JP2015217797A - Work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work vehicle capable of ensuring traveling performance and driving performance in a wide operation range while suppressing an increase in the number of motors for traveling.SOLUTION: A work vehicle comprises: an engine; a hydraulic pump driven by the engine to discharge pressure oil; a work device conducting work with the hydraulic pump used as a driving source; a traveling motor applying power to wheels; a transmission including a plurality of gear positions and transmitting the power from the traveling motor to the wheels; and a transmission control unit 150 setting the gear position of the transmission so as to reduce the loss of the traveling motor in response to a vehicle velocity and a target driving torque of the wheels.

Description

  The present invention relates to a work vehicle.

  A work vehicle including an engine and an electric motor is known (see Patent Document 1). A work vehicle such as a wheel loader needs a large driving force in a stopped state or in a very low speed region during excavation work, and travels at a vehicle speed of about 30 to 40 km / h when traveling without working. For this reason, the work vehicle is required to have a traveling drive performance in a wide operation range.

  In order to realize the traveling drive performance in this wide operating range with a single traveling motor, it is necessary to employ a large traveling motor having characteristics that generate a large torque in a low speed region and can travel at a high speed. However, when a large traveling motor is employed, the cost increases, and the work vehicle may become large in order to secure a space for arranging the traveling motor.

  Patent Document 1 discloses a work vehicle including first and second electric motors, and a torque distribution transmission mechanism that distributes and transmits drive torque of these electric motors to a drive shaft of a traveling body and a drive shaft of a work machine. Is disclosed. In the work vehicle described in Patent Document 1, the driving torque of the first electric motor and the driving torque of the second electric motor are added and transmitted to the travel output shaft.

JP 2006-205777 A

  When a plurality of electric motors that generate travel driving force are provided as in the work vehicle described in Patent Document 1, it is necessary to provide auxiliary parts such as an inverter for controlling the electric motors accompanying the electric motors. For this reason, there is a problem that as the number of electric motors is increased, the number of auxiliary parts is increased and the cost is increased.

The work vehicle according to claim 1 includes an engine, a hydraulic pump that is driven by the engine and discharges pressure oil, a working device that operates using the hydraulic pump as a drive source, a traveling motor that provides power to the wheels, And a transmission control device for setting the speed stage of the transmission so that the loss of the traveling motor is reduced in accordance with the vehicle speed and the target driving torque of the wheel. With.
According to a second aspect of the present invention, in the work vehicle according to the first aspect, the speed change control device switches the speed stage of the transmission at a lower vehicle speed as the target drive torque increases.
A work vehicle according to a third aspect is the work vehicle according to the first or second aspect, wherein an operation amount detection device that detects an operation amount of an accelerator pedal, a vehicle speed detection device that detects a vehicle speed, and an operation amount detection device. Torque determining means for determining a target drive torque according to the detected operation amount and the vehicle speed detected by the vehicle speed detecting device, and the shift control device switches the switching vehicle speed for determining the switching vehicle speed for switching the speed stage of the transmission. A speed stage setting unit configured to compare the vehicle speed detected by the vehicle speed detection device and the switching vehicle speed determined by the switching vehicle speed determination means to set a speed stage of the transmission;
According to a fourth aspect of the present invention, the work vehicle according to the third aspect includes a storage device that stores the reference vehicle speed, and the switching vehicle speed determining unit determines a correction value that increases as the target drive torque increases. Then, the vehicle speed for switching is determined by subtracting the correction value from the reference vehicle speed.
According to a fifth aspect of the present invention, in the work vehicle according to the third aspect, the work vehicle according to the third aspect includes a storage device that stores a characteristic of the switching vehicle speed that decreases as the target drive torque increases. Based on this, the vehicle speed for switching according to the target drive torque is determined.
The work vehicle according to claim 6 is the work vehicle according to claim 1 or 2, wherein an operation amount detection device that detects an operation amount of an accelerator pedal, a vehicle speed detection device that detects a vehicle speed, and an operation amount detection device. Torque determining means for determining a target drive torque in accordance with the detected operation amount and the vehicle speed detected by the vehicle speed detection device, and the shift control device is provided for the travel motor according to the vehicle speed detected by the vehicle speed detection device. The loss determining unit that determines the loss for each speed stage of the transmission, and the speed stage with the smallest loss among the losses for each speed stage determined by the loss determining unit is selected, and the transmission speed stage is selected. A speed stage setting unit for setting the speed stage.

  According to the present invention, it is possible to ensure traveling drive performance in a wide operating range while reducing fuel consumption and suppressing an increase in the number of traveling motors.

The side view of the wheel loader which is an example of the series hybrid type work vehicle by this invention. The figure which shows an example of a structure of a wheel loader. The functional block diagram of the control apparatus for demonstrating the automatic transmission control process which concerns on 1st Embodiment. The figure which shows the relationship between a vehicle speed (horizontal axis) and target drive torque (vertical axis). The figure which shows the relationship between the vehicle speed (horizontal axis) and the target drive torque (vertical axis) in each of the first speed stage and the second speed stage. The figure which shows the relationship between a vehicle speed (horizontal axis) and the loss (vertical axis) of a driving | running | working motor. The functional block diagram of the control apparatus for demonstrating the automatic transmission control process which concerns on 2nd Embodiment. (A) is a figure which shows the relationship between target drive torque (horizontal axis) and correction speed (vertical axis). (B) is a figure which shows the relationship between target drive torque (horizontal axis) and the vehicle speed for switching (vertical axis). The functional block diagram of the control apparatus for demonstrating the automatic transmission control process which concerns on 3rd Embodiment. The figure which shows the relationship between a vehicle speed (horizontal axis) and a mechanical loss (vertical axis).

Hereinafter, an embodiment of a work vehicle according to the present invention will be described with reference to the drawings.
FIG. 1 is a side view of a wheel loader 100 that is an example of a series hybrid work vehicle according to the present invention. The wheel loader 100 includes a front vehicle body 105 having an arm 101, a bucket 102, a front wheel 103F, and the like, and a rear vehicle body 106 having an operator cab 107, a machine room 108, a rear wheel 103R, and the like.

  The wheel loader 100 of the present embodiment is an articulated wheel loader 100 in which a front vehicle body 105 and a rear vehicle body 106 are bent left and right with a connecting shaft 109 as a rotation axis. The front vehicle body 105 and the rear vehicle body 106 are rotatably connected to each other by a connecting shaft 109, and the front vehicle body 105 is refracted to the left and right with respect to the rear vehicle body 106 by the expansion and contraction of the steering cylinder 105A.

