Abstract:
A tree felling machine has a main pump for operating functions of the machine such as the drive wheels or tracks, the steering, the brakes, and the lifting and extension of the boom, and a separate saw pump for driving the cutting element, for example, a circular disc saw driven by a hydraulic motor. Both pumps are driven by the same prime mover, i.e. the same internal combustion engine, and the power division between the two pumps is determined by the operator and by the hydraulic control system. In particular, a control provided in the cab is controllable by the human operator to limit the maximum power that the saw pump can draw from the prime mover. In addition, the power that the saw pump can draw from the prime mover is limited by a combination of the displacement setting of the main pump, the output pressure of the saw pump, and the pressure exerted on the load by the main pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This claims the benefit of U.S. Provisional Patent Application No. 60/560,494 filed Apr. 8, 2004. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       FIELD OF THE INVENTION  
       [0003]     This invention relates to fellers for cutting down trees, and in particular to a hydraulic control system for a tree feller for managing the division of power available for the cutting and other functions of the feller.  
       BACKGROUND OF THE INVENTION  
       [0004]     Tree fellers for cutting trees, called feller/bunchers if they have accumulating arms, are well known in the logging industry. In a typical arrangement, a disc saw is carried at the front of a boom of a back hoe type vehicle, that may be a tracked or wheeled vehicle, that has a gasoline or diesel engine. The engine typically drives two or more variable displacement hydraulic pumps, at least one of which is for the drive functions of the vehicle and the other of which is for turning the disc saw. In the past, the engine power useable to drive these two pumps has been determined by the characteristics of the pump and by the load to which the pump was subjected. The displacement of both pumps is manually controlled by the operator with suitable controls provided in the cab. Usually, the saw drive pump is operated at full displacement once the saw is brought up to speed, and the main pump displacement is controlled by the operator, depending on how fast the operator wants to operate the machinery or the loading placed on the machine by the various functions of the machine, with limits placed on it by the system so as not to overload the prime mover. However, there are times when it is desirable to limit the amount of engine power available to drive the saw, so as to make more power available for the other machine functions, such as driving the wheels or track in rough terrain, operating the clamp arms of the saw head in windy conditions, or operating the boom with a large load of trees held by the saw head, or while cutting a tree. This invention is directed toward a new way to divide power between the saw and main pumps in a tree felling machine.  
       SUMMARY OF THE INVENTION  
       [0005]     A tree felling machine of the invention has a hydraulic system that has at least two hydraulic pumps operated by the same prime mover, the two pumps including a pump for driving a cutting element of the machine and the other pump being a main pump for providing fluid under pressure to operate other functions of the machine. In one aspect of the invention, the machine has a control in the cab, apart from any manually adjustable pump displacement controls operable by the operator, that is adjustable by the operator so as to place an upper limit on the amount of power the saw pump can draw from the prime mover. Thereby, the operator can limit the saw power so as to make more power available to operate the other functions of the machine.  
         [0006]     Preferably, the control can be set by the operator to result in automatic de-stroking of the saw pump when the saw pump pressure reaches the limit set by the operator.  
         [0007]     In another aspect of the invention, de-stroking of the saw pump is automatically effected at least in part in response to a displacement setting of the main pump. If the main pump is operating at full displacement, the combination of saw pump and main pump output pressures necessary to de-stroke the saw pump will be less than if the main pump is being de-stroked by the main pump de-stroking cylinder. Likewise, if there is no or relatively little load on the main pump, it will be automatically de-stroked so that a relatively high power is available to be used by the saw pump and therefore it would take a relatively higher saw pump pressure to result in de-stroking the saw pump.  
         [0008]     In another aspect of the invention, a saw pump de-stroking valve has opposed pilot pressure ports that normally balance each other when the saw pump is not being de-stroked in a non-de-stroking position of the de-stroking valve, but that when imbalanced, move the de-stroking valve into a position in which the valve pressurizes a saw pump de-stroking cylinder to reduce the displacement of the saw pump, and thereby reduce the power consumed by the saw pump. The pilot pressure ports of the de-stroking valve include a non-destroking port that when pressurized biases the de-stroking valve into the non-de-stroking position. The non-de-stroking port is in communication with a limit valve that vents the non-de-stroking port to a pressure that permits the de-stroking valve to de-stroke the saw pump dependent, at least in part, on the displacement setting of the main pump, the pressure exerted by the saw pump, and the pressure exerted on the load by the main pump. Thus, more power will be available to the saw pump if the main pump load pressure is lower, and/or if the main pump is de-stroked.  
