Steering gear for vehicles, especially commercial vehicles

Abstract

The present invention relates to a ball-and-nut type steering gear (10) for a steering system of a vehicle, in particular a commercial vehicle, comprising at least one housing (12), at least one steering spindle (14), at least one steering spindle nut (16) guided axially slidably in the housing (12) and connected to the steering spindle (14) via a plurality of balls (14a) in an assembled state, and at least one bearing device (18) supporting the steering spindle (14) in the housing (12), wherein the bearing device (18), the steering spindle (14), and the housing (12) form an abutted support.

Description

[Technical field]

[0001] The present invention relates to a ball-and-nut steering gear for a steering system of a vehicle, in particular a commercial vehicle, which has at least one housing, at least one steering spindle, at least one steering spindle nut guided axially slidably in the housing and connected in an assembled state to the steering spindle via a number of balls, and at least one bearing device.

[0002] Modern steering gears for commercial vehicles or heavy commercial vehicles are often designed as ball and nut steering gears. This type of design offers the advantage of a high steering force or steering moment assist, especially in the case of heavy commercial vehicles with high axle loads, while at the same time having a simple construction principle.

[0003] Ball-and-nut steering gears of this type are already known from the prior art.

[0004] Thus, DE 37 14 833 A1 shows a power steering device which comprises a first force amplifier with an actuating piston which is integrated in a basic housing of the steering gear and which engages in a threaded spindle. The actuating piston drives a steering shaft which supports a steering segment via a toothed row. As a second force amplifier, an electric motor is provided which drives an extension shaft via a reduction gear and a switchable clutch. The extension shaft is connected to the threaded spindle in a non-rotatable manner. The second force amplifier is accommodated in a housing which is flange-fixed to the basic housing.

[0005] Furthermore, European Patent Application Publication No. 3192719 discloses an electric power steering device including a housing, a steering rotary shaft, a worm wheel, a worm shaft, a tip bearing, an electric motor, and a preload mechanism. The preload mechanism includes a wedge and a wedge elastic member. The wedge is disposed between the outer circumferential surface of the tip bearing and the inner circumferential surface of the housing in a state in which it is capable of displacement in the circumferential direction. The wedge elastic member applies a force to the wedge in one circumferential direction.

[0006] Furthermore, US Pat. No. 9,731,753 shows a steering gear component for a vehicle, which comprises a worm supported so as to be rotatable but not axially displaceable, and a ball nut, the worm having a ball circulation spindle for accommodating a row of balls, the ball nut being drivingly connected to the worm via the row of balls, the ball nut acting as a piston of a cylinder for steering force assist, a signal transmitter for a sensor element being arranged on the steering spindle and a sensor element being arranged on the worm, or alternatively, a sensor element being arranged on the steering spindle and a signal transmitter for the sensor element being arranged on the worm.

[0007] Furthermore, WO2013058752 discloses a power steering system for multi-axis steering of a motor vehicle, the power steering system having a primary steering gear and a second steering gear, the primary steering gear being controlled by a steering wheel, the steering wheel including a piston attached to a steerable wheel on a first axle of the motor vehicle, the second steering gear being attached to a steerable wheel on a second axle of the motor vehicle, the power steering system further having a transmission assembly connecting the first power steering gear and the second power steering gear to each other, the primary steering gear having a fluid control valve with an output element coupled to the piston and coupled to the transmission assembly.

[0008] Furthermore, German Patent No. 10351618 discloses a commercial vehicle steering with a steering gear, which transmits the steering movement introduced into the gear input to a pitman arm via a shaft rotatably supported in a gear housing and a piston movable along the shaft by rotation of the shaft, and the commercial vehicle steering further comprises a hydraulic auxiliary force amplifier, which assists the piston movement by controlled pressure application by a hydraulic fluid, in which an additional auxiliary force amplifier is provided, which comprises an electric motor, the torque of which is transmitted to the shaft via a reduction gear.

[0009] The core element of such a ball-and-nut steering gear is a ball screw spindle with a connected ball spindle nut and a ball circuit connecting these two components. However, this component is subject to considerable wear during operation, particularly in the steering spindle, due to the complex three-dimensional stress states. This is especially the case when the ball spindle nut rotates the sector shaft which meshes with it and is subjected to radial force components due to the engagement of the sector shaft, which leads to a deflection of the steering spindle. This occurs in particular when the steering assist energy is provided to the ball screw spindle via a servo gear stage and an electric motor.

