the vehicle is therefore longer than it need be. Systems of said type already in production use an electromagnetically actuable brake booster combined with a device capable of determining the actuating speed of the brake pedal. If said device detects an actuating speed above a defined threshold value, it is assumed that an emergency braking situation exists and the brake booster is set by means of the electromagnetic actuating device to maximum output, i.e. provides its maximum boosting power.
Brake boosters with an electromagnetic actuating facility are however too expensive for motor vehcles in the low- to medium-price category, which is why solutions have been developed which provide a brake assist function without an electromagnetically actuable control valve. The brake assist function in said solutions is realized in that, after a defined cut—in threshold is exceeded, an armature, which is rigidly coupled to a valve seat controlling the supply of atmospheric pressuire into the brake booster (atmospheric seal seat), is pulled into abutment with a permanent magnet and then holds the said valve seat open until the driver by means of a fixed return stroke of the brake pedal detaches the armature from the permanent magnet.
With said solutions, relatively loud and hence intrusive noises may occur when the brake assist function cuts out, i.e. when the armature pulls away from the permanent magnet. Said noises may occur because the armature, after detaching from the permanent magnet, returns almost immediately into its starting position and therefore, on the one hand, closes the atmospheric seal seat and, on the other hand, opens the connection of the working chamber to the vacuum chamber, with the result that the power assistance generated by the brake booster ceases almost instantaneously. All of the forces, which a master cylinder connected to the brake booster exerts because of the hydraulic pressure generated therein, therefore react fully upon the input element of the brake booster and upon components workingly connected to the input element. Said hydraulic reaction forces are added to the spring forces, which reset the actuating components of the brake booster, resulting in a hard impact of said parts against the corresponding end stops, which causes the said undesirable noises.
SUMMARY OF THE INVENTION
The object of the invention is to provide a vacuum brake booster of the described type, i.e. having a brake assist function capable of being cut in and out without electromagnetic assistance, in which said undesirable impact noises no longer occur or at any rate are no longer an intrusive phenomenon.
Said object is achieved according to the invention by a vacuum brake booster having the features indicated in claim 1.
In a vacuum brake booster of the required type a permanent magnet and an armature cooperating therewith are disposed in the housing of the control valve. The armature is rigidly coupled, on the one hand, to the input element of the brake booster and/or of the control valve and, on the other hand, to the first valve seat (atmospheric seal seat). The armature, which is movable to and fro relative to the permanent magnet, is spring-biased counter to actuating direction and in the starting position of the control valve is held at a first distance from the permanent magnet, preferably by means of the spring bias counter to actuating direction. In the course of a movement towards the permanent magnet which occurs upon actuation of the brake booster, the armature may move until it is less than a previously fixed, second distance away from the permanent magnet, which is smaller than the first distance. The armature, once it is less than said distance away, is pulled counter to the spring bias force acting upon the armature and with simultaneous cancellation of its, in actuating direction, rigid coupling to the input element by the permanent magnet into abutment with the permanent magnet. Thus, even when the actuating force introduced into the brake booster does not increase, the first valve seat coupled to the armature remains fully open (brake assist function) so that the brake booster builds up the highest possible pressure difference between its vacuum chamber and its working chamber, i.e. the brake booster provides its maximum boosting power.
According to the invention, the return stroke motion of the input element and/or of control valve components workingly connected to the input element, which follows a detaching of the armature from the permanent magnet, is cushioned before the input element has completed its maximum possible return stroke relative to the control valve housing. Said cushioning or damping of the return stroke motion is achieved in the present invention by the same spring, which biases the armature counter to actuating direction. To said end, said armature-restoring spring is coupled to the input element in such a way that the latter runs onto the spring only after detachment of the armature from the permanent magnet, i.e. after a cut-out of the brake assist function, and indeed before the input element has completed its return stroke. In all other operating states the spring is supported against a housing-fixed component and does not impede the return motion of the input element and/or of components connected to the latter. According to the invention, therefore, the energy introduced into the input element after cut-out of the brake assist function is taken up at least partially by the said spring, thereby preventing a metallically hard impact of the input element and/or of components connected thereto against parts of the control valve housing, which delimit the return stroke.
In a preferred form of construction of the vacuum brake booster according to the invention, a transmission piston, which is rigidly coupled to the input element, is provided in the region of its end remote from the input element with an annular groove, which has a fixed axial extension. Guided in an axially displaceable manner in said annular groove is an annular disk, against which the end of the armature-restoring spring remote from the armature is supported. The annular groove is so positioned and its axial extension is so dimensioned that the annular disk may come into contact with the edge of the annular groove remote from the input element only after detaching of the armature from the permanent magnet, i.e. only after a cut-out of the brake assist function.
The last-mentioned form of construction is preferably developed in such a way that the annular disk, when it is not in contact with the edge of the annular groove remote from the input element—i.e. in the majority of all of the operating states, is pressed by the armature-restoring spring towards a cover of the control valve housing. In said form of construction, the cover is the above-mentioned housing-fixed component, against which the spring is supported.
For further damping of possible metal impact noises, the annular disk at the side, which after cut-out of the brake assist function comes into contact with the edge of the annular groove, is preferably provided with a shock-absorbing elastomeric layer. With said elastomeric layer the annular disk is supported a
Lopez F. Daniel
Lucas Industries plc
MacMillan Sobanski & Todd LLC
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