EP0719201A1

EP0719201A1 - Hydraulic system

Info

Publication number: EP0719201A1
Application number: EP94927887A
Authority: EP
Inventors: Jerzy Janczak
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 1993-09-16
Filing date: 1994-09-05
Publication date: 1996-07-03
Also published as: SE501941C2; SE9303017D0; ZA947108B; WO1995007801A1; SE9303017L; AU7712494A

Abstract

A hydraulic system for operating a working device, such as a hand tool, at a distance from a hydraulic-oil pressure source, wherein the working device is driven by means of a single-acting hydraulic cylinder. To enable the hydraulic cylinder to be connected by means of one single line, the system includes a valve (17) which is connected to the pressure source (10), with associated tank (8), and which has a pressure port for receiving hydraulic oil from the pressure source (10) and a return port for delivering return oil to the tank (8), and a working port for delivering hydraulic oil to and receiving return oil from the hydraulic cylinder through the medium of one single, common pressure-and-return line connected between the valve and the cylinder. The valve (17) is adapted to be controlled by the inlet pressure acting on a valve slide which can be adjusted positionally against a spring tension force, such that when the valve slide is in a rest position, i.e. at low inlet pressure, the working port will communicate with the return port, whereas when the inlet pressure is increased the slide setting is adjusted against the action of spring biassing force so that the working port will communicate with the pressure port. This enables the hydraulic cylinder to be driven by one single line (6) and to be controlled by the pressure applied on the valve (17).

Description

HYDRAULIC SYSTEM

The present invention relates to a hydraulic system for operating a working device, such as a hand-held tool, which is located at a distance from a hydraulic-oil pressure source and which is driven by a single-acting hydraulic cylinder, wherein the hydraulic system in order to enable the hydraulic cylinder of the working device to be connected to the system by means of a single supply line, includes a valve which is connected to the pressure source which has an associated tank. The valve includes a valve chamber which has a pressure port for receiving hydraulic oil from the pressure source and a return port for delivering return oil to the tank, and a working port for delivering hydraulic oil to and receiving return oil from the hydraulic cylinder through the medium of a common pressure-and-return line connected between the valve and the cylinder.

Hydraulic systems have long been used in the performance of many different types of working and maneuvering operations, and are also being used to an ever increasing extent in the operation of manual tools of different kinds. It is important in this latter case that the equipment can be used easily, i.e. that the working movements are guided by simple means and that the tool has good maneuverability. It is particularly important in the case of tools fitted to long shafts or handles that the handle can be moved easily in the required manner and that the working movements of the tool can be controlled and guided without the tool operator needing to release his hold on the tool handle. Furthermore, it is necessary for the hydraulic-oil delivery line between the handle and the hydraulic-oil pressure source to be simple and constructed so as to minimize the risk of injury from the high oil pressure.

CH-A5-330590 describes a hydraulic system which includes several moveable parts and which requires the simultaneous activation of two different devices in order to achieve the desired function.

The main object of the present invention is to provide a simple hydraulic system which can be used with hand-held tools, including tools fitted on long handles, and which will enable the tool to be maneuvered with one hand and which includes the least possible number of parts, particularly moveable parts and sealing surfaces and lead-throughs or throughlets.

According to the invention, a hydraulic system of the kind defined in the first paragraph is mainly characterized in that the valve is adapted to be controlled automatically by the inlet pressure that acts on a pressure-controlled valve slide which is mounted in the valve chamber and which can be adjust¬ ed positionally against the action of a biassing spring, such that when in a rest position, i.e. at low inlet pressures, the slide will hold the pressure port closed while the working port communicates with the return port, whereas at higher inlet pressures the position of the valve slide is adjusted against the spring tension to a position in which the working port communicates with the pressure port and the return port is closed.

Such a hydraulic system will enable, for instance, a handle- mounted tool to be connected to the pressure source by means of one single line which will delivers high-pressure oil only during the actual working stage. The tool can also be con- trolled by a switching on and off a hydraulic pump which thus need only generate a high pressure during the actual working stage. This lowers the extent to which the oil is heated and reduces the need for additional tank volume for the purpose of cooling the oil. Furthermore, the hydraulic system obviates the need of a complicated, heavy valve assembly for the switching of a high oil pressure. The hydraulic pump may be switched on and off with the aid of a speed-dependant coupling, conveniently a so-called centrifu¬ gal clutch, connected between the pump and the pump drive motor. The pump may also be switched on and off by control- ling the speed of the drive motor, which in the case of an internal combustion motor, or engine, may be effected with the aid of a gas throttle mounted on an operating shaft.

The hydraulic cylinder of the working device is conveniently provided with spring return means.

