GB2134054A

GB2134054A - Hydraulic power steering assembly

Info

Publication number: GB2134054A
Application number: GB08333124A
Authority: GB
Inventors: Valery Yakovlevich Obidin; Olga Andreevna Zueva; Vladimir Mikhailovich Inochkin; Andrei Vladimirovi Zhavoronkov; Leonid Kazimirovich Voinich; Jury Vasilievich Polushin; Petr Alexandrovich Zakhodyakin; Zinaida Ivanovna Rodionova; Nikolai Nikolaevich Judchits; Vladimir Viktorovich Belyanin; Andrei Andreevich Yarkin; Vyacheslav Nikolaevic Kalmykov; Mikhail Mikhailovich Ageechkin; Sergei Mikhailovic Arakelyants
Original assignee: MO N PROIZV OB STR DOROZH MASH
Current assignee: MO N PROIZV OB STR DOROZH MASH
Priority date: 1983-01-31
Filing date: 1983-12-12
Publication date: 1984-08-08
Also published as: GB2134054B; DK582583A; GB8333124D0; DK582583D0; DE3346205A1

Abstract

A power steering assembly comprises a housing (1) of a fluid distributor having arranged therein a control valve (2) the central bore of which receives a steering shaft (4) provided with screw transmission element (5), and a servohydraulic actuator (6). The steering shaft (4), servohydraulic actuator (6) and the control valve (2) are kinematically linked for the control valve (2) to be capable of axial movement when the steering shaft (4) is turned. The kinematic linkage has the form of a sleeve (7) provided with a receiving element of the screw transmission, the sleeve (7) being located inside a central bore (3) of the control valve (2) for rotative, non-axial movement, one end of the sleeve (7) being connected to the steering shaft (4) by way of the screw transmission. The invention can find application in hydraulically operated power steering systems of vehicles employed in construction, road-building and agriculture, as well as in tractors, trucks and cars. <IMAGE>

Description

SPECIFICATION Power steering assembly This invention relates to vehicle engineering.

More particularly, the invention concerns hydraulically-operated power steering assemblies of vehicles.

The invention can find application in hydraulically-operated power steering systems of vehicles used predominantly in construction, road-building and agriculture, as well as in tractors, trucks and cars when turning the vehicle steerable wheels or collapsing the sections of hinged-frame vehicles is effected by a hydraulic power cylinder.

The aim of the invention is attained by that in a power steering assembly comprising a housing of a fluid distributor accommodating a control valve having a central bore receiving a steering shaft provided with a screw transmission element, and a servohydraulic actuator, the steering shaft, servohydraulic actuator and control valve being kinematically linked for the control valve to be capable of axial displacement when the steering shaft is turned, according to the invention, the above kinematic linkage includes a tubular sleeve provided with a receiving element of the screw transmission, the sleeve being arranged inside the central bore of the control valve to move tangentiaily and be fixed axially, one end of the sleeve being connected to the steering shaft through the screw transmission.

The arrangement of the kinematic linkage in the form of the tubular sleeve makes it possible to dispense with rotational movement of the control valve to thereby obviate the transmission of torque thereto, which improves the reliability and extends the service life of the power steering assembly.

Preferably, the other end of the sleeve is connected through a spline shaft having outer splines on the two ends thereof to a satellite gear engageable with a crown gear secured in the housing of the fluid distributor, a central bore of the satellite gear having a bearing secured therein and journalled on an eccentric shaft connected to the servohydraulic actuator.

The above construction of the kinematic linkage provides for increased rotation of the servohydraulic actuator and greater efficiency of the power steering especially pronounced at slow turning rates of the steering shaft. Concurrently, the mechanical efficiency is improved during the transmission of torque from the steering shaft to the shaft of the servohydraulic actuator, which is especially important when the power assistance source fails and the vehicle is to be steered by the manual effort of the driver.

Advisably, the servohydraulic actuator includes a housing with two through bores, the interior of the bores accommodating gears of external engagement secured on shafts, the housing being confined on the opposite sides by cover plates with bearings to journal the shafts of the gears, the cover plate adjacent the fluid distributor being provided with two through holes to receive the shafts of the gears of external engagement.

The arrangement of the servohydraulic actuator described above makes it possible to provide reliable hermiticity of the interior thereof due to machining the bores of the housing and through holes of the cover plates in the sequence "housing-upper cover plate-lower cover plate". In consequence, the servohydraulic actuator can operate with working fluids of low viscosity.

