JP2735978B2 - Hydraulic construction machine torque control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque control device for a hydraulic motor used in a hydraulic construction machine such as a wheel-type hydraulic excavator, and more particularly to an engine stall prevention when the operating oil temperature is low.

[0002]

2. Description of the Related Art Generally, a wheel type hydraulic excavator includes a variable displacement hydraulic pump driven by a prime mover (engine), and discharges oil from the variable displacement hydraulic pump via a control valve to a traveling hydraulic motor or a work hydraulic motor. It leads to an actuator such as a cylinder, which drives the vehicle or drives the work front. Among such excavators, there is known one that performs pump tilt angle control as described below. That is, this type of excavator
(1) Calculate the deviation between the target differential pressure and the LS differential pressure (the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the actuator), calculate the amount of change in the target value from this deviation, and integrate this. An LS control unit for obtaining a first target pump tilt angle for performing load sensing control; and (2) an engine stall (hereinafter, stall) based on a deviation between an engine speed and a governor lever position of an engine governor. A torque control unit that calculates a target torque for preventing the rotation and calculates a second target pump tilt angle for performing input torque limiting control based on the target torque. Then, the actual pump tilt angle is controlled to a smaller value among the first and second target pump tilt angles obtained above.

Here, according to the load sensing control, the tilt angle of the variable displacement hydraulic pump is controlled so that the LS differential pressure becomes a constant value, and the pump pressure is set to a predetermined target value lower than the load sensing pressure. Since it is kept high, the pump tilt angle is controlled so that the pump discharge flow rate is equal to the flow rate required by the control valve, so that excess flow rate is not discharged, waste due to throttle loss is eliminated, and fuel consumption and operability are improved. I can do it. Further, according to the input torque limiting control, the torque of the hydraulic pump is maintained within the range of the output torque of the engine (motor), thereby preventing the engine from being overloaded.

[0004]

However, when the temperature of the hydraulic oil is low and the viscosity is high, such as immediately after the start of the engine at a low temperature, the sliding resistance of the hydraulic pump becomes large, so that the viscosity of the hydraulic oil becomes moderate. The input torque increases as compared with the case of. On the other hand, the starting rotation speed of the engine at a low temperature is relatively low, and the engine output torque is considerably small due to factors such as sliding friction of engine components. As described above, immediately after the start of the engine at a low temperature, the pump input torque exceeds the engine output torque because the pump input torque exceeds the engine output torque in addition to the large pump input torque.

An object of the present invention is to provide a torque control device for a hydraulic construction machine, which prevents engine stall immediately after starting a prime mover at a low temperature.

[0006]

The present invention will be described with reference to FIGS. 2 and 4 showing an embodiment.
Variable hydraulic pump 1 driven by the hydraulic pump, hydraulic actuators 4 and 21 driven by oil discharged from the variable hydraulic pump 1, and control means 60 for controlling the input torque of the variable hydraulic pump 1. Applied to torque control devices of hydraulic construction machines. The first aspect of the present invention solves the above problem by configuring the control means 60 as follows. That is, when the control means 60 determines that the temperature of the hydraulic oil is lower than the predetermined value, the control means 60 lowers the input torque than when it determines that the temperature is higher than the predetermined value. Here, whether the temperature of the hydraulic oil is lower than a predetermined value may be determined by detecting the actual hydraulic oil temperature to or by detecting the temperature tw of the motor cooling water. Good. Alternatively, the determination may be made based on the elapsed time from the start of the prime mover. Furthermore, in particular, the invention of claim 5 further includes a rotation speed control means 80 for controlling the rotation speed of the prime mover 27 in accordance with a manual operation, and when it is determined that the temperature of the hydraulic oil is lower than the first predetermined value, The rotation speed of the prime mover is controlled to a value at which a prime mover output torque equal to or greater than a predetermined value is obtained.

