Actor

Abstract

Actuator with an electric motor-rotatable spindle (12) for axially displacing a spindle nut to apply an actuating force and a driving disc (16) connected to the spindle (12) in a rotationally fixed manner, wherein the driving disc (16) presses against a friction surface (18) for frictionally braking the spindle (12) in an actuated position when a restoring force (14) is directed counter to the actuating force.

Description

[0001] The invention relates to an actuator with the aid of which in particular a friction clutch for coupling a drive shaft of a motor vehicle engine with at least one transmission input shaft of a motor vehicle transmission can be actuated, in particular by the actuator axially displacing a pressure plate of the friction clutch between an open position and a closed position.

[0002] It is known to actuate a friction clutch with an electric motor-driven actuator. The actuator can apply sufficient actuating force via a spindle drive to axially displace a pressure plate against a counterplate coupled to a drive shaft of a motor vehicle engine, whereby a clutch disc connected to a transmission input shaft of a motor vehicle transmission can be frictionally pressed between the pressure plate and the counterplate. In the closed position of the friction clutch, a restoring force counteracting the actuating force is applied by the pressed clutch disc and, if applicable, a return spring connected to the pressure plate to move the pressure plate into the open position.

[0003] A relevant actuator for clutch actuation is known, for example, from US 2010 / 0219034 A1.

[0004] There is a constant need to reduce the electrical energy consumption of electrical consumers in a motor vehicle.

[0005] It is the object of the invention to show measures that enable a low electrical demand of electrical consumers in a motor vehicle.

[0006] The object is achieved according to the invention by an actuator having the features of claim 1. Preferred embodiments of the invention are specified in the subclaims, which can each individually or in combination represent an aspect of the invention.

[0007] According to the invention, an actuator, in particular for actuating a friction clutch for coupling a drive shaft of a motor vehicle engine with at least one transmission input shaft of a motor vehicle transmission, is provided with an electric motor-rotatable spindle for axially displacing a spindle nut for applying an actuating force and a driving disc connected to the spindle in a rotationally fixed manner, wherein the driving disc presses against a friction surface for frictionally braking the spindle in an actuated position when a restoring force is directed counter to the actuating force.

[0008] The actuator can move a pressure plate of the friction clutch from an unactuated position to an actuated position. The actuated position corresponds in particular to the closed position of the friction clutch, while the unactuated position corresponds to the open position of the friction clutch (“normally open”). However, it is also possible for the actuated position to correspond to the open position of the friction clutch, while the unactuated position corresponds to the closed position of the friction clutch (“normally closed”). The restoring force occurring in the actuated position can act in an axial direction on the spindle nut and the spindle. This can press the drive plate against the friction surface with a corresponding normal force. The restoring force can introduce a reverse torque into the spindle in a reverse rotation direction via the spindle nut.However, due to the frictional contact of the drive plate on the friction surface, at least part of the reverse torque can be absorbed by friction, so that a correspondingly lower actuating force provided by the electric motor needs to be applied to hold the actuator and thus the pressure plate in the actuated position. With the help of the drive plate, which is pressed against the friction surface by the actuating force, a frictional resistance moment can be applied against a return movement into the unactuated position, so that the actuator can be held in the actuated position with a lower actuating force applied by the electric motor, thereby enabling a lower electrical demand from electrical consumers in a motor vehicle. Due to the lower consumption of electrical energy in the actuator, power losses can be reduced, thus also avoiding unnecessary heating of the actuator.The service life of the actuator can be improved and / or it is possible to make the actuator smaller.

[0009] The actuator can, in particular, have an electric motor for rotating the spindle in the actuation direction and / or in the return direction. For this purpose, a rotor of the electric motor can be connected to the spindle, while a stator of the electric machine can be supplied with electrical energy, in particular from a motor vehicle battery. The electric machine is, in particular, operated exclusively in motor mode. The spindle nut, in particular, is screwed onto the spindle and can be axially displaced along the longitudinal direction of the spindle upon rotation of the spindle.

