System for handling a tool at a vehicle

The invention relates to a system for handling an implement on a vehicle which comprises a frame. The system comprises a lifting apparatus arranged between the frame and the implement for raising and lowering the implement in relation to the frame, a pump (11) coupled to the lifting apparatus for supplying this with a fluid in order to produce said movements, and an operating valve (10) arranged between the pump and the lifting apparatus for controlling the flow of said fluid to the of said fluid to and from the lifting apparatus. The system further comprises a control device (9) which is designed to disconnect the control of the lifting apparatus via said fluid. The control device is coupled in such a way to an operating element 814) arranged in the vehicle cab (13) that control of the control device via the operating element is permitted independently of the control of the operating valve.

This application is a continuation of International Application No. PCT/SE2003/001808, filed Nov. 19, 2003, which claims priority to Swedish Application No. 0203414-8, filed Nov. 19, 2002, both of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a system for handling an implement on a vehicle which comprises a frame, the system comprising a lifting apparatus arranged between the frame and the implement for raising and lowering the implement in relation to the frame, 'a pump coupled to the lifting apparatus for supplying this with a fluid in order to produce said movements, and an operating valve arranged between the pump and the lifting apparatus for delivering said fluid to the lifting apparatus and evacuating it therefrom.

The invention will be described below in connection with a machine in the form of a wheeled loader. This is a preferred, but in no way restrictive application of the invention.

A wheeled loader is equipped with a lifting apparatus in the form of a load arm assembly for raising/lowering the implement. The load arm assembly in turn comprises a number of hydraulic cylinders for undertaking said movement of the implement. The implement may consist for example of a load shovel or excavator blade.

In certain operating situations there is a need to disconnect the hydraulic control of the lifting apparatus in order to allow the implement to follow the ground with a force corresponding to its own weight and accordingly to remain unaffected by the vehicle hydraulic system. This will hereinafter be referred to as the free-floating function.

DESCRIPTION OF THE PRIOR ART

According to a known solution for obtaining the free-floating function, this function is achieved by means of the operating valve. The free-floating function may be said to be integrated into the operating valve. A number of servo valves are coupled to the operating valve which, in response to a signal that free-floating is required, control the operating valve in such a way that connections of the hydraulic cylinders are coupled to a tank via the operating valve. However, this is associated with certain problems; it has a negative effect on the maximum slide deflection for lowering of the implement and the free-floating function may interfere with other functional characteristics of the operating valve.

SUMMARY OF THE INVENTION

An object of the invention is to provide a system for handling an implement which will lead to increased operating reliability.

This object is achieved in that the system comprises a control device which is designed to disconnect the control of the lifting apparatus via said fluid, and in that the control device is coupled in such a way to an operating element arranged in the vehicle of cab that control by the control device via the operating element is permitted independently of the control of the operating valve.

The operating valve is therefore disengaged from controlling the lifting apparatus when free-floating is required and free-floating is instead achieved via said control device. By disconnecting the control via said fluid, the lifting apparatus can instead be disconnected in such a way that the only force acting on the implement is its own weight.

According to a preferred embodiment the control device is coupled to ports of the lifting apparatus for the supply and evacuation of said fluid in order to connect the ports to atmospheric pressure in the event of disconnection. The control device preferably ensures that all ports of the lifting apparatus are connected to atmospheric pressure. The ports are suitably coupled to a tank.

According to another preferred embodiment the control device comprises a first control valve. The first control valve is connected between the operating valve and the lifting apparatus in the circuit for said fluid in order to achieve said disengagement of the operating valve.

According to a development of the preceding embodiment the control device comprises a second control valve. The second control valve is connected between the operating element and the operating valve and connected to the first control valve.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a side view of a wheeled loader1. The wheeled loader1has an implement2in the form of a shovel, which can be raised and lowered in relation to the vehicle frame3, and more specifically the front part thereof, via a lifting apparatus4. The lifting apparatus4here consists of a load arm assembly and comprises two hydraulic cylinders5,6, each of which is connected at one end to the front vehicle part3and at its other end to a beam7on the load arm assembly.

The shovel2can furthermore be tilted in relation to the load arm assembly via a third hydraulic cylinder8, which is connected by one end to the front vehicle part3and by its other end to the shovel2via a linkage system.

