EP3538422A1

EP3538422A1 - Damper with variable torsional stiffness for hydraulic steering system steering columns

Info

Publication number: EP3538422A1
Application number: EP17797314.6A
Authority: EP
Inventors: Sergio Magrini
Original assignee: CNH Industrial Italia SpA
Current assignee: CNH Industrial Italia SpA
Priority date: 2016-11-09
Filing date: 2017-11-07
Publication date: 2019-09-18
Also published as: IT201600113081A1; WO2018087096A1

Abstract

A damping assembly (212) controlling vibrations from a hydraulic steering unit (204) in a power steering system (200) of a work machine (100) includes a bowl-shaped flywheel (214), a bowl-shaped axial/transverse damper (216) in the flywheel (214) and a rotor (218) operable in the axial/transverse damper (216). The rotor (218) includes arms (262, 264, 266, 268). Clockwise dampers (272, 276) and counterclockwise dampers (274, 278) operate between the arms (262, 264, 266, 268) and pediments (228) of the flywheel (214) that are exposed in the axial/transverse damper (216).

Description

DAMPER WITH VARIABLE TORSIONAL STIFFNESS FOR HYDRAULIC STEERING SYSTEM STEERING COLUMNS

BACKGROUND OF THE INVENTION

The present invention relates generally to work machines such as agricultural tractors, more particularly to hydraulic power steering systems for such work machines, and still more particularly to steering column damper systems to overcome vibrations from the power steering system hydraulic steering unit in such work machines.

Work machines of many different types, such as agricultural tractors and other self- propelled implements, are provided with hydraulic steering systems to facilitate machine operation. Operators commonly spend prolonged time periods operating a machine in a more or less continuous manner. For example, in farming operations, the available windows of time for preparing fields and planting crops and for harvesting the crops at optimum crop condition can be quite limited. Hydraulic steering systems lessen fatigue and enhance the comfort of an individual operating the implement. Modern work machines of these types frequently are provided with operator cabins for both safety and comfort of the operator.

A typical hydraulic steering system includes a hydraulic steering unit connected by hydraulic fluid lines to hydraulic actuators operatively connected to the steerable wheels. A steering wheel is connected mechanically to the hydraulic steering unit by a steering column in a way for controlling operation of the hydraulic steering system. By turning the steering wheel clockwise or counterclockwise, an operator of the machine controls operation of the hydraulic steering unit to effect turning of the steerable wheels.

The hydraulic steering unit naturally generates vibrations by its pumping action. The vibrations are transmitted through the steering column and to all things connected thereto. The hydraulic steering unit induced vibrations can be felt by an operator while grasping the steering wheel and can cause noise that may be amplified in or by the operator cab. Vibrations felt through the steering wheel, and unnecessary noises in the operator cab are undesirable, and can contribute to operator fatigue and discomfort. Damping or controlling the hydraulic steering unit induced vibrations is challenging in that the vibrations generated vary as the hydraulic steering unit performance changes based on the steering commands issued through rotation of the steering wheel. Soft damping that may be advantageous or desirable under conditions of little or no steering wheel rotation can be too soft and too yielding when the steering wheel is operated and greater torque is applied. Conversely, torsional rigidity that is too high can be ineffective in damping vibrations under some conditions.

United States Patent Application Publication 2002/0190450 teaches a damper mechanism for a steering device to avoid micro vibrations generated by wheels that can be transferred to the steering wheel. An inner member is connected to a steering shaft, an outer member is connected to a universal joint and an elastic body is positioned between the two members. The elastic body has a variable thickness. For small angular rotations the thicker part of the elastic body provides the only damping structure until a gap is covered. For larger angular rotations the thick part and thin part are combined to provide resistance. While variable torsional stiffness is provided, it is provided as only two steps.

Accordingly, it is desirable to have a damper with low vibration transmissibility torsionally, axially and transversely. It is desirable to have a damper of variable resistance in a steering column of a hydraulic steering system, which can be customized easily for different machines and machine uses, and which is softer or more yielding in some steering system operating conditions and stiffer or more resistant in other steering system operating conditions. More specifically, it is desirable to provide a damper in a steering column of a hydraulic steering system having variable torsional stiffness according to the applied torsional torque, to optimize the transmissibility of the system, making the resonance frequency variable, depending on the instantaneous torque transmitted.