[0010] The spindle nut can, for example, pivot a lever element engaging the pressure plate of the friction clutch, in particular a lever spring configured essentially as a disc spring, or axially displace an actuating pot engaging the pressure plate, which is essentially exclusively axially displaceable. Preferably, the friction clutch actuated by the actuator is part of a dual clutch, wherein in particular both friction clutches of the dual clutch can each be actuated by means of an actuator according to the invention. The drive plate is, in particular, connected to the spindle in a rotationally fixed manner, for example by gluing or welding. The friction surface is decoupled from the rotation of the spindle, in particular at least in the actuated position of the actuator. For example, the friction surface is part of a stationary component, in particular an actuator housing. The friction surface and / or the drive plate can have a friction lining.However, it is also possible for the drive plate to rest against the friction surface without a friction lining. A metal-on-metal friction pairing may be sufficient, particularly with a sufficiently high surface roughness, to dissipate a significant portion of the restoring torque introduced by the restoring force. The area of ​​frictional contact between the drive plate and the friction surface, a radius of the radially inner edge and the radially outer edge of the frictional contact surface, and / or the coefficient of friction can be suitably selected depending on the expected restoring force.

[0011] Particularly preferably, the spindle has axial play for lifting the drive disc from the friction surface when the spindle rotates in the actuation direction. When the spindle rotates in the actuation direction, the frictional contact between the drive disc and the friction surface can be eliminated, so that the spindle can be rotated with high efficiency. This means that a correspondingly lower electrical power consumption is required to actuate the actuator. In the actuated position, the frictional contact between the drive disc and the friction surface can achieve a low level of efficiency, which offers correspondingly high resistance to unwanted rotation of the spindle.

[0012] In particular, the drive plate resting against the friction surface can completely dissipate any return torque generated at a maximum designated return force through frictional engagement. This makes it possible for the actuator to no longer require any electrical power after reaching the actuated position. Preferably, the friction between the drive plate and the friction surface is dimensioned such that, at the expected return force, the static friction between the drive plate and the friction surface is sufficient to absorb the entire return torque, while the sliding friction between the drive plate and the friction surface can only provide a maximum resistance moment below the return torque.This means that when the actuator is moved from the actuated position to the deactuated position, a brief electromotive energy input may be sufficient to overcome the static friction between the drive plate and the friction surface. Afterward, without further electromotive energy input, the actuator can be moved to the deactuated position essentially solely by means of the restoring force. In this case, the drive plate can slide along the friction surface in slip mode, similar to a slip clutch.

[0013] Preferably, the friction surface is coupled to a freewheel, wherein the freewheel rotates freely when the drive disc rotates in an actuating direction and blocks when the drive disc rotates in a return direction opposite to the actuating direction. Particularly preferably, the freewheel is coupled to a stationary component, in particular an actuator housing. When the spindle rotates in the actuating direction, the blocking effect of the frictional contact between the drive disc and the friction surface can be canceled by the freewheel being in the freewheeling position, so that the spindle can be rotated with high efficiency. Accordingly, a correspondingly lower electrical power consumption is required to actuate the actuator.In the actuated position, the freewheel can switch to the locking position and restore the locking effect of the frictional contact between the drive disc and the friction surface, thus achieving a low efficiency that provides a correspondingly high resistance to unwanted rotation of the spindle. An axial displacement of the drive disc relative to the friction surface is not required for this, making it possible to minimize axial play in the spindle.

[0014] In particular, when a preload force is applied in the direction of the actuating force, the drive disc presses against an additional friction surface to frictionally brake the spindle in a non-actuated position. The non-actuated position of the actuator therefore does not have to coincide with a position that depends on the return force. For example, the non-actuated position of the actuator can correspond to a position that extends beyond a position automatically controlled by a return spring connected to the pressure plate, in which the return spring is preloaded in the actuating direction. This means, for example, that the position of the actuator in the non-actuated position can be independent of wear-related changes in the return force.Due to the frictional contact of the drive plate with the additional friction surface, the spindle can be held frictionally in the unactuated position, so that electrical power consumption for holding the actuator in the unactuated position can be at least reduced and in particular eliminated. Preferably, the drive plate can be brought into contact with a first axial side on the friction surface and with a second axial side, facing away from the first axial side, on the additional friction surface. Particularly preferably, the drive plate is in contact either with the friction surface or with the additional friction surface, or with neither the friction surface nor the additional friction surface, for example as a result of axial play in the spindle. The drive plate is therefore not in contact with the friction surface and the additional friction surface at the same time.The drive disc can be positioned in the axial direction between the friction surface and the additional friction surface so that axial play of the spindle can be limited by the friction surface and the additional friction surface.