[0010] The deflection of the steering spindle further leads to locally increased pressure on the individual rows of balls of the ball circuit, which can cause the permissible surface pressure of the ball circuit to be exceeded at certain points, resulting in damage to the balls and the raceways of the ball screw spindle or the steering spindle and the ball spindle nut.

[0011] SUMMARY OF THE DISCLOSURE The object of the invention is therefore to develop a steering gear of the type mentioned at the beginning in an advantageous manner, in particular in order to minimize wear on the steering gear and to optimize the space required for constructing the steering gear.

[0012] This problem is solved according to the invention by a steering gear with the features of claim 1. It is envisaged that in a ball-and-nut steering gear for a steering system of a vehicle, in particular a commercial vehicle, the ball-and-nut steering gear has at least one housing, at least one steering spindle, at least one steering spindle nut guided axially slidably in the housing and connected to the steering spindle in the assembled state via balls, and at least one bearing arrangement supporting the steering spindle in the housing, the bearing arrangement, the steering spindle and the housing form an abutted support.

[0013] The idea behind the invention is that, by means of the applied support, the steering spindle can be preloaded by the bearing arrangement at least with respect to the housing, which is not possible in the prior art with normal fixed and movable bearings. Preloading the steering spindle reduces the deflection of the steering spindle, which is caused in particular by the radial force components of the engagement of the sector shaft. This reduction in deflection also results in a uniform contact pattern of the balls or ball circuits, so that partial or point-like overloads can be effectively avoided. Furthermore, with regard to the component dimensions required for a life-span-appropriate force transmission in the steering gear, the invention also takes into account the trend towards purely electromechanical steering, since by eliminating the hydraulic steering assistance the steering spindle is exposed to higher wear in the future. In order to guarantee a predictable service life, an increase in the spindle diameter and an increase in the number of ball circuits are necessary for purely electromechanical applications, which therefore creates problems with construction space. In this respect, preloading the steering spindle can address such construction space problems and increased wear and therefore provide for the associated optimization of the steering gear. However, within the scope of the invention it is also possible for the steering gear according to the invention to be provided in addition to a purely electromechanical design, or additionally or alternatively in an electromechanical-hydraulic design.

[0014] In particular, the applied support creates a preload on the spindle.

[0015] In an advantageous embodiment, the bearing arrangement, the steering spindle and the housing form a resting support, whereby the steering spindle is preloaded, which allows the diameter of the spindle to be reduced, i.e. the preloading results in a diameter reduction, which in turn allows the overall dimensions of the entire assembly, which at least includes the bearing arrangement, the steering spindle and the housing, or the required construction space to be reduced.

[0016] It may further be provided that the bearing arrangement has at least one preloading device, with which the steering spindle can be preloaded axially and / or radially in an adjustable manner. Such a preloading device allows a precise and defined adjustment of the preload of the steering spindle, which is particularly important since it is desirable to keep the preload within narrow limits. If an excessively large preload is selected, this will have a negative effect on the wear of the steering spindle and the balls or ball tracks of the ball circulation nut. On the other hand, if an excessively small preload is selected, then the engagement of the ball circulation nut on the sector shaft will also result in excessively large deflections, which will also have a negative effect on the wear of this component.

[0017] It may further be envisaged that the bearing arrangement comprises at least one first bearing unit and at least one second bearing unit. Dividing the bearing arrangement into at least one first bearing unit and a second bearing unit is advantageous, since this allows the preload to be adjusted even more precisely. Furthermore, by suitable arrangement and configuration of the bearing units, the loads, stresses and wear acting on the steering spindle and the ball circulation nut can be further optimised.

[0018] It is further conceivable that in the assembled state, the first bearing unit is arranged in the region of the first end of the steering spindle and the second bearing unit is arranged in the region of the second end of the steering spindle. Such an arrangement of the two bearing units results in a more rigid configuration of the bearing arrangement, in particular in the radial direction, since with an increase in the axial distance relative to one another, the axial support distance can be increased (at least to a significant limit) and thus forces, in particular moments, acting on the steering spindle and the ball circulation nut can be countered more effectively. Furthermore, an arrangement in the region of both ends of the steering spindle is advantageous in terms of the assembling possibilities and accessibility, since this is simplified.

