Variable ratio hand pump

1. In a hand operated hydraulic pump having a lever, the lever including a handle and a pivot, the pump including a pumping unit with a plunger that engages the lever between the handle and the pivot, the handle being operable to reciprocate the plunger so as to pump hydraulic fluid as the lever is pivoted back and forth, the improvement wherein:

the pivot of the lever is pivoted to a cam at a lever pivot;

the cam is pivoted to a frame of the pump at a frame pivot, the frame pivot on the cam being spaced away from the lever pivot such that pivoting the cam about the frame pivot changes the distance between the lever pivot and the plunger of the pumping unit; and

a compensation device that is subjected to the output pressure of the pump and slidingly engages the cam so as to rotate the cam about the frame pivot in relation to the output pressure of the pump so as to reduce the distance between the lever pivot and the plunger of the pumping unit as the output pressure increases.

2. A hand operated hydraulic pump as claimed in claim 1 , wherein the operating handle when pivoted against the plunger of the pumping unit tends to rotate the cam back against rotation of the cam by the compensation device so as to increase the distance between the lever pivot and the plunger of the pumping unit.

3. A hand operated hydraulic pump as in claim 1 , wherein the compensation device is a cylinder and a plunger of the compensation device rotates the cam as the output pressure of the pump increases.

4. A hand operated hydraulic pump as claimed in claim 1 , wherein the compensation device is biased to retract and thereby increase the distance from the lever pivot to the pump plunger.

5. A hand operated hydraulic pump as claimed in claim 1 , wherein the plunger of the pumping unit slides in a slot of the lever.

6. A hand operated hydraulic pump as claimed in claim 1 , wherein the cam is generally triangular.

7. A hand operated hydraulic pump, comprising:

a housing including a pressure port;

a pumping unit supported by the housing and including a first plunger being movable to draw hydraulic fluid from a reservoir and deliver the hydraulic fluid to the pressure port;

a compensation cylinder supported by the housing and including a second plunger being movable in response to the hydraulic fluid being delivered to the pressure port;

a cam slidingly engaging the second plunger and pivotally connected to the housing at a housing pivot spaced apart from the second plunger, the cam pivoting about the housing pivot in response to movement of the second plunger; and

a lever having a first end pivotally connected to the cam at a lever pivot spaced apart from the second plunger and the housing pivot, the lever having a user handle at a second end, and a slot slidably receiving the first plunger between the first end and the second end, and the lever moving such that the lever pivot moves closer to the first plunger as the cam pivots about the housing pivot to reduce an amount of force required to pivot the lever.

8. A hand operated hydraulic pump as claimed in claim 7 , wherein the cam has a generally triangular shape, the second plunger engages the cam along a first leg of the triangular shape, the lever pivot is located along a second leg of the triangular shape, and the housing pivot is located at an intersection of the first leg and the second leg.