Abstract:
A power take-off (PTO) control system for a work vehicle equipped with an implement, comprising a hydraulic multi-plate PTO clutch ( 6 ) whereby power from the work vehicle is interruptibly transmitted to the implement; a control valve ( 15 ) for adjusting an actuating pressure of the PTO clutch; a manually operable clutch operation tool ( 17, 21 ) for sending an operation instruction to the control unit; and a control unit ( 19 ) for switching the PTO clutch from a disengaged state to an engaged state by controlling the control valve on the basis of the target control characteristics in response to the operation instruction of the clutch operation tool ( 17, 21 ). The target control characteristics are generated and set on the basis of the operational behavior of the clutch operation tool ( 17, 21 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power take off (PTO) control system for a work vehicle equipped with an implement, and particularly to hydraulic control of a PTO clutch. 
         [0003]    2. Description of the Related Art 
         [0004]    A tractor disclosed in Japanese Laid-open Patent Publication No. 2006-11843, which is one example of a work vehicle, comprises a hydraulic multi-plate PTO clutch that is able to transmit and interrupt power to an implement coupled to a machine body (see C3 of FIGS. 3 and 4 of the abovementioned document), a control valve for supplying hydraulic fluid to the PTO clutch (V4 of FIG. 7 of Patent Document 1), and a PTO clutch lever (43 of FIG. 7 of the abovementioned document). A driver operates the control valve in the tractor by operating the PTO clutch lever. When hydraulic fluid is supplied to the PTO clutch, the PTO clutch enters an engaged state, and when hydraulic fluid is discharged from the PTO clutch, the PTO clutch enters a disengaged state. 
         [0005]    Coupling a variety of small- to large-size implements to the machine body allows the tractor to perform a variety of tasks. 
         [0006]    The weight of a driven part and the starting torque of a small-sized implement are comparatively low, and therefore even when the PTO clutch is moved to the engaged state and power is transmitted to the small-sized implement, the shock when a drive is initially provided to the small-sized implement is a comparatively small amount. In contrast, the weight of the driven part and the starting torque of a large-sized implement (for example, a large grass mower) are comparatively large, and therefore when the PTO clutch is moved to the engaged state and power is transmitted to the large-sized implement, the shock when a drive is initially provided to the large-sized implement is a comparatively great amount. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide a PTO control system which can cause a PTO clutch to be suitably operated in accordance with a variety of implements in cases where any of a variety of implements is coupled to the machine body, and work is performed. 
         [0008]    In order to achieve the aforesaid object, the PTO control system according to the present invention, which is intended for a work vehicle equipped with an implement, comprises a hydraulic multi-plate PTO clutch whereby power from the work vehicle is interruptibly transmitted to the implement; a control valve for adjusting an actuating pressure of the PTO clutch; a manually operable clutch operation tool for sending an operation instruction to the control unit; and a control unit for switching the PTO clutch from a disengaged state to an engaged state by controlling the control valve on the basis of target control characteristics in response to the operation instruction of the clutch operation tool. The control unit has target control characteristics generating means for generating the target control characteristics, and target control characteristics setting means for setting the generated target control characteristics. 
         [0009]    According to the PTO control system, the target control characteristics used when the PTO clutch is switched from the disengaged state to the engaged state are generated by the target control characteristics generating means each time in response to the operation instruction of the clutch operation tool. Therefore, the hydraulic pressure of the PTO clutch is controlled according to the appropriate control characteristics based on a variety of implements and, when necessary, on the operational state of the clutch operation tool as well. 
         [0010]    According to one preferred embodiment of the present invention, pre-recorded control characteristics are employed and the target control characteristics are generated. This obviates the need to generate the entirety of the target control characteristics when the PTO clutch is shifted from the disengaged state to the engaged state, and enables pre-recorded control characteristics to be partially employed. Furthermore, new appropriate target control characteristics can be generated merely by modifying the pre-recorded control characteristics. The process load of the target control characteristics generating means can be reduced thereby. 
