Material handling vehicle

Claim 2

A vehicle for use in moving a load, said vehicle comprising suPport means including an upstanding mast and a load supporting carriage connected with said mast for movement therealong, fluid motor means for tilting said mast and moving said carriage along said mast in such a manner that the load subjects the vehicle to an increasing moment which tends to overturn the vehicle in one given direction of movement of said fluid motor means, variable displacement pump means for supplying fluid to said fluid motor means, actuator means for varying the displacement of said pump means, displacement control means operable to position said actuator means in response to the pressure differential between the variable displacement pump output and the input pressure to the fluid motor means, detector means for detecting variations in the overturning moment to which the vehicle is subjected by transmitting a signal which is representative of the pressure differential across that portion of said fluid motor means which effects the tilting of said mast and, means causing said detector means to control the displacement of said variable displacement pump independently of said displacement control means to reduce the displacement of said pump means in response to the detection of an increase in the overturning moment to a value in excess of a predetermined overturning moment.

Claim 3

A vehicle as set forth in claim 1 wherein said tilt motor includes a cylinder defining a chamber and a piston disposed within said chamber, said piston being effective to divide said chamber into first and second end portions, said pump means being operable to supply fluid under pressure to one of said end portions of said chamber to effect relative movement between said piston and cylinder and a change in the inclination of said mast, said detector means including means for detecting a change in the fluid pressure in one of said end portions of said chamber relative to the fluid pressure in the other of said end portions of said chamber to thereby detect a variation in the overturning moment applied to the vehicle independent of variations in the absolute pressure of said fluid supplied by said pump.

Claim 4

A vehicle as set forth in claim 2 wherein said detector means includes a second cylinder defining a second chamber, a second piston disposed in said second chamber, said second piston being effective to divide said second chamber into first and second end portions, first conduit means connecting said first end portion of said chamber in said tilt motor in fluid communication with said first end portion of said second chamber, second conduit means for connecting said second end portion of said chamber in said tilt motor in fluid communication with said second end portion of said second chamber to thereby apply a pressure differential across said second piston equal to the pressure differential across said piston in said tilt motor, and means for effecting operation of said actuator means in response to relative movement between said second piston and cylinder under the influence of the pressure differential across said second piston.

Claim 5

A vehicle as set forth in claim 3 wherein said detector means further includes biasing means for retarding relative movement between said second piston and cylinder to prevent operation of said actuator means until the predetermined overturning moment is present.

Claim 6

A vehicle as set forth in claim 3 wherein said piston in said tilt motor has a head end surface exposed to the fluid pressure in said first end portion of said chamber in said tilt motor and a rod end surface exposed to the fluid pressure in said second end portion of said chamber in said tilt motor, said rod end surface having an area which is smaller than the area of said head end surface, said second piston having a head end surface exposed to the fluid pressure in said first end portion of said second chamber and a rod end surface exposed to the fluid pressure in said second end portion, said rod and head end surface areas of said tilt motor having the same ratio to Each other as said rod and head end areas of said second piston.

Claim 7

A vehicle as set forth in claim 1 further including valve means operable between a first condition blocking fluid flow from said pump means to said motor means and a second condition enabling fluid to flow from said pump means to said motor means, and compensator means for detecting when the fluid pressure output of said pump means is greater than a predetermined pressure when said valve means is in said first condition and for effecting operation of said actuator means to reduce the displacement of said pump means in response to detection of a fluid pressure output which is greater than the predetermined pressure when said valve means is in said first condition.

Claim 8

A vehicle as set forth in claim 6 further including means for rendering said compensator means ineffective to effect operation of said actuator means when the fluid pressure output of said pump means is greater than the predetermined pressure and said valve means is in said second condition to enable said pump means to supply fluid to said motor means at a pressure which is greater than the predetermined pressure when said valve means is in said second condition.

Claim 9

A vehicle as set forth in claim 1 wherein said motor means includes first and second piston and cylinder assemblies each having first and second operating chambers, said detector means including detector chamber means for receiving fluid, conduit means for conducting fluid pressure to said detector chamber means, and valve means for porting the fluid pressure differential between said first and second operating chambers containing fluid at a higher pressure than said other first and second operating chambers from the said operating chambers to said conduit means.

Claim 10

A vehicle as set forth in claim 1 further including means for detecting when said motor means is in a predetermined operating condition and for rendering said detector means ineffective to reduce the displacement of said pump means when said motor is in the predetermined operating condition.

Claim 11

A vehicle as set forth in claim 1 wherein said support means includes an upstanding mast and a load engaging carriage connected with said mast, said motor means including a tilt motor connected with said mast and operable in a first direction to decrease the angle of inclination of the mast relative to a vehicle support surface and operable in a second direction to increase the angle of inclination of the mast relative to the vehicle support surface, and means for rendering said detector means ineffective to reduce the displacement of said pump means during operation of said motor means in said second direction.

