GB2033969A - Hydraulically Operated Tilting System for Electrically Driven Vehicles - Google Patents

Abstract

A hydraulically operated tilting system for electrically driven vehicles, preferably trucks, is described, having hydraulically operated working devices, for example lifting devices, steering devices and the like. A control valve (14) therefor is incorporated in a hydraulic system of pipes having a pump means (2) or arranged to coact with pump means. The system of pipes incorporates an accumulator (12) for storing control medium and a device (21) for detecting the pressure in the system of pipes, said pressure- detecting means (21) being arranged to coact with the pump means (2) in a manner such that said pump (2) is activated at a predetermined low pressure value and de-activated at a predetermined high pressure value. A hydraulic piston-cylinder arrangement (20b) having a piston (20c) for activating the tilting device is connected to the system of pipes via a control valve (22). Control medium from the system of pipes (13) is supplied to the hydraulic cylinder (20b) in dependence upon the position to which the control valve (22) is set, thereby to enable said piston-cylinder arrangement to tilt the frame (20a') between two terminal positions. <IMAGE>

Description

SPECIFICATION Hydraulically Operated Tilting System for Electrically Driven Vehicles Field of the Invention The present invention relates to an hydraulically operated tilting system for an electrically driven vehicle, preferably a truck, having hydraulically operated working means, such as lifting means, steering means and the like, and including a control valve incorporated in an hydraulic system of pipes provided with pump means or arranged to co-operate with pump means, said system of pipes having an accumulating device for control medium and a device for detecting pressure in said system of pipes, said pressure-detecting means being arranged to co-operate with the pump means in a manner such that the pump is activated at a predetermined low pressure value and deactivated at a predetermined high pressure value.

Description of the Prior Art Electrically operated trucks of the aforedescribed kind are previously known, these trucks being provided with electrically operated pump means for generating the hydraulic pressure required to drive the lifting devices, steering devices and other functions.

The electrical accumulators of these electrically operated trucks are pre-dimensioned with small tolerances, and it has been found practically impossible to connect and use a continuously operating hydraulic system.

The present invention, however, can only be used advantageously in such trucks which also have a control valve incorporated in a hydraulic circuit including a pump menas or arranged to cooperate with a pump means, said control valve being preferably intended to control the steering device. The hydraulic circuit incorporates an accumulating device or reservoir for the control medium and a device for detecting the pressure in the hydraulic circuit, said pressure-detecting device co-acting with the pump means in a manner such that the pump means is activated at low pressure value and de-activated at a predetermined high pressure value. The control medium reservoir ensures that a control medium of sufficiently high pressure is constantly present in the truck, i.e. a pressure exceeding the low pressure valve which activates the pump means.

With regard to a hydraulic drive for the tilting means associated with the truck, it has previously been proposed that a) if the electrically operated truck has only one heavily dimensioned pump for generating the hydraulic pressure required for lifting means, steering means, etc., this pump is activated with each tilting movement or b) if the electrically operated truck has in addition to the single powerfully dimensioned pump for generating the requisite hydraulic pressure for lifting means and steering means, there is used a small pump solely intended for the tilting function, which is alone activated with each tilting movement.

Summary of the Invention Technical Problem As previously mentioned, the accumulators used are dimensioned with small tolerances and any unnecessary current output must be eliminated. The current output each time the powerfully dimensioned pump is started in accordance with "a" above loads the accumulators to an unnecessarily high degree.

This is the result of a powerful initiating current for each tilting movement.

It is true that this initiating current is reduced when an additional, small pump is used, but the provision of an additional pump with associated equipment requires an additional investment.

Taken together with the installation costs, the provision of this additional pump becomes expensive.