Known hydraulic steering systems can provide difficult installations and assemblies. Known hydraulic steering systems provide minimum angular articulation and little or no axial adjustment. Since assembly tolerances for the steering column support on the cab can be quite narrow, during production it can be difficult to keep the distance between the position of the hydraulic steering unit on the wall of the operator cab and the steering column support on the cab within the tight tolerances that are common. Accordingly, it is desirable to have a steering column in a hydraulic steering system that is self-aligning and automatically adjustable axially between the steering wheel and hydraulic steering unit, to facilitate assembly and installation.

SUMMARY OF THE INVENTION

The present invention provides a compact damper structure providing torsional, axial and transverse damping functions within a compact structure. The translational damper can be shaped in different ways to obtain different torsional stiffness strategies as desired. At lower loads, damper contact surfaces are small so that the initial compression zone is small. At higher loads, the contact surface is larger and a larger compression zone is applied.

The invention in one form is directed to a damping assembly for a power steering system to control vibrations from a hydraulic steering unit to a steering shaft in the power steering system. The damping assembly is provided with vibration dampers between the steering shaft and the hydraulic steering unit. The damping assembly includes both clockwise and counterclockwise dampers that are configured to provide changing resistance in response to rotation of the steering shaft.

The invention in another form is directed to a damping assembly for a power steering system to control vibrations from a hydraulic steering unit to a steering shaft in the power steering system. The damping assembly is provided with vibration dampers between the steering shaft and the hydraulic steering unit. The damping assembly includes a flywheel having a bottom and a side defining a cavity, and a cover over the cavity. Clockwise and counterclockwise dampers are disposed in the cavity and are configured to provide changing resistance in response to rotation of the steering shaft.

The invention in yet another form is directed to a damping assembly for a power steering system to control vibrations from a hydraulic steering unit to a steering shaft in the power steering system. The damping assembly is provided with vibration dampers between the steering shaft and the hydraulic steering unit. The damping assembly includes a flywheel having a bottom and a side defining a cavity. A rotor having a hub with arms is disposed in the cavity and has a collar extending through the cover and connected to the steering shaft. Clockwise and counterclockwise dampers are provided between the arms of the rotor and pediments in the flywheel.

The invention in a further form is directed to a damping assembly for a power steering system to control vibrations from a hydraulic steering unit to a steering shaft in the power steering system. The damping assembly is provided with vibration dampers between the steering shaft and the hydraulic steering unit. The damping assembly includes a flywheel configured to have a natural frequency below vibration frequencies generated from operation of the hydraulic steering unit.

An advantage of the damping assembly is that it provides damping of axial, transverse and torsional vibrations in a compact arrangement that is easy to assemble.

Another advantage of the damping assembly is that it provides variable torsional stiffness against torsional vibrations from a hydraulic steering unit.

Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic, fragmentary illustration of a work machine with a hydraulic power steering system in which the damper assembly disclosed herein can be used;

Fig. 2 is a perspective view of the power steering column of the power steering system;

Fig. 3 is an exploded view of a portion of the power steering system; Fig. 4 is an elevational view of a portion of the power steering system; Fig. 5 is a cross-sectional view of the portion of the power steering system shown in Fig. 4, taken along line 5-5 of Fig. 4;

Fig. 6 is a cross-sectional view of the portion of the power steering system shown in Fig. 5, taken along line 6-6 of Fig. 5;

Fig. 7 is a perspective view of the end of the damping assembly; Fig. 8 is an end elevational view of the damping assembly;

Fig. 9 is an end elevational view similar to that of Fig. 8, but illustrating the damping assembly in a condition of clockwise rotation of the power steering system;

Fig. 10 is an end elevational view similar to those of Figs. 8 & 9, but illustrating the damping assembly in a condition of clockwise rotation of the power steering system; and