         [0009]     The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic hydroelectric circuit diagram for a control system of the invention; and  
         [0011]      FIG. 2  is a more detailed schematic of the hydroelectric circuit of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     A common prime mover M, such as a gasoline or diesel engine, drives both a main pump unit MP (also sometimes referred to as a boom pump unit) and a saw pump unit SP. Each of the pump units MP and SP includes a variable displacement pump P m  or P s  ( FIG. 2 ) respectively such as a variable displacement axial piston pump. The pump units MP and SP also are provided with a number of other valves and orifices as indicated in  FIG. 2  by the components within the alternating long and short dashed line boxes, that represent the envelopes or housings of the pump units. The output from the boom pump unit MP goes to the main valve (not shown) through the port B that is connected to pump P m  in  FIG. 2 , the main valve being operated by the machine operator to provide control of the hydraulic power delivered to the various functions of the machine, such as the boom lift and extension cylinders, the drive motors for the drive wheels or tracks of the vehicle, the steering system of the vehicle, the brakes, and the clamp arms of the saw head. The output of the saw pump unit SP is directed to an on/off saw valve V 1  (in  FIG. 2 , the port B connected to the pump P s  is connected to the valve V 1 , not shown in  FIG. 2 ) and from there to the saw motor SM, which drives the cutting element of the feller, such as a disc saw blade.  
         [0013]     In a system of the invention, the operator is able to select the power split between the saw pump unit SP and the main pump unit MP. As seen in  FIG. 1 , the operator is provided with a control C, for example a potentiometer, that is connected to a solenoid S 1  of the saw pump unit SP. If the operator wants the saw pump unit SP to be able to draw as much power as possible from the prime mover M, the operator sets the control to 100 and, as long as the main pump unit MP does not demand more power than what the prime mover M can produce, when combined with the demand from the saw pump unit SP, the saw pump unit SP will run at maximum capacity. However, if the operator wants to limit the maximum power that the saw pump can draw, the operator can set the control C to a value less than 100, which will place a limit on the amount of prime mover power that the saw pump unit SP can draw.  
         [0014]     Also illustrated in  FIG. 1  is a limit valve V 2  that is controlled on its right side by the stroke setting of the main pump unit MP and receives two pilot pressure inputs on its left side, one from the load sense pressure of the main pump unit MP and the other from the output of the saw pump SP. If the main pump unit MP is operating at its maximum displacement, the spring force on the right side of the valve V 2  will be reduced so that only a relatively low combination of the pressures acting on the left side of valve V 2  will keep valve V 2  closed. If either or both of the pressures on the left pilot pressure ports of valve V 2  increase enough, valve V 2  will open, which will vent the pilot pressure acting at pilot pressure port PP 2  of valve V 5  of the saw pump unit SP to tank, which has the effect of de-stroking (i.e., reducing the displacement and therefore the flow rate of) the saw pump unit SP and thereby relieving the power demand of the saw pump unit SP on the prime mover M. This makes more power available to the main pump MP. It is noted that the operator adjusting the control C downwardly also de-strokes the saw pump unit SP, to relieve the power demand on the motor M by the saw pump unit SP, thereby making more of the prime mover power available to the main pump unit MP.  
         [0015]     Referring to  FIG. 2 , detailed schematics of the main pump unit MP and saw pump unit SP are illustrated, and it is illustrated how they are connected together. The components contained within the prior art pump units MP and SP were not modified to create the invention, but what was changed was the plumbing of ports P 1  and P 2  of the main pump unit MP, the connection of port X of the saw pump unit SP to the port P 1  of the main pump unit MP, and the addition of an external electrical control in the vehicle cab to control a proportional electric valve of the saw pump unit SP, as described below, for the operator to be able to remotely control the setting of the proportional electrical valve S 1  of the saw pump unit SP. In the main pump unit MP as it existed previously, port P 1  was connected to the internal circuit of the main pump unit at the point below orifice O 2 , where the upper line connected to P 2  is connected in  FIG. 2 , and P 2  was not connected there but was unused (plugged) or used for another purpose. In making the invention, this line was connected to P 2 , as illustrated in  FIG. 2 , and the X port of the prior art saw pump unit SP was connected to port P 1  of the main pump unit MP, as illustrated in  FIG. 2 .  
