Steering actuator for the rear axle steering of a motor vehicle

Abstract

Steering actuator (1) of a rear axle steering system of a motor vehicle, comprising a drive motor (10), a belt drive (20), a gearbox (30) and a brake device (40), wherein the gearbox (30) is configured to convert a rotary motion of the drive motor (10), which is fed into the gearbox (30) via the belt drive (20), into a translational motion of a threaded spindle (31), wherein the belt drive (20) comprises a first pulley (21), a second pulley (22) and a belt (23) encircling them, wherein the brake device (40) is configured to brake the second pulley (22), characterized in that the brake device (40) comprises a stationary housing (41) which at least partially accommodates at least one contact element (42), at least one electromagnet (43) and at least one spring element (44), wherein the at least one spring element (44) is configured toa spring force is applied to the at least one contact element (42) to decelerate the second pulley (22) in a de-energized state of the at least one electromagnet (43), wherein the at least one electromagnet (43) is configured in a energized state to displace the at least one contact element (42) against the spring force to allow rotation of the second pulley (22), and a friction element (45) is arranged non-rotatably on the second pulley (22), wherein the at least one contact element (42) is configured to generate a frictional torque to decelerate the second pulley (22) on the friction element (45), wherein the contact element (42) presses axially against the friction element (45) on the second pulley (22) in a de-energized state of the electromagnet (43).

Description

[0001] The invention relates to a steering actuator with belt drive and locking device for a rear axle steering system of a motor vehicle.

[0002] For example, DE 10 2018 115 787 A1 discloses a steering actuator for use in the rear axle steering system of a motor vehicle, comprising a threaded drive designed as a planetary gear drive and having a plurality of planets arranged with preload between a threaded spindle and a nut. A friction device interacts with the nut, generating a frictional torque that depends on an axial load acting on the threaded spindle. In this way, the efficiency of the linear actuator is kept significantly below 50%, i.e., in the self-locking range, under a wide variety of operating conditions.

[0003] Furthermore, DE 10 2006 020 041 A1 discloses a steering device with belt drive and locking device, the electromagnetically actuated plunger of which engages in holes of a pulley in the event of a power failure and locks it.

[0004] DE 10 2018 209 819 A1 discloses a spindle drive for an actuator of a steer-by-wire steering system, the roller screw drive of which operates with low friction in the forward direction and is almost self-locking in the reverse direction. Optionally, an additional, preferably electromagnetic, locking unit is mentioned, which locks under spring tension in the event of a power failure and couples the spindle, spindle nut, and / or housing by positive / negative locking. Specific details regarding the design of the locking unit are not disclosed.

[0005] The object of the invention is to provide an alternative steering actuator with belt drive and locking device. In particular, the steering actuator should exhibit high operational reliability, be inexpensive to manufacture, and have a compact design. This object is achieved by the subject matter of claim 1. Preferred embodiments can be found in the dependent claims, the description, and the figures.

[0006] A steering actuator according to the invention for a rear axle steering system of a motor vehicle comprises a drive motor, a belt drive, a transmission, and a braking device, wherein the transmission is configured to convert a rotary motion of the drive motor, which is fed into the transmission via the belt drive, into a translational motion of a threaded spindle, wherein the belt drive has a first pulley, a second pulley, and a belt encircling them, wherein the braking device is configured to brake the second pulley and has a stationary housing that at least partially accommodates at least one contact element, at least one electromagnet, and at least one spring element, wherein the at least one spring element is configured to apply a spring force to the at least one contact element.to brake the second pulley in a non-energized state of the at least one electromagnet, wherein the at least one electromagnet in an energized state is configured to displace the at least one contact element against the spring force in order to release a rotation of the second pulley.

