Integral power steering device

1. An integral power steering device comprising:

a housing constructed by a gear housing formed of a metallic material and configured to be closed at one axial end and to have an opening at the other axial end, and a valve housing formed of a metallic material and configured to close the opening end of the gear housing and to have a shaft insertion hole axially formed through the valve housing;

a steering shaft adapted to be linked at one end to a steering wheel, the other end of the steering shaft being configured to be inserted into the valve housing so as to face an internal space of the gear housing;

a piston linked to the other end of the steering shaft and configured to partition the internal space of the gear housing into a first pressure chamber and a second pressure chamber;

a first motion converter interposed between the steering shaft and the piston for converting rotary motion of the steering shaft into axial movement of the piston;

a second motion converter configured to be meshed-engagement with a toothed portion formed on an outer periphery of the piston for converting the axial movement of the piston into rotary motion for turning;

a rotary valve provided to be linked to the steering shaft in the shaft insertion hole and adapted to selectively introduce working oil supplied from an external hydraulic pressure source to either of the first pressure chamber and the second pressure chamber depending on a rotation direction of the steering shaft;

a first valve disposed in the valve housing and configured to discharge hydraulic pressure in the second pressure chamber into the first pressure chamber when the piston has reached a first predetermined stroke position at which a volume of the first pressure chamber becomes a minimum permissible capacity by a movement of the piston; and

a second valve disposed in the gear housing and configured to discharge hydraulic pressure in the first pressure chamber into the second pressure chamber when the piston has reached a second predetermined stroke position at which a volume of the second pressure chamber becomes a minimum permissible capacity by a movement of the piston,

wherein at least the first valve comprises:

a first valve accommodation hole formed by machining the valve housing itself;

a first valve seat portion disposed in the first valve accommodation hole and arranged on a side of the first pressure chamber and having a first pin insertion hole axially formed through the first valve seat portion;

a first valve element arranged to be opposed to the first valve seat portion and installed to axially slide in the first valve accommodation hole and configured to cut off a movement of working oil from the second pressure chamber to the first pressure chamber with the first valve element seated on the first valve seat portion;

a first pin portion integrally connected to the first valve element and configured to face an internal space of the first pressure chamber through the first pin insertion hole and to apply a moving force to the first valve element by pushing the first pin portion by the piston immediately when the first predetermined stroke position of the piston has been reached; and

a first biasing member configured to bias the first valve element toward the first valve seat portion.

2. The integral power steering device as recited in claim 1 , wherein:

the first valve accommodation hole comprises a large-diameter portion in which the first valve element is accommodated, and a small-diameter portion whose diameter is reduced from an end of the large-diameter portion, facing the first pressure chamber, and in which the first pin portion is inserted; and

the first valve seat portion is formed into a cylindrical shape, one end of the first valve seat portion being configured to abut on a stepped portion defined by a border between the large-diameter portion and the small-diameter portion.

3. The integral power steering device as recited in claim 2 , wherein:

the first valve accommodation hole is formed by machining from a side of the large-diameter portion; and

an outside opening end of the large-diameter portion is hermetically plugged by a sealing member.

4. The integral power steering device as recited in claim 3 , wherein:

a coil spring, which serves as the first biasing member, is interposed such that one axial end of the coil spring abuts on the sealing member and that the other axial end abuts on the first valve element.

5. The integral power steering device as recited in claim 4 , wherein:

the sealing member comprises a small-diameter portion placed into the first valve accommodation hole and a large-diameter portion having an outside diameter dimensioned greater than the small-diameter portion and placed on an outside of the first valve accommodation hole so as to be exposed to the outside, the large-diameter portion being adapted to have an engaging portion with which a tool for installing the sealing member is brought into engagement.

6. The integral power steering device as recited in claim 5 , wherein:

the engaging portion of the scaling member adapted to engage with the tool is recessed substantially in a radial center of an outside end lace of the large-diameter portion of the sealing member.

7. The integral power steering device as recited in claim 1 , wherein:

a substantially center of a top end face of a first one of two opposite longitudinal ends of the first pin portion is brought into abutted-engagement with the piston.

8. The integral power steering device as recited in claim 1 , wherein:

the valve housing is formed at an opposite end facing the gear housing with a reduced-diameter fitting protrusion configured to protrude toward the gear housing; and

the gear housing is formed at the opening end with an enlarged-diameter fitting recess configured to receive the fitting protrusion.

9. The integral power steering device as recited in claim 1 , wherein:

the first valve element comprises a large-diameter portion slidably fitted on an inner peripheral surface of the first valve accommodation hole and a small-diameter portion the first valve sent portion configured on a side of the first valve seat portion with respect to the large-diameter portion and having an outside diameter set less than the large-diameter portion.

10. The integral power steering device as recited in claim 1 , wherein:

the first valve element has a through hole to which a second one of two opposite longitudinal ends of the first pin portion is press-fitted and fixed; and

the first pin portion is press-fitted and fixed to the through hole by pushing a first one of the two opposite longitudinal ends by the piston during non-operation of a hydraulic pressure source.

