Rack and Pinion Steering Device

In my copending U.S. applications Ser. No. 801,882 and 811,112 a rack and pinion steering device communicated fluid pressure to pressure chambers on opposite sides of a piston in order to move the piston and attached steering rod, thereby controlling the direction of a pair of dirigible wheels. In U.S. application Ser. No. 801,882, the piston is slidably mounted within the rack, while in U.S. application Ser. No. 811,112 the piston is slidably mounted within the housing. As the pistons in both U.S. applications Ser. Nos. 801,882 and 811,112 require close tolerances with their corresponding bores, it is believed to be an improvement in the art to provide a rack and pinion steering device which functions in the absence of such a piston.

The present invention relates to a rack and pinion power steering device wherein a housing defines a cavity and a pinion extends into the cavity to engage a rack therein. The housing includes portions extending into the housing cavity and slidably supporting a sleeve member which, in turn, slidably supports the rack. The sleeve member forms a pair of openings which open in opposite directions and are separated by a partition on the sleeve member, so that the sleeve member is substantially H-shaped.

In order to couple the steering device to a pair of dirigible wheels, a pair of rods are fixedly secured to the partition and coupled to the dirigible wheels so that movement of the sleeve member imparts a change in direction for the dirigible wheels. The housing portions cooperate with the pair of rods and the sleeve member to substantially define pressure chambers which communicate with a pressure source. A valve member carried by the sleeve member engages the rack and communicates with the pressure source such that movement of the rack by rotation of the pinion causes the valve member to move relative to the sleeve member, thereby communicating the pressure source with one of the pressure chambers. The increase of pressure in the one of the pressure chambers acts against the housing partition to move the sleeve member and pair of rods relative to the housing.

The sole FIGURE is a schematic illustration partly in cross section, of a rack and pinion power steering device made in accordance with the present invention.

The rack and pinion power steering device 10 illustrated in the sole FIGURE includes a steering wheel 12 which is generally positioned within a vehicle operator's compartment for rotation by a vehicle operator and a pair of dirigible wheels 14 for steering the vehicle. The steering gear of the rack and pinion power steering device 10 is disposed within a housing 20 which defines a cavity 22.

A pinion 24 coupled to the steering wheel 12 extends into the housing cavity 22 and engages a rack 26. Teeth 28 on the rack 26 engage matching teeth 31 on the pinion 24 so that rotation of the pinion 24 imparts transverse movement to the rack 26.

In accordance with the invention a sleeve member 30 is provided with openings 32 and 34 which face opposite directions and housing portions at 36 and 38 extend into the respective openings 32 and 34 to slidably support the sleeve member within the housing cavity 22. The housing portions 36 and 38 form bores 40 and 42 therethrough for slidably and sealingly receiving respective rods 44 and 46 which connect with the right wheel and the left wheel, respectively.

The openings 32 and 34 are separated by a partition 50 on the sleeve member 30 and the rods 44 and 46 are fixedly secured to the partition by any suitable means. The partition cooperates with the sleeve member, the pair of rods 44 and 46 and the portions 36 and 38 to define a pair of pressure chambers 54 and 56.

In order to provide a power assist to the vehicle operator, a power steering pump or pressure source 58 communicates with an inlet port 48 on the housing portion 38 and a passage 57 in the portion 38 communicates the power steering pump 58 with the pressure chamber 56. The sleeve member 30 supports a valve member 60 in a stepped bore 62 and a passage 64 communicates the pressure chamber 56 with the bore 62, while a passage 66 communicates the stepped bore 62 with the pressure chamber 54. Flanges 68 on the rack 26 engage the valve member 60 to move the latter within the stepped bore 62 when the rack is moved by rotation of the pinion 24.

A pair of springs at 70 oppose arms 72 on the sleeve member 30 and the flanges 68 in order to position the valve member 60 in a neutral position within the stepped bore 62. In this neutral position sustantially one-half of the pressure from the pressure chamber 56 is communicated to the pressure chamber 54 in view of the restriction provided in the passage 64 by the land 74 and the opening of the return port 76 by the land 78. Consequently, the cross-sectional area of the rod 44 is substantially one-half of the cross-sectional area of the rod 46 at the partition 50 so that the sum of the forces acting against the partition 50 are equal in the neutral position.

During normal vehicle operation, the power steering pump 58 communicates pressurized fluid to the pressure chamber 56 via inlet port 48 and passage 57. With the valve member 60 in the neutral position, the pressurized fluid within chamber 56 is communicated through passages 64 and 66 into pressure chamber 54, past restriction 74. A portion of the pressurized fluid within the stepped bore 62 is communicated to the return port 76 so that the restriction provided by land 74 and the return port 76 cooperate in the neutral position to communicate substantially one-half of the pressure in chamber 56 to the chamber 54. Consequently, the forces acting against the partition 50 by the pressurized fluid within chambers 54 and 56 are opposed by one another so that the sleeve member 30 remains fixed relative to the housing.

When the vehicle operator rotates the steering wheel 12 through an increment in order to change the direction of the vehicle, the pinion 24 is also rotated to impart transverse movement to the rack 26. The flanges 68 on the rack are also moved, thereby moving the valve member 60 within the stepped bore 62. If the valve member 60 is moved to the right, the land 74 increases the restriction across passage 64 to increase the pressure within chamber 56 while concurrently increasing the opening of the return port 76 by the land 78 to decrease the pressure within the chamber 54. Therfore, the forces acting against the partition 50 are greater on the chamber 56 side so that the sleeve member 30 and rods 44 and 46 are moved to the right until the valve member 60 is again disposed in a neutral position relative to the sleeve member 30. If the valve member 66 is moved to the left, the land 74 increases the opening across passage 64 to reduce the restriction across passage 64 and the land 78 reduces the opening across return port 76 to increase the restriction across return port 76, thereby substantially equating the pressures within chambers 54 and 56. With substantially equal pressures in the chambers, the increased area of the partition 50 exposed to chamber 54 results in the forces in chamber 54 overcoming those in chamber 56 to move the sleeve member 30 to the left until the sleeve member and valve member are disposed in the neutral position.

If the pressure source 58 fails to communicate pressurized fluid to the housing 20, the rack and pinion steering device will function manually as the rack flanges 68 are engageable with the portion of the sleeve member 30 which supports the valve member 60 in order to impart transverse movement to the sleeve member and attached rods.

Although the present invention is illustrated with different sizes for the rods 44 and 46, it is readily apparent that a pair of rods of substantially the same diameter and cross-sectional area could be provided. With the same size for the rods the valve member 60 would require slight modification to communicate equal pressures of pressurized fluid to chambers 54 and 56 in the neutral position.

Moreover, many modifications and/or alterations to the present invention are possible by one skilled in the art and it is intended that these modifications and/or alterations fall within the scope of the appended claims.