Power steering system with reaction force limiting means

Claim 2

In combination with a fluid power steering device having a source (38) of fluid medium under a storage pressure, a fluid motor (1) having a pressure chamber (21 or 22) and control valve means (8) displaceable from a neutral position for supply of the fluid medium to the pressure chamber under an operating pressure, said control valve means including means operative in said neutral position for blocking flow of the fluid medium from the source, and operating pressure responsive means for producing reaction force to resist said displacement of the control valve means from the neutral position including a force limiting piston (43 or 45) having opposed pressure faces (50 or 56) respectively exposed to said storage and operating pressures to limit the reaction force and force transmitting means (42 or 44) connected to the forces limiting piston and operatively engageable with the control valve means for exerting said reaction force thereon.

Claim 3

The combination of claim 1 wherein the power steering device includes actuating means (10 or 11) engageable with the control valve means and the reaction force producing means, said force transmitting means including a reaction piston (42 or 44) engaged by the actuating means and coacting with the force limiting piston to form an operating chamber (48 or 49) therebetween in fluid communication with the pressure chamber.

Claim 4

The combination of claim 2 wherein said opposed pressure faces are dimensioned to produce equal opposing forces acting on the force limiting piston at a predetermined value of the operating pressure.

Claim 5

The combination of claim 3 wherein said predetermined value of the operating pressure is approximately 30 to 50% of the storage pressure.

Claim 6

The combination of claim 4 wherein the opposing forces acting on the force limiting piston depend on the surface area ratio of said opposed pressure faces and the ratio of said storage and operating pressures.

Claim 7

The combination of claim 5 including stop means (64) engageable by the force limiting piston for limiting movement thereof to a terminal position, and adjustable means (53-54 or 59-60) connecting the reaction piston to the force limiting piston for positioning the reaction piston in contact with the actuating means in the terminal position of the limiting piston.

Claim 8

The combination of claim 6 wherein said adjustable means includes spring means (55 or 61) carried by the force limiting piston and acting through the reaction piston for biasing the actuating means and the control valve means to said neutral position.

Claim 9

The combination of claim 2 including stop means engageable by the force limiting piston for limiting movement thereof to a terminal position, and adjustable means connecting the reaction piston to the force limiting piston for positioning the reaction piston in contact with the actuating means in the terminal posiTion of the limiting piston.

Claim 10

The combination of claim 8 wherein said adjustable means includes spring means (55 or 61) carried by the force limiting piston and acting through the reaction piston for biasing the actuating means and the control valve means to said neutral position.

Claim 11

The combination of claim 1 wherein said opposed pressure faces are dimensioned to produce equal opposing forces acting on the force limiting piston at a predetermined value of the operating pressure.

Claim 12

The combination of claim 10 wherein said predetermined value of the operating pressure is approximately 30 to 50% of the storage pressure.

Claim 13

The combination of claim 10 wherein the opposing forces acting on the force limiting piston depend on the ratio of said opposed pressure faces and the ratio of said storage and operating pressures.

Claim 14

In combination with a fluid power steering device having a source of fluid medium under a storage pressure, and a fluid motor (1) having a pressure chamber, control valve means connected to said source and displaceable from a neutral position for supplying the fluid medium at a varying operating pressure to the pressure chamber and a valve actuator, means (9) for yieldably resisting actuation of the control valve means by the valve actuator, comprising reaction pressure means (42 or 44) engageable with the actuator for opposing said displacement of the control valve means from said neutral position with a reaction force that is a function of the operating pressure, and fluid pressure control means (43 or 45) connected to the reaction pressure means for limiting the reaction force developed as a function of the ratio of the storage and operating pressures, said control valve means including means operative in the neutral position for blocking flow of the fluid medium from the source.

Claim 15

In combination with a fluid power steering device having a source of fluid medium under a storage pressure, and a fluid motor (1) having a pressure chamber, control valve means connected to said source and displaceable from a neutral position for supplying the fluid medium at a varying operating pressure to the pressure chamber and a valve actuator, means (9) for yieldably resisting actuation of the control valve means by the valve actuator, comprising reaction pressure means (42 or 44) engageable with the actuator for opposing said displacement of the control valve means from said neutral position with a reaction force that is a function of the operating pressure, and fluid pressure control means (43 or 45) connected to the reaction pressure means for limiting the reaction force developed as a function of the ratio of the storage and operating pressures, said control valve means including means operative in the neutral position for blocking flow of the fluid medium from the source.

Claim 16

The combination of claim 13 wherein said fluid pressure controlled means includes a piston having opposed pressure faces respectively exposed to the storage and operating pressures, said pressure faces being dimensioned to equalize the opposing forces acting on the piston at a predetermined value of the operating pressure to prevent any further increase in the reaction force developed.

Claim 17

The combination of claim 14 wherein said predetermined value of the operating pressure is approximately 30 to 50% of the storage pressure.