GB2044701A

GB2044701A - Power Steering Device

Info

Publication number: GB2044701A
Application number: GB8007226A
Authority: GB
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1979-03-12
Filing date: 1980-03-04
Publication date: 1980-10-22
Also published as: JPS6158346B2; GB2044701B; JPS55123566A

Abstract

A power steering device comprising an input shaft (2) and an output shaft (5) connected to each other by a torsion bar (3) in a manner to be relatively rotatable in the same direction; a valve spool (20, 21) concentrically disposed around the input shaft (2) and axially movably; balls (15) provided in first movement guide paths in the input shaft (2) and engaged with the valve spool (20); and pins (17) provided on the output shaft (5) and engages with second movement guide paths in the spool. The first guide paths extend at an angle with respect to the second guide paths so that the valve spool is axially moved in accordance with a relative rotation between said input and output shafts to change oil flow from one oil channel (1c) over to another channel (1d). The first guide paths for the balls are in the form of spiral grooves (15) provided in the periphery of an enlargement formed on the input shaft and the second guide paths for the pins (14) are axial slots in an end portion of the valve spool member (20). <IMAGE>

Description

SPECIFICATION Power Steering Device This invention relates to a power steering device for use with auxiiiary means for transmitting a steering force from a steering wheel to tires in a vehicle such as a motor car.

Heretofore, the power steering devices generally used have been of the recirculating ball type and the rack and pinion type.

For the rack and ponion type power steering device, a construction has been proposed in which a pawl provided on a rotatable, axially movable valve spool is engaged with a spiral groove and caused to slide axially along the spiral groove, whereby the valve spool is moved axially to change flow from one oil channel over to the second such channel. However, the above described prior art device has presented disadvantages since the pawl is fixed, and once it is fixed cannot be displaced, so that unless the groove surface of the spiral groove is formed with high precision, the pawl cannot slide freely along the groove surface.Alternatively, if the clearance between the groove surface and the pawl is increased to avoid this difficulty, then the responsiveness of the power steering device is reduced in accordance with the period of time required for taking up the slack in the system caused by the increased clearance.

The invention has been developed in view of the disadvantages of the prior art described hereinabove, and has as its object the provision of a power steering device capable of smoothly effecting the change-over of oil channels by a valve spool in proportion to a steering reaction torque.

In order to accomplish the above described object, the power steering device according to the present invention is characterized in that: an input and an output shafts rotatably set in a common axis in a valve housing are connected to each other through a torsion bar; a valve spool concentrically disposed around said input shaft and axially movably provided is engaged with balls set in first moving paths; further, pins provided on said output shaft and radially extending are engaged with second moving paths formed in said valve spool; and first moving paths are given torsions through a certain angle with respect to said second moving paths; and, when said input shaft and said output shaft make a relative rotation, said valve spool is axially moved to change an oil channel over to the other.

The abovementioned and other features and advantages of the invention will hereinafter be made evident in conjunction with the description of the presently preferred embodiment of the invention illustrated in the accompanying drawings.

Fig. 1 is a sectional view showing an embodiment of a power steering device according to the present invention; Fig: 2 is a sectional view taken along the line Il-Il in Fig. 1; Fig. 3 shows the spiral ball groove and the ball; and Figs. 4A and 4B are a plan view and a front view showing the sleeve, respectively.

Fig. 1 is a sectional view showing an embodiment of the power steering device according to the invention. As apparent from Fig.

1, the power steering device according to the present embodiment is of a rack and pinion type, wherein a hollow main shaft 2 (input shaft) for steering is disposed in a valve housing 1, said main shaft 2, through a torsion bar 3 provided therein, is connected to a pinion shaft 5 (output shaft) in a pinion housing 4 in a manner to be rotatable in the same direction, and said pinion shaft 5 is meshed at pinions provided on the outer periphery thereof with a rack bar 6. The main shaft 2 is positioned by said torsion bar 3 which is fixed by two right and left needle bearings 7 and also two right and left pins 8. Furthermore, the pinion shaft 5 is positioned in the pinion housing 4 with no looseness through two right and left anguiar bearings 9.

The interior of the valve housing 1 is sealed by a seal ring 12 secured by seals 10, 10 and a spacer 11. Oil is fed into said valve housing 1 from a pump, not shown, through a pressure port 1 a in a direction indicated by an arrow A, and a supply of oil is fed to a reserver, not shown, from a return port 1 b. Further, the oil channels in the valve housing 1 are communicated with cylinder chambers of cylinders through cylinder ports 1 c and 1 d as indicated by arrows C and D.