Claim 12

A vehicle as set forth in claim 1 wherein said motor means includes a hoist motor operable to move said carriage along said mast between a lowered position in which said carriage is disposed adjacent to a lower end portion of said mast and said hoist motor is in a relatively lightly loaded condition and a raised position in which said carriage is disposed adjacent to an upper end portion of said mast and said hoist motor is in a relatively heavily loaded condition, and means responsive to the existence of said lightly loaded condition for rendering said detector means ineffective to reduce the displacement of said pump means when said carriage is in the lowered position.

Claim 13

A vehicle comprising a base, an upstanding mast connected with said base, load engaging means connected with said mast and movable therealong for engaging and lifting a load, tilt motor means for moving said mast and load engaging means relative to said base in such a manner as to vary an overturning moment to which said vehicle is subjected by a load engaged by said load engaging means, said tilt motor means including first and second chambers, variable displacement pump means including load responsive displacement control means for supplying fluid under pressure to said first chamber of said motor means, said tilt motor means including means for subjecting fluid in said second chamber to forces which vary as a function of variations in the overturning moment to which the vehicle is subjected and as a function of variations in the fluid pressure in said first chamber, actuator means operable to vary the displacement of said pump means, further said displacement control means is operable to position said actuator means in response to the pressure differential between the variable displacement pump output and the input pressure to said first chamber and comparator means for comparing the fluid pressures in said first and second chambers independent of said load responsive displacement control means and effecting operation of said actuator means independent of said load responsive displacement control means to reduce the displacement of said pump means when the fluid pressure in said second chamber exceeds the fluid pressure in said first chamber by a predetermined amount.

Claim 14

A vehicle comprising a base, an upstanding mast connected with said base, load engaging means connected with said mast and movable therealong for engaging and lifting a load, tilt motor means for moving said mast and load engaging means relative to said base in such a manner as to vary an overturning moment to which said vehicle is subjected by a load engaged by said load engaging means, said tilt motor means including first and second chambers, variable displacement pump means including load responsive displacement control means for supplying fluid under pressure to said first chamber of said motor means, said tilt motor means including means for subjecting fluid in said second chamber to forces which vary as a function of variations in the overturning moment to which the vehicle is subjected and as a function of variations in the fluid pressure in said first chamber, actuator means operable to vary the displacement of said pump means, further said displacement control means is operable to position said actuator means in response to the pressure differential between the variable displacement pump output and the input pressure to said first chamber and comparator means for comparing the fluid pressures in said first and second chambers independent of said load responsive displacement control means and effecting operation of said actuator means independent of said load responsive displacement control means to reduce the displacement of said pump means when the fluid pressure in said second chamber exceeds the fluid pressure in said first chamber by a predetermined amount.

Claim 15

A vehicle as set forth in claim 12 wherein said comparator means includes a cylinder, piston which cooperates with said cylinder to define third and fourth chambers, first conduit means for conducting fluid pressure from said first chamber to said third chamber and second conduit means for conducting fluid pressure from said second chamber to said fourth chamber, said piston and cylinder being movable relative to each other under the influence of the fluid pressure in said fourth chamber, and biasing means for retarding relative movement between said piston and cylinder.

Claim 16

A vehicle sa set forth in claim 13 further including restrictor means for restricting fluid flow in said second conduit means to retard transient fluctuations in the fluid pressure in said fourth chamber.

Claim 17

A vehicle as set forth in claim 12 further including lift motor means for raising and lowering said load engaging means relative to said base.

Claim 18

A vehicle as set forth in claim 12 further including valve means for controlling the flow of fluid from said pump means to said motor means, said valve means being operable between a closed condition blocking fluid flow to said pump means and an open condition enabling fluid to flow to said motor means, and means for effecting operation of said actuator means to reduce the displacement of said pump means when said valve means is in the closed condition.

Claim 19

A vehicle as set forth in claim 13 wherein said tilt motor means is operable in a first direction to move said mast and load engaging means in such a manner as to increase the overturning moment to which said vehicle is subjected by the load and is operable in a second direction to move said mast and load engaging means in such a manner as to decrease the overturning moment to which said vehicle is subjected by the load, and valve means operable in response to operation of said tilt motor means in said second direction to move from a first position wherein said fluid pressure is conducted from said second chamber to said fourth chamber and a second position blocking said fluid pressure from said second chamber and communicating said fourth chamber with a system reservoir thereby preventing operation of said actuator means to reduce the displacement of said pump means when said motor means is being operated in the second direction and the fluid pressure in said second chamber exceeds the fluid pressure in said first chamber by the predetermined amount.

Claim 20

A vehicle as set forth in claim 13 further including lift motor means for moving said load engaging means along said mast between a raised position adjacent to an upper end portion of said mast wherein the load on said lift motor is relatively high and a lowered position adjacent to a lower end portion of said mast wherein the load on said lift motor is relatively low, and valve means operative in response to the existence of said relatively low load on said motor for preventing operation of said actuator means to reduce the displacement of said pump means when said load eNgaging means is in the lowered position and the fluid pressure in said second chamber exceeds the fluid pressure in said first chamber by the predetermined amount.