JPH0129182Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a rack-type power steering device.

As a conventional rack-type power steering device, the one shown in FIG. 1 is known, for example, from Japanese Utility Model Application Publication No. 56-75066. First, the configuration of this power steering device will be described. Reference numeral 1 denotes a cylinder extending in the width direction of the vehicle body, and both sides of the cylinder 1 are closed by housings 2 and 3. A rack shaft 4 is loosely inserted into the cylinder 1, and both ends of the rack shaft 4 slidably pass through the housings 2 and 3 and are connected to a tie rod (not shown). . A rack 5 is formed in the portion of the rack shaft 4 that passes through the housing 3, and the housing 3 is attached to this rack 5.
A pinion 6 rotatably supported is engaged with the pinion 6. This pinion 6 is connected to a steering wheel via a hydraulic control mechanism 7.
Shaft portion 8 of rack shaft 4 loosely inserted into cylinder 1
A floating piston 9 is fixed to the cylinder 1, and the cylinder 1, the rack shaft 4, and the floating piston 9 define a first hydraulic chamber 10 and a second hydraulic chamber 11. . These first hydraulic chamber 10 and second hydraulic chamber 11 communicate with a hydraulic pump (not shown) via a hydraulic control mechanism 7. 12 is a seal ring interposed between the floating piston 9 and the cylinder 1.

In general, easy-type power steering devices,
In order to reduce the rotation angle of the steering wheel, the gear ratio between the rack 5 and the pinion 6 is large when the steering wheel is near the straight-ahead position, as shown by straight line A in Figure 2, and as the rotation angle of the steering wheel increases. The gear ratio is small. Therefore, when the steering wheel must be turned considerably, such as when parking the vehicle in a garage, the load on the steering wheel increases, so the hydraulic fluid in the first or second hydraulic chambers 10, 11 is There was a problem that the assist force generated was insufficient and the steering wheel became difficult to operate. On the other hand, if the inner diameter of the cylinder 1 is increased in order to generate sufficient assist force, the hydraulic oil supplied to the first or second hydraulic chambers 10, 11 when the steering wheel is rotated at a high rotational speed. However, increasing the capacity of the hydraulic pump to ensure a sufficient amount of hydraulic oil increases the weight of the vehicle and the installation space. arise.

This invention was made with attention to the above problem, and includes a cylinder, a pinion connected to the steering wheel via a hydraulic control mechanism, a rack part that meshes with the pinion, and a shaft part that passes freely through the cylinder. a rack shaft, and a piston fixed to the shaft and defining a first hydraulic chamber and a second hydraulic chamber that can be communicated with the cylinder and a hydraulic control mechanism; The piston has large diameter parts on both sides, and the piston has a seal ring that can expand and contract in the radial direction, and this seal ring expands and contracts as the inner diameter of the cylinder changes so that it can come into close contact with the inner wall of the cylinder. It is an object of the present invention to solve the above problems by providing a power steering device.

This invention will be explained below based on the drawings.

FIG. 4 is a diagram showing an embodiment of this invention,
First, the configuration will be explained. A cylinder 15 extends in the width direction of the vehicle body, and both sides of the cylinder 15 are closed by housings 16 and 17. The cylinder 15 has a small diameter part 18 and a large diameter part 19 whose inner diameter gradually increases on both sides of the small diameter part 18, and a rack shaft 20 is loosely inserted into the cylinder 15. Both ends of the rack shaft 20 are connected to housings 16 and 17.
It is connected to a tie rod (not shown) by slidingly passing through the housing 16 and the rack shaft 2.
0, an oil seal 21 is interposed between the two. Reference numeral 22 denotes a flexible tube protruding from the housing 17 into the cylinder 15. An oil seal 2 is provided between the adapter 23 fitted to the tip of the flexible tube 22 and the rack shaft 20, and between the flexible tube 22 and the housing 17.
4 and 25 are respectively interposed. Rack axis 2
A rack 26 is formed in a portion penetrating through the housing 17 of the pinion 2, which is rotatably supported by the housing 17.
7 is engaged. This pinion 27 is connected to a steering wheel via a hydraulic control mechanism 28. As shown in FIGS. 4 and 5, a pair of annular grooves 30 and 31 are formed in the shaft portion 29 of the rack shaft 20, which is loosely inserted into the cylinder 15, at a constant distance from each other. , annular groove 30,
31, washers 32 and 33 are fitted. Snap rings 34 and 35 are inserted into the annular grooves 30 and 31, respectively, to fix the positions of the washers 32 and 33, so that an annular groove 36 is defined between the washers 32 and 33. A floating piston 37 is inserted into this groove 36, and an annular groove 38 is formed on the outer periphery of the floating piston 37. . As shown in FIG. 6, a part of the seal ring 39 made of synthetic resin is cut away from the annular groove 38, and stepped portions 40, 41 are formed therein. In addition, in the free state, the stepped portions 40 and 41 do not partially overlap, and the seal ring 39 in this state
Since the radius of is larger than the inner diameter of the cylinder 15, when the seal ring 39 is inserted into the cylinder 15, the seal ring 39 expands. Reference numeral 42 denotes an elastic body interposed between the piston 37 and the seal ring 39, which, together with a spring 43, brings the seal ring 39 into close contact with the cylinder 15. . A seal ring 44 is also interposed between the rack shaft 20 and the floating piston 37. Seal ring 39,
Piston 37, cylinder 15 and rack shaft 20
defines a first hydraulic chamber 45 and a second hydraulic chamber 46, and these hydraulic chambers 45, 46 can be selectively communicated with a hydraulic pump or a reservoir tank (not shown) via a hydraulic control mechanism 28. be.