The pressure dependant valve may conveniently be mounted directly on the hydraulic pump with the pressure port connected to the pump outlet and the return port connected to the tank to which the pump is coupled. This provides a very compact unit.

The valve pressure port is suitably in the form of a hollow screw which can be screwed firmly into the pump outlet so as to firmly attach the valve to the pump while providing a direct flow connection between the pressure port and the pump outlet.

An extremely compact unit can be obtained by immersing the pump and the valve in the oil contained in the tank, the tank preferably being fully closed and provided with a filling opening located in a position which will prevent the tank from being filled completely.

Such a compact unit is very light in weight and can be readily handled by the tool operator. The unit also has only one external hose connection, which results in a readily handled and flexible unit.

The invention will now be described in more detail with refer¬ ence to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which Figure 1 illustrates the use of a hand tool provided with an inventive hydraulic system;

Figure 2 illustrates the drive motor and hydraulic pump used in the hydraulic system shown in Figure 1;

Figure 3 is a view corresponding to the view of Figure 2 but with the end-connection of the oil tank removed;

Figure 4 is a partially sectioned side-view of part of the equipment shown in Figure 2;

Figures 5 and 6 are vertical sectional views of a valve used in the embodiment illustrated in Figure 4, said valve being shown in two different states;

Figure 7 is a side view of the tool included in the equipment shown in Figure 1;

Figures 8 and 9 are partial sectioned views of the tool illustrated in Figure 7 and show the tool in two different working stages;

Figures 10 and 11 illustrate the tool shown in Figure 7 from above and from beneath respectively; and

Figures 12 and 13 illustrate fitting of a part of the tool illustrated in Figure 7.

Figure l illustrates a workman 1 cutting high branches from a tree with the aid of a pruning tool 3 fitted to a long handle 2. The workman carries an internal combustion engine 4 and a hydraulic pump fitted thereto, for operating the tool. The hydraulic pump is connected to the tool 3 by means of a single hose or delivery line 5, the the majority of which extends inside the handle 2, the tool being driven by a single-acting hydraulic cylinder in which the piston is returned by a spring. The workman is able to adjust the engine or motor speed by means of a throttle control 6 which is connected to the engine 4 by a throttle cable 7. Connected between the engine output shaft and the hydraulic pump is a speed-dependent coupling which will ensure that the pump is not activated until a predetermined speed is reached. The workman 1 is thus able to control the working strokes of the tool 3 with the aid of the throttle control 6.

The simple connection of the hydraulic pump to the tool shown in Fig. 1 is achieved because the hydraulic hose 5 is used both as a pressure line and as a return line during different working stages. Thus, that part of the line which lies adjacent the body will solely transfer oil under high pressure and for very short working periods, which greatly reduces the risks of accidents. Neither is the system subjected to high pressures in any other respect and the system is essentially pressurelesε with the exception of when the tool is at work.

Figs. 2 and 3 illustrate the internal combustion engine 4 and a thereto connected housing 8 on which there is fitted an end- connection 9, which has been removed in the Fig. 3 illustra¬ tion. The housing 8 serves as a tank for hydraulic oil and encloses a hydraulic pump 10 which is immersed in the oil and which is provided with a pressure-controlled valve 17.

As will be seen from the sectioned view of Figure 4, a centrifugal clutch 12 (shown schematically) is arranged between the engine or motor 4 and the drive shaft 13 of the hydraulic pump 10. The drive shaft 13 is terminated in the form of a non-round pin which fits with a given clearance in a corresponding opening in a coupling sleeve 14 driven by the centrifugal clutch 12 and journaled by means of a ball bearing 15. This arrangement reduces the needs for accurate alignment of the engine drive shaft with the pump drive shaft. The pump 10 is fully immersed in the oil 11 in the tank 8 and sucks in oil through an inlet 16, see Figures 5 and 6, and delivers hydraulic oil, i.e. pressure oil, to the pump-mounted valve 17. This valve is provided with a working port 26 having a connector nipple 18 which is joined to the line 5, see Figure 2, through which hydraulic oil is delivered to the tool and return oil passes from the tool to the tank or reservoir. Oil returned to the valve 17 passes therefrom to the tank through an outlet 19. The oil-filling opening 20 on the tank 8 is located at a level such as to prevent the tank from being filled completely. The tank will therefore always be able to accommodate return oil. Because the tank is completely closed, the tank will be placed under a certain subpressure when oil is taken therefrom during a working stroke. This facilitates the return of oil to the tank and also facilitates return movement of the piston in the hydraulic system-cylinder device upon completion of a working stroke.

