GB2373834A

GB2373834A - Free rotation coupling for brake actuator

Info

Publication number: GB2373834A
Application number: GB0205957A
Authority: GB
Inventors: Hans-Martin Heinkel; Guenther Schmidt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-03-24
Filing date: 2002-03-14
Publication date: 2002-10-02
Also published as: DE10114471A1; GB0205957D0; JP2002364683A

Abstract

A vehicle brake 12 actuation device comprises electro-motor 14 driving toothed wheel step down gearing 18 and a nut 32 and spindle 34 rotation to translation actuator via a claw coupling 16 The coupling has circular parallel discs 38, 40 with claws 42, 44 on the peripheries of their facing sides. The discs have a free rotation angle of almost 180{ in both directions of rotation before the claws abut to define the free rotational angle. When the coupling is idle spring 50 positions the discs to ensure free rotation on motor start. The electromotor starts smoothly over the free rotational angle until the claws abut. Motor inertia gained is used to overcome initial breakaway torque of gearing mechanisms to actuate the brake. Removes the need for oversized motors to handle breakaway torque. The motor may be initially turned opposite to its running direction to ensure maximum free rotation.

Description

DESCRIPTION

Coupling. a device comprising the coupling for actuating a vehicle brake and method of starting the device The invention relates to a coupling device comprising the coupling for actuating a vehicle brake and a method of starting the device.

When starting gearing mechanisms or units and devices which can generally be driven in a rotating manner, the problem arises that it is necessary to overcome the so-called initial breakaway torque, in order to set the gearing mechanism in motion from standstill. The initial breakaway torque occurs as a result of static friction which must be overcome, in order to set the gearing mechanism in motion from standstill. With respect to a moving gearing mechanism, it is merely necessary to overcome a lower amount of sliding friction.

By virtue of the transition from static friction to sliding friction when setting the gearing mechanism in motion from standstill, i.e. starting the gearing mechanism, drive torque decreases abruptly. After a lengthy period of inactivity, lubricating films can be interrupted in bearings and on sliding points, e.g. of toothed flanks, which slide against each other, of mutually meshing toothed wheels or toothed wheel gearing mechanisms, on engaged threads of spindles and nuts of a spindle drive etc.. The static friction and thus the required initial breakaway torque can be up to 30% above the sliding friction or the drive torque of the gearing mechanism in motion.

A drive motor must be dimensioned with a torque reserve for the purpose

Let! of overcoming the initial breakaway torque during the start procedure, in order to ensure that the gearing mechanism or the like starts up even after ageing' in the event of under-voltage when using an electromotor and at low temperature. The drive motor is thus actually over-dimensioned for driving the gearing mechanism, if the initial breakaway torque is not taken into consideration. The required torque reserve is considered to be disadvantageous in practice, in particular when using an electromotor as the drive motor, which is why the invention is directed in particular to an electromotor as the drive motor. The required torque reserve requires a larger and heavier electromotor which has an increased current consumption and in turn necessitates an adequate power supply.

The invention is directed specifically to a device for actuating a vehicle brake which in particular comprises an electromotor as a drive motor which actuates the brake by way of a rotation/translation conversion gearing mechanism, e.g. a helical gearing mechanism. If the brake is designed as a parking brake, then the rotation/translation conversion gearing mechanism is self-locking for the purpose of maintaining an applied braking force for an unlimited period of time if the electrometer is not supplied with current. In the case of a self- locking gearing mechanism, the initial breakaway torque is typically particularly high, which is why the invention is directed in particular to a device for actuating a brake, in particular a parking brake of a vehicle.

According to one asprect of the invention, there is provided a coupling for the purpose of transmitting a rotational movement, the coupling comprising a free (

rotational angle in at least one direction of rotation and includes a rotational stop which defines the free rotational angle.

coupling in accordance with the invention thus includes a free rotational angle in at least one direction of rotation which is defined by means of a rotational stop. When driving e.g. a gearing mechanism or even another device or unit, which can be driven in a rotating manner, by means of a drive motor, in particular an electromotor, during the starting procedure the free rotational angle of the coupling serves to start the electromotor while initially the gearing mechanism is still at a standstill. The swing or the inertia of the rotating masses of the already started electromotor overcomes the initial breakaway torque of the gearing mechanism still at a standstill, wherein in order to overcome the initial breakaway torque of the gearing mechanism, the rotational stop of the coupling is designed to function in the most abrupt manner possible. Since the swing of the already started electromotor is used for the purpose of overcoming the initial breakaway torque of the gearing mechanism, the electromotor does not need to be dimensioned with a torque reserve for starting the gearing mechanism or in any event the torque reserve of the electromotor is less than without the interconnection of the coupling in accordance with the invention. The coupling in accordance with the invention thus allows a smaller, lighter and lower-power electromotor or other drive motor for the purpose of driving a gearing mechanism or other device.

