HYDRAULIC CONTROL SYSTEM FOR LINEAR ACTUATION

Abstract

A hydraulic control system for linear actuation that includes an electric motor connected to a hydraulic pump and a hydraulic cylinder connected to the pump by a first flow line. A pressure transducer, a pressure control valve, and a check valve are connected to the first flow line between the pump and the cylinder and a tank is connected to the pump by a second flow line and the cylinder by a return line. A control valve is connected between the first flow line and the return line.

Claims

1. A hydraulic control system for linear actuation, comprising: an electric motor connected to a hydraulic pump; a hydraulic cylinder connected to the pump by a first flow line; a pressure transducer, a pressure control valve, and a check valve connected to the first flow line between the pump and the cylinder; a tank connected to the pump by a second flow line and the cylinder by a return line; and a control valve connected between the first flow line and the return line.

2. The system of claim 1 wherein the control valve is connected to the first flow line between the check valve and the pump.

3. The system of claim 2 further comprising a proportional control valve connected between the first flow line and the return line.

4. The system of claim 3 wherein the proportional control valve is connected to the flow line between the check valve and the pressure control valve.

5. The system of claim 2 wherein the proportional control valve is connected to a processor and an operator command.

6. The system of claim 5 wherein an opening area of the proportional control valve is controlled by the processor.

7. The system of claim 6 wherein the processor controls the proportional control valve based upon a pressure measurement.

8. The system of claim 7 wherein the pressure measurement is determined from a command signal from the operator command and a signal from the pressure transducer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic view of a lift system; and

[0021] FIG. 2 is a schematic view of a hydraulic control system for linear actuation of a lift system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] With reference to the figures, a hydraulic control system for linear actuation 10 includes an electric motor 12 connected to a hydraulic pump 14. The pump 14 is connected to a hydraulic cylinder 16 by flow line 18. Connected between the pump 14 and cylinder 16 on the flow line 18 is a pressure transducer 20, a pressure control valve 22, and a check valve 24. The pump 14 is also connected to a tank 26 via flow line 28.

[0023] The cylinder 16 is connected to the tank 26 by return line 30. Connected between flow line 18 and return line 30 is a control valve 32. Control valve 32 is connected to flow line 18 between check valve 24 and pump 14. Also connected between flow line 18 and return line 30 is a proportional control valve 34. The proportional control valve 34 is connected to the flow line 18 between the check valve 24 and the pressure control valve 22.

[0024] The proportional control valve 34 is connected to a processor 36 having software 38. Also connected to the processor 36 is an operator command 40 such as a joystick command. A common approach to achieve proportional speed control and load independent control is to use a proportional flow control valve together with a hydraulic compensator where the proportion control valve controls the flow rate, or lower speed, and the hydraulic compensator maintains the speed regardless of the load weight.

[0025] In one example of the present system, the pressure transducer 29 is used to estimate the pressure in the cylinder 16. Thus, the hydraulic compensator may be eliminated and the software 38 is used to change the proportional control valve's 34 opening area to maintain the speed regardless of load weight.

[0026] In operation, the processor 36 receives a command signal from the joystick command 40 and a signal from the pressure transducer 20 that provides a pressure measurement. The joystick command 40 from an operator represents the expectation of the operator on the lowering speed of the platform. The pressure measurement is used by the processor 36 to estimate the load on the platform. Using the software 38, the processor determines a valve command based upon the joystick command 40 and the pressure measurement. The desired valve command is then sent from the processor 36 to the proportional control valve 24 to achieve the desired opening area of the proportional control valve.

[0027] For example, the joystick command 40 is used as a desired lowering speed, which defines V in Equation 2. The pressure measurement is approximated as the pressure differential ΔP in Equation 1. The processor 36 is used to calculate the correct opening area A.sub.orifice so that the desired speed can be achieved based on the weight of the load in the platform. Look up tables or other techniques can be used to make the software 38 easy to tune and more flexible for different systems.

[0028] Thus, as has been disclosed, is a control system that enables the lowest actuation speeds to be achieved without violating the operating envelope of the power pack pump. This is accomplished by using a proportional control valve to divert pump flow away from the cylinder and back to the tank.

[0029] From the above discussion and accompanying figures and claims it will be appreciated that the hydraulic control system for linear actuation 10 offers many advantages over the prior art. It will be appreciated further by those skilled in the art that other various modifications could be made to the device without parting from the spirit and scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in the light thereof will be suggested to persons skilled in the art and are to be included in the spirit and purview of this application.