The main shaft 2 has an enlarged diameter portion 2a adjacent one end thereof on the side of the pinion shaft 5, and said enlarged diameter portion 2a is provided at diametrical positions on the circumference thereof with two spiral ball grooves 13, i.e., first moving paths (Refer to Figs.

2 and 3).

On the other hand, arranged coaxially movably with the main shaft 2 and the pinion shaft 5 and axially movably around the outer periphery of a connecting portion between the main shaft 2 and the pinion shaft 5 is a sleeve 14. Coupled into diametrical positions on the circumference of said sleeve 14 are balls 15, which are fitted into said ball grooves 13. As will hereinafter be described, said balls 1 5 are movable in the ball grooves 13 axially of the main shaft 2 to either one of the opposite directions depending on the rotating direction of the main shaft 2.

As apparent from Figs. 1, 4A and 4B, the sleeve 14 is provided at two diametrical positions of its end portion on the side of pinion shaft 5 with axial cutouts 16, i.e., second moving paths.

Pins 1 7 fixed on the pinion shaft 5 are inserted into said cutouts 16, whereby said sleeve 14 and the pinion shaft 5 are connected to each other in a manner that rotation can be transmitted therebetween. Consequently, the sleeve 14 cannot be rotated relative to the pinion shaft and can be only axially moved. As a result, even if the main shaft 2 and the pinion shaft 5 are rotated, the sleeve 14 cannot be rotated because of the engagement of the cutouts 1 6 with the pins 1 7, and consequently, the balls 1 5 slide axially in the ball grooves 13, so that said sleeve 14 can be guided by the cutouts 16 and the pins 17 to axially slide.

A ring-shaped annulus 1 8 is provided outwardly of said balls 1 5 for holding said balls 15, the inner peripheral surface of said annulus 18 is tapered off, and the inner diameter thereof at the right side is smaller than the inner diameter at the left side in Fig. 1. Furthermore, the annulus 18 is urged by a spring 19 to the left in Fig. 1.

Consequently, the balls 1 5 are constantly urged against the groove surfaces of said ball grooves 1 3 by said tapered surfaces with no clearances, so that the steering responsiveness can be extremely improved.

On the other hand, pawls 20 are projectingly provided at two positions corresponding to said cotouts 1 6 at the other end of said sleeve 14 (to the left end in Fig. 1) as shown in Figs. 1,4A and 4B, and said pawls 20 are coupled into peripheral grooves on the outer periphery of the valve spool 21, whereby the sleeve 14 and the spool 21 are connected to each other, so that said sleeve 14 and the spool 21 constitute a valve spool mechanism for changing over the oil channels.

The spool 21 is adapted to change one oil channel over to the other in the valve housing 1, for which purpose said spool 21 is arranged to by axially movable. Positioning of the oil grooves of the spool 21 and the valve housing 1 in the axial direction can be adjusted by changing the thickness of said spacer 11, and said spacer 11 is positioned by said ring 12.

Furthermore, two cutouts are formed on the circumference of the spool 21 at the left side in the axial direction (refer to Fig. 1), and projections 23 integrally formed on the spacer 22 are fitted in said cutouts, whereby said projections 23 prevent the spool 21 from being rotated, so that the unitary rotation of the sleeve 14 with the spool 21 can prevent the occurrence of unnecessary friction.

In addition, as shown in Figs. 1 and 2, two cutouts 24 are formed at positions rotated through 90 degrees from said ball grooves 13 on the main shaft 2 at the right side thereof in the axial direction (as viewed in Fig. 1), and projections 25 integrally formed on the pinion shaft 5 are coupled into said cutouts 24 with a certain clearance in the circumferential direction therebetween, respectively. The provisions of said cutouts 24 and said projections 25 are intended for preventing excessive torsion of the torsion bar 3 when a torque is transmitted, and for allowing said projections to abut against the wall surfaces of the cutouts 24 to transmit a torque from the main shaft 2 to the pinion shaft 5 when manual operation is required due to troubles in the hydraulic system.