[0007]

When the control means determines that the temperature of the hydraulic oil is lower than the first predetermined value, the control means lowers the input torque of the hydraulic pump 1 than when the temperature is determined to be higher than the first predetermined value. As a result, the input torque of the hydraulic pump 1 is less likely to exceed the output torque of the prime mover 27 immediately after the start of the prime mover where the temperature of the hydraulic oil is low, and engine stall is suppressed. In particular, in the invention of claim 5, the temperature of the hydraulic oil is set to the first level.
Is determined to be less than the predetermined value, the rotation speed of the prime mover is controlled to a value at which a prime mover output torque equal to or greater than the predetermined value is obtained. Therefore, the input torque of the hydraulic pump 1 does not exceed the output torque of the prime mover 27 when the prime mover is started, and a more reliable engine stall suppression effect can be obtained.

[0008] In the means and means for solving the above-mentioned problems which explain the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a torque control device of a wheel hydraulic excavator will be described with reference to FIGS. FIG. 3 is a side view of the wheel type hydraulic excavator. Reference numeral 4 denotes a traveling hydraulic motor. The rotation of the hydraulic motor 4 drives a rear wheel 103 via a transmission 101 and a propeller shaft 102, so that the vehicle travels. The boom 104, which is a part of the front attachment, is moved up and down by the expansion and contraction of the boom cylinder 21. FIG. 1 is a diagram showing the overall configuration of the torque control device of the above-mentioned hydraulic shovel, and FIG. 2 is a partially enlarged view showing the same. A reference numeral 1 denotes a variable displacement hydraulic pump driven by an engine (motor) 27. The rotation speed of the engine 27 is controlled by rotating a governor lever 27b of the governor 27a by a pulse motor 28. Then, the discharge oil of the variable displacement hydraulic pump 1 corresponding to the engine speed is guided to the hydraulic motor 4 via the traveling control valve 2 and the working hydraulic cylinder 21 via the working control valve 20.
It is led to.

Now, for example, when the forward / reverse selector switch SW1 is operated to "F" to switch the forward / reverse selector valve 8 to the forward position (F position), and then the pedal 6a of the pilot valve 6 is operated, the hydraulic pump 5 discharges. Oil is pilot control valve 2
The control valve 2 is switched by a stroke amount according to the pilot oil pressure. Thereby, the oil discharged from the variable displacement hydraulic pump 1 is supplied to the hydraulic motor 4 via the pipe 91, the pressure compensating valve 23, the control valve 2 and the pipe 93, and the vehicle runs. The speed of the vehicle depends on the depression amount of the travel pedal 6a.

When the pedal 6a is released during traveling, the pilot valve 6 shuts off the pressure oil, and its outlet port communicates with the tank 10. As a result, the pressure oil acting on the pilot port 2a returns to the tank 10 via the forward / reverse switching valve 8, the slow return valve 7, and the pilot valve 6. At this time, the return oil is throttled by the throttle 7a of the slow return valve 7, so that the vehicle is gradually decelerated while the pilot control valve 2 is gradually switched to the neutral position.

When the work lever 58 is operated, the hydraulic pilot type work control valve 20 is switched by the pressure reduced by the pressure reducing valve 59 in accordance with the operation amount, and the discharge oil from the hydraulic pump 1 is supplied to the pipeline 94. , The pressure is guided to the working hydraulic cylinder 21 via the pressure compensating valve 24 and the control valve 20, and the working attachment such as the boom 104 is moved up and down by the expansion and contraction of the hydraulic cylinder 21. Here, the pressure compensating valves 23 and 2
Numeral 4 is for compensating the operations of the hydraulic motor 4 and the hydraulic cylinder 21 independently, and causing the hydraulic pump 1 to supply a pressure higher than each load pressure by a predetermined pressure.

The displacement angle of the variable displacement hydraulic pump 1, that is, the displacement volume, is controlled by a displacement angle control device 40.
The tilt angle control device 40 controls a piston position by a hydraulic pump 41 driven by the engine 27, a pair of solenoid valves 42, 43, and pressure oil from the hydraulic pump 41 according to switching of the solenoid valves 42, 43. The tilt angle of the hydraulic pump 1 is controlled according to the piston position of the servo cylinder 44. Here, the pair of solenoid valves 42 and 43 are switch-controlled by the controller 50.

