Power steering device

Abstract: A rack (11) and pinion (12) are housed in a gear box (1), a valve sleeve (3) that is joined to the pinion (12) being housed in a valve housing (2) such that the sleeve (3) is free to rotate. A mechanism is provided that joins the gear box (1) and valve housing (2) in any desired relative rotation position. As the gear box (1) and valve housing (2) are formed independently, they may be formed by different manufacturing methods, and replacement of either of them is also easy. Further, an oil pressure port (78) provided at a fixed position in the valve housing (2) may be disposed at any desired rotation angle by selecting the relative rotation position of the gear box (1) and valve housing (2).

Description: This invention relates to a power steering device according to the preamble of claim 1 and known for example from US-A-4 788 877. Rack and pinion type power steering devices used in automobiles comprise a rack and pinion that directly transmits steering wheel operations to a steering mechanism, a power cylinder that uses the pressure of an oil pump to drive the steering mechanism, and a control valve that supplies this oil pressure to the power cylinder according to steering wheel operations. In this type of power steering device, a gear housing that houses the rack and pinion is generally formed in a one-piece construction with the control valve housing, and the power cylinder is independent. Such a device is disclosed for example in USP 4,809,806 published by the U.S. Patent Office. According to this power steering device, the gear box and control valve housing are formed in a one-piece construction by casting. In recent automobiles for passengers, there has been a trend towards smaller vehicle size and front wheel drive leading to smaller engine room capacity. As a result, when it is attempted to apply power steering devices to various types of vehicles and engine shapes, it may occur that the control valve port interferes with the engine or other mechanisms, so the position of the control valve port and the layout of the pipe leading to the port have to be changed. However, when the control valve housing and gear box are formed in a one-piece construction, changing the port position requires that modifications be made to part of the casting process which lead to increase of manufacturing costs. Thermal deformation also occurs when the housing of the control valve is cast in the gear box. A costly post-casting treatment is required on the inner circumference of the valve housing, such as honing. Moreover, as the gear box and housing of the control valve are formed in a one-piece construction, both have to be rejected if a fault occurs in either the gear box or the housing during the manufacturing process, which leads to decreased yields in the manufacture of the power steering device. From prior art document US-A-4 788 877 a power steering device is known. Said steering device comprises a rotary valve housing portion and a main body. Said main body receives a rack and a pinion, and the rotary valve housing portion receives a valve sleeve connected with the input shaft via a torsion bar. The valve housing portion is rotatable and press fitted into the main body. The rotary valve housing portion and the main body are additionally secured to each other by a retaining ring formed by injecting plastic material into related grooves formed on the main body and the valve housing portion, respectively, for constituting joining means for joining a valve housing portion and said main body in a predetermined position. It is an objective of the present invention to provide a power steering device as mentioned above which allows a joining of the housing and the gear box in any desired relative rotation position, wherein there is no obstruction to the flow of oil when the relative rotation position of said housing and said box is adapted. According to the present invention this objective is solved by a power steering device having the features of claim 1. It is an advantage of this invention to improve the adaptability of a power steering device to different types of vehicle. It is a further advantage of this invention to facilitate the machining of a control valve housing. Hereinafter the present invention is illustrated and explained in further detail by means of preferred embodiments in conjunction with the accompanying drawings. In said drawings wherein: Fig. 1 is a vertical sectional view of a power steering device, Fig. 2 is