JP2004116706A - Travelling controller for hydraulic driven vehicle and hydraulic driven vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an excessive rotation of a travelling motor upon moving on a downward slope while an accelerator pedal is stepped on. <P>SOLUTION: A manipulated variable of the accelerator pedal 22a is detected by a pressure sensor 41. A function generator 501 outputs target rotating speed Nt of an engine 1 corresponding to the manipulated variable of the accelerator pedal 22a. Travelling driving pressure P is detected by a pressure sensor 42. When the travelling driving pressure P is a prescribed value Pa or lower, a function generator 502 outputs corrected rotating speed Ns. A value obtained by subtracting the corrected rotating speed Ns from the target rotating speed Nt is outputted as a target rotating speed command value Ny to control engine rotating speed to the target rotating speed command value Ny. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a travel control device for a hydraulically driven vehicle such as a wheel hydraulic excavator, and a hydraulically driven vehicle.
[0002]
[Prior art]
A hydraulically driven vehicle such as a wheeled hydraulic excavator that travels by controlling the flow rate and direction of hydraulic oil discharged from a hydraulic pump driven by a prime mover using a control valve, and driving a travel motor with the controlled hydraulic oil. Is known (for example, see Patent Document 1). In this type of vehicle, the control valve is switched by depressing an accelerator pedal, and when the load pressure of the traveling motor increases, the displacement volume of the traveling motor is increased to control the motor speed.
[0003]
The device described in Patent Document 1 is configured as follows. The operating state of the traveling control valve is detected, and the switching position of the traveling transmission that can be switched between high speed and low speed is detected. Then, when it is detected that the control valve is in the neutral position and the transmission is at the high speed position, the displacement volume of the traveling motor is increased to the maximum displacement volume. Accordingly, when the vehicle travels downhill with the control valve neutral without stepping on the accelerator pedal, the motor displacement volume increases to a maximum value, and a large braking force can be obtained.
[0004]
[Patent Document 1]
JP-A-8-270788
[0005]
[Problems to be solved by the invention]
By the way, when traveling downhill, the vehicle is accelerated by the inertial force, and the traveling load is reduced. Therefore, for example, when the vehicle runs downhill with the accelerator pedal fully depressed, the engine speed exceeds the rated speed, the pump discharge amount increases, and the running motor may rotate excessively. In order to prevent the traveling motor from rotating excessively, it is desirable to suppress the rotation of the traveling motor during downhill traveling.
[0006]
However, in the device described in the above-mentioned publication, when the vehicle runs downhill with the accelerator pedal depressed, the displacement volume of the traveling motor remains small, and it is not possible to suppress the motor from rotating excessively during downhill traveling.
[0007]
An object of the present invention is to provide a travel control device for a hydraulic traveling vehicle and a hydraulic traveling vehicle that can prevent the traveling motor from rotating excessively during downhill traveling.
[0008]
[Means for Solving the Problems]
A traveling control device for a hydraulically driven vehicle according to the present invention includes a hydraulic pump driven by a prime mover, a traveling motor driven by pressure oil supplied from the hydraulic pump, and a hydraulic oil supplied to the traveling motor from the hydraulic pump. A travel control valve for controlling the flow rate, an operating means for operating the travel control valve, an overspeed detection means for detecting an overspeed occurrence state causing an overspeed of the travel motor, and an overspeed occurrence The above-mentioned object is achieved by providing a motor over-rotation prevention means for suppressing the rotation of the traveling motor when the state is detected.
Further, the hydraulic drive vehicle according to the present invention achieves the above-described object by including such a travel control device.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
-1st Embodiment-
Hereinafter, a first embodiment of a travel control device according to the present invention will be described with reference to FIGS.
FIG. 1 shows a wheel type hydraulic excavator to which the present invention is applied. The wheel-type hydraulic excavator includes a lower traveling body 81 and an upper revolving body 82 that is rotatably mounted above the lower traveling body 81. The upper swing body 82 is provided with a driver's cab 83 and a work front attachment 84. The front attachment 84 includes a boom 84a rotatably connected to the main body of the upper swing body 82, an arm 84b rotatably connected to the boom 84a, and a bucket 84c rotatably connected to the arm 84b. . The boom 84a is moved up and down by a boom cylinder 84d, the arm 84b is moved up and down by an arm cylinder 84e, and the bucket 84c is subjected to cloud and dump operations by a bucket cylinder 84f. The lower traveling body 81 is provided with a traveling hydraulic motor 85, a transmission 86, and a propeller shaft 87, and the front tire 88F and the rear tire 88R are driven by the propeller shaft 87. 90 is a fender cover.
