JP3999618B2 - Hydraulic drive vehicle travel control device and hydraulic drive vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a travel control device for a hydraulically driven vehicle such as a wheeled hydraulic excavator and a hydraulically driven vehicle.
[0002]
[Prior art]
A hydraulically driven vehicle, such as a wheel-type hydraulic excavator, that controls the flow rate and direction of pressure oil discharged from a hydraulic pump driven by a prime mover with a control valve and drives a travel motor with the controlled pressure oil Is known (see, for example, Patent Document 1). In this type of vehicle, the control valve is switched by depressing the accelerator pedal, and when the load pressure of the traveling motor increases, the displacement of the traveling motor is increased to control the motor speed.
[0003]
The apparatus 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. When it is detected that the control valve is neutral and the transmission is in the high speed position, the displacement volume of the travel motor is increased to the maximum displacement volume. As a result, when the vehicle runs downhill with the control valve neutral without stepping on the accelerator pedal, the motor displacement volume increases to the 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, if the vehicle travels downhill with the accelerator pedal fully depressed, the engine rotational speed exceeds the rated rotational speed, the pump discharge amount increases, and the traveling motor may rotate excessively. In order to prevent such over-rotation of the travel motor, it is desirable to suppress the rotation of the travel motor during downhill travel.
[0006]
However, in the device described in the above publication, if the vehicle is driven downhill while the accelerator pedal is depressed, the displacement volume of the travel motor remains small, and it is not possible to suppress over-rotation of the motor during downhill travel.
[0007]
An object of the present invention is to provide a traveling control device for a hydraulic traveling vehicle and a hydraulic traveling vehicle capable of preventing overtravel of a traveling motor during downhill traveling.
[0008]
[Means for Solving the Problems]
A travel control device for a hydraulically driven vehicle according to the present invention is driven by a hydraulic pump driven by a prime mover and pressure oil supplied from the hydraulic pump. Variable capacity type A traveling motor; Provided between the hydraulic pump and the travel motor; A travel control valve for controlling the flow rate of the pressure oil supplied from the hydraulic pump to the travel motor, and an operating means for operating the travel control valve; A counter balance valve provided between the variable displacement hydraulic motor and the travel control valve; a conduit for guiding return oil from the travel control valve to the tank; By means of a rotational speed detection means for detecting the rotational speed of the prime mover, a setting means for arbitrarily setting the target rotational speed of the prime mover, a rotational speed control device for controlling the prime mover to the target rotational speed, and a reduction in the load acting on the prime mover, At least the engine speed greater than the target speed is detected by the speed detection means. An over-rotation detecting means for detecting an over-rotation occurrence state that causes over-rotation of the travel motor, and an over-rotation detection state is detected by the over-rotation detection means. The over-rotation detecting means for detecting the over-rotation occurrence state and the motor over-rotation prevention means for suppressing the rotation of the traveling motor when the over-rotation occurrence state is detected by the over-rotation detection means. To achieve.
Moreover, the hydraulic drive vehicle by this invention achieves the objective mentioned above by providing such a traveling control apparatus.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
-First embodiment-
A travel control device according to a first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 shows a wheeled hydraulic excavator to which the present invention is applied. This wheel-type hydraulic excavator includes a lower traveling body 81 and an upper revolving body 82 that is rotatably mounted on the upper portion of the lower traveling body 81. The upper turning body 82 is provided with a cab 83 and a work front attachment 84. The front attachment 84 includes a boom 84a that is rotatably connected to the main body of the upper swing body 82, an arm 84b that is rotatably connected to the boom 84a, and a bucket 84c that is rotatably connected to the arm 84b. . The boom 84a is lifted and lowered by a boom cylinder 84d, the arm 84b is lifted and lowered by an arm cylinder 84e, and the bucket 84c is operated for clouding and dumping by the 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. Reference numeral 90 denotes a fender cover.
[0010]
FIG. 2 shows a traveling hydraulic circuit for 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 traveling control valve 11 for controlling the flow rate and direction of the discharged oil of the hydraulic pump 10, and a traveling control valve. 1, a variable displacement hydraulic motor 12 for traveling driven by pressure oil controlled by 11 (85 in FIG. 1), a counter balance valve 13 interposed between the traveling control valve 11 and the hydraulic motor 12, and hydraulic pressure The pump regulator 10A for adjusting the displacement volume of the pump 10, the motor regulator 14 for adjusting the displacement volume 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. Cross overload relief valves 15 and 16 are provided.