Solution In a hydraulic tilting system at present proposed and intended for an electrically driven vehicle, preferably a truck, having hydraulically operated working devices, for example lifting devices, steering devices and the like and having a control valve incorporated in an hydraulic circuit provided with pump means or arranged to co-act with pump means, said hydraulic circuit having an accumulating device for control medium and a device for detecting the pressure in the hydraulic circuit, said pressure-detecting device being arranged to co-act with the pump means in a manner such that said pump means is activated at a predetermined low pressure value and deactivated at a pre-determined high pressure value (there shall only be used a pump means according to "a" above), the tilting function is connected to the hydraulic circuit comprising the accumulating device for control medium.

Advantages The following advantages are afforded hereby.

Only one pump means is required for ail the hydraulic devices of the truck as a whole. This pump means need not be activated with each tilting movement; the pump means need not be activated until the tilting movements require such small quantities of control medium that the pressure in the hydraulic system falls below the given value.

In addition to a smaller flow consumption, the following advantages are also afforded.

1) Simpler installation, since only one pump means is required.

2) Less maintenance on the associated components.

3) Less sound generated, since the pump means need not be activated for each tilting movement.

4) Simple installation in trucks in which the hydraulic system is already installed.

Brief Description of the Drawings A proposed embodiment of the invention having the characterizing features of the present invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a side view of an electrically operated truck, Figure 2 shows a hydraulic coupling diagram of the devices incorporated in the vehicle, and Figure 3 illustrates schematically the hydraulic tilting system coupled to the hydraulic coupling diagram of Figure 2.

Description In Figure 1 there is illustrated in side view an electrically operated truck 20 having a forward fork-part 20a. This fork-part can be tilted between positions "A" and "B" by means of a hydraulic piston-cylinder arrangement 20b, the piston of said arrangement having a piston rod 20c.

Since the present invention is not directly concerned with the supply of current to the electrically operated drive means or the arrangement including the electrical accumulators, these parts have been omitted from Figure 1 for the sake of simplicity.

It will be understood that the invention can be applied with pneumatically driven devices as well as with hydraulically driven devices, although the invention will hereinafter be described solely with reference to an hydraulically operated system.

Referring now to Figure 2, the hydraulic system according to the invention utilizes an electric motor 1 arranged to drive a hydraulic pump 2, the input side 2a of which is coupled to a tank 4 for control medium via a pipe 3. The output side 2b of the pump is coupled to a control-medium distributing device 6 via a pipe 5. Coupled to the control-medium distributing device 6 are, inter alia, two pipes 7 and 8. The pipe 7 is coupled to a valve 9 arranged to conduct control medium to working cylinder (not shown) associated with the working device. The pipe 8 is a return pipe and extends between the device 6 and the valve 9.

The control-medium distributing device 6 and the valve are connected with a pipe 10 through the pipe 8, said pipe 10 forming the actual return line to the tank 4. The control-medium distributing device 6 also has a connection for a pipe 11 forming part of an hydraulic system utilizing the control means. The pipe 11 co-operates with a device 12 for accumulating control medium, said device 12 being connected through a pipe 1 3 with a control valve associated with the actual control arrangement. The control valve is referenced 14 and comprises a valve sold under the designation "Orbitol" DSP-160. This valve can be regulated and the extent of vehicle steering wheel movement is determined by the valve.The valve is regulated so that when in a neutral positon, i.e. when the wheels are set for the vehicle to be driven in a straight line, the passage of working medium through the control valve 14 is blocked. Thus, the distributing device 6 is constructed so that pressure can build up upstream of the control valve 14. Pipes 1 5 and 1 6 extend from the control valve 14 to the control cylinder 1 7 incorporated in the hydraulic system of the steering apparatus. The piston 18 actuates linkages (not shown in Figure 1) for setting the position of the vehicle wheels or for determining the extent of wheel movement. A pipe 1 9 is also connected from the control valve 14 to the tank 4.

Oil fed back from the control cylinder 1 7 passes through the valve 14 to the tank 4 via the pipe 19.

