JPH0694114A - Automatic shift controller for wheel loader - Google Patents

Abstract

PURPOSE:To improve workability by preventing the reduction of traction due to unnecessary automatic shift-up at the time of the tire slip of a wheel loader. CONSTITUTION:The average vehicle speed is calculate at every regular time from the detection value of a transmission output shaft portion rotary speed detector 6 and is memorized, and when the present average vehicle speed has reached a shift point, A vehicle speed increase amount is calculated from the present average vehicle speed and the average vehicle speed before a predetermined time, and on the basis of the data of the present thrown-in speed step and the present average vehicle speed, a possible acceleration amount acceleratable without tire slip is calculated from the average vehicle speed before the predetermined time with a motor throttle fully opened, and in a case in which the vehicle speed increase amount surpasses the possible acceleration amount, the present thrown-in speed step is maintained until a preset time elapses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic shift control system capable of preventing automatic shift-up when a tire of a wheel loader slips.

[0002]

2. Description of the Related Art Conventionally, as an automatic gear shift control device for a wheel loader, a method of detecting the rotational speed of the output shaft of the transmission and switching the speed stage based on the vehicle speed, and a method of correcting the rotational speed of the prime mover, etc. In addition, a system of switching the speed stage was used.

[0003]

Generally, traveling, excavation,
In a wheel loader that continuously performs a series of operations of transportation and loading, in order to overcome a reaction force from the earth and sand 3 when the vehicle 1 is moved forward and the bucket 2 is pushed into the earth and sand 3, as shown in FIG. The operator depresses the accelerator pedal to generate a large traction force with the prime mover throttle being fully opened or an opening close to fully opened. Therefore, it is inevitable that tire slip will occur, and when tire slip occurs,
It is necessary for the operator to suppress the tire slip by slightly returning the opening of the prime mover throttle by operating the accelerator pedal.

However, a conventional automatic gear shift system is one in which the rotational speed of the output shaft of the transmission is detected and the speed stage is switched based on the vehicle speed, and in which a speed stage is switched by correcting the rotational speed of the prime mover. When a control device is used, when tire slip occurs, the detected value of the rotation speed of the output shaft of the transmission becomes high even if the vehicle speed that should be upshifted is not actually output. Assuming that the shift point has been reached, the shift-up operation will be automatically performed, as when the shift point to the speed increasing stage is reached without tire slip. In this case, contrary to the operator's intention, the traction force is significantly reduced, and the workability is deteriorated.

Further, in the wheel loader, the load ratio applied to the front axle becomes extremely larger than that of the rear axle during excavation and scooping work. There is no differential mechanism in the vehicle, and the differential mechanism installed between the left and right wheels is often limited by so-called high traction differentials or limited slip differentials, so tire slip during work is There is a problem that wheels are likely to occur at the same time, and it is difficult to detect tire slip from the rotational speed difference of the four wheels as in a traveling vehicle such as a passenger car.

The present invention solves such a problem in a wheel loader, and can prevent a decrease in traction force due to an unnecessary shift-up to a speed increasing stage when a tire slips, thereby improving workability. An object is to provide an automatic control device for a wheel loader.

[0007]

According to the automatic shift control device of the present invention, in a wheel loader equipped with a transmission that shifts to a plurality of speed stages by engaging and disengaging a hydraulic clutch, an output shaft portion of the transmission is provided. The transmission output shaft rotation speed detector that detects the rotation speed and the average vehicle speed between the transmission output shaft rotation speed detector and the detection value of the transmission output shaft rotation speed detector are calculated and stored at specified intervals, and the current average vehicle speed is stored. Compared to the shift point,
When the current average vehicle speed reaches the shift point, the vehicle speed increase amount is calculated by subtracting the average vehicle speed of a predetermined time before from the current average vehicle speed, and the engine throttle is fully opened based on the data of the current input speed stage and the current average vehicle speed. Calculate the possible acceleration amount that can accelerate without tire slip from the average vehicle speed a predetermined time before, compare the vehicle speed increase amount and the possible acceleration amount, and if the vehicle speed increase amount does not exceed the possible acceleration amount, change the speed stage. The above problem is solved by providing switching means and control means for maintaining the current input speed stage without switching the speed stage until the preset time elapses when the vehicle speed increase amount exceeds the possible acceleration amount.

