Patent Publication Number: US-7210395-B2

Title: System for handling a tool at a vehicle

Description:
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, &#39;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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in more detail below with reference to the embodiments shown in the drawings attached, in which 
       FIG. 1  shows a side view of a wheeled loader, 
       FIGS. 2–7  show a first, second, third, fourth, fifth and sixth embodiment of the system. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a side view of a wheeled loader  1 . The wheeled loader  1  has an implement  2  in the form of a shovel, which can be raised and lowered in relation to the vehicle frame  3 , and more specifically the front part thereof, via a lifting apparatus  4 . The lifting apparatus  4  here consists of a load arm assembly and comprises two hydraulic cylinders  5 , 6 , each of which is connected at one end to the front vehicle part  3  and at its other end to a beam  7  on the load arm assembly. 
   The shovel  2  can furthermore be tilted in relation to the load arm assembly via a third hydraulic cylinder  8 , which is connected by one end to the front vehicle part  3  and by its other end to the shovel  2  via a linkage system. 
   Various embodiments of a system for the handling of an implement of the wheeled loader  1  are described below with reference to  FIGS. 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. 2  illustrates a system  9  for handling of the implement. The system  9  comprises an operating valve  10 , which is hydraulically connected to the hydraulic cylinders  5 , 6  and to a pump  11  and tank  12  for supplying the hydraulic cylinders with a hydraulic fluid via a hydraulic circuit. According to this embodiment the operating valve  10  comprises only one slide. 
   The vehicle engine  24  drives said pump  11  for supplying the hydraulic system. The hydraulic system is of load-sensing type, which means that the pump  11  only delivers oil when and where it is required. The pump  11  senses 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 system  9  further comprises an operating element  14  arranged in the cab  13  of the wheeled loader  1  and intended for manual operation by the driver. The operating element  14  consists of a control, such as a lever or a button in the cab. The system  9  further comprises a control device  15  which is designed to disconnect the control of the lifting apparatus, and more specifically the hydraulic cylinders  5 , 6 , by way of said fluid. The control device  15  is coupled to the operating element  14  in such a way that control by the control device via the operating element  14  is permitted independently of the control of the operating valve  10 . The hydraulic cylinders  5 , 6  are accordingly disconnected from control via the operating valve  10  and are controlled via the control device  15 . 
   The control device  15  comprises a first control valve  16  which is operatively connected in parallel with the operating valve  10 . The first control valve  16  is more specifically connected between the operating valve  10  and the hydraulic cylinders  5 , 6  in the circuit for said fluid. In order to achieve the free-floating function the hydraulic cylinders  5 , 6  are disconnected from control by the operating valve  10  and are controlled by the first control valve  16 . The control device  15  further comprises a second control valve  17  which is operatively connected between the operating element  14  and the operating valve  10 . The second control valve  17  is moreover operatively connected to the first control valve  16  for controlling the latter. The first and second control valves  16 , 17  are hydraulically controlled. The first and second control valves  16 , 17  each comprise only one slide. 
   The method of achieving the free-floating function is as follows: Operation of the operating element  14  delivers a pressure of 0–18 bar, for example, to the operating valve  10  via the second control valve  17  for normal lowering movement of the hydraulic cylinders  5 , 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 element  14  is shifted through this position and beyond, the pressure increases and at a second set pressure value, for example 20 bar, the second control valve  17  shifts, which means that the control pressure for the slide of the operating valve  10  is 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 valve  16  and at a third set pressure value, for example 25 bar, the valve  16  shifts, the hydraulic cylinders  5 , 6  are connected to a tank, and the free-floating function is achieved. 
     FIG. 3  illustrates a second preferred embodiment of the system  109 . This is a variant of the first embodiment. 
   The difference is that the second control valve  117  of the control device  115  comprises two slides  22 , 23 . 
   Operating the operating element  14  delivers a pressure of 0–18 bar, for example, to the operating valve  10  via the first slide  22 . At a first preset pressure, for example 18 bar, the first control valve  22  closes, thereby shutting off the supply of fluid to the operating valve  10 . At a third preset pressure value, for example 25 bar, the second valve  23  is opened, which means that a pressure is delivered to the first control valve  116  via the second slide  23 . The first control valve  116  is thereby opened for normal lowering movement of the hydraulic cylinders  5 , 6 . 