         [0011]    According to another preferred embodiment of the present invention, the target control characteristics generating means generates target control characteristics in accordance with the speed at which the clutch operation tool is operated. According to this embodiment, when the clutch operation tool is suddenly moved from the disengaged position to the engaged position, the PTO clutch is suddenly switched from the disengaged state to the engaged state. When the clutch operation tool is moved slowly from the disengaged position to the engaged position, the PTO clutch is slowly switched from the disengaged state to the engaged state. For example, when a small-sized implement is coupled to the machine body, the operator can suddenly move the clutch operation tool from the disengaged position to the engaged position. This causes the PTO clutch to be suddenly switched from the disengaged state to the engaged state, power to be quickly transmitted, and the small-sized implement to be driven without delay. When a large-sized implement is coupled to the machine body, the operator can move the clutch operation tool slowly from the disengaged position to the engaged position. This causes the PTO clutch to slowly switch from the disengaged state to the engaged state, power to be slowly transmitted, and shock to be minimized. 
         [0012]    More specifically, according to a preferred embodiment, there is provided a sensor for detecting the operational behavior of the clutch operation tool, and when the clutch operation tool is operated at a speed that is greater than a previously set control reference speed, the target control characteristics generating means uses pre-recorded control characteristics for the target control characteristics. This makes it possible to avoid the problem of the PTO clutch being switched from the disengaged state to the engaged state unusually quickly, and shock increasing when the implement is driven. The problem can be avoided even when the operator mistakenly moves the clutch operation tool from the disengaged position to the engaged position unusually quickly. 
         [0013]    Other characteristics and advantages of the present invention will become more apparent from the following description of the embodiments taken with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a side view of an entire tractor equipped with a PTO control system according to the present invention; 
           [0015]      FIG. 2  is a schematic diagram showing the construction of the PTO control system; 
           [0016]      FIG. 3  is a diagram showing the relationship between the operation position of the PTO lever and the actuating pressure of the PTO clutch; 
           [0017]      FIG. 4  is a flowchart showing one example of hydraulic pressure control through the PTO control system; and 
           [0018]      FIG. 5  is a schematic diagram of the right and left side brake pedals used as a clutch operating tool. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    A tractor, which is one example of a work vehicle, is shown in  FIG. 1 . The tractor has right and left front wheels  1  that can be steered to the right and left, right and left rear wheels  2 , an engine  3 , a transmission casing  4 , and an operator part  5 . As can be understood from  FIGS. 1 and 2 , the power generated by the engine  3  is transmitted to the front wheels  1  and the rear wheels  2  via a hydrostatic continuously variable speed change device (not shown) and a gearshift-type secondary speed change device (not shown) provided to the transmission casing  4 . The power generated by the engine  3  can also be transmitted to a PTO shaft  7  provided to a rear part of the transmission casing  4 , via a PTO speed change device (not shown) and a PTO clutch  6  provided to the transmission casing  4 . 
         [0020]    As shown in  FIG. 1 , a top link  8  and right and left lower links  9  are supported on the rear part of the transmission casing  4  so as to be capable of moving upward and downward, a lift arm  11  that is pivotably driven by a hydraulic cylinder  10  is provided, and a connecting rod  12  spanningly connects the lift arm  11  to the right and left lower links  9 . The top link  8  and the right and left lower links  9  are driven up and down by the hydraulic cylinder  10  and the lift arm  11 . A variety of implements can be coupled to the top link  8  and the right and left lower links  9 . 
         [0021]    In  FIG. 1 , a rotary cultivator device  13  (an implement) is coupled to the tractor at the top link  8  and the right and left lower links  9 , and a transmission shaft  14  spanningly connects the PTO shaft  7  and the rotary cultivator device  13 . The power generated by the engine  3  is thereby able to be transmitted to the rotary cultivator device  13  via the PTO speed change device, the PTO clutch  6 , the PTO shaft  7 , and the transmission shaft  14 . 
         [0022]    As shown in  FIG. 2 , the PTO clutch  6  is a hydraulic multi-plate clutch. The clutch is changed to the engaged state as a result of hydraulic fluid being supplied, is biased to the disengaged state by a spring (not shown), and is changed to the disengaged state as a result of the hydraulic fluid being discharged. There is provided an electromagnetic proportional control valve  15  via which hydraulic fluid is supplied to and drained from the PTO clutch  6 , and the hydraulic pressure behavior (control characteristics) of the control valve  15  is controlled by a control unit  19 . As shown in  FIGS. 1 and 2 , a PTO lever  17  (a clutch operating tool) and a setting switch  18  are provided to the right side of an operation seat  16  of the operation part  5 . 