  An arm 101 is connected to the front vehicle body 105 so as to be rotatable in the vertical direction, and the arm 101 is rotated in the vertical direction (up and down movement) by driving the arm cylinder 101A. A bucket 102 is connected to the tip of the arm 101 so as to be rotatable in the vertical direction, and the bucket 102 is rotated (cloud or dumped) in the vertical direction by driving the bucket cylinder 102A.

  FIG. 2 is a diagram illustrating an example of the configuration of the wheel loader 100. The wheel loader 100 includes a control device 150, an engine 161, an engine controller 160, a traveling electric device 120, a work hydraulic device 110, and a power transmission mechanism 130. The control device 150 and the engine controller 160 are configured to include an arithmetic processing device having a CPU and a storage device such as ROM and RAM, and other peripheral circuits.

  The control device 150 is, for example, an integrated control device HCU (Hybrid Control Unit) that controls the entire vehicle. The control device 150 controls the entire system including the traveling system and the hydraulic working system of the wheel loader 100, and the engine 161, the generator motor 121, the traveling motor 124, and the transmission so that the entire system exhibits the best performance. 131 and the like are controlled in an integrated manner. The control device 150 is connected to a pedal operation amount sensor 143a for detecting the operation amount of the accelerator pedal 143 and an ignition switch 149 for starting and stopping the vehicle. An operation amount signal from the pedal operation amount sensor 143a and an operation position signal from the ignition switch 149 are input to the control device 150, respectively.

  When the ignition switch 149 is turned on by the operator, an operation start signal is input from the control device 150 to the engine controller 160, and the engine controller 160 controls the starter (not shown) and the fuel injection device 161a to Start. When the ignition switch 149 is turned off by the operator, an operation stop signal is input from the control device 150 to the engine controller 160, and the engine controller 160 controls the fuel injection device 161a to stop the engine 161.

  The working hydraulic apparatus 110 includes a working hydraulic pump 111 mechanically coupled to the engine 161, an arm 101 and a bucket 102 (see FIG. 1), and an arm cylinder 101A and a bucket cylinder 102A. The work hydraulic device 110 performs work using a work hydraulic pump 111 driven by the engine 161 as a drive source, and is driven by pressure oil discharged from the work hydraulic pump 111.

  The pressure oil discharged from the working hydraulic pump 111 is supplied to the arm cylinder 101A and the bucket cylinder 102A with the direction and flow rate controlled by the control valve 112. When an arm operation lever (not shown) and a bucket operation lever (not shown) in the cab 107 are operated, the control valve 112 operates, and hydraulic oil is appropriately distributed to the arm cylinder 101A and the bucket cylinder 102A. The bucket 102 performs a predetermined operation. The operator operates the arm operation lever and the bucket operation lever to expand and contract the arm cylinder 101A and the bucket cylinder 102A, and controls the height and inclination of the bucket 102 to perform excavation and cargo handling operations.

  The power transmission mechanism 130 includes an axle 134, a differential device 133, a propeller shaft 135, and a transmission 131, and transmits power generated by the traveling motor 124 to the wheels 103. In the present embodiment, each of front wheel 103F and rear wheel 103R is a drive wheel.

  The transmission 131 is an automatic transmission that has a first speed (low speed) and a second speed (high speed) speed ratio that is smaller than the first speed, and has a solenoid valve corresponding to each speed speed. These solenoid valves are driven by a control signal (target speed stage signal) output from the control device 150 to the transmission control apparatus 131c, and the speed stage of the transmission 131 is switched according to the control signal (target speed stage signal). . The set speed stage of the transmission 131 is detected by the control device 150. The automatic transmission control of the transmission 131 will be described later.

  The pair of front wheels 103 </ b> F (the pair of wheels 103) are respectively connected to the axle 134. Similarly, the pair of rear wheels 103 </ b> R (the pair of wheels 103) are respectively connected to the axle 134. The axle 134 is connected to a differential device 133, and the differential device 133 is coupled to the output shaft of the transmission 131 via a propeller shaft 135. The input shaft of the transmission 131 is connected to the rotor shaft 132 of the traveling motor 124.

  The traveling electric device 120 includes a generator motor 121, an MG inverter 122, a traveling motor 124, a traveling inverter 125, a power storage device 127, and a converter 128.

  The traveling motor 124 is an induction motor including a squirrel-cage rotor, is connected to the generator motor 121 and the power storage device 127 via a power line, and is driven by power supplied from one or both of the generator motor 121 and the power storage device 127. Thus, traveling driving force is applied to the wheels 103.

  The generator motor 121 is a synchronous motor including a rotor having a permanent magnet, and is connected to the output shaft of the engine 161 directly or via a belt or gear. The generator motor 121 functions as a generator that is driven by the engine 161 to generate three-phase AC power. The three-phase AC power is converted into DC power by the MG inverter 122 and supplied to an inverter for a traveling motor (hereinafter referred to as a traveling inverter 125). When the charging rate is reduced to a predetermined value, the DC power converted by MG inverter 122 is also supplied to power storage device 127 via converter 128, and power storage device 127 is charged.

  The generator motor 121 also functions as an electric motor that is driven by the three-phase AC power converted by the MG inverter 122 and generates rotational torque, and performs torque assist of the engine 161.

  The MG inverter 122 and the traveling inverter 125 are power converters that control conversion from DC power to three-phase AC power, or conversion from three-phase AC power to DC power, by the operation of a switching semiconductor element. The MG inverter 122 and the traveling inverter 125 each include a power module (not shown) having a switching element, a driver circuit (not shown), and power controllers 122c and 125c.

  Each power conversion device includes six switching semiconductor elements, and performs power conversion by switching operations (on / off) of the six switching semiconductor elements.

  The power controllers 122c and 125c are electronic circuit devices for controlling the switching operation of the six switching semiconductor elements. A torque command from the control device 150 is input to the power controllers 122c and 125c via a CAN (Controller Area Network) 140.

  The power controller 122c of the MG inverter 122 includes an MG current sensor 141 that detects a current value of an alternating current flowing between the generator motor 121 and the MG inverter 122, and an MG that detects the rotational speed of the generator motor 121. A signal from the speed sensor 142 is input. The rotational speed signal detected by the MG speed sensor 142 is also input to the control device 150 via the power controller 122c.

  The power controller 125c of the traveling inverter 125 includes a traveling motor current sensor (hereinafter referred to as a traveling current sensor 144) that detects a current value of an alternating current flowing between the traveling motor 124 and the traveling inverter 125. Signal is input. In addition, a signal from a speed sensor (hereinafter referred to as a motor speed sensor 145) for detecting the rotational speed of the travel motor 124 is input to the power controller 125c of the travel inverter 125. The rotation speed signal detected by the motor speed sensor 145 is also input to the control device 150 via the power controller 125c.