[0011]
The pump regulator 10A includes a torque limiting unit, and pump discharge pressure (running driving pressure) is fed back to the torque limiting unit to perform horsepower control. The horsepower control is so-called P-qp control as shown in FIG. By this horsepower control, the pump tilt amount is controlled so that the load determined by the pump discharge pressure and the pump tilt amount does not exceed the engine output. That is, when the feedback pressure P is led to the regulator 10A, the pump tilt amount qp is controlled along the P-qp diagram of FIG. Further, the regulator 10A is provided with a maximum tilt limiting portion, and the maximum tilt limiting portion limits the pump maximum tilt amount to a predetermined value qpmax. The predetermined value qpmax defines the pump maximum discharge amount. The travel drive pressure P varies depending on the road surface gradient. In FIG. 3, for example, P ≦ P1 when traveling downhill, P> P2 when traveling uphill or starting traveling, and P1 <P ≦ P2 when traveling on normal flat ground. Further, the pump maximum tilt amount qpmax is set to a value such that the traveling motor 12 does not over-rotate when the engine 1 is driven at the rated rotational speed, for example.
[0012]
The motor regulator 14 includes a piston 141 and a servo valve 142. The rod chamber 141a of the piston 141 is connected to a shuttle valve 18 that selects high-pressure oil in the main pipelines L1A and L1B via a pipeline L11. The bottom chamber 141b of the piston 141 is connected to the servo valve 142 via a pipe 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 the 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 / reverse switching valve that is switched to a forward position, a reverse position, and a neutral position by operating a forward / reverse 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 by the pressure sensor 41 and output as the pilot pressure Pt.
[0014]
The direction and flow rate of the pressure oil discharged from the hydraulic pump 10 is controlled by the control valve 11 and supplied to the hydraulic motor 12 through the counter balance valve 13. As a result, the hydraulic motor 12 rotates. The rotation of the hydraulic motor 12 is transmitted to the transmission 86, decelerated at a predetermined gear ratio, and then transmitted to the tires 88F and 88R via the propeller shaft 87. As a result, the hydraulic excavator travels.
[0015]
FIG. 2 shows a state where the forward / reverse switching valve 23 is neutral (N position) and the pilot valve 22 is not operated. In this state, the pilot pressure does not act 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 11 switches to the F position side or the R position side by a stroke amount corresponding to the pilot pressure. As a result, the hydraulic motor 12 is driven and the vehicle travels.
[0017]
At the start of vehicle travel, travel drive pressure corresponding to the load is generated in the pipe 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 pipe L11, whereby the servo valve 142 is switched to the position B. By switching the servo valve 142, the rod chamber 141a and the bottom chamber 141b of the piston 141 communicate with each other, and a 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 volume q of the hydraulic motor 12 increases, and the vehicle travels at low speed and high torque.
[0018]
When the traveling drive pressure decreases due to the vehicle traveling at a constant speed, the torque control pressure acting on the regulator 14 decreases, and the servo valve 142 is switched to the lower position side by the spring 142c. By this switching, the bottom chamber 141b is communicated with the drain circuit via the pipe line LD, and the piston is degenerated. As a result, the displacement volume q of the hydraulic motor 12 is reduced, and the vehicle travels at high speed and low torque.
[0019]
By the way, when traveling downhill, the vehicle is accelerated by inertial force, so the travel 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 increase beyond the rated speed N1 by the reduced load. (N1 → N2). If the engine speed N exceeds the rated speed N1 during downhill travel, the pump discharge amount exceeds the rated maximum discharge amount (N1 × qpmax), and the travel motor 12 over-rotates to reduce the motor life. In this embodiment, the engine speed is controlled as follows in order to prevent overtravel of the travel motor 12 caused by such a decrease in travel load.
[0020]
FIG. 5 is a block diagram of a control circuit for controlling the engine speed and the amount of pump tilt. Each device is controlled by a controller 50 including a CPU. The governor 51 of the engine (prime mover) 1 is connected to the pulse motor 53 via the link mechanism 52, and the rotation speed of the engine 1 is controlled by the rotation of the pulse motor 53. That is, the rotational speed increases when the pulse motor 53 rotates forward and decreases when the pulse motor 53 rotates backward. 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 the governor lever angle corresponding to the rotational speed of the engine 1 and inputs it to the controller 50 as the engine control rotational speed Nθ. Is done. The controller 50 is also connected to pressure sensors 41 and 42 for detecting a traveling pilot pressure Pt and a pump pressure (traveling drive 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 in which the target engine speed Nt corresponding to the accelerator pedal depression amount, that is, the traveling pilot pressure Pt detected by the pressure sensor 41 and the target speed of the engine 1 are associated with each other. The target rotational speed Nt determined by is output. According to the function L1, the target rotational speed Nt increases proportionally to the rated rotational speed N1 as the pilot pressure Pt increases.
[0022]