[0019] Furthermore, it is possible for the preloading device to have at least one first preloading element which, in the assembled state, is arranged in the region of the first end of the steering spindle or in the region of the second end of the steering spindle. In addition to these improved assembly possibilities due to the arrangement of the bearing unit and the preloading unit in the region of both ends, the accessibility and adjustability of the preloading unit can be simplified and made more precise. This allows a more accurate and precise adjustment of the preload on the steering spindle, which further reduces the wear on the ball raceway, the ball race nut and the steering spindle, which results in a longer service life and improved functional reliability of the steering gear.

[0020] It may further be provided that the preloading device has at least one second preloading element which is arranged in the region of the second end of the steering spindle in the assembled state, the first preloading element being arranged in the region of the first end of the steering spindle. By providing two preloading elements in the region of both ends of the steering spindle, preloading towards one side in the axial and radial directions of the steering spindle is prevented. Thus, the preloading of the steering spindle can be applied substantially symmetrically if the distances of both bearing units and preloading elements from the axial center point of the steering spindle are selected to be substantially equal. This arrangement reduces the stresses and loads occurring in the ball circulation, the ball circulation nut and the steering spindle, and thus their wear can be further effectively reduced.

[0021] It is also conceivable that the first bearing unit has at least one first tapered roller bearing and the second bearing unit has at least one second tapered roller bearing. Tapered roller bearings are already known from the prior art as complete and reliable machine elements and are particularly well suited for preloaded supports, since their force absorption or support capacity is high in the radial and axial directions and at the same time allows for a very simple, precise and reliable adjustment of the preload and preload of the entire support. Furthermore, the preloading of both tapered roller bearings allows the support as a whole to be reinforced, so that the deflection of the steering spindle in particular under load (i.e. in dynamic engagement with the sector shaft) is further reduced, which allows the above-mentioned advantages with regard to wear, safety and service life. In order to increase the stiffness of the entire support and / or the first bearing unit and / or the second bearing unit, the first bearing unit may be configured as a multi-row, e.g. two-, three- or four-row tapered roller bearing, which also applies to the second bearing unit. The multi-row tapered roller bearing may be formed from individual tapered roller bearings joined together or by a combined integral tapered roller bearing.

[0022] It is further conceivable that the first tapered roller bearing and the second tapered roller bearing form an O-shaped arrangement in the assembled state. The O-shaped arrangement increases the absorbable tilting moment of the support due to the position of the pressure lines (force streamlines) passing through both tapered roller bearings, which are axially located outside the first and second bearing units in the O-shaped arrangement or intersect. The reason for the increased absorption of the tilting moment is the increased distance between the pressure centers of the pressure lines, which allows the stiffness of the support to be further increased.

[0023] Furthermore, in the assembled state, the first preload element can be screwed to the steering spindle in the region of the first end of the steering spindle and can rest against at least one inner race of the first tapered roller bearing. This configuration facilitates the manufacture of the steering gear, since no additional threads need to be machined in the bearing bore of the housing to accommodate the first preload element. Furthermore, the preload element can be smaller and therefore more conveniently constructed, and can be assembled more simply.

[0024] Additionally, it may also be provided that in the assembled state, the second preload element is screwed onto the steering spindle in the region of the second end of the steering spindle and rests against at least one inner race of the second tapered roller bearing. Such an arrangement provides the same advantages as those already mentioned above with respect to the first preload element. Furthermore, the cooperation of both preload elements with respect to the steering spindle allows a particularly precise, symmetrical and accurate adjustment of the preload of the steering spindle, since both preload elements act directly on the steering spindle or are screwed onto it.

[0025] It is furthermore conceivable that in the assembled and applied state of the first and second preloading elements, the preload of the steering spindle is at least embodied as a tensile preload. The tensile preload initially acts against the elastic deflection of the steering spindle in the unloaded state, which has the advantage that, on the one hand, this deflection can be reduced. On the other hand, the deformation potential is in any case maximized with this configuration, since the sector shaft acts at the point of maximum deflection of the steering spindle. Thus, when a tensile force is applied to the shaft, the elastic deflection of the steering spindle can first be reduced in the unloaded state. Thus, in a first step, the deformation potential is reduced, since the elastic deformation in the unloaded state can practically no longer cooperate with the deformation in the loaded state. Therefore, even in the loaded state, the steering spindle only deforms very slightly, since the elastic deformation proportions are practically eliminated by the tensile preload. The tensile preload therefore reduces the elastic deformation of the steering spindle both in the unloaded and loaded state of the steering gear, which further reduces wear on the ball race and the ball race nut.