     FIG. 4  illustrates a system  209  for handling the implement. According to this embodiment the first and second control valves  216 , 217  of the control device  215  are 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. 5  illustrates a system  309  for handling the implement. According to this embodiment the first control valve  316  of the control device  315  and the operating valve  110  are electrically controlled. 
   Furthermore, a control unit  18 , or computer, is electrically connected to the operating element  114 . The control unit  18  is also electrically connected to the first control valve  216  and the operating valve  110  for controlling these. 
   An activating element  19 , suitably in the form of a button or other control, is coupled to the control unit  18  and arranged in the cab  13  for operation by the driver of the vehicle. The activating element  19  enables the driver to choose whether the free-floating function or ordinary lowering function is required. If the activating element  19  is in the off position the lowering function is operated via the operating element  114 . In this position the free-floating function cannot be engaged. If the activating element  19  is in the on position the free-floating function can be activated proportionally via the operating element  1114 . 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 valve  216  may be either of the on-off type or proportional to the lever deflection. 
   The same control, the operating element  1114 , is therefore used for operation both of the lowering function and of the free-floating function. 
     FIG. 6  illustrates a system  409  for handling the implement. The normal lowering movement (that is to say not the free-floating function) is achieved by means of an electrical input signal  450  to the operating valve (main valve)  10 . The slide of the main valve  10  is then moved one step to the left in the drawing. The pump  11  then delivers a pressure to the first control valve (load-maintaining valve)  416 . In this embodiment the load-maintaining valve  416  is connected in series downstream of the main valve  10 , that is to say between the main valve  10  and the hydraulic cylinders  5 , 6 . The load-maintaining valve  416  will 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 valve  416  is drained to the tank. The pump pressure is then delivered to the piston rod sides of the hydraulic cylinders  5 , 6 . 
   The piston sides of the hydraulic cylinders  5 , 6  are connected the tank  12  via the main valve  10  in a line  470  in parallel with load-maintaining valve  416 . 
   In order to achieve the free-floating function, the second control valve  417  is opened by means of an electrical signal. The second control valve  417  is directly coupled to the load-maintaining valve  416  for controlling the latter. The load-maintaining valve  416  is then closed by the pump pressure via the second control valve  417  (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 cylinders  5 , 6  will then be closed. Closing of the load-maintaining valve  416  means that the pump flow can be used for other functions/components in the hydraulic system. The system  409  comprises an electrically controlled third control valve  420  coupled to the piston sides of the hydraulic cylinders  5 , 6  and to the tank  12 . The third control valve  420  is more specifically coupled between the piston sides of the hydraulic cylinders  5 , 6  and the tank  12 . The third control valve  420  is opened by means of an electrical signal, and the piston rod sides of the hydraulic cylinders  5 , 6  are thereby connected to the tank  12  and the free-floating function is achieved. 
   An arrangement of non-return valves and a fourth control valve  430  is located on a line  431  for 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 valves  416 , 417 ,  420  may alternatively be hydraulically controlled. 
     FIG. 7  illustrates a system  509  for handling the implement. This sixth embodiment differs from the fifth embodiment in  FIG. 6  in that here the load-maintaining valve  416  is closed by means of a load-sensing signal  531  from another function/component. In other words the load-maintaining valve  416  is closed when the pump  11  delivers pump pressure to another function/component. In this case the pump  11  is left to pump to the tank through the main valve  10  and the load-maintaining valve  416  when no other function/component in the hydraulic circuit is in use. The second control valve  417  is accordingly arranged on a line  532  which delivers a load-sensing pressure from said second function/component for opening/closing this. According to the fifth embodiment the load-maintaining valve  3  is instead closed by means of the pump pressure. The system according to the sixth embodiment comprises a somewhat different arrangement  530  of non-return valves and the fourth control valve in order to deliver the load-sensing signal partly to the line  532  to the second control valve  417  on the one hand and to the pump  11  on the other. 
   In the fifth and sixth embodiments, se  FIGS. 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 device  15 , 115 ,  215 , 315 ,  415 , 515  is accordingly designed to be controlled independently of the operating valve  10 , 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 valve  10 , 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.