Brake lever for drum brake

1. A brake lever for drum brake of a vehicle comprising:

a lever section for connection with a brake cylinder;

a housing section for attachment to a splined S-cam shaft; and

an adjustment device received in said housing section, the adjustment device comprising a first clutch (K 1 ), the first clutch (K 1 ) being biased by a first spring element with a spring force, and a second clutch (K 2 ) formed as a one-way clutch with a number of teeth (Z 2 ), the second clutch (K 2 ) being biased by a second spring element with a spring force;

characterized in that the teeth (Z 2 ) of the second clutch (K 2 ) have a slope angle and the second spring element is configured to apply the spring force, the slope angle and the spring force of the second spring element being tuned relative to each other so that the second clutch (K 2 ) generates a driving torque (M d ) which is always larger than a sum of all friction forces (M f ) which are induced into the adjustment device by friction, the driving torque (M d ) shifting the second clutch (K 2 ) into a completely engaged position as long as the first clutch (K 1 ) remains in a disengaged position.

2. The brake lever according to claim 1 , in which the adjustment device comprises a worm wheel for connection with the splined S-cam shaft and a worm screw in engagement with the worm wheel, the worm screw comprising a clutch wheel rotatably mounted on it, which is in engagement with the worm screw by means of the first clutch (K 1 ) under application of the spring force of the first spring element, in which a control arrangement is provided which transmits a control movement onto the clutch wheel subject to the angular position of the brake lever in relation to a fixed reference point, and in which the control arrangement comprises the second clutch (K 2 ).

3. The brake lever according to claim 2 , in which the control arrangement comprises a control disc being rotatable arranged coaxially to the worm wheel and connected to a control ring which comprises a control arm which is connected to a fixed part of the vehicle chassis for defining the reference point, a pinion being in engagement with the control disc by means of a gear toothed connection, and an adjustment screw being arranged coaxially to the pinion and connected to the clutch wheel by means of a gear toothed connection, in which the axis of the worm screw is directed perpendicular to the common axis of the pinion and the adjustment screw.

4. The brake lever according to claim 1 , in which the adjustment device comprises a worm wheel and a worm screw in engagement with the worm wheel, the worm screw comprising a clutch wheel rotatably mounted on it, and the first clutch (K 1 ) comprises a number of teeth (Z 1 ) on conical surfaces of both the worm screw and the clutch wheel.

5. The brake lever according to claim 4 , in which a control arrangement is provided which transmits a control movement onto the clutch wheel subject to the angular position of the brake lever in relation to a fixed reference point, the control arrangement comprising the second clutch (K 2 ) and an adjustment screw connected to the clutch wheel by means of a gear toothed connection, the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 2×Z 1 /U, where U is a gear ratio between the clutch wheel and the adjustment screw.

6. The brake lever according to claim 1 , in which the adjustment device comprises a worm wheel and a worm screw in engagement with the worm wheel, the worm screw comprising a clutch wheel rotatably mounted on it, and the first spring element applies the spring force via a washer onto the end of the worm screw, in which the washer is configured in such a way that the force contact is restricted to a conical surface and/or to a radius which almost corresponds to a support diameter of the worm screw.

7. The brake lever according to claim 1 , in which a control arrangement is provided which transmits a control movement onto the clutch wheel subject to the angular position of the brake lever in relation to a fixed reference point, the control arrangement comprising the second clutch (K 2 ) and an adjustment screw connected to the clutch wheel by means of a gear toothed connection, the spring force acting onto the adjustment screw is only provided by the spring force acting onto the second clutch (K 2 ).

8. The drum brake for a vehicle, in particular for a heavy road vehicle, comprising the brake lever for the splined S-cam shaft according to claim 1 .

9. The brake lever according to claim 5 , in which the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 1.5×Z 1 /U.

10. The brake lever according to claim 5 , in which the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 1.0×Z 1 /U.

11. The brake lever according to claim 3 , in which the first clutch (K 1 ) comprises a number of teeth (Z 1 ) on conical surfaces of both the worm screw and the clutch wheel.

12. The brake lever according to claim 11 , in which the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 2×Z 1 /U, where U is a gear ratio between the clutch wheel and the adjustment screw.

13. The brake lever according to claim 11 , in which the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 1.5×Z 1 /U, where U is a gear ratio between the clutch wheel and the adjustment screw.

14. The brake lever according to claim 11 , in which the number of teeth (Z 2 ) of the second clutch (K 2 ) is smaller than 1.0×Z 1 /U, where U is a gear ratio between the clutch wheel and the adjustment screw.

15. The brake lever according to claim 3 , in which the spring force acting onto the adjustment screw is only provided by the spring force acting onto the second clutch (K 2 ).