JP2013011361A - Device and method for controlling working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smooth clutch action by making a mechanical shock through a pressure fluctuation on releasing the clutch or engaging the clutch less to prevent damage on a hydraulic circuit or like while keeping a low fuel efficiency.SOLUTION: The device for controlling the working vehicle includes a 1-pump 2-motor-style HST, wherein power is transmitted to an output shaft of an HST motor 10a via the clutch 13 or release or engagement of a clutch to run the vehicle with power of the HST motors 10a and 10b. A load of the vehicle is obtained through a throttle output flow rate and an engine speed of the engine. Further the device includes an HST controller 31 for controlling the following: when a control for a shift of the clutch 13 to releasing the same under the upper-limit discharge of an HST pump 4, previously obtained from the vehicle load, the control renders the pump discharge of the HST pump 4 less; when a control for a shift of the clutch 13 to release the same under the lower-limit discharge of the HST pump 4, previously obtained from the vehicle load, the control renders the pump discharge of the HST pump 4 much.

Description

  In the present invention, a hydraulic pump driven by an engine and two hydraulic motors driven by hydraulic oil discharged from the hydraulic pump are connected by a closed hydraulic circuit, and the two hydraulic motors are connected in parallel to the hydraulic pump. The clutch is released or engaged so that power is transmitted from one hydraulic motor to the output shaft via the clutch, and the vehicle is driven by the driving force (hereinafter, power) of the one or two hydraulic motors. The present invention relates to a control device for a working vehicle and a control method thereof.

  Conventionally, construction machines such as wheel loaders equipped with HST (Hydrostatic Transmission: hydrostatic power transmission device), work machines such as agricultural machines and industrial vehicles are known. A work vehicle equipped with an HST has a configuration in which a hydraulic pump and a hydraulic motor are communicated with each other through a closed hydraulic circuit and travels with the power of the hydraulic motor. Recently, an engine, a hydraulic pump, and a hydraulic motor can be driven with an optimal output, pump capacity, and motor capacity by electronic control technology to improve work efficiency and save fuel.

  As a work vehicle equipped with this HST, for example, two hydraulic motors are connected in parallel to a hydraulic pump, and only one hydraulic motor is connected to a clutch, and power is transmitted to four wheels via a power transmission mechanism such as an axle. There is something. Such an HST is a so-called 1-pump 2-motor type HST. This one-pump two-motor type HST may be employed when a large hydraulic motor cannot be manufactured or when there is no place on the work vehicle where the large hydraulic motor is installed. In addition, when a large hydraulic motor is used, it is difficult to quickly control response to inertia due to the rotation of the hydraulic motor, and mechanical resistance increases. For this reason, this one-pump two-motor type HST is adopted. Sometimes. This 1-pump 2-motor type HST is driven by two hydraulic motors when the work vehicle is traveling at a low speed, and when the work vehicle reaches a high-speed travel range, the clutch connected to one hydraulic motor is released, and the other 1 The work vehicle is driven by the power of only one hydraulic motor.

JP-A-11-230333

  As the HST pump (travel hydraulic pump), for example, a swash plate type variable displacement piston pump is used, and the discharge amount of the hydraulic oil discharged from the HST pump can be changed by changing the tilt angle of the swash plate. In recent work vehicles, in order to reduce fuel consumption compared to conventional work vehicles, the running hydraulic pump or the working hydraulic pump is matched to perform work and running in a low engine output range. Yes. Accordingly, the pump absorption torque of the HST pump (travel hydraulic pump) increases. Therefore, the swash plate angle of the HST pump is increased in order to obtain the discharge amount of hydraulic fluid of the HST pump equivalent to that of the conventional work vehicle even in the low rotation region. For this reason, in the low rotation region, the torque of the HST pump, that is, the generated hydraulic oil pressure increases. Here, the 1-pump 2-motor type HST does not use a large hydraulic pump, so it is small and has good response. However, since the above-mentioned hydraulic oil pressure is increased using a clutch, the clutch can be engaged or released. Occasionally, there is an impact that the work vehicle suddenly decelerates or accelerates through the hydraulic circuit or hydraulic equipment due to the acceleration of clutch wear due to the occurrence of hydraulic surge pressure, damage to hydraulic equipment, or the occurrence of hydraulic surge pressure. There may be problems in terms of durability and operational feeling of the work vehicle. In addition, the clutch is released when shifting from low speed to high speed, but since the HST motor itself is also small, the transmission gear ratio before and after the clutch is released is larger than before, and suddenly after the clutch is released. It is conceivable that there will be a problem in operation feeling that a feeling of acceleration appears.

  The present invention has been made in view of the above, and suppresses sudden fluctuations in hydraulic pressure such as generation of surge pressure of hydraulic pressure when the work vehicle travels while maintaining low fuel consumption, and the clutch is disengaged. Control device for work vehicle that can suppress impact at the time of clutch engagement and clutch, prevent damage to clutch, hydraulic circuit and hydraulic equipment, and give operator a good feeling of operation by smooth clutch operation and control thereof It aims to provide a method.

  In order to solve the above-described problems and achieve the object, a control device for a work vehicle according to the present invention includes a hydraulic pump driven by an engine and two hydraulic motors in a closed circuit, with respect to the hydraulic pump. The two hydraulic motors have a hydraulic circuit connected in parallel, and the clutch is released or engaged so that power is transmitted to the output shaft of one hydraulic motor via the clutch. In a control device for a work vehicle that travels by the power of two or two hydraulic motors, load detection means for obtaining a work vehicle load of the work vehicle from a throttle output amount and an engine speed of the engine, and at the time of clutch release transition control And the pump of the hydraulic pump under the limit of the upper limit discharge amount of the hydraulic pump determined in advance based on the work vehicle load determined by the load detecting means. The hydraulic pump is controlled under the restriction of the lower limit discharge amount of the hydraulic pump obtained in advance based on the work vehicle load obtained by the load detecting means during the engagement transition control of the clutch. Control means for performing control to increase the pump discharge amount is provided.

  In the work vehicle control device according to the present invention as set forth in the invention described above, the work vehicle load is determined based on an engine speed and an accelerator opening or an intake manifold pressure.

  In the work vehicle control device according to the present invention, in the above invention, the control means has a clutch status indicating a clutch state including a clutch open state, a released state, an engaged state, and an engaged state. The clutch release transition control and the engagement transition control are determined based on the above.

  In the work vehicle control device according to the present invention as set forth in the invention described above, the clutch status of the output shaft obtained based on a vehicle status indicating a transition of a traveling state of the work vehicle and an accelerator opening degree. It changes based on the number of rotations.

  The work vehicle control method according to the present invention is a hydraulic circuit in which a hydraulic pump driven by an engine and two hydraulic motors are in a closed circuit, and the two hydraulic motors are connected in parallel to the hydraulic pump. The clutch is released or engaged so that power is transmitted to the output shaft of one hydraulic motor via the clutch, and the vehicle travels by the power of the one or two hydraulic motors. In the vehicle control method, the work vehicle load of the work vehicle is obtained from the throttle output amount and the engine speed of the engine, and is obtained in advance based on the obtained work vehicle load during the clutch release transition control. The control is performed to reduce the pump discharge amount of the hydraulic pump under the restriction of the upper limit discharge amount of the hydraulic pump, and during the clutch engagement transition control, And performing meta work vehicle load control to increase the pump discharge amount of the hydraulic pump under restrictions previously obtained lower discharge rate of the hydraulic pump based on.