  Based on the information from the MG current sensor 141 and the MG speed sensor 142 and the torque command output from the control device 150, the MG inverter 122 adjusts the voltage of the generator motor 121 so that a desired motor torque is generated. Control. The traveling inverter 125 controls the voltage of the traveling motor 124 based on the information from the traveling current sensor 144 and the motor speed sensor 145 and the torque command output from the control device 150 so that a desired motor torque is generated. To do.

  The power controllers 122c and 125c generate a switching operation command signal (for example, a PWM (pulse width modulation) signal) for the switching semiconductor element. The generated command signal is output to a driver circuit (not shown).

  The driver circuit (not shown) generates drive signals for the six switching semiconductor elements based on the switching operation command signals output from the power controllers 122c and 125c. This drive signal is output to the gate electrodes of the six switching semiconductor elements. The switching (on / off) of the six switching semiconductor elements is controlled based on a drive signal output from a driver circuit (not shown).

  The MG inverter 122 and the traveling inverter 125 are connected to the power storage device 127 via the converter 128, and the converter 128 exchanges power between the MG inverter 122, the traveling inverter 125 and the power storage device 127. The charging / discharging voltage of power storage device 127 is controlled by power controller 128 c built in converter 128. The power controller 128 c receives a voltage command from the control device 150 via the CAN 140 and increases or decreases the charge / discharge voltage of the power storage device 127.

  The power storage device 127 stores electric power generated by a certain amount of electrical work (for example, work of several tens of kW for several seconds) and can discharge an electric charge stored at a desired time or a secondary capacitor A plurality of power storage elements such as batteries are provided.

  The power storage device 127 is charged with the generated power of the generator motor 121 and the regenerative power of the traveling motor 124. The three-phase AC power generated by the generator motor 121 is converted to DC power by the MG inverter 122, supplied to the power storage device 127 via the converter 128, and the power storage device 127 is charged. The three-phase AC power generated by the traveling motor 124 is converted to DC power by the traveling inverter 125, supplied to the power storage device 127 via the converter 128, and the power storage device 127 is charged.

  During powering operation, one or both of the power generated by the generator motor 121 and converted from AC power to DC power by the MG inverter 122 and the DC power output from the power storage device 127 are supplied to the traveling inverter 125. Supplied and converted into three-phase AC power by the traveling inverter 125. The traveling motor 124 is driven by the three-phase AC power converted by the traveling inverter 125 to generate rotational torque.

  The rotational torque generated by the traveling motor 124 is transmitted to the transmission 131 connected to the rotor shaft 132 of the traveling motor 124. The rotation of the rotor shaft 132 is shifted by the transmission 131, and the rotated rotation is transmitted to the wheels 103 via the propeller shaft 135 and the axle 134.

  During the regenerative operation, the traveling motor 124 is rotated by the rotational torque transmitted from the wheels 103, and three-phase AC power is generated. The three-phase AC power generated by the traveling motor 124 is converted to DC power by the traveling inverter 125 and supplied to the power storage device 127 via the converter 128. The power storage device 127 is converted by the DC power converted by the traveling inverter 125. Charged.

  At the time of excavation work, electric power is supplied from the power storage device 127 to the generator motor 121 via the MG inverter 122 as necessary, and the generator motor 121 functions as an electric motor, and torque assist of the engine 161 is performed.

  The control device 150 controls the engine 161, the generator motor 121, and the traveling motor 124 so that the traveling motor 124 outputs a required torque corresponding to the vehicle information including the operation amount (depression amount) of the accelerator pedal 143. The control device 150 sets a target rotational speed of the engine 161 in order to cause the generator motor 121 to generate electric power necessary for the traveling motor 124, and outputs a target rotational speed command to the engine controller 160. The control device 150 outputs a torque command for operating the generator motor 121 as a generator to the power controller 122c of the MG inverter 122 and outputs a torque command for operating the traveling motor 124 as a motor. It outputs to 125 power controllers 125c.

  The engine controller 160 receives a signal from the engine speed sensor 146 that detects the actual speed of the engine 161. The engine controller 160 compares the actual rotation speed of the engine 161 detected by the engine rotation speed sensor 146 with the target rotation speed of the engine 161 from the control device 150 to bring the actual rotation speed closer to the target rotation speed. A control signal is output to the fuel injection device 161a to control the fuel injection device 161a.

  Hereinafter, the automatic shift control process during the power running operation will be described in detail. FIG. 3 is a functional block diagram of the control device 150 for explaining the automatic shift control process. The control device 150 functionally includes a torque calculation unit 151, loss calculation units 152L and 152H, a speed stage setting unit 153 that sets the speed stage of the transmission 131, and a vehicle speed calculation unit 154 that calculates the vehicle speed V. Yes.

  The vehicle speed calculation unit 154 is based on the currently set speed ratio of the transmission 131 and the rotational speed of the traveling motor 124 detected by the motor speed sensor 145 and input via the power controller 125c. Is calculated (hereinafter referred to as vehicle speed V).

  The torque calculation unit 151 calculates a target torque (hereinafter referred to as target drive torque Td) of a wheel (drive wheel) to which the travel drive force of the travel motor 124 is applied. The torque calculation unit 151 calculates a target drive torque Td based on the operation amount S of the accelerator pedal 143 detected by the pedal operation amount sensor 143a and the vehicle speed V calculated by the vehicle speed calculation unit 154. FIG. 4 is a diagram showing the relationship between the vehicle speed V (horizontal axis) and the target drive torque Td (vertical axis). FIG. 4 shows three torque curves. In the drawing, the thick solid line indicates the characteristic Ct100 of the target drive torque Td when the operation amount S of the accelerator pedal 143 is 100%, that is, the maximum depression operation. In the figure, the broken line indicates the characteristic Ct50 of the target drive torque Td when the operation amount S is 50%, and the thin solid line indicates the characteristic Ct20 of the target drive torque Td when the operation amount S is 20%.

  The storage device of the control device 150 stores a table (torque curve) of the characteristics Ct100, Ct50, Ct20 of the target drive torque Td with respect to the vehicle speed V shown in FIG. 4 for each manipulated variable S (100%, 50%, 20%). Has been. Each characteristic Ct100, Ct50, Ct20 is set such that the target drive torque Td is inversely proportional to the vehicle speed V. In FIG. 4, for convenience of explanation, three torque curves are shown, but three or more torque curves may be stored in the storage device.