[0026] It is also conceivable that the first preloading element is designed as a grooved nut and the second preloading element is designed as a grooved nut, which is a very robust, proven or proven, non-disengaging mechanical element that allows a very precise preload with a correspondingly defined tightening moment.

[0027] Further details and advantages of the invention are explained in detail with reference to the illustrated embodiment. [Brief description of the drawings]

[0028] [Figure 1] 1 is a schematic cross-sectional view of an embodiment of a steering gear according to the invention;

[0029] The single drawing (FIG. 1) shows a schematic cross-sectional view of an embodiment of a steering gear 10 according to the invention.

[0030] The steering gear 10 is formed as a ball-and-nut type steering gear 10 for the steering system of a commercial vehicle (not shown in FIG. 1).

[0031] The steering gear 10 includes a housing 12, a steering spindle 14, and a steering spindle nut 16 guided axially slidably within the housing.

[0032] In this case, the steering spindle nut 16 is guided within a circular guide hole 12a of the housing 12 so as to be axially slidable.

[0033] The guide bore 12a may in particular have a circular cross section, the guide surface of the steering spindle nut 16 then being in contact with the guide bore 12a over the entire circumference or over a portion of the circumference.

[0034] The steering spindle nut 16 is further connected to the steering spindle 14 via a plurality of balls or ball circulation paths 14a in an assembled state.

[0035] In this case, the ball circulation passage 14a can be understood to have a plurality of screw-shaped circulation passages along the balls 14a in the axial direction, as can be seen from FIG.

[0036] The balls 14a are therefore guided in an axially extending screw-like or helical spindle groove 14b of the steering spindle, the spindle groove 14b having a semicircular cross section.

[0037] The balls or ball circuits 14a cooperate correspondingly with a separate axially extending threaded or helical nut groove 16a of the steering spindle nut 16, which likewise has a semicircular cross section.

[0038] According to FIG. 1, the rotational motion of the steering spindle 14 is transmitted to the steering spindle nut 16 via a number of balls or ball circuits 14 a, resulting in an axial sliding motion of the steering spindle nut 16 within the housing 14 .

[0039] The steering spindle nut 16 furthermore has a partial toothing 16b in a partial region of its circumferential surface, which in the mounted state engages with a sector gear of the sector shaft.

[0040] The steering gear 10 further comprises, according to FIG. 1, a bearing arrangement 18 which supports the steering spindle 14 in the housing 12 .

[0041] The bearing arrangement 18, the steering spindle 14 and the housing 12 form an abutted support in this case.

[0042] The bearing arrangement 18 further includes a preload device 20 capable of applying an adjustable axial preload to the steering spindle 14 .

[0043] Additionally or alternatively, it is also conceivable that the steering spindle 14 can be correspondingly radially preloaded in an adjustably manner by means of a preload device 20 .

[0044] The bearing device 18 further includes a first bearing unit 18a and a second bearing unit 18b.

[0045] The first bearing unit 18a is arranged in the region 14c of the first end of the steering spindle 14 in the assembled state.

[0046] Correspondingly, the second bearing unit 18b is arranged in the region 14d of the second end of the steering spindle 14.

[0047] For this purpose, the steering spindle 14 has, in its first end region 14c and in its second end region 14d or section, a respective bearing mount for accommodating a first bearing unit 18a and a second bearing unit 18b.

[0048] The first end of the steering spindle 14 is further integrally coupled with a steering insert engagement portion 14e that is connectable to a steering column (not shown in FIG. 1) and a steering wheel.

[0049] The above-mentioned preload device 20 further comprises a first preload element 20 a which, in the assembled state, is arranged in the region 14 c of the first end of the steering spindle 14 .

[0050] Correspondingly, the preload device 20 has a second preload element 20b which is also arranged in the assembled state in the region 14d of the second end of the steering spindle 14.