Preferably, the servohydraulic actuator is provided with two wear plates interposed between the housing and the cover plates.

The provision of such wear plates simplifies the manufacture of the servohydraulic actuator and extends the service life and increases resistance to wear of the gears thereof thanks to the availability of a wide range of materials to be used for the gears and the wear plates mating therewith.

Alternatively, one of the gears of external engagement is composite comprised of at least two gear sections the total weight of which equals the height of the other gear, a spring being interposed between the gear sections to cooperate with these sections in order to offset one such section relative to the other one by a value of side play in the engagement of the gear sections.

The use of spring-loaded composite gears facilitates noiseless, smooth and reliable operation of the power steering assembly by virtue of obviating impacts in cooperation between the gears, especially with rotation of the servohydraulic actuator is reversed.

The above spring may be an annular or ring spring, with ends thereof crimped to the opposite sides in a plane substantially perpendicular to the plane of the spring whereas the end faces of the adjacent gear sections are provided with annular grooves and recesses in which this spring is placed.

The above spring-loading of the gears is simple to fabricate.

Advisably, the above spring is an annular spring, the end faces of the adjacent gear sections having annular grooves in which the spring is located, each of the gear sections being provided with a longitudinal slot extending to the annular groove and having a stop element therein.

Such construction of the spring is the simplest.

When the gear sections are no less than three in number, the inside surface of each of the three gear sections is provided with a longitudinal slot, the above spring being preferably a flat leaf spring with ends thereof crimped to be received in the slot so that the spring midpoint contacts the middle gear section.

The employment of such multiple gear sections increases the contact surface between the gears of the servohydraulic actuator to result in less noise, longer life and more accurate operation of the power steering assembly.

When the power steering assembly employs means for aligning the control valve, it is necessary that the body of the steering shaft be provided with a bore, this bore accommodating the control valve aligning means, the aligning means having the form of a rod with thrust washers capable of limited axial movement, a compression spring being interposed between the thrust washers, outer end faces of the thrust washers being adapted to cooperate with the steering shaft, a free end of the rod having a hole to couple with a pin arranged inside the sleeve.

The means for aligning the control valve described above is simple to fabricate and assemble. It ensures highly reliable operation due to the use of the compression spring.

The invention will now be described in greater detail with reference to various specific embodiments thereof taken in conjunction with the accompanying drawings, in which: Fig. 1 shows kinematic linkage between steering shaft, servohydraulic actuator and control valve of a power steering assembly according to the invention; Fig. 2 illustrates the manner in which a tubular sleeve is connected to the servohydraulic actuator; Fig. 3 shows construction of the servohydraulic actuator according to the invention; Fig. 4 illustrates the manner in which wear plates are disposed between the housing of the servohydraulic actuator and the cover plates; Fig. 5 is an alternative modification of the servohydraulic actuator with composite gears; Fig. 6 shows composite gear sections with a spring element interposed therebetween;; Fig. 7 is a section taken on the line VIl-VIl in Fig. 6; Fig. 8 shows an alternative attachment of the spring between the composite gear sections; Fig. 9 is a section taken on the line IX-IX in Fig. 9; Fig. 10 is another possible arrangement of the spring between the composite gear sections; Fig. 11 is a section taken on the line Xl-Xl in Fig. 10; Fig. 12 is a view of means for aligning the control valve; and Fig. 1 3 is a general sectional view of the power steering assembly embodying the present invention.

A power steering assembly embodying the present invention comprises a housing 1 (Fig. 1) of a fluid distributor the central bore of which accommodates a control valve 2 of this fluid distributor. A steering shaft 4 with an element 5 of screw transmission is arranged inside a central bore 3 of the control valve 2. The power steering assembly also includes a servohydraulic actuator 6.

Normally, when the working fluid is delivered to the servohydraulic actuator 6 from a powerassistance feed source (not shown), this servohydraulic actuator 6 functions as a hydraulic motor.

When operating in an emergency (e.g., in case of failure of the power-assistance feed source), the servohydraulic actuator 6 operates as a hydraulic pump driven manually through the steering wheel of a vehicle by the driver.

The servohydraulic actuator 6, steering shaft 4 and control valve 2 of the fluid distributor are kinematically linked to provide for the axial movement of the control valve 2 when the steering shaft 4 is turned.