Fig. 1 1 is a schematic, fragmentary illustration similar to Fig. 1 , but illustrating several dimensional relationships.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to Fig. 1 , there is shown in fragmentary, schematic illustration a work machine 100, such as an agricultural tractor 100, having a frame 102, an operator cab 104 attached to frame 102 and a power steering system 200 extending into operator cab 104 and operatively connected to hydraulic actuators 106 operating steerable wheels 108. The manner in which power steering system 200 is connected to steerable wheels 108 for the operation thereof is well known to those skilled in the art and will not be described further herein. While the present application refers to an agricultural tractor as the work machine described, it should be understood that the damping assembly disclosed herein can be used on various types of power steering systems for various types of work machines, as well as machines of other types.

Power steering system 200 is anchored within operator cab 104 by a column support 1 10 anchored to operator cab 104 at connections 1 12. Pivotal connections 1 14 connect column support 1 10 to an adjustable steering column housing 1 16. The in- cab portion of power steering system 200 is anchored to cab 104 by anchors 1 18.

Referring now also to Fig. 2, power steering system 200 includes a steering column 202 operatively connected to a power steering hydraulic steering unit 204 connected to cab 104 by anchors 1 18. Steering column 202 includes a steering wheel 206, a steering shaft 208 and a steering shaft alignment assembly 210 connected to hydraulic steering unit 204. A power steering damping assembly 212 is operatively disposed between steering shaft 208 and steering alignment assembly 210 which, as shown in the drawings and to be described subsequently herein are merely exemplary and do not limit application of the damping assembly. Damping assembly 212, for example, can be used without the type of alignment system shown herein and may connect more directly to hydraulic steering unit 204.

Referring now to Figs. 3-6, power steering damping assembly 212 includes a flywheel 214, an axial/transverse damper 216, a rotor 218 and a cover 220. Flywheel 214 is an open-ended, somewhat bowl-like housing for receiving axial/transverse damper 216 and rotor 218 therein. Rotor 218 nests within axial/transverse damper 216, which itself nests within flywheel 214. Cover 220 is attached to flywheel 214 with axial/transverse damper 216 and rotor 218 nested therein. Accordingly, torsional, axial and translational dampers are contained within the compact assembly of flywheel 214 and cover 220.

In a preferred embodiment, flywheel 214 is made of metal or other rigid, strong material. Flywheel 214 includes a bottom 222 and a generally cylindrical side 224. A center post 226 projects from bottom 222. Peripheral pediments 228 are spaced from center post 226 and from one another about the periphery of flywheel 214 as defined by side 224. Flywheel 214 thereby defines there within a four-lobed cavity 230 between side 224 and center post 226, the lobes of cavity 230 being spaces between and among pediments 228. Cavity 230 is configured to receive axial/transverse damper 216 therein.

Flywheel 214 can be used to attenuate vibration and sound conveyed into cab 104 by controlling the weight and dimensions of flywheel 214 relative to the vibration frequency of the hydraulic steering unit 204. In conventional arrangements, the natural frequencies of components in steering column 202 can approach the range of vibration frequencies from hydraulic steering unit 204 such that noise and vibration are transmitted through resonance and amplified. Flywheel 214 provides a readily configurable mass for which the composition, weight and dimensions can be selected by design to have a natural frequency outside the frequency range annoying to human operators. For example, by changing the size and mass of flywheel 214, the natural frequency of flywheel 214 can be controlled to be lower than the frequency range generated by the operation of hydraulic steering unit 204, thereby attenuating resonant transmission of vibrations from hydraulic steering unit 214. More specifically, if hydraulic steering unit 214 generates frequencies in the range of 1 10- 540 Hz, designing flywheel 214 with mass and dimensions for a natural frequency of less than 100 Hz can achieve desired attenuation.