         [0016]     Referring to the main pump unit MP, as stated above, the main pump unit MP includes a pump P m  that draws from tank port S, and ports L 1  and L are also drain ports that are connected to the tank (not shown), like S. X is the load sense pressure port which is connected to the load sense pressure port of the main valve (not shown). As is well known, the main pump output B is connected to the pressure input port of the main valve and the main valve is controlled by the operator to direct hydraulic pressure to the various functions of the machine such as the drive system, steering system, boom control, clamp arms, etc. The load sense pressure is the pressure demanded by the operator, downstream of the main valve, that is determined by the load and the operator&#39;s operation of the machine. If no or relatively low load is being called for by the operator, the main pump will be de-stroked to no or relatively low flow, so as to conserve energy. As the load sense pressure at port X builds, it makes it more likely that the saw pump unit SP will be destroked by the action of valve V 2 , as further described below.  
         [0017]     The main pump P m  also has a leakage line that is connected to L and L 1 . The output from the pump P m  is also connected to three-way, two-position valve V 3  and to three-way, two-position valve V 4 . Valve V 3  is a load sense valve that accelerates the main pump so as to balance the pump output and load sense pressures, and valve V 4  is a valve that protects the main pump from high pressure. The left side pilot pressure ports of the valves V 3  and V 4  are connected to the output of the pump P m  and the right side pilot pressure port of the valve V 3  is connected to the load sense port X, through orifice O 2 . The right side of the protection valve V 4  is connected to the drain port L. If the pump P m  output pressure gets too high, valve V 4  is shifted to the right against its adjustable spring, which connects the output of the pump P m  to the input of de-stroking cylinder D m , which moves the piston of the cylinder D m  leftwardly and has a mechanical linkage to the pump P m  so as to reduce its displacement and therefore its flow rate. This action is reacted against by start-up cylinder C m  that has an internal spring that reacts against de-stroking the pump P m , in combination with a connection to the pump output pressure that biases the pump toward the fully stroked (maximum flow rate) state. The cylinder C m  is provided for the main function of biasing the pump P m  into a fully-stroked, or maximum displacement position, as is desirable especially at start-up of the machine.  
         [0018]     Pressurizing the cylinder D m  has the effect of reducing the displacement, and therefore the flow output, of the pump P m . In addition, actuating the de-stroke cylinder D m  leftwardly also acts on the adjustable spring of valve V 2  to further compress the spring and therefore increase the force that biases the valve V 2  closed, which is the same valve V 2  as shown in  FIG. 1 , although schematically depicted somewhat differently. As seen, de-stroking pump P m  tends to close valve V 2 , so as to close off the connection through it of port P 1  of the main pump unit MP to tank, through port L and L 1 .  
         [0019]     Valve V 2  ( FIG. 2 ) also has its two leftward pilot pressure ports connected, one to port P 1  and the other to port P 2  of the main pump unit MP. As stated above, port P 2  is connected to the load sense port X of the main pump unit MP below orifice O 2 . In  FIG. 2 , line L 1  corresponds to line L 1  in  FIG. 1 , and line L 2  in  FIG. 2  corresponds to line L 2  in  FIG. 1 .  
         [0020]     Orifices O 5  and O 4  are provided to relieve the pressure in the respective lines between V 3  and V 4  and between V 4  and D m  to tank, to assure that leakage does not build-up pressure that would falsely move the de-stroking cylinder D m  to a de-stroked position.  
