WO1988003098A1

WO1988003098A1 - Arrangement for a hydraulically operated lifting arrangement

Info

Publication number: WO1988003098A1
Application number: PCT/SE1987/000485
Authority: WO
Inventors: Hans-Åke PETTERSSON; Per Göran LARSSON
Original assignee: Strömsholmens Mekaniska Verkstad Ab; Thoreb Ab
Priority date: 1986-10-31
Filing date: 1987-10-20
Publication date: 1988-05-05
Also published as: SE8604678D0; SE8604678L; SE455853B

Abstract

An arrangement for a hydraulically operated lifting arrangement, for example a so-called tail lift, comprising at least one cylinder/piston unit (8) for actuating a lifting platform. This is connected via a hand valve (7) to the pressure side of a pump (2) by means of a hydraulic line (10). The pump (2) communicates on its suction side with a hydraulic tank (3), and on its pressure side with a pressure accumulator (6). A characteristic feature of the invention is that the arrangement comprises two hydraulic machines (4, 5) acting as a pump/motor and operatively connected via their shafts (14) and in a previously disclosed manner. These are reversible, and one of the hydraulic machines (5) is connected to the line (10) between the pressure side (2) of the pump and the valve (7). The other hydraulic machine (4), which is also capable of being regulated, is connected in parallel with the pump (2).

Description

Arrangement for a hydraulically operated lifting arrangement

The present invention relates to an arrangement for a hydraulically operated lifting arrangement, for example a so—called tailgate lift, consisting of at least one cylinder/piston unit for actuating .a lifting platform, which unit is connected via a hand valve to the pressure side of a pump by means of a hydraulic line, which pump communicates on its suction side with a hydraulic tank and on its pressure side with a pressure accumulator.

Many distribution vehicles and similar are now equipped with a tailgate lift in order to facilitate and simplify the loading and unloading of goods. In order to be able to use the lift at those times when the ordinary drive motor of the vehicle, which is more often than not an internal combustion engine, cannot be operated for environmental or safety reasons, the pump in a previously disclosed lift is so arranged as to be driven by an electric motor, the energy supply to which is provided from the vehicle battery. The design of the lift outlined briefly above results in relatively high energy consumption, however, which in turn leads

^■ to the interruption of operation due to the battery becoming discharged. A discharged battery also means, of course, that the drive motor cannot be restarted by means of the vehicle starter motor.

A further complicating detail in this respect is the fact that the driving pattern of distribution vehicles involves many and frequent stops, which means that the charging of the batteries is ineffective.

The object of the present invention is to make available an arrangement for a hydraulically operated lifting arrangement, by means of which lifting and lowering operations can be performed at a significantly lower level of energy consumption. The manner in which this is made possible in accordance with the invention is for the arrangement to comprise two hydraulic machines acting as a pump/motor and operatively connected via their- shafts and in a

„previously disclosed fashion, which machines are reversible, and of which one is connected to the line'between the pressure side of the pimp and the valve, and the other, which is also capable of being regulated, is connected in parallel with the pump. The arrangement in accordance with the invention causes energy to be fed back into the pressure accumulator as a load is lowered. This accumulated energy can be utilized at any time to perform a lifting operation.

The invention is described in greater detail below with reference to the accompanying drawing, which illustrates in schematic form the construction of an arrangement in accordance with the present invention. Omitted from the drawing and from the following specification are those details which are self—evident to an expert, such as throttles, pressure relief valves, and other safety features. In spite -of the fact that the invention is described below in relation to a specific application, in this case a so—called tail lift, it is obvious that the invention must not be regarded as being restricted to this application. _τ0n the contrary, the invention is capable of being used in -all those applications in which hydraulics are used for the lifting and lowering of a load, for example in a hydraulic truck.

The designation 8 is used in the drawing in respect of a hydraulically operated cylinder/piston unit with two cylinders, the piston rods of which are operatively connected in a conventional, manner, which is accordingly not represented in detail, to a load-carrying platform for the purpose of lifting and lowering same. The piston/cylinder unit 8 is connected via a hand valve 7 to the pressure side of a hydraulic pump 2 by means of a hydraulic line 10, which pump communicates on its suction side with a hydraulic tank 3 via a hydraulic line 11. Manual actuation of the lever 12 of the hand valve 7 determines which of the two cylinder/piston units 8 shown in the drawing is to be selected and is to represent tipping or lifting/lowering of the load— arrying platform.

The pressure side of the pump 2 communicates with a hydraulic accumulator 6 via a line 13 connected to the line 10. Also present in accordance with the invention are two reversible hydraulic machines 4, 5 capable of acting as a pump/motor, which machines are operatively connected to one another via their shafts 14. The fact that the hydraulic machines are reversible is indicated in the Figure by means of a bi-directional rotating arrow 15. The pump/motor machine 5 is connected to the line 10 between the pressure side of the hydraulic pump 2 and the valve 7.

