Power-steering device

1. A power steering device, comprising:

an input shaft rotated in response to a steering operation of a steering wheel;

an output shaft coupled to the input shaft through a torsion bar;

a power cylinder having a pair of hydraulic pressure chambers defined by a piston to generate a steering assist force based on hydraulic pressures in the hydraulic pressure chambers;

a rotary valve that selectively supplies hydraulic fluid from an external hydraulic pressure source to the pair of hydraulic pressure chambers in accordance with relative rotation of the input shaft and the output shaft;

a hollow motor arranged to surround at least an axial portion of the input shaft and control rotation of the input shaft based on vehicle driving conditions; and

input-shaft-side and rotor-side engagement parts arranged between an outer circumference of the input shaft and an inner circumference of the hollow motor so as to allow relative movement of the input shaft and a rotor of the hollow motor in an axis direction but to restrict relative movement of the input shaft and the rotor of the hollow motor in a rotation direction.

2. The power steering device according to claim 1 ,

wherein the rotor of the hollow motor is substantially cylindrical in shape; and

wherein the hollow motor includes: a stator disposed around an outer circumference of the rotor; a motor housing accommodating therein the rotor and the stator; and first and second bearings disposed in the motor housing and supporting the rotor.

3. The power steering device according to claim 2 ,

wherein the rotor has: a large-diameter region formed at a middle thereof in the rotation axis direction of the input shaft and facing the stator; and first and second small-diameter regions formed on one side and the other side of the large-diameter region in the axis direction and made smaller in diameter than the large-diameter region;

wherein the stator extends to the one side and the other side of the large-diameter region in the axis direction;

wherein the first bearing is disposed between the first small-diameter region and the stator; and

wherein the second bearing is disposed between the second small-diameter region and the stator.

4. The power steering device according to claim 3 ,

wherein the hollow motor is in the form of a brushless motor having a resolver to detect a rotational position of the rotor; and

wherein the resolver is located outside the first bearing in the axis direction.

5. The power steering device according to claim 4 ,

wherein the motor housing has, formed on an inner circumferential side thereof, a first bearing accommodating part accommodating therein the first bearing;

wherein the resolver includes: a resolver rotor disposed around the outer circumference of the rotor; and a resolver stator disposed around the resolver rotor; and

wherein an outer diameter of the resolver rotor is set smaller than an inner diameter of the first bearing accommodating part.

6. The power steering device according to claim 5 ,

wherein a region of the rotor in which the resolver rotor is disposed is set smaller in outer diameter than a region of the rotor in which the first bearing is disposed.

7. The power steering device according to claim 2 ,

wherein at least one of the first and second bearings is in the form of a ball bearing adapted to restrict movement of the rotor in the axis direction.

8. The power steering device according to claim 1 ,

wherein the rotor of the hollow motor is substantially cylindrical in shape;

wherein the hollow motor includes: a stator arranged around an outer circumference of the rotor; and a motor housing accommodating therein the rotor and the stator; and

wherein the motor housing includes: a cylindrical member arranged radially outside the stator; and an axial end closing member closing a rotary-valve-side end of the cylindrical member.

9. The power steering device according to claim 1 ,

wherein the rotor of the hollow motor is substantially cylindrical in shape;

wherein the hollow motor is in the form of a brushless motor having: a stator arranged around an outer circumference of the rotor; a motor housing accommodating therein the rotor and the stator; and a resolver arranged on an side of the rotor opposite from the rotary valve in the axis direction so as to detect a rotational position of the rotor;

wherein the motor housing has a recessed engagement portion formed in a rotary-valve-side surface thereof in the axis direction so as to surround the input shaft;

wherein the power steering device further comprises a valve housing part accommodating therein the rotary valve; and

wherein the valve housing part has, formed on a motor-housing-side surface thereof, a protruding engagement portion engageable in the recessed engagement portion.

10. The power steering device according to claim 1 ,

wherein the input-shaft-side engagement part and the rotor-side engagement part are provided on only a rotary-valve-side region of the rotor in the axis direction.

11. The power steering device according to claim 1 ,

wherein the input-shaft-side engagement part and the rotor-side engagement part are formed with respective serrations and engaged with each other by the serrations.

12. The power steering device according to claim 11 ,

wherein there is a resin material filled in between the input-shaft-side engagement part and the rotor-side engagement part.

13. The power steering device according to claim 1 ,

wherein the input-shaft-side engagement part and the rotor-side engagement part are provided on a predetermined region of the rotor in the axis direction; and

wherein remaining regions of the input shaft and the rotor are formed with flat circumferential surfaces and adapted to allow contact between the flat circumferential surfaces along entire circumferences thereof.

14. The power steering device according to claim 1 ,

wherein there is provided a torque limiter between the input-shaft-side engagement part and the rotor-side engagement part.

15. The power steering device according to claim 1 ,

wherein the rotor of the hollow motor is substantially cylindrical in shape;

wherein the hollow motor includes a plurality of stator elements having respective coils wound around the outer circumference of the rotor; and

wherein the power steering device further comprises different energization circuits to which the coils of the stator elements are connected, respectively.

16. The power steering device according to claim 1 , further comprising:

a ball screw mechanism arranged between the output shaft and the piston so as to convert rotation of the output shaft to movement of the piston in the axis direction;

rack teeth formed integral with the piston; and

a sector shaft engaged with the rack teeth so as to rotate with movement of the rack teeth and transmit rotation to steerable wheels via pitman arms,

wherein the rotary valve is arranged between the hollow motor and the power cylinder.

17. A power steering device, comprising:

an input shaft rotated in response to a steering operation of a steering wheel;

an output shaft coupled to the input shaft through a torsion bar;

a power cylinder having a pair of hydraulic pressure chambers defined by a piston to generate a steering assist force based on hydraulic pressures in the hydraulic pressure chambers;

a rotary valve that selectively supplies hydraulic fluid from an external hydraulic pressure source to the pair of hydraulic pressure chambers in accordance with relative rotation of the input shaft and the output shaft;

a hollow motor arranged to surround at least an axial portion of the input shaft and control rotation of the input shaft based on driving conditions of the vehicle;

input-shaft-side and rotor-side engagement parts arranged between an outer circumference of the input shaft and an inner circumference of the hollow motor so as to allow relative movement of the input shaft and a rotor of the hollow motor in an axis direction but to restrict relative movement of the input shaft and the rotor of the hollow motor in a rotation direction; and

a controller that performs drive control of the hollow motor based on information from a camera that recognizes another vehicle travelling ahead or white lines on a travelling lane, information from a car navigation system or information from a yaw rate sensor that detects a yaw moment of the vehicle.

18. The power steering device according to claim 17 ,

wherein the rotor of the hollow motor is substantially cylindrical in shape; and

wherein the hollow motor includes: a stator arranged around an outer circumference of the rotor; a motor housing accommodating therein the rotor and the stator; and first and second bearings disposed in the motor housing and supporting the rotor.

19. The power steering device according to claim 18 ,

wherein the rotor has: a large-diameter region formed at a middle thereof in the rotation axis direction of the input shaft and facing the stator; and first and second small-diameter regions formed on one side and the other side of the large-diameter region in the axis direction and made smaller in diameter than the large-diameter region;

wherein the stator extends to the one side and the other side of the large-diameter region in the axis direction;

wherein the first bearing is disposed between the first small-diameter region and the stator; and

wherein the second bearing is disposed between the second small-diameter region and the stator.

20. The power steering device according to claim 19 ,

wherein the hollow motor is in the form of a brushless motor having a resolver to detect a rotational position of the rotor; and

wherein the resolver is located outside the first bearing in the axis direction.