[0010]
FIG. 2 shows a traveling hydraulic circuit of a hydraulically driven vehicle according to an embodiment of the present invention. This hydraulic circuit is operated by a variable displacement hydraulic pump 10 driven by the engine 1, a pilot hydraulic circuit 20, and a travel control valve 11 for controlling the flow rate and direction of oil discharged from the hydraulic pump 10, and a travel control valve. A variable hydraulic motor for traveling 12 (85 in FIG. 1) driven by the pressure oil controlled by 11; a counterbalance valve 13 interposed between the traveling control valve 11 and the hydraulic motor 12; A pump regulator 10A for adjusting the displacement of the pump 10, a motor regulator 14 for adjusting the displacement of the hydraulic motor 12, and the maximum pressure of the main lines L1A and L1B connecting the control valve 11 and the hydraulic motor 12 are regulated. And crossover load relief valves 15 and 16.
[0011]
The pump regulator 10A includes a torque limiting section, and the pump discharge pressure (running driving pressure) is fed back to the torque limiting section to perform horsepower control. The horsepower control is so-called P-qp control as shown in FIG. By the horsepower control, the pump displacement is controlled so that the load determined by the pump discharge pressure and the pump displacement does not exceed the engine output. That is, when the feedback pressure P is guided to the regulator 10A, the pump displacement qp is controlled along the P-qp diagram of FIG. The regulator 10A is provided with a maximum displacement limiting portion, and the maximum displacement limiting portion limits the pump maximum displacement amount to a predetermined value qpmax. The predetermined value qpmax defines the pump maximum discharge amount. Note that the traveling drive pressure P changes according to the gradient of the road surface. In FIG. 3, for example, P ≦ P1 during downhill traveling, P> P2 during uphill traveling or at the start of traveling, and P1 <P ≦ P2 during ordinary flat-land traveling. Further, the pump maximum displacement qpmax is set to a value such that, for example, when the engine 1 is driven at the rated speed, the traveling motor 12 does not over rotate.
[0012]
The motor regulator 14 includes a piston 141 and a servo valve 142. The rod chamber 141a of the piston 141 is connected via a line L11 to a shuttle valve 18 for selecting high-pressure oil in the main lines L1A and L1B. The bottom chamber 141b of the piston 141 is connected to the servo valve 142 via a line L12. The servo valve 142 is switched by the traveling drive pressure selected by the shuttle valve 18. The traveling drive pressure is detected and output as a pump pressure P by the pressure sensor 42.
[0013]
The pilot hydraulic circuit 20 includes a pilot hydraulic pump 21, a traveling pilot valve 22 operated by an accelerator pedal 22a, and a forward / backward switching valve that is switched to a forward position, a reverse position, and a neutral position by operating a forward / backward switching switch (not shown). 23. The switching direction and stroke amount of the control valve 11 are controlled by the traveling pilot pressure from the pilot hydraulic circuit 20. The traveling pilot pressure is detected and output by the pressure sensor 41 as a pilot pressure Pt.
[0014]
The direction and the flow rate of the pressure oil discharged from the hydraulic pump 10 are controlled by the control valve 11 and supplied to the hydraulic motor 12 through the counter balance valve 13. This causes the hydraulic motor 12 to rotate. The rotation of the hydraulic motor 12 is transmitted to the transmission 86 and decelerated at a predetermined gear ratio, and then transmitted to the tires 88F and 88R via the propeller shaft 87. Thereby, the hydraulic shovel runs.
[0015]
FIG. 2 shows a state in which the forward / reverse switching valve 23 is neutral (N position) and the pilot valve 22 is not operated. In this state, no pilot pressure acts on the control valve 11, and the control valve 11 is in the neutral position. Therefore, the pressure oil from the hydraulic pump 10 is not supplied to the hydraulic motor 12, and the vehicle is stopped.