  The work vehicle control method according to the present invention is characterized in that, in the above invention, the work vehicle load is obtained based on an engine speed and an accelerator opening or an intake manifold pressure.

  According to the present invention, when the work vehicle travels, during the clutch release transition control, the discharge amount of the hydraulic pump is controlled under the restriction of the upper limit discharge amount of the hydraulic pump obtained in advance based on the load of the work vehicle. When the clutch engagement transition control is performed, control is performed to increase the discharge amount of the hydraulic pump under the restriction of the lower limit discharge amount of the hydraulic pump determined in advance based on the load of the work vehicle. Therefore, the work vehicle can maintain a low fuel consumption while suppressing a shock caused by damage to the clutch, hydraulic circuit or hydraulic equipment when the clutch is disengaged or when the clutch is engaged, or a shock caused by a sudden fluctuation in hydraulic pressure. By performing a proper clutch operation, it is possible to give the operator a good feeling of operation as well as a good clutch response.

FIG. 1 is a diagram showing an overall configuration of a wheel loader according to an embodiment of the present invention. FIG. 2 is a diagram showing a circuit configuration centering on the drive system of the wheel loader according to the embodiment of the present invention. FIG. 3 is a time chart showing a control process at the time of clutch release transition. FIG. 4 is a time chart showing a control process at the time of clutch engagement transition. FIG. 5 is an explanatory diagram for explaining the clutch status. FIG. 6 is a flowchart showing a clutch control procedure and a pump discharge amount control procedure based on the clutch status by the HST controller. FIG. 7 is a graph showing the upper limit value of the HST pump command value corresponding to the vehicle load at the time of clutch release transition. FIG. 8 is a graph showing the lower limit value of the HST pump command value according to the vehicle load at the time of clutch engagement transition. FIG. 9 is a diagram illustrating a transition condition of the clutch status. FIG. 10 is a diagram illustrating a transition condition between the vehicle status and the vehicle status. FIG. 11 is a graph showing the vehicle status transition condition when the vehicle status is “1” or “2”. FIG. 12 is a graph showing vehicle status transition conditions when the vehicle status is “3” to “6”. FIG. 13 is an explanatory diagram for explaining the outline of control performed by the control device and the control method according to this embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

[overall structure]
FIG. 1 is a diagram illustrating an overall configuration of a wheel loader 50 that is an example of a work vehicle. FIG. 2 is a diagram showing a circuit configuration centered on the drive system of the wheel loader 50. As shown in FIG. 1, the wheel loader 50 includes a vehicle body 51, a lift arm 52 attached to the front portion of the vehicle body 51, a bucket 53 attached to the tip of the lift arm 52, a bell crank 56, and the like. A vehicle, four tires 54 that rotate while supporting the vehicle body 51 to travel the vehicle body 51, and a cab (cab) 55 mounted on the upper part of the vehicle body 51.

  The vehicle body 51 includes an engine room that houses the engine 1, working machine hydraulic cylinders 19 a and 19 b that operate the lift arm 52 and the bell crank 56, a control valve 18 that controls the working machine hydraulic cylinders 19 a and 19 b, A machine hydraulic cylinder 19a, 19b, a work machine hydraulic pump 2, an HST pump (travel hydraulic pump) 4, and a vehicle body controller 30 for controlling actuators such as travel hydraulic motors 10a, 10b. Further, as shown in FIG. 2, the engine 1, the vehicle body controller 30, the engine controller 32, and the like are mounted on the vehicle body 51. The lift arm 52 is a link member for lifting the bucket 53 attached to the tip, and moves up and down as the working machine hydraulic cylinder (lift cylinder) 19a connected to the lift arm 52 expands and contracts. The bucket 53 is attached to the tip of the lift arm 52, and further, the working machine hydraulic cylinder (bucket cylinder) 19b connected via a link member called a bell crank 56 is extended and retracted to be dumped and tilted. .

[Circuit configuration]
As shown in FIG. 2, the wheel loader 50 drives HST motors (travel hydraulic motors) 10a and 10b with hydraulic oil discharged from an HST pump (travel hydraulic pump) 4 driven by the engine 1. An HST circuit 20 for running the wheel loader 50 is included. The HST circuit 20 is a one-pump two-motor HST system in which two HST motors 10a and 10b are connected in parallel to the HST pump 4 to form a closed hydraulic circuit. Further, the HST circuit 20 drives the two HST motors 10a and 10b to transmit the power to the output shaft 15 to travel the wheel loader 50 during low speed traveling, and disengages the clutch 13 during high speed traveling. The transmission of power from the HST motor 10a to the output shaft 15 is disconnected, and only the HST motor 10b is driven to run the wheel loader 50.

  The wheel loader 50 includes a work implement side mechanism including a work implement hydraulic pump 2 driven by the engine 1, a travel side mechanism including an HST pump 4 driven by the engine 1, and the work implement side mechanism and the travel side mechanism. A hydraulic drive mechanism including an engine controller 32, a vehicle body controller 31, and the like.

  The hydraulic drive mechanism includes an engine 1, a working machine hydraulic pump 2, a charge pump 3, an HST pump 4, HST motors 10a and 10b, a clutch 13, an engine controller 32, a vehicle body controller 30, an accelerator opening sensor 33, and a forward / reverse switching lever. 34, a vehicle speed sensor 36, an HST pressure sensor 37, and an HST circuit 20. The forward / reverse switching lever 34 is provided near the steering column in the cab 55 (cab), and can be switched between forward (F), reverse (R), and neutral (N) when operated by the operator. Thus, the position of the switched lever is electrically detected. Further, a speed stage switch capable of setting the vehicle speed range of the wheel loader 50 is provided near the steering column. The speed stage switch may be an independent dial switch or button switch, or may be attached to the forward / reverse switching lever 34. When the speed stage switch is operated by the operator, the set speed stage position is electrically detected.

  The engine 1 is a diesel engine, and output torque generated by the engine 1 is transmitted to the work machine hydraulic pump 2, the charge pump 3, the HST pump 4, and the like. The engine 1 is connected to an engine controller 32 that controls the output torque and the rotational speed of the engine 1. The engine controller 32 adjusts the fuel injection amount according to the accelerator opening that is the operation amount of the accelerator pedal 33a. The engine 1 also includes an engine speed sensor 1 a that detects the actual speed of the engine 1, and inputs a speed signal of the engine speed sensor 1 a to the engine controller 32. The engine 1 is connected to a fuel injection device 1b. The engine controller 32 adjusts the engine torque and the engine speed by controlling the fuel injection amount 1b according to the accelerator opening. As the fuel injection device 1b, for example, a common rail fuel injection system including a fuel pump, a common rail, an injector, and the like is used.

  The accelerator pedal 13a is provided below the operation seat in the cab 55, and an operator of the wheel loader 50 performs a stepping operation to adjust the amount of depression. The accelerator pedal 13a is provided with an accelerator opening sensor 13 for detecting the amount of depression of the accelerator pedal 13a (throttle output amount). The accelerator opening sensor 13 is realized by a potentiometer or the like, and outputs the detected accelerator opening to the engine controller 32. The engine controller 32 controls the fuel injection device 1b according to the input accelerator opening, and adjusts the fuel injection amount to the engine 1. Instead of the accelerator pedal 13a, the throttle output amount to the engine 1 may be determined by operating means such as an operating lever or a dial that can be manually operated by the operator.