Description will hereunder be given of action of the present embodiment. In the steering operation, a reaction torque T' from the tires is transmitted to the pinioffshaft 5 through the rack bar 6, and the torsion bar 3 is given a torsion commensurate to the reaction torque T', whereby the main shaft 2 is rotated by a turning torque T.

At this time, the sleeve 14 connected through the balls 15 to the main shaft 2 in a manner that rotation can be transmitted therebetween tends to turn in unison with the main shaft 2, but said sleeve 14 cannot freely turn because the pins 1 7 fixed on the pinion shaft 5 are inserted in the cutouts 1 6 of said sleeve 14, whereby the balls 1 5 slidingly move in the ball grooves 13 in the axial direction of the main shaft 2 in dependence on the rotating direction of the main shaft 2, so that said sleeve 14 is guided by said ball grooves 13 to be moved in the axial direction of said main shaft 2.The axial movement of said sleeve 14 causes the valve spool 21 connected to said sleeve 14to move axially to block the return port 1 b, so that a supply of oil which has flowed into the valve housing 1 from the pump through the pressure port 1 a is prevented from flowing out into the reserver, not shown, as indicated by an arrow B, a supply of oil is fed to either one of cylinder chambers as indicated by an arrow of either C or D to raise hydraulic pressure in said cylinder chamber, so that an auxiliary action for steering operation can be performed, thereby enabling to carry out very smooth and highly responsive steering operation. In addition, in Fig.

1, the spool 21 is in the neutral position.

Furthermore, when the main shaft 2 is rotated at a certain torque, the main shaft 2, pinion shaft 5 and sleeve 14 tend to turn unitarily, but the spool 21 cannot turn due to the stop action of the projections 23 of the spacer 22 abutting against the cutouts of the spool 21, and is moved only in the axial direction.

In addition, in the case the adjustment in hydraulic pressure between the right and left portions is to be made in this embodiment, the hydraulic pressure is adjusted with the spacer 11 being inspected, the thickness of the spacer 11 is chosen based on the adjustment thus made, and the adjustment in positioning the oil channel of the spool 21 and the valve housing 1 in the axial direction can be made based on the thickness of the spacer 11. Alternatively, if the pin 8 shown at the left end in Fig. 1 is inserted finally, then the spacer 11 can be omitted. More specifically, firstly, the neutral position of the hydraulic pressure is inspected without inserting said pin 8 and, if said pin 8 is inserted when the hydraulic pressure reaches the neutral condition, then the main shaft 2 and the torsion bar 3 can be assembled to each other at a desirable state of hydraulic adjustment without using the spacer 11.

As has been described above, the present invention can offer such excellent advantaged that the steering responsiveness in the power steering device can be improved, the smooth change-over of oil channels with low friction can be made by use of the spool, and further, the difference in hydraulic pressure between the right and left portions is eliminated during steering, so that the adjustment to bring the hydraulic pressure to the neutral condition can be facilitated.

Claims

1. A power steering device wherein: an input shaft and an output shaft which are rotatably set along a common axis in a valve housing, are connected through a torsion bar; a valve spool which is concentrically disposed around said input shaft and is axially movable, is engaged with balls set in first movement guide paths located with respect to the input shaft; pins, which are provided on said output shaft and project radially thereform are engaged with second movement guide paths formed in said valve spool; and said first guide paths extend at an angle with respect to said second guide paths, so that, when said input shaft and said output shaft make a relative rotation, said valve spool is axially moved to change flow from an oil channel over to another such channel.

2. A power steering device as claimed in claim 1, wherein there is provided an annulus for externally locating said balls, and the inner peripheral surface of said annulus for engaging the balls is tapered.

3. A power steering device as claimed in claim 2, wherein the annulus is resiliently biased in an axial direction thereof so as to urge balls inwardly against said first guide paths.

4. A power steering device as claimed in any preceding claim, wherein said first guide paths are spiral ball grooves formed at portions on the outer periphery of said input shaft at a certain angle and said balls slide, in use, along said spiral ball grooves.

5. A power steering device as claimed in any preceding claim, wherein said second guide paths of said valve spool are slots or cutouts provided in one end portion of said valve spool and extending in the axial direction thereof, and said pins are engaged in said slots or cutouts, whereby relative rotation of said valve spool with respect to said output shaft is prevented.

6. A power steering device substantially as hereinbefore described with reference to and as illustrated in, the accompanying drawings.

7. A vehicle having a power steering device as claimed in any preceding claim.