[0015] Preferably, the drive plate resting against the additional friction surface can completely dissipate a preload torque generated at a maximum designated preload force through frictional engagement. This makes it possible for the actuator to no longer require any electrical power after reaching the unactuated position. Preferably, the friction between the drive plate and the friction surface is dimensioned such that, at the expected preload force, the static friction between the drive plate and the friction surface is sufficient to absorb the entire reverse torque, while the sliding friction between the drive plate and the friction surface can only provide a maximum resistance moment below the preload torque.This means that when the actuator is actuated from the unactuated position to the actuated position, it may be sufficient to overcome the static friction between the drive plate and the friction surface by briefly applying electromotive energy. Afterward, the actuator can be moved over part of the actuation travel without further electromotive energy input, essentially using only the preload force. This allows the actuated position to be reached more quickly and energy-efficiently. In this case, the drive plate can slide along the additional friction surface in slip mode, similar to a slip clutch.

[0016] Particularly preferably, the friction surface and the additional friction surface are coupled to the same freewheel, in particular via a common friction carrier, wherein the freewheel runs freely when the drive disc rotates in one actuation direction and blocks when the drive disc rotates in a return direction opposite to the actuation direction. The additional friction surface can thus limit maximum axial play of the spindle. If the drive disc strikes the additional friction surface, the drive disc can drive the additional friction surface along in the actuation direction of the spindle in the freewheeling direction of the freewheel, so that easy actuation of the actuator in the actuation direction is maintained. At the same time, unnecessarily high axial forces during the movement of the spindle nut between the actuated position and the unactuated position can be dissipated by the additional friction surface and / or the friction surface.

[0017] In particular, the friction surface for dissipating axial forces applied by the restoring force and / or the additional friction surface for dissipating axial forces applied by the preload force are mounted on a stationary component, in particular an actuator housing. This allows the occurring axial forces to be safely dissipated without impairing the spindle's rotatability.

[0018] Preferably, the friction surface and / or the additional friction surface are axially supported by an axial bearing and / or the friction surface and the additional friction surface are axially supported by a common radial bearing. The axial bearing allows the axial forces occurring in the actuated and / or unactuated position to be easily absorbed. The radial bearing makes it possible to provide a single radial bearing for the absorption of axial forces in two different axial directions, thereby reducing the number of components.

[0019] The invention further relates to a friction clutch for coupling a drive shaft of a motor vehicle engine to at least one transmission input shaft of a motor vehicle transmission, comprising an axially displaceable pressure plate for frictionally pressing a clutch disc between the pressure plate and a counter-plate, an actuator, which can be designed and further developed as described above, for displacing the pressure plate, and a return spring acting on the pressure plate for applying a restoring force. With the aid of the drive plate of the actuator, which is pressed against the friction surface by the actuating force, a frictional resistance moment can be applied against a return movement into the unactuated position, so that the actuator can be held in the actuated position with a lower actuating force applied by an electric motor, thereby enabling a lower electrical demand from electrical consumers in a motor vehicle.

[0020] The invention is explained below by way of example with reference to the accompanying drawings, wherein the features presented below can represent an aspect of the invention both individually and in combination. They show: Fig. 1: a schematic diagram of a first embodiment of an actuator, Fig. 2: a schematic diagram of a second embodiment of an actuator, Fig. 3: a schematic diagram of a third embodiment of an actuator and Fig. 4: a schematic diagram of a fourth embodiment of an actuator.

[0021] The Fig. The actuator 10, partially shown in Figure 1, can be used to actuate a friction clutch for coupling a drive shaft of a motor vehicle engine to at least one transmission input shaft of a motor vehicle transmission, in order to directly or indirectly axially displace a pressure plate for pressing a clutch disc by displacing a spindle nut (not shown) screwed onto a spindle 12. In the actuated position of the actuator 10, which corresponds in particular to a closed position of the friction clutch, a restoring force 14 can act in the axial direction on the spindle nut and the spindle 12. A drive plate 16 is connected to the spindle 12 in a rotationally fixed manner and can be pressed against a friction surface 18 by the restoring force 14.As a result, such great friction can occur between the driving disc 16 and the friction surface 18 that the spindle 12 is frictionally secured against reverse rotation against the actuating direction as a result of the acting restoring force 14. The spindle 12 can have a slight axial play, so that the driving disc 16 can lift off the friction surface 18 when the spindle 12 is actuated in the actuating direction against the restoring force 14. In the embodiment shown in . Fig. 1, the friction surface 18 is formed by a fixed actuator housing 20 of the actuator 10.