[0016]
The hydraulic circuit of FIG. 2 operates as follows.
When the forward / reverse switching valve 23 is switched to forward (F position) or reverse (R position) and the accelerator pedal 22a is depressed, the pilot pressure oil output from the pilot valve 22 reaches the pilot port of the control valve 11, and the control valve Reference numeral 11 switches to the F position side or the R position side with a stroke amount according to the pilot pressure. Thus, the hydraulic motor 12 is driven, and the vehicle runs.
[0017]
When the vehicle starts running, a running drive pressure corresponding to the load is generated in the pipeline L1A or L1B between the control valve 11 and the counter balance valve 13. This pressure is guided as torque control pressure from the shuttle valve 18 to the regulator 14 via the line L11, whereby the servo valve 142 is switched to the position A. By switching the servo valve 142, the rod chamber 141a and the bottom chamber 141b of the piston 141 communicate with each other, and the torque control pressure is guided to both of them. As a result, since the pressure receiving area of the bottom chamber 141b is larger than the pressure receiving area of the rod chamber 141a, the piston 141 extends, the displacement q of the hydraulic motor 12 increases, and the vehicle runs at low speed and high torque.
[0018]
When the traveling drive pressure decreases due to the constant speed traveling of the vehicle, the torque control pressure acting on the regulator 14 decreases, and the servo valve 142 is switched to the low position by the spring 142c. By this switching, the bottom chamber 141b is connected to the drain circuit via the pipeline LD, and the piston retracts. As a result, the displacement volume q of the hydraulic motor 12 is reduced, and the vehicle runs at high speed and low torque.
[0019]
By the way, when traveling downhill, the vehicle is accelerated by the inertial force, so that the traveling load decreases. As a result, as shown in the engine characteristics of FIG. 4, when the engine 1 is driven at the rated speed, the engine speed N may exceed the rated speed N1 and increase in speed by the reduced load. (N1 → N2). If the engine speed N exceeds the rated speed N1 during downhill running, the pump discharge amount exceeds the rated maximum discharge amount (N1 × qpmax), and the traveling motor 12 is over-rotated to shorten the motor life. In order to prevent the traveling motor 12 from over-rotating due to such a decrease in the traveling load, the present embodiment controls the engine speed as follows.
[0020]
FIG. 5 is a block diagram of a control circuit that controls the engine speed, the amount of displacement of the pump, and the like. Each device is controlled by a controller 50 including a CPU and the like. The governor 51 of the engine (motor) 1 is connected to a pulse motor 53 via a link mechanism 52, and the rotation speed of the pulse motor 53 controls the rotation speed of the engine 1. That is, the rotation speed increases with the forward rotation of the pulse motor 53 and decreases with the reverse rotation. The rotation of the pulse motor 53 is controlled by a control signal from the controller 50. A potentiometer 54 is connected to the governor 51 via a link mechanism 52. The potentiometer 54 detects a governor lever angle corresponding to the rotational speed of the engine 1, and inputs the detected angle to the controller 50 as an engine control rotational speed Nθ. Is done. The controller 50 is also connected with pressure sensors 41 and 42 for detecting a traveling pilot pressure Pt and a pump pressure (traveling driving pressure) P, respectively.
[0021]
FIG. 6 is a block diagram illustrating details of the controller 50 according to the first embodiment. The function generator 501 is a function (target speed characteristic) L1 that associates the target engine speed Nt according to the accelerator pedal depression amount, that is, the traveling pilot pressure Pt detected by the pressure sensor 41 with the target speed of the engine 1. The target rotation speed Nt determined by the above is output. According to the function L1, the target rotation speed Nt increases proportionally to the rated rotation speed N1 with an increase in the pilot pressure Pt.
[0022]
The function generator 502 is a function that associates a corrected engine speed Ns (hereinafter, referred to as a corrected speed Ns) according to the traveling drive pressure, that is, a function that associates the pump pressure P detected by the pressure sensor 42 with the corrected speed of the engine 1. (Correction rotation speed characteristic) A correction rotation speed Ns determined by L2 is output. According to the function L2, in a range where the pump pressure P is equal to or less than the predetermined value Pa, the corrected rotation speed Ns gradually decreases with an increase in the pump pressure P, and when the pump pressure P exceeds the predetermined value Pa, the corrected rotation speed Ns becomes It is constant (= 0). The predetermined value Pa is set to the pressure at the start of the downhill traveling, that is, P1 in FIG.