an enlarged plan view of a link between a pinion and a valve sleeve, Fig. 3 is a schematic diagram showing the displacement of a port, Fig. 4 is similar to Fig. 1, but showing another arrangement related to the support of the valve sleeve, Fig. 5 is similar to Fig. 1, but showing yet another arrangement related to the support of the valve sleeve, Fig. 6 is an enlarged plan view of the link between a pinion and valve sleeve of Fig. 5, Fig. 7 is a vertical sectional view of the power steering device showing the dimensions of a valve housing, Fig. 8 is similar to Fig. 7, but showing another valve housing of a different diameter, Fig. 9 is similar to Fig. 8, but showing yet another valve housing of a different length, Fig. 10 is similar to Fig. 3, but showing a variation related to a port forming position, Fig. 11 is an perspective view of a port showing a variation related to a port shape. Referring to Fig. 1 of the drawings, a gear box 1 housing a rack and pinion type steering gear and cylindrical valve housing 2 which houses a rotary valve are linked together. A pinion 12 and rack 11 are housed in the gear box 1. The pinion 12 is supported such that its base end is free to rotate on a bearing 17. The rack 11 is supported by the gear box 1 such that it is free to slide along a slide axis effectively perpendicular to the center axis of the pinion 12. The rack 11 is connected to a steering mechanism, not shown. The operation of this rack 11 is also assisted by a power cylinder, not shown. The rack 11 in the gear box 1 is guided in the sliding direction by a pressure pad 13. This pressure pad 13 is pushed toward the pinion 12 by a spring 14. The spring 14 is supported by an adjusting cover 15 that screws into the gear box 1. The link between the gear box 1 and the valve housing 2 is formed in a cylindrical shape, and the end of the valve housing 2 which is also formed in a cylindrical shape screws into the inner circumference of this cylindrical part 1A. A female screw 10 of predetermined pitch is formed on the inner circumference of this cylindrical part 1A, a male screw 20 of predetermined pitch being formed on the outer circumference of the end of the valve housing 2. A lock nut 8 also screws onto the outer circumference of the valve housing 2 so as to restrict the relative rotation of the gear box 1 and valve housing 2. A seal member 18 is interposed between the cylindrical part 1A and end of the valve housing 2 in order to maintain the interior of the gear box sealtight. The pinion 12 projects toward the valve housing 2 through the inside of this cylindrical part 1A. The end of the pinion 12 that projects into the valve housing 2 is supported that it is free to rotate via a bearing 21. A serration 6A formed at one end of a torsion bar 6 is pressed into the coaxially into the pinion 12 inside this end. A control valve comprises a stub shaft 5 and a valve sleeve 3 inside the valve housing 2. The stub shaft 5 is joined to a steering column, not shown, and is inserted into the valve housing 2 from the opposite side to the link between the gear box 1 and valve housing 2. The torsion bar 6 is coaxially housed in the stub shaft 5, and its end is connected to a stub shaft 5 by a pin 50. The stub shaft 5 is supported free to rotate on a bushing 22 joined to the end of the valve housing 2 via a bearing 23. The tip of the stub shaft 5 slides on the pinion 12, and the stub shaft 5 rotates relative to the pinion 12 according to the twist of the torsion bar 6. The valve sleeve 3 is disposed between the inner circumference of the valve housing 2 and the outer circumference of the stub shaft 5. The valve sleeve 3 slides on the outer circumference of the stub shaft 5 via a seal member 31, and is supported so as to permit rotation relative to the stub shaft 5. The valve sleeve 3 is supported such that it is also free to rotate relative to the valve housing 2. The rotation of the valve sleeve 3 relative to the pinion 12 is restricted due to the engaging of a U-shaped notch 30 formed at a predetermined position with a pin 9 projecting in a radial direction from the pinion 12. A snap ring 24 is attached to the outer circumference of the stub shaft 5 when the pin 9 is in contact with the deepest part of the notch 30. This limits also the relative displacement of the valve sleeve 3 and pinion 12 in an axial direction. Ports 7P, 7T, 7L, 7R which are connected to an oil pressure source, not shown, and to the power steering, are provided at predetermined positions on the outer