         [0023]    As shown in  FIG. 2 , the PTO lever  17  is constructed so as to be capable of being manually moved between the engaged position and the disengaged position, and the operation position of the PTO lever  17  is input to the control unit  19 . A pressure sensor  20  for detecting the actuating pressure P of the PTO clutch  6  is provided, and a value detected by the pressure sensor  20  is inputted to the control unit  19 . A lever sensor  17   a  for detecting operational displacement of the PTO lever  17  is provided in order for the operational parameters of the PTO lever  17 , e.g., the operating speed, to be calculated by the control unit  19 . A signal outputted by the lever sensor  17   a  is input to the control unit  19 . The setting switch  18  is of a dial type, and can be operated manually. The operation position of the setting switch  18  is inputted to the control unit  19 . Operating the setting switch  18  causes a control reference speed V 1  described hereafter to be selected from between a high speed and a low speed. 
         [0024]    Operation tool operation parameter computing means  19 A, target control characteristics generating means  19 B, target control characteristics setting means  19 C, hydraulic pressure control means  19 D, and a control characteristics table  19 E for storing predetermined reference control characteristics are provided to the control unit  19  as functional parts specifically relating to the present invention. These functional parts are substantially realized using a computer program and a process data group associated therewith. The operation tool operation parameter computing means  19 A calculates the operation parameters of the PTO lever  17 ; i.e., the operating position, operating speed, rate of change in operating speed, and the like, on the basis of the signal output from the lever sensor  17   a . The target control characteristics generating means  19 B generates target control characteristics to be used as a target when the PTO clutch  6  is to be switched from the disengaged state to the engaged state, on the basis of the operating parameters of the PTO lever  17  as calculated by the operation tool operation parameter computing means  19 A. The target control characteristics setting means  19 C sends the target control characteristics generated by the target control characteristics generating means  19 B to the hydraulic pressure control means  19 D, and sets the characteristics as a control target. The hydraulic pressure control means  19 D controls the control valve  15  while evaluating the signal from the pressure sensor  20 , so as to switch the PTO clutch  6  from the disengaged state to the engaged state in accordance with the target control characteristics that have been set. The reference control characteristics stored in the control characteristics table  19 E are retrieved as needed by the target control characteristics setting means  19 C, and are employed when the target control characteristics are to be generated. 
         [0025]    The target control characteristics generating means  19 B generates target control characteristics to be used as a target when the PTO clutch  6  is to be switched from the disengaged state to the engaged state, on the basis of the operating parameters that constitute the operational behavior of the PTO lever  17  as calculated by the operation tool operation parameter computing means  19 A. Accordingly, the operational behavior of the PTO lever  17  and the behavior of the PTO clutch  6  when moving from the disengaged state to the engaged state are harmonized. As a result, PTO clutch control that provides exceptional maneuverability is attained. 
         [0026]    A specific example of the control occurring in the above-described PTO control system is described below using  FIGS. 3 and 4 .  FIG. 3  is a graph showing the relationship between the operating position of the PTO lever and the actuating pressure of the PTO clutch, and expresses one example of the control characteristics used as a target.  FIG. 4  is a flowchart of the hydraulic pressure control of the first embodiment. 
         [0027]    In this specific example, in a case in which the PTO lever  17  is moved from the disengaged position to the engaged position, the control changes according to whether the operating speed V, when the PTO lever  17  moves from the disengaged position to the engaged position, is faster or slower than the control reference speed V 1 . 
