Motors: expansible chamber type – Working member position feedback to motive fluid control – Plural input signal means for single motor valve
Reexamination Certificate
2001-02-02
2003-01-14
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
C091S369200
Reexamination Certificate
active
06505539
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a vacuum brake booster comprising a vacuum chamber and a working chamber separated from one other in a pressure-proof manner by a movable wall, as well as a control valve which comprises a housing workingly coupled to the movable wall and containing a first valve seat, which is disposed in said housing and to achieve a pressure difference at the movable wall is capable of controlling the supply of at least atmospheric pressure to the working chamber in dependence upon the displacement of an input element of the brake booster coupled to the first valve seat. Vacuum brake boosters of said type have been known for some time and millions of them are being used to boost the actuating forces of a vehicle hydraulic brake system and thereby keep them at a level, which is comfortably low for the driver of a vehicle.
Also known are so-called braking assistants. By said term is usually meant a system, which in an emergency braking situation, given substantially the same actuating force, may provide a driver with increased braking power. Systems of said type were developed because research revealed that most vehicle users in an emergency braking situation do not press on the brake pedal as hard as is needed to achieve the maximum braking power. The stopping distance of the vehicle is therefore longer than necessary. Systems of said type, which are already in production, use an electromagnetically actuable brake booster combined with a device which is capable of determining the actuating speed of the brake pedal. When said device detects an actuating speed above a preset threshold value, it is assumed that an emergency braking situation exists and the brake booster is set by the electromagnetic actuating device to full output, i.e. it provides its maximum boosting power.
Brake boosters with an electromagnetic actuating facility are however too expensive for low- to medium-priced motor vehicles.
There is therefore a call for solutions which achieve a braking assistance function with a lower outlay.
SUMMARY OF THE INVENTION
The object of the invention is to provide a vacuum brake booster of the described type with a braking assistance function without having to have recourse to an electromagnetically actuable control valve. At the same time, unintentional tripping of the braking assistance function is to be avoided as far as possible.
According to the invention, therefore, 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. The armature, which is reciprocable relative to the permanent magnet, is preloaded resiliently 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 resilient preloading counter to actuating direction. In the course of an approach to the permanent magnet, which occurs when the brake booster is actuated, the armature may become less than a previously defined second distance away from the permanent magnet, which is smaller than the first distance. When the armature is less than said distance away, the armature is pulled by the permanent magnet counter to the resilient preloading force acting upon the armature and with simultaneous cancellation of its rigid coupling in actuating direction to the input element into contact with the permanent magnet. Thus, even if the actuating force introduced into the brake booster does not increase, the first valve seat coupled to the armature remains fully open so that the brake booster builds up the maximum pressure difference between its vacuum chamber and its working chamber, i.e. the brake booster provides its maximum boosting power.
In preferred embodiments of the vacuum brake booster according to the invention, said second distance is defined by the magnitude of the resilient preloading force acting upon the armature. When the resilient preloading force acting upon the armature is low, this means that the said second distance is relatively great, i.e. the threshold which has to be crossed to trip the braking assistance function is relatively low. The opposite applies when the resilient preloading force acting upon the armature is high. Thus, by suitably selecting the resilient preloading force acting upon the armature and the said first distance it is possible to preselect a tripping threshold, which on the one hand prevents unintentional full brake applications but on the other hand may still be reliably crossed when necessary, even by drivers who possess less strength.
To enable the previously described tripping threshold to be selected according to requirements without excessively varying the forces to be summoned up by the user during a braking operation, according to a preferred embodiment of the vacuum brake booster according to the invention an element, which is movable relative to the armature, is resiliently preloaded relative to the armature in such a way that it projects from the armature in the direction of the permanent magnet and in the starting position of the control valve (neutral position) is not in contact with the permanent magnet. It is only when the element, which is movable relative to the armature, upon actuation of the vacuum brake booster has been applied against the permanent magnet that the resilient preloading force, which defines the said second distance, acts upon the armature. When the armature is of a hollow-cylindrical design, the element movable relative to the armature and projecting from the latter in the direction of the permanent magnet may, for example, take the form of a spacer sleeve disposed concentrically with the armature. Such a spacer sleeve may be situated radially outside of, or alternatively radially inside, the armature. However, the element movable relative to the armature need not be sleeve-shaped and may alternatively be of a different configuration, e.g. pin-shaped.
In preferred embodiments of the vacuum brake booster according to the invention, the permanent magnet is guided displaceably in the control valve housing and is preferably moreover preloaded counter to actuating direction resiliently against a stop. Such an embodiment has the advantage that, when the armature in the course of a rapidly effected actuation of the brake booster has become less than the previously defined second distance away from the permanent magnet and has consequently been pulled into contact with the permanent magnet and the actuating force exerted upon the input element is further increased, said actuating force is not transmitted from the input element via the unit comprising armature and permanent magnet to the control valve housing and from there to a master cylinder disposed downstream of the vacuum brake booster, rather an increased actuating force exerted upon the input element is transmitted directly from the input element to the downstream master cylinder. The magnetic device, in particular the armature, the permanent magnet and the components accommodating said parts, may therefore be of a less stable design. When, for all conceivable actuating situations, the intention is to prevent the magnetic device from changing into a force-transmitting state, then the permanent magnet has to be displaceable in actuating direction relative to the control valve housing by a distance which is greater than the maximum possible actuating stroke of the input element minus the said first distance.
Given the provision of a stop for the permanent magnet, in order to prevent a misalignment of the contact face of the permanent magnet with the contact face of the armature from arising as a result of manufacturing tolerances and possibly leading to canting and subsequent jamming of the armature and/or permanent magnet, in preferred embodiments the stop for the permanent magnet and/or the contact face, which is formed on the permanent
Lopez F. Daniel
Lucas Industries plc
MacMillan Sobanski & Todd LLC
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