Spreader unit for a motor vehicle drum brake
A spreader unit for a drum brake is provided with a readjustment device which ensures that the clearance remains substantially constant even in the case of wear on the brake linings. The readjustment device is arranged between actuating pistons and changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value. A thermally actuable blocking device mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value.
1. A spreader unit for a drum brake, comprising:
a housing;
a first and second brake shoe holders that are rotationally secured to the housing, and actuatable linearly along an axis, respectively away from one another in a spreading direction and respectively toward one another in a release direction;
a first and a second brake shoe provided respectively with a brake lining;
a readjustment device arranged between the actuating pistons, wherein the readjustment device changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value;
a thermally actuable blocking device mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value;
an electromechanical actuator comprising an electric motor to drive the spreader unit; and
an electric load measurement device acting one of directly and indirectly on the spreader unit.
2. The spreader unit as claimed in claim 1 , wherein the readjustment device further comprises a freewheel clutch having two claws, wherein the claws carry out a relative stroke during freewheeling and wherein one claw is rotationally secured to the first brake shoe holder and the other claw is connected to the second actuating piston via a threaded spindle, and wherein the blocking device is arranged operatively parallel to the clutch to keep the claws apart in the activated state.
3. The spreader unit as claimed in claim 2 , wherein the claws have, on a respective one of their end faces, sawtooth ramps that extend in a circle and engage in one another, wherein the length of a ramp on the circular arc defines the predetermined step width and the height of the ramp defines a maximum claw stroke.
4. The spreader unit as claimed in claim 2 , wherein the claw connected to the first brake shoe holder is a latching sleeve which is firmly connected to the first brake shoe holder, and the other claw coupled to the second actuating piston is a readjustment piston, wherein the latching sleeve is rotationally secured with respect to the second brake shoe holder, is axially movable with respect to the second actuating piston, and is elastically preloaded against the readjustment piston.
5. A spreader unit for a drum brake, comprising:
a housing;
a first and second brake shoe holders that are rotationally secured to the housing, and actuatable linearly along an axis, respectively away from one another in a spreading direction and respectively toward one another in a release direction;
a first and a second brake shoe provided respectively with a brake lining;
a readjustment device arranged between the actuating pistons, wherein the readjustment device changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value; and
a thermally actuable blocking device mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value;
wherein the readjustment device further comprises a freewheel clutch having two claws, wherein the claws carry out a relative stroke during freewheeling and wherein one claw is rotationally secured to the first brake shoe holder and the other claw is connected to the second actuating piston via a threaded spindle, and wherein the blocking device is arranged operatively parallel to the clutch to keep the claws apart in the activated state;
wherein the blocking device has a bimetallic element, and a blocking space is located between and is laterally delimited by the claws, wherein at least a portion of the bimetallic element passes into the blocking space at least when the maximum claw stroke has been reached.
6. The spreader unit as claimed in claim 5 , wherein the bimetallic element has a spiral spring, the diameter of which changes depending on temperature and wherein an outer edge of the spiral spring passes into the blocking space upon temperature-dependent expansion.
7. The spreader unit as claimed in claim 5 , wherein the bimetallic element has at least one arm extending from a center, which lengthens depending on temperature and wherein a distal end passes into the blocking space upon temperature-dependent lengthening of the arm.
8. The spreader unit as claimed in claim 7 , wherein the bimetallic element has a plurality of arms.
9. The spreader unit as claimed in claim 8 , wherein the plurality of arms are arranged in a star shape.
10. The spreader unit as claimed in claim 5 , wherein the bimetallic element has two disk springs which are arranged in opposite directions, one respective side face of which assumes a convex or concave shape depending on temperature and at least the outer edges of which are located in the blocking space.
11. The spreader unit as claimed in claim 10 , wherein at least two pairs of disks are provided.
12. The spreader unit as claimed in claim 11 , wherein a spacer ring is located between the pairs of disks.
13. A spreader unit for a drum brake comprising:
a housing;
a first and second brake shoe holders that are rotationally secured to the housing, and actuatable linearly along an axis, respectively away from one another in a spreading direction and respectively toward one another in a release direction;
a first and a second brake shoe provided respectively with a brake lining, having at least one rotation-translation converter mechanism;
a readjustment device arranged between the actuating pistons, wherein the readjustment device changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value; and
a thermally actuable blocking device which mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value;
wherein the spreader is electromechanically drivable with the aid of an electromechanical actuator comprising an electric motor; and
wherein the spreader is equipped indirectly or directly with an electric load measurement device.
14. The speader unit of claim 13 , wherein the at least one rotation-translation converter mechanism is at least one of:
a ball-ramp apparatuses, wherein a first ball-ramp apparatus has a first actuating piston that is arranged so as to be rotatable about an axis and optionally a second ball-ramp apparatus has a second actuating piston that is arranged so as to be rotatable about an axis;
at least one nut-spindle transmission; and
a mixed configuration having features of the ball-ramp apparatuses and the at least one nut-spindle transmission.
15. The speader unit of claim 13 , wherein the electric load measurement devices cooperates with the load measurement device for the purpose of applying the drum brake under electrical open-loop and/or closed-loop control.
16. The speader unit of claim 13 , wherein the at least one nut-spindle transmission has inserted rolling bodies.