Reference numeral 51 denotes a tilt angle sensor for detecting the tilt angle θs of the hydraulic pump 1, and 52 denotes a discharge pressure Pp of the hydraulic pump 1.
Is a pressure sensor for detecting the rotation speed N of the engine 27.
The rotational speed sensor 54 for detecting r is the larger of the discharge pressure of the hydraulic pump 1 and the maximum load pressure of the actuator (the load pressure of the hydraulic motor 4 or the load pressure of the hydraulic cylinder 21, This is a differential pressure sensor that detects a differential pressure between the pressure difference and the LS differential pressure ΔPLS. Reference numeral 55 denotes a potentiometer for detecting the amount of rotation Nθ of the governor lever 27b, and reference numeral 56 denotes an oil temperature sensor for detecting the temperature (hydraulic oil temperature) to of the hydraulic oil. Is entered. Reference numeral 57 denotes a rotation speed setting device for instructing a displacement X according to a manual operation of the fuel lever 57a, and a command signal thereof is also input to the controller 50.

The controller 50 has a first control circuit section 60 as shown in FIG. 4, and this control circuit section 60 includes a load sensing control section (hereinafter, LS control section) 61, a torque control section 62, , A selector 63 and a servo controller 64
, A function generator 65, and a multiplication circuit 66. LS
The control unit 61 determines the target differential pressure ΔPLSR and the differential pressure sensor 54
The deviation Δ (PLS) from the LS differential pressure ΔPLS detected in the step is calculated, and the variation Δθ of the target value is calculated from the deviation Δ (PLS).
L is calculated and integrated to obtain and output a target pump tilt angle θL for load sensing control.

The torque control unit 62 controls the engine speed Nr detected by the speed sensor 53 and the potentiometer 5.
5 to calculate a deviation ΔT from the governor lever position Nθ, perform speed sensing, calculate a target torque Tpo for preventing engine stall from this deviation ΔT, and detect the target torque Tpo by the pressure sensor 52. Is calculated by multiplying the reciprocal of the pump discharge pressure Pp, and the value θps is filtered by a temporary delay element to obtain a target pump tilt angle θT for input torque limiting control.

The selecting section 63 determines the two target tilt angles θ
The smaller value of L and θT is selected as the target tilt angle θr1, and this is input to the multiplication circuit 66. On the other hand, the detection result of the oil temperature sensor 56, that is, the operating oil temperature to is input to the function generator 65, and a constant α to be multiplied by the target tilt angle θr ₁ is determined based on the operating oil temperature to. The constant α is a value from 0 to ₁ as shown in the drawing. When the input hydraulic oil temperature to is equal to or more than the predetermined value to _1, α is fixed to _1; Becomes smaller. The determined constant α is input to the multiplying circuit 66, is multiplied by the target tilt angle θr ₁ input from the selector 63, and the result is input to the servo controller 64 as a tilt angle command value θr. . The servo control unit 64 compares the tilt angle command value θr with the tilt angle feedback value θs detected by the tilt angle sensor 51, and determines the pump tilt angle θs as the tilt angle command value θr. Is controlled so as to coincide with.

Here, according to the load sensing control, the displacement of the variable displacement hydraulic pump 1 (hereinafter, also referred to as the tilt angle) is controlled so that the LS differential pressure becomes a constant value.
Since the pump pressure is maintained higher than the load sensing pressure by a predetermined target value, the pump tilt angle is controlled so that the pump discharge flow rate is equal to the required flow rate of the control valve 2 or 20, and an extra flow rate is discharged. This eliminates waste due to throttle loss and improves fuel efficiency and operability. Further, according to the input torque limiting control, the torque of the hydraulic pump 1 is maintained within the range of the output torque of the engine 27, and the overload on the engine 27 is prevented.

Further, when the oil temperature sensor 56 detected hydraulic oil temperature to at _one or more predetermined values to the function generator 6
5 outputs the constant α, the target tilt angle θr ₁ selected by the selector 63 is output as the target tilt angle θr as it is, and the actual tilt angle of the hydraulic pump 1 is accordingly changed. Controlled. That is, the same tilt angle control as that in the related art is performed, and the input torque of the hydraulic pump 1 becomes the same as the related art. On the other hand, when the hydraulic oil temperature to is less than the predetermined value to _1, the
Since the constant α becomes smaller than ₁ , the value smaller than the target tilt angle θr ₁ selected by the selector 63 is set to the target tilt angle θr.
And the tilt angle of the hydraulic pump 1 is controlled accordingly. Therefore, the operating oil temperature to becomes the predetermined value to ₁
When the input torque of the hydraulic pump 1 is less than to ₁ or more, the pump input torque
7 is less likely to be exceeded, and engine stall is suppressed. In particular, in this embodiment, held in the case the hydraulic oil temperature To is lower than the predetermined value-to _1, since the to lower the target tilting angle θr by reducing the extent To lower alpha, the input torque to the optimum state can do.