  The torque calculation unit 151 reads a target drive torque Td corresponding to the vehicle speed V calculated by the vehicle speed calculation unit 154 with reference to a torque curve corresponding to the operation amount S detected by the pedal operation amount sensor 143a. In addition, when there is no table corresponding to the detected operation amount S, the torque calculation unit 151 has two tables (for example, for example) corresponding to the operation amounts before and after the detected operation amount S (for example, 60%). The target driving torque Td is calculated by a known interpolation calculation with reference to the 50% table and the 100% table. Based on the calculated target driving torque Td of the driving wheel and the currently set speed stage of the transmission 131, the torque calculating unit 151 determines the driving motor 124 necessary for setting the driving wheel torque as the target driving torque. A torque command corresponding to the torque is output to the power controller 125 c of the traveling inverter 125.

  In the present embodiment, the rotational speed and torque of the traveling motor 124 are converted by the transmission 131. FIG. 5 is a diagram showing the relationship between the vehicle speed V (horizontal axis) and the target drive torque Td (vertical axis) at each of the first speed stage and the second speed stage. In the drawing, the broken line indicates the characteristic Ct100 (see FIG. 4) when the operation amount S of the accelerator pedal 143 is 100%.

  In the present embodiment, in the entire speed range from the lowest speed Vmin (= 0) to the highest speed Vmax, the vehicle speed V is a target corresponding to the characteristic Ct100 by at least one of the first speed stage and the second speed stage. The motor characteristics of the traveling motor 124 and the transmission gear ratio of the transmission 131 are determined so that the driving torque Td can be output.

  The target drive torque Td in the area A indicated by hatching in FIG. 5 can be output at either the first speed stage or the second speed stage. However, if the speed stage is arbitrarily set from the two speed stages, the loss of the traveling motor 124 becomes large and the fuel consumption may be deteriorated. Therefore, in the present embodiment, the speed stage of the transmission 131 is set so that the loss of the traveling motor 124 is reduced.

  As shown in FIG. 3, the loss calculators 152L and 152H have a loss Lm of the traveling motor 124 according to the vehicle speed V calculated by the vehicle speed calculator 154 and the target drive torque Td calculated by the torque calculator 151. To decide. The loss Lm represents the sum of the copper loss and the iron loss of the electric motor. Copper loss is Joule loss and increases as the torque of the motor increases. The iron loss is an energy loss (hysteresis loss and eddy current loss) consumed by the magnetic hysteresis and eddy current as heat in the iron core of the motor, and increases as the rotation speed of the motor increases. For this reason, in the loss Lm, the copper loss is dominant due to the influence of torque when the rotation speed of the electric motor is low, and the iron loss is dominant due to the influence of the rotation speed when the rotation speed of the electric motor is high.

  When the electric motor is used as the driving force source of the work vehicle as in the present embodiment, the torque when the vehicle speed is lower than that of a general driving vehicle such as an ordinary automobile is important. In particular, a work vehicle such as a wheel loader travels while receiving a reaction force from soil or earth and sand with a driving rod during excavation, and therefore requires a much higher torque than a general traveling vehicle at low speeds. . If this torque is to be realized by normal motor control, the size and cost of the motor become enormous. Therefore, in a traveling motor for a work vehicle, a high torque at a low speed is realized by flowing a current larger than the rated value (that is, by overload operation). For this reason, at a low speed and a high torque, the copper loss is increased as compared with the normal time when the motor is operated with the rated current.

  The relationship among the loss Lm of the traveling motor 124, the target drive torque Td, the vehicle speed V, and the speed stage of the transmission 131 will be described with reference to FIG. FIG. 6 is a diagram showing the relationship between the vehicle speed V (horizontal axis) and the loss Lm (vertical axis) of the traveling motor. FIG. 6 shows six loss curves. In the figure, the thick solid line indicates the characteristic of the loss Lm when the target drive torque Td = Td3. In the figure, the broken line indicates the characteristic of the loss Lm when the target drive torque Td = Td2. In the figure, the thin solid line indicates the characteristic of the loss Lm when the target drive torque Td = Td1. The magnitude relationship between Td1, Td2, and Td3 is Td1 <Td2 <Td3.

  Of the same type of lines representing the same target drive torque Td, the left line is the loss Lm (hereinafter referred to as Lm1) when the first speed stage (low speed stage) is used, and the right line is the second speed stage ( The loss Lm (hereinafter referred to as Lm2) when the high speed stage is used is shown. As shown, the loss Lm increases as the target drive torque Td increases. When the vehicle speed V is the same, the greater the operation amount S of the accelerator pedal 143, the greater the target drive torque Td (see FIG. 4), and the greater the loss Lm.

  Each loss curve has a minimum point P. The loss Lm increases as the vehicle speed V increases from the minimum point P, and the loss Lm increases as the vehicle speed V decreases from the minimum point P.

  As shown in the figure, even when the vehicle speed V is the same and the target drive torque Td is the same, the loss Lm of the traveling motor varies depending on the speed stage. For example, when the vehicle speed V = Ve and the target drive torque Td = Td3, the loss Lm = Lm1e at the first speed stage, the loss Lm = Lm2e at the second speed stage, and the loss values are different (Lm1e ≠ Lm2e). This is because, even with the same motor output, the torque and rotational speed of the traveling motor 124 are different for each speed stage, and the balance of copper loss and iron loss is not the same between the first speed and the second speed. .

  The point X where the same type of lines intersect is the point where the magnitude of the loss Lm is switched between the first speed stage (low speed stage) and the second speed stage (high speed stage), and the intersection point X becomes the lower speed side as the target drive torque Td increases. Is displaced.

  The storage device of the control device 150 stores a loss characteristic table (loss curve) shown in FIG. 6 for each target drive torque Td. In FIG. 6, for convenience of explanation, six loss curves are shown, but six or more loss curves may be stored in the storage device.

  The loss calculation unit 152L selects a loss curve when using one speed stage corresponding to the target drive torque Td calculated by the torque calculation unit 151, refers to the selected loss curve, and is calculated by the vehicle speed calculation unit 154. The loss Lm1 when using the first speed stage corresponding to the vehicle speed V is read.

  The loss calculation unit 152H selects a loss curve when using the two-speed stage corresponding to the target drive torque Td calculated by the torque calculation unit 151, refers to the selected loss curve, and is calculated by the vehicle speed calculation unit 154. The loss Lm2 when using the second speed stage corresponding to the vehicle speed V is read out.

  When there is no table (loss curve) corresponding to the target drive torque Td (for example, Td = Td12, Td1 <Td12 <Td2), the loss calculators 152L and 152H have target values before and after the target drive torque Td. With reference to two tables corresponding to the driving torque Td (for example, a table of Td = Td1 and a table of Td = Td2), the loss Lm is calculated by a known interpolation calculation.