[0051] As an alternative to the first preload element 20a and the second preload element 20b, the preload device 20 may have only one preload element 20a, 20b arranged in the first end region 14c or in the second end region 14d of the steering spindle 14.

[0052] In this case, the preload of the steering spindle 14 is applied via a corresponding shoulder (not shown in FIG. 1) of the steering spindle 14, which is arranged in the region 14c of the opposite first end or in the region 14d of the opposite second end of the steering spindle 14, where only one preload element 20a, 20b is not arranged.

[0053] The first bearing unit 18a, according to FIG. 1, has a first tapered roller bearing, whereas the second bearing unit 18b correspondingly has a second tapered roller bearing.

[0054] As shown in FIG. 1, the first tapered roller bearing and the second tapered roller bearing form an O-shaped arrangement in an assembled state.

[0055] Both tapered roller bearings are formed as single-row tapered roller bearings, but it is also conceivable that both tapered roller bearings are formed as multi-row tapered roller bearings, in which case the individual tapered roller bearings may be connected to one another or formed as one piece.

[0056] In particular, double-row or four-row tapered roller bearings come into consideration in this regard.

[0057] In the case of multiple row tapered roller bearings, the bearings may be formed in an X-arrangement, an O-arrangement, or a tandem arrangement, respectively.

[0058] As further shown in FIG. 1, in the assembled state, the first preload element 20a is screwed to the steering spindle in the region 14c of the first end of the steering spindle 14 and rests against the inner race of the first tapered roller bearing.

[0059] Correspondingly, in the assembled state, the second preload element 20b is screwed into the steering spindle in the region 14d of the second end of the steering spindle 14 and bears against the inner race of the second tapered roller bearing.

[0060] Therefore, the first bearing unit 18a and the second bearing unit 18b are formed or arranged symmetrically with respect to the axial center axis, and have the same components.

[0061] The first preload element 20a and the second preload element 20b are each formed as a grooved nut.

[0062] Therefore, since both grooved nuts are pressed against both inner races of each tapered roller bearing, the preload of the steering spindle 14 is formed as a tension preload in the assembled and pressed state of both preload elements.

[0063] Both grooved nuts are furthermore prevented from undesired disengagement by respective fastening lamellae, which are not shown in FIG.

[0064] Furthermore, in the assembled state, the outer race of the first tapered roller bearing rests in the region 14c of the first end of the steering spindle 14 against a first housing shoulder of the housing 12 or of the first housing cover.

[0065] The outer race of the second tapered roller bearing therefore rests in the region 14d of the second end of the steering spindle 14 against a second housing shoulder of the housing 12 or of the second housing cover.

[0066] As can further be seen in FIG. 1, the steering gear 10 is shown without a separate auxiliary drive device, such as a hydraulic pump, hydraulic pistons or an electric motor, for generating an additional steering assist moment.

[0067] In particular, it may be assumed in this connection that the steering gear 10 of FIG. 1 has an electric motor or servo motor flange-mounted thereto and non-rotatably connected to the steering spindle 14 either directly via a coupling or indirectly via a reduction gear.

[0068] The electric motor may be flanged to the housing 12 so as to be coupled to the steering spindle 14 at a region 14c at the first end of the steering spindle 14 or at a region 14d at the second end of the steering spindle 14.

[0069] Additionally or alternatively, the intermediate space of the circular guide bore 12a of the housing 12, which is formed between the steering spindle nut 16 and the two bearing units 18a, 18b, can be loaded with oil pressure via a hydraulic pump.

[0070] Thus, additionally or alternatively, a hydraulic supplementary steering force assist can be realized.

[0071] However, the housing lines required for this, the hydraulic pump or the corresponding control valves for controlling the two intermediate chambers of the circular guide bore 12a of the housing 12 are not shown in FIG.

[0072] The same applies to the adaptation of the steering spindle nut 16 for sealing these two intermediate chambers against each other and against the bearing units 18a, 18b, whereby the steering spindle nut 16 additionally also functions as a hydraulic piston.

[0073] The function of the steering gear 10 according to the invention is explained as follows: The rotating spindle is rotated according to the steering intention of the vehicle driver via a steering insert engagement portion 14e in an area 14c of a first end of the steering spindle 14, which can be non-rotatably connected to the steering wheel via a steering column.