  The HST pump 4 is a variable displacement hydraulic pump (for example, a swash plate variable displacement piston pump) driven by the engine 1. The hydraulic fluid discharged from the HST pump 4 is sent to the HST motors 10a and 10b via the HST circuit 20 including the high pressure relief valves 7 and 8 and the low pressure relief valve 9, respectively. The pressure of hydraulic oil in the HST circuit 20 hydraulic piping (hereinafter referred to as HST pressure) is detected by an HST pressure sensor 37 provided in the HST circuit 20, and a signal indicating the detected pressure is generated in the vehicle body controller 30. To the HST controller 31. Further, the HST pump 4 includes a pump control valve 5 that controls the swash plate angle and hydraulic fluid flow direction for controlling the capacity of the HST pump 4, and a pump that drives the swash plate according to a control instruction of the pump control valve 5. A displacement control cylinder 6 is connected.

  The HST motors 10a and 10b are variable displacement hydraulic motors. Each HST motor 10a, 10b is driven by the hydraulic oil discharged from the HST pump 4, and outputs power for running the wheel loader 50. The HST motors 10a and 10b have motor cylinders 12a and 12b for controlling swash plate angles, and motor control electronic servo valves 11a and 11b for controlling the motor cylinders 12a and 12b, respectively. The motor control electronic servo valves 11a and 11b are electromagnetic control valves that operate according to a control signal transmitted from the HST controller 31 in the vehicle body controller 30, and control the motor cylinders 12a and 12b, respectively. In this way, the motor capacities of the HST motors 10a and 10b can be arbitrarily changed.

  The clutch 13 is controlled to release the clutch or engage the clutch by driving the clutch control valve 14 in accordance with a control signal transmitted from the HST controller 31. When the clutch 13 is released or engaged, the HST motor 10a transmits power to the output shaft 15 or disconnects transmission. On the other hand, the HST motor 10 b always transmits power to the output shaft 15.

  The vehicle speed sensor 36 is a sensor that detects the rotation speed of the output shaft 15, that is, the vehicle speed of the wheel loader 50. The vehicle speed sensor 36 may detect the vehicle speed from the number of rotations of the tire 54 by appropriately determining the installation location.

  The charge pump 3 is a pump that is driven by the engine 1 and supplies hydraulic oil to the HST circuit 20. The charge pump 3 supplies hydraulic oil to the pilot circuit of the HST pump 4.

  The HST controller 31 in the vehicle body controller 30 includes an HST pressure detected by the HST pressure sensor 37, an accelerator opening input via the engine controller 32, and a rotational speed signal (engine rotational speed) input from the engine rotational speed sensor 1a. Based on the forward / reverse signal determined by the operating position of the forward / reverse switching lever 34 operated by the operator, the rotational speed signal (output shaft rotational speed) input from the vehicle speed sensor 36, etc., the hydraulic fluid discharged from the HST pump 4 is discharged. Pump discharge amount (if the engine speed is constant, it is the pump capacity. This is because the following formula, pump discharge amount = engine speed x pump capacity) and the HST motor 10a, The motor capacity of 10b is controlled, and the release and engagement of the clutch 13 are controlled. The engine controller 32 and the vehicle body controller 30 are connected to each other, and can exchange information such as data and signals with each other.

[Outline of clutch release / engagement control]
Here, an outline of control when the HST controller 31 is shifted to release the clutch and an outline of control when the clutch is shifted to engagement will be described. First, with reference to the time chart shown in FIG. 3, the control at the time of clutch release transition for shifting the clutch 13 from the engaged state to the released state will be described. FIG. 3A shows changes in motor command values instructed to the HST motors 10a and 10b with respect to time (vehicle speed), a characteristic line La shows a motor command value for the HST motor 10a, and a characteristic line Lb shows the HST motor. The motor command value for 10b is shown. FIG. 3B shows a change in the clutch command value for instructing the state of disengagement and engagement of the clutch 13 with respect to time (vehicle speed). Here, the clutch command value of 0% means that the clutch 13 is released, and the clutch command value of 100% means that the clutch 13 is completely engaged. FIG. 3C shows a change in the pump command value instructed to the HST pump 4 with respect to time (vehicle speed). In FIG. 3, as the time advances from 0, the vehicle speed of the wheel loader 50 shifts from low speed travel to high speed travel. First, when the wheel loader 50 starts to travel by increasing the accelerator opening when the operator depresses the accelerator pedal 33a while the two HST motors 10a and 10b are engaged, the load increases and the pump command value is reduced to 100%. (Here, the swash plate angle is tilted to 100% (the pump capacity is maximized)), and a large torque is output together with a large pump discharge amount. For example, when the vehicle speed reaches a shift point of Sp (km / h) at a time point t1 after 5 seconds, a release preparation state is established, and at this time point t1, a 100% pump command value is smaller than an upper limit value Pd described later. The pump command value Pd is smaller than the previous pump command value (FIG. 3C), and the pump discharge amount of the HST pumps 10a and 10b is suppressed. Further, the motor command value (motor capacity determined by the inclination angle of the swash plate angle) of the HST motor 10a is gradually decreased as the vehicle speed increases as shown in FIG. The clutch command value is such that the clutch command value of 100% gradually decreases (modulates) from the time t2 when the motor capacity reaches 27%, and the clutch 13 is completely at the time t3 when the clutch command value reaches 30%. As a result, the clutch command value is set to 0% at once (FIG. 3B). Since the clutch 13 is disengaged at this time point t3, the pump command value is increased to 100% without being limited by the upper limit value Pd from this time point t3 (FIG. 3 (c)).

  That is, the pump command value is suppressed to reduce the pump capacity and the power transmission to the output shaft 15 is disconnected during the period from the time t1 to the time t3 when the clutch 13 shifts from the engaged state to the released state. Reduces the pump discharge amount for the pump capacity that does not need to be supplied to the HST motor 10a, suppresses the generation of hydraulic surge pressure in the hydraulic circuit, suppresses impact, and realizes smooth clutch operation with good responsiveness doing. Therefore, friction of the clutch 13 due to a large torque at the time of clutch release transition can be suppressed, and damage to hydraulic equipment and hydraulic piping can be prevented. In addition, since the smooth clutch operation suppresses rapid acceleration when the clutch is released, it gives a good operational feeling to the operator. The pump command value for suppressing the pump discharge amount of the HST pump 4 when the clutch is disengaged is obtained in advance as an upper limit value Pd corresponding to the load of the work vehicle, and does not exceed the upper limit value Pd. . Thus, the pump command value does not exceed the upper limit value Pd, the pump discharge amount supplied to the HST motor 10a before clutch release (before time t3) is suppressed, and the motor capacity of the HST motor 10a is reduced. . The reduction in the motor capacity of the HST motor 10a means that the amount of hydraulic oil discharged from the HST pump 4 does not require that much hydraulic oil to be discharged. That is, unless the pump command value when the clutch is released does not exceed the upper limit value Pd, excess hydraulic oil is discharged from the HST pump 4 toward the HST motor 10a, and the hydraulic oil that has lost its place of travel has a surge pressure. It is a cause of occurrence. On the other hand, the load of the work vehicle determines the degree of load based on the relationship between the engine speed and the accelerator opening. A predetermined upper limit value Pd of the pump command value corresponding to the degree of load is stored in the memory of the HST controller 31. For example, if the degree of load is obtained from the engine speed and the accelerator opening at a certain point in time and the upper limit value Pd corresponding to the degree of load is 70%, the pump command value does not exceed 70%. .

