Patent ID: 7497448

Claim:
A tugger cart for transporting a load having a weight, comprising: a support frame; a bed pivotably mounted to the support frame for receiving the load thereon, the bed movable between a first position wherein the bed is lies in a generally horizontal plane and a second position wherein the bed is at a predetermined acute angle to the horizontal plane; and a wheel assembly operatively connected to the support frame for supporting the support frame above a supporting surface; a cylinder assembly, the cylinder assembly including: a cylindrical housing having first and second ends and an inner surface defining a cavity in the housing for receiving a fluid therein, the cylinder housing operatively connected one of the bed and the support frame; a piston slidably extending through the cavity in the housing, the piston having a first end connected to the other of the bed and the support frame and a second end; a flange projecting from the piston and being positioned within the cavity so as to divide the cavity in the housing into first and second portions, the flange terminating at a radially outer edge that forms a slidable interface with the inner surface of the housing; and a differential pressure valve assembly including: a differential pressure valve having an upstream input communicating with the first portion of the cavity and a downstream output communicating with the second portion of the cavity, the flow rate of the fluid at the output of the differential pressure valve being constant in response to various pressures of the fluid at the input, the differential pressure valve including: a flow regulator including a generally tubular sleeve having an inner surface defining a chamber and including an aperture having a size therethrough, the aperture through the sleeve allowing the chamber to communicate with the output of the differential pressure valve; and an impeller slidably received with chamber of the sleeve and having a closed forward end with a port therethrough so as to allow the input of the differential pressure valve to communicate with the chamber, the impeller moveable between a low pressure position and a high pressure position; a check valve having an input communicating with the output of the differential pressure valve and an output communicating with the input of the differential pressure valve, the check valve controlling the flow of fluid from the second portion to the first portion of the cavity; wherein the impeller moves from the low pressure position to the high pressure position and selectively restricts the size of the aperture through the sleeve of the flow regulator solely in response to the pressure of the fluid on the closed end of the impeller.