Next, the effect will be explained. First, when the steering wheel is in the straight-ahead position, the floating piston 37 is located in the small diameter portion 18. When the steering wheel is rotated from this state, the floating piston 37 slides on the small diameter part 18 when the rotation angle is below a certain value, but because the gear ratio between the rack 26 and the pinion 27 is large, the first or second hydraulic room 4
Sufficient assist can be obtained with the assist force generated by the hydraulic oil in the cylinders 5 and 46. Next, when the rotation angle of the steering wheel exceeds a certain value, the gear ratio between the rack 26 and the pinion 27 becomes smaller, but the floating piston 37 has moved to the large diameter section 19, and the seal ring 39 has moved to the position shown in FIG. As it expands as shown, the pressure receiving area increases. Therefore, the first
Alternatively, the assist force generated by the hydraulic fluid in the second hydraulic chambers 45, 46 also increases, so that even if the load on the steering wheels increases, the steering wheel operation does not become heavy. Therefore, the pressure of the hydraulic oil required to obtain the necessary assisting force can be lowered compared to the conventional system (as shown by curve C), as shown by curve B in FIG. FIG. 9 is a diagram showing another example of a seal ring inserted into the annular groove 38 of the floating piston 37, with a groove 48 at one end of the seal ring 47 and a protrusion 49 insertable into the groove 48 at the other end. are formed respectively.

As explained above, according to this invention, the easy type power steering device is equipped with a cylinder,
A pinion connected to the steering wheel via a hydraulic control mechanism, a rack shaft having a rack part that meshes with the pinion and a shaft part that passes freely through the cylinder, and a rack shaft that is fixed to the shaft part and can communicate with the hydraulic control mechanism together with the cylinder. a piston that defines a first hydraulic chamber and a second hydraulic chamber, the cylinder is provided with a small diameter part near the neutral position of the piston and a large diameter part on both sides of the small diameter part, and the piston expands and contracts in the radial direction. It has a flexible seal ring that expands and contracts as the inner diameter of the cylinder changes, allowing it to come into close contact with the inner wall of the cylinder.This has the effect that steering wheel operation does not become heavy even when the rotation angle of the steering wheel is increased. can get.

[Brief explanation of drawings]

Figure 1 is a front sectional view showing a conventional rack-type power steering device, Figure 2 is a graph showing the relationship between the rotation angle of the steering wheel and the gear ratio, and Figure 3 is a diagram of a rack-type power steering device according to this invention. 4 is an enlarged view of the vicinity of the floating piston of FIG. 3, FIG. 5 is an enlarged view of the vicinity of the seal ring of FIG. 4, and FIG.
A perspective view of the seal ring shown in the figure, FIG.
Figure 8 is a front sectional view showing the expanded state of the seal ring, Figure 8 is a graph showing the relationship between the hydraulic oil pressure required to obtain the necessary assist force and the rotation angle of the steering wheel, and Figure 9 is FIG. 7 is a perspective view showing another example of the seal ring. 15...Cylinder, 18...Small diameter part, 19...
Large diameter part, 20...Rack shaft, 26...Rack part (Rack), 27...Pinion, 28...Hydraulic control mechanism, 29...Shaft portion, 37...Piston, 39, 47...Seal ring, 45...1st
Hydraulic chamber, 46...second hydraulic chamber.

Claims (1)

[Scope of utility model registration request] A cylinder, a pinion connected to the steering wheel via a hydraulic control mechanism, a rack shaft having a rack part that meshes with the pinion and a shaft part that runs loosely through the cylinder, and a rack shaft fixed to the shaft part and connected to the hydraulic control mechanism together with the cylinder. A rack-type power steering device comprising a piston defining a first hydraulic chamber and a second hydraulic chamber that can communicate with each other, and in which the piston is located at a neutral position within the cylinder when the steering wheel is in the straight-ahead position. A small diameter part is provided near the neutral position of the piston, and a large diameter part is provided on both sides of the small diameter part, and the piston has a seal ring that can expand and contract in its radial direction, and this seal ring expands and contracts as the inner diameter of the cylinder changes, thereby sealing the cylinder. A simple power steering device that is characterized by being able to fit closely against the inner wall of the vehicle.