This kinematic linkage includes a tubular sleeve 7 having a receiving element of the screw transmission, the sleeve 7 being secured inside the central bore 3 of the control valve 2 to move tangentially and be stationary in the axial direction. One end of the sleeve 7 is connectable to the steering shaft 4 through the element 5 of the screw transmission and the receiving element of the screw transmission arranged on the inside surface thereof. Another end of the sleeve 7 (Fig.

2) is connected through a spline shaft 8 having splines on two ends thereof to a satellite gear 11 secured in the housing 1 of the fluid distributor.

The central bore of the satellite gear 10 houses a bearing 1 2 journalled on an eccentric shaft 13 connected to the servohydraulic actuator 6.

The hereabove proposed kinematic linkage affords to increase the rate of rotation of the servohydraulic actuator 6 and improve the volumetric efficiency of the power steering assembly at slow turning rates of the steering shaft 4.

Concurrently, this is accompanied by an increase in the mechanical efficiency when torque is transmitted from the steering shaft 4 to the shaft of the servohydraulic actuator 6, which is especially important when maintaining steering control in an emergency to initiate a road turn by the muscular effort of the driver.

The provision of the sleeve 7 enables to obviate rotation of the control valve 2 to thereby prevent a torque force from being exerted on the control valve 2, which results in a more reliable and lasting operation of the power steering assembly.

With reference to Fig. 3, the servohydraulic actuator 6 is generally fashioned as a housing 14 having two parallel through bores 15, the insides of the bores 15 accommodating gears 17 of external engagement on shafts 1 6. The opposite faces of the housing 1 4 are confined by upper and lower cover plates 1 8 with bearings 1 9 to journal the shafts 1 6 of the gears 17. The upper cover plate 1 8 facing the fluid distributor has two through holes 20 to receive the shafts 16 of the gears 17.

The aforedescribed construction of the servohydraulic actuator 6 facilitates the simultaneous drilling of the bores 15 in the housing 14 to accommodate the gears 17 and holes in the cover plates 1 8 to secure therein the bearings 19 of the shafts 16 by virtue of assembling these elements prior to machining the holes and bores in the following sequence: housing 14upper cover plate 1 8-lower cover plate 18.

Precision machining of the holes and bores makes it possible to attain high hermeticity of the interior volumes of the servohydraulic actuator 6 for it to be capable to be operated by a lowviscosity working fluid.

Referring now to Fig. 4, wear plates 21 may be installed between the housing 14 of the servohydraulic actuator 6 and the cover plates 18.

The provision of the wear plates 21 simplifies the fabrication of the servohydraulic actuator 6 to provide for a variety of materials to be selected for increasing the service life and wear resistance of the "gear 1 7/plate 21" mating pair.

One of the gears 1 7 of external engagement (Fig. 5) may alternatively be of sectional construction to be therefore comprised of at least two gear sections 22 the total height of which equals the height of the other gear 1 7. Interposed between these gear sections 22 is a spring 23 adapted to engage with the two gear sections 22 to force-turn one such section relative to the other one by a value of side play in the engagement of the gear sections 22.

The use of spring-loaded gear sections 22 ensures noiseless, smooth and durable operation of the power steering assembly through obviating impacts between the cooperating gears 1 7 arid 22, especially when reversing the servohydraulic actuator 6.

Concurrently, thanks to the smooth rotation of the gears 1 7 and 22, a more accurate operation of the power steering assembly is attained, this improved accuracy being especially pronounced at slow turning rates of the steering shaft 4.

The spring 23 may have an annular shape as best seen in Figs. 6 and 7 with ends thereof crimped to the opposite sides in a plane substantially perpendicular to the plane of the spring 23. The adjoining end faces of the gear sections 22 have annular grooves 24 and recesses 25 to accommodate the spring 23.

The above arrangement of spring-loading is deemed most preferable, since difficulties associated with machining the gear sections 22 are minimized.

Alternatively, the spring 23 may take the form of an annular spring 23a as illustrated in Figs. 8 and 9. In this case the end faces of the adjacent gear sections 22 are likewise provided with the annular grooves 24 wherein the annular spring 23a is placed, each of the gears 22 being further provided with a longitudinal slot 26a; the spring toward said annular groove 24 and having a stop element 27 therein.

The above arrangement of the spring 23a is the simplest, although it requires the provision of additional stops 27.

When gear sections 22a (Figs. 10 and 11) are no less than three in number, the inside surface of each of the three gear sections 22a is preferably porovided with a longitudinal slot 26a; the spring 23b is preferably a flat leaf spring with ends thereof crimped to be received in the slot 26a so that the midportion of this spring 23b contacts the medium gear section 22a.