[0023]
The function generator 503 outputs a high-level signal when the accelerator pedal 22a is operated at a predetermined value or more, for example, when the accelerator pedal 22a is fully operated, and closes the switch 504. When the switch 504 is closed, the subtractor 505 outputs a value obtained by subtracting the corrected rotation speed Ns from the target rotation speed Nt as a target rotation speed command value Ny. When the switch 504 is open, the subtractor 505 outputs the target rotation speed Nt as it is as the target rotation speed command value Ny.
[0024]
The target rotational speed command value Ny is compared with the control rotational speed Nθ corresponding to the displacement amount of the governor lever detected by the potentiometer 54 by the servo control unit 510, and the pulse motor 53 is controlled according to the procedure shown in FIG. Is done.
[0025]
In FIG. 7, first, in step S21, the target rotation speed command value Ny and the control rotation speed Nθ are read, and the process proceeds to step S22. In step S22, the result of Nθ−Ny is stored in the memory as the rotation speed difference A, and in step S23, it is determined whether or not | A | ≧ K using a predetermined reference rotation speed difference K. If the result is affirmative, the process proceeds to step S24, where it is determined whether or not the rotational speed difference A> 0. In step S25, a signal for commanding the motor to rotate in reverse is output to the pulse motor 53 in order to lower the engine speed. As a result, the pulse motor 53 rotates in the reverse direction, and the rotation speed of the engine 1 decreases.
[0026]
On the other hand, if A ≦ 0, the control rotation speed Nθ is smaller than the target rotation speed command value Ny, that is, since the control rotation speed is lower than the target rotation speed, the motor rotation is commanded in step S26 to increase the engine rotation speed. Output a signal. As a result, the pulse motor 53 rotates forward, and the rotation speed of the engine 1 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 1 is maintained at a constant value. After executing steps S25 to S27, the process returns to the beginning.
[0027]
The operation of the travel control device according to the first embodiment configured as described above will be described more specifically.
(1) Traveling on level ground, traveling uphill
When traveling on flat ground or traveling uphill, the traveling load is greater than when traveling downhill, so the pump pressure P (traveling drive pressure) detected by the pressure sensor 42 is greater than a predetermined value Pa (P1). Therefore, the corrected rotation speed Ns output from the function generator 502 becomes 0, and the target rotation speed Nt output from the function generator 501 is changed regardless of whether the switch 504 is opened or closed, that is, whether or not the accelerator pedal 22a is fully operated. It is output as the target rotation speed command value Ny. Thus, the engine speed N is controlled to a speed Nt according to the operation amount of the accelerator pedal 22a defined by the function L1.
[0028]
(2) Downhill driving
When traveling downhill with the accelerator pedal 22a fully operated, the traveling load is small during downhill traveling, so the pump pressure P detected by the pressure sensor 42 becomes equal to or lower than the predetermined value Pa, causing the traveling motor 12 to over rotate. A light load condition is detected. As a result, a corrected rotation speed Ns (> 0) corresponding to the pump pressure P is output from the function generator 502, and a value obtained by subtracting the corrected rotation speed Ns from the target rotation speed Nt (= N1) is set as a target rotation speed command value Ny. Is output. As a result, the engine speed N is controlled to be smaller than the target speed Nt by the correction speed Ns, and does not exceed the rated speed N1 even if the engine speed increases due to a decrease in the running load. Therefore, the pump discharge amount is suppressed to the rated maximum discharge amount or less, and the overrun of the traveling motor 12 can be prevented.
[0029]
In this case, the steeper the slope, the lower the pump pressure P, and the higher the corrected rotation speed Ns from the function generator 502. Therefore, even when the running load is significantly reduced, an increase in the engine speed can be reliably prevented.
