Patent Publication Number: US-10323381-B2

Title: Work vehicle and method of controlling work vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a work vehicle. 
     BACKGROUND ART 
     A work vehicle such as a hydraulic excavator includes a work implement containing a boom, an arm, and a bucket. In this connection, a work implement having a tilt type bucket (a tilt bucket) of which opposing ends in a direction of vehicle width can be inclined with respect to the direction of vehicle width has been known. The tilt type bucket is inclined by a tilt actuator having a hydraulic cylinder for tilting a bucket with respect to an arm as shown in Japanese Patent Laying-Open No. 2014-74319 (PTD 1). 
     In order to detect a position and an attitude of the work implement, a stroke of the hydraulic cylinder is measured. 
     For example, Japanese Patent Laying-Open No. 2006-258730 (PTD 2) discloses a hydraulic excavator including a position sensor which detects a piston stroke position of a hydraulic cylinder which drives a work implement based on rotation of a rotary roller on a cylinder rod. Since slight slippage occurs between the rotary roller and the cylinder rod, an error is caused between a stroke position obtained based on a result of detection by the position sensor and an actual stroke position. Then, a scheme for resetting at a reference position, the stroke position obtained based on the result of detection by the position sensor is disclosed. 
     CITATION LIST 
     Patent Document 
     
         
         PTD 1: Japanese Patent Laying-Open No. 2014-74319 
         PTD 2: Japanese Patent Laying-Open No. 2006-258730 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     When a stroke position is reset with a stroke end of the hydraulic cylinder being defined as the reference position, the stroke position may be reset while the reference position is not reached due to manufacturing errors or wobble of a work implement. Accordingly, a deviation in stroke length may not accurately be corrected. 
     The present invention was made to solve the problem above, and an object thereof is to provide a work vehicle with a tilt type bucket which can accurately correct a deviation in stroke length. 
     Solution to Problem 
     A work vehicle according to one aspect of the present invention includes a vehicular body, a work implement, a hydraulic cylinder, a regulation valve, a position sensor, and a control unit. The work implement has a boom pivotable with respect to the vehicular body, an arm pivotable with respect to the boom, and a bucket pivotable around a bucket axis which is a pivot axis with respect to the arm and a tilt axis orthogonal to the bucket axis. The hydraulic cylinder has the bucket pivot around the tilt axis. The regulation valve regulates an amount of supply of a hydraulic oil to be supplied to the hydraulic cylinder based on a command signal. The position sensor measures a stroke length of the hydraulic cylinder. The control unit resets a stroke length measured by the position sensor. The control unit determines proximity to a stroke end of the hydraulic cylinder and generates a command signal for increasing a degree of opening of the regulation valve in the proximity of the stroke end. The control unit resets the stroke length measured by the position sensor while the regulation valve is open in response to the command signal. 
     Preferably, the work vehicle includes a stopper. The stopper stops pivot of the bucket by abutting to the bucket. The control unit determines proximity to the stroke end of the hydraulic cylinder based on presence of the stopper, generates the command signal for increasing a degree of opening of the regulation valve in the proximity of the stroke end, and resets the stroke length measured by the position sensor when the bucket abuts to the stopper while the regulation valve is open in response to the command signal. 
     Preferably, the bucket pivots in a first direction and a second direction opposite to the first direction around the tilt axis, and the stopper includes first and second stopper members which stop the bucket which pivots in the first direction and third and fourth stopper members which stop the bucket which pivots in the second direction. The control unit determines proximity to the stroke end of the hydraulic cylinder based on abutment to any one of the first and second stopper members or abutment to any one of the third and fourth stopper members and generates the command signal for increasing a degree of opening of the regulation valve in the proximity of the stroke end. The control unit resets the stroke length measured by the position sensor when the bucket abuts to both of the first and second stopper members or to both of the third and fourth stopper members while the regulation valve is open in response to the command signal. 
     Preferably, the control unit compares the stroke length measured by the position sensor with a reference value, determines proximity to the stroke end of the hydraulic cylinder based on a result of comparison, and generates the command signal for increasing a degree of opening of the command signal for regulating a degree of opening of the regulation valve in the proximity of the stroke end. 
     Preferably, the work vehicle further includes a control lever apparatus which drives the regulation valve. The control unit determines whether or not an operation command from the control lever apparatus is equal to or greater than a prescribed value, and generates the command signal for increasing a degree of opening of the regulation valve when the control unit determines that the operation command from the control lever apparatus is equal to or greater than the prescribed value in the proximity of the stroke end. 
     Preferably, the control unit calculates a cylinder speed of the hydraulic cylinder based on a measurement value from the position sensor, and generates the command signal for increasing a degree of opening of the regulation valve when the control unit determines that the cylinder speed of the hydraulic cylinder calculated in the proximity of the stroke end is equal to or smaller than a prescribed value and that the operation command from the control lever apparatus is equal to or greater than the prescribed value. 
     Preferably, the control unit determines whether or not a duration of the operation command equal to or greater than the prescribed value from the control lever apparatus is equal to or longer than a prescribed period, and resets the stroke length measured by the position sensor when the duration of the operation command equal to or greater than the prescribed value from the control lever apparatus is equal to or longer than the prescribed period while the regulation valve is open in response to the command signal. 
     Preferably, the work vehicle includes an engine which rotates in accordance with supply of a fuel, a fuel regulation unit which regulates an amount of supply of the fuel for adjusting a speed of the engine, and a pump which supplies the hydraulic oil at a pump pressure in accordance with the speed of the engine. The control unit determines whether or not the amount of supply of the fuel regulated by the fuel regulation unit is equal to or greater than a prescribed amount, and generates the command signal for increasing a degree of opening of the regulation valve when the amount of supply of the fuel is equal to or greater than the prescribed amount in the proximity of the stroke end of the hydraulic cylinder. 
     Preferably, the control unit determines whether or not a prescribed condition is satisfied, and when the control unit determines that the prescribed condition is satisfied in the proximity of the stroke end, the control unit does not generate the command signal for increasing a degree of opening of the regulation valve as compared with a degree of opening in a case other than being in the proximity of the stroke end. 
     Preferably, the work vehicle further includes an intervention control unit which automatically controls at least a part of the work implement. The control unit determines whether or not the intervention control unit is carrying out automatic control as the prescribed condition, and does not generate the command signal for increasing and regulating a degree of opening of the regulation valve when the automatic control is being carried out in the proximity of the stroke end. 
     A work vehicle according to one aspect of the present invention includes a work implement, a hydraulic cylinder, a regulation valve, and a position sensor. The work implement has a boom pivotable with respect to a vehicular body, an arm pivotable with respect to the boom, and a bucket pivotable around a bucket axis which is a pivot axis with respect to the arm and a tilt axis orthogonal to the bucket axis. The hydraulic cylinder has the bucket pivot around the tilt axis. The regulation valve regulates an amount of supply of a hydraulic oil to be supplied to the hydraulic cylinder. The position sensor measures a stroke length of the hydraulic cylinder. A method of controlling the work vehicle includes the steps of measuring a stroke length of the hydraulic cylinder by using the position sensor, determining proximity to a stroke end of the hydraulic cylinder, generating a command signal for increasing a degree of opening of the regulation valve in the proximity of the stroke end, and resetting the measured stroke length. 
     Advantageous Effects of Invention 
     A work vehicle according to the present invention can accurately correct a deviation in stroke length. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing one example of a work vehicle based on an embodiment. 
         FIG. 2  is a front view showing one example of a bucket  8  according to the embodiment. 
         FIG. 3  is a rear view showing one example of bucket  8  according to the embodiment. 