  Next, referring to the time chart shown in FIG. 4, the control at the time of clutch engagement transition for shifting the clutch 13 from the released state to the engaged state will be described. FIG. 4A shows changes in motor command values instructed to the HST motors 10a and 10b with respect to time (vehicle speed), a characteristic line LLa shows a motor command value for the HST motor 10a, and a characteristic line LLb shows the HST motor. The motor command value for 10b is shown. FIG. 4B shows a change in the clutch command value (target value) for instructing the state of clutch release and engagement with respect to time (vehicle speed). FIG. 4C shows a change in the pump command value instructed to the HST pump 4 with respect to time (vehicle speed). In FIG. 4, as the time advances from 0, the vehicle speed of the wheel loader 50 shifts from high speed to low speed. On the other hand, as shown in FIG. 4, the control at the time of clutch engagement transition for shifting the clutch 13 from the disengaged state to the engaged state is performed while the HST motor 10b is transmitting power to the output shaft 15, as shown in FIG. When the wheel loader 50 decelerates from high-speed traveling to decelerating traveling with no power transmitted to the clutch 13 (the clutch 13 is in an open state), that is, the operator depresses the accelerator pedal 33a by operating the accelerator pedal 33a. When the amount is reduced and the accelerator opening is decreased, the pump command value for the HST pump 4 is decreased as shown in FIG. Thereafter, the clutch command value is changed from near 0% to 100% from the time point t11 when the clutch 13 starts to shift from the released state to the engaged state until the time point t12 when the engaged state is completed, and the clutch 13 is engaged. (FIG. 4B). This clutch command value is a target value, and a clutch command value obtained by increasing the clutch command value (for example, 100%) is output for a short time from the time point t11. After a short time, the clutch command value is decreased, The clutch command value is increased to 100% as time t12 elapses. Therefore, the actual degree of engagement of the clutch 13 responds with a slight delay to the clutch command value, and the clutch 13 gradually shifts from disengagement to engagement. During this time t11 to t12, the pump command value is a value larger than the previously obtained lower limit value Pu and is set to a pump command value increased from the immediately preceding pump command value (FIG. 4C). The pump command value is a value immediately before time t11 after time t12. Further, after time t12, the clutch 13 is engaged and the motor command value (motor capacity) of the HST motor 10a increases as shown by the characteristic line LLa (FIG. 4A).

  That is, the pump command value is increased to increase the pump capacity (pump discharge amount) of the HST pump 4 from time t11 to time t12 when the clutch 13 shifts from the disengaged state to the engaged state. As the wheel loader 50 decelerates, the clutch 13 is engaged to transmit the power output from the HST motor 10a to the output shaft 15, but the hydraulic oil (pump capacity) that needs to be supplied to the HST motor 10a. The hydraulic pressure supplied from the HST pump 4 to the HST motor 10a is secured before the clutch command 13 is engaged by increasing the pump command value by time t12. Therefore, when the clutch is engaged, the HST motor 10a is driven with high responsiveness, and the clutch is operated with high responsiveness and smoothness while suppressing the shock by suppressing the sudden fluctuation of the hydraulic pressure in the HST motor 10b or the like. Is realized. The pump command value to be increased is obtained in advance as a lower limit value Pu corresponding to the load of the work vehicle, so that the lower limit value Pu is not lowered. By preventing the pump command value from falling below the lower limit value Pu in this way, the pressure and amount of hydraulic fluid supplied to the HST motor 10a are ensured, and the HST motor 10a can be driven reliably. On the other hand, the load of the work vehicle determines the degree of load based on the relationship between the engine speed and the accelerator opening. A predetermined value of the upper limit value Pu of the pump command value corresponding to the degree of the load is stored in the memory of the HST controller 31. For example, when the degree of load is obtained from the engine speed and the accelerator opening at a certain point in time and the lower limit value Pu corresponding to the degree of load is 70%, the pump command value does not fall below 70%.

  In this embodiment, the pump discharge amount is reduced within a range in which the pump discharge amount does not exceed a predetermined upper limit at the time of clutch release transition. Then, the pump discharge amount supplied to the HST motor 10a from which the transmission of power to the output shaft 15 is disconnected is suppressed before the clutch is released, and the occurrence of hydraulic surge pressure is suppressed and smooth clutch operation with high responsiveness is achieved. To suppress the impact. Further, when the clutch is engaged, the pump discharge force is increased within a range in which the pump discharge amount does not fall below a predetermined lower limit value. The hydraulic oil supplied to the HST motor 10a for transmitting the power to the output shaft 15 is secured before the clutch is engaged, and a smooth clutch operation is realized by suppressing a sudden change in hydraulic pressure, thereby suppressing the impact. Yes.

[Details of clutch control (release control / engagement control)]
Here, the above-described clutch control (release control / engagement control) and pump discharge amount control are performed using the concept of clutch status. As shown in FIG. 5, there are six types of status definitions as shown in FIG. 5. When the clutch status is “0”, it is “preparation for release”, when it is “1”, it is “complete release”, and when it is “2” Is “engaged”, “3” is “forced engagement”, “4” is “engagement complete”, and “5” is “released”. The transition between the clutch statuses, that is, clutch control (release control / engagement control) is executed by the HST controller 31 outputting the target clutch command value shown in FIG. In addition, the graph showing the relationship between time and the target clutch command value shown in FIG. 5 represents both FIG. 3 (b) and FIG. 4 (b).

  The clutch status “engagement complete” is a status indicating that the clutch 13 is completely connected and the power of the HST motor 10a is transmitted to the output shaft 15, and the target clutch command value is 100%. In this clutch status (engagement complete), the vehicle status, accelerator opening (throttle output amount) (%), clutch status stay time (current clutch status is kept unchanged), which will be described later, in preparation for the release of the clutch 13. Shift speed (output shaft speed determined by referring to the first map or the second map) is determined according to the shift time), and the speed of the output shaft 15 detected (hereinafter referred to as output shaft speed). Are compared, and if a transition condition described later is satisfied, the clutch status is shifted to “preparation for release”. The clutch status transition timing is a shift point Vo as shown in FIG.

  The clutch status “preparation for release” is a status indicating a state in which the motor capacity of the HST motor 10a is reduced to a certain value (for example, 27%) in preparation for the release of the clutch 13. Here, when the following transition condition is satisfied, the clutch status shifts to “released”. In other words, when the motor capacity of the HST motor 10a becomes smaller than a certain value (for example, 27%) and a transition condition (details will be described later) that a predetermined time has passed is satisfied, the clutch status is changed to “opening”. Let

  The clutch status “released” is a status indicating a state in which the clutch 13 is released, and the clutch command value is gradually decreased (modulated) from 100% to 30%, for example, to reduce the clutch 13 and release the clutch 13. When the clutch command value reaches 30%, the clutch status is shifted to “completed release”. The clutch command value 30% is merely an example numerical value, and this embodiment can be realized by setting another value in advance.