[0074] The steering spindle 14 is connected to the steering spindle nut 16 via a ball circuit 14 a , which results in an axial sliding or translational movement of the steering spindle nut 16 within the housing 12 .

[0075] As can be further seen in FIG. 1, the steering spindle nut 16 itself engages with a sector gear of the sector shaft via a partial toothing provided on its circumferential surface.

[0076] Thus, the axial sliding or translational movement of the steering spindle nut 16 is transmitted to the sector gear, which results in rotation of the sector shaft.

[0077] The sector shaft is, on the other hand, non-rotatably connected to a pitman arm (not shown in FIG. 1), and the pitman arm is caused to pivot by rotation of the sector shaft, and this pivoting motion is transmitted to the steering mechanism, which then turns the wheels of the axle in accordance with the driver's intentions.

[0078] Due to the meshing between the steering spindle nut 16 and the sector gear, the steering spindle nut 16 is subjected to a radial force during each translational movement and transmits this radial force to the steering spindle 14 via the ball circuits 14a.

[0079] However, since the steering spindle 14 according to the present invention is preloaded with axial tensile stress, the steering spindle 14 is subjected to relatively small radial forces or deformations from the steering spindle nut 16, and therefore wear on the steering spindle 14, ball race 14a and steering spindle nut 16 is reduced according to the present invention. [Explanation of symbols]

[0080] 10 Ball-nut type steering gear 12. Housing 12a Guide hole 14 Steering spindle 14a Ball or ball circulation path 14b Spindle groove 14c: the region of the first end of the steering spindle 14d. Area of ​​the second end of the steering spindle 14e Steering insertion engagement portion 16 Steering spindle nut 16a Nut groove 16b Partial dentition 18 Bearing device 18a First bearing unit 18b Second bearing unit 20 Preload device 20a First preload element 20b Second preload element

Claims

1. A ball-and-nut type steering gear (10) for a steering system of a vehicle, in particular a commercial vehicle, comprising: At least one housing (12); At least one steering spindle (14); at least one steering spindle nut (16) guided axially slidably within the housing (12) and connected to the steering spindle (14) in an assembled state via a plurality of balls (14a); at least one bearing device (18) supporting the steering spindle (14) within the housing (12); A ball-nut type steering gear (10) having The bearing device (18) has at least one preload device (20); The preload device (20) preloads the steering spindle (14), and the preload of the steering spindle (14) reduces deflection of the steering spindle (14); the preload device (20) comprises a first preload element (20a) which, in an assembled state, is arranged in the region (14c) of a first end of the steering spindle (14), the preload device (20) comprises a second preload element (20b) which, in an assembled state, is arranged in the region (14d) of a second end of the steering spindle (14), Ball and nut type steering gear (10).

2. 2. The ball-and-nut type steering gear (10) according to claim 1, wherein the bearing device (18) comprises at least one first bearing unit (18a) and at least one second bearing unit (18b).

3. 3. The ball-and-nut type steering gear (10) according to claim 2, wherein, in an assembled state, the first bearing unit (18a) is arranged in the region (14c) of the first end of the steering spindle (14) and the second bearing unit (18b) is arranged in the region (14d) of the second end of the steering spindle (14).

4. 3. The ball-and-nut type steering gear (10) of claim 2, wherein the first bearing unit (18a) has at least one first tapered roller bearing and the second bearing unit (18b) has at least one second tapered roller bearing.

5. 5. The ball-and-nut type steering gear (10) according to claim 4, wherein, in an assembled state, the first preload element (20a) is screwed to the steering spindle (14) in the region (14c) of the first end of the steering spindle (14) and is pressed against at least one inner race of the first tapered roller bearing.

6. 6. The ball-and-nut type steering gear (10) according to claim 4 or 5, wherein, in an assembled state, the second preload element (20b) is screwed to the steering spindle (14) in the region (14d) of the second end of the steering spindle (14) and is pressed against at least one inner race of the second tapered roller bearing.

7. 7. The ball-and-nut steering gear (10) according to claim 1, wherein in the assembled and applied state of the first and second preload elements (20b), the preload of the steering spindle (14) is formed at least as a tensile preload.

8. 8. The ball-nut type steering gear (10) according to claim 1, wherein the first preload element (20a) is formed as a grooved nut and the second preload element (20b) is formed as a grooved nut.

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