[0030]
When the accelerator pedal 22a is not fully operated during downhill traveling, the switch 504 is opened, and the target rotation speed Nt (<N1) from the function generator 501 is output as the target rotation speed command value Ny. In this case as well, the engine speed increases due to the decrease in the running load, but since the target speed Nt is smaller than the rated speed N1, the engine speed can be suppressed to the rated speed N1 or less. As a result, the pump discharge amount is suppressed to the rated maximum discharge amount or less, and it is possible to prevent the traveling motor 12 from over-rotating. Further, since the engine speed is not reduced unnecessarily, good running performance can be exhibited. Note that in order to further reduce the increase in the engine speed during downhill running, for example, to ensure that the engine speed is equal to or lower than the rated speed N1 during downhill running, the switch 504 must be turned off before the accelerator pedal 22a is fully operated. The output of function generator 503 may be adjusted to close.
[0031]
According to the first embodiment described above, the following effects can be obtained.
(1) The traveling drive pressure (travel load) P is detected by the pressure sensor 42, and when the travel drive pressure P is equal to or less than the predetermined value Pa, a light load state that causes the traveling motor 12 to over rotate is detected, and the engine speed The value Ny is set to be lower than the target rotation speed Nt. Thus, it is possible to prevent the engine speed from exceeding the rated speed N1 during downhill running, and to prevent the running motor 12 from over-rotating.
(2) Since the switch 504 is closed when the accelerator pedal 22a is fully operated to reduce the engine speed command value Ny, the engine speed is not reduced unnecessarily, resulting in good running performance. Can be demonstrated.
(3) The function L2 is determined so that the correction rotation speed Ns increases as the running load decreases, and the engine speed command value Ny decreases greatly as the running load decreases. As a result, even when the slope of the slope is steep and the engine speed is significantly increased, the engine speed can be surely made smaller than the rated speed N1, and the overspeed of the traveling motor 12 is reliably prevented. Can be.
[0032]
-2nd Embodiment-
A second embodiment of the travel control device according to the present invention will be described with reference to FIGS.
In the first embodiment, the engine speed is controlled during downhill running to prevent the traveling motor 12 from over-rotating. In the second embodiment, the maximum displacement of the pump is controlled. In the following, differences from the first embodiment will be mainly described.
[0033]
The second embodiment differs from the first embodiment in the structure of the pump regulator 10A and the configuration of the control circuit. FIG. 8 is a diagram showing a detailed structure of a pump regulator 10A according to the second embodiment. The same parts as those in FIG. 2 are denoted by the same reference numerals.
[0034]
As shown in FIG. 8, the pump regulator 10A is provided with a torque limiting section 110, and the torque limiting section 110 includes a spring 113 for urging a piston 112 connected to the pump swash plate 111 to the maximum tilt limiting section 114. Is interposed. The pump discharge pressure P is fed back to the torque limiting section 110, and the above-described horsepower control is performed. That is, when the feedback pressure P is guided to the torque limiting unit 110, the piston 112 is driven against the spring force, and the pump displacement qp is reduced along the P-qp diagram in FIG. On the other hand, in a region where the pump pressure P is equal to or less than P2, the piston 112 is restricted by the maximum displacement restricting portion 114 by the spring force, and the pump displacement becomes the maximum displacement qpmax.
[0035]
Further, the regulator 10A is provided with a maximum displacement control unit 120. The maximum displacement control unit 120 includes a piston 121 arranged in series with the piston 112, and the piston 121 is urged by a spring 122 in a direction opposite to the piston 112. The maximum displacement control unit 120 is connected to the hydraulic pressure source 30 via an electromagnetic proportional pressure reducing valve 31, and the electromagnetic proportional pressure reducing valve 31 is switched by a control signal from the controller 50. When the electromagnetic proportional pressure reducing valve 31 is switched to the position A, the pressure oil from the hydraulic power source 30 acts on the maximum displacement control unit 120. As a result, the piston 121 moves rightward in the figure against the spring force, and limits the upper limit of the movement range of the piston 112 to a smaller value. As a result, as shown by the dotted line in FIG. 11, the maximum pump displacement is reduced by a predetermined amount Δqp from qpmax. When the electromagnetic proportional pressure reducing valve 31 is switched to the position B side, the maximum displacement control unit 120 communicates with the tank as shown in FIG. 8, and the maximum displacement of the pump becomes qpmax.
