Steering gear for a motor vehicle with a ball nut type hydraulic steering mechanism and a steering system

Abstract

The invention relates to a steering transmission (1) for a ball nut type hydrostatic steering mechanism of a motor vehicle, having a working cylinder (10) which is divided by a piston (20) into a first pressure chamber (22) and a second pressure chamber (24, 124). The steering transmission (1) furthermore has a damping device (28, 128) which interacts with the second pressure chamber (24, 124) of the working cylinder (10) and is configured in such a way that the compression stiffness of the volume of hydraulic fluid arranged in the second pressure chamber (24, 124) is damped such that it substantially corresponds to the compression stiffness of the volume of hydraulic fluid arranged in the first pressure chamber (22). The invention furthermore relates to a steering system (100) for a motor vehicle.

Description

TECHNICAL FIELD

[0001] The invention relates to a steering transmission for a ball nut type hydrostatic steering mechanism of a motor vehicle. The invention furthermore relates to a steering system for a motor vehicle. BACKGROUND

[0002] DE 10 2016 122 743 A1 discloses a steering transmission for a ball nut type hydrostatic steering mechanism of a motor vehicle, having a steering transmission housing and a steering spindle joint configured at the steering transmission housing, in which a working cylinder is configured, the steering spindle joint being configured for transmitting a rotational movement introduced by a steering spindle onto a worm and converting it by a ball screw into an axial movement of a piston arranged in the working cylinder, wherein the piston divides the working cylinder into a first pressure chamber and a second pressure chamber, and wherein the first pressure chamber has a greater volume than the second pressure chamber.

[0003] Furthermore a sector gear shaft arranged at right angles to the longitudinal axis of the piston is provided, which is connected to the piston by a toothing configured in the piston, wherein the sector gear shaft can be brought into rotational movement by the axial movement of the piston.

[0004] When a collision from the road acts onto the steering transmission in such a conventional steering transmission, the collision can be transmitted by the mechanical force transmission line to both cylinder chambers filled with hydraulic fluid and is supported there. Since the hydraulic fluid, in particular oil, is compressible, the stiffness present for the force support is smaller due to the greater volume in the large cylinder chamber than in the small chamber and can exert a steering influence.

[0005] If alternating collisions acting onto the steering transmission occur during straight driving, the collisions then lead to different large adjustment travel of the steering transmission due to the different cylinder chamber stiffnesses. The piston thus moves with a greater travel about the middle position of the steering in the direction of the large cylinder chamber and the wheels connected by the mechanical force transmission line move with a greater wheel steering angle.

[0006] The force support involves a mass-spring system with different stiffnesses. In certain driving situations, the system can be in resonance. Since the oscillation has a frequency with a fixed period duration, however, the stiffnesses are different, the adjustment travel continues to become larger in the direction of the smaller stiffness, thereby causing a steering of the wheels.

[0007] It is therefore the object of the present application to provide an improved steering transmission for a ball nut type hydrostatic steering mechanism of a motor vehicle, which compensates for different stiffnesses of two pressure chambers and thus avoids that a collision acting on the steering transmission from the road exerts a steering influence. SUMMARY

[0008] This object is achieved by a steering transmission for a ball nut type hydrostatic steering mechanism of a motor vehicle.

[0009] Furthermore, this object is achieved by a steering system for a motor vehicle.

[0010] The present application achieves a steering transmission for a ball nut type hydrostatic steering mechanism of a motor vehicle. The steering transmission comprises a steering transmission housing in which a working cylinder is configured.

[0011] Furthermore, the steering transmission comprises a steering spindle joint configured at the steering transmission housing, which is configured for transmitting a rotational movement introduced by a steering spindle onto a worm and converting it by means of a ball screw into an axial movement of a piston arranged in the working cylinder, wherein the piston divides the working cylinder into a first pressure chamber and a second pressure chamber, and wherein the first pressure chamber has a greater volume than the second pressure chamber.

[0012] Furthermore, the steering transmission comprises a sector gear shaft arranged at right angles to the longitudinal axis of the piston, which is connected to the piston by means of a toothing configured in the piston, wherein the sector gear shaft can be brought into rotational movement by the axial movement of the piston.