         FIG. 4  is a diagram illustrating a tilt cylinder  30  provided in bucket  8 . 
         FIG. 5  is a diagram illustrating a stop position of bucket  8  when bucket  8  pivots around a tilt pin  80 . 
         FIG. 6  is a diagram illustrating a construction of a hydraulic system of a hydraulic excavator CM based on the embodiment. 
         FIG. 7  is a diagram illustrating a position sensor  110 . 
         FIG. 8  is a diagram illustrating a value in reset processing based on the embodiment. 
         FIG. 9  is a flowchart illustrating an operation by a reset processing unit  130 A based on the embodiment. 
         FIG. 10  is a flowchart illustrating an operation by reset processing unit  130 A based on a first modification of the embodiment. 
         FIG. 11  is a flowchart illustrating an operation by reset processing unit  130 A based on a second modification of the embodiment. 
         FIG. 12  is a flowchart illustrating an operation by reset processing unit  130 A based on a third modification of the embodiment. 
         FIG. 13  is a flowchart illustrating an operation by reset processing unit  130 A based on a fourth modification of the embodiment. 
         FIG. 14  is a diagram schematically showing one example of an operation of a work implement  2  when excavation limit control (intervention control) is carried out. 
         FIG. 15  is a flowchart illustrating an operation by reset processing unit  130 A based on another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Though an embodiment according to the present invention will be described hereinafter with reference to the drawings, the present invention is not limited thereto. Constituent features in each embodiment described below can be combined as appropriate. Some constituent elements may not be employed. 
     [Overall Construction of Work Vehicle] 
       FIG. 1  is a perspective view showing one example of a work vehicle based on an embodiment. 
     As shown in  FIG. 1 , in the present example, a hydraulic excavator CM including a work implement  2  actuated with a hydraulic pressure will be described by way of example as a work vehicle. 
     Hydraulic excavator CM includes a vehicular body  1  and work implement  2 . 
     A controller  200  which controls work implement  2  is mounted on hydraulic excavator CM. 
     Vehicular body  1  has a revolving unit  3 , an operator&#39;s cab  4 , and a traveling apparatus  5 . 
     Revolving unit  3  is arranged on traveling apparatus  5 . Traveling apparatus  5  supports revolving unit  3 . Revolving unit  3  can revolve around an axis of revolution AX. Operator&#39;s cab  4  is provided with an operator&#39;s seat  4 S where an operator sits. The operator operates hydraulic excavator CM in operator&#39;s cab  4 . Traveling apparatus  5  has a pair of crawler belts  5 Cr. Hydraulic excavator CM travels as crawler belts  5 Cr rotate. Traveling apparatus  5  may include wheels (tires). 
     In the present embodiment, positional relation among portions will be described with the operator seated at operator&#39;s seat  4 S being defined as the reference. 
     A fore/aft direction refers to a fore/aft direction with the operator who sits at operator&#39;s seat  4 S being defined as the reference. A lateral direction refers to a lateral direction with the operator who sits at operator&#39;s seat  4 S being defined as the reference. The lateral direction corresponds to a direction of width of the vehicle (a direction of vehicle width). A direction in which the operator sitting at operator&#39;s seat  4 S faces is defined as a fore direction and a direction opposed to the fore direction is defined as an aft direction. A right side and a left side at the time when the operator sitting at operator&#39;s seat  4 S faces front are defined as a right direction and a left direction, respectively. The fore/aft direction corresponds to the X-axis direction, and the lateral direction corresponds to the Y-axis direction. The direction in which the operator sitting at operator&#39;s seat  4 S faces is the fore direction (a +X direction), and the direction opposite to the fore direction is the aft direction (a −X direction). A direction on one side of the direction of vehicle width at the time when the operator sitting at operator&#39;s seat  4 S faces is the right direction (a +Y direction), and a direction on the other side of the direction of vehicle width is the left direction (a −Y direction). 
     Revolving unit  3  has an engine compartment  9  accommodating an engine and a counter weight provided in a rear portion of revolving unit  3 . In revolving unit  3 , a handrail  19  is provided in front of engine compartment  9 . In engine compartment  9 , an engine and a hydraulic pump are arranged. 
     Work implement  2  is connected to revolving unit  3 . 
     Work implement  2  has a boom  6 , an arm  7 , a bucket  8 , a boom cylinder  10 , an arm cylinder  11 , a bucket cylinder  12 , and a tilt cylinder  30 . 
     Boom  6  is connected to revolving unit  3  with a boom pin  13  being interposed. Arm  7  is connected to boom  6  with an arm pin  14  being interposed. Bucket  8  is connected to arm  7  with a bucket pin  15  and a tilt pin  80  being interposed. Boom cylinder  10  drives boom  6 . Arm cylinder  11  drives arm  7 . Bucket cylinder  12  drives bucket  8 . A proximal end portion of boom  6  (a boom foot) and revolving unit  3  are connected to each other. A distal end portion of boom  6  (a boom top) and a proximal end portion of arm  7  (an arm foot) are connected to each other. A distal end portion of arm  7  (an arm top) and a proximal end portion of bucket  8  are connected to each other. Each of boom cylinder  10 , arm cylinder  11 , bucket cylinder  12 , and tilt cylinder  30  is implemented by a hydraulic cylinder driven with a hydraulic oil. 
     Work implement  2  has a first stroke sensor  16 , a second stroke sensor  17 , and a third stroke sensor  18 . First stroke sensor  16  is arranged in boom cylinder  10  and detects a stroke length of boom cylinder  10  (a boom cylinder length). Second stroke sensor  17  is arranged in arm cylinder  11  and detects a stroke length of arm cylinder  11  (an arm cylinder length). Third stroke sensor  18  is arranged in bucket cylinder  12  and detects a stroke length of bucket cylinder  12  (a bucket cylinder length). 
     Boom  6  is pivotable with respect to revolving unit  3  around a boom axis J 1  which is a pivot axis. Arm  7  is pivotable with respect to boom  6  around an arm axis J 2  which is an axis of rotation in parallel to boom axis J 1 . Bucket  8  is pivotable with respect to arm  7  around a bucket axis J 3  which is a pivot axis in parallel to boom axis J 1  and arm axis J 2 . Bucket  8  is pivotable with respect to arm  7  around a tilt axis J 4  which is a pivot axis orthogonal to bucket axis J 3 . Boom pin  13  has boom axis J 1 . Arm pin  14  has arm axis J 2 . Bucket pin  15  has bucket axis J 3 . Tilt pin  80  has tilt axis J 4 . 
     Boom axis J 1 , arm axis J 2 , and bucket axis J 3  are each in parallel to the Y axis. Boom  6 , arm  7 , and bucket  8  are each pivotable in the θy direction. 
     In the description below, a stroke length of boom cylinder  10  is also referred to as a boom cylinder length or a boom stroke. A stroke length of arm cylinder  11  is also referred to as an arm cylinder length or an arm stroke. A stroke length of bucket cylinder  12  is also referred to as a bucket cylinder length or a bucket stroke. A stroke length of tilt cylinder  30  is also referred to as a tilt cylinder length. 
     In the description below, a boom cylinder length, an arm cylinder length, a bucket cylinder length, and a tilt cylinder length are also collectively referred to as cylinder length data. 
     [Construction of Bucket] 
     Bucket  8  based on the embodiment will now be described. 
       FIG. 2  is a front view showing one example of bucket  8  according to the embodiment.  FIG. 3  is a rear view showing one example of bucket  8  according to the embodiment. 
     Bucket  8  is a tilt type bucket. 
     As shown in  FIGS. 2 and 3 , work implement  2  has bucket  8  which is pivotable with respect to arm  7  around tilt pin (tilt axis)  80 . 