  As shown in FIG. 3, the speed stage setting unit 153 includes a loss Lm1 (for example, Lm1 = Lm1e) calculated by the loss calculation unit 152L and a two speed stage calculated by the loss calculation unit 152H. A speed stage (for example, 1st gear) with a low loss is selected by comparing with a loss Lm2 (for example, Lm2 = Lm2e) during use. The speed stage setting unit 153 outputs a control signal (target speed stage signal) for setting the speed stage of the transmission 131 to the selected speed stage to the transmission control device 131c. The transmission control device 131c sets the speed stage of the transmission 131 to the speed stage selected by the speed stage setting unit 153 based on the input target speed stage signal.

  Each loss curve shown in FIG. 6 can be obtained by experiment, simulation, or the like. The loss curve data is not required in the entire vehicle speed range from Vmin to Vmax, and the characteristics near the intersection X may be stored in the storage device. In the present embodiment, since the speed stage setting unit 153 compares the loss Lm1 and the loss Lm2 in the entire vehicle speed region, the loss in the vehicle speed region without the loss curve is set as Lmx. Lmx, which is a value set for convenience for comparison, may be a value larger than the maximum value of the loss Lm obtained in each loss curve.

  That is, as shown in FIG. 6, there is a case where the target drive torque Td = Td3 at the second speed stage and the vehicle speed V is equal to or lower than V3L, and a case where the target drive torque Td = Td3 at the first speed stage. Thus, each of the losses Lm when the vehicle speed V is V3H or higher is set to Lmx. If the vehicle speed V at the intersection X of the loss curve of the target drive torque Td = Td3 is V3X, the magnitude relationship among V3L, V3H, and V3X is V3L <V3X <V3H. Further, the loss Lm when the target drive torque Td = Td2 at the second speed stage and the vehicle speed V is V2L or less, and the loss Lm when the target drive torque Td = Td2 at the first speed stage and the vehicle speed V is V2H or more. Each loss Lm was set to Lmx. When the vehicle speed V at the intersection X of the loss curve of the target drive torque Td = Td2 is V2X, the magnitude relationship among V2L, V2H, and V2X is V2L <V2X <V2H. Further, the loss Lm when the target drive torque Td = Td1 at the second speed stage and the vehicle speed V is V1L or lower, and the loss Lm when the target drive torque Td = Td1 at the first speed stage and the vehicle speed V is V1H or higher. Each loss Lm was set to Lmx. When the vehicle speed V at the intersection X of the loss curve of the target drive torque Td = Td1 is V1X, the magnitude relationship among V1L, V1H, and V1X is V1L <V1X <V1H.

  As described above, the intersection point X is displaced toward the low speed side as the target drive torque Td increases (see FIG. 6). That is, the speed stage of the transmission 131 is switched at a lower vehicle speed V as the target drive torque Td increases.

  When the ignition switch 149 is turned on, an automatic shift control program is started, and the vehicle speed calculation process in the vehicle speed calculation unit 154, the target drive torque calculation process in the torque calculation unit 151, and the one speed in the loss calculation unit 152L. The controller 150 repeatedly executes the loss calculation process when using the stage, the loss calculation process when using the two speed stages in the loss calculation unit 152H, and the speed stage selection process in the speed stage setting unit 153. By such automatic shift control, a speed stage with a small loss Lm is automatically set during traveling of the vehicle, so that fuel efficiency can be improved.

According to the first embodiment described above, the following operational effects are obtained.
(1) Since the work vehicle includes the transmission 131 that transmits the power from the traveling motor 124 to the wheels 103, it is possible to ensure traveling driving performance in a wide operating range while suppressing an increase in the number of traveling motors 124. Can do.

(2) The speed stage of the transmission 131 is set so that the loss of the traveling motor 124 is reduced, that is, the traveling efficiency is improved, according to the vehicle speed V and the target driving torque Td of the wheel 103. , Fuel consumption can be improved.

(3) The loss Lm of the traveling motor 124 corresponding to the vehicle speed V is determined for each speed stage of the transmission 131, and the speed stage with the smallest loss is selected from the determined losses Lm1 and Lm2 for each speed stage. The speed stage of the transmission 131 is set to the selected speed stage. Thereby, it is possible to accurately select a speed stage in which the loss of the traveling motor 124 is minimized.

-Second Embodiment-
With reference to FIG. 7 and FIG. 8, the work vehicle which concerns on 2nd Embodiment is demonstrated. In the figure, the same reference numerals are assigned to the same or corresponding parts as those in the first embodiment, and the differences will be mainly described. The work vehicle according to the second embodiment has the same configuration as the work vehicle according to the first embodiment. In the first embodiment, the loss Lm1 of the traveling motor 124 when the first speed stage is used is compared with the loss Lm2 of the traveling motor 124 when the second speed stage is used, and the speed stage with a low loss is set. did. On the other hand, in the second embodiment, the switching vehicle speed VC (threshold value) indicating the vehicle speed for switching the speed stage of the transmission 131 is compared with the vehicle speed V (current vehicle speed) calculated by the vehicle speed calculation unit 154. Then, the speed stage of the transmission 131 is set.

  FIG. 7 is a functional block diagram of the control device 250 for explaining the automatic shift control processing according to the second embodiment. In the second embodiment, a control device 250 is provided in place of the control device 150 of the first embodiment. As shown in FIG. 7, the control device 250 functionally includes a vehicle speed calculation unit 154, a torque calculation unit 151, a correction unit 255, a subtracter 256, and a speed stage setting unit 253.

  FIG. 8A is a diagram showing the relationship between the target drive torque Td (horizontal axis) and the correction speed ΔV (vertical axis). FIG. 8B is a diagram showing the relationship between the target drive torque Td (horizontal axis) and the switching vehicle speed VC (vertical axis). The storage device of the control device 250 stores a table of the characteristic Cv of the correction speed ΔV with respect to the target drive torque Td shown in FIG.

  The correction unit 255 determines the correction speed ΔV based on the target drive torque Td calculated by the torque calculation unit 151. Specifically, the correction unit 255 reads the correction speed ΔV corresponding to the target drive torque Td with reference to the table of the characteristic Cv. The correction speed ΔV increases as the target drive torque Td increases.

  The storage device of the control device 250 stores a reference vehicle speed Vb (constant). The reference vehicle speed Vb is a vehicle speed at which switching between the first speed stage and the second speed stage, that is, a shift change, is performed when the target drive torque Tb is zero. The reference vehicle speed Vb can be set to an arbitrary constant value.