[0008]

As described above, tire slip occurs during the operation of the wheel loader when the prime mover throttle is fully opened or close to it as described above, and the tire rotation speed (that is, the transmission output of the transmission when the slip occurs at the time of operation). The rate of increase in the shaft rotation speed is usually higher than the rate of increase in vehicle speed of the vehicle that is accelerating without slipping. Therefore, the automatic speed change control device of the present invention calculates and stores the average vehicle speed during the specified time period from the detected value of the transmission output shaft rotation speed detector, and when the vehicle reaches the shift point, The vehicle speed increase amount is calculated by comparing the average vehicle speed with the average vehicle speed of a predetermined time before, and the tire slip from the average vehicle speed of a predetermined time before the motor engine throttle fully opening is calculated based on the data of the current input speed stage and the current average vehicle speed. Calculates the possible acceleration amount without acceleration, compares the vehicle speed increase amount with the possible acceleration amount, and if the vehicle speed increase amount exceeds the possible acceleration amount, switches the speed stage until the preset time elapses. Without maintaining the current input speed stage. Therefore, the automatic shift-up to an unnecessary speed-up stage due to tire slip is not performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of a control unit of an automatic shift control device according to an embodiment of the present invention. here,
Controller 5 that is supplied with power from the vehicle-mounted battery 4
Is the INPUT-I / F 21, CPU 22, ROM 2
3, a RAM 24, and an OUTPUT-I / F 25. The transmission output shaft rotation detection unit 1 is connected to the controller 5.
The rotation speed information detected by the transmission output shaft rotation speed detector 6 provided in No. 1 is input. Also this controller 5
To the first-speed closing solenoid valves 7 and 2 for switching the speed stage by operating the connection / disconnection of the hydraulic clutch (not shown) of the transmission.
Solenoid valve 8 for rapid closing, solenoid valve 9 for rapid closing,
A control signal is sent to the 4th-speed closing solenoid valve 10.

FIG. 2 is a graph showing an example of gear shifting performance at the time of shift-up in the state where the prime mover throttle of the wheel loader is fully opened. At the time of work, the controller 5 receives the rotation speed information detected by the transmission output shaft rotation speed detector 6, and normally this input information and each solenoid valve 7,
It is only necessary to select the speed stage to be input, such as upshift, downshift, or maintain the current speed stage, based on the information on the currently selected and applied speed stage obtained from the outputs to 8, 9, and 10. For example, in FIG. 2, when the vehicle reaches the vehicle speed V1 → 2 at the first speed, the first speed setting solenoid valve 7
Is turned off and a control signal is output to turn on the second speed setting solenoid valve 8. FIG. 3 is a graph showing shift performance at the time of shift down in the state where the prime mover throttle is fully opened. Here, the vehicle speed V2 → 1 at the shift point is lower than the vehicle speed V1 → 2 of the shift point at the shift up, and hunting near the shift point is performed. We are trying to prevent it.

The controller 5 of this embodiment further performs the following control. Transmission output shaft rotation speed detector 6
The average vehicle speed Vm during the predetermined time Tm is sequentially calculated from the detected value of the above, and is stored in the RAM 24, and the current average vehicle speed Vp is stored in the ROM 23. If the speed is 2nd speed, V2
→ 3, if the speed is 3rd, compare with V3 → 4). Here, the specified time Tm is 0.5 seconds. When the current average vehicle speed Vp reaches the shift point Vup, the vehicle speed increase amount ΔV = Vp−Vr is calculated by subtracting the average vehicle speed Vr before the predetermined time Tr from the current average vehicle speed Vp. Further, based on the data of the current input speed stage and the current average vehicle speed Vp, the possible acceleration amount ΔVc that can accelerate from the average vehicle speed Vr before the predetermined time Tr without the tire slip when the prime mover throttle is fully opened is stored in the ROM 23 by the following formula. calculate. Here, the predetermined time Tr is 0.5 seconds. Then, the vehicle speed increase amount ΔV and the possible acceleration amount ΔVc are compared. When the vehicle speed increase amount ΔV does not exceed the possible acceleration amount ΔVc, the speed stage is switched. When the vehicle speed increase amount ΔV exceeds the possible acceleration amount ΔVc, the current gear speed stage is maintained without switching the speed stage until the preset time Td elapses. Here, the preset time Td is 3 seconds.