[0013] Furthermore, the steering transmission has a damping device which coacts with the second pressure chamber, which is configured for damping the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber such that the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber substantially corresponds to the compression stiffness of the hydraulic fluid volume arranged in the first pressure chamber.

[0014] The present application furthermore achieves a steering system for a motor vehicle, which has a steering spindle and a steering transmission according to the present application, wherein the steering transmission is configured for receiving a rotational movement introduced by the steering spindle.

[0015] The idea of the application is that the different stiffnesses of the two pressure chambers are compensated for by providing a damping device which coacts with the second pressure chamber, which is either integrated directly in the steering gear or is connected to the second pressure chamber by a pressure line as a separate unit, in such a way that the stiffer, that is to say the smaller, pressure chamber is adapted to the smaller stiffness of the larger pressure chamber by the additional damping device. In this way, it is possible in an advantageous manner to avoid an undesirable force transmission from the road influences acting on the steering gear to the mechanical force transmission path of the steering gear.

[0016] Advantageous embodiments and refinements result from the description in conjunction with the figures.

[0017] According to a preferred refinement, the damping device has a compensation chamber which is fluidically connected to the second pressure chamber, in which a compensation piston which is loaded with a predefined spring force by a spring damper can move axially.

[0018] The solution to this structural aspect is thus based on the mechanism of action of the spring damper, which adapts the higher stiffness of the second pressure chamber to the lower stiffness of the first pressure chamber on the basis of the fluidic connection of the compensation chamber to the second pressure chamber of the steering gear.

[0019] According to another preferred refinement, the spring characteristic curve of the spring damper is designed in such a way that the spring damping caused by the spring damper reduces the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber to the level of the compression stiffness of the hydraulic fluid volume arranged in the first pressure chamber.

[0020] In this way, it is possible in an advantageous manner to achieve a balanced compression stiffness in the two pressure chambers and thus to prevent the return stroke pulses which arise in the case of a pressure reduction of the hydraulic fluid from having an influence on the mechanical force transmission path in the sense of steering the steering mechanism.

[0021] According to another preferred refinement, the damping device has a cylindrical space which is constructed integrally with the steering gear housing or is arranged separately from the steering gear housing, which is fluidically connected to the second pressure chamber by a bore and / or a hydraulic line.

[0022] It is thus possible to introduce a defined hydraulic fluid volume from the second pressure chamber into the cylindrical space of the damping device by means of the bore, whereby the cylindrical space in combination with the spring characteristic curve of the spring damper can achieve a balancing effect on the stiffnesses of the two pressure chambers.

[0023] According to a further preferred refinement, the balancing piston is supported, in particular slidingly supported, in the cylindrical space, and wherein the balancing piston is sealed against the housing of the cylindrical space by means of a seal which is interposed between the bearing and the housing of the cylindrical space.

[0024] Thus, a low-friction axial movement of the balancing piston in the cylindrical space can be achieved while at the same time ensuring the sealing against the housing.

[0025] According to a further preferred refinement, the spring buffer has at least one Belleville spring, in particular a plurality of Belleville springs, which are received in the cylindrical space at the side opposite the balancing chamber. The provision of at least one Belleville spring, preferably a plurality of Belleville springs, is particularly advantageous in this embodiment, since the Belleville springs enable a large force transmission with a small stroke.

[0026] According to a further preferred refinement, the section of the cylindrical space in which the spring buffer is arranged is dry and sealed outwardly or is connected by means of a hydraulic line to a return of the oil circuit. Thus, for example, a durable seal can be used which enables the section of the cylindrical space in which the spring buffer is arranged to be dry.

[0027] Alternatively, for example, a floating seal can be used which enables an excess of hydraulic fluid to be returned to the oil circuit.

[0028] According to a further preferred refinement, the balancing piston can abut against a stop of the buffer device which is arranged adjacent to the second pressure chamber at a first axial end section of the cylindrical space without play by means of the spring buffer. Thus, the hydraulic fluid volume in the balancing chamber can be precisely controlled in an advantageous manner.