As will be seen from Figure 2, one and the same hydraulic pump 2 serves both the steering apparatus and the working device.

A more detailed description of the components of said hydraulic coupling system is found in the US patent specification number 3 992 882, granted November 23, 1976.

In accordance with the characterizing features of the present invention, as can best be seen from Figure 3, there is connected to the system of pipes 11, 12, 13 in Figure 2 via a control valve 22 a hydraulic piston-cylinder device 20b whose piston 20c with associated piston rod co-acts with the tilting frame 20a'. Control medium is supplied to the cylinder 20b from the system of pipes via the pipe 1 3 in dependence upon the position to which the control valve 22 is set. The setting of control valve 22 is effected by means of a manually operated lever 22a.

The system of pipes also incorporate a device for detecting the pressure in the said system, said device being referenced 21 and being arranged within the control-medium distributing device 6.

The device 21 is described in more detail in the aforementioned US patent.

Although the control valve 22 has not been shown in detail, it will be understood that said valve is of such nature that in dependence upon the tilting position of the actuating means 22a there is supplied when increasing tilting angles more and more hydraulic oil under pressure to the cylinder 20b and an increasing force acts on the piston rod 20c.

By moving the lever 22a to the left in Figure 1, the piston 20c will be urged to the left and tilt the frame 28' forwards to the position "A". Similarly, when the lever 22a is moved to the right, the piston 20c is urged to the right and tilts the frame at 28' to the position "B".

Since the valve 22 is of the so-called "closed centre" type, the piston 20c is able to stop at any selected position between the terminal positions "A" and "B" said valve requiring no control medium in the zero position (shown in Figure 3).

The aforedescribed embodiment is exemplary only, and can be modified.

Claims (7)

Claims

1. A fiuid-pressure operated tilting system for electrically driven vehicles, preferably trucks, having fluid-pressure operated working devices, such as lifting devices, steering devices and the like, and having a control valve incorporated in a fluid circuit provided with a pump means or arranged to co-operate with a pump means, said circuit having a reservoir for control medium and a device for detecting the pressure in said circuit, said pressure-detecting device co-operating with the pump in a manner such that said pump is activated at a pre-determined low pressure value and de-activated at a pre-determined high pressure value, characterised, in that connected to the system of pipes via a control valve is a fluid operable cylinder having an associated piston for activating the tilting means, control medium being supplied to the piston-cylinder arrangement from the system of pipes in dependence upon the position to which the control valve is set, thereby to enable said piston-cylinder arrangement to tilt the tilting frame between two terminal positions.

2. A tilting system according to claim 1, characterised in that the control valve is activated by a pivotable lever.

3. A tilting system according to claim 1 or claim 2 characterised in that the control valve is of the so-called "closed centre" type.

4. A fluid-pressure operated tilting system for lifting equipment of electrically operated lift trucks having fluid pressure driven equipment in addition to the tilting system, the vehicle having a fluid pressure supply-line system provided with, or arranged to co-operate with, pump means, the supply-line system having a device arranged to accumulate pressurized working medium and a device for detecting the pressure in the supplyline system, said pressure-detecting device being arranged to activate the pump means when a given low-pressure value is sensed and to deactivate the pump means when a given highpressure value is sensed; the tilting system having a fluid pressure operable cylinder and piston for tilting the lifting equipment, the cylinder being connected to the said circuit via a control valve, pressurized fluid being supplied to the cylinder from the pressurized supply upon operation of the control valve, and thereby causing the piston and cylinder to effect tilting of the lifting equipment.

5. A tilting system according to claim 4 wherein the cylinder is double acting, with a pair of fluid chambers separated by the piston, each chamber being separately connected to the control valve, and the control valve being operable to direct fluid to either chamber as desired.

6. A tilting system according to claim 5 wherein the valve also has a position blocking fluid flow, tilting movement ceasing when the valve is placed in that position.

7. A tilting system substantially as herein described with reference to the drawings.