[0036]
FIG. 9 is a block diagram of a control circuit of the traveling control device according to the second embodiment. The same portions as those in FIG. 5 are denoted by the same reference numerals, and differences will be mainly described. The controller 50 is connected with a pressure sensor 41 for detecting the traveling pilot pressure Pt, a speed sensor 43 for detecting the actual speed N of the engine 1, and a potentiometer 54 for detecting the engine control speed Nθ. ing. The controller 50 outputs a control signal to the pulse motor 53 and the electromagnetic proportional pressure reducing valve 31 as described below.
[0037]
FIG. 10 is a conceptual diagram illustrating details of a controller 50 according to the second embodiment. The same parts as those in FIG. 6 are denoted by the same reference numerals, and the differences will be mainly described below. In the second embodiment, the target engine speed Nt according to the operation amount of the accelerator pedal 22a is output as the target engine speed command value Ny without obtaining the corrected engine engine speed Ns. The servo control unit 210 executes the same processing as described above, and controls the engine speed to the target speed command value Ny.
[0038]
The subtractor 511 subtracts the target engine speed Nt from the actual engine speed N detected by the engine speed sensor 43 to obtain a deviation ΔN of the engine speed. The function generator 512 outputs a corrected tilt amount Δqp corresponding to the deviation ΔN by a function L3 in which the rotational speed deviation ΔN and the corrected tilt amount Δqp are associated. According to the function L3, the corrected tilt amount Δqp = 0 when the deviation ΔN is equal to or smaller than 0, and the corrected tilt amount Δqp decreases proportionally when the deviation ΔN becomes larger than zero.
[0039]
The function generator 513 outputs a high-level signal when the accelerator pedal 22a is operated at a predetermined value or more, for example, when the accelerator pedal 22a is fully operated, and switches the switch 514 to the contact a side. A level signal is output to switch the switch 514 to the contact b side. When the switch 514 is switched to the contact a side, a control signal is output from the function generator 512 so as to make the correction tilt amount Δqp (≦ 0). When the switch 514 is switched to the contact b side, the correction tilt is output from the setting unit 515. A control signal is output such that the shift amount Δqp = 0. The electromagnetic proportional pressure reducing valve 31 is switched by this control signal, and the maximum pump displacement is reduced by qqp from qpmax.
[0040]
The operation of the traveling control device according to the second embodiment configured as described above will be described more specifically.
(1) Traveling on level ground, traveling uphill
The traveling load is larger when traveling on level ground or traveling uphill than when traveling downhill. Therefore, when the vehicle travels on flat ground or on a slope while the accelerator pedal 22a is fully operated, the target rotation speed Nt (= N1) output from the function generator 501 is smaller than the actual engine rotation speed N detected by the rotation speed sensor 43. Greater or almost equal. Therefore, the correction tilt amount Δqp output from the function generator 512 becomes 0, and the electromagnetic proportional pressure reducing valve 31 is switched to the position B. As a result, the maximum displacement control of the pump by the displacement control unit 120 is not performed in the regulator 10A, and the pump displacement is controlled in accordance with the traveling drive pressure acting on the torque control unit 110 with qpmax as an upper limit.
[0041]
When the accelerator pedal 22a is released and the vehicle is decelerated while traveling on level ground, the actual rotation speed N becomes larger than the target rotation speed Nt. In this case, since the accelerator pedal 22a is not fully operated, the switch 514 is switched to the contact b side, and Δqp = 0. Therefore, also in this case, the maximum displacement control of the pump by the displacement control unit 120 is not performed.
[0042]
(2) Downhill driving
When the vehicle is running downhill with the accelerator pedal 22a fully operated, the vehicle is accelerated by the inertial force during the downhill running, so that the actual rotation speed N becomes larger than the target rotation speed Nt (= N1). As a result, the correction tilt amount Δqp (<0) corresponding to the deviation ΔN of the engine speed is output from the function generator 512, and the electromagnetic proportional pressure reducing valve 31 is switched to the position A. As a result, the pump maximum displacement decreases by the corrected displacement Δqp. Therefore, even when the rotation speeds of the engine 1 and the hydraulic pump 10 increase due to a decrease in the traveling load, the pump discharge amount is suppressed to the rated maximum discharge amount (N1 × qpmax) or less, and the traveling motor 12 is prevented from over-rotating. can do.