In accordance with claim 4, a resilient element is provided which in the

case of a torque-free coupling moves the drive-side and the driven-side thereof away from the rotational stop and thereby provides the free rotational angle for the starting procedure. After switching off the drive motor, the resilient element serves to turn the drive-side and the drive motor back over the range of the free rotational angle. The resilient element can be e.g. a metal spring, it can also comprise a rubber-elastic element or an elastomer.

In accordance with claim 5, the coupling can be integrated into an electromotor. This has the advantage of a compact construction of the electromotor including the coupling, which comprises the free rotational angle, for the purpose of the starting the motor. In accordance with claim 6, the coupling which is integrated into the electromotor is connected between the armature and a motor shaft. In the case of this embodiment of the invention, the armature can be rotated with respect to the motor shaft over the limited free rotational angle provided by the coupling.

Claim 7 is directed to a device for actuating a brake, in particular a parking

brake of a vehicle which can be actuated by means of a drive motor, in particular an electromotor, wherein the term actuation is intended to refer both to the application and release of the brake. By way of a rotation/translation conversion gearing mechanism with the interconnection of the coupling in accordance with the invention, a rotating drive movement of the drive motor is converted into a linear movement for the purpose of actuating the brake.

In accordance with claim 8, the coupling of the device for the purpose of

-; actuating the brake comprises a free rotational angle in the direction in which the brake is released. When the brake is applied, the rotation/translation conversion gearing mechanism and an optionally preconnected step-down gearing mechanism are also at a standstill under loading, the gearing mechanism is prestressed and as a result the initial breakaway torque is high. The free rotational angle is therefore provided in the direction in which brake is released, in order to make it easier to start the motor and the gearing mechanism when releasing the applied brake. In order to apply the released brake, a free rotational angle of the coupling can be omitted from the coupling, since the torque required for actuating the brake is low at the beginning of the brake application procedure and moreover the initial breakaway torque dependent thereupon is likewise low.

In order to be able to use the brake as a parking brake, the device, in particular its rotation/translation conversion gearing mechanism, is formed in a self-locking manner in accordance with claim 12, so that an applied braking force is retained when no current is supplied to the motor. In the case of a self-locking gearing mechanism, the initial breakaway torque is typically particularly high and therefore it is particularly advantageous to use the coupling in accordance with the invention. In order to overcome the initial breakaway torque, the method in accordance with the invention having the features of claim 14 renders it possible to drive the drive motor, prior to the actual start, for a short period in an opposite direction of rotation to an intended rotational direction and immediately thereafter

to drive it in the intended direction of rotation. By rotating the drive motor in th opposite direction prior to the actual start-up, all of the play present in the gearing mechanism and the free rotational angle of the coupling are utilized completely for the purpose of starting the motor. During the start-up in the intended direction of rotation, the drive motor is set in motion thus utilizing the free rotational angle of the coupling and the play in the gearing mechanism, before a load is moved by the gearing mechanism, e.g. the brake is applied. The initial breakaway torque is thereby overcome utilizing the free rotational angle of the coupling and the play in the gearing mechanism. If the play in the gearing mechanism is adequate, then it is possible to dispense with the coupling which comprises the free rotational angle.

The invention will be described in detail hereinunder, by way of example only, with reference to two exemplified embodiments which are illustrated in the accompanying drawings, in which Figure I shows a simplified and schematic illustration of a device in accordance with the invention for the purpose of actuating a vehicle brake using a coupling in accordance with the invention; Figure 2 shows a view of an end face of a part of the coupling according to arrow II in Figure 1; and Figure 3 shows an electromotor having an integrated coupling in accordance with the invention.

The device 10 in accordance with the invention and illustrated in Figure 1 for the purpose of actuating a brake 12 illustrated as a symbol comprises an electromotor 14 as a drive motor. The electromotor 14 drives a toothed wheel gearing mechanism 18 by way of coupling 16 to be described hereinafter. The toothed wheel gearing mechanism 18 is a step- down gearing mechanism and in the illustrated exemplified embodiment of the invention it is formed in two stages with a first and a second gearing mechanism stage 20,22. The first gearing mechanism stage 20 comprises a (small) drive toothed wheel 24 which meshes with a (large) driven toothed wheel 26. The drive toothed wheel 24 of the first gearing mechanism stage 20 can be driven in a rotating manner by way of the coupling 16 with the electrometer 14. The driven toothed wheel 26 of the first gearing mechanism stage 20 is non-rotatable with a (small) drive wheel 28 of the second gearing mechanism stage 22 which meshes with a (large) driven toothed wheel 30 of the second gearing mechanism stage 22.