Because the hydraulic pump 10 and the valve 17 are both disposed in the oil tank, the unit shown in Figure 4 is very compact. The construction is further simplified by virtue of the valve 17 (see Figures 5 and 6) being mounted directly on the pump 10 by means of a hollow screw 21, which is screwed directly into the pump outlet. The screw 21 thus functions as a valve mounting device and also as an inlet port 22 to the valve chamber 23, in which a slide 24 can be moved against the action of a biassing spring 25. The valve chamber 23 is also provided with the return port 19 and the working port 26 to which the connector nipple 18 of the line 5 is connected.

The system works as follows: when the engine 4 runs at a speed which is below the speed at which the centrifugal clutch 12 is activated, the pump 10 will be at rest. The valve slide 24 will then be located in its rest position, shown in Figure 5, in the absence of high pressure on the port 22. The working port 26 is therewith connected directly to the return port 19 via the valve chamber 23, which means that the system is essentially pressureless, wherein the tool 3 is held in its starting position by a return spring acting on the piston of an associated cylinder device.

When the workman increases the engine speed by adjusting the throttle setting, the centrifugal clutch 12 will be activated and therewith activate the pump 10 so that oil under high pressure is delivered to the valve chamber 23 through the port 22. This pressure causes the valve slide 24 to move to the position shown in Figure 6 against the action of the spring

25. The port 22 is therewith connected to the working port

26, causing oil under pressure to be delivered to the tool 3 for the execution of a working stroke. When the workman slackens on the throttle, the pump 10 will stop and the return spring 25 will return the valve slide 24 to its starting position immediately the pressure falls to beneath a predeter¬ mined value, suitably beneath 1-3 bars. This results in reopening of the return connection between the working port 26 and the return port 19.

The aforedescribed valve 17 mounted on the pump 10 provides a very compact construction and eliminates the need for filters and like devices, since the entire unit is encapsula- ted and immersed in the oil. The requirement of only one single lead through to an external line also minimizes the risk of leakage. However, if desired, the valve 17 can be replaced with a separate valve the pressure port and return port of which can be connected to a hydraulic pump and to an associated tank respectively by means of conventional lines, while connecting the working port to the tool concerned by means of one single line in the aforedescribed manner.

Figure 7 is a side view of the tool 3 shown in Figure 1 when used as a pruning tool. The tool includes a reciprocatingly moveable knife 31 which coacts with a pad 33 fitted to a fixed anvil 32, the pad 33 being made of a softer material than the knife so as to enable thin fibers to be severed.

As shown in Figures 8 and 9, the tool is driven by the piston 25 of a hydraulic cylinder 34. The piston is activated by hydraulic oil delivered to the device 34 through the hose 5 enclosed in the handle 2, in accordance with Figure 1.

Figure 8 shows the cylinder in a pressureless state, with a branch 36 located between the knife 31 and the pad 33.

Figure 9 illustrates the tool at the end of a working stroke, wherewith hydraulic oil has moved the piston 35 so as to press the knife 31 against the pad 33 while severing the branch 36. During the process, energy has been stored in the return spring 37 mounted between the cylinder housing 34 and the piston 35, this spring drawing the knife back to its starting position in preparation for the next working operation, when the hydraulic pressure falls.

The knife 31 is pivotally attached to the top of the piston 35 by means of a hinge pin 28. The hinge pin 28 fits relatively loosely into a corresponding hole in the piston, so that force transmission from the piston to the knife 31 will take place essentially through the medium of mutually coacting surfaces 37 on the top of the piston and on the knife. As the knife 31 moves forwards it is guided by a channel defined by two mutually joined side pieces 38 and 29 that form the frame bar 40, as clearly shown in Figures 10-13. The knife 31 is restrained against vertical movement in the channel with the aid of two pins 41, 42 which pass through corresponding holes in the knife 31 and which are guided in longitudinally extending grooves 43, 44 provided in respective sidepieces 38, 39. This provides for stable guidance of the knife 31 without risk of the knife jamming or fastening along the channel. The grooves 43 and 44 are kept clean by the pins 41 and 42 as they move in the grooves, any scrap that might be deposited in the grooves being pressed therefrom by the pins at the rounded ends of the grooves, see the enlarged illustration in Figure 9.

Figures 12 and 13 illustrate the simple manner in which the knife 31 is mounted, thereby enabling the knife to be quickly replaced if required. Prior to mounting the knife, the pad 33 which functions as an additional anvil plate is removed and the knife 31 is then moved in the position shown in Figure 12 to a position closely adjacent the anvil 32. A pin 41 is then inserted through a hole 45 in the sidepieces 38 and 39, which in this position are located opposite one of a pair of mounting holes 46 in the knife 31. The knife 31 is then rotated anti-clockwise and positioned with its other mounting hole opposite the hole 45, see Figure 13, whereafter the other pin 42 is inserted into this mounting hole. The knife is then moved to the end of the piston 35 and connected thereto with the aid of the aforesaid mounting pin 28, which is inserted through a slightly oversized hole in the knife.