  The subtracter 256 subtracts the correction speed ΔV calculated by the correction unit 255 from the reference vehicle speed Vb stored in the storage device, determines the switching vehicle speed VC, and outputs it to the speed stage setting unit 253. As shown in FIG. 8B, the switching vehicle speed VC, which is a threshold value, has a characteristic that decreases as the target drive torque Td increases.

  The speed stage setting unit 253 compares the vehicle speed V calculated by the vehicle speed calculation unit 154 with the switching vehicle speed VC calculated by the subtracter 256. When the vehicle speed V is equal to or higher than the switching vehicle speed VC (V ≧ VC), the speed stage setting unit 253 outputs a control signal (target speed stage signal) for setting the speed stage to the second speed to the transmission control device 131c. When V is less than the switching vehicle speed VC (V <VC), a control signal (target speed stage signal) for setting the speed stage to the first speed is output to the transmission control device 131c. The transmission control device 131c sets the transmission 131 to the speed stage selected by the speed stage setting unit 253 based on the input control signal (target speed stage signal).

  When the ignition switch 149 is turned on, the automatic shift control program is started, and the vehicle speed calculation process in the vehicle speed calculation unit 154, the target drive torque calculation process in the torque calculation unit 151, and the correction speed calculation in the correction unit 255 are performed. The control device 250 repeatedly executes the process, the switching vehicle speed calculation process in the subtracter 256, and the speed stage selection process in the speed stage setting unit 253.

  The change rate of the correction speed ΔV shown in FIG. 8A with respect to the increase in the target drive torque Td is the intersection of the loss curve when using the first speed stage and the loss curve when using the second speed stage in the same target drive torque shown in FIG. The vehicle speed V at X is determined based on a characteristic that decreases as the target drive torque Td increases. As the target drive torque Td increases, the speed stage switching vehicle speed VC (threshold value) is decreased, so that the speed L of the transmission 131 is reduced so that the loss Lm of the traveling motor 124 is reduced as shown in FIG. Is automatically set.

  As described above, in the second embodiment, the correction speed ΔV that increases as the target drive torque Td increases is determined, and the switching speed VC is determined by subtracting the correction speed ΔV from the reference vehicle speed Vb. According to the second embodiment that performs such automatic shift control, as in the first embodiment, since the speed stage with a small loss Lm is automatically set during traveling of the vehicle, the fuel efficiency is improved. Can be achieved. Furthermore, since the arithmetic processing is simple compared to the first embodiment, the processing capability of the control device 250 can be suppressed and the cost can be reduced.

-Third embodiment-
With reference to FIG. 9, a work vehicle according to a third embodiment will be described. In the figure, the same or corresponding parts as those in the second embodiment are denoted by the same reference numerals, and the differences will be mainly described. The work vehicle according to the third embodiment has the same configuration as the work vehicle according to the second embodiment. In the second embodiment, the correction vehicle speed ΔV is subtracted from the reference vehicle speed Vb to determine the switching vehicle speed VC. On the other hand, in the third embodiment, a characteristic table of the switching vehicle speed VC (threshold value) indicating the vehicle speed at which the speed stage of the transmission 131 is switched is stored in advance in the storage device, and is calculated by the torque calculation unit 151. The switching vehicle speed VC is determined based on the target drive torque Td.

  FIG. 9 is a functional block diagram of a control device 350 for explaining automatic shift control processing according to the third embodiment. In the third embodiment, a control device 350 is provided in place of the control device 250 of the second embodiment. As shown in FIG. 9, the control device 350 functionally includes a vehicle speed calculation unit 154, a torque calculation unit 151, and a speed stage setting unit 353.

  The speed stage setting unit 353 receives the information on the vehicle speed V calculated by the vehicle speed calculation unit 154 and the information on the target drive torque Td calculated by the torque calculation unit 151. The speed stage setting unit 353 refers to the characteristic table of the switching vehicle speed VC stored in the storage device, and reads the switching vehicle speed VC corresponding to the input target drive torque Td.

  The speed stage setting unit 353 compares the read vehicle speed VC for switching with the input vehicle speed V. When the vehicle speed V is equal to or higher than the switching vehicle speed VC (V ≧ VC), the speed stage setting unit 353 outputs a control signal (target speed stage signal) for setting the speed stage to the second speed to the transmission control device 131c. When V is less than the switching vehicle speed VC (V <VC), a control signal (target speed stage signal) for setting the speed stage to the first speed is output to the transmission control device 131c. The transmission control device 131c sets the transmission 131 to the speed stage selected by the speed stage setting unit 353 based on the input control signal (target speed stage signal).

  When the ignition switch 149 is turned on, an automatic shift control program is started, and the vehicle speed calculation process in the vehicle speed calculation unit 154, the target drive torque calculation process in the torque calculation unit 151, and the switching in the speed stage setting unit 353 are performed. The vehicle speed calculation process and the speed stage selection process are repeatedly executed by the control device 350.

  The characteristics of the switching vehicle speed VC shown in FIG. 9 are the same as the characteristics of the switching vehicle speed VC shown in FIG. That is, the characteristic table of the switching vehicle speed VC shown in FIG. 8 is the vehicle speed V at the intersection X between the loss curve when using the first speed stage and the loss curve when using the second speed stage at the same target drive torque shown in FIG. Is determined based on a characteristic that decreases as the target drive torque Td increases. As the target drive torque Td increases, the speed stage of the transmission 131 is automatically reduced so as to reduce the loss Lm of the traveling motor 124 as shown in FIG. 6 by reducing the speed stage switching vehicle speed. Is set.

  As described above, the third embodiment includes a storage device that stores the characteristics of the switching vehicle speed VC that decreases as the target drive torque Td increases. Based on the characteristics, the switching device according to the target drive torque Td is provided. The vehicle speed VC was determined. According to the third embodiment that performs such automatic shift control, the same operational effects as those of the second embodiment can be obtained.

The following modifications are also within the scope of the present invention, and one or a plurality of modifications can be combined with the above-described embodiment.
(Modification 1)
Although the loss Lm1 and Lm2 calculated by the loss calculation units 152L and 152H of the first embodiment described above are the sum of the copper loss and the iron loss, respectively, the present invention is not limited to this. Further, mechanical loss may be taken into account. FIG. 10 is a diagram showing the relationship between the vehicle speed (horizontal axis) and the mechanical loss (vertical axis). Since there is a possibility that the output cannot be performed when the two-speed stage is used depending on the torque, the mechanical loss when the two-speed stage is used in the low speed region is indicated by a broken line. The mechanical loss Lg is caused by the loss caused by the friction when the gears constituting the transmission 131 mesh with each other to transmit torque, the bearings supporting the respective shafts constituting the power transmission mechanism, and the rotor shaft 132 of the traveling motor 124. This includes losses caused by friction at the bearings to be supported. The mechanical loss Lg increases as the vehicle speed V increases.