[0007] Thus, the at least one spring element pre-tensions the at least one contact element, at least indirectly, on the second pulley, whereby rotation of the second pulley is only released when the at least one electromagnet is energized, thereby displacing the at least one contact element against the spring force. This eliminates the need for a self-locking gearbox and / or other self-locking means for the steering actuator. As a result, the steering actuator becomes more efficient, compact, and quieter. Furthermore, the drive unit can be more compact and requires less drive power to change the steering angle of the wheels, since the drive unit does not operate against self-locking.The at least one spring element is designed such that, in the event of a power interruption to the at least one electromagnet, the braking device can exert its full holding force and lock the steering mechanism to prevent any changes to the steering setting. This function is used both during normal operation of the steering mechanism and in emergencies, particularly during a power failure. This increases operational safety.

[0008] In particular, the braking device is arranged adjacent to the second pulley and is at least indirectly connected to it. The drive power from the drive motor, which is preferably an electric motor, is introduced at the first pulley, and the drive power is transmitted to the second pulley via the belt. The arrangement of the braking device at the second pulley is particularly advantageous because the braking force can be introduced into the steering actuator's drive train most effectively at this point to lock it, as the minimum holding force is required in the drive train to interrupt rotation at this location. Furthermore, this area also offers spatial advantages for integrating the braking device into the steering actuator's housing.Preferably, the housing of the braking device is arranged in a rotationally fixed manner within the housing of the steering actuator, in particular by press-fitting, whereby an air gap between the at least one electromagnet and the at least one contact element can be adjusted during the press-fitting process. Furthermore, the engagement of the braking device with the second pulley also increases safety, since the application of the braking force occurs downstream of the belt in the power flow. Preferably, the gearbox is arranged at least partially or completely within the second pulley. This results in an even more compact design of the steering actuator.

[0009] According to one embodiment, the at least one contact element is ring-shaped and positively connected to the housing. For example, the entire brake assembly is ring-shaped. In particular, the housing of the brake assembly is ring-shaped and accommodates a ring-shaped contact element, a ring-shaped electromagnet, and at least one spring element. For example, the at least one spring element is designed as a wave spring, which improves assembly and increases compactness. Alternatively, several compression springs can be arranged around the circumference of the contact element to pre-tension the contact element, at least indirectly, on the second pulley. The ring-shaped design of the contact element creates a particularly large contact area for transmitting a spring force.In particular, the contact element is made of a magnetic metal sheet, so that the electromagnet can act directly on the contact element to move it axially.

[0010] For example, positive-locking elements are arranged on an outer circumferential surface of the at least one contact element and interact with positive-locking elements on an inner circumferential surface of the housing. Preferably, a splined connection is arranged on an outer circumferential surface of the annular contact element, wherein the splined connection on the contact element interacts with a splined connection on the inner circumferential surface of the housing to form a positive-locking connection. The splined connection allows axial displacement of the contact element within the housing of the steering device and prevents rotation of the contact element within the housing of the steering device.

[0011] A friction element is fixedly arranged on the second pulley, with the at least one contact element configured to generate a frictional torque for braking and locking the second pulley against the friction element. Thus, the at least one contact element does not act directly on the second pulley, but indirectly via the friction element. In particular, the friction element is designed as a friction disc and is arranged on the end face of the second pulley, especially screwed or bonded to it. The friction element allows, on the one hand, the frictional force of the at least one contact element to be adjusted, in particular increased, according to the application, and on the other hand, reduces wear of the second pulley caused by the action of the contact element.

[0012] Preferably, the braking device is arranged coaxially with the gearbox, with the threaded spindle guided axially through the braking device. This makes the steering actuator even more compact. For example, the braking device is arranged at least partially or completely axially overlapping with the second pulley, thus saving axial installation space.

[0013] According to one embodiment, the transmission is at least partially arranged within the second pulley and is designed as a planetary gear drive with several planets rolling on the threaded spindle, a cage guiding the planets, and a nut in which the planets roll. In particular, the nut is rotatably mounted by means of a rolling bearing having balls as rolling elements. Preferably, the rolling bearing is designed as a double-row angular contact ball bearing. Furthermore, preferably, the cage is provided as the drive element of the planetary gear drive and is effectively connected to the second pulley for this purpose.