Axial/transverse damper 216 is made of rubber or other resilient material shaped to nest within cavity 230 and cover a substantial portion of the inner surfaces of flywheel 214. Accordingly, axial/transverse damper 216 includes a bottom 240, and a side 242. Side 242 includes cutout indentations 244 configured to surround pediments 228 while exposing the side surfaces thereof. A center cylinder 246 projects from bottom 240 and is both sized and shaped to slide over center post 226. Axial/transverse damper 216 defines pediment covers 248 extending inwardly from side 242 near the outer edge thereof, thereby spaced from bottom 240 and from center cylinder 246. Pediment covers 248 are spaced from one another about the periphery of axial/transverse damper 216 as defined by side 242. Pediment covers 248 cover the outer end surfaces of pediments 228, leaving the side surfaces of pediments 228 exposed in cutout indentations 244. Axial/transverse damper 216 thereby defines an annular, open ended cavity 250 above bottom 240 and between side 242 and center cylinder 246, the cavity 250 being interrupted by cutout indentations 244. Cavity 250 is configured to receive rotor 218 therein. As can be seen in Figs. 5 and 6, axial/transverse damper 216 substantially covers the inner surfaces of flywheel 214 except for the exposed side surfaces of pediments 228, and provides a cushion between flywheel 214 and rotor 218. Accordingly, axial/transverse damper 216 provides cushioning or dampening against the transmission of vibrations from flywheel 214 to rotor 218, and primarily the axial and transverse vibrations.

Rotor 218 includes an axially extending, bifurcated collar 260 that extends through cover 220 and is configured to receive steering shaft 208 therein. Rotor 218 further defines four radially extending arms 262, 264, 266, 268 from a central hub 270. As thus far described, rotor 218 can be of metal or other strong, rigid material. Arms 262, 264, 266, 268 are associated with dampers 272, 274, 276, 278, the dampers being made of rubber or other resilient material. Dampers 272, 274, 276, 278 are rotational dampers operative when steering wheel 206 is rotated either clockwise or counterclockwise. Accordingly, dampers 272, 274, 276, 278 are positioned on alternating sides of arms 262, 264, 266, 268 such that during clockwise rotation of rotor 218, two dampers 272, 276 are carried forward of the respective arms 262, 266 with which they are associated, and during counterclockwise rotation of rotor 218 the other two dampers 274, 278 are carried forward of the respective arms 264, 268 with which they are associated. Hub 270 and arms 262, 264, 266, 268 thereof, together with dampers 272, 274, 276, 278 associated therewith, are sized, shaped and configured to fit within cavity 250 of axial/transverse damper 216, as limited by pediments 228 exposed therein.

With reference now more particularly to Figs. 7-10, the operation of damping assembly 212 will be described. References made herein to a "forward rotational direction" of any of the dampers 272, 274, 276, 278 is intended to mean the rotational direction in which the damper leads the support arm 262, 264, 266, 268 with which it is associated. Accordingly, the forward rotational direction of dampers 272, 276 is clockwise rotation of rotor 218, and the forward rotational direction of dampers 274, 278 is counterclockwise rotation of rotor 218. Further, during clockwise rotation, dampers 272, 276 may be referred to as leading dampers and dampers 274, 278 may be referred to as trailing dampers with respect to the arms 262, 266, 264, 268 with which they are associated. During counterclockwise rotation, dampers 274, 278 are leading dampers and dampers 272, 276 are trailing dampers with respect to the rotor arms 264, 268, 262, 266 with which they are associated. Upon rotation of rotor 218 in the forward rotational direction of a damper, the damper confronts a peripheral pediment 228 of flywheel 214 exposed in a cutout indentation 244 of axial transverse damper 216. Leading faces of dampers 272, 274, 276, 278 are backwardly reclined relative to the confronting faces of pediments 228 in the forward rotational directions, and trailing faces of the dampers 272, 274, 276, 278 are forwardly inclined relative to the confronting faces of the arm 262, 264, 266, 268 associated therewith. A minimal preload compression is provided of dampers 272, 274, 276, 278 between associated arms 262, 264, 266, 268 and the pediments 228. Accordingly, as shown in Figs. 7-9 without rotation of rotor 218 (that is, with steering wheel 206 centrally positioned) minimal contact areas exist between each of the dampers 272, 274, 276, 278 and the arm 262, 264, 266, 268 associated therewith, and with the pediment 228 immediately ahead in the forward rotational direction. As a result, the damper is in a soft condition and will dampen torsional vibrations from hydraulic steering unit 204. Upon the application of increased torsional force from turning steering wheel 206 in either direction, the forward facing, leading dampers begin to compress, thereby increasing the contact areas with the adjacent arms and encountered pediments. As the contact areas increase, torsional resistance increases as well, and the responsiveness of hydraulic steering unit 204 to the rotation of steering wheel 206 is maintained. Figs. 9 and 10 illustrate the minimal contact areas "A" and the increased contact areas "B" for one of the clockwise dampers (272) that occurs from clockwise rotation. It should be understood that a similar change has also occurred for the other clockwise damper (276) in Fig. 10; and that similar changes will occur on the counterclockwise dampers (274, 278) when rotated in the forward rotational directions thereof.