     Bucket  8  is connected to a distal end portion of arm  7  with a connection member (a base frame)  91  being interposed. Tilt pin  80  couples connection member  91  and bucket  8  to each other. Bucket  8  is pivotably connected to arm  7  with connection member  91  being interposed. 
     Bucket  8  has a bottom plate  92 , a back plate  93 , an upper plate  83 , a side plate  84 , and a side plate  85 . Bottom plate  92 , upper plate  83 , side plate  84 , and side plate  85  define an opening of bucket  8 . 
     Bucket  8  has a bracket provided above upper plate  83 . The bracket is placed at front and rear positions of upper plate  83 . In the present example, by way of example, brackets  87 A and  87 B (also collectively referred to as a bracket  87 ) are provided in front and rear positions. Brackets  87 A and  87 B are coupled to connection member  91  and tilt pin  80 . 
     Connection member  91  has stoppers  90 A to  90 D which are also collectively referred to as a stopper  90 . 
     Stopper  90  is provided as a stop position when bucket  8  pivots around tilt pin  80 . By providing stopper  90 , bucket  8  can be prevented from interfering with arm  7 . 
     Bracket  87  has a projection portion. In the present example, bracket  87 A has projection portions  88 A and  88 B on its left and right. Bracket  87 B has projection portions  88 C and  88 D on its left and right. Projection portions  88 A to  88 D (also collectively referred to as a projection portion  88 ) are provided in correspondence with stoppers  90 A to  90 D, respectively. Projection portion  88  is provided at a position where it abuts to corresponding stopper  90  when bucket  8  pivots. 
       FIG. 4  is a diagram illustrating tilt cylinder  30  provided in bucket  8 . 
     As shown in  FIG. 4 , tilt cylinders  30 A and  30 B are provided on the left and right with respect to tilt pin  80 . Tilt cylinders  30 A and  30 B contract and extend such that bucket  8  pivots around tilt pin  80 . A total stroke length of tilt cylinders  30 A and  30 B when tilt cylinders  30 A and  30 B contract and extend is constant. 
       FIG. 5  is a diagram illustrating a stop position of bucket  8  when bucket  8  pivots around tilt pin  80 . 
     As shown in  FIG. 5  (A), tilt cylinders  30 A and  30 B contract and extend so that bucket  8  pivots in a first direction. Specifically, tilt cylinder  30 A contracts and tilt cylinder  30 B extends so that bucket  8  pivots in the first direction. 
     When bucket  8  continues to pivot in the first direction, projection portion  88 B provided in bracket  87 A of bucket  8  abuts to stopper  90 B. Similarly, projection portion  88 C provided in bracket  87 B of bucket  8  abuts to stopper  90 C. 
     Therefore, when bucket  8  pivots in the first direction around tilt pin  80 , projection portions  88 B and  88 C abut to stoppers  90 B and  90 C, respectively. 
     As shown in  FIG. 5  (B), tilt cylinders  30 A and  30 B contract and extend so that bucket  8  pivots in a second direction opposite to the first direction. Specifically, tilt cylinder  30 B contracts and tilt cylinder  30 A extends so that bucket  8  pivots in the second direction. 
     When bucket  8  continues to pivot in the second direction, projection portion  88 A provided in bracket  87 A of bucket  8  abuts to stopper  90 A. Similarly, projection portion  88 D provided in bracket  87 B of bucket  8  abuts to stopper  90 D. 
     Therefore, when bucket  8  pivots in the second direction around tilt pin  80 , projection portions  88 A and  88 D abut to stoppers  90 A and  90 D, respectively. 
     Though the description will be given later, in the present example, reset processing is performed at a stroke end where tilt cylinders  30 A and  30 B extend, or contract and extend. 
     [Construction of Hydraulic System] 
       FIG. 6  is a diagram illustrating a construction of a hydraulic system of hydraulic excavator CM based on the embodiment. 
     As shown in  FIG. 6 , the hydraulic system includes controller  200 , a control lever apparatus  101 , a fuel dial  201 , tilt cylinder  30 , an engine  3 A, a control valve  102 , a hydraulic pump  103 , a servo mechanism  104 , a fuel regulation mechanism  105 , a discharge oil path  106 , oil paths  107  and  108 , a flow rate regulation mechanism  109 , and a measurement controller  300 . 
     An electric signal is input from electric control lever apparatus  101  to controller  200  and a control electric signal is supplied from controller  200  to control valve  102  for hydraulic cylinder (tilt cylinder)  30  and flow rate regulation mechanism  109 , so that tilt cylinder  30  is driven. Though control valve  102  and flow rate regulation mechanism  109  are provided separately from each other, they can also be integrally formed. 
     Though tilt cylinders  30 A and  30 B are actually provided, they are described as tilt cylinder  30  for the sake of convenience of illustration in the present example. When tilt cylinder  30 A extends, tilt cylinder  30 B contracts. In contrast, when tilt cylinder  30 A contracts, tilt cylinder  30 A extends. 
     Though hydraulic cylinders of boom cylinder  10 , arm cylinder  11 , and bucket cylinder  12  are provided in actual hydraulic excavator CM, only tilt cylinder  30  is shown and others are not shown for brevity of illustration. 
     Tilt cylinder  30  is driven, for example, by hydraulic pump  103  of a variable capacity type serving as a drive source. Hydraulic pump  103  is driven by engine  3 A. A swash plate  103 A of hydraulic pump  103  is driven by servo mechanism  104 . Servo mechanism  104  is actuated in response to a control signal (an electric signal) output from controller  200  so that swash plate  103 A of hydraulic pump  103  is moved to a position in accordance with the control signal. A speed of engine  3 A is controlled based on an amount of supply of a fuel controlled by fuel regulation mechanism  105 . 
     A discharge port of hydraulic pump  103  communicates with control valve  102  through discharge oil path  106 . Control valve  102  communicates with oil chambers  40 B and  40 H of tilt cylinder  30  through respective oil paths  107  and  108 . The hydraulic oil discharged by hydraulic pump  103  is supplied to control valve  102  through discharge oil path  106 , and the hydraulic oil which has passed through control valve  102  is supplied to oil chamber  40 B or oil chamber  40 H of tilt cylinder  30  through oil path  107  or  108 . 
     Oil paths  107  and  108  are provided with flow rate regulation mechanism  109  which regulates a flow rate of the hydraulic oil. Specifically, flow rate regulation mechanism  109  includes a flow rate valve (a regulation valve) and regulates a flow rate of the hydraulic oil by regulating a degree of opening in accordance with an instruction from controller  200 . For example, by increasing a degree of opening of the flow rate valve in accordance with the instruction, an amount of the hydraulic oil supplied to tilt cylinder  30  can be increased. By increasing a value for a command signal for increasing a degree of opening, an amount of supply of the hydraulic oil to tilt cylinder  30  increases. 
     Position sensor  110  is attached to tilt cylinder  30 . Position sensor  110  is a stroke sensor which measures a stroke of a piston. 
     Control lever apparatus  101  has, for example, a control lever  101 A provided in operator&#39;s cab  4  and a detection unit  101 B which detects an operation signal indicating a direction of operation and an amount of operation of control lever  101 A. The operation signal detected by detection unit  101 B is input to controller  200 . Control valve  102  is connected to controller  200  through an electric signal line. 
     When control lever  101 A is operated, an operation signal from control lever  101 A is input to controller  200  and controller  200  generates a signal for actuating control valve  102 . The signal is supplied from controller  200  through an electric signal line to control valve  102  so as to vary a position of control valve  102 . 