Incidentally, the controller 50 also includes:
It has a second control circuit section 80 shown in FIG. The second control circuit section 80 includes a displacement amount X of the fuel lever 57a of the rotation speed setting device 57, a displacement amount (governor position detection value) Nθ of the governor lever 27b detected by the potentiometer 55, The operating oil temperature to detected by the oil temperature sensor 56 is input. The second control circuit unit 80
A target rotation speed (governor position target value) Nroa according to the input displacement amount X of the fuel lever 57a is calculated, and based on the governor position target value Nroa, the governor position detection value Nθ, and the hydraulic oil temperature to, The pulse motor 28 is controlled according to the procedure shown in FIG.

In FIG. 6, first, in step S21, the governor position target value Nroa, the governor position detected value Nθ, and the hydraulic oil temperature to are read, and in step S21A, the appropriate target rotational speed Nr corresponding to the hydraulic oil temperature to from the characteristics shown in the drawing.
Ob. Here, according to this characteristic, the hydraulic oil temperature t
When o is equal to or more than the predetermined value to ₁ , Nrob becomes the idle speed, and when o is less than the predetermined value to ₁ , Nrob decreases as to decreases. The maximum value of the appropriate target rotation speed Nrob is a value at which the maximum engine output torque is obtained. In step S21B, the governor position target value Nroa is compared with an appropriate target rotation speed Nrob. If Nroa ≧ Nrob, Nroa is set as the target rotation speed Nro in step S21C, and if Nroa <Nrob, step S21D is performed. N
rob is set as the target rotation speed Nro. That is,
The larger one of Nroa and Nrob is the target rotation speed Nro
And

Next, in step S22, the difference Nθ-Nro between the governor position detection value Nθ and the target rotation speed Nro is stored in a memory as a rotation speed difference A, and in step S23, a predetermined reference rotation speed difference K is used. , | A | ≧ K. If affirmative, the process proceeds to step S24,
It is determined whether or not the rotational speed difference A> 0. If A> 0, the governor position detected value Nθ is larger than the target rotational speed Nro, that is, since the control rotational speed is higher than the target rotational speed, the engine rotational speed is reduced. Therefore, in step S25, a signal for commanding motor reverse rotation is output to the pulse motor 28. As a result, the pulse motor 28 rotates in the reverse direction, and the rotation speed of the engine 27 decreases.

On the other hand, if A ≦ 0, the governor position detection value Nθ
Is smaller than the target rotation speed Nro, that is, since the control rotation speed is lower than the target rotation speed, a signal for commanding the motor to rotate forward is output in step S26 to increase the engine rotation speed. As a result, the pulse motor 28 rotates forward and the rotation speed of the engine 27 increases. If step S23 is denied, the process proceeds to step S27 to output a motor stop signal, whereby the rotation speed of the engine 27 is maintained at a constant value.
After executing steps S25 to S27, the process returns to the beginning.

According above, if the hydraulic oil temperature to is less than the predetermined value to ₁ approaches the value which the maximum engine output torque is obtained the lower the hydraulic oil temperature to the proper target speed Nrob increased Therefore, the hydraulic oil temperature to is equal to the predetermined value to ₁
The engine output torque increases as compared with the above case. Therefore, the input torque does not exceed the output torque of the engine 27, and the engine stall suppressing effect can be improved.

In the configuration of the above embodiment, the hydraulic motor 4 and the working hydraulic cylinder 21 function as a hydraulic actuator, the first control circuit 60 controls the control means, and the second control circuit 80 controls the rotation speed control means. Configure each.