  The clutch status “completely opened” is a status indicating a state in which the clutch command is set to 0% for failure detection (for detecting the clutch solenoid power of the clutch control valve 14). When the clutch status is “completely open”, the clutch command value is set to 0% when the detected output shaft rotational speed is equal to or higher than a certain rotational speed and the vehicle speed stage is 3rd speed or 4th speed. Further, when the rotational speed is lower than the other rotational speed, the clutch command value is set to 30%, for example. In the state where the clutch status is “completely released”, the clutch status shifts under the following transition condition (details will be described later). That is, in preparation for the engagement of the clutch 13, the shift point (the output shaft rotational speed obtained by referring to the first map or the second map) is determined by the vehicle status, the throttle output amount (%), and the clutch status stay time, When the output shaft rotation speed detected is smaller than this shift point, the clutch status is shifted to “engaged”. That is, this clutch status transition timing is the shift point Vc as shown in FIG. The clutch command value 30% is merely an example numerical value, and this embodiment can be realized by setting another value in advance.

  The clutch status “engaged” is a status indicating a state in which the clutch command value is changed in order to engage the clutch 13. When the clutch status is “engaged”, the clutch status shifts under the following transition condition (details will be described later). That is, when the vehicle speed of the wheel loader 50 is increased, the detected output shaft rotational speed is equal to or higher than a certain rotational speed, and the vehicle speed stage is 3rd speed or 4th speed, the clutch status shifts to “open complete”. Further, as shown in FIG. 5, after the clutch status becomes “engaged”, a predetermined normal engagement end time R <b> 2 (see FIG. 5) elapses, and the clutch command value becomes 100%. In this case, the clutch status shifts to “engagement complete”. Furthermore, when a predetermined transition condition (details will be described later) is satisfied while the clutch 13 is engaged, the clutch 13 performs an engagement operation called forced engagement. The clutch status shifts from “engaged” to a clutch status “forced engagement” described later. Here, the purpose of the engaging operation of the clutch 13 called forced engagement will be described. Normally, when the clutch 13 is engaged, the clutch 13 receives a clutch command value as shown by a solid line in FIG. However, when the wheel loader 50 is traveling at a predetermined speed or less (particularly at a speed that is traveling at a low speed), the wheel loader 50 is stopped by an impact when the clutch 13 is engaged. There is a possibility that the operator may feel uncomfortable. In addition, when a load is placed on the bucket 53 of the wheel loader 50 and approaches the climbing path, there is a scene where it is desired to quickly engage the released clutch 13 to generate traction force. In the above case, if it is normal engagement, the clutch 13 is engaged during the normal engagement time R2 shown in FIG. By setting and determining a transition condition that shifts to “intermediate”, the clutch 13 is engaged (forced engagement) in a shorter time than the normal engagement time R2 (see FIG. 5). That is, the time required for the forced engagement, which is defined as the forced engagement time R2 ′ (see FIG. 5), is shorter than the normal engagement time R2.

  The clutch status “forcibly engaged” is a status indicating a state in which the clutch command value is increased to 100% at a predetermined rate from the target clutch command value when the clutch status is shifted to “forcibly engaged”. (See the broken line in FIG. 5). If the vehicle speed of the wheel loader 50 increases while the clutch status is “forcibly engaged” and the following transition conditions (details will be described later) are satisfied, the clutch status shifts to “completely released”. That is, when the output shaft rotational speed is equal to or higher than a certain rotational speed and the vehicle speed stage is the third speed or the fourth speed, the clutch status shifts to “completely opened”. Alternatively, when the following transition condition (details will be described later) is satisfied, the clutch status shifts to “engagement complete”. If the clutch command value reaches 100% while the clutch status is “forced engagement”, the clutch status is shifted to “engagement complete”. That is, when the forced engagement time R2 'shown in FIG. 5 has elapsed and the clutch command value is increased to reach 100% as indicated by the broken line in FIG. 5, the clutch status is shifted to "engagement complete". .

  Of the clutch status, a period including the release preparation “0” and the release “5” is defined as the release transition time R1 (see FIG. 5), and the clutch 13 is performing preparation for release and release operation. It corresponds to time (at the time of opening transition). In the clutch status, “2” during engagement is defined as the normal engagement time R2 as described above, and corresponds to the time during which the clutch 13 is engaged (when engaged). Alternatively, the forced engagement time R2 ', which is the period “3” during forced engagement, corresponds to the time during which the clutch 13 is engaged (when engaged).

  The clutch control (release control / engagement control) and pump discharge amount control by the HST controller 31 will be described with reference to the flowchart shown in FIG. First, the HST controller 31 determines which clutch status is currently in the clutch status described above (step S101). Thereafter, it is determined whether or not the determined current clutch status is “completely released” (step S102). When the clutch status is “completely released” (step S102, Yes), the target discharge amount of the HST pump 4 is further calculated (step S103). Then, a signal (pump command value) for instructing the angle of the swash plate angle is output to the pump control valve 5 of the HST pump 4 so as to be the target discharge amount, and the pump discharge amount is controlled and the clutch 13 A signal (clutch command value) for maintaining the released state of the clutch 13 is output to the clutch control valve 14, clutch release control is performed (step S104), and the process proceeds to step S101.

  On the other hand, if the clutch status is not “release complete” (step S102, No), it is further determined whether or not the clutch status is “engaged complete” (step S105). When the clutch status is “engagement complete” (step S105, Yes), the target discharge amount of the HST pump 4 is further calculated (step S106). Then, the pump command value is output to control the pump discharge amount so that the target discharge amount is obtained, and the clutch command value is output to maintain the engagement state of the clutch 13 and the clutch engagement control is performed. (Step S107), the process proceeds to Step S101.

  On the other hand, when the clutch status is not “engagement complete” (step S105, No), it is further determined whether the clutch status is “engaged” or “forced engagement” (step S108). . When the clutch status is “engaged” or “forced engagement” (step S108, Yes), the target discharge amount of the HST pump 4 is further calculated (step S109). Next, the lower limit value of the pump command value of the HST pump 4 is acquired (step S110). Then, as shown in FIG. 4, a clutch command value for controlling the pump discharge amount by outputting a pump command value so as to be the target discharge amount under the restriction of the lower limit value and engaging the clutch 13. Is output to control during clutch engagement (step S111), and the process proceeds to step S101. In the clutch engagement control, as shown in FIG. 4, motor capacity control for the HST motors 10 a and 10 b, clutch control for the clutch 13, and pump discharge for the HST pump 4, which are performed from time t 11 to t 12. Means the total of three types of control. The time during clutch engagement control performed between time t11 and time t12 corresponds to the normal engagement end time R2 shown in FIG.

  On the other hand, when the clutch status is not “engaged” or “forced engagement” (No in step S108), the clutch status is “preparation for release” or “under release” (step S112), and the HST pump 4 The target discharge amount is calculated (step S113). Further, the upper limit value of the pump command value of the HST pump 4 is acquired (step S114). Then, as shown in FIG. 3, under the limitation of the upper limit value, the pump command value is output so as to be the target discharge amount, the pump discharge amount control is performed, and the clutch command value for releasing the clutch 13 is set. The output is performed to perform the clutch release control (step S115), and the process proceeds to step S101. As shown in FIG. 3, the clutch release control is a motor capacity control for the HST motors 10a and 10b, a clutch control for the clutch 13, and a pump discharge amount for the HST pump 4, which are performed from time t1 to time t3. It means a combination of the three controls. The time during the clutch release control that is performed between time t1 and time t3 corresponds to the release transition time R1 shown in FIG. 5 as described above.