     Control lever  101 A in the present example accepts from an operator, an instruction for a tilt operation for pivoting bucket  8  laterally around tilt pin  80 . Detection unit  101 B detects an operation signal indicating a direction of operation and an amount of operation of control lever  101 A and outputs the operation signal to controller  200 . 
     Controller  200  generates a signal for regulating a position of control valve  102  in accordance with a lateral direction of operation of control lever  101 A. Controller  200  has tilt cylinder  30  extend by allowing supply of the hydraulic oil to oil chamber  40 B of tilt cylinder  30  through oil path  107  based on adjustment of a position of control valve  102 . Controller  200  has tilt cylinder  30  contract by allowing supply of the hydraulic oil to oil chamber  40 H of tilt cylinder  30  through oil path  108  based on adjustment of a position of control valve  102 . 
     Controller  200  has tilt cylinder  30  extend or contract in accordance with the lateral direction of operation of control lever  101 A. Accordingly, bucket  8  pivots laterally around tilt pin  80 . 
     Controller  200  generates a command signal for regulating a degree of opening of flow rate regulation mechanism  109  in accordance with an amount of operation of control lever  101 A. Controller  200  regulates a flow rate of the hydraulic oil to be supplied to tilt cylinder  30  based on regulation of a degree of opening of flow rate regulation mechanism  109 . Controller  200  varies a value of a command signal output to flow rate regulation mechanism  109  in accordance with an amount of operation of control lever  101 A. An amount of supply of the hydraulic oil supplied to tilt cylinder  30  is regulated in accordance with a value of the command signal, so that a pivot speed of bucket  8  varies. 
     When an amount of operation of control lever  101 A is great, a value of the command signal is greater and a degree of opening of flow rate regulation mechanism  109  is greater. Accordingly, an amount of supply of the hydraulic oil to tilt cylinder  30  increases. 
     When an amount of operation of control lever  101 A is small, a value of the command signal is smaller and a degree of opening of flow rate regulation mechanism  109  is smaller. Accordingly, an amount of supply of the hydraulic oil to tilt cylinder  30  decreases. 
     Position sensor  110  which detects an amount of stroke of the hydraulic cylinder as an amount of rotation is attached to tilt cylinder  30 . 
     Position sensor  110  is electrically connected to measurement controller  300 . Measurement controller  300  measures a stroke length of tilt cylinder  30  based on a detection signal from position sensor  110 . The measured stroke length is output to controller  200 . 
     Controller  200  can operate a position and an attitude of bucket  8  based on a stroke length measured by measurement controller  300 . 
     Fuel dial  201  is provided, for example, in operator&#39;s cab  4 . Fuel dial  201  is constructed such that it can be operated and turned by an operator. Fuel dial  201  is a dial switch which regulates an amount of supply of a fuel to be supplied to engine  3 A. By turning fuel dial  201  toward Max, an amount of supply of a fuel to engine  3 A increases. By turning fuel dial  201  toward Min, an amount of supply of a fuel to engine  3 A decreases. A speed of engine  3 A is varied in accordance with an amount of supply of the fuel. Since hydraulic pump  103  is coupled to engine  3 A, a pump pressure also varies in accordance with the speed of engine  3 A. Specifically, as the speed of engine  3 A is higher, a pump pressure increases, and when the engine speed is lower, a pump pressure decreases. 
     Controller  200  controls the entire hydraulic excavator CM. In the present example, a reset processing unit  130 A and an intervention control unit  130 B are included as some of functions of controller  200 . Though not shown, controller  200  has a memory which stores a program and a numeric value necessary for operations by reset processing unit  130 A and intervention control unit  130 B. 
     Reset processing unit  130 A performs processing for resetting a stroke length measured by measurement controller  300  because an error is caused between a stroke position obtained based on a result of detection by position sensor  110  and an actual stroke position. 
     Intervention control unit  130 B carries out intervention control which will be described later. 
     [Configuration of Position Sensor] 
       FIG. 7  is a diagram illustrating position sensor  110 . 
     As shown in  FIG. 7 , position sensor  110  is provided in tilt cylinder  30 . Though position sensor  110  attached to tilt cylinder  30  is described for the sake of convenience of illustration, similar position sensor  110  is attached also to other cylinders. 
     Tilt cylinder  30  has a cylinder tube  4 X and a cylinder rod  4 Y which is movable relatively to cylinder tube  4 X in cylinder tube  4 X. A piston  4 V is slidably provided in cylinder tube  4 X. Cylinder rod  4 Y is attached to piston  4 V. Cylinder rod  4 Y is slidably provided in a cylinder head  4 W. A chamber delimited by cylinder head  4 W, piston  4 V, and an inner wall of the cylinder forms oil chamber  40 H on a side of the cylinder head. An oil chamber opposite to oil chamber  40 H on the side of cylinder head with piston  4 V being interposed forms oil chamber  40 B on a side of a cylinder bottom. Cylinder head  4 W is provided with a sealing member which hermetically seals a gap between the cylinder head and cylinder rod  4 Y so as to prevent dust or the like from entering oil chamber  40 H on the side of the cylinder head. 
     Cylinder rod  4 Y retracts as a result of supply of the hydraulic oil to oil chamber  40 H on the side of the cylinder head and discharge of the hydraulic oil from oil chamber  40 B on the side of the cylinder bottom. Cylinder rod  4 Y extends as a result of discharge of the hydraulic oil from oil chamber  40 H on the side of the cylinder head and supply of the hydraulic oil to oil chamber  40 B on the side of the cylinder bottom. Cylinder rod  4 Y linearly moves in the lateral direction in the figure. 
     A case  114  which covers position sensor  110  and accommodates position sensor  110  is provided at a location outside oil chamber  204 H on the side of the cylinder head and in intimate contact with cylinder head  4 W. Case  114  is fixed to cylinder head  4 W as being fastened by a bolt or the like to cylinder head  4 W. 
     Position sensor  110  has a rotary roller  111 , a central shaft of rotation  112 , and a rotation sensor unit  113 . Rotary roller  111  is provided to come in contact with a surface of cylinder rod  4 Y at its surface and to be rotatable with linear movement of cylinder rod  4 Y. Rotary roller  111  converts rectilinear motion of cylinder rod  4 Y into rotary motion. Central shaft of rotation  112  is arranged to be orthogonal to a direction of linear movement of cylinder rod  4 Y. 
     Rotation sensor unit  113  is configured to be able to detect an amount of rotation (an angle of rotation) of rotary roller  111 . A signal indicating an amount of rotation (an angle of rotation) of rotary roller  111  detected by rotation sensor unit  113  is sent to measurement controller  300  through an electric signal line. Measurement controller  300  converts a signal indicating an amount of rotation into a position of cylinder rod  4 Y (a stroke position) of tilt cylinder  30 . 
     [Description of Reset Processing] 
       FIG. 8  is a diagram illustrating a value in reset processing based on the embodiment. 
     As shown in  FIG. 8 , an initial value is shown and a maximal value Pmm and a minimal value Qmm are shown. A value stored in advance may be made use of as an initial value, or a value obtained by calibration can also be made use of. Specifically, a value may be obtained by rotating bucket  8  a plurality of times laterally around tilt pin  80 , measuring a stroke length of tilt cylinder  30  a plurality of times, and calculating an average value of measurement values. 
     [Control of Reset Processing Unit  130 A] 
       FIG. 9  is a flowchart illustrating an operation by reset processing unit  130 A based on the embodiment. 
     Referring to  FIG. 9 , reset processing unit  130 A obtains a stroke length (step S 2 ). Reset processing unit  130 A obtains a stroke length of tilt cylinder  30  measured by measurement controller  300 . 