[0029] According to a further preferred refinement, the cylindrical space of the buffer device has a screwed-in cover at a second axial end section of the cylindrical space which is arranged opposite the first axial end section of the cylindrical space, the screwed-in cover pre-tensioning the spring buffer. The pre-tensioning of the spring buffer in combination with its spring characteristic curve thus enables a precise balancing of the stiffness of the two pressure chambers.

[0030] According to a further preferred refinement, the cylindrical space of the buffer device has a stepped bore, wherein the balancing piston is arranged in a first section of smaller diameter of the cylindrical space, and wherein the spring buffer is arranged in a second section of larger diameter of the cylindrical space.

[0031] Thus, the piston can be guided in a favorable manner in separate sections of the cylindrical space as a spring damper. Furthermore, the stepped configuration of the cylindrical space enables an improved sealing of the balancing chamber, in particular of the portion of the balancing chamber which receives hydraulic fluid.

[0032] The described design solutions and refinements can be combined with one another at will.

[0033] Further possible design solutions, refinements and embodiments of the application also include combinations of the features described previously or hereinafter with respect to the embodiments which are not explicitly mentioned. BRIEF DESCRIPTION OF DRAWINGS

[0034] The drawings are intended to further illustrate embodiments of the application. The drawings show embodiments and, together with the specification, serve the explanation of the principles and the concept of the application.

[0035] Numerous other embodiments and many of the noted advantages will be further appreciated from the following detailed description of the application, when read in conjunction with the accompanying drawings.

[0036] wherein:

[0037] Figure 1 a schematic view of a steering transmission of a ball nut type hydrostatic steering mechanism for a motor vehicle is shown according to a preferred embodiment of the application; and

[0038] Figure 2 a schematic view of a steering transmission of a ball nut type hydrostatic steering mechanism for a motor vehicle is shown according to another preferred embodiment of the application.

[0039] In the drawings identical reference signs indicate identical or functionally equivalent elements, components or assemblies, unless stated otherwise. DETAILED DESCRIPTION

[0040] The steering transmission 1 shown in Figure 1 is a component of a ball nut type hydrostatic steering mechanism of a steering system of a motor vehicle. Remaining components of the ball nut type hydrostatic steering mechanism, such as for example a rotary slide and a primary valve, are not shown in the present drawing.

[0041] The steering transmission 1 has a steering transmission housing 2 in which the working cylinder 10 is constructed.

[0042] Furthermore, the steering gear 1 has a steering spindle joint 14 which is configured at the steering gear housing 2 and is configured to transmit a rotational movement introduced by means of a steering spindle 42 to the worm 16 and to convert it into an axial movement of a piston 20 which is arranged in the working cylinder 10 by means of a ball screw 18.

[0043] The piston 20 divides the working cylinder 10 into a first pressure chamber 22 and a second pressure chamber 24. The first pressure chamber 22 has a greater volume than the second pressure chamber 24 here.

[0044] Furthermore, the steering gear 1 has a sector gear shaft 26 which is arranged at right angles to the piston longitudinal axis L and is connected to the piston 20 by means of a toothing which is configured in the piston 20, wherein the sector gear shaft 26 can be placed into a rotational movement by means of the axial movement of the piston 20.

[0045] Furthermore, the steering gear 1 has a damping device 28 which interacts with the second pressure chamber 24 and is configured to dampen the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber 24 so that the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber 24 substantially corresponds to the compression stiffness of the hydraulic fluid volume arranged in the first pressure chamber 22.

[0046] The damping device 28 has a compensation chamber 30 which is fluidically connected to the second pressure chamber 24. A compensation piston 34 which is loaded with a predefined spring force F by means of a spring damper 32 can be moved axially in the compensation chamber 30. Alternatively, the spring damper 32 can be connected to a return line RL of an oil circuit, for example by means of a hydraulic line.

[0047] The spring characteristic curve of the spring damper 32 is designed in such a way that the spring damping caused by the spring damper 32 reduces the compression stiffness of the hydraulic fluid volume arranged in the second pressure chamber 24 to the level of the compression stiffness of the hydraulic fluid volume arranged in the first pressure chamber 22.