In this embodiment, the possible acceleration amount ΔVc is calculated as follows. FIG. 4 shows a speed change in the case of accelerating without a tire slip in a speed stage in a general working state of a wheel loader, approximated by a combination of straight lines within a range where there is no practical problem. In this graph, there is a point Va at which the acceleration changes within 0.5 seconds immediately before the shift point Vup, and a point Vb is 0.5 seconds after the point Va.
Before the point Va, the speed increase for 0.5 seconds is ΔVa, and after the point Va, the speed increase for 0.5 seconds is ΔVb.

The vehicle accelerates and the current average vehicle speed Vp for 0.5 seconds
When the vehicle crosses the shift point Vup and reaches the point Vo in the figure, if there is no tire slip, the average vehicle speed Vm 0.5 seconds before should have been equal to or higher than the point Vn in the figure. Therefore,
The possible acceleration amount ΔVc = Vo−Vn at this time is expressed by the following equation. When Vo> = Vb ΔVc = ΔVb When Vup <= Vo <Vb ΔVc = C ₁ Vo + C
₂ where C ₁ and C ₂ are constants and C ₁ = 1− (ΔVa / ΔV
b) C ₂ = ΔVa−Va + (ΔVa / ΔVb) × Va FIG. 5 is a flowchart showing an example of the above control. Here, the tire slip flag is a data area indicating the presence or absence of tire slip set on the RAM 24, and the presence or absence of tire slip is displayed by rewriting the value of the tire slip flag to ON or OFF. When the value of the tire slip flag is rewritten to ON, the timer is reset and the preset time Td, that is, this state is held for 3 seconds.

In this flow chart, the flow of upshifting from the third speed to the fourth speed is shown as a representative, and the parts for upshifting from the second speed to the third speed and from the first speed to the second speed are omitted, but the same control is performed. To be done. In this embodiment, the prescribed time Tm for obtaining the average vehicle speed Vm is 0.5 seconds, the predetermined time Tr for obtaining the vehicle speed increase amount ΔV is 0.5 seconds, and the preset time Td for suspending the speed change during tire slip is 3 seconds. Seconds are used, but these values can be set individually according to the characteristics of the vehicle and work.

[0015]

As described above, the automatic shift control system for a work vehicle according to the present invention prevents a reduction in traction force due to an unnecessary shift-up to the speed-increasing stage when a tire slips, and improves workability. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control unit of an automatic shift control device according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of gear shifting performance at the time of upshift in a prime mover throttle fully open state.

FIG. 3 is a graph showing an example of gear shifting performance during downshifting in a prime mover throttle fully open state.

FIG. 4 is a graph approximating a speed change in the case of accelerating without a tire slip at a speed stage in a general work state.

FIG. 5 is a flowchart showing an example of control.

FIG. 6 is an explanatory view of the work of the wheel loader.

[Explanation of symbols]

 1 Vehicle 2 Bucket 3 Sediment 5 Controller 6 Transmission output shaft rotation speed detector 7 1st speed closing solenoid valve 8 2nd speed closing solenoid valve 9 3rd speed closing solenoid valve 10 4th speed closing solenoid valve

Claims (1)

[Claims] 1. A wheel loader equipped with a transmission that shifts and shifts to a plurality of speed stages by disconnecting a hydraulic clutch, and a transmission output shaft rotation speed detector for detecting a rotation speed of an output shaft portion of the transmission. Then, the average vehicle speed during the specified time is calculated from the detection value of the transmission output shaft rotation speed detector and stored, and the current average vehicle speed is compared with the shift point, and the current average vehicle speed reaches the shift point. Then, the vehicle speed increase amount is calculated by subtracting the average vehicle speed a predetermined time before from the current average vehicle speed, and based on the data of the current input speed stage and the current average vehicle speed, the tires are calculated from the average vehicle speed a predetermined time before fully opening the prime mover throttle. Calculates the possible acceleration amount that can be accelerated without slipping, compares the vehicle speed increase amount and the possible acceleration amount, and if the vehicle speed increase amount does not exceed the possible acceleration amount, switches the speed stage to enable the vehicle speed increase amount. An automatic speed change control device for a wheel loader, comprising: a control means for maintaining the current input speed stage without switching the speed stage until a preset time has elapsed when the acceleration amount is exceeded.