  If the vehicle speed is the same, the mechanical loss Lg at the first speed stage (hereinafter referred to as mechanical loss Lg1) is larger than the mechanical loss Lg at the second speed stage (hereinafter referred to as mechanical loss Lg2). This is because the speed ratio is larger at the first speed stage, and the rotational speed of the traveling motor 124 is higher at the first speed stage than at the second speed stage at the same vehicle speed.

  In this modification, a table of the characteristic Cg1 of the mechanical loss Lg1 generated when the first speed stage is used and a table of the characteristic Cg2 of the mechanical loss Lg2 generated when the second speed stage is used are stored in the storage device in advance. The loss calculation unit 152L reads the mechanical loss Lg1 corresponding to the vehicle speed V with reference to the table of the characteristic Cg1. The loss calculation unit 152L adds the calculated mechanical loss Lg1 to the loss Lm1, and outputs the result to the speed stage setting unit 153. The loss calculator 152H reads the mechanical loss Lg2 corresponding to the vehicle speed V with reference to the table of the characteristic Cg2. The loss calculation unit 152H adds the calculated mechanical loss Lg2 to the loss Lm2, and outputs the result to the speed stage setting unit 153.

  The speed stage setting unit 153 includes the total value of the loss Lm1 and the mechanical loss Lg1 when using the first speed stage calculated by the loss calculation unit 152H, the loss Lm2 when using the second speed stage and the machine calculated by the loss calculation unit 152L. The speed stage having a low total value of the loss Lm and the mechanical loss Lg is selected by comparing with the total value of the loss Lg2. The speed stage setting unit 153 outputs a control signal (target speed stage signal) for setting the speed stage of the transmission 131 to the selected speed stage to the transmission control device 131c.

  In the first modification, the speed stage of the transmission 131 is set so that not only the copper loss and the iron loss but also the mechanical loss is taken into account, and the total loss of the copper loss, the iron loss and the mechanical loss is reduced. Although the mechanical loss is smaller than the copper loss and the iron loss, the fuel consumption can be further improved by taking the mechanical loss into consideration.

(Modification 2)
In the first embodiment described above, the loss in the vehicle speed region without the loss curve is set as Lmx so that the speed stage setting unit 153 compares the loss Lm1 and Lm2 in the entire vehicle speed region. It is not limited to this. When the vehicle speed is less than the first predetermined value, the first speed stage is set. When the vehicle speed is higher than the second predetermined value greater than the first predetermined value, the second speed stage is set, and the vehicle speed is equal to or higher than the first predetermined value and the second predetermined value. In a range less than the value, the speed stage may be set by comparing the loss Lm1 and the loss Lm2 calculated by the loss curve. In this case, a loss curve corresponding to a plurality of target drive torques Td is stored in the storage device for each speed stage within a range not less than the first predetermined value and less than the second predetermined value.

(Modification 3)
In the first embodiment described above, the loss calculation units 152L and 152H calculate the losses Lm1 and Lm2 of the traveling motor 124, and the speed stage setting unit 153 uses the loss Lm1 when using the first speed stage and when using the second speed stage. However, the present invention is not limited to this. The loss calculated by the loss calculation units 152L and 152H may be a physical quantity having a correlation with the loss of the traveling motor 124. For example, the loss calculation units 152L and 152H calculate the traveling efficiency, and the speed stage setting unit 153 compares the traveling efficiency when using one speed stage with the traveling efficiency when using two speed stages, By selecting a high speed stage, the speed stage of the transmission 131 is set so that the loss of the traveling motor 124 is reduced.

(Modification 4)
In the first embodiment described above, the loss calculation units 152L and 152H obtain the loss Lm corresponding to the vehicle speed V with reference to a predetermined loss curve regardless of the temperature of the traveling motor 124. The present invention is not limited to this. The temperature of the traveling motor 124 may be taken into account when calculating the loss. In this case, the characteristics of the loss curve for each temperature are stored in the storage device, and the loss Lm corresponding to the vehicle speed V is read by referring to the loss curve corresponding to the temperature of the traveling motor 124 detected by a sensor or the like.

  If the characteristics of the correction speed ΔV and the characteristics of the switching vehicle speed VC are stored for each temperature of the traveling motor 124, the influence of the temperature of the traveling motor 124 is also taken into account in the second and third embodiments. Automatic transmission control can be realized.

(Modification 5)
In the above-described embodiment, the example in which the vehicle speed V is determined based on the information from the motor speed sensor 145 that detects the rotational speed of the traveling motor 124 and the information on the set speed stage of the transmission 131 has been described. Is not limited to this. The vehicle speed V may be obtained from information from a sensor that detects the rotational speed of the wheel 103. Various methods can be adopted as the vehicle speed detection method.

(Modification 6)
In the above-described embodiment, the example in which the torque calculation process, the loss calculation process, and the speed stage selection process are executed using the vehicle speed V has been described, but the present invention is not limited to this. In the present specification, the vehicle speed may be a physical quantity having a correlation with the vehicle speed. For example, torque calculation processing, loss calculation processing, and speed stage selection processing can be executed using the rotation speed of the output shaft of the transmission 131 and the rotation speed of the axle 134. The rotational speed of the output shaft of the transmission 131 and the rotational speed of the axle 134 may be detected by a sensor, or calculated by the control device 150 based on the rotational speed signal of the traveling motor 124 and information on the set speed stage. Also good.

(Modification 7)
In the above-described first embodiment, the transmission 131 having the first speed stage and the second speed stage has been described as an example, but the present invention is not limited to this. The present invention may be applied to a transmission 131 having three or more speed stages. When the present invention is applied to the transmission 131 having three or more speed stages, the present invention can be applied to some or all of a plurality of shift changes. For example, in the transmission 131 having the first to third speed stages, the loss Lm of the traveling motor 124 at one or both of the shift change between the first speed and the second speed and the shift change between the second speed and the third speed. The speed stage of the transmission 131 can be set so that becomes smaller.

(Modification 8)
In the embodiment described above, torque curve characteristics (see FIG. 4), loss curve characteristics (see FIG. 6), correction speed characteristics (see FIG. 8A), and switching vehicle speed characteristics (see FIG. 9). However, the present invention is not limited to this. Each characteristic may be stored in a storage device as a function, and the target drive torque Td, loss Lm, correction speed ΔV, and switching vehicle speed VC may be calculated using this function.