[0048] In the present embodiment, the damping device 28 has a cylindrical space 36 which is configured integrally with the steering gear housing 2. The cylindrical space 36 is fluidically connected to the second pressure chamber 24 here by means of a bore 37a.

[0049] The compensation piston 34 is supported, in particular slidingly supported, in the cylindrical space 36. The compensation piston 34 is sealed against the housing 35 of the cylindrical space 36 by means of a seal 40 which is interposed between the O-ring or pretension ring 38 and the housing 35 of the cylindrical space 36.

[0050] The spring buffer 32 has a plurality of Belleville springs which are received in the cylindrical space 36 at the side opposite the balancing chamber 30. Furthermore, the section of the cylindrical space 36 in which the spring buffer 32 is arranged is dry and outwardly sealed.

[0051] The balancing piston 34 can abut against the stop of the cushioning device 28 which is arranged adjacent to the second pressure chamber 24 at the first axial end section 36a of the cylindrical space 36 without play by means of the spring buffer 32.

[0052] The cylindrical space 36 of the cushioning device 28 has a screwed-in cover 39 at the second axial end section 36b of the cylindrical space 36 which is arranged opposite the first axial end section 36a of the cylindrical space 36, which pre-tensions the spring buffer 32.

[0053] The cylindrical space 36 of the cushioning device 28 furthermore has a stepped bore. The balancing piston 34 is arranged in the first section 36c of the cylindrical space 36 of smaller diameter, and the spring buffer 32 is arranged in the second section 36d of the cylindrical space 36 of larger diameter.

[0054] Figure 2 A schematic view of a steering transmission of a ball nut type hydrostatic steering gear for a motor vehicle is shown, which is in accordance with another preferred embodiment of the present application.

[0055] In contrast to the embodiment shown in Figure 1 The cushioning device 128 which interacts with the second pressure chamber 124 is arranged separately from the steering transmission. For this purpose, the cushioning device 128 is fluidically connected to the second pressure chamber 124 by means of a hydraulic line 37b.

[0056] The hydraulic line 37b is connected to the balancing chamber 130 of the cushioning device 128 in such a way that the hydraulic line 37b is fluidically connected to the balancing chamber 130 by means of a region of the wall of the cushioning device 128 which is in the centre or, alternatively, is off-centre.

[0057] The cushioning device 128 has a balancing chamber 130 which is fluidically connected to the second pressure chamber 124. A balancing piston 134 which is loaded with a predefined spring force F by means of a spring buffer 132 can move in the balancing chamber 130 in the axial direction. Alternatively, the spring buffer 132 can be connected to the return flow RL of the oil circuit, for example, by means of a hydraulic line.

[0058] The balancing piston 134 is supported, in particular slidingly supported, in a cylindrical space 136. The balancing piston 134 is sealed with respect to the housing 135 of the cylindrical space 136 by means of a seal 140 which is interposed between the O-ring or pre-tensioning ring 138 and the housing 135 of the cylindrical space 136.

[0059] The cylindrical space 136 of the damping device 128 has a screwed-in cap 139 at a second axial end section of the cylindrical space 136, which is arranged opposite the first axial end section of the cylindrical space 136, which pre-tensions the spring damper 132.

Claims

1. A steering transmission mechanism (1) for a ball-nut type hydraulic steering mechanism for motor vehicles, said steering transmission mechanism having: Steering transmission mechanism housing (2), in which a working cylinder (10) is constructed; A steering spindle joint (14) is constructed at the steering transmission housing (2). This steering spindle joint is configured to transmit the rotational motion introduced by the steering spindle (42) to the worm gear (16) and convert it into axial motion of the piston (20) arranged in the working cylinder (10) via the ball screw (18). The piston (20) divides the working cylinder (10) into a first pressure chamber (22) and a second pressure chamber (24, 124), wherein the first pressure chamber (22) has a larger volume than the second pressure chamber (24, 124); A sector gear shaft (26) is arranged perpendicular to the longitudinal axis (L) of the piston. The sector gear shaft is connected to the piston (20) via teeth constructed in the piston (20), wherein the sector gear shaft (26) can be placed in rotational motion by the axial movement of the piston (20); and A buffer device (28, 128) interacts with the second pressure chamber (24, 124) and is configured to buffer the compressive rigidity of the hydraulic fluid volume disposed in the second pressure chamber (24, 124) such that the compressive rigidity of the hydraulic fluid volume disposed in the second pressure chamber (24, 124) substantially corresponds to the compressive rigidity of the hydraulic fluid volume disposed in the first pressure chamber (22).