The use of three or more gear sections 22a tends to increase the contact surface between the gears 22a and 1 7 of the servohydraulic actuator 6 to result in still less noise, extended service life and improved accuracy of operation of the power steering assembly.

Referring to Fig.12, the power steering assembly according to the invention can be provided with means for aligning the control valve for which purpose a central bore 28 is made in the body of the steering shaft 4, this bore 28 accommodating the control valve aligning means having the form of a rod 29 with thrust washers 30 capable of limited axial displacement, a compression spring 31 being placed between the two thrust washers 30.

Outer end faces of the thrust washers 30 are adapted to cooperate with the steering shaft 4. A free end of the rod 29 has a hole 32 to couple with a pin 33 arranged inside the sleeve 7.

The above described construction of the control valve alignment means ensures high reliablilty of operation thanks to the employment of the compression spring 31. The control valve aligning means is structurally simple to find employment in the power steering assembly.

The power steering assembly according to one possible embodiment thereof represented in Fig.

1 3 operates as follows.

When the steering shaft 4 is turned, the sleeve 7 is moved axially under the action of the pin 33 positioned in the threads of the steering shaft 4 along splines 34. The movement of the sleeve 7 results in axial displacements of the control valve 2 of the fluid distributor essentially in the same direction to provide for the delivery of the working fluid from a pressure line of a fluid pump (not shown) to a power cylinder. The gears 1 7 and 22 of the servohydraulic actuator 6 are revolved to rotate the eccentric shaft 1 3 thereof. The satellite gear 10 tends to run about the crown gear 11 translating a planetary motion to the end of the spline shaft 8 accommodated inside the splined bore of the satellite gear 10.The opposite end of the spline shaft 8 received a rotary motion at a speed which is less than the rotational speed of the eccentric shaft 13 by a value of the transmission ratio of the "satellite gear 1 Ocrown gear 11" gearing. Because the spline shaft 8 is connected by the splines 34 with the splined end of the sleeve 7, the latter is caused to rotate at a speed equal to the speed of rotation of the steering shaft 4 which prevents a further axial displacement of the sleeve 7 and, consequently, of the control valve 2 of the fluid distributor. At a constant rate of turning of the steering shaft 4 the entire kinematic linkage is rotated uniformly to provide for a constant delivery rate of the working fluid to the power cylinder of the vehicle.When the rotation of the steering shaft 4 is terminated, the shaft 13 of the servohydraulic actuator 6 continues to rotate by virtue of the kinematic linkage "eccentric shaft 13-sateilite gear 10crown gear 11 -spline shaft 8-sleeve 7-element 5 of the screw transmission" to move the control valve 2 axially in a direction opposite to the initial one until the delivery of the working fluid is terminated. Therewith, the turning of steerable wheels or sections of a hinged-frame vehicle is stopped.The proposed construction of the sleeve 7 and kinematic linkage between the steering shaft 4, control valve 2 and servohydraulic actuator 6 affords to improve the reliability and extend the life of the power steering assembly by virtue of providing exclusively longitudinal movement to the control valve 2 and preventing torsional forces from being exerted on the control valve. Such a construction also enables to considerably increase the volumetric efficiency of the power steering assembly to facilitate its operation at low rates of turning of the steering shaft.

The aforedescribed advantages also result in improved mechanical efficiency of the power steering assembly when torque is transmitted from the steering shaft 4 to the shaft 13 of the servohydraulic actuator 6, which is especially important when the power assistance source fails.

The movement of the sleeve 7 relative to the steering shaft 4 causes displacement of the rod 29 of control valve alignment means connected to the sleeve 7 by the pin 33 and compression of the spring 31 by forcing one of the thrust washers 30 to travel a certain distance axially of the rod 29.

When the driver's manual force applied to the steering wheel and consequently to the steering shaft 4 is released, the spring 31 acts to move the above elements in a reverse sequence to return the control valve 2 to the natural position.

The proposed control valve aligning means is very reliable, simple to fabricate and easy to assemble.

The construction of the valve aligning means provides for the use of a very powerful compression spring 31 capable of ensuring the return of the control valve 2 to the neutral position to fix the steering shaft 4 for straightahead travel.

The employment of the spring-loaded composite gears 22 in the servohydraulic actuator 6 results in that these gear sections 22 under the action of the spring 23 tend to offset by their teeth relative to the teeth of the mating gear 17 by a value of side engagement play to ensure smooth operation of the servohydraulic actuator 6.