circumference of the valve housing 2. For example, the ports 7P and 7T are provided at a predetermined interval in an axial direction, and the ports 7L, 7R are provided at a predetermined interval in an axial direction at positions effectively opposite the ports 7P, 7T. Annular grooves facing these ports are formed on the outer circumference of the valve sleeve 3. These grooves are alternately blocked by seal rings. The stub shaft 5 comprises an oil path arranged so that the port 7P is connected to one of the ports 7L, 7R, and the port 7T is connected to the other of the ports 7L, 7R via these annular grooves according to the relative rotation position of the valve sleeve 3. The structure of the oil path in this type of control valve is known from the prior art. The stub shaft 5 rotates against the torsion bar 6 when the steering wheel, not shown, is rotated. The stub shaft 5 and valve sleeve 3 therefore rotate relative to each other, and the oil pressure of the pump port 7P is supplied to the port 7L or 7R so as to drive the power cylinder, not shown. At the same time, steering force of directly transmitted to the rack 11 via the pinion 12 due to the twisting of the torsion bar 6. The wheels are therefore steered by the driving force of the power cylinder and the steering force directly input to the rack 11. When the rack 11 is displaced and the pinion 12 rotates, the sleeve 3 rotates together with the pinion 12 in such a direction as to reduce the relative rotation angle of the sleeve 3 relative to the stub shaft 5. When the valve sleeve 3 rotates to a position equivalent to the rotation control angle of the stub shaft 5, steering is complete. According to this embodiment, the pitches of the female screw 10 and male screw 20 are set so that even when the valve housing 2 is displaced at least 1 pitch interval in an axial direction relative to the valve sleeve 3, i.e. even when there is a relative displacement of one rotation, there is no effect on the connections between the ports 7P, 7T, 7L and 7R and the oil path of the valve sleeve 3. In other words, the dimensions of the ports 7P, 7T, 7L and 7R, and of the oil path in the control valve, are set so that displacements in the axial direction are absorbed. Hence, when the rotation position is locked by the lock nut 8 at any rotation angle of the housing 2, it is possible to adapt to any desired relative rotation angle of the gear box 1 and the valve housing 2. The embodiment can therefore be applied to different vehicle types and vehicles having different engine types. The valve sleeve 3 limits axial displacement relative to the pinion 12 due to the pin 9 and snap ring 24, and its rotation relative to the pinion 12 is also limited by the pin 9, hence even if the valve housing 2 displaces in the axial direction or rotation direction relative to the pinion 12, the relative positions of the sleeve 3 and pinion 12 do not vary in either the rotation or axial directions. For example, as shown in Fig. 3, if the valve housing 2 assembled with a predetermined phase relative to the gear box 1 is rotated by  1 , the ports 7P-7R move into positions 7P' - 7R' rotated by  1 . The valve housing 2 is displaced in an axial direction relative to the valve sleeve 3 depending on this angle  1 and the pitch, however as a predetermined working oil flowpath is maintained between the ports 7P' - 7R' at least when  1 < 360°, oil pressure is still supplied without interruption to the power cylinder, not shown. As modifications to the positions of the ports 7P - 7R can be made simply and quickly even after the power steering device is assembled by loosening the lock nut 8, rotating the housing 2 relative to the gear box 1 and tightening the nut 8 again, a single power steering device can be applied to many types and models of vehicles. The gear box 1 is manufactured by casting, and the housing 2 is formed by drawing or extruding steel pipe followed by a plasticizing treatment. Hence, there is no thermal deformation of the housing due to casting as in the prior art, and post-casting treatment such as honing is also unnecessary. When a defect is discovered in the valve housing 2 or gear box 1 during a final inspection of the power steering device, the lock nut 8 may be loosened. and the undamaged part removed to be used again. If a pair of snap rings 24, 24 is provided on the stub shaft 5 as shown in Fig. 4 the axial displacement of the valve sleeve 3 can be even more definitively restricted. Axial and rotation displacements may