2. The steering transmission mechanism according to claim 1, wherein, The buffer device (28, 128) has a balance chamber (30, 130) fluidly connected to the second pressure chamber (24, 124), and a balance piston (34, 134) loaded with a predetermined spring force (F) by a spring buffer (32, 132) is capable of moving axially in the balance chamber.

3. The steering transmission mechanism according to claim 2, wherein, The spring characteristic curves of the spring buffers (32, 132) are designed in such a way that the spring buffering caused by the spring buffers (32, 132) reduces the compressive stiffness of the hydraulic fluid volume arranged in the second pressure chamber (24, 124) to the level of the compressive stiffness of the hydraulic fluid volume arranged in the first pressure chamber (22).

4. The steering transmission mechanism according to claim 2 or 3, wherein, The buffer device (28, 128) has a cylindrical space (36, 136) integrally constructed with or separately arranged from the steering transmission housing (2), the cylindrical space being fluidly connected to the second pressure chamber (24, 124) via a borehole (37a) and / or a hydraulic line (37b).

5. The steering transmission mechanism according to claim 4, wherein, The balance pistons (34, 134) are supported in the cylindrical spaces (36, 136), and the balance pistons (34, 134) are sealed relative to the housings (35, 135) of the cylindrical spaces (36, 136) by means of seals (40, 140) embedded between the preload rings (38, 138) and the housings (35, 135) of the cylindrical spaces (36, 136).

6. The steering transmission mechanism according to claim 5, wherein, The balance pistons (34, 134) are slidably supported in the cylindrical space (36, 136).

7. The steering transmission mechanism according to claim 5 or 6, wherein, The spring buffer (32, 132) has at least one butterfly spring, which is received in the cylindrical space (36, 136) at a side opposite to the balance chamber (30, 130).

8. The steering transmission mechanism according to claim 7, wherein, The spring buffers (32, 132) have multiple butterfly springs.

9. The steering transmission mechanism according to claim 4, wherein, The section of the cylindrical space (36, 136) in which the spring buffer (32, 132) is arranged is dry and sealed to the outside or connected to the return section (RL) of the oil circuit via a hydraulic line.

10. The steering transmission mechanism according to claim 4, wherein, The balance pistons (34, 134) can abut against the stop of the buffer device (28, 128) at the first axial end section (36a, 136a) of the cylindrical space (36, 136) adjacent to the second pressure chamber (24, 124) without gap via the spring buffers (32, 132).

11. The steering transmission mechanism according to claim 10, wherein, The cylindrical spaces (36, 136) of the buffer devices (28, 128) have screw-in caps (39, 139) at the end sections (36a) of the cylindrical spaces (36, 136) arranged in the first axial direction and the end sections (36b) of the cylindrical spaces (36, 136) arranged in the second axial direction, the screw-in caps pre-tightening the spring buffers (32, 132).

12. The steering transmission mechanism according to claim 4, wherein, The cylindrical spaces (36, 136) of the buffer devices (28, 128) have stepped holes, wherein the balance pistons (34, 134) are arranged in a first section (36, 136c) of the cylindrical spaces (36, 136) with a smaller diameter, and wherein the spring buffers (32, 132) are arranged in a second section (36, 136d) of the cylindrical spaces (36, 136) with a larger diameter.

13. A steering system (100) for a motor vehicle, said steering system having: Steering spindle (42); and The steering transmission mechanism (1) according to any one of claims 1 to 12, wherein, The steering transmission mechanism (1) is configured to receive rotational motion introduced through the steering spindle (42).

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