[0043]
In this case, the steeper the slope, the larger the deviation ΔN of the engine speed becomes, and the smaller the correction tilt amount Δqp from the function generator 512 becomes. Therefore, even when the running load is significantly reduced, an increase in the engine speed can be reliably prevented.
[0044]
When the accelerator pedal 22a is not fully operated during downhill traveling, the switch 515 is switched to the contact b side, and the pump maximum tilt amount control is not performed. Also in this case, the actual rotation speed N becomes larger than the target rotation speed Nt due to the decrease in the traveling load. In addition, since the pump discharge amount is not reduced more than necessary, good running performance can be exhibited. The output of the function generator 513 may be adjusted so that the switch 514 is switched to the contact a before the accelerator pedal 22a is fully operated in order to further reduce the increase in the pump discharge amount during downhill traveling.
[0045]
According to the second embodiment described above, the following effects can be obtained.
(1) The actual rotational speed N of the engine 1 is detected by the rotational speed sensor 43, and when the actual rotational speed N is larger than the target rotational speed Nt, a light load state that causes the traveling motor 12 to over rotate is detected, and the hydraulic pump The maximum tilt amount of No. 10 was reduced. Accordingly, it is possible to prevent the pump discharge amount from increasing due to an increase in the engine speed during downhill traveling, and to prevent the traveling motor 12 from over-rotating.
(2) When the accelerator pedal 22a is fully operated, the switch 514 is switched to the contact point a to reduce the maximum pump displacement, so that the pump displacement is not reduced more than necessary. Good running performance can be exhibited.
(3) As the actual rotational speed N becomes greater than the target rotational speed Nt, the maximum pump displacement is greatly reduced, so that even when the slope is steep, the traveling motor 12 is reliably prevented from over-rotating. be able to.
[0046]
In the above description, attention is paid to the phenomenon that the traveling load is reduced during traveling on a downhill and the traveling motor 12 is excessively rotated, and the traveling is performed based on the traveling drive pressure P and the deviation ΔN between the actual engine speed N and the target speed Nt. Although the light load state that causes the motor 12 to rotate excessively is detected, the light load state may be detected based on another physical quantity correlated with the running load. Further, an over-rotation occurrence state that causes over-rotation of the traveling motor 12 regardless of the traveling load may be detected. Here, the over-rotation occurrence state refers to both the case where the traveling motor 12 is actually over-rotating and the case where the traveling motor 12 is not actually over-rotating but is likely to over-rotate.
[0047]
The overspeed of the travel motor 12 is suppressed by controlling the engine speed or controlling the maximum displacement of the pump. However, other methods (for example, the displacement control of the travel motor 12 and the control valve 11 Excessive rotation of the traveling motor 12 may be suppressed by drive control, relief pressure control of the relief valves 15 and 16). The switches 504 and 513 may be omitted, and the corrected rotation speed Ns or the corrected tilt amount Δqp may always be output regardless of the operation amount of the accelerator pedal 22a.
[0048]
The control valve 11 may be operated by means other than the accelerator pedal 22a. In the above description, the control valve 11 and the engine speed are controlled in accordance with the operation amount of the accelerator pedal 22a (accelerator control). However, only the control valve 11 may be controlled in accordance with the operation amount of the accelerator pedal 22a ( Valve control). The hydraulic motor 12 may be a fixed displacement hydraulic motor. In the first embodiment, the hydraulic pump 10 may be a fixed displacement hydraulic pump. Although the target rotation speed Nt of the engine 1 is set by the accelerator pedal 22a, it may be set by another operation member (for example, a lever or a switch).
[0049]
Although the wheel-type hydraulic excavator has been described above, the present invention can be similarly applied to other work vehicles that are driven by the traveling motor 12. The present invention can also be realized by a so-called HST hydraulic circuit in which the hydraulic pump 10 and the traveling motor 12 are connected in a closed circuit.
[0050]
【The invention's effect】
As described in detail above, according to the present invention, the rotation of the traveling motor is suppressed when the over-rotation occurrence state that causes the traveling motor to be over-rotated is detected. It is possible to prevent the traveling motor from rotating excessively.
[Brief description of the drawings]
FIG. 1 is a side view of a wheel type hydraulic excavator to which the present invention is applied.