The driven toothed wheel 30 of the second gearing mechanism stage 22 is non-rotatable with a nut 32 which is in engagement with a spindle 34. By virtue of the rotating drive of the nut 32, the spindle 34 is displaced in an axial manner.

By way of a brake actuation mechanism [not illustrated], the spindle 34 actuates the brake 12, wherein the term actuation refers both to the application and release of the brake 12. Braking mechanisms of this type are known to the person skilled in the art and will not be explained in detail here because they do not form part of the actual subject matter of the invention. A sliding spring 36, which lies both in

a groove of the spindle 34 and also in a groove in a spindle bearing, serves to hold the spindle 34 in a non-rotational manner. The spindle 34 together with the nut 32 forms a spindle drive 32,34 which converts a rotational movement of the nut 32 into a translation movement (displacement) of the spindle 34. The spindle drive 32,34 is thus a rotation/translation conversion gearing mechanism.

The spindle drive 32,34 is self-locking, i.e. the spindle 34 cannot be displaced by an axial force upon the spindle 34 but only by rotating the nut 32.

Therefore, the brake 12 can be used not only as a service brake but also as a parking brake which maintains an applied braking force when no current is supplied to the electrometer 14.

The coupling 16 is formed as a claw coupling, it comprises two circular discs 38, 40 which are disposed in parallel and flush with each other and at a mutual spacing. On mutually facing end faces, the discs 38, 40 each comprise a claw 42, 44 which are disposed on the periphery of the discs 38,40 (Figure 2). By virtue of the claws 42,44, the two discs 38,40 can be rotated against each other over the range of a free rotational angle. Starting from a middle position, in which the two claws 42, 44 are diametrically opposed to each other, the free rotational angle amounts to almost 180 in both directions of rotation. Both discs 38,40 are nonrotatable with the shafts 46,48, wherein one shaft 46 is non-rotatable with a motor shaft of the electromotor 14 and the other shaft 48 is nonrotatable with the drive toothed wheel 24 of the first gearing mechanism stage 20 of the toothed wheel gearing mechanism 18. The shaft 46 which is non-rotatable with the motor

shaft of the electromotor 14 forms a drive shaft of the coupling 16, the disc 38 which is non-rotatable with the drive shaft 46 forms a drive disc 38. The drive shaft 46 and the drive disc 38 form a drive-side 38, 46 of the coupling 16. The shaft 48 which is non-rotatable with the toothed wheel 24 forms a driven shaft 48 of the coupling 16, the disc 40 which is non-rotatable with the driven shaft 48 forms a driven disc 40. The driven disc 40 and the driven shaft 48 form a driven-

side 40, 48 of the coupling 16. The two claws 42, 44 form a rotational stop 42, 44 of the claw coupling 16 which defines the free rotational angle of the drive disc 38 with respect to the driven disc 40 in both directions of rotation.

Disposed in an intermediate space between the two discs 38,40 of the claw coupling 16 is a resilient element 50. In the illustrated exemplified embodiment, the resilient element 50 is formed as a helical spring, of which one end is connected by means of an alignment pin 52 to the drive disc 38 and the other end thereof is connected by means of an alignment pin 54 to the driven disc 40. The resilient element 50 forms a torsion spring which upon torque-free coupling 16 rotates its two discs 38,40 against each other to the illustrated middle position, in which the two claws 42,44 are diametrically opposed. In this middle position, the coupling 16 comprises in both directions the aforementioned free rotational angle of almost 180 , until the two claws 42,44 abut against each other and thereby define the free rotational angle.

The coupling 16 is provided for the purpose of overcoming the initial breakaway torque of the toothed wheel gearing mechanism 18, the spindle drive

32, 34 and the actuation mechanism [not illustrated] of the brake 12. If the electrometer 14 is supplied with current for the purpose of actuating the brake 12, then a rotor of the electromotor starts together with the motor shaft, the drive shaft 46 and the drive disc 38 of the claw coupling 16. Since, as the electrometer 14 starts, the gearing mechanisms 18, 32, 34 and the actuation mechanism of the brake 12 are at a standstill until the claws 42, 44 of the claw coupling 16 impinge upon each other, it is readily possible to start the motor. If the claws 42, 44 impinge upon each other, the swing, i.e. a moment of inertia of the rotating masses of the started eleetromotor 14 is transmitted abruptly to the gearing mechanisms 18, 32, 34 and the actuation mechanism of the brake 12, so that the initial breakaway torque for the purpose of overcoming static friction of the gearing mechanisms 18, 32, 34 and the actuation mechanism of the brake 12 during the transition from a standstill position to a position of motion is overcome by the swing of the already started electromotor 14. By virtue of the claw coupling 16, the swing of the starting electromotor 14 is used for the purpose of overcoming the initial breakaway torque of the gearing mechanisms 18, 32, 34 and the actuation mechanism ofthe brake 12. This applies to the direction in which the brake 12 is both applied and released.

