Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Patent
1993-05-28
1995-04-25
Peng, John K.
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
340453, 188 111, 200 6140, 200 6144, B60Q 100
Patent
active
054102936
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for indicating wear on the cooperating frictional surfaces in vehicle brakes, comprising an electrical switch means disposed, upon a certain amount of wear on at least one of the said frictional surfaces, to activate a warning device.
Devices for indicating brake lining wear, so-called wear-detectors, are used for example in drum brakes for trucks, which have devices for automatically adjusting the play between the brake shoe lining and the wear surface of the drum in pace with the wear on the brake lining and the drum.
The wear detector serves in this case to increase safety and help the vehicle owner to plan for replacement of brake linings, thus reducing both down-time and shop costs.
A known type of wear detector comprises a sensor in the form of a switch cast in the lining material and connected to an electric circuit. When the lining layer above the switch has been worn away exposing the switch and when it comes into contact with the metal in the drum, a circuit is closed which activates a warning device, e.g. a warning light on the instrument panel of the vehicle.
A wear detector of this type has a number of disadvantages. The sensor embedded in the lining must be of the disposable type and thus be disconnected when the lining is replaced. It measures (indicates) only lining wear, and this creates uncertainty as to the total wear (lining and drum wear) and how must adjustment can be done before replacement is necessary. This is especially pronounced for asbestos-free linings which are made of a material which causes more wear to the drums than asbestos lining. If, for example, the lining is only halfway worn but the drum is so worn that the combined total wear is such that the adjustment device has reached a position corresponding to the maximum stroke length of the braking mechanism, there will still be no activation of the warning device in this previously known type of wear detector.
One purpose of the present invention is in general to provide a wear detector of the type described by way of introduction, which can indicate when the combined drum and lining wear amounts to a pre-determined value, regardless of the individual wear to each of the components, and which does not need to be disconnected or replaced during normal lining replacement.
This is achieved according to the invention by virtue of the fact that said switch means has a sensor means which is coordinated with a pair of interacting adjustment elements for adjusting play between the friction surfaces, said elements being adjustable to various positions relative to each other, and in that the sensor means are disposed to sense the relative positions of the adjustment elements and, at a certain pre-determined setting, actuate the switch means to activate the warning device.
By coordinating, in accordance with the invention, the wear detector with the adjustment mechanism instead of with the brake lining, one eliminates the uncertainty arising when only the lining wear is measured. The wear detector does not need to be disconnected when the linings or drums are replaced and it can be placed in an environment which is more protective than that of the lining material itself and, if needed, it can be easily replaced.
An additional purpose of the invention is to provide a wear detector which is particularly suited to a vehicle brake where the adjusting elements consist of a screw and nut device, e.g. of the type used in a so-called "Z cam brake". This type of brake has an internally threaded lifter head, into which a lifter screw has been screwed. A further development of the invention described above for such a vehicle brake is characterized in that the sensor means is displaceably supported by the nut means and has a portion in contact with the threaded portion of the screw, that its threaded portion is made with at least one interruption in the uniformity of the thread, and that the sensing means, upon contact with said interruption, is disposed to actuate the switch means to activate the warnin
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AB Volvo
Peng John K.
Tong Nina
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