JPH05106245A - Working car with hst hydraulic travel gear - Google Patents

Abstract

PURPOSE:To set the matching point of an engine and an HST travelling hydraulic circuit arbitrarily, and to lower tractive force and increase lifting force until a front working machine starts its operation at the time of the relief of a hydraulic circuit for the front working machine. CONSTITUTION:A self-advancing type working car, on which an HST travelling hydraulic system is loaded, has a variable displacement hydraulic pump 12 and a variable displacement hydraulic motor 14 for travelling connected to the pump 12 in a closed circuit manner by a pair of main lines 13a, 13b, and travelling force is obtained by the output torque of the hydraulic motors. When the detected driving pressure of a hydraulic cylinder 18 for a front working machine reaches at least a fixed value or more, the discharge of the variable displacement hydraulic motor 14 is reduced until the detected working speed of the front working machine reaches a fixed value. Accordingly, travelling torque is lowered when large front driving force is required, large lifting force is acquired only by the lowering section of travelling torque, and the front working machine positively starts its operation even in any soil and sand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work provided with an HST hydraulic traveling device, such as a wheel loader, which needs to distribute the output torque of a prime mover to a front force and a traveling force for excavation in a well-balanced manner. Regarding the vehicle.

[0002]

2. Description of the Related Art FIG. 4 shows a wheel representing a self-propelled work vehicle.
It is the whole schematic diagram of an example of a ruler. This wheel lo
The traveling driving force of da 1 is obtained by a so-called HST hydraulic traveling device. The wheel loader 1 is provided with a front working machine 2 for performing excavation, loading work, etc. The front working machine 2 is driven by a hydraulic cylinder for a lift arm and a hydraulic cylinder for a bucket. Is
It is driven by pressure oil from a hydraulic pump driven by the same engine as the hydraulic pump of the HST hydraulic traveling system.

A wheel loader equipped with this type of HST traveling hydraulic circuit is described in, for example, Japanese Utility Model Laid-Open No. 13362/1993. In this circuit, a 2-speed motor is used as the hydraulic motor, and the hydraulic motor is fixed to the 2-speed during excavation work by a switch that selects excavation work and dozer work. During dozer work, until the main pipeline pressure reaches a predetermined value. The second speed is set, and when the predetermined value or more is reached, the first speed is selected and the traction force is increased.

By the way, the work of the wheel loader is generally performed by so-called combined operation such as traveling and excavation. Therefore, how to distribute the output horsepower of the engine to the running and the front is an important issue in terms of performance. Next, this point will be described in detail. FIG. 5 shows the engine torque curve ET.
(ETH) and the HST traveling hydraulic circuit show the absorption torque curve TT at the time of relief. At the time of relief of the hydraulic pump for the front working machine, the torque curve of the engine is
As shown in FIG. 5, a downward parallel movement is made from the solid line ET to the curve of the broken line ETH, which is lower by the absorption torque Tb of the hydraulic pump for the front working machine. Then, the torque curve shown by the broken line
Absorption torque curve of the ETH and HST traveling hydraulic pumps T
The intersection B with T becomes the matching point between the so-called engine and the HST traveling hydraulic circuit, and the torque Tb 'becomes the traveling drive torque. At this time, the engine speed drops to Nb.
As described above, when the specifications of the engine, the hydraulic pump for the front working machine, and the HST hydraulic traveling circuit are set, only one matching point B is determined.

FIG. 6 shows the mechanism of shear failure of the earth and sand during excavation. The vertical stress Pb and the shear stress τ acting on the earth and sand are determined by the stress σf and the lift force σr due to the running driving force, and the above Pb. , Τ are determined on the circle of the Mohr's stress circle R as shown in FIG. Then, when the stress state of the stress circle of the molding satisfies the failure condition of the earth and sand, shear failure of the earth and sand occurs. In other words, the symbol Lτ shown in FIG. 7 is a fracture diagram of earth and sand, and Lτ = C + Pbtanφ where C is the adhesive force of the earth and sand and φ is indicated by the internal friction angle. Point Q that touches
However, the point is that the earth and sand can be sheared and excavated.