  That is, in step S111, control during clutch engagement transition (control during clutch engagement) between time points t11 to t12 in FIG. 4 is performed, and in step s115, clutch release transition between time points t1 to t3 in FIG. 3 is performed. Time control (clutch release control).

  Next, how to determine the upper limit value or the lower limit value of the pump command value will be described. 7 and 8 are diagrams showing the upper limit value or the lower limit value of the pump command value according to the accelerator opening with respect to the engine speed. Here, the upper limit value of the pump command value acquired in step S114 is acquired with reference to the graph data shown in FIG. The upper limit data is stored in advance in a storage device such as a memory of the HST controller 31. Further, the lower limit value of the pump command value acquired in step S110 is acquired with reference to the data of the graph shown in FIG. The lower limit data is stored in advance in a storage device such as a memory of the HST controller 31. The upper limit value or the lower limit value of the data in the graphs shown in FIGS. 7 and 8 is the load on the work vehicle (in this embodiment, the wheel loader 50) determined by the engine speed and the accelerator opening. Correspondingly, it is preset. The data in the graphs shown in FIGS. 7 and 8 are the upper limit value or the lower limit value of the pump command value, not the value indicating the load. Here, curves LA11 and LA21 in FIGS. 7 and 8 indicate when the accelerator opening is large, for example, when the accelerator opening is 90% or more, and curves LA12 and LA22 indicate when the accelerator opening is medium. For example, the accelerator opening is 70%, and the curves LA13 and LA23 indicate when the accelerator opening is small, for example, when the accelerator opening is 50% or less. Moreover, the data of the graphs shown in FIGS. 7 and 8 are set differently depending on the type and the vehicle type of the work vehicle. The upper limit value or lower limit value of such a pump command value (pump discharge amount) is set in advance, and the upper limit value or the lower limit value is selected according to the load of the work vehicle, and motor capacity control, clutch control, pump discharge amount control As a result, the suppression or increase of the pump discharge amount at the time of clutch release transition or clutch engagement transition is reliably and appropriately controlled.

  As described with reference to FIG. 5 and the like, the clutch status has six types of clutch status, and the clutch status shifts when a condition called a transition condition is satisfied. Details of this transition condition will be described. FIG. 9 shows clutch status transition conditions. Each clutch status has been described with reference to FIG. 5, but the clutch status is changed when the respective clutch status satisfies the respective transition conditions.

Transition condition 1- (1) When the clutch status shifts from disengagement complete to engaged The transition condition when the disengagement complete clutch status “1” shifts to the engaged clutch status “2” will be described. If the condition (engagement condition (1)) that is equal to or less than a certain threshold value of the output shaft rotational speed is satisfied when the clutch status is less than 1 second after the clutch status becomes “1”, the process shifts to the clutch status “2”. Here, the output shaft rotational speed at a certain threshold is the output shaft rotational speed obtained with reference to the graph shown in FIG. That is, the threshold output shaft speed is obtained from the accelerator opening (throttle output amount) detected by the accelerator opening sensor 33 using the graph corresponding to the engagement condition (1). On the other hand, the time during which the clutch status continues to be the same (less than 1 second after the clutch status becomes “1” as described above) is measured by a counter or the like. When the clutch status becomes “1” and is 1 second or longer, if the condition (engagement condition (2)) that is equal to or greater than a certain threshold output shaft speed is satisfied, the clutch status is shifted to “2”. Here again, the output shaft rotational speed at a certain threshold is the output shaft rotational speed obtained with reference to the graph of the engagement condition (2) shown in FIG.

Transition condition 2- (2) When the clutch status shifts from engaged to forced engagement Regarding transition conditions when the clutch status “2” during engagement shifts to the clutch status “3” during forced engagement explain. If the condition (forced engagement condition (1)) that is equal to or lower than a certain threshold output shaft speed is satisfied at the time of high load, the state shifts to the clutch status “3”. Here again, the output shaft rotational speed with a certain threshold is obtained with reference to the graph of the forced engagement condition (1) shown in FIG. Moreover, the state at the time of high load means the following things. The hydraulic pressure (HST pressure) detected by the HST pressure sensor 37 is equal to or higher than a predetermined value, the vehicle status is not FR shuttle or RF shuttle, and the clutch status is “engaged”. The vehicle speed sensor 36 detects that a predetermined amount of rotation speed has decreased from the output shaft rotation speed at the time when a predetermined time (for example, 0.3 seconds) has passed and became “engaged”. State. In other words, as described above, when a load is placed on the bucket 53 of the wheel loader 50 and approaches the climbing path, the scene in which the clutch 13 that has been released is quickly engaged and the traction force is to be generated is the case when the load is high. Corresponds to the state. Further, if the condition (forced engagement condition (2)) that is equal to or less than a certain threshold value of the output shaft rotation speed is satisfied at the time of shuttle or low load, the clutch status from the engaged clutch status “2” to the forced engagement clutch status. Move to “3”. Here, the output shaft rotational speed at a certain threshold is obtained with reference to the forced engagement condition (2) graph shown in FIG. Moreover, the state at the time of shuttle or at the time of low load means the following states. The time of shuttle is when the wheel loader 50 loads the load into the bucket 53, when traveling forward and switching to reverse traveling without stopping completely, or when traveling backward and switching to forward traveling without completely stopping. . In other words, the shuttle time is a vehicle status “3” or “4” which means a shuttle time in terms of a vehicle status described later.

Transition condition 4- (1) When the clutch status shifts from engagement complete to release preparation The transition condition when the engagement completion clutch status “4” shifts to the release preparation clutch status “0” will be described. When the engagement is complete, the clutch command value is 100% as shown in FIG. Therefore, when the clutch status “4” is less than 2 seconds and the condition (open condition (1)) equal to or higher than a certain output shaft rotational speed is satisfied, the clutch status “0” is entered. Here, the output shaft rotational speed at a certain threshold is the output shaft rotational speed obtained by referring to the graph of the open condition (1) shown in FIG. Further, when the clutch status “4” becomes 2 seconds or longer and the condition (opening condition (2)) that is equal to or higher than a certain threshold output shaft rotational speed is satisfied, the state shifts to the clutch status “0”. Here, the output shaft rotational speed at a certain threshold is the output shaft rotational speed obtained by referring to the graph of the open condition (2) shown in FIG.

Transition condition 2- (1) When the clutch status shifts from engaged to fully engaged The transition condition when shifting from engaged clutch status “2” to engaged clutch status “4” will be described. . When the normal engagement end time R2 shown in FIG. 5 has elapsed, the clutch status shifts to “4”.

Transition condition 2- (3) When the clutch status shifts from engaged to fully released The transition condition when shifting from engaged clutch status “2” to fully released clutch status “1” will be described. If the detected output shaft rotational speed is equal to or higher than a predetermined rotational speed and the condition that the speed stage is 3rd speed or 4th speed is satisfied, the clutch status is shifted to “1”.