         [0021]     Port P 1  of the main pump unit MP is connected to port X of the saw pump unit SP. Port X is connected to orifice O 1 , which corresponds to the orifice O 1  in  FIG. 1 . Orifice O 1  is connected to the outlet port B of the saw pump P s . The displacement stroke of the saw pump P s  is controlled by the de-stroking cylinder D s  and by the start-up cylinder C s , much like in the main pump unit MP. Also, as in the main pump unit MP, the ports S, L 1 , and L of the saw pump unit SP are all connected to tank. The leakage port from the pump P s  is also connected to port L and therefore to tank. The pump P s  output line is connected to the pilot pressure port of three-way, two-position valve V 5 , that is biased leftwardly by an adjustable spring, and to the pressure port of the valve V 5 , and through the orifice O 1  to port X, and from there to the right side pilot pressure port of valve V 5 , and to the pressure port and right side pilot pressure port of control valve V 6 . The opposite (lower as illustrated) side port of valve V 5  is connected to the de-stroking cylinder D s  and through an orifice O 3  to the tank port L. The lower side port of valve V 6  is also connected to tank through the port L, and the valve V 6  has an adjustable spring on its left side and a proportional solenoid S 1 , which corresponds to S 1  in  FIG. 1 , on its right side. On the right side of valve V 6 , the pilot pressure port is identified PP 1 , which corresponds to PP 1 in  FIG. 1 , and is connected to the X port of the saw pump unit SP, which is connected through orifice  01  to the output of the saw pump P s .  
         [0022]     Valve V 5  is balanced by the output pressure of the saw pump P s  and by the pressure at port X of the saw pump unit SP, and also by the adjustable spring at the right side of the valve V 5 . As long as the pressure at port X of the saw pump unit SP is sufficiently high, valve V 5  will stay in the position illustrated, with the output of the pump P s  blocked. However, if the pressure at port X goes down sufficiently, valve V 5  will be permitted to shift rightwardly, which will pressurize de-stroking cylinder D s , and therefore reduce the displacement of the saw pump P s , thereby off-loading the prime mover M.  
         [0023]     The pressure at the port X of the saw pump unit SP can be relieved either through the valve V 2  or through the valve V 6 . If an operator turns control C to a setting of 100, corresponding to a zero current to the adjustable solenoid S 1 , for example, the spring at the left of V 6  will urge the valve V 6  closed so that it will take a relatively higher pressure at port PP 1  to open it, thereby relieving the pressure at port X to tank and shifting the valve V 5  rightwardly and correspondingly de-stroking the saw pump P s . If the operator sets the control C to, for example, 50, then the solenoid S 1  will be exerting a force on the valve V 6  tending to move it leftwardly, so it will take less pressure at port PP 1  to shift the valve V 6  to an open state, which, as stated above, has the effect of shifting valve V 5  rightwardly and de-stroking the saw pump P s .  
         [0024]     The saw pump P s  can also be de-stroked by the main pump unit MP, depending on its operating conditions. This happens when the pressure at point P 1  is reduced sufficiently so as to allow valve V 5  to shift into its rightward position. The pressure at port P 1  is controlled by the valve V 2 , which is dependent on the pressure at port X of the saw pump unit SP, on the load sense pressure input to the main pump through port X of the main pump unit MP downstream of orifice O 2 , and by the stroke setting of the main pump P m . If the main pump P m  is fully stroked, the force exerted by the adjustable spring on the right side of valve V 2  will be reduced relative to what it would be if the main pump P m  were de-stroked, so that a lower load sense pressure in line L 1  would tend to open the valve V 2 , than would be the case if the pump P m  were at least partially de-stroked. Opening valve V 2  vents port X of the saw pump P s  to tank, which shifts valve V 5  rightwardly thereby de-stroking the saw pump. The pressure required in line L 1  to open valve V 5  is also reduced if the pressure at port X of the saw pump unit SP is greater, since that pressure adds to the force acting on the same side of the valve V 2  as does the pressure in line L 1 . If the main pump P m  is at least partially de-stroked, the spring acting on the right side of valve V 2  is compressed by the de-stroking cylinder D m , which causes the force acting on the right side of valve V 2  to be greater, which force biases the valve V 2  closed. Under those conditions, the combination of forces produced by the two pilot pressures acting on the left side of valve V 2  must be greater in order to open the valve V 2 . Opening valve V 2  has the effect of de-stroking the saw pump P s . Thus, when the main pump is operating at less than full flow rate, more power is available for use by the saw pump P s , for a given pressure of the main pump, than at full main pump flow rate, at the same main pump pressure. Thereby, the power available to be used by the saw pump is set by the operator with the control C, but can be no greater than that available as determined by the requirements of the main pump.  
         [0025]     A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described.