If the electromotor 14 is switched off, the self-locking spindle drive 32, 34 holds the toothed wheel gearing mechanism 18 and by means of this the driven-

side 4(), 48 of the claw coupling 16 in a non-rotational manner. The spring element 50 rotates the drive-side 38, 46 of the claw coupling 16 and the motor

shaft and the rotor of the electromotor 14 by almost 180 back to the middle position of the claw coupling 16, in which the claws 42, 44 are diametrically opposed. In this manner, the resilient element SO provides the free rotational angle in both directions of rotation for the next starting procedure of the electromotor 14.

The method in accordance with the invention renders it possible to supply current to the electromotor 14, for the purpose of actuating the brake 12, initially for a short period in an opposite direction of rotation to the intended direction of rotation for the purpose of actuating the brake 12 and immediately thereafter to supply current to the said electromotor conversely in the intended direction of rotation. By means of the brief counter-rotation of the electromotor 14 before it actually starts in the intended direction of rotation, the free rotational angle of the coupling 16 is used to the maximum extent. In addition, any play in the toothed wheel gearing mechanism 18 and the spindle drive 32, 34 is utilized for starting the electromotor 14 for the purpose of overcoming the initial breakaway torque.

The resilient element 50 can be dispensed with in this case, since the brief counter-rotation of the electromotor 14 prior to it actually starting ensures the free rotational angle of the claw coupling 16.

Figure 3 shows an electromotor 56, into which a coupling 58 is integrated which provides a free rotational angle for starting the electromotor 56. The electromotor 56 can be used, for example, in the device for actuating the brake 12 as illustrated in Figure 1. In this case, the electromotor 56 as shown in Figure 3

replaces the electromotor 14 including the claw coupling 16 as shown in Figure 1, the drive toothed wheel 24 of the first gearing mechanism stage 20 is attached directly in a non-rotational manner to an end 62 of a motor shaft 64 of the electromotor 56 which end protrudes from a motor housing 60 of the electromotor 56.

The electrometer 56 as shown in Figure 3 comprises the motor shaft 64 which is mounted in a rotatable manner in the motor housing 60 by means of ball bearings 66. Arranged on the motor shaft 64 is an armature 68 having an armature core pack 70 and armature windings 72. The armature core pack 70 is not directly arranged on the motor shaft 64 but rather to a tube which forms a hollow shaft 74.

The hollow shaft 74 and thus the armature 68 as a whole can be rotated on the motor shaft 64.

Disposed in a manner known per se around the armature is a number of permanent magnets 69 on an inner side of the motor housing 60 which form a stator of the electromotor 56.

The claw coupling 58 of the electrometer 56 comprises two cylindrical pins 76, 78. One of the two cylindrical pins 76 is pressed into a transverse bore of the motor shaft 64 and protrudes on one side from the motor shaft 64. This cylindrical pin 76 is located on one front end of the annature 68. The other cylindrical pin 78 is pressed, axis-parallel with the motor shaft 64, into a hole 80 in the armature core pack 70. This cylindrical pin 78 protrudes from the front end of the armature 68, on which is disposed the cylindrical pin 76 which is pressed

into the motor shaft 64. Upon rotation of the armature 68 with respect to the motor shaft 64, the cylindrical pin 76 which is pressed into the motor shaft 64 abuts with its end, which protrudes from the motor shaft 64, against the cylindrical pin 78 which is pressed into the armature core pack 70 and protrudes from the armature core pack 70. This defines a free rotational angle, over which the armature 68 can be rotated with respect to the motor shaft 64.

