Brakes – With condition indicator – Electrical
Patent
1998-11-19
2000-08-22
Oberleitner, Robert J.
Brakes
With condition indicator
Electrical
3242072, 3242075, F16D 6600
Patent
active
061057304
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a device for indicating wear of brake linings in a vehicle brake, preferably actuated via an automatic brake lever with a built-in brake adjuster, the lever being intended for transmitting brake force from a brake cylinder and being mounted on a brake actuating cam shaft. The device may also be used for indicating the stroke of a brake cylinder push rod connected to the brake lever. Although the device is stated to be used with a brake lever, other similar uses are possible within the scope of the invention.
BACKGROUND OF THE INVENTION
Many devices for the above purpose are known, ranging from simple mechanical devices to rather complicated electrical or electronic devices. A good example of the latter category is the device shown in U.S. Pat. No. 5,253,735, which is regarded is the closest prior art. Here, three discs, which are rotatable relative to each other and are arranged on the cam shaft adjacent the brake lever, are provided with magnets and hall-elements in a certain arrangement for supplying certain information about the condition of the brake.
The basic function of a device as defined is to supply information about the wear of the brake linings, so that they can be replaced in time, and accordingly the name wear sensor may be used. However, a wear sensor properly designed and installed can also supply useful information about the piston stroke of the brake cylinder used and about the overall function of the brakes on the vehicle.
It is of great importance that a wear sensor is sturdy and can resist the extremely harsh environmental conditions under the vehicle. The sensor shall also have small dimensions due to the often very limited available space. The information provided from the sensor shall be as accurate as possible and shall be compatible with other information available in modern vehicles, where computers and other electronic equipment are used to an increasingly large extent.
THE INVENTION
A wear sensor fulfilling the above and other requirements is according to the invention obtained in that a coded disc, on its surface being divided into a number of equally large circle sectors, has at least one coded path, shaped as a circle segment, with equally long magnetic areas in each sector, the magnetic areas being of different lengths in different coded paths, and that a hall-element is provided in a part adjacent the coded disc for sensing each coded path, the coded disc and said part being rotationally arranged in relation to each other.
The coded disc is preferably connected to the cam shaft, whereas the hall-elements are arranged in a cover of a housing for the device.
In a practical and preferred embodiment the coded disc has three sectors each with an angle of 120.degree., which in principle will be the maximal operating range of the wear sensor; two of these sectors have two coded paths each, whereas the third sector has three coded paths, and the number of hall-elements is seven.
In this way the accuracy of the device will be 10.degree., which is regarded as very good.
If only information about the wear condition is required, the wear sensor housing is connected to the brake lever, which gives a simple device with comparatively few variants.
If also information about the brake cylinder piston stroke and the brake function is desired, the housing shall be connected to a fixed part in the vehicle underframe.
Electronic circuitry for transforming the signals from the hall-elements into an analog or digital output signal suitable for further processing in the vehicle is mounted in the cover.
The total thickness of the device (coded disc and housing with hall-elements as well as electronic circuitry) may be as small as 10 mm, which in many instances is the only available space for the sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in further detail below, reference being made to the accompanying drawings, in which FIG. 1 is a side view, partly in section, of an automatic brake lever with a first embodiment of
REFERENCES:
patent: 4440268 (1984-04-01), Karlsson
patent: 5253735 (1993-10-01), Larson
patent: 5313159 (1994-05-01), Allwine
patent: 5757180 (1998-05-01), Chou
Haldex Brake Products AB
Kramer Devon
Oberleitner Robert J.
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