JP2009236138A - Working vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a working vehicle that does not need, especially, sensitive operation of an accelerator to prevent a slip when accelerating in starting, and that does not need limitation of the maximum towing force to prevent a slip. <P>SOLUTION: This working vehicle includes a HST travelling device 8, a controller 12 for outputting a control signal for increasing/decreasing discharge capacity of a HST pump 8a in response to an increase/decrease of the rotating speed of an engine 10, a primary delay converter 14 for giving a time lag to fluctuation of the control signal relative to fluctuation of the engine speed, and a selector switch 16 for selectively switching a lag converting signal, which is converted with a primary lag as a control signal to be output to the HST pump, and a nonconverting signal, which is not converted yet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a work vehicle that can reduce slip on a road surface having a low coefficient of friction such as on snow, particularly slip during acceleration.

  When working on a road surface with a low coefficient of friction, such as on snow or soft ground, with a work vehicle such as a wheel loader, the accelerator pedal that controls the engine speed is sensitive to prevent slipping, especially when starting acceleration. Operation is required. In addition, since the work vehicle often travels on rough terrain, in this case, it is difficult to finely operate the accelerator pedal due to the inclination or vibration of the vehicle body. Therefore, it becomes a work with a high degree of fatigue for the driver.

In order to prevent the work vehicle from slipping on the road surface such as on snow or soft ground, a vehicle that limits the maximum driving force of the HST traveling device has been developed (see, for example, Patent Document 1).
JP 2004-144254 A

  The work vehicle having the form as described above has a problem that further improvement is desired.

  In other words, the work vehicle that limits the maximum driving force does not prevent slipping at the time of starting acceleration, so that the sensitive and difficult operation of the accelerator pedal is not improved. Further, in order to increase the work amount, for example, the snow removal amount, a complicated change operation of the driving force is required to increase the driving force as necessary.

  The present invention has been made in view of the above-mentioned facts, and its technical problem is that, in particular, the sensitive operation of the engine accelerator for preventing the slip at the time of start acceleration is unnecessary, and the maximum traction force is limited. It is to provide a work vehicle without any.

  According to the present invention, as a work vehicle that solves the above technical problem, an HST traveling device and a control signal that increases or decreases the discharge volume of the HST pump according to the increase or decrease of the rotational speed of the engine that is the power source of the HST traveling device are output. Controller, a first-order lag converter for giving a time delay to the fluctuation of the control signal with respect to the fluctuation of the engine speed, and a “lag-converted signal” converted to the first-order lag as a control signal to be output to the HST pump or not converted There is provided a work vehicle including a changeover switch for selectively switching a “non-conversion signal”.

  Preferably, the changeover switch is provided in the vicinity of the steering handle of the driver's seat of the work vehicle.

  A work vehicle configured in accordance with the present invention includes a first-order lag converter that gives a time delay to a variation in a control signal that increases or decreases the discharge volume of an HST pump with respect to a variation in engine rotation speed. The change in the volume of the HST pump is made possible by selectively switching between “conversion signal” or “non-conversion signal” without delay conversion and selecting “delay conversion signal” to delay the fluctuation of the pump control signal with respect to the fluctuation of the engine speed. It is mitigated and sudden acceleration of the work vehicle is suppressed. Therefore, it becomes difficult to slip even in a sudden accelerator operation, and the driver does not have to be sensitive to the accelerator operation. Furthermore, since the control signal is merely delayed, the maximum traction force of the work vehicle is not limited.

  Hereinafter, a work vehicle configured according to the present invention will be described in more detail with reference to the accompanying drawings showing a preferred embodiment of a wheel loader which is a typical work vehicle.

  The wheel loader will be described with reference to FIG. The wheel loader 2 includes a front vehicle body 4 equipped with a work device 4a and a front wheel 4b, and a rear vehicle body 6 equipped with a driver's seat 6a, a rear wheel 6b, an engine compartment 6c, and an engine and an HST travel device described later.

  A description will be given with reference to FIG. The wheel loader 2 (FIG. 5) is configured such that the HST traveling device 8 that drives the front wheels 4b and the rear wheels 6b and the discharge volume of the HST pump 8a according to the increase / decrease in the rotational speed of the engine 10 that is the power source of the HST traveling device 8. As a control signal to be output to the HST pump 8a, a controller 12 that outputs a control signal for increasing or decreasing the control signal, a first-order lag converter 14 provided in the controller 12 for giving a time delay to the fluctuation of the control signal with respect to the fluctuation of the engine speed. A selector switch 16 provided in the vicinity of the steering handle 6d of the driver's seat 6a (FIG. 5) is provided to selectably switch the "delay conversion signal" converted by the first-order delay or the "no conversion signal" not converted. . The changeover switch 16 is an on / off type manual switch.

  The HST traveling device 8 is a well-known one in which the variable displacement HST pump 8a and a variable displacement HST motor 8b having outputs connected to the front wheels 4b and the rear wheels 6b are connected by a closed loop hydraulic circuit. The variable displacement device 8c of the HST pump 8a, for example, in a swash plate type variable displacement pump, tilts the swash plate by an electromagnetic valve that converts an electrical signal that is a control signal from the controller 12 into a hydraulic signal, and its output hydraulic pressure. It is a well-known thing provided with the control mechanism.