The coupling 58 which is integrated into the electromotor 56 comprises a resilient element 82 which is formed as a torsion helical spring. In the region of the two cylindrical pins 76, 78 of the coupling 58, the resilient element 82 is arranged on the motor shaft 64 on one sides remote from the armature 68, of the cylindrical pin 76 which is pressed into the motor shaft 64. One end 84 of the resilient element 82 is curved radially inwardly and lies in a longitudinal groove 86 of the motor shaft 64. As a consequence, this end 84 of the resilient element 82 is connected in a non-rotational manner to the motor shaft 64. The other end of the resilient element 82 is curved with respect to an outward protruding eyelet 88 which lies in a circumferential groove in the end, which protrudes from the armature core pack 70, of the cylindrical pin 78 which is pressed into the armature core pack 70. By means of the eyelet 88, which surrounds the cylindrical pin 78 which is pressed into the armature core pack 70, the resilient element 82 is connected to the armature 68 in a non-rotational manner in both directions of rotation. When no current is supplied to the electromotor 56, the spring-elasticity of

the resilient element 82 causes it to rotate the armature 68 with respect to the motor shaft 64 in such a manner that the end, which protrudes from the motor shaft 64, of the cylindrical pin 76, which is pressed into the motor shaft 64, is remote from the cylindrical pin 78 which is pressed into the armature core pack 70. Consequently, as the electromotor starts, the armature 68 comprises in both directions of rotation a free rotational angle of almost 180 , until the cylindrical pin 78 which is pressed into the armature core pack 70 abuts against the cylindrical pin 76 which is pressed into the motor shaft 64 and as a consequence the rotating armature 68 causes the motor shaft 64 to rotate.

If a free angle of rotation is sufficient in one direction of rotation, the resilient element 82 is designed in such a manner that when no current is supplied to the electromotor 56 the resilient element rotates the armature 68 on the motor shaft 64 in such a manner that the two cylindrical pins 76, 78 lie against each other. Consequently, the armature 68 comprises in one direction of rotation a free rotational angle of almost 360 , until the two cylindrical pins 76, 78 abut against each other and during its rotational movement the armature 68 entrains the motor shaft 64.

The armature 68 which can be rotated with respect to the motor shaft 64 forms a drive-side of the coupling 58, the motor shaft 64 forms a drivenside of the coupling 58.

Claims

1. A coupling for the purpose of transmitting a rotational movement, the coupling comprising a free rotational angle in at least one direction of rotation and including a rotational stop which defines the free rotational angle.

2. A coupling according to claim 1, wherein the coupling comprises free rotational angles in both directions of rotation and one or two rotational stops which define(s) the free rotational angles in both directions of rotation.

3. A coupling according to claim 1, wherein the coupling is formed as a claw coupling comprising rotational play between a drive-side and a driven-side.

4. A coupling according to claim 1, wherein the coupling comprises a resilient element which rotates the drive-side and the driven-side away from the rotational stop in the case of a torque-free coupling and thereby provides a free rotational angle for starting the coupling.

5. A coupling according to claim 1, wherein the coupling is integrated into an electromotor.

6. A coupling according to claim 5, wherein the coupling is connected between an armature and a motor shaft of the electromotor.

7. A device for the purpose of actuating a vehicle brake, having a drive motor, with a rotation/translation conversion gearing mechanism which can be driven by the drive motor, and having a brake actuation mechanism which can be actuated by the rotation/translation conversion gearing mechanism, wherein the device comprises a coupling which is connected between the drive motor and the

rotation/translation conversion gearing mechanism and which transmits a rotational movement of the drive motor to the rotation/translation conversion gearing mechanism, and wherein the coupling comprises a free rotational angle in at least one direction of rotation and comprises a rotational stop which defines the free rotational angle.

8. A device according to claim 7, wherein the coupling comprises a free rotational angle in the direction in which the brake is released.

9 A device according to claim 7, wherein the coupling is formed as a claw coupling with rotational play between a drive-side and a driven-side.

10. A device according to claim 7, wherein the coupling comprises a resilient element which moves the drive-side and the driven-side away from the rotational stop in the case of a torque-free coupling and thereby provides a free rotational angle for starting the drive motor when the drive motor is at a standstill

11 A device according to claim 7, wherein the rotation/translation conversion gearing mechanism comprises a helical gearing mechanism.

12. A device according to claim 7, wherein the device is self locking.

13. A device according to claim 7, wherein the device comprises an electrometer as the drive motor.

14. A method of starting a drive motor, to which is connected a gearing mechanism, wherein, prior to it actually starting, the drive motor is driven in an opposite direction of rotation to the intended direction of rotation and is then

driven in the intended direction of rotation.

15. A method according to claim 14, wherein the drive motor is an electromotor.

16. A method according to claim 14, where a coupling having a free rotational angle and a rotational stop which dehmes the free rotational angle is connected to the drive motor.

17. A coupling for the purpose of transmitting a rotational movement, substantially as hereinbefore described with reference to the accompanying drawings.

18. A device for the purpose of actuating a brake, substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of starting a drive motor, substantially as hereinbefore described with reference to the accompanying drawings.