Brakes – Wheel – Transversely movable
Patent
1996-07-03
1997-09-09
Poon, Peter M.
Brakes
Wheel
Transversely movable
192111A, F16D 5100
Patent
active
056646470
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FILED
This invention relates to a brake lever for an automotive S-cam drum brake, having a toothed clutch for transmitting torque in one direction between two coaxial members rotatably arranged relative to each other.
BACKGROUND OF THE INVENTION
The applicant has produced a brake lever of the above kind in large amounts for many years. This brake lever containing a slack adjuster for keeping the slack or distance between the brake linings and the brake drum constant irrespective of the brake lining wear is very well known in the art.
The brake lever has the general function of transmitting the brake force from a brake cylinder to a splined S-cam shaft, on which it is mounted. The main parts of the slack adjuster in the brake lever are a worm wheel mounted on the S-cam shaft and a worm screw meshing with the worm wheel. A slack adjusting movement may be transmitted from a control unit to the worm screw via the following parts coaxially arranged on the worm screw: a locking sleeve and a clutch sleeve, which are connected by means of a one-way clutch in the form of a locking spring, the clutch sleeve being connected to the worm screw by the toothed conical clutch referred to under the heading "Technical Field". This clutch is held engaged by a powerful clutch spring acting axially on the worm screw.
The primary function of the toothed conical clutch is to disconnect the adjusting mechanism during the elasticity part of the brake application so as to obtain a true slack adjusting function. During the adjustment, which occurs at brake release, the clutch is engaged and transmits an angular movement and a torque, the latter being great enough for affecting slack adjustment.
The clutch, however, has also to allow a manual rotation of the worm screw at replacement of worn out brake linings and at installation of the lever, which means that the maximum torque which may be transmitted shall not be too high.
In the present design with a certain number of symmetrical teeth in the clutch a balance between the above two factors has been reached with a certain angle between each tooth flank and the normal; in a practical case this angle is 68.degree. or in total 136.degree. between the two flanks.
It has appeared that the main reason for performance failure of the slack adjuster is that the conical clutch slips due to worn out teeth.
THE INVENTION
An improved toothed clutch with a longer life is according to the invention obtained in that each clutch tooth is made asymmetrical, its torque transmitting flank forming a greater angle with the normal than its opposite flank.
This improved design is based on the knowledge that the two functions of the clutch as mentioned above are performed by the same tooth flank, whereas the opposite one is never actually utilized.
The result of the asymmetrical design is that the active flank length increases and accordingly that the useful life greatly increases.
If according to the invention the number of clutch teeth and the angle of the torque transmitting flank are unchanged in relation to the conventional clutch with symmetrical clutch teeth, the added advantage is obtained that parts for conventional, symmetrical clutches are interchangeable with parts for asymmetrical clutches according to the invention, which simplifies the spare parts business.
It is a type of a paradox that the clutch according to the invention transmits torque in the rotational direction that normally at toothed one-way clutches is the release direction.
The invention has been described in conjunction with a special brake lever or slack adjuster. However, it is not limited to use herein. Other brake levers designed with the same operational characteristics can take advantage of the improvement according to the invention.
Also, the toothed clutch in the described slack adjuster is conical, but the principle of the invention can equally well be used in any toothed clutch of the kind referred to.
THE DRAWING
The invention will be described in further detail below under reference to the accompan
REFERENCES:
patent: 3901357 (1975-08-01), Reitz et al.
patent: 4094390 (1978-06-01), Neuman
patent: 4440268 (1984-04-01), Karlsson
patent: 4583622 (1986-04-01), Ebbinghaus et al.
patent: 4875557 (1989-10-01), Hagin et al.
Brown Laurence R.
Haldex AB
Poon Peter M.
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