Various embodiments of a system for the handling of an implement of the wheeled loader1are described below with reference toFIGS. 2 to 7. The description relates more specifically to a system which allows the hydraulic control of the lifting apparatus to be disconnected in order to allow the implement to follow the ground with a force corresponding to its own weight and accordingly to remain unaffected by the vehicle hydraulic system. This will be referred to below as the free-floating function.

FIG. 2illustrates a system9for handling of the implement. The system9comprises an operating valve10, which is hydraulically connected to the hydraulic cylinders5,6and to a pump11and tank12for supplying the hydraulic cylinders with a hydraulic fluid via a hydraulic circuit. According to this embodiment the operating valve10comprises only one slide.

The vehicle engine24drives said pump11for supplying the hydraulic system. The hydraulic system is of load-sensing type, which means that the pump11only delivers oil when and where it is required. The pump11senses the pressure from the hydraulic cylinders and subsequently adjusts to a pressure which is a specific number of bar higher than the pressure in the cylinders.

The system9further comprises an operating element14arranged in the cab13of the wheeled loader1and intended for manual operation by the driver. The operating element14consists of a control, such as a lever or a button in the cab. The system9further comprises a control device15which is designed to disconnect the control of the lifting apparatus, and more specifically the hydraulic cylinders5,6, by way of said fluid. The control device15is coupled to the operating element14in such a way that control by the control device via the operating element14is permitted independently of the control of the operating valve10. The hydraulic cylinders5,6are accordingly disconnected from control via the operating valve10and are controlled via the control device15.

The control device15comprises a first control valve16which is operatively connected in parallel with the operating valve10. The first control valve16is more specifically connected between the operating valve10and the hydraulic cylinders5,6in the circuit for said fluid. In order to achieve the free-floating function the hydraulic cylinders5,6are disconnected from control by the operating valve10and are controlled by the first control valve16. The control device15further comprises a second control valve17which is operatively connected between the operating element14and the operating valve10. The second control valve17is moreover operatively connected to the first control valve16for controlling the latter. The first and second control valves16,17are hydraulically controlled. The first and second control valves16,17each comprise only one slide.

The method of achieving the free-floating function is as follows: Operation of the operating element14delivers a pressure of 0–18 bar, for example, to the operating valve10via the second control valve17for normal lowering movement of the hydraulic cylinders5,6. This is usually termed “powerdown”. At a first set pressure value of 18 bar, for example, the lever attains a threshold position, in the form of a power index usually termed “prefeeling”. When the operating element14is shifted through this position and beyond, the pressure increases and at a second set pressure value, for example 20 bar, the second control valve17shifts, which means that the control pressure for the slide of the operating valve10is relieved and the slide moves to the neutral position. At the same time a pressure is built up in order to control the first control valve16and at a third set pressure value, for example 25 bar, the valve16shifts, the hydraulic cylinders5,6are connected to a tank, and the free-floating function is achieved.

FIG. 3illustrates a second preferred embodiment of the system109. This is a variant of the first embodiment.

The difference is that the second control valve117of the control device115comprises two slides22,23.

Operating the operating element14delivers a pressure of 0–18 bar, for example, to the operating valve10via the first slide22. At a first preset pressure, for example 18 bar, the first control valve22closes, thereby shutting off the supply of fluid to the operating valve10. At a third preset pressure value, for example 25 bar, the second valve23is opened, which means that a pressure is delivered to the first control valve116via the second slide23. The first control valve116is thereby opened for normal lowering movement of the hydraulic cylinders5,6.

FIG. 4illustrates a system209for handling the implement. According to this embodiment the first and second control valves216,217of the control device215are electrically controlled. This means that the free-floating function can be engaged without first passing through the “powerdown” position. As a result there is no need to expose the underlying surface or the implement being used to large forces before the free-floating function is engaged.

FIG. 5illustrates a system309for handling the implement. According to this embodiment the first control valve316of the control device315and the operating valve110are electrically controlled.

Furthermore, a control unit18, or computer, is electrically connected to the operating element114. The control unit18is also electrically connected to the first control valve216and the operating valve110for controlling these.