also be restricted by making the pin 9 engage with a throughole 30' formed in the end of the valve sleeve 3 as shown in Fig. 5 and Fig. 6. In this case, the aforesaid snap rings 24 are unnecessary, and the position of the valve sleeve 3 relative to the pinion 12 may be precisely determined while reducing the number of component elements in the assembly. Fig. 7 - Fig. 9 show an example where the same gear box 1 is applied to a power steering device of different capacity. The internal diameter of the valve housing 2 is D and its overall length is L as shown in Fig. 7. In Fig. 8, the same gear box 1 is assembled with a valve housing 2' having a larger internal diameter D 1 . In Fig. 9, the same gear box 1 is assembled with a valve housing 2'' having a greater overall length L 1 . As the gear box 1 and valve housing 2 are independent and joined by screws and the lock nut 8, the valve housings 2', 2'' having larger capacities than that of the housing 2 of the first embodiment may respectively be joined to the gear box 1 provided the power steering device has the same gear ratio. In Fig. 10, a valve housing 2A wherein the positions of the ports 7P - 7R are modified, is assembled with the gear box 1. The valve housing 2A comprises ports 7L', 7R' wherein the ports 7L, 7R have been rotated in the anticlockwise direction of the figure by  1 '. A port 7P' is provided at a position rotated anticlockwise by an angle  2 ' from the port 7P, and a port 7T' is provided at a position rotated clockwise by an angle  3 ' from the port 7T. The valve housing 2A wherein the positions of certain ports are modified so as not to interfere with the vehicle chassis, may therefore be assembled with the gear box 1. If this type of layout should lead to mutual interference between neighboring ports, the two ports 7 may be formed together as one port 7' by casting, and this port 7' joined to the valve housing 2A by projection welding or the like, as shown in Fig. 11.

Claims: A power steering device comprising an input shaft (5) that rotates according to a steering input, a pinion (12) connected to said input shaft (5) via a torsion bar (6), a rack (11) engaging with said pinion (12), a steering mechanism moving in synchronism with said rack (11), a valve sleeve (3) joined to said pinion (12), a power cylinder that drives said steering mechanism, a gear box (1) housing said pinion (12), a valve housing (2) that houses said valve sleeve (3) such that it is free to rotate, an oil pressure port (7P) provided in said housing (2), and an oil path that supplies oil pressure to said power cylinder from said oil pressure port (7P) according to the relative rotation positions of said sleeve (3) and said input shaft (5), said housing (2) and said gear box (1) are independent, and said device further comprises means (8,10,20) for joining said housing (2) and said gear box (1), characterized in that said joining means (8,10,20) comprises screw parts (10,20) that screw into each other formed in both said gear box (1) and valve housing (2) coaxially with said pinion (12) for joining said housing (2) and said gear box (1) in any desired relative rotation position and a lock nut (8) that limits the relative rotation of said housing (2) and gear box (1) joined via said screw parts (10,20), said screw parts (10,20) having pitches such that there is no obstruction to the flow of oil in said oil path when the relative rotation position of said housing (2) and gear box (1) is varied within one rotation. A power steering device according to claim 1, characterized in that said screw parts comprise a female screw (10) formed on an inner circumference of a cylindrical part (1A) of the gear box (1) and a male screw (20) formed on an outer circumference of an end of the valve housing (2). A power steering device according to claim 2, characterized in that said lock nut (8) is screwed onto the outer circumference of the end of the valve housing (2) at the male screw (20) thereof. A power steering device according to claim 2 or 3, characterized in that a seal member (18) is interposed between the cylindrical part (1A) of the gear box (1) and the end of the valve housing (2).

Inventors: HIRANO TAKURO, SAKO MASAYUKI, SUO SHIRO, HIRANO, TAKURO, SAKO, MASAYUKI, SUO, SHIRO, Hirano, Takuro, c/o Kayaba Kogyo K. K., Sako, Masayuki, c/o Kayaba Kogyo K. K., Suo, Shiro, c/o Kayaba Kogyo K. K.
Applicants: KAYABA INDUSTRY CO LTD, KAYABA KOGYO KABUSHIKI KAISHA
Application year: 1995
Main classification: B62D5
IPC codes: B62D5