In addition to or in place of the angular orientation of the faces of dampers 272, 274, 276, 278; the arms 262, 264, 266, 268 also can be shaped to affect the changes in contact areas upon rotation of rotor 218. Material selections for the contacting surfaces also can be selected with desired characteristics influencing the change in torsional resistance. With the damper assembly described herein, the change of torsional resistance is highly controllable. It is even possible to provide one rate of change for clockwise rotation and a different rate of change for counterclockwise rotation by selecting desirable materials and shaping the contacting surfaces to achieve the desired result. While the exemplary embodiment has been shown and described with rotor 218 including four arms 262, 264, 266, 268; two clockwise dampers 272, 276 and two counterclockwise dampers 274, 278; it should be understood that more or fewer arms/or dampers can be used. By way of examples, a single clockwise arm and damper and a single counterclockwise arm and damper can be provided; or three or more of each can be used. Further, it is not necessary that clockwise and counterclockwise rotation be provided with equal numbers of dampers. If so desired, either direction can be provided with more or fewer dampers than the other. The dampers can behave differently for clockwise rotation and counterclockwise rotation of the steering shaft, if such a difference is desired.

It should be appreciated that the open, bowl-like structures of flywheel 214 and axial/transverse damper 216 to receive rotor 218 and the torsional dampers allows for easy assembly of the entire damper assembly.

With reference now to Fig. 1 1 , it can be appreciated that the interface of operator cab 104 with column support 1 10, steering column 202 and hydraulic steering unit 204, if varied from design tolerances, can interrupt proper alignment of steering shaft 208 with hydraulic steering unit 204. More specifically, proper alignment can be affected by the relationships between a dimension "W" representing the width between the axis of steering column 202 and support connections 1 12 and a dimension "L" representing the length from the anchor surface of cab 104 to the pivotal connections 1 14. Proper alignment is important to minimize vibration transmission.

Steering shaft 208 is segmented, with a proximal portion 210 and a distal portion 212 and connected at a cardan joint 214.

Referring again primarily to Fig. 3 and additionally Figs. 4-6, steering shaft alignment assembly 210 provides simple articulation for small movements, and provides self- aligning features. A stub connector 290 includes a gear element 292 at the distal end thereof engaged in a receiver 294 of hydraulic steering unit 204 (Fig. 1 1 ). A globular element 296 at the proximal end of stub connector 290 defines transverse openings 298. A shaft 300 extends through transverse openings 298, and is secured by pins 302. At a center portion 304 thereof, shaft 300 is cylindrical. A pivot 306 is held also in the globular proximal end 296 by a pin 308. The inside of pivot 306 defines a spherical part 310 to cooperate with the cylindrical portion 304 of shaft 300. The spherical contact points between center portion 304 and spherical part 310 provide ready relative rotation between shaft 300 and pivot 304. A spring 312 urges pivot 306 to maintain contact between pivot 306 and shaft 300.

Damper assembly 212 provides sufficient flexing ability to compensate for misalignment caused by variations in the for aforedescribed dimensions "W" and "L". The rolling surface contact between shaft 300 and pivot 304 allows for compensation easily and quickly.

