Brakes – With condition indicator – Wear
Reexamination Certificate
1999-07-14
2001-04-10
Schwartz, Christopher P. (Department: 3613)
Brakes
With condition indicator
Wear
C188S085000, C188S072400, C073S130000
Reexamination Certificate
active
06213253
ABSTRACT:
BACKGROUND OF INVENTION
This invention is concerned with the testing apparatus for disc brakes.
FIELD OF THE INVENTION
A disc brake comprises a disc which rotates with a hub, two brake pads positioned on opposite sides of the disc, and pad moving means operable to cause the pads to be urged against the disc into a “brakes on” condition in which they apply significant braking forces to the disc. The pad moving means is often a calliper mechanism which often comprises a hydraulically-operated piston and cylinder assembly. Disc brakes normally do not provide for the pads to be pulled fully away from the disc after a brake application. Instead, when the pad moving means ceases to urge the pads against the disc, the pads are “knocked” away by the disc into a “brakes off” condition in which the pads are close to the disc but out of contact therewith.
SUMMARY OF THE INVENTION
In designing disc brakes, eg to select a combination of materials to form the disc and the pads, it is conventional to carry out testing programmes in which the disc brake is mounted on a testing apparatus (commonly called a dynamometer) and operated repeatedly so that measurements of performance and wear can be taken. Conventionally, such a testing apparatus is equipped with operating means operable to operate the pad moving means so that the brake alternates between its “brakes on” and “brakes off” conditions. Where the pad moving means operates hydraulically, the operating means varies the pressure of hydraulic fluid between a high pressure, eg about 30 bar, which causes the “brakes on” condition and substantially no pressure which allows the “brakes off” condition to occur. Repeated operation of the operating means simulates the application of the brakes in normal use. Hitherto, however, such testing apparatus has not been efficient in detecting whether a disc brake is susceptible to the phenomenon known as “brake judder”.
Brake judder occurs when a disc has an uneven thickness. Such uneven thickness results from parts of the disc intermittently contacting the pads when the brakes are in the “brakes off” condition. Conventional dynamometers do not control the position of the pads during the “brakes off” condition so that the possibility of disc thickness variation occurring is somewhat random and tests are not reliably repeatable.
It is an object of the present invention to provide a disc brake testing apparatus which is efficient at detecting whether a disc brake is susceptible to brake judder.
The invention provides a disc brake testing apparatus comprising operating means operable to operate pad moving means of the disc brake to cause the moving means to urge pads of the brake towards the disc thereof, the operating means being operable to urge the pads against the disc with a higher pressure sufficient to cause the pads to maintain constant contact with the disc and apply a significant braking force thereto, characterised in that the operating means is alternatively operable to urge the pads against the disc with a lower pressure selected to cause the pads to make intermittent contact with the disc during each revolution of the disc.
In an apparatus according to the invention, when the operating means operates with said lower pressure, the pads do not significantly brake the disc but make intermittent contact therewith (due to run-out, ie axis wobble, or disc thickness variation), thereby simulating, in a controlled and reproducible manner, the conditions which give rise to disc thickness variation. Said lower pressure has to be selected to suit the particular brake but pressures below 1 bar are suitable, eg 0.4 to 0.1 bar. Any disc thickness variation caused can then be measured after the test.
A testing apparatus according to the invention may also comprise monitoring means operable to monitor displacements of the pads, when the operating means operates with said lower pressure. Such monitoring means may, for example, detect variations in the pressure applied by the operating means. Such monitoring means can detect whether intermittent contact is occurring and, hence, whether said lower pressure requires adjustment.
Conveniently, a testing apparatus according to the invention comprises operating means comprising a high pressure fluid supply which is arranged to supply said higher pressure, and a low pressure supply which is arranged to supply said lower pressure. This arrangement avoids constant adjustment of the pressure of a single fluid supply. The pressures supplied by the high and low pressure fluid supplies will be different in different circumstances but, typically, said high pressure supply operates at about 30 bar and the low pressure supply at less than 1 bar, eg about 0.4 bar.
Where the operating means comprises low and high pressure fluid supplies, preferably, the operating means may be operable to adjust said lower pressure by altering the volume occupied by the fluid. For example, the operating means may alter said volume by operating a stepper motor or other servo device.
There now follows a detailed description, to be read with reference to the accompanying drawing, of a testing apparatus which is illustrative of the invention.
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Ferdani Philip
Hudson Simon Mathew
Paul Hans-Gunter
Federal-Mogul Technology Limited
Kramer Devon
Schwartz Christopher P.
Synnestvedt & Lechner LLP
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