Next, the lift force and the traction force (traveling force or traveling driving force) will be described with reference to FIGS. 8 and 9.
FIG. 8 is a graph showing the relationship between the lift force and the traction force when the front working machine hydraulic circuit relieves, and FIG. 9 is a force line diagram of the lift force and the traction force at the bucket tip. Here, as can be seen from FIG. 9A, a part of the thrust force of the lift arm hydraulic cylinder that generates the lift force is canceled by the reaction force of the traction force, so that if the pressure of the front working machine hydraulic circuit is kept constant. As the traction force increases, the lift force decreases. Therefore, if the traction force is too large (Fig. 9
(B)) Since the lift force is relatively small, it is difficult to apply a load to the tire and the tire easily slips. On the other hand, when the lift force is relatively large, the traction force is insufficient, and the direction of the force line diagram is upward as shown in FIG. 9 (c). That is, the so-called thrusting property is poor, and the lift arm is lifted before a load enters the bucket. In either case, the work efficiency becomes poor.

[0007]

The characteristics such as the adhesive force C between the particles of the earth and sand and the internal friction angle φ are various according to the kind of earth and sand, and the desired excavating force can be adjusted according to the characteristics of the earth and sand. In order to obtain it, the matching between the traveling drive force and the lift force has to be adjusted each time, but the working vehicle described in the above publication has only one matching point during excavation, and the operator depending on the state of the earth and sand. However, it is often necessary to delicately operate the accelerator pedal and bucket operation lever. More specifically, the engine output (engine speed) is controlled by adjusting the amount of depression of the accelerator pedal according to the work content, thereby increasing or decreasing the traction force, and at the same time controlling the work lever to obtain the optimum matching point. Is selected.
Therefore, such simultaneous work requires a high degree of skill and is not easy for even a seasoned operator, and when working for a long time, fatigue is caused and work efficiency decreases.

According to the circuit disclosed in the above publication, the traction force is limited to a low level when the excavation is selected, so that a large lift force can be exerted as compared with the first speed during the dozer work. However, the first speed of such a conventional system is set to match the dozer work and is not suitable for excavation, and the number of matching points between the engine and the HST traveling hydraulic circuit during excavation is also one. That is, with this conventional circuit, it is not possible to set an arbitrary matching point according to the type of soil and the road surface on which the vehicle travels.

An object of the present invention is to make it possible to arbitrarily set the matching point between the engine and the HST traveling hydraulic circuit, and reduce the traction force by lowering the traction force until the front working machine starts operating during relief of the front working machine hydraulic circuit. It is an object of the present invention to provide a work vehicle provided with an HST hydraulic traveling device having a large size.

[0010]

The present invention will be described with reference to FIGS. 1 and 2 showing an embodiment. In the present invention, a variable displacement hydraulic pump 12 driven by a prime mover 11, and a variable displacement hydraulic pump 12 are paired. Variable displacement hydraulic motor 14 for traveling, which is connected in a closed circuit by the main pipelines 13a and 13b, a motor discharge capacity adjusting means 16 for adjusting the discharge capacity of the variable capacity hydraulic motor 14, and a front working machine driven by the prime mover 11. The present invention is applied to a work vehicle including an HST hydraulic traveling device including a hydraulic pump 17 for a vehicle and a hydraulic cylinder 18 for a front working machine that drives the front working machine 2 with pressure oil discharged from the hydraulic pump 17 for a front working machine. .. Then, the pressure detecting means 32 for detecting the driving pressure of the front working machine hydraulic cylinder 18, the operating speed detecting means 35, 44 for detecting the operating speed of the front working machine 2, and at least the detected front working machine hydraulic pressure. When the driving pressure of the cylinder 18 is equal to or higher than a predetermined value, the motor displacement control means 30 for controlling the displacement control means 16 to reduce the displacement of the variable displacement hydraulic motor 14 until the detected operation speed reaches a predetermined value.
By including the above, the above-mentioned object is achieved.