FIG. 2 is a traveling hydraulic circuit diagram of the hydraulically driven vehicle according to the first embodiment of the present invention.
FIG. 3 is a diagram showing P-qp characteristics of the hydraulic pump according to the first embodiment.
FIG. 4 is a diagram showing a relationship between a rotation speed and a load of the engine shown in FIG. 2;
FIG. 5 is a block diagram of a control circuit of the travel control device according to the first embodiment.
FIG. 6 is a conceptual diagram illustrating details of a controller shown in FIG. 5;
FIG. 7 is a flowchart illustrating an example of processing performed by a servo control unit in FIG. 6;
FIG. 8 is a hydraulic circuit diagram showing details of a pump regulator of a hydraulic drive vehicle according to a second embodiment.
FIG. 9 is a block diagram of a control circuit of the traveling control device according to the second embodiment.
FIG. 10 is a conceptual diagram illustrating details of a controller shown in FIG. 9;
FIG. 11 is a diagram showing P-qp characteristics of the hydraulic pump according to the second embodiment.
[Explanation of symbols]
1 engine 10 hydraulic pump
10A Pump regulator 11 Travel control valve
12 Hydraulic motor for traveling 22a Accelerator pedal
31 Electromagnetic proportional pressure reducing valve 41, 42 Pressure sensor
50 Controller 53 Pulse motor
54 Potentiometer

Claims (9)

A hydraulic pump driven by a prime mover,
A traveling motor driven by pressure oil supplied from the hydraulic pump,
A traveling control valve for controlling a flow rate of pressure oil supplied from the hydraulic pump to the traveling motor,
Operating means for operating the traveling control valve;
Over-rotation detecting means for detecting an over-rotation occurrence state causing over-rotation of the traveling motor,
A travel control device for a hydraulically driven vehicle, comprising: motor over-rotation prevention means for suppressing rotation of the travel motor when an over-rotation occurrence state is detected by the over-rotation detection means. The travel control device for a hydraulically driven vehicle according to claim 1,
The overspeed detection means includes a load detection means for detecting a magnitude of a load acting on the prime mover, and detects an overspeed occurrence state of the traveling motor when a light load state is detected by the load detection means. A travel control device for a hydraulically driven vehicle, characterized in that: The travel control device for a hydraulically driven vehicle according to claim 1 or 2,
A driving pressure detecting unit that detects a driving pressure of the traveling motor,
The travel control device for a hydraulically driven vehicle, wherein the overspeed detection means detects an overspeed occurrence state of the travel motor when at least the detected drive pressure is equal to or less than a predetermined value. The travel control device for a hydraulically driven vehicle according to claim 3,
An operation amount detection unit that detects an operation amount of the operation unit,
The hydraulic drive vehicle, wherein the overspeed detection means detects an overspeed occurrence state of the traveling motor when the detected drive pressure is equal to or less than the predetermined value and the operation means is operated at a maximum. Travel control device. The travel control device for a hydraulically driven vehicle according to claim 1 or 2,
Rotation speed detection means for detecting the rotation speed of the prime mover,
A rotation speed control device that controls the prime mover to a target rotation speed,
The travel control device for a hydraulically driven vehicle, wherein the overspeed detection means detects an overspeed occurrence state of the travel motor when at least the detected speed of the prime mover is greater than the target speed. The travel control device for a hydraulically driven vehicle according to claim 5,
An operation amount detection unit that detects an operation amount of the operation unit,
A hydraulic drive vehicle, wherein the overspeed detection means detects an overspeed occurrence state of the traveling motor when the detected speed is greater than the target speed and the operating means is operated at a maximum. Travel control device. The travel control device for a hydraulically driven vehicle according to any one of claims 1 to 6,
The travel control device for a hydraulically driven vehicle, wherein the motor overspeed prevention means is a rotation speed reduction means for reducing the rotation speed of the prime mover. The travel control device for a hydraulically driven vehicle according to any one of claims 1 to 6,
The hydraulic pump is a variable displacement hydraulic pump,
The travel control device for a hydraulically driven vehicle, wherein the motor overspeed prevention means is a tilting amount reducing means for reducing a tilting amount of the hydraulic pump. A hydraulically driven vehicle having the traveling control device according to claim 1.

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