Transition condition 3- (1) When the clutch status shifts from being engaged forcibly to complete engagement Regarding the transition condition for shifting from the clutch status “3” during forced engagement to the clutch status “4” when engagement is complete explain. Transition is made when the pump target command value reaches 100%. As described above with reference to FIG. 5, when the clutch 13 is forcibly engaged while the clutch 13 is engaged, the pump command value is increased and the pump command value is set to 100 to immediately engage the clutch 13. % (See the broken line in FIG. 5), but when it reaches 100%, the clutch status shifts to engagement complete.

Transition condition 3-(2) When the clutch status shifts to the fully released state from the forced engagement The transition condition when the clutch status “3” during the forced engagement shifts to the fully closed clutch status “1” will be described. . Here, the clutch status is shifted under the same condition as the transition condition 2- (3).

Transition condition 0- (1) When the clutch status shifts from the release preparation to the release state The transition condition when the release preparation clutch status “0” changes to the release clutch status “5” will be described. In the opening preparation, the clutch command value is 100% as shown in FIG. 5, but the motor command value is decreased as shown in FIG. When a predetermined time (for example, 0.01 seconds) elapses after the motor command value becomes equal to or less than a certain value (for example, 27%), the clutch status is shifted.

Transition condition 5- (1) When the clutch status shifts from being released to fully released The transition condition when shifting from the clutch status “0” for release preparation to the clutch status “5” being released will be described. During release, as shown in FIG. 5, the clutch command value is decreased at a predetermined rate. When the clutch command value falls below a certain value (for example, 30%), the clutch status is shifted.

  Next, the vehicle status will be described. As shown in FIG. 10, the vehicle status includes “0” during stop, “1” forward, “2” reverse, “FR shuttle“ 3 ”, RF shuttle“ 4 ”, forward N stop“ 5 ”, reverse N stop. There are seven types of status “6”. The current vehicle status (current vehicle status) of the vehicle status is the next vehicle status determined from the state of the previous work vehicle. That is, the next vehicle status is determined by the information of the four elements of the current vehicle status, the position of the forward / reverse switching lever 34, the rotational direction detected by the vehicle speed sensor 36, and the output shaft rotational speed. The forward / reverse switching lever 34 has three types of positions: forward “F”, reverse “R”, and neutral “N”. The position of the forward / reverse switching lever 34 is determined by an operator's operation. That is, when the wheel loader 50 is moved forward, it is operated to the forward “F”. When the wheel loader 50 is moved backward, the wheel loader 50 is operated to the reverse “R”, and the engine 1 is idled to stop the wheel loader 50. Operated to neutral “N”. The position of the forward / reverse switching lever 34 is electrically detected by a contact switch or the like, and forward “F”, reverse “R”, and neutral “N” are acquired as operation selection forward / reverse data.

  The current state being stopped is a state where the wheel loader 50 is not traveling. The current state is forward. The wheel loader 50 is traveling forward. The current state is backward. In this state, the vehicle is traveling backward. Further, the vehicle state FR shuttle is a state in which the wheel loader 50 is immediately switched from forward travel to reverse travel, and the vehicle state is RF shuttle in which the wheel loader 50 is immediately switched from reverse travel to forward travel. State. The vehicle state is forward N stop is a state in which the forward / reverse switching lever 34 is operated neutrally while the wheel loader 50 is traveling forward. Further, the vehicle state is reverse N stop is a state in which the forward / reverse switching lever 34 is operated to be neutral while the wheel loader 50 is traveling backward.

  When it is detected that the rotation direction detected by the vehicle speed sensor 36 is a direction in which the wheel loader 50 is moved forward, “F” is acquired as data of the vehicle speed sensor rotation direction, and on the other hand, the wheel loader 50 is moved backward. Is detected as “R” as data of the rotation direction of the vehicle speed sensor. Further, as shown in FIG. 10, the output shaft rotational speed detected by the vehicle speed sensor 36 has a magnitude relationship with preset threshold values (Vzero, Vs) depending on the current vehicle status and operation selection forward / reverse data. Are compared. The threshold value Vzero is a value for determining whether or not the wheel loader 50 is in a stopped state, and the output shaft rotational speed is a value close to 0 (rpm). Further, the threshold value Vs is a value larger than Vzero. The threshold value Vs is used to determine whether or not the next vehicle status should be “0” when the wheel loader 50 performs the shuttle operation. In the shuttle operation, since the forward / reverse switching is performed immediately, the output shaft rotational speed has a certain value immediately after the switching. Therefore, not only the threshold value Vzero but also two threshold values, the threshold value Vs, are set, and the next vehicle status is determined using a logical sum described later.

  The transition condition from the current vehicle status to the next vehicle status is the logical product (AND) of the position of the forward / reverse switching lever 34 (operation selection forward / backward data), the rotational direction data of the vehicle speed sensor, and the output shaft rotational speed data. Is determined by using a logical sum (OR) of the condition A that is and the condition B that is the output shaft rotation speed. The vehicle status can be obtained by constantly monitoring the conditions A and B related to the transition condition.

  “Output shaft rotational speed as a threshold value” necessary for changing the clutch status based on the vehicle status obtained as described above and the accelerator opening (throttle output amount) detected by the accelerator opening sensor 33 (The output shaft rotation speed at a certain threshold is determined). That is, when the vehicle status is forward “1” or reverse “2”, the output shaft rotational speed as a threshold can be obtained by using the data of the graph shown in FIG. 11 (hereinafter referred to as the first map). . When the vehicle status is FR shuttle “3”, RF shuttle “4”, forward N stop “5”, reverse N stop “6”, the data of the graph shown in FIG. 12 (hereinafter referred to as second map) is used. By using it with reference, the output shaft rotation speed as a threshold value is obtained. The first map or the second map is the above-described clutch status transition condition (engagement condition (1), engagement condition (2), forced engagement condition (1), forced engagement condition (2), release. Each condition (1) and opening condition (2)) is preset according to the throttle output amount (%) (FIGS. 11 and 12).

  Then, the output shaft rotational speed detected by the vehicle speed sensor 36 is compared with the output shaft rotational speed as a threshold shown in the first map or the second map, and the clutch status transition condition (engagement condition (1), When any one of the engagement condition (2), the forced engagement condition (1), the forced engagement condition (2), the release condition (1), and the release condition (2)) is satisfied, the clutch status is changed. . The “output shaft rotational speed as a threshold value” is a shift point Vo from the low speed travel to the high speed travel or a shift point Vc from the high speed travel to the low speed travel. The shift point Vo is a point where the clutch 13 shifts from the engaged state to the released state, and the shift point Vc is a point where the clutch 13 shifts from the released state to the engaged state. If the vehicle status can be determined using FIG. 10 as described above, the first map of FIG. 11 or the second map of FIG. The clutch status is determined by referring to the output shaft speed. The current clutch status is obtained by monitoring changes in the output shaft speed. Then, as described above, by determining the current clutch status including step S101 shown in FIG. 6, pump discharge amount control and clutch control (release control / engagement control) according to the clutch status are performed. Is called. This embodiment described above will be summarized with reference to FIG.

  That is, in FIG. 13, first, the vehicle status (next vehicle status) is determined (step S210). In order to determine the vehicle status, as shown in FIG. 10, information on the current vehicle status is obtained, information on the position of the forward / reverse switching lever is obtained, and information on the rotational direction and output shaft rotational speed is obtained by the vehicle sensor. get.