[0011]

When the driving pressure of the front working machine hydraulic cylinder 18 is equal to or higher than a predetermined value (for example, when the pressure is a relief pressure), the displacement of the hydraulic motor 14 is reduced until the operating speed of the front working machine reaches a target value, and the vehicle travels. The torque becomes smaller.
As a result, a large lift force corresponding to the decrease in the traction force is obtained, and the front working machine reliably starts operating regardless of the soil.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for making the present invention easy to understand. It is not limited to.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The variable displacement hydraulic pump 12 driven by the engine 11 is connected to a variable displacement hydraulic motor 14 in a closed circuit via a forward main passage 13a and a reverse main pipeline 13b, and hydraulic oil is discharged from the hydraulic pump 12 by a hydraulic pressure. The motor 14 is driven. The rotation of the hydraulic motor 14 drives the axle via a traveling drive mechanism (not shown) to drive the vehicle. Here, the rotation speed of the engine 11 is adjusted by operating a traveling pedal (not shown).

Reference numeral 15 is a pump regulator for controlling the discharge capacity and the discharge direction of the variable displacement hydraulic pump 12 based on the discharge capacity signal qp and the forward / reverse signal fr sent from the control device 30. The forward / backward movement of the vehicle is selected by a switch (not shown) and input to the control device 30. 16
Is a motor regulator that controls the discharge capacity of the variable displacement hydraulic motor 14 based on the discharge capacity signal qm sent from the control device 30. The pump regulator 15 and the motor regulator 16 are not particularly limited in their forms, and conventionally known methods and mechanisms can be adopted, and detailed description thereof will be omitted here. When so-called automatic control is adopted, the pump regulator 15 controls the pump discharge capacity by the engine speed and the HST circuit differential pressure.

Reference numeral 17 denotes a hydraulic pump for a front working machine, which is driven by the same engine 11 as the variable displacement hydraulic pump 11. Reference numeral 18 is a lift arm hydraulic cylinder, and 19 is a bucket hydraulic cylinder, which are driven and controlled by switching control valves 20 and 21 connected in parallel. That is, the oil discharged from the hydraulic pump 17 is supplied to the bucket hydraulic cylinder 19 via the control valve 20.
On the other hand, the lift arm hydraulic cylinder 19 is driven via the control valve 21. The control valves 20 and 21 are switched by an operating lever on the driver's seat.

The control device 30 is composed of a microcomputer and the control circuit shown in FIG. 1, and the like. The input side thereof has a pressure sensor 31 for detecting the discharge pressure Pf of the front working machine hydraulic pump 17 and a lift. Pressure sensor 32 for detecting the pressure Ps on the input side of the arm hydraulic cylinder 18
, Pressure sensors 33 and 34 for detecting the pressures Ph1 and Ph2 of the main pipelines 13a and 13b, respectively, and a rotation angle sensor 35 for outputting a signal according to the rotation amount of the lift arm, respectively. .. Further, the pump regulator 15 and the motor regulator 1 are provided on the output side of the control device 30.
6 is connected.

The control circuit shown in FIG.
6 for controlling the HST traveling hydraulic circuit, the absolute value of the pressure difference between the main pipelines 13a and 13b (| Ph1-P
h2 |) subtractor 41, a function generator 42 that determines the motor discharge capacity qm based on this pressure difference, and a function generator that determines the motor discharge capacity qm based on the load pressure Pf of the front working machine hydraulic pump 17. And 43. The function generator 42 fixes the hydraulic motor discharge capacity qm to the minimum value until the difference Ph between the pipeline pressures Ph1 and Ph2 of the main pipelines 13a and 13b reaches a first predetermined value, and exceeds the first predetermined value. And increase the discharge volume qm, and when the second predetermined value is exceeded, a signal for fixing the discharge volume qm to the maximum value is generated. On the other hand, the function generator 43 generates a signal that gradually decreases the hydraulic motor discharge capacity qm as the load pressure Pf of the working machine hydraulic pump increases. For example, the discharge capacity of the hydraulic motor is limited to 60% to 75% of its maximum value at the relief pressure of the hydraulic pump for the front working machine.