[0022] In the Fig. The embodiment of the actuator 10 shown in Figure 2 is compared to the one shown in Fig. In the embodiment of the actuator 10 shown in Figure 1, the friction surface 18 is formed by a friction carrier 22, which is axially rotatably supported on the stationary actuator housing 20 via a first axial bearing 24. The friction carrier 22 is coupled to a freewheel 26, which runs freely when the spindle 12 rotates in the actuation direction and locks when the spindle 12 rotates counter to the actuation direction in the return direction. As a result, even without axial play of the spindle 12, a moment of resistance of the friction pairing between the drive plate 16 and the friction surface 18 can be canceled when the spindle 12 rotates in the actuation direction and can be provided when the spindle 12 rotates counter to the actuation direction in the return direction.

[0023] At the Fig. The embodiment of the actuator 10 shown in Figure 3 is compared to the embodiment shown in Fig. In the embodiment of the actuator 10 shown in Figure 2, an additional friction surface 28 is provided, in particular also formed by the friction carrier 22, against which the drive disc 16 can frictionally engage with an axial side facing away from the friction surface 18 when the actuator 10 is actuated in the actuation direction. The additional friction surface 28 can be mounted and axially supported on the actuator housing 20 via a second axial bearing 30. Axial play of the spindle 12 can be limited by abutment against the friction surface 18 and the additional friction surface 28. Furthermore, axial forces in both axial directions can be dissipated via the friction carrier 22 and the actuator housing 20.

[0024] At the Fig. 4 are compared to the embodiment of the actuator 10 shown in Fig.In the embodiment of the actuator 10 shown in Figure 3, the axial bearings 24, 30 are replaced by a single radial bearing 32 designed as a fixed bearing. Additionally, the freewheel 26 is offset from a position radially outside the drive plate 16 to a position axially adjacent to the drive plate 16. The number of components can thus be reduced. List of reference symbols 10 Actuator 12 spindle 14 Restoring force 16 Driving disc 18 Friction surface 20 actuator housings 22 friction carriers 24 first thrust bearing 26 Freewheel 28 Additional friction surface 30 second thrust bearing 32 radial bearings

Claims

[1] Actuator with an electric motor-rotatable spindle (12) for axially displacing a spindle nut to apply an actuating force and a driving disc (16) connected to the spindle (12) in a rotationally fixed manner, wherein the driving disc (16) presses against a friction surface (18) for frictionally braking the spindle (12) in an actuated position when a restoring force (14) is directed counter to the actuating force. [2] Actuator according to claim 1 characterized by that the spindle (12) has an axial play for lifting the driving disc (16) from the friction surface (18) when the spindle (12) rotates in the actuating direction. [3] Actuator according to claim 1 or 2 characterized by that the driving disc (16) lying against the friction surface (18) can completely dissipate a return torque arising at a maximum designated return force (14) in a frictionally engaged manner. [4] Actuator according to one of claims 1 to 3 characterized byin that the friction surface (18) is coupled to a freewheel (26), wherein the freewheel (26) runs freely upon rotation of the driving disc (16) in an actuating direction and blocks upon rotation of the driving disc (16) in a return direction opposite to the actuating direction. [5] Actuator according to one of claims 1 to 4 characterized by that the driving disc (16) presses against an additional friction surface (28) for frictionally braking the spindle (12) in an unactuated position when a preload force is directed in the direction of the actuating force. [6] Actuator according to claim 5 characterized by that the driving disc (16) resting on the additional friction surface (28) can completely frictionally transfer a preload torque arising at a maximum designated preload force. [7] Actuator according to claim 5 or 6 characterized bythat the friction surface (18) and the additional friction surface (28) are coupled to the same freewheel (26), wherein the freewheel (26) runs freely when the driving disc (16) rotates in an actuating direction and blocks when the driving disc (16) rotates in a return direction opposite to the actuating direction. [8] Actuator according to one of claims 1 to 7 characterized by that the friction surface (18) for absorbing axial forces applied by the restoring force (14) and / or the additional friction surface (28) for absorbing axial forces applied by the preload force is mounted on a fixed component. [9] Actuator according to claim 8 characterized by that the friction surface (18) and / or the additional friction surface (28) is axially supported via an axial bearing (24, 30) and / or the friction surface (18) and the additional friction surface (28) are axially supported via a common radial bearing (32). [10] Friction clutch for coupling a drive shaft of a motor vehicle engine with at least one transmission input shaft of a motor vehicle transmission, with an axially displaceable pressure plate for frictionally pressing a clutch disc between the pressure plate and a counter-plate, an actuator (10) according to one of claims 1 to 9 for displacing the pressure plate and a return spring acting on the pressure plate for applying a return force.

Images