  Further, the accelerator opening sensor 33 acquires information on the accelerator opening, and further acquires information on the output shaft rotation speed (shift point) according to the vehicle status (step S202). The information on the output shaft rotation speed (shift point) is acquired from the first map or the second map. Further, information on the current clutch status is acquired (step S203). Further, information on the current output shaft speed is acquired by the vehicle speed sensor (step S204).

Thereafter, a determination is made as to whether the clutch status transition condition shown in FIG. 9 is satisfied (step S205). As information used to determine whether this transition condition is satisfied,
(1) Current clutch status information (2) Current output shaft rotation speed information (3) Output shaft rotation speed (shift point) information (4) Elapsed time (5) HST pressure detected by HST pressure sensor (6) Current vehicle speed of the work vehicle (7) Current vehicle status information (8) Current pump command value information. Depending on the transition condition, the transition condition is determined to be established using one or a plurality of pieces of information (1) to (8).

  Thereafter, the clutch status transition is performed based on the determination result of the transition condition in step S205 (step S206). Then, the control shown in the flowchart of FIG. 6 is executed (step S207). That is, clutch control (engagement control / release control), pump discharge amount control of the HST pump, and motor capacity control of the HST motor are performed. Thereafter, the process proceeds to step S210 and the above-described processing is repeated.

[Modification]
In the embodiment described above, the load on the work vehicle is obtained based on the engine speed and the accelerator opening. However, the load on the work vehicle is obtained based on the engine speed and the intake manifold pressure. Also good. Detecting the accelerator opening is indirectly detecting the load state of the engine 1. Therefore, if the pressure of the air passing through the intake manifold (intake manifold pressure) in the intake manifold, which is a path for sucking air into the engine 1, is detected using a pressure sensor, the load state of the engine 1 can be determined. Since it is detected directly, the load on the work vehicle can be detected more stably and accurately. As a result, the transition of the clutch status can be performed with high accuracy, and the accuracy of clutch control (release control / engagement control) can be improved.

  In this embodiment, the pump discharge amount is suppressed under the restriction of the upper limit value of the pump command value when the clutch is released, and the pump discharge amount is increased under the restriction of the lower limit value of the pump command value when the clutch is engaged. Therefore, the HST motors 10a and 10b are reduced in size so that a large transmission gear ratio is required, and further, a design in which the performance of the engine 1 is improved and a large pump absorption torque is required. According to the control device and the control method according to this embodiment, the impact at the time of engagement or release of the clutch 13 can be suppressed and a smooth clutch operation can be performed, and a good operational feeling is given to the operator. Therefore, it is not necessary to provide a special measure for improving the durability of the clutch or hydraulic equipment of the work vehicle. Therefore, it is possible to quickly and easily cope with a new design or design change of a work vehicle such as the wheel loader 50.

DESCRIPTION OF SYMBOLS 1 Engine 1a Engine speed sensor 1b Fuel injection apparatus 2 Hydraulic pump for work machines 3 Charge pump 4 Hydraulic pump for driving (HST pump)
5 Pump Control Valve 6 Pump Capacity Control Cylinder 7, 8 High Pressure Relief Valve 9 Low Pressure Relief Valve 10a, 10b Traveling Hydraulic Motor (HST Motor)
11a, 11b Motor-controlled electronic servo valves 12a, 12b Motor cylinder 13 Clutch 14 Clutch control valve 15 Output shaft 19a Working machine hydraulic cylinder (lift cylinder)
19b Hydraulic cylinder for work equipment (bucket cylinder)
20 HST circuit 30 vehicle body controller 31 HST controller 32 engine controller 33 accelerator opening sensor 33a accelerator pedal 34 forward / reverse switching lever 36 vehicle speed sensor 37 HST pressure sensor 50 wheel loader

Claims (9)

The hydraulic pump driven by the engine and the two hydraulic motors are closed circuits, and the hydraulic pump has a hydraulic circuit in which the two hydraulic motors are connected in parallel to the hydraulic pump. In a control device for a work vehicle in which the clutch is released or engaged so that power is transmitted through the clutch, and the vehicle is driven by the power of the one or two hydraulic motors,
Load detecting means for obtaining a work vehicle load of the work vehicle from a throttle output amount and an engine speed of the engine;
Control for reducing the pump discharge amount of the hydraulic pump under the restriction of the upper limit discharge amount of the hydraulic pump obtained in advance based on the work vehicle load obtained by the load detection means at the time of clutch release transition control. A control device for a work vehicle, comprising control means for performing. The hydraulic pump driven by the engine and the two hydraulic motors are closed circuits, and the hydraulic pump has a hydraulic circuit in which the two hydraulic motors are connected in parallel to the hydraulic pump. In a control device for a work vehicle in which the clutch is released or engaged so that power is transmitted through the clutch, and the vehicle is driven by the power of the one or two hydraulic motors,
Load detecting means for obtaining a work vehicle load of the work vehicle from a throttle output amount and an engine speed of the engine;
Control to increase the pump discharge amount of the hydraulic pump under the restriction of the lower limit discharge amount of the hydraulic pump obtained in advance based on the work vehicle load obtained by the load detection means during the clutch engagement transition control. A control device for a work vehicle, comprising control means for performing.   The work vehicle control device according to claim 1, wherein the work vehicle load is obtained based on an engine speed and an accelerator opening or an intake manifold pressure.   The control means determines the time of clutch release transition control based on a clutch status indicating a clutch state including a clutch open state, a released state, an engaged state, and an engaged state. The work vehicle control device according to claim 1 or 3.   The control means determines the time of clutch engagement transition control based on a clutch status indicating a clutch state including a clutch open state, a released state, an engaged state, and an engaged state. The work vehicle control device according to claim 2 or 3.   The clutch status is changed based on a vehicle status indicating a transition of a running state of the work vehicle and a rotation speed of the output shaft obtained based on an accelerator opening. 5. The work vehicle control device according to 5. The hydraulic pump driven by the engine and the two hydraulic motors are closed circuits, and the hydraulic pump has a hydraulic circuit in which the two hydraulic motors are connected in parallel to the hydraulic pump. In a method for controlling a work vehicle in which the clutch is released or engaged so that power is transmitted through a clutch, and the vehicle is driven by the power of the one or two hydraulic motors,
Obtaining the work vehicle load of the work vehicle from the throttle output amount and the engine speed of the engine;
In the clutch disengagement transition control, control is performed to reduce the pump discharge amount of the hydraulic pump under the restriction of the upper limit discharge amount of the hydraulic pump obtained in advance based on the obtained work vehicle load. Control method of work vehicle. The hydraulic pump driven by the engine and the two hydraulic motors are closed circuits, and the hydraulic pump has a hydraulic circuit in which the two hydraulic motors are connected in parallel to the hydraulic pump. In a method for controlling a work vehicle in which the clutch is released or engaged so that power is transmitted through a clutch, and the vehicle is driven by the power of the one or two hydraulic motors,
Obtaining the work vehicle load of the work vehicle from the throttle output amount and the engine speed of the engine;
During clutch engagement transition control, control is performed to increase the pump discharge amount of the hydraulic pump under the restriction of the lower limit discharge amount of the hydraulic pump determined in advance based on the determined work vehicle load. Control method for working vehicle.   9. The work vehicle control method according to claim 7, wherein the work vehicle load is obtained based on an engine speed and an accelerator opening or an intake manifold pressure.

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