     Then, reset processing unit  130 A makes determination as to proximity to a stroke end (step S 4 ). Tilt cylinder  30  extends or contracts in accordance with a tilt operation instruction through control lever  101 A from an operator. Reset processing unit  130 A determines whether or not a current stroke length is in the proximity of the stroke end based on the obtained stroke length. The stroke end means both of a maximum state in which tilt cylinder  30  extends and a minimum state in which tilt cylinder  30  contracts. Specifically, as to proximity to the stroke end when tilt cylinder  30  extends, whether or not a stroke length is within a prescribed range with maximal value Pmm of the initial value described with reference to  FIG. 8  being defined as the reference is determined. Alternatively, as to proximity to the stroke end when tilt cylinder  30  contracts, whether or not a stroke length is within a prescribed range with minimal value Qmm being defined as the reference is determined. In the present example, though an example in which determination as being in the proximity of the stroke end is made when the stroke length is within the prescribed range with the maximal or minimal value for the initial value being defined as the reference is described, limitation thereto is not intended. For example, when the stroke length exceeds maximal value Pmm in the case of extension, determination as being in the proximity of the stroke end may be made, and when the stroke length is smaller than minimal value Qmm in the case of contraction, determination as being in the proximity of the stroke end may be made. 
     Then, when reset processing unit  130 A makes determination as not being in the proximity of the stroke end (NO in step S 4 ), the process returns to step S 2  and measurement of a stroke length is continued. 
     When reset processing unit  130 A makes determination as being in the proximity of the stroke end (YES in step S 4 ), it performs supply amount regulation processing (step S 6 ). Specifically, reset processing unit  130 A regulates an amount of supply of the hydraulic oil to be supplied to tilt cylinder  30 . In the present example, an amount of supply of the hydraulic oil to be supplied to tilt cylinder  30  is increased. Reset processing unit  130 A instructs flow rate regulation mechanism  109  to increase an amount of supply of the hydraulic oil to tilt cylinder  30  in the proximity of the stroke end as compared with an amount of supply in a case other than being in the proximity of the stroke end. Specifically, reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . For example, reset processing unit  130 A increases a value of the command signal given to flow rate regulation mechanism  109 . Reset processing unit  130 A may set a value of the command signal to the maximal value. Accordingly, a degree of opening of flow rate regulation mechanism  109  is regulated to be greater so that an amount of supply of the hydraulic oil to tilt cylinder  30  increases. Therefore, the tilt cylinder is further pushed from the proximity of the stroke end toward the stroke end. 
     Reset processing unit  130 A performs reset processing (step S 8 ). 
     Reset processing unit  130 A instructs measurement controller  300  to reset the measured stroke length. Specifically, reset processing unit  130 A makes setting again (resets) to stroke length Pmm in the case of extension and to stroke length Qmm in the case of contraction which are the initial values. 
     Then, the process ends (end). 
     When the stroke length is reset with the stroke end of tilt cylinder  30  (hydraulic cylinder) being defined as the reference position, the stroke length may be reset in such a situation that the reference position is not reached due to manufacturing errors or wobble of work implement  2 . 
     Therefore, when determination as being in the proximity of the stroke end is made, by further pushing the tilt cylinder from the proximity of the stroke end toward the stroke end through supply amount regulation processing, the reference position can be reached. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. Thus, a stroke length can highly accurately be measured. 
     In the present example, a stroke end of tilt cylinder  30  is defined by stopper  90 . 
     Specifically, pivot of bucket  8  is stopped by abutment between projection portion  88  provided in bracket  87  of bucket  8  and stopper  90 . 
     In this connection, pivot may be stopped while projection portion  88  and stopper  90  partially abut to each other due to manufacturing errors in positional relation between projection portion  88  and stopper  90  or wobble. When reset processing is performed at such a position, reset processing is performed with an error being incorporated and correction is not accurately made. Therefore, a stroke length with an error may be measured. 
     Therefore, by further pushing the tilt cylinder from the proximity of the stroke end toward the stroke end through supply amount regulation processing in the proximity of the stroke end representing the feature above, the reference position (a state of full abutment between projection portion  88  and stopper  90 ) can be reached. By performing reset processing in such a state, a deviation in stroke length can accurately be corrected. Thus, a stroke length can highly accurately be measured. Though abutment between projection portion  88  and stopper  90  is described in the present example, description is the same also in a construction without projection portion  88 . 
     When stopper  90  is provided for each of brackets  87 A and  87 B provided in the fore/aft direction of bucket  8 , projection portion  88  may abut to only one stopper  90  and projection portion  88  may not abut to the other stopper  90  due to manufacturing errors or wobble of the work implement. By way of example, in  FIG. 5  (A), projection portion  88 B provided in bracket  87 A abuts to stopper  90 B, whereas projection portion  88 C provided in bracket  87 B may not abut to stopper  90 C. When reset processing is performed at such a position, reset processing is performed with an error being incorporated and correction is not accurately made. Therefore, a stroke length with an error may be measured. 
     Therefore, by further pushing the tilt cylinder from the proximity of the stroke end toward the stroke end through supply amount regulation processing in the proximity of the stroke end representing the feature above, the reference position where projection portion  88 C provided in bracket  87 B also abuts to stopper  90 C can be reached. By performing reset processing in such a state, a deviation in stroke length can accurately be corrected. Thus, a stroke length can highly accurately be measured. 
     Though controller  200  outputs an electric signal as a command signal which regulates a degree of opening of flow rate regulation mechanism  109  in the present example, limitation to an electric signal is not particularly intended. When a scheme is such that flow rate regulation mechanism  109  regulates a flow rate in accordance with a pressure signal, a value of a pressure signal as the command signal may be increased. 
     (First Modification) 
       FIG. 10  is a flowchart illustrating an operation by reset processing unit  130 A based on a first modification of the embodiment. 
     Referring to  FIG. 10 , addition of steps S 10  and S 12  is different from the flowchart in  FIG. 9 . Since other features are the same as those described with reference to  FIG. 9 , detailed description thereof will not be repeated. 
     When reset processing unit  130 A makes determination in step S 4  as being in the proximity of stroke end (YES in step S 4 ), it determines whether or not a tilt operation has been input (step S 10 ). Reset processing unit  130 A determines whether or not an operation signal has been input from control lever  101 A. When an operation signal has been input from control lever  101 A, the reset processing unit determines that a tilt operation has been input. 
     Then, when reset processing unit  130 A determines in step S 10  that a tilt operation has been input (YES in step S 10 ), it determines whether or not an operation command is equal to or greater than a prescribed amount (step S 12 ). Reset processing unit  130 A determines whether or not an instruction for an amount of operation included in the operation signal from control lever  101 A is equal to or greater than a prescribed amount. The prescribed amount is set to any value and stored in advance in a not-shown memory. 
     When reset processing unit  130 A determines in step S 12  that the operation command is equal to or greater than the prescribed amount (YES in step S 12 ), it performs supply amount regulation processing (step S 6 ). Specifically, reset processing unit  130 A instructs flow rate regulation mechanism  109  to regulate an amount of supply of the hydraulic oil to be supplied to tilt cylinder  30 . In the present example, an amount of supply of the hydraulic oil to be supplied to tilt cylinder  30  is increased. Reset processing unit  130 A instructs flow rate regulation mechanism  109  to increase an amount of supply of the hydraulic oil to tilt cylinder  30  in the proximity of the stroke end as compared with an amount of supply in a case other than being in the proximity of the stroke end. Specifically, reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . For example, reset processing unit  130 A increases a value of the command signal given to flow rate regulation mechanism  109 . Reset processing unit  130 A may set a value of the command signal to the maximal value. Accordingly, a degree of opening of flow rate regulation mechanism  109  is regulated to be greater so that an amount of supply of the hydraulic oil to tilt cylinder  30  increases. Therefore, the tilt cylinder is further pushed from the proximity of the stroke end toward the stroke end. Since subsequent processing is the same as described above, detailed description thereof will not be repeated. 