(Modification 9)
Hysteresis may be added to the condition (set value) for shift change. For example, in the first embodiment, when the currently set speed stage is the first speed, the speed stage setting unit 153 shifts up to the second speed when Lm1 ≧ Lm2 + α. When the current set speed stage is the second speed, the speed stage setting unit 153 shifts down to the first speed when Lm1 ≦ Lm2. Thereby, the complexity of a shift change can be suppressed.

  For example, in the second and third embodiments, when the currently set speed stage is the first speed, speed stage setting units 253 and 353 shift up to the second speed when V ≧ VC + β. When the currently set speed stage is the second speed, the speed stage setting units 253 and 353 shift down to the first speed when V ≦ VC. Thereby, the complexity of a shift change can be suppressed.

(Modification 10)
In the above-described embodiment, as the target drive torque Td increases, the vehicle speed at which the speed stage of the transmission 131 is switched (shift change) (in the first embodiment, the vehicle speed at the intersection X (see FIG. 6)), In the second and third embodiments, the switching vehicle speed VC (see FIGS. 8B and 9)) has been described as an example. However, the present invention is not limited to this. The relationship between the vehicle speed V at which the shift change is performed and the target drive torque Td is determined by the loss characteristics of the traveling motor 124. For this reason, the vehicle speed at which a shift change is performed may increase as the target drive torque Td increases.

(Modification 11)
In the above-described embodiment, the shift control process during the power running operation has been described as an example, but the present invention is not limited to this. Even when the speed stage of the transmission 131 is set so as to reduce the loss Lm of the traveling motor 124 during the regenerative operation, the present invention can be applied to improve fuel efficiency. In this case, the target drive torque Td calculated during regeneration is a negative value. Therefore, in the first embodiment, the loss Lm of the traveling motor 124 is calculated based on the absolute value of the target drive torque Td (see FIG. 6). If there is a difference in the characteristics of the loss curve between power running and regeneration, the respective loss curves during power running and regeneration are stored in the storage device, and whether the operating state is power running or regenerative operation. After determining whether or not there is, the loss Lm is calculated. In the second embodiment, the correction speed ΔV is calculated based on the absolute value of the target drive torque Td (see FIG. 8). In the third embodiment, the switching vehicle speed VC is calculated based on the absolute value of the target drive torque Td (see FIG. 9).

(Modification 12)
In the above-described embodiment, the series hybrid work vehicle including the traveling motor 124 driven by the electric power generated by the generator motor 121 that is driven by the engine 161 and generates electric power has been described as an example. It is not limited to. The present invention can also be applied to a parallel hybrid work vehicle or an all-electric work vehicle that drives a traveling motor only by electric power from a power storage device.

(Modification 13)
In the above-described embodiment, the example in which the present invention is applied to the wheel loader has been described. However, the present invention is not limited thereto, and the present invention can be applied to various wheel-type work vehicles such as a wheel excavator and a forklift. it can.

  As long as the characteristics of the present invention are not impaired, the present invention is not limited to the above-described embodiments, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. .

DESCRIPTION OF SYMBOLS 100 Wheel loader, 101 arm, 101A arm cylinder, 102 bucket, 102A bucket cylinder, 103 wheel, 103F front wheel, 103R rear wheel, 105 front vehicle body, 105A steering cylinder, 106 rear vehicle body, 107 cab, 108 machine room, 109 Connecting shaft, 110 Working hydraulic device, 111 Working hydraulic pump, 112 Control valve, 120 Traveling motor, 121 Generator motor, 122 MG inverter, 122c Power controller, 124 Traveling motor, 125 Traveling inverter, 125c Power controller, 127 Power storage device, 128 converter, 128c power controller, 130 power transmission mechanism, 131 transmission, 131c transmission control device, 132 Rotor shaft, 133 differential device, 134 axle, 135 propeller shaft, 141 MG current sensor, 142 MG speed sensor, 143 accelerator pedal, 143a pedal operation amount sensor, 144 driving current sensor, 145 motor speed sensor, 146 engine rotation Speed sensor, 149 ignition switch, 150 control device, 151 torque calculation unit, 152H loss calculation unit, 152L loss calculation unit, 153 speed stage setting unit, 154 vehicle speed calculation unit, 160 engine controller, 161 engine, 161a fuel injection device, 250 Control device, 253 Speed stage setting section, 255 Correction section, 256 Subtractor, 350 Control apparatus, 353 Speed stage setting section

Claims (6)

Engine,
A hydraulic pump driven by the engine to discharge pressure oil;
A working device for working with the hydraulic pump as a drive source;
A running motor that powers the wheels;
A transmission having a plurality of speed stages and transmitting power from the traveling motor to the wheels;
A work vehicle comprising: a shift control device that sets a speed stage of the transmission so that a loss of the traveling motor is reduced according to a vehicle speed and a target drive torque of the wheels. The work vehicle according to claim 1,
The shift control device is a work vehicle that switches a speed stage of the transmission at a lower vehicle speed as the target drive torque is larger. In the work vehicle according to claim 1 or 2,
An operation amount detection device for detecting an operation amount of an accelerator pedal;
A vehicle speed detection device for detecting the vehicle speed;
Torque determining means for determining the target drive torque according to the operation amount detected by the operation amount detection device and the vehicle speed detected by the vehicle speed detection device;
The shift control device includes:
Switching vehicle speed determining means for determining a switching vehicle speed for switching the speed stage of the transmission;
A work vehicle comprising: a speed stage setting unit configured to set a speed stage of the transmission by comparing a vehicle speed detected by the vehicle speed detection device with a switching vehicle speed determined by the switching vehicle speed determination unit. In the work vehicle according to claim 3,
A storage device storing the reference vehicle speed;
The switching vehicle speed determining means determines a correction value that increases as the target drive torque increases, and subtracts the correction value from the reference vehicle speed to determine the switching vehicle speed. In the work vehicle according to claim 3,
A storage device storing the characteristics of the switching vehicle speed that decreases as the target drive torque increases;
The switching vehicle speed determining means is a work vehicle that determines the switching vehicle speed according to the target drive torque based on the characteristics. In the work vehicle according to claim 1 or 2,
An operation amount detection device for detecting an operation amount of an accelerator pedal;
A vehicle speed detection device for detecting the vehicle speed;
Torque determining means for determining the target drive torque according to the operation amount detected by the operation amount detection device and the vehicle speed detected by the vehicle speed detection device;
The shift control device includes:
A loss determination unit that determines the loss of the traveling motor according to the vehicle speed detected by the vehicle speed detection device for each speed stage of the transmission;
An operation comprising: a speed stage setting unit that selects a speed stage with the smallest loss among the losses for each speed stage determined by the loss determination unit, and sets the speed stage of the transmission to the selected speed stage vehicle.

Images