In addition to its use as a conventional pruning tool or secateurs, the device can also be used as a forest clearing or forest cleaning tool, a tree delimbing tool or for similar work. Both the knife and the anvil can be replaced with other tool-parts for carrying out other types of work.

However, the inventive hydraulic system can be used in many other contexts irrespective of the construction of the tool. Because the system uses a single-acting hydraulic cylinder it must be seen that means are provided for returning the piston. This can be achieved with the aid of a spring force, as shown, or by some other returning force, such as the force of gravity. The piston may also be returned manually. As will be understood, the hydraulic system may also be used in conjunction with maneuvering and operating devices and like devices in addition to the tool. It will also be understood that the afore described and illus¬ trated exemplifying embodiment of an inventive hydraulic syst¬ em can be modified in several ways within the scope of the following claims. For instance, the hydraulic pump can be driven by some other form of motor, for instance an electric motor, or the hydraulic pressure can be obtained through the medium of some other activatable and deactivatable pressure source. Neither need the pump or valve be enclosed in the tank, but may be separated therefrom in a conventional manner. The valve may also be integral with the pump. Although the drive unit is shown to be carried by means of a harness it will be understood that the unit may be moved around in some other way, for instance hanging from a raisable and lowerable working platform.

Claims

1. A hydraulic system for operating a working device, such as a hand-held tool (3) which is located at a distance from a hydraulic-oil pressure source and which is driven by means of a single-acting hydraulic cylinder (34) , wherein in order to enable the hydraulic cylinder (34) of the working device to be connected by one single line the hydraulic system includes a valve (17) which is connected to the pressure source (10) , having an associated tank (8) , and which includes a valve chamber (23) which has a pressure port (22) for receiving hydraulic oil from the source (10) and a return port (19) for delivering return oil to the tank (8) and a working port (26) for delivering hydraulic oil to and receiving return oil from the hydraulic cylinder (34) through the medium of one single, common pressure-and-return line (5) connected between the valve and the cylinder, characterized in that the valve (17) is adapted to be controlled automatically by the inlet pressure which acts on a pressure-controlled valve slide (24) which is mounted in the valve chamber (23) and which can be adjusted positionally against the action of a biassing spring, such that in its rest position, i.e. at a low inlet pressure, the slide (24) will hold the pressure port (22) closed with the working port (26) communicating with the return port (19) , and such that when the inlet pressure increases, the valve slide (24) is moved against a spring bias such that the working port (26) will communicate with the pressure port (22) while the return port (19) is closed.

2. A hydraulic system according to claim 1, characterized in that the valve (17) is mounted directly on a hydraulic pump (10) with the pressure port (22) connected to the pump outlet and the return port (19) connected to the pump-connected tank (8).

3. A hydraulic system according to claim 2, characterized in that the pressure port (22) of the valve has the form of a hollow screw (21) which can be screwed firmly into the pump outlet and therewith secure the valve (17) firmly on the pump and providing direct flow connection between the pressure port and the pump outlet.

4. A hydraulic system according to claim 2 or 3, character¬ ized in that the pump (10) and the valve (17) are emersed in the oil contained in the tank (8) .

5. A hydraulic system according to any one of claims 2-4, characterized in that the tank (8) is completely closed and provided with a filling opening (20.) which is located so as to prevent the tank from being completely filled.

6. A hydraulic system according to any one of claims 1-5, characterized in that the hydraulic pump (10) can be switched on and off to control the working strokes of the hydraulic cylinder (34) .

7. A hydraulic system according to any one of claims 1-6, characterized in that the system includes a pump (10) driven by an internal combustion engine (4) , and a speed-dependant coupling (12) , suitably a so-called centrifugal clutch, mount¬ ed between the engine output shaft and the pump, so as to enable the working strokes performed by the hydraulic cylinder (34) to be controlled in dependence on engine speed.

8. A hydraulic system according to any one of claims 1-7, characterized in that the hydraulic cylinder (34) driving the working device is provided with spring return (37) .

9. A hydraulic system according to claim 9, characterized in that the hydraulic cylinder (34) is mounted on one end of a tool maneuvering handle (2) ; and in that the single line (5) connected to the cylinder is housed in the handle.

10. A hydraulic system according to claim 8 or 9, character¬ ized in that the working device (3) is pivotally connected to the piston (35) of the hydraulic cylinder (34) ; and in that the device is guided in a channel provided in a frame bar (40).