         [0028]    First, a check is performed to confirm whether or not the PTO lever  17  has been operated (# 01 ). If the PTO lever  17  has been operated (“Yes” branch of # 01 ), a check is performed to confirm the direction in which the PTO lever  17  was moved; i.e., whether the direction is from the disengaged position to the engaged position, or from the engaged position to the disengaged position (# 02 ). When operation of the PTO lever  17  from the disengaged position to the engaged position is detected in step # 02 , the operating speed V of the PTO lever  17  is computed (# 03 ). The operating speed V of the PTO lever  17  and the control reference speed V 1  set by the setting switch  18  are compared (# 04 ). If the operating speed V is less than the control reference speed V 1  (“yes” branch of # 04 ), the control valve  15  is controlled (# 05 ) so that the relationship between the operational position of the PTO lever  17  and the actuating pressure P of the PTO clutch  6  becomes the relationship shown by the solid line marked by the symbol A 1  in  FIG. 3 . In the control process A 1  of step # 05 , when the PTO lever  17  is moved quickly, the actuating pressure P of the PTO clutch  6  accordingly is controlled to increase at a comparatively high speed, as long as the operating speed V of the PTO lever  17  is lower than the control reference speed V 1 . Alternatively, if the PTO lever  17  is moved slowly, the actuating pressure P of the PTO clutch  6  accordingly is controlled to increase at a comparatively low speed. When the PTO lever  17  is stopped and held at a desired operating position, the control for increasing the actuating pressure P of the PTO clutch  6  is temporarily suspended, and the actuating pressure P of the PTO clutch  6  is maintained along with the actuating pressure corresponding to the operational position of the PTO lever  17 . 
         [0029]    In step # 04 , if the operating speed V is not less than the control reference speed V 1  (“no” branch of # 04 ), the actuating pressure P of the PTO clutch  6  and a half clutch actuating pressure P 1  (previously set) are compared (# 07 ). In a case in which the actuating pressure P of the PTO clutch  6  is less than the half clutch actuating pressure P 1  (“no” branch of # 07 ), the process returns to step # 05 , and the control valve  15  is controlled in a manner based upon the solid line indicated by the symbol A 1  in  FIG. 3 . In a case in which the actuating pressure P of the PTO clutch  6  is equal to or greater than the half clutch actuating pressure P 1  (“yes” branch of # 07 ), the control valve  15  is controlled so that the relationship between the operational position of the PTO lever  17  and the actuating pressure P of the PTO clutch  6  becomes the relationship shown by the dotted line indicated by the symbol A 2  in  FIG. 3  (# 07 ). In the control process A 2  of step # 07 , the actuating pressure P of the PTO clutch  6  corresponding to the operational position of the PTO lever  17  is lower in comparison with the control process A 1  of step # 05  during an in crease in pressure from the half clutch actuating pressure P 1  to an engaged actuating pressure P 2 . Therefore, the process of increasing the pressure from the half clutch actuating pressure P 1  tends to be slow. Although this is not shown in the flowchart of  FIG. 4 , once the control process A 2  commences, the inconvenience that occurs when the PTO lever  17  is operated at abnormally high speed can be eliminated by having the control process A 2  continue up to the point that the PTO lever  17  reaches the engaged position, without the control process A 1  being performed. 
         [0030]    When operation of the PTO lever  17  from the engaged position to the disengaged position is detected in step # 02 , a check is performed to confirm whether the PTO lever  17  has been moved to the disengaged position or to an area regarded as the disengaged position (# 08 ). When the PTO lever  17  has been moved to the disengaged position or to the area regarded as the disengaged position (“yes” branch of # 08 ), the actuating pressure P of the PTO clutch  6  is reduced according to the previously set high speed control characteristics, and a disengaging process for switching the PTO clutch  6  to the disengaged state is performed, regardless of the operating speed (# 09 ). 
         [0031]    The control reference speed V 1  can be switched between high speed and low speed by operating the setting switch  18 . When the control reference speed V 1  is switched to high speed, then as long as the PTO lever  17  is not moved at a fairly high speed from the disengaged position to the engaged position, the process will not diverge to step # 06  after the check performed in step # 04 . It is therefore possible to control the actuating pressure P of the PTO clutch  6  harmonized with the speed at which the PTO lever  17  is operated. This control is suitable when comparatively small-sized implements are attached. 
         [0032]    When the control reference speed V 1  is switched to low speed, then should the PTO lever  17  be operated even slightly quickly, the process will diverge to step # 06 . Accordingly, it is possible to impart a delayed sensation to the control of the actuating pressure P of the PTO clutch  6  achieved by operating the PTO lever  17 . This control is suitable when comparatively large-sized implements are attached. 