     In the present example, reset processing unit  130 A performs supply amount regulation processing when a tilt operation is input and when an operation command is equal to or greater than a prescribed amount. Therefore, since reset processing is performed in response to an operation instruction from an operator in the proximity of the stroke end, reset processing as intended by the operator can be performed. 
     (Second Modification) 
       FIG. 11  is a flowchart illustrating an operation by reset processing unit  130 A based on a second modification of the embodiment. 
     Referring to  FIG. 11 , addition of step S 7  is different from the flowchart in  FIG. 10 . Since other features are the same as those described with reference to  FIG. 10 , detailed description thereof will not be repeated. 
     In step S 6 , reset processing unit  130  performs supply amount regulation processing and then determines whether or not the supply amount regulation processing has been continued for a prescribed period (step S 7 ). The prescribed period is set to any value and stored in advance in a not-shown memory. 
     When reset processing unit  130 A determines in step S 7  that the supply amount regulation processing has not been continued for a prescribed period (NO in step S 7 ), the process returns to step S 10  and the reset processing unit determines whether or not a tilt operation has been input. Subsequent processing is the same. 
     When reset processing unit  130 A determines in step S 7  that the supply amount regulation processing has been continued for the prescribed period (YES in step S 7 ), it performs reset processing (step S 8 ). 
     Therefore, in the present example, reset processing unit  130 A performs the supply amount regulation processing when a tilt operation is input and when an operation command is equal to or greater than a prescribed amount, and performs reset processing when a tilt operation instruction has continued for a prescribed period. Therefore, in performing reset processing in response to an operation instruction from an operator, when a tilt operation is input in response to an erroneous operation (a tilt operation is input for a period shorter than a prescribed period), reset processing is not performed. In performing reset processing in response to an operation instruction from an operator, when a tilt operation is input for a period equal to or longer than a prescribed period, reset processing is performed with an intention of an operator being reflected. 
     With such a scheme, reset processing with an erroneous operation being prevented and an intention of an operator being properly determined can be performed. 
     (Third Modification) 
       FIG. 12  is a flowchart illustrating an operation by reset processing unit  130 A based on a third modification of the embodiment. 
     Referring to  FIG. 12 , addition of steps S 14  and S 16  is different from the flowchart in  FIG. 10 . Since other features are the same as those described with reference to  FIG. 10 , detailed description thereof will not be repeated. 
     When reset processing unit  130 A determines in step S 12  that an operation command is equal to or greater than a prescribed amount (YES in step S 12 ), it obtains a cylinder speed (step S 14 ). Reset processing unit  130 A obtains a cylinder speed based on variation in measured stroke length. 
     Then, whether or not the cylinder is equal to or lower than a prescribed speed is determined (step S 16 ). Reset processing unit  130 A determines whether or not the obtained cylinder speed is equal to or lower than the prescribed speed. The prescribed speed is stored in advance in a not-shown memory. 
     When it is determined in step S 16  that the cylinder is not equal to or lower than the prescribed speed (NO in step S 16 ), reset processing ends (end). 
     When it is determined in step S 16  that the cylinder is equal to or lower than the prescribed speed (YES in step S 16 ), supply amount regulation processing is performed. Since subsequent processing is the same as described with reference to  FIG. 9 , detailed description thereof will not be repeated. 
     Therefore, in the present example, reset processing unit  130 A checks a cylinder speed when a tilt operation is input and when an operation command is equal to or greater than a prescribed amount, and performs supply amount regulation processing when the cylinder speed is equal to or lower than a prescribed speed. When an error in stroke length measured by measurement controller  300  is great, reset processing may be performed based on determination as being in the proximity of the stroke end which results from erroneous recognition. 
     In the present example, proximity to the stroke end is further checked based on a cylinder speed. When determination as not being in the proximity of the stroke end in which case a cylinder speed is equal to or higher than a prescribed speed is made based on determination as to proximity to the stroke end where a cylinder speed is equal to or lower than a prescribed speed, reset processing is not performed. When determination as being in the proximity of the stroke end where a cylinder speed is equal to or lower than a prescribed speed is made, reset processing is performed. 
     Through the processing, even when an error in stroke length measured by measurement controller  300  is great, reset processing based on erroneous recognition is not performed but the reference position can reliably be reached by checking a cylinder speed. A stroke length can thus highly accurately be measured. 
     (Fourth Modification) 
       FIG. 13  is a flowchart illustrating an operation by reset processing unit  130 A based on a fourth modification of the embodiment. 
     Referring to  FIG. 13 , addition of steps S 20  and S 22  is different from the flowchart in  FIG. 9 . Since other features are the same as those described with reference to  FIG. 9 , detailed description thereof will not be repeated. 
     When reset processing unit  130 A determines in step S 4  as being in the proximity of the stroke end (YES in step S 4 ), it checks a value of fuel dial  201  (step S 20 ). Reset processing unit  130 A determines whether or not a value of fuel dial  201  is equal to or greater than a prescribed value (step S 22 ). The prescribed value is stored in advance in a not-shown memory. 
     When it is determined in step S 22  that a value of fuel dial  201  is equal to or greater than the prescribed value (YES in step S 22 ), supply amount regulation processing is performed (step S 6 ). Since subsequent processing is the same as described above, detailed description thereof will not be repeated. 
     In the present example, whether or not a value of fuel dial  201  is equal to or greater than a prescribed value is checked. Fuel dial  201  regulates an amount of supply of a fuel to engine  3 A. An amount of supply of a fuel to engine  3 A correlates with a speed of engine  3 A. Therefore, when a value of fuel dial  201  is small, the speed of engine  3 A is low and a pump pressure of hydraulic pump  103  may be low. When a pump pressure is low, appropriate supply amount regulation processing may not be performed. 
     Therefore, in the present example, whether or not a value of fuel dial  201  is equal to or greater than a prescribed value is checked. When a value of fuel dial  201  is equal to or greater than a prescribed value, a pump pressure of hydraulic pump  103  is equal to or greater than the prescribed value. Therefore, appropriate supply amount regulation processing for reaching the reference position by further pushing the tilt cylinder from the proximity of the stroke end toward the stroke end can be performed. By reliably performing reset processing at the reference position in consideration of a pump pressure through the processing, a deviation in stroke length can accurately be corrected. A stroke length can thus highly accurately be measured. 
     Another Embodiment 
     A configuration for performing reset processing in the proximity of a stroke end has been described in the embodiments above. In another embodiment, a configuration not performing reset processing when a prescribed condition is satisfied will be described. 
     Intervention control unit  130 B controls an excavation operation in which work implement  2  is used. Control of the excavation operation has excavation limit control by way of example. 
       FIG. 14  is a diagram schematically showing one example of an operation of work implement  2  when excavation limit control (intervention control) is carried out. 
     As shown in  FIG. 14 , excavation limit control is carried out such that entry of bucket  8  into target design topography which represents a two-dimensional target shape of an object to be excavated at a work implement motion plane MP is avoided. 
     Intervention control unit  130 B automatically controls excavation by bucket  8  such that boom  6  is raised with respect to an excavation operation of arm  7 . Intervention control having an operation to raise boom  6  is carried out such that entry of bucket  8  into target design topography is avoided during excavation. 
     In the present example, while intervention control unit  130 B is operating, reset processing is not performed. 
       FIG. 15  is a flowchart illustrating an operation by reset processing unit  130 A based on another embodiment. 