Linear adjustment along the length of steering column 202 is effected by steering shaft 208 received in bifurcated collar 260 and held therein by a bolt, pin or key 314 (Fig. 2) received in a channel 316 of shaft 208 (Fig. 3).

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

CLAIMS:

1 . A damping assembly (212) for a power steering system (200), to control vibrations from a hydraulic steering unit (204) to a steering shaft (208) in the power steering system (200); the damping assembly (212) comprising: vibration dampers (216, 272, 274, 276, 278) between the hydraulic steering unit (204) and the steering shaft (208); characterized in that: said vibration dampers include a clockwise damper (272, 276) and a counterclockwise damper (274, 278); the clockwise damper (272, 276) and counterclockwise damper (274, 278) provide varying resistance to torsional vibrations of the hydraulic steering unit (204); and the varying resistance of the clockwise and counterclockwise dampers (272, 274, 276, 278) is in response to rotation of the steering shaft.

2. The damping assembly (212) of claim 1 , wherein: pluralities of clockwise dampers (272, 276) and counterclockwise dampers (274, 278) are provided.

3. The damping assembly (212) of either claim 1 or claim 2, further characterized in that: a flywheel (214) is connected between said steering shaft (208) and said hydraulic steering unit (204); and said clockwise and counterclockwise dampers (272, 274, 276, 278) are contained in said flywheel.

4. The damping assembly (212) of any of claims 1 -3, further characterized in that: said damping assembly (212) includes a rotor (218); and said clockwise and counterclockwise dampers (272, 274, 276, 278) are carried against the rotor (218).

5. The damping assembly (212) of claim 1 , further characterized in that: a flywheel (214) including a bottom (222) and a side (224) defining a cavity (230) is disposed between the steering shaft (208) and the hydraulic steering unit (204); a cover (220) is provided over said cavity (230); and said clockwise and counterclockwise dampers (272, 274, 276, 278) are disposed in said cavity (230).

6. The damping assembly (212) of claim 5, further characterized in that; a rotor (218) has a hub (270) with arms (262, 264, 266, 268) disposed in said cavity (230) and a collar (260) extending through said cover (220) and connected to said steering shaft (208); and said clockwise and counterclockwise dampers (272, 274, 276, 278) are carried against said arms (262, 264, 266, 268).

7. The damping assembly (212) of either claim 5 or claim 6, wherein: pluralities of clockwise dampers (272, 276) and counterclockwise dampers (274, 278) are provided.

8. The damping assembly (212) of any of claims 5 through 7, wherein: said flywheel (214) defines pediments (228) along said side (224); and said clockwise and counterclockwise dampers (272, 274, 276, 278) operate against said pediments (228).

9. The damping assembly (212) of any of claims 5 through 8, further characterized in that: an axial/transverse damper (216) is disposed in said flywheel (214).

10. The damping assembly (212) of any of claims 5 through 9, wherein: two clockwise dampers (272, 276) and two counterclockwise dampers (274, 278) are provided.

1 1 . The damping assembly (212) of any of claims 1 -10, wherein: the clockwise and counterclockwise dampers (272, 274, 276, 278) have forward rotational directions and are reclined at forward facing surfaces thereof in the forward rotational directions.

12. The damping assembly (212) of any of claims 1 -10, wherein: the clockwise and counterclockwise dampers (272, 274, 276, 278) are configured to create increasing areas of contact upon increased rotation of said steering shaft (208).

13. The damping assembly (212) of any of claims 1 -101 wherein the flywheel (214) is configured to have a natural frequency below a range of vibration frequencies caused by operation of the hydraulic steering unit (204).

14. The damping assembly (212) of any of claims 1 -10 wherein the flywheel (214) is configured to have a natural frequency that attenuates vibrations caused by the hydraulic steering unit (204).

15. The damping assembly (212) of claim 1 , further characterized in that: a flywheel having spaced pediments (228) is provided; a rotor having arms (262, 264, 266, 268) within the flywheel is provided; and said clockwise and counterclockwise dampers (272, 274, 276, 278) are compressively preloaded between said pediments (228) and said arms (262, 264, 266, 268).