11. An integral power steering device comprising:

a housing constructed by a gear housing formed of a metallic material and configured to be closed at one axial end and to have an opening at the other axial end, and a valve housing formed of a metallic material and configured to close the opening end of the gear housing and to have a shaft insertion hole axially formed through the valve housing;

a steering shaft adapted to be linked at one end to a steering wheel, the other end of the steering shaft being configured to be inserted into the valve housing so as to face an internal space of the gear housing;

a piston linked to the other end of the steering shaft and configured to partition the internal space of the gear housing into a first pressure chamber and a second pressure chamber;

a first motion converter interposed between the steering shaft and the piston for converting rotary motion of the steering shaft into axial movement of the piston;

a second motion converter configured to be meshed-engagement with a toothed portion formed on an outer periphery of the piston for converting the axial movement of the piston into rotary motion for turning;

a rotary valve provided to be linked to the steering shaft in the shaft insertion hole and adapted to selectively introduce working oil supplied from an external hydraulic pressure source to either of the first pressure chamber and the second pressure chamber depending on a rotation direction of the steering shaft;

a first valve disposed in the valve housing and configured to discharge hydraulic pressure in the second pressure chamber into the first pressure chamber when the piston has reached a first predetermined stroke position at which a volume of the first pressure chamber becomes a minimum permissible capacity by a movement of the piston; and

a second valve disposed in the gear housing and configured to discharge hydraulic pressure in the first pressure chamber into the second pressure chamber when the piston has reached a second predetermined stroke position at which a volume of the second pressure chamber becomes a minimum permissible capacity by a movement of the piston,

wherein at least the first valve comprises:

a first valve accommodation hole provided in the valve housing and configured to be substantially conformable to a direction of movement of the piston;

a first valve seat portion disposed in the first valve accommodation hole and arranged on a side of the first pressure chamber and having a first pin insertion hole axially formed through the first valve seat portion;

a first valve element arranged to be opposed to the first valve seat portion and installed to axially slide in the first valve accommodation hole and configured to cut off a movement of working oil from the second pressure chamber to the first pressure chamber with the first valve element seated on the first valve seat portion;

a first pin portion integrally connected to the first valve element and configured to face an internal space of the first pressure chamber through the first pin insertion hole and to apply a moving force to the first valve element by pushing the first pin portion by the piston immediately when the first predetermined stroke position of the piston has been reached; and

a first biasing member configured to bias the first valve element toward the first valve seat portion.

12. The integral power steering device as recited in claim 11 , wherein:

the first valve accommodation hole comprises a large-diameter portion in which the first valve element is accommodated, and a small-diameter portion whose diameter is reduced from an end of the large-diameter portion, facing the first pressure chamber, and in which the first pin portion is inserted; and

the first valve seat portion is formed into a cylindrical shape, one end of the first valve seat portion being configured to abut on a stepped portion defined by a border between the large-diameter portion and the small-diameter portion.

13. The integral power steering device as recited in claim 12 , wherein:

the first valve accommodation hole is formed by machining from a side of the large-diameter portion; and

an outside opening end of the large-diameter portion is hermetically plugged by a sealing member.

14. The integral power steering device as recited in claim 13 , wherein:

a coil spring, which serves as the first biasing member, is interposed such that one axial end of the coil spring abuts on the sealing member and that the other axial end abuts on the first valve element.

15. The integral power steering device as recited in claim 14 , wherein:

the sealing member comprises a small-diameter portion placed into the first valve accommodation hole and a large-diameter portion having an outside diameter dimensioned greater than the small-diameter portion and placed on an outside of the first valve accommodation hole so as to be exposed to the outside, the large-diameter portion being adapted to have an engaging portion with which a tool for installing the sealing member is brought into engagement.

16. The integral power steering device as recited in claim 15 , wherein:

the engaging portion of the sealing member adapted to engage with the tool is recessed substantially in a radial center of an outside end face of the large-diameter portion of the sealing member.

17. The integral power steering device as recited in claim 11 , wherein:

a substantially center of a top end face of a first one of two opposite longitudinal ends of the first pin portion is brought into abutted-engagement with the piston.

18. The integral power steering device as recited in claim 11 , wherein:

the valve housing is formed at an opposite end facing the gear housing with a reduced-diameter fitting protrusion configured to protrude toward the gear housing; and

the gear housing is formed at the opening end with an enlarged-diameter fitting recess configured to receive the fitting protrusion.

19. The integral power steering device as recited in claim 11 , wherein:

the first valve element comprises a large-diameter portion slidably fitted on an inner peripheral surface of the first valve accommodation hole and a small-diameter portion configured on a side of the first valve seat portion with respect to the large-diameter portion and having an outside diameter set less than the large-diameter portion.

20. The integral power steering device as recited in claim 11 , wherein:

the first valve element has a through hole to which a second one of two opposite longitudinal ends of the first pin portion is press-fitted and fixed; and

the first pin portion is press-fitted and fixed to the through hole by pushing a first one of the two opposite longitudinal ends by the piston during non-operation of a hydraulic pressure source.