[0014] Furthermore, the invention also relates to a motor vehicle with such a steering actuator. In particular, the steering actuator is arranged on a rear axle of the motor vehicle and is connected to the wheels of the rear axle via the threaded rod and further steering rods in such a way that a steering angle is achieved by an axial displacement of the threaded rod.

[0015] Further measures improving the invention are described in more detail below, together with a description of a preferred embodiment of the invention, with reference to the figures. Fig. 1 a simplified schematic sectional view of a section of the steering actuator according to the invention with belt drive and braking device and Fig. 2 a simplified schematic exploded view of the braking device of the steering actuator according to the invention Fig. 1.

[0016] In Fig. Figure 1 shows a section of a steering actuator 1 according to the invention for a rear axle steering system of a motor vehicle (not shown in detail). The steering actuator 1 comprises a drive motor 10 designed as an electric machine, a belt drive 20, a transmission 30 designed as a planetary roller gear, and a brake device 40. The transmission 30 converts a rotary motion of the drive motor 10, which is fed into the transmission 30 via the belt drive 20, into a translational motion of a threaded spindle 31, which is at least indirectly connected to the wheels of the rear axle (not shown in detail) in order to adjust a steering angle.

[0017] The belt drive 20 comprises a first pulley 21, which is arranged together with the drive motor 10 on a first axis of rotation 3, a second pulley 22, which is arranged together with the gearbox 30 and the brake 40 on a second axis of rotation 4, which is parallel to the first axis of rotation 3, and a belt 23 that wraps around both pulleys 21 and 22. The drive motor 10 drives the belt drive 20 via the rotor shaft 11, which is non-rotatably connected to the first pulley 21. A friction element 45 is arranged on the end face of the second pulley 22 and is non-rotatably connected to it, in particular bonded to the second pulley 22, and configured to interact with the brake 40 to lock the second pulley 22. The brake 40 is arranged coaxially with the gearbox 30, with the threaded spindle 31 extending axially through the brake 40.In this design, the brake assembly 40 is essentially axially overlapping with the second pulley 22, thereby saving axial installation space. Furthermore, the gearbox 30 is essentially located within the second pulley 22, further increasing the compactness of the steering actuator 1.

[0018] The gearbox 30 comprises, in addition to the threaded spindle 31, several planetary gears 32 that roll on the threaded spindle 31, with a cage 33 guiding the planetary gears 32, and a nut 34 in which the planetary gears 32 roll. The drive power is fed into the gearbox 30 via the cage 33, which is rotationally fixed to the second pulley 22, and transmitted to the threaded spindle 31 via the planetary gears 32. The planetary gears 32 interact with the nut 34 via a first threaded section and with the threaded spindle 31 via a second threaded section. The threaded spindle 31 is axially displaced relative to the nut 34. The nut 34 is rotatably mounted by means of a rolling bearing 35, which has balls (not shown) as rolling elements. This further increases the efficiency of the steering actuator 1.

[0019] The braking device 40 comprises a housing 41 that at least partially accommodates an annular contact element 42, an annular electromagnet 43, and a spring element 44 designed as a wave spring. The housing 41 of the braking device 40 is stationary within a housing 2 of the steering actuator 1. The spring element 44 is configured to apply a spring force to the contact element 42 in order to decelerate and lock the second pulley 22 when the electromagnet 43 is not energized. In doing so, the contact element 42 presses axially against the friction element 45 on the second pulley 22, generating a frictional torque to decelerate and lock the second pulley 22. The electromagnet 43 is cast into the housing 41 and is configured, when energized, to displace the contact element 42 against the spring force to allow rotation of the second pulley 22.Thus, the spring element 44 pre-tensions the contact element 42 in the direction of the friction element 45 on the second pulley 22, whereby rotation of the second pulley 22 is only released when the electromagnet 43 is energized and thereby displaces the contact element 42 against the spring force. This eliminates the need for a self-locking gear and / or other means of self-locking the steering actuator. Furthermore, the drive motor can be designed more compactly and requires less drive power to change the steering angle of the wheels, since the drive motor does not operate against self-locking. The spring force and pre-tension of the spring element 44 are dimensioned such that the braking device 40 can exert its full holding force when the electromagnet 43 is de-energized and locks the steering device 1 to prevent any change in the steering setting.This function is used both during operation of the steering device 1 and in emergencies, particularly in the event of a power failure. This increases operational safety.