     Referring to  FIG. 15 , addition of steps S 30  and S 32  is different from the flowchart in  FIG. 9 . Since other features are the same as those described with reference to  FIG. 9 , detailed description thereof will not be repeated. 
     When reset processing unit  130 A determines in step S 4  as being in the proximity to the stroke end (YES in step S 4 ), it checks a control mode (step S 30 ). Reset processing unit  130 A checks a status of intervention control unit  130 B. 
     Then, reset processing unit  130 A determines whether or not intervention control is being carried out (step S 32 ). Reset processing unit  130 A determines whether or not intervention control unit  130 B is operating, and when the intervention control unit is operating, the reset processing unit determines that intervention control is being carried out. 
     When reset processing unit  130 A determines in step S 32  that intervention control is being carried out (YES in step S 32 ), reset processing ends (end). Specifically, reset processing unit  130 A does not generate a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     When reset processing unit  130 A determines that intervention control is not being carried out (NO in step S 32 ), it performs supply amount regulation processing (step S 6 ). Since subsequent processing is the same as described above, detailed description thereof will not be repeated. 
     In the present example, when excavation limit control (intervention control) in which intervention control unit  130 B is operating is being carried out, reset processing unit  130 A does not perform reset processing, and when intervention control is not being carried out, the reset processing unit performs reset processing. 
     Through the processing, when reset processing is performed during intervention control, processing different from processing in a normal operation is performed and a process may be interrupted. An operator may feel strange, which may cause an erroneous operation. Therefore, by not performing reset processing during intervention control, intervention control can smoothly be carried out. 
     Though excavation limit control has been described by way of example of intervention control in the present example, other intervention control such as stop control is also similarly applicable. 
     &lt;Others&gt; 
     Combination of each of first to fourth modifications with another embodiment for reset processing by reset processing unit  130 A can also be employed. 
     &lt;Function and Effect&gt; 
     A function and effect of the present embodiment will now be described. 
     As shown in  FIG. 1 , work vehicle CM in the present embodiment is provided with vehicular body  1  and work implement  2 . Work implement  2  has boom  6  pivotable with respect to vehicular body  1  and bucket  8  pivotable around bucket axis J 3  which is a pivot axis with respect to arm  7  and tilt axis J 4  orthogonal to bucket axis J 3 . As shown in  FIG. 6 , work vehicle CM is provided with tilt cylinder  30 , flow rate regulation mechanism  109 , position sensor  110 , and reset processing unit  130 A. Tilt cylinder  30  has bucket  8  pivot around tilt axis J 4 . Flow rate regulation mechanism  109  regulates an amount of supply of a hydraulic oil to be supplied to tilt cylinder  30  based on a command signal. Position sensor  110  measures a stroke length of tilt cylinder  30 . Reset processing unit  130 A resets a stroke length measured by position sensor  110 . Reset processing unit  130 A determines proximity to a stroke end of tilt cylinder  30  and generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end. Reset processing unit  130 A resets the stroke length measured by position sensor  110  while flow rate regulation mechanism  109  opens in response to the command signal. 
     Reset processing unit  130 A makes determination as to proximity to the stroke end, and when it determines as being in the proximity of the stroke end, it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . Flow rate regulation mechanism  109  increases a degree of opening in response to the command signal. Accordingly, supply amount regulation processing for increasing an amount of supply of the hydraulic oil to tilt cylinder  30  is performed. By further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end through the supply amount regulation processing, the tilt cylinder can reach the reference position. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. Accordingly, a stroke length can highly accurately be measured. 
     As shown in  FIG. 2 , work vehicle CM is provided with stopper  90  which stops pivot of bucket  8  by abutting to the bucket. Reset processing unit  130 A determines proximity to a stroke end of tilt cylinder  30  based on presence of stopper  90 , and generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end. Reset processing unit  130 A resets the stroke length measured by position sensor  110  when bucket  8  abuts to stopper  90  while flow rate regulation mechanism  109  opens in response to the command signal. 
     Pivot of bucket  8  may be stopped by partial abutment to stopper  90  due to manufacturing errors in positional relation of stopper  90  or wobble. When reset processing is performed at such a position, reset processing is performed with an error being incorporated and correction is not accurately made. Therefore, a stroke length with an error may be measured. Reset processing unit  130 A makes determination as to proximity to the stroke end, and when it makes determination as being in the proximity to the stroke end, it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . Flow rate regulation mechanism  109  increases a degree of opening in response to the command signal. Accordingly, supply amount regulation processing for increasing an amount of supply of the hydraulic oil to tilt cylinder  30  is performed. By further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end through the supply amount regulation processing, the tilt cylinder can reach the reference position where full abutment to stopper  90  is achieved. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. Accordingly, a stroke length can highly accurately be measured. 
     Bucket  8  pivots in the first direction and the second direction opposite to the first direction around tilt axis J 4 . As shown in  FIG. 5  (A), stopper  90  includes stoppers  90 B and  90 C which stop bucket  8  which pivots in the first direction. As shown in  FIG. 5  (B), stopper  90  includes stoppers  90 A and  90 D which stop bucket  8  which pivots in the second direction. Reset processing unit  130 A determines proximity to the stroke end of tilt cylinder  30  based on abutment to any one of stoppers  90 B and  90 C or abutment to any one of stoppers  90 A and  90 D. Reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end. Reset processing unit  130 A resets the stroke length measured by position sensor  110  when the bucket abuts to both of stoppers  90 B and  90 C or when the bucket abuts to both of stoppers  90 A and  90 D while flow rate regulation mechanism  109  opens in response to the command signal. 
     Pivot of bucket  8  may be stopped by abutment only to stopper  90 B (stopper  90 C) or stopper  90 A (stopper  90 D) due to manufacturing errors in positional relation of stoppers  90 B and  90 C or stoppers  90 A and  90 D or wobble. When reset processing is performed at such a position, reset processing is performed with an error being incorporated and correction is not accurately made. Therefore, a stroke length with an error may be measured. Reset processing unit  130 A determines proximity to the stroke end of tilt cylinder  30  based on abutment to any one of stoppers  90 B and  90 C or abutment to any one of stoppers  90 A and  90 D, and when it makes determination as being in the proximity of the stroke end, it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . Flow rate regulation mechanism  109  increases a degree of opening in response to the command signal. Accordingly, supply amount regulation processing for increasing an amount of supply of the hydraulic oil to tilt cylinder  30  is performed. By further pushing the tilt cylinder from the proximity of the stroke end toward the stroke end through the supply amount regulation processing, the reference position where abutment to both of stoppers  90 B and  90 C or both of stoppers  90 A and  90 D is achieved can be reached. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. Accordingly, a stroke length can highly accurately be measured. 
     Reset processing unit  130 A compares a stroke length measured by position sensor  110  with the reference value ( FIG. 8 ) and determines proximity to the stroke end of tilt cylinder  30  based on a result of comparison. Reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end. 
     Reset processing unit  130 A can readily make determination as to proximity to the stroke end by comparing the stroke length measured by position sensor  110  with the reference value. 
     As shown in  FIG. 6 , work vehicle CM is provided with control lever apparatus  101  which drives flow rate regulation mechanism  109 . Reset processing unit  130 A determines whether or not an operation command from control lever apparatus  101  is equal to or greater than a prescribed value, and when it determines that the operation command from control lever apparatus  101  is equal to or greater than the prescribed value in the proximity of the stroke end, it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     Reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in accordance with an operation instruction from an operator indicating that an operation command from control lever apparatus  101  be equal to or greater than a prescribed value in the proximity of the stroke end. Flow rate regulation mechanism  109  increases a degree of opening in response to the command signal. Accordingly, supply amount regulation processing for increasing an amount of supply of the hydraulic oil to tilt cylinder  30  is performed. By further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end through the supply amount regulation processing, the reference position can be reached. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. In performing reset processing, reset processing in accordance with an intention for operation by an operator can be performed. 