The pump/motor machine 4 is capable of being regulated, that is to say its displacement can be varied, and is connected in parallel with the hydraulic pump 2 by means of a hydraulic line 16, which is thus connected to the lines 10 and 11. A hydraulic machine which is capable of being regulated in this way may, for example, be an axial piston pump/motor, the pressure disc of which has a variable operating angle.

The hydraulic pump 2 is operatively connected via its shaft 17 with a drive arrangement 1 so arranged as to drive the shaft 17 of the pump round in a direction such as is illustrated with a rotating arrow 18. The drive arrangement 1 is, for example, an electric motor supplied with energy from the vehicle battery a hydraulic motor connected in the hydraulic system of the vehicle, or even the drive motor of the vehicle.

In order automatically to maintain a certain pressure inside the pressure accumulator 6, a pressure sensor 9 is connected in the line 10. The pressure se sor 9 is so arranged as to cause the pump 2 to operate in order to increase the pressure inside the pressure accumulator 6 when a predetermined first pressure value is .no achieved, and as to stop the pump 2 when a second pressure value has been reached. It is obvious that the latter is greater than the first pressure value. In the event of the drive arrangement being an electric motor, actuation takes place from the pressure sensor -9 via a contactor (not illustrated in the drawing) connected between the vehicle battery and the drive arrangement. If the drive arrangement 1 is a hydraulic motor connected to the hydraulic system of the vehicle, actuation from the pressure sensor 9 can take place via a solenoid valve, or via a coupling (not referred to in more detail) connected on the shaft 17 between the drive arrangement 1 and the hydraulic pump 2. The last—mentioned actuation is also applicable in the case in which the hydraulic motor 2 is driven by the main drive engine of the vehicle.

What is achieved through the arrangement in accordance with the invention is that at least a part of the potential energy possessed by a load which is to be lowered can be transferred to and stored in the pressure accumulator 6. The arrangement in accordance with the invention operates in the following manner:

Hydraulic fluid is pumped with the help of the hydraulic pump 2 from the tank 3 into the pressure accumulator 6 until the pre— etermined pressure is reached. Once this pressure has been reached, the pumping function of the hydraulic motor is stopped by the effect of the pressure sensor 9. In order to lift a load which has been placed on the load—carrying platform, the hydraulic machine 4 is caused to operate as a motor, in which case hydraulic fluid flows from the pressure accumulator 6, via the lines 10 and 16 to the hydraulic tank 3. This hydraulic flow thus drives the hydraulic machine 4, which in turn, via the shaft 14, drives the hydraulic machine 5 so that a pressure increase is obtained in the line 10 to the cylinder/piston unit 8. If the load were to be small, and if the rate of lifting were to be too great, the lifting movement would be braked by the hydraulic machine 5 being caused to operate as a pump, in which case hydraulic fluid is pumped from the hydraulic tank 3 to the accumulator 6. Effective and accurate regulation of the rate of lifting is achieved in this way. This regulation is associated with relatively speaking very small losses. In the event of the load which is to be lowered balancing the pressure inside the accumulator- 6, the hydraulic machine 4 is re—set to its neutral position, and the hydraulic flow can pass through the hydraulic machine 5 with minimal losses. If the weight of the load were to be such as to exceed the pressure inside the accumulator, then the variable hydraulic machine 4 would be caused to operate as a motor, as described above, driven by a hydraulic flow from the accumulator 6 to the hydraulic tank 3, in which case a pressure increase would be obtained across the hydraulic machine 5, which would now operate as a pump.

When a load ^' which is heavier than the pressure 1 inside the accumulator 6 is lowered, the hydraulic machine 4 acts as a brake for the lowering motion, in which case hydraulic fluid is pumped from the tank 3 into the accumulator 6. The rate of lowering can be adjusted accurately in this way by controlling the regulation of the hydraulic machine 4. If the load which is to be lowered is unable to overcome the pressure inside the accumulator 6, the hydraulic machine 4 will be caused to operate as a motor, as described above, driven by a hydraulic flow from the pressure accumulator 6 to the tank 3, thereby causing the hydraulic machine 5 to operate as a pump and to increase the pressure above the value existing inside the pressure accumulator. Accordingly, it is the regulation of the hydraulic machine 4 in such a way as to cause it to act as a pump or as a motor which indicates the direction of movement of the piston of the cylinder/piston unit 8, that is to say which determines whether the cylinder/piston unit 8 will describe a lifting movement or a lowering movement.

Claims

Pa tent C l a i m

Arrangement for a hydraulically operated lifting arrangement, for example a so—called tail lift, comprising at least one cylinder/ piston unit C8) for actuating a lifting platform, which unit is connected via a hand valve (7) to the pressure side of a pump ⁽2) by means of a hydraulic line C10), which pump communicates on its suction side with a hydraulic tank (3), and on its pressure side with a pressure accumulator (6), c h a r a c t e r i z e d in that the arrangement comprises two hydraulic machines (4, 5) acting as a pump/motor and operatively connected via their shafts (14) and in a previously disclosed fashion, which machines are reversible, and of which one (5) is connected to the line (10) between the pressure side of the pump (2) and the valve (7), and the other (4), which is also capable of being regulated, is connected in parallel with the pump (2).