[0020] Fig. Figure 2 shows the brake assembly 40 according to an exploded view. From Fig. Figure 2 shows that the brake assembly 40 is an annular component. For a rotationally fixed connection between the contact element 42 and the housing 41, positive-locking elements are arranged on an outer circumferential surface of the contact element 42, which interact with positive-locking elements on an inner circumferential surface of the housing 41. In this case, the positive-locking elements are designed as a circumferential splined connection. The brake assembly 40 is frictionally engaged in position within the housing 2 of the steering actuator 1 according to Fig. 1 joined, in particular pressed, and an air gap was set between the friction element 45 and the contact element 42. Reference symbol list 1 steering actuator 2 cases 3 first axis of rotation 4 second axis of rotation 10 Drive machine 11 Rotor shaft 20 Belt drive 21 first pulley 22 second pulley 23 belts 30 gearboxes 31 Threaded spindle 32 Planet 33 Cage 34 Mother 35 Rolling bearing 40 Brake system 41 cases 42 Contact element 43 Electromagnet 44 Spring element 45 Friction element

Claims

Steering actuator (1) of a rear axle steering system of a motor vehicle, comprising a drive motor (10), a belt drive (20), a gearbox (30) and a brake device (40), wherein the gearbox (30) is configured to convert a rotary motion of the drive motor (10), which is fed into the gearbox (30) via the belt drive (20), into a translational motion of a threaded spindle (31), wherein the belt drive (20) comprises a first pulley (21), a second pulley (22) and a belt (23) encircling them, wherein the brake device (40) is configured to brake the second pulley (22), characterized in that the brake device (40) comprises a stationary housing (41) which at least partially accommodates at least one contact element (42), at least one electromagnet (43) and at least one spring element (44), wherein the at least one spring element (44) is configured toa spring force is applied to the at least one contact element (42) to decelerate the second pulley (22) in a de-energized state of the at least one electromagnet (43), wherein the at least one electromagnet (43) is configured in a energized state to displace the at least one contact element (42) against the spring force to allow rotation of the second pulley (22), and a friction element (45) is arranged non-rotatably on the second pulley (22), wherein the at least one contact element (42) is configured to generate a frictional torque to decelerate the second pulley (22) on the friction element (45), wherein the contact element (42) presses axially against the friction element (45) on the second pulley (22) in a de-energized state of the electromagnet (43). Steering actuator (1) according to claim 1, characterized in that the at least one contact element (42) is ring-shaped and positively connected to the housing (41). Steering actuator (1) according to claim 2, characterized in that positive locking elements are arranged on an outer circumferential surface of the at least one contact element (42) and interact with positive locking elements on an inner circumferential surface of the housing (41). Steering actuator (1) according to one of the preceding claims, characterized in that the at least one spring element (44) is designed as a wave spring. Steering actuator (1) according to one of the preceding claims, characterized in that the housing (41) of the brake device (40) is arranged in a rotationally fixed manner in a housing (2) of the steering actuator (1). Steering actuator (1) according to one of the preceding claims, characterized in that the braking device (40) is arranged coaxially to the transmission (30), wherein the threaded spindle (31) is guided axially through the braking device (40). Steering actuator (1) according to one of the preceding claims, characterized in that the transmission (30) is at least partially arranged within the second pulley (22) and is designed as a planetary roller transmission with several planets (32) rolling on the threaded spindle (31), with a cage (33) guiding the planets (32), and with a nut (34) in which the planets (32) roll. Steering actuator (1) according to claim 7, characterized in that the nut (34) is rotatably mounted by means of a rolling bearing (35) which has balls as rolling elements.

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