     Reset processing unit  130 A calculates a cylinder speed of tilt cylinder  30  based on a measurement value from position sensor  110 . When the reset processing unit determines that the cylinder speed of tilt cylinder  30  calculated in the proximity of the stroke end is equal to or smaller than a prescribed value and that an operation command from control lever apparatus  101  is equal to or greater than a prescribed value, it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     Even when an operation command from control lever apparatus  101  is equal to or greater than a prescribed value in the proximity of the stroke end, a cylinder speed of tilt cylinder  30  is equal to or smaller than a prescribed value. Therefore, by checking a cylinder speed, proximity to the stroke end can be determined without erroneous recognition. By thus reliably making determination as to proximity to the stroke end of tilt cylinder  30 , the reference position can reliably be reached by further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end through supply amount regulation processing. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. 
     Reset processing unit  130 A determines whether or not a duration of an operation command equal to or greater than a prescribed value from control lever apparatus  101  is equal to or longer than a prescribed period, and when the duration of the operation command equal to or greater than the prescribed value from control lever apparatus  101  is equal to or longer than the prescribed period while the regulation valve is open in response to the command signal, the reset processing unit resets the stroke length measured by position sensor  110 . 
     Since reset processing unit  130 A determines whether or not a duration of an operation command equal to or greater than a prescribed value is equal to or longer than a prescribed period in connection with an operation instruction from an operator in resetting, an operation instruction from the operator given in response to an erroneous operation can be eliminated and reset processing with an intention of an operator being properly reflected can be performed. 
     As shown in  FIG. 6 , work vehicle CM is provided with engine  3 A, fuel regulation mechanism  105 , and hydraulic pump  103 . Engine  3 A rotates in accordance with supply of a fuel. Fuel regulation mechanism  105  regulates an amount of supply of a fuel for adjusting a speed of engine  3 A. Hydraulic pump  103  supplies the hydraulic oil at a pump pressure in accordance with the speed of engine  3 A. Reset processing unit  130 A determines whether or not an amount of supply of a fuel regulated by fuel regulation mechanism  105  is equal to or greater than a prescribed amount, and when the amount of supply of a fuel is equal to or greater than the prescribed amount in the proximity of the stroke end of tilt cylinder  30 , it generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     Reset processing unit  130 A determines whether or not an amount of supply of a fuel regulated by fuel regulation mechanism  105  is equal to or greater than a prescribed amount, and checks whether or not a pump pressure of hydraulic pump  103  is equal to or greater than a prescribed value. When the pump pressure of hydraulic pump  103  is equal to or greater than the prescribed value, reset processing unit  130 A generates a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . When a pump pressure is low, supply amount regulation processing for further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end may not sufficiently be performed. By performing the supply amount regulation processing when a pump pressure is equal to or greater than a prescribed value in which case supply amount regulation processing can reliably be performed, the reference position can reliably be reached. By performing the reset processing at the reference position, a deviation in stroke length can accurately be corrected. 
     Reset processing unit  130 A determines whether or not a prescribed condition is satisfied, and when it determines that the prescribed condition is satisfied in the proximity of the stroke end, it does not generate a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     Reset processing unit  130 A can perform efficient reset processing by excluding supply amount regulation processing for increasing an amount of supply of the hydraulic oil when it is not appropriate to perform reset processing in which case a prescribed condition is satisfied. 
     As shown in  FIG. 6 , work vehicle CM is provided with intervention control unit  130 B. Intervention control unit  130 B automatically controls at least a part of work implement  2 . Reset processing unit  130 A determines whether or not intervention control unit  130 B is carrying out automatic control as a prescribed condition, and when automatic control is being carried out in the proximity of the stroke end, it does not generate a command signal for increasing a degree of opening of flow rate regulation mechanism  109 . 
     When intervention control unit  130 B automatically controls at least a part of the work implement, reset processing unit  130 A can allow automatic control to be carried out without interruption, by not performing supply amount regulation processing for increasing an amount of supply of the hydraulic oil. 
     As shown in  FIG. 1 , work vehicle CM in the present embodiment is provided with vehicular body  1  and work implement  2 . Work implement  2  has boom  6  pivotable with respect to vehicular body  1  and bucket  8  pivotable around bucket axis J 3  which is a pivot axis with respect to arm  7  and tilt axis J 4  orthogonal to bucket axis J 3 . As shown in  FIG. 6 , work vehicle CM is provided with tilt cylinder  30 , flow rate regulation mechanism  109 , and position sensor  110 . Tilt cylinder  30  has bucket  8  pivot around tilt axis J 4 . Flow rate regulation mechanism  109  regulates an amount of supply of a hydraulic oil to be supplied to tilt cylinder  30 . Position sensor  110  measures a stroke length of tilt cylinder  30 . In a method of controlling work vehicle CM, the steps of measuring a stroke length of tilt cylinder  30  by using position sensor  110 , determining proximity to a stroke end of tilt cylinder  30 , generating a command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end, and resetting the measured stroke length are performed. 
     A stroke length of tilt cylinder  30  is measured and proximity to the stroke end of tilt cylinder  30  is determined. A command signal for increasing a degree of opening of flow rate regulation mechanism  109  in the proximity of the stroke end is generated and the measured stroke length is reset. Flow rate regulation mechanism  109  increases a degree of opening in response to the command signal. Accordingly, supply amount regulation processing for increasing an amount of supply of the hydraulic oil to tilt cylinder  30  is performed. By further pushing tilt cylinder  30  from the proximity of the stroke end toward the stroke end through the supply amount regulation processing, the reference position can be reached. By performing reset processing at the reference position, a deviation in stroke length can accurately be corrected. Accordingly, a stroke length can highly accurately be measured. 
     Though a hydraulic excavator has been described by way of example of a work vehicle in the present example, application also to such a work vehicle as a crawler dozer or a wheel loader is possible. 
     Though the embodiments of the present invention have been described above, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1  vehicular body;  2  work implement;  3  revolving unit;  3 A engine;  4  operator&#39;s cab;  4 S operator&#39;s seat;  4 V piston;  4 W cylinder head;  4 X cylinder tube;  4 Y cylinder rod;  5  traveling apparatus;  5 Cr crawler belt;  6  boom;  7  arm;  8  bucket;  9  engine compartment;  10  boom cylinder;  11  arm cylinder;  12  bucket cylinder;  13  boom pin;  14  arm pin;  15  bucket pin;  16  first stroke sensor;  17  second stroke sensor;  18  third stroke sensor;  19  handrail;  30 ,  30 A,  30 B tilt cylinder;  40 B,  40 H,  204 H oil chamber;  80  tilt pin;  83  upper plate;  84 ,  85  side plate;  87 ,  87 A,  87 B bracket;  88 ,  88 A,  88 B,  88 C,  88 D projection portion;  90 ,  90 A,  90 B,  90 C,  90 D stopper;  91  connection member;  92  bottom plate;  93  back plate;  101  control lever apparatus;  101 A control lever;  101 B detection unit;  102  control valve;  103  hydraulic pump;  103 A swash plate;  104  servo mechanism;  105  fuel regulation mechanism;  106  discharge oil path;  107 ,  108  oil path;  109  flow rate regulation mechanism;  110  position sensor;  111  rotary roller;  112  central shaft of rotation;  113  rotation sensor unit;  114  case;  130 A reset processing unit;  130 B intervention control unit;  200  controller;  201  fuel dial; and  300  measurement controller.