As shown in FIG. 7, the oil temperature sensor 5
Instead of 6, a water temperature sensor 156 for detecting the temperature tw of the engine coolant provided, in the same manner as described above, when the engine coolant temperature tw is lower than the predetermined value tw _1, the pump input than when a predetermined value tw ₁ or more The same operation and effect as described above can be obtained even when the control for reducing the torque is performed. Further, when the time from the start of the engine 27 is less than the predetermined time, it may be determined that the temperature of the hydraulic oil is lower than the predetermined value, and the pump input torque may be reduced.
Further, when the oil temperature or the water temperature is lower than the predetermined value, the pump input torque is made to gradually decrease as the temperature becomes lower, but for example, as shown in FIG. A function generator may be configured. Furthermore, although the one that performs the load sensing control has been described, the one that does not perform the load sensing control may be used. Further, although the description has been given of the wheel type excavator, the present invention can be applied to other construction machines.

[0027]

According to the present invention, when it is determined that the temperature of the hydraulic oil is lower than the predetermined value, the input torque of the hydraulic pump is made lower than when it is determined that the temperature is higher than the predetermined value. The input torque of the hydraulic pump does not exceed the output torque of the prime mover when the prime mover starts when the temperature of the hydraulic oil is low, and engine stall can be suppressed. In particular, according to the invention of claim 5, when it is determined that the temperature of the hydraulic oil is lower than the predetermined value, the rotation speed of the motor is controlled to a value at which the engine output torque equal to or higher than the predetermined value is obtained. The output torque of the engine at the time of starting the prime mover with a low temperature of the hydraulic oil is increased, and the input torque of the hydraulic pump is less likely to exceed the output torque of the prime mover, so that a more reliable engine stall suppression effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a torque control device for a hydraulic construction machine according to the present invention.

FIG. 2 is an enlarged view showing a part of the torque control device.

FIG. 3 is a side view of the hydraulic excavator.

FIG. 4 is a block diagram illustrating a first control circuit unit.

FIG. 5 is a block diagram illustrating a second control circuit unit.

FIG. 6 is a flowchart illustrating a procedure of engine speed control.

FIG. 7 is a block diagram of a first control circuit unit showing another embodiment.

FIG. 8 is a diagram showing a modified example of the function generator.

[Explanation of symbols]

 Reference Signs List 1 variable displacement hydraulic pump 2, 20 control valve 4 hydraulic motor 27 engine 27a governor 27b governor lever 28 pulse motor 40 tilt angle control device 50 controller 51 tilt angle sensor 52 pressure sensor 53 rotation speed sensor 54 differential pressure sensor 55 potentiometer 56 56 Oil temperature sensor 57 Rotation speed setting device 60 First control circuit unit 61 LS control unit 62 Torque control unit 63 Selection unit 64 Servo control unit 65 Function generator 66 Multiplication unit 80 Second control circuit unit 156 Water temperature sensor

Claims (5)

(57) [Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a hydraulic actuator driven by oil discharged from the variable displacement hydraulic pump, and control means for controlling an input torque of the variable displacement hydraulic pump. In the torque control device for a hydraulic construction machine, when the control means determines that the temperature of the hydraulic oil is less than a first predetermined value, the control means may increase the input torque more than when the temperature is determined to be equal to or more than a first predetermined value. A torque control device for a hydraulic construction machine, wherein the torque control device reduces the torque. 2. The hydraulic system according to claim 1, further comprising a detection unit that detects a temperature of the hydraulic oil, wherein the control unit performs the state determination based on the detected temperature of the hydraulic oil. Construction machine torque control device. A detecting means for detecting a temperature of the motor cooling water, wherein the control means sets the temperature of the hydraulic oil to the first temperature when the detected temperature of the motor cooling water is less than a second predetermined value. The torque control device for a hydraulic construction machine according to claim 1, wherein the torque control device determines that the state is less than a predetermined value. 4. The system according to claim 1, wherein the controller determines that the temperature of the hydraulic oil is lower than a first predetermined value when an elapsed time from a start of the prime mover is less than a predetermined time. Item 2. A torque control device for a hydraulic construction machine according to item 1. 5. A rotation speed control means for controlling a rotation speed of the prime mover according to a manual operation, wherein the rotation speed control means determines that the temperature of the hydraulic oil is lower than a first predetermined value. The torque control device for a hydraulic construction machine according to any one of claims 1 to 4, wherein the rotation speed of the prime mover is controlled to a value at which a prime mover output torque equal to or greater than a predetermined value is obtained.