         [0033]    In the above embodiment, the PTO lever  17  is employed as a clutch operation tool; however, as shown in  FIG. 5 , right and left side brake pedals  21  can be employed as the clutch operation tool in place of the PTO lever  17 . In a tractor of such description, as shown in  FIG. 5 , a right side brake (not shown) capable of braking the right rear wheel  2 , and a left side brake (not shown) capable of braking the left rear wheel  2  are provided; right and left side brake pedals  21  are provided to the lower right side of the front part of the operation part  5 , the right side brake pedal  21  and the right side brake are mechanically connected via a connecting mechanism; and the left side brake pedal  21  and the left side brake are mechanically connected via a connecting mechanism. As shown in  FIG. 5 , the left and right side brake pedals  21  are capable of being depressed to a canceling position and a limit position, and are biased to the canceling position. The depressed position of the right and left side brake pedals  21  is detected and inputted to the control unit  19 . When the right and left side brake pedals  21  are in the canceling position, the right and left side brake are moved to the cancelled state; and when the right and left side brake pedals  21  are depressed from the canceling position, the right and left side brakes are moved to the braking side after a slight amount of play is experienced (in a state wherein the right and left side brakes are in the cancelled state), and an adequate amount of braking power applied by the right and left side brakes (braking power adequate for stopping the machine) is obtained at an intermediate position. As a result, the braking power of the right and left side brakes is maximized at the limit position. The range between the canceling position and the intermediate position of the right and left side brake pedals  21  is set as the engaged position, and the limit position is set as the disengaged position. When the right and left side brake pedals  21  are depressed to the canceling position and the intermediate position (engaged position), the PTO clutch  6  is in the engaged state. When the right and left side brake pedals  21  start to descend from the intermediate position (engaged position) to the limit position (disengaged position), the PTO clutch  6  is promptly switched from the engaged state to the disengaged state, regardless of the speed at which the right and left side brake pedals  21  are depressed from the intermediate position (engaged position) to the limit position (disengaged position). In a state in which the right and left side brake pedals  21  are depressed to the limit position (disengaged position; when the PTO clutch  6  is in the disengaged state), when the right and left side brake pedals  21  begin to return to the intermediate position (engaged position) from the limit position (disengaged position), the speed at which the right and left side brake pedals  21  return from the limit position (disengaged position) to the intermediate position (engaged position) is detected. A hydraulic pressure control is performed as shown in the flowchart of  FIG. 5  on the basis of the speed at which the right and left side brake pedals  21  return from the limit position (disengaged state) to the intermediate position (engaged state), and the PTO clutch  6  is switched to the engaged state. 
         [0034]    The hydraulic pressure control depicted in the flowchart of  FIG. 4  is also performed in a state in which the right and left side brake pedals  21  are both depressed at the same time (machine stopping operation), and in a state in which the right and left side brake pedals  21  both return at the same time (machine starting operation or the like). However, a hydraulic pressure control of such description is not performed in a state in which only one of the right and left side brake pedals  21  is depressed (when the machine is making a turn or the like) or only one of the right and left side brake pedals  21  has subsequently returned. 
         [0035]    Plot A 1  (solid line) in the graph shown in  FIG. 3  need not be in the form of a linear function (straight line), but may be in the form of a quadratic function (curving line) arching upward or downward. Similarly, the plot A 2  (dashed line) may be set in the form of a quadratic function (curving line) arching upward or downward. 
         [0036]    In the above specific example, the target control characteristics generating means  19 B generates the target control characteristics in response to the operation parameters of the clutch lever  17  as computed by the operation tool operation parameter computing means  19 A. However, alternatively, the target control characteristics may be generated by compiling the reference control characteristics stored in the characteristics table  19 E. For example, the slope and shape of the reference control characteristics may be changed according to the operation parameters of the clutch lever  17 , and used as the target control characteristics; and the slope and shape of the reference control characteristics may be changed according to the value set by the setting switch  18 , and used as the target control characteristics. Finally, the slope and shape of the reference control characteristics may be changed according to the operation parameters of the clutch lever  17  and the value set by the setting switch  18 , and used as the target control characteristics. When a plurality of reference control characteristics is stored in the characteristics table  19 E, an advantageous increase is obtained in terms of the variability of the control characteristics.