Further, the control circuit of FIG. 1 differentiates the detection signal of the rotation angle sensor 35 with respect to time to calculate the actual angular velocity ωr of the lift arm, and the actual angular velocity ωr and a predetermined target angular velocity. A deviation device 45 that takes a deviation from ωa (≈0), and a correction ejection volume q by multiplying the deviation by an integral gain.
and a gain setter 46 that calculates ma. further,
A function generator 47 that outputs a high level signal when the lift arm cylinder pressure Ps is equal to or higher than a predetermined value (Ps≈relief pressure), and a switch 48 that closes due to the high level.
And an adder 52 for adding the output signal of the function generator 43 and the output signal of the switch 48. 49 is a first-order lag element that gives a first-order lag to the output of the function generator 42, and 50
Is the motor discharge capacity qm determined by the function generator 42 by the pressure difference between the main pipelines 13a and 13b and the motor discharge capacity qm determined by the function generator 43 by the load pressure Pf of the front working machine hydraulic pump 17 or It is a minimum value selection circuit that selects the minimum value of the added value of the motor discharge capacity qm and the corrected discharge capacity qma.

The operation of the work vehicle thus configured will be described. When the lift arm cylinder pressure Ps is less than the predetermined value, the switch 48 is open, so the main pipe line 13
Of the motor discharge capacity qm determined by the function generator 42 by the pressure difference between a and 13b and the motor discharge capacity qm determined by the function generator 43 by the load pressure Pf of the front working machine hydraulic pump 17, the minimum The smaller discharge capacity qm selected by the value selection circuit 50 is input to the motor regulator 16, and the discharge capacity of the hydraulic motor 14 is operated at the selected discharge capacity.

When the lift arm cylinder pressure Ps is equal to or higher than a predetermined value, the switch 48 is closed, so that the motor discharge capacity qm determined by the function generator 43 is corrected by the load pressure Pf of the front working machine hydraulic pump 17. The value qm + qma obtained by adding the discharge volume qma and the main pipe line 13
Of the motor discharge capacity qm determined by the function generator 42 according to the pressure difference between a and 13b, the smaller discharge capacity qm selected by the minimum value selection circuit 50 is input to the motor regulator 16, and the hydraulic motor 14 becomes Operates with the selected discharge capacity.

As described above, when the front working machine hydraulic pump 17 is in the relief state, the hydraulic motor discharge capacity qm determined by the pump pressure Pf is 60 to 75% of the maximum value.
The minimum value selection circuit 50 outputs the discharge capacity determined by the function generator 43 to the motor regulator 16. Therefore, when the hydraulic pump 17 for the front working machine is in relief, the traveling drive force is reduced and a large lift force is obtained.

However, the lift arm may not operate even if the traveling driving force is reduced in this way. In this case, when the lift arm does not rotate, the actual rotation angular velocity ωr
Is zero, and the deviation device 45 outputs a negative value.
After this negative value is integrated, it is switched from the switch 48 to the adder 5
2 and is added to the output qm of the function generator 43. Therefore, the discharge capacity qm applied to the motor regulator 16 becomes a smaller value, the traveling driving force becomes further smaller, and the lift force becomes larger. The control for further reducing qm determined by the function generator 43 is performed until the angular velocity of the lift arm reaches the target value ωa. As a result, no matter what kind of sediment,
It is possible to reliably rotate the lift arm.