  As shown in the characteristic diagram of FIG. 2, the HST pump 8a basically has a “small” capacity and a “large” capacity indicated by an arrow X in accordance with the increase / decrease in the control signal according to the increase / decrease in the engine speed. The discharge amount varies so as to be constant, for example, horsepower according to the variation of the load (hydraulic pressure). The volume ratio between the pump 8a and the motor 8b is controlled by the balance with the running load (hydraulic pressure) of the HST motor 8b.

  The description will be continued with reference to FIG. Based on the output of the speed sensor 18 that detects the engine rotational speed, the controller 12 calculates the control signal to the HST pump 8a, the first-order lag converter 14, and the calculated control signal as the primary. A switch 22 is provided for switching output to the variable capacity device 8c of the HST pump 8a through the delay converter 14 or directly to the variable capacity device 8c. The first-order lag converter 14 is a known one that changes the time constant of the output signal with respect to the input signal.

  When the changeover switch 16 is ON, the switch 22 connects the output of the arithmetic unit 20 to the first-order lag converter 14, and when it is OFF, the output of the calculator 20 does not pass through the first-order lag converter 14. Connect to 8c.

  Accordingly, with reference to FIG. 3 together with FIG. 1, the engine speed increases and increases to a predetermined speed in accordance with the accelerator opening (FIG. 3A) by the accelerator operation (FIG. 3B). Correspondingly, two types of “non-conversion signal” and “delay conversion signal” corresponding to the increase in engine speed are generated as pump control signals (FIG. 3C).

  In an actual work vehicle, for example, it is convenient to call and identify the “non-conversion signal” state as “normal mode” and the “delay conversion signal” state as “on-snow mode”.

A control procedure in the work vehicle 2 will be described with reference to FIG. 4 together with FIG.
In step S1, the engine speed is detected by the speed sensor 18, and the process proceeds to step S2.
In step S2, a pump control signal is calculated by the calculator 20, and the process proceeds to step S3.
In step S3, it is determined whether the switch 22 is in the "delay conversion signal" mode that is ON or in the "no conversion signal" mode that is OFF. If the switch 22 is in the "delay conversion signal" mode, the process proceeds to step S4. In step S5, the process proceeds to step S5.
In step S4, the first-order lag converter 14 performs first-order lag conversion on the calculated pump control signal, and the process proceeds to step S5.
In step S5, a control signal is output to the variable capacity device 8c of the HST pump 8a, and the process returns to step S1.

  In the above description, the control signal changes with respect to the engine rotational speed fluctuations with a time delay in the rising direction in which the engine rotational speed increases, but in the falling direction in which the engine rotational speed decreases. As for the fluctuation, the control signal can have a time delay. In this case, for example, when the accelerator is suddenly operated in the deceleration direction, the work vehicle can be prevented from suddenly decelerating and slipping.

  The effects of the work vehicle 2 as described above will be described.

  The work vehicle 2 includes a first-order lag converter 14 that gives a time lag to fluctuations in the control signal that increases or decreases the discharge volume of the HST pump 8a with respect to fluctuations in the rotational speed of the engine 10, and this "lag conversion signal" ”Or“ no conversion signal ”without delay conversion can be switched by the changeover switch 16, so that the“ delay conversion signal ”is selected and the fluctuation of the pump control signal with respect to the fluctuation of the engine rotation speed is delayed, whereby the HST pump 8 a The volume change of is reduced, and sudden acceleration of the work vehicle 2 is suppressed. Therefore, it becomes difficult to slip even in a sudden accelerator operation, and the driver does not have to be sensitive to the accelerator operation. Furthermore, since the control signal is merely delayed, the maximum traction force of the work vehicle 2 is not limited.

  If the “no conversion signal” is selected by the changeover switch 16, there is no time delay in the pump control signal with respect to the fluctuation of the engine speed due to the accelerator operation, so that the work vehicle 2 can perform normal work.

  Since the changeover switch 16 is provided in the vicinity of the steering handle 6d of the driver's seat 6a, when the work vehicle 2 is driven, it can be easily turned ON / OFF together with the steering handle 6d according to the state of the traveling road surface. Can do.

The structure explanatory view of the work vehicle constituted according to the present invention. The characteristic explanatory view of an HST pump. An explanatory diagram of a control form in a controller. The flowchart which shows the control procedure of a controller. The side view of the wheel loader which is a typical example of a work vehicle.

Explanation of symbols

2: Wheel loader (work vehicle)
6a: Driver's seat 6d: Steering handle 8: HST traveling device 8a: HST pump 10: Engine 12: Controller 14: First-order lag converter 16: Changeover switch

Claims (2)

An HST traveling device;
A controller that outputs a control signal for increasing or decreasing the discharge volume of the HST pump in accordance with an increase or decrease in the rotational speed of the engine that is a power source of the HST traveling device;
A first-order lag converter for giving a time delay to the fluctuation of the control signal with respect to the fluctuation of the engine speed;
A changeover switch for selectively switching a “delay conversion signal” that has been subjected to first-order delay conversion or a “no-conversion signal” that has not been converted as a control signal to be output to the HST pump;
A working vehicle characterized by that. A changeover switch is provided in the vicinity of the steering handle of the driver's seat of the work vehicle.
The work vehicle according to claim 1.

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