Coupling device for rotationally coupling drive shaft and driven shaft

1. A coupling device for rotationally coupling a drive shaft of a drive device and a driven shaft of an operation device which are arranged on a rotation axis, the coupling device comprising:

a drive portion formed on the drive shaft to face in the circumferential direction and having a drive wall surface extending in the direction of the rotation axis;

a driven portion formed on the driven shaft to face the drive wall surface and having a driven wall surface extending in the direction of the rotation axis;

a convex curved portion formed on one of the drive wall surface and the driven wall surface and extending along the rotation axis at a position spaced from the rotation axis as viewed in the direction of the rotation axis; and

a concave curved portion having a smaller curvature than that of the convex curved portion and formed on the other of the drive wall surface and the driven wall surface to contact the convex curved portion and extending along the rotation axis at a position spaced from the rotation axis as viewed in the direction of the rotation axis.

2. The coupling device as set forth in claim 1 , wherein:

the convex curved portion and the concave curved portion are formed so that a component in the direction of a common normal to the convex curved portion and the concave curved portion at a contact portion of a force with which one of the convex curved portion and the concave curved portion presses the other thereof at the contact portion therebetween becomes larger than a component in the direction of a common tangent to the convex curved portion and the concave curved portion at the contact portion of the force.

3. The coupling device as set forth in claim 1 , wherein:

the wall surface with the convex curved portion provided thereon is formed to be depressed only at both side portions of the convex curved portion as viewed in the direction of the rotation axis so that the convex curved portion is formed along a radial outer edge portion of the wall surface and extends along the rotation axis; and

the concave curved portion is concaved to face the convex curved portion and extends along the rotation axis.

4. The coupling device as set forth in claim 1 , wherein:

the drive shaft and the driven shaft is made of steel on which heat treatment has been performed; and

at least one of the convex curved portion and the concave curved portion is coated with diamond-like carbon.

5. The coupling device as set forth in claim 1 , wherein:

the drive device is an electric motor in a vehicle brake system;

the drive shaft is a motor shaft of the electric motor;

the operation device is a pump driven by the electric motor; and

the driven shaft is a pump shaft of the pump.

6. A coupling device for rotationally coupling a drive shaft of a drive device and a driven shaft of an operation device which are arranged on a rotation axis, the coupling device comprising:

a coupling protrusion formed on one of the drive shaft and the driven shaft and having two outer wall surfaces extending mutually in parallel in the direction of the rotation axis;

a coupling recess formed on the other of the drive shaft and the driven shaft and having two inner wall surfaces extending mutually in parallel in the direction of the rotation axis to be engaged with the coupling protrusion;

convex curved portions respectively formed on the two outer wall surfaces of the coupling protrusion and extending along the rotation axis at positions which are point-symmetrical with respect to the rotation axis as viewed in the direction of the rotation axis; and

concave curved portions each having a smaller curvature than that of a corresponding one of the convex curved portions and respectively formed on the two inner wall surfaces of the coupling recess and extending along the rotation axis at positions which are point-symmetrical with respect to the rotation axis as viewed in the direction of the rotation axis, to contact the convex curved portions.

7. The coupling device as set forth in claim 6 , wherein:

each of the convex curved portions and the corresponding concave curved portion are formed so that a component in the direction of a common normal to each convex curved portion and the corresponding concave curved portion at a contact portion of a force with which one of each convex curved portion and the corresponding concave curved portion presses the other thereof at the contact portion therebetween becomes larger than a component in the direction of a common tangent to each convex curved portion and the corresponding concave curved portion at the contact portion of the force.

8. The coupling device as set forth in claim 6 , wherein:

the wall surface with each of the convex curved portions provided thereon is formed to be depressed only at both side portions of each convex curved portion as viewed in the direction of the rotation axis so that each convex curved portion is formed along a radial outer edge portion of the wall surface and extends along the rotation axis; and

each of the concave curved portion is concaved to face the corresponding convex curved portion and extends along the rotation axis.

9. The coupling device as set forth in claim 6 , wherein:

the drive shaft and the driven shaft is made of steel on which heat treatment has been performed; and

at least either of the convex curved portions and the concave curved portions are coated with diamond-like carbon.

10. The coupling device as set forth in claim 6 , wherein:

the drive device is an electric motor in a vehicle brake system;

the drive shaft is a motor shaft of the electric motor;

the operation device is a pump driven by the electric motor; and

the driven shaft is a pump shaft of the pump.