FIG. 3 shows a modification of FIG. The same parts as those in FIG. 1 are designated by the same reference numerals, and the differences are mainly described. In this embodiment, basically, the discharge capacity reduction control by the load pressure Pf of the front working machine hydraulic pump 17 is omitted, and the discharge capacity determined by the function generator 42 until the lift arm cylinder pressure Ps reaches a predetermined value. When qm is input to the motor regulator 16 and the lift arm cylinder pressure Ps becomes equal to or higher than a predetermined value, the actual angular velocity ωr and the predetermined target angular velocity ωa with respect to the discharge volume qm determined by the function generator 42. The integrated value of the deviation is added and the discharge capacity qm + qma is input to the motor regulator 16. Even if such a control method is adopted,
Similar to the previous embodiment, the motor discharge capacity qm is gradually reduced to reduce the traveling driving force until the lift arm starts to operate.

A mode changeover switch may be provided so that a mode for arbitrarily setting the matching point between the traveling driving force and the lifting force can be selected. In addition to the mode changeover switch, a selection switch is also provided. When the above mode is selected, the selection switch is operated to cancel the mode, and when the mode changeover switch is not operated, the selection switch is operated. You may make it select the said mode. This selection switch is preferably installed on the knob of the lift arm operating lever. Further, the present invention can be applied to various types of self-propelled work vehicles other than wheel loaders.

In the structure of the above embodiment, the motor regulator 16 serves as a discharge capacity adjusting means of the variable displacement hydraulic motor, the engine 20 serves as a prime mover, the lift arm cylinder pressure sensor 32 serves as pressure detecting means, and the rotation angle sensor 35 serves as a turning angle sensor 35. The differentiating circuit 44 constitutes speed detecting means, and the control device 30 constitutes discharge volume controlling means.

[0026]

As described above in detail, according to the present invention, when the pressure of the hydraulic cylinder for the front working machine exceeds a predetermined value, the front working machine starts operating at the target speed. Since the discharge capacity of the hydraulic motor is reduced, the traveling traction force is reduced and the lift force is increased. Therefore, the front working machine can be surely operated regardless of the soil without any special operation, and the working machine having improved operability and less fatigue can be provided.

[Brief description of drawings]

FIG. 1 is a detailed block diagram of a control device shown in FIG.

FIG. 2 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 3 is a block diagram showing another embodiment of FIG.

FIG. 4 is an overall schematic side view of the wheel loader.

FIG. 5: Engine torque curve and pump absorption torque curve
Diagram showing matching with

FIG. 6 is a diagram for explaining the mechanism of earth and sand destruction.

[Fig.7] Sediment failure diagram and stress circle of Mohr

FIG. 8 is a graph showing the relationship between traction force and lift force.

FIG. 9 is a force diagram showing traction force and lift force.

[Explanation of symbols]

 1 Wheel Loader 2 Front Working Machine 11 Engine 12 Variable Capacity Hydraulic Pump 13a, 13b Main Line 14 Variable Capacity Hydraulic Motor 15 Pump Regulator 16 Motor Regulator 17 Working Machine Hydraulic Pump 18 Lift Arm Hydraulic Cylinder 19 Bucket Hydraulic Cylinder 20, 21 Control Valve 30 Control device 31 Load pressure sensor of working machine hydraulic pump 32 Pressure sensor of lift arm hydraulic cylinder 33, 34 Main line pressure sensor 35 Rotation angle sensor

Claims (1)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a traveling variable displacement hydraulic motor connected to the variable displacement hydraulic pump in a closed circuit by a pair of main pipes, and a discharge displacement of the variable displacement hydraulic motor is adjusted. A motor discharge capacity adjusting means, a front working machine hydraulic pump driven by the prime mover, and a front working machine hydraulic cylinder driving the front working machine by pressure oil discharged from the front working machine hydraulic pump. In a work vehicle equipped with the HST hydraulic traveling device, a pressure detection unit that detects a driving pressure of the front work machine hydraulic cylinder, and an operation speed detection unit that detects an operation speed of the front work machine are detected. When the driving pressure of the hydraulic cylinder for the front working machine is equal to or higher than a predetermined value, the detected operation speed reaches the predetermined value. H which controls the serial motor discharge volume adjustment means characterized by comprising a motor discharge capacity control means for reducing the discharge capacity of the variable capacity hydraulic motor
A work vehicle equipped with an ST hydraulic traveling device.