The alternative construction of the gear-type servohydraulic actuator 6 employing a larger number of the gear sections 22 provides for better gear engagement contact between the gears 1 7 and 22 resulting in still further improved durability and reliability of the servohydraulic actuator 6.

Such use of the multiple gears 22 does not affect the volumetric efficiency of the actuator 6, because pressure differentials involved and consequently leaks between the working chambers of this actuator 6 are quite negligeable.

The amount of pressure differential is determined exclusively by resistance to the displacement of the movable elements of the power steering assembly.

In case of failure of the power-assistance feed source, the working fluid can be delivered to the power cylinder of the vehicle steering system by the muscular effort of the driver. In such a case torque from the steering shaft 4 is transmitted through the kinematic linkage described above to the servohydraulic actuator 6 which in turn is caused to function as a manually operated hydraulic pump. The spring 23 is designed to a force corresponding to a small pressure differential between the inlets of the servohydraulic actuator 6 under normal operating conditions. This pressure is therefore not capable to return the gear sections 22 to the initial position whereby side play between gear teeth are taken up continuously during normal operation of the power steering assembly. When operated manually, torque exerted on the eccentric shaft 13 of the servohydraulic actuator 6 and, as a consequence, pressure differential are considerably increased. The spring 23 is therefore not capable to overcome the load exerted whereby the gear sections 22 are offset relative to each other to the initial position to function as a single unit gear providing for a highly reliable mesh, which is very important in emergencies.

Claims

1. A power steering assembly comprising: a housing of a fluid distributor accommodating a control valve the central bore of which receives a steering shaft provided with a screw transmission element; a servohydraulic actuator; the steering shaft, servohydraulic actuator and control valve being kinematically linked therebetween for the control valve to move axially when the steering shaft is turned; the kinematic linkage including a sleeve having a receiving element of the screw transmission, this sleeve being arranged inside a central bore of the control valve movably in the tangential and fixedly in the axial directions, one end of the sleeve being connected to the steering shaft by way of the screw transmission.

2. A power steering assembly as claimed in claim 1, wherein the other end of the sleeve is connected through a spline shaft having outer splines on the two ends thereof to a satellite gear engageable with a crown gear secured in the housing of the fluid distributor, a central bore of the satellite gear having a bearing secured therein and journalled on an eccentric shaft connected to the servohydraulic actuator.

3. A power steering assembly as claimed in claims 1 and 2, wherein the servohydraulic actuator includes a housing with two through bores, the insides of the bores accommodating gears of external engagement secured on shafts, the housing being confined on the opposite ends thereof by cover plates with bearings to journal the shafts of the gears, the cover plate adjoining the fluid distributor being provided with two through holes to receive the shafts of the gears of external engagement.

4. A power steering assembly as claimed in claim 3, wherein the servohydraulic actuator is provided with two wear plates interposed between the housing of the servohydraulic actuator and the cover plates thereof.

5. A power steering assembly as claimed in claim 3, wherein one of the gears of external engagement is composite comprised of at least two gear sections the total height of which equals the height of the other gear, a spring being interposed between the gear sections adapted to cooperate with the two gear sections to offset one section relative to the other one by a value of side play in the engagement of the gear sections.

6. A power steering assembly as claimed in claim 5, wherein said spring is an annular spring with ends thereof crimped to the opposite sides in a plane substantially perpendicular to the plane of said spring, the ends faces of the adjacent gear sections having annular grooves and recesses to accommodate said spring.

7. A power steering assembly as claimed in claim 5, wherein said spring is an annular spring, the end faces of the adjacent gear sections having annular grooves in which said spring is placed, each of the gear sections being provided with a longitudinal slot extending to the annular groove and having a stop element therein.

8. A power steering assembly as claimed in claim 5, wherein when the gear sections are no less than three in number, the inside surface of each of the three gear sections is provided with a longitudinal slot, the spring being preferably a ffat leaf spring with ends thereof crimped to be received in the slot so that its midpoint contacts the middle gear section.

9. A power steering assembly as claimed in claim 1, wherein means is provided for aligning the control valve and having a central bore made in the body of the steering shaft, this bore accommodating the control valve aligning means, the means having the form of a rod with thrust washers capable of limited axial displacement, a compression spring being interposed therebetween, outer end faces of the thrust washers being adapted to cooperate with the steering shaft, a free end of the rod having a hole to couple with a pin arranged inside the sleeve.

10. A power steering assembly as disclosed in the description with reference to the accompanying drawings.