An activating element19, suitably in the form of a button or other control, is coupled to the control unit18and arranged in the cab13for operation by the driver of the vehicle. The activating element19enables the driver to choose whether the free-floating function or ordinary lowering function is required. If the activating element19is in the off position the lowering function is operated via the operating element114. In this position the free-floating function cannot be engaged. If the activating element19is in the on position the free-floating function can be activated proportionally via the operating element1114. In this position the lowering function is deactivated. In the extreme position of the operating element, which in the figure consists of a lowering lever, it can also be locked by means of a hold function.

The first valve216may be either of the on-off type or proportional to the lever deflection.

The same control, the operating element1114, is therefore used for operation both of the lowering function and of the free-floating function.

FIG. 6illustrates a system409for handling the implement. The normal lowering movement (that is to say not the free-floating function) is achieved by means of an electrical input signal450to the operating valve (main valve)10. The slide of the main valve10is then moved one step to the left in the drawing. The pump11then delivers a pressure to the first control valve (load-maintaining valve)416. In this embodiment the load-maintaining valve416is connected in series downstream of the main valve10, that is to say between the main valve10and the hydraulic cylinders5,6. The load-maintaining valve416will then be opened, that is to say the slide is shifted to the left in the drawing, via a system of sequence valves (not shown). The sequence valves are more specifically designed so that the left-hand side of the load-maintaining valve416is drained to the tank. The pump pressure is then delivered to the piston rod sides of the hydraulic cylinders5,6.

The piston sides of the hydraulic cylinders5,6are connected the tank12via the main valve10in a line470in parallel with load-maintaining valve416.

In order to achieve the free-floating function, the second control valve417is opened by means of an electrical signal. The second control valve417is directly coupled to the load-maintaining valve416for controlling the latter. The load-maintaining valve416is then closed by the pump pressure via the second control valve417(the slide of the load-maintaining valve is moved back to the right in the drawing). The opening for the pump flow to the hydraulic cylinders5,6will then be closed. Closing of the load-maintaining valve416means that the pump flow can be used for other functions/components in the hydraulic system. The system409comprises an electrically controlled third control valve420coupled to the piston sides of the hydraulic cylinders5,6and to the tank12. The third control valve420is more specifically coupled between the piston sides of the hydraulic cylinders5,6and the tank12. The third control valve420is opened by means of an electrical signal, and the piston rod sides of the hydraulic cylinders5,6are thereby connected to the tank12and the free-floating function is achieved.

An arrangement of non-return valves and a fourth control valve430is located on a line431for a load-sensing signal from another function/component to the pump. This arrangement ensures that if another function/component is used, it is this load pressure that controls the pump.

The first, second and third control valves416,417,420may alternatively be hydraulically controlled.

FIG. 7illustrates a system509for handling the implement. This sixth embodiment differs from the fifth embodiment inFIG. 6in that here the load-maintaining valve416is closed by means of a load-sensing signal531from another function/component. In other words the load-maintaining valve416is closed when the pump11delivers pump pressure to another function/component. In this case the pump11is left to pump to the tank through the main valve10and the load-maintaining valve416when no other function/component in the hydraulic circuit is in use. The second control valve417is accordingly arranged on a line532which delivers a load-sensing pressure from said second function/component for opening/closing this. According to the fifth embodiment the load-maintaining valve3is instead closed by means of the pump pressure. The system according to the sixth embodiment comprises a somewhat different arrangement530of non-return valves and the fourth control valve in order to deliver the load-sensing signal partly to the line532to the second control valve417on the one hand and to the pump11on the other.

In the fifth and sixth embodiments, seFIGS. 6 and 7, the activation of the free-floating function via the operating element has not been shown. This can be done in any of the ways described in the previous embodiments.

The control device15,115,215,315,415,515is accordingly designed to be controlled independently of the operating valve10,110, and thereby designed to be capable of functioning separately from the operating valve. The control device is designed to disconnect the control of the lifting apparatus via said fluid with the aim of providing a free-floating function for the implement.

However, the control device need not necessarily be controlled entirely without actuation of the operating valve10,110. The concept of controlling the control device independently of the operating valve therefore also includes the facility for controlling the operating valve by means of the operating element. The control device is nevertheless designed to be controlled independently, which means that it is shifted/activated independently of what is actually done with the operating valve.

The invention must not be regarded as being limited to the examples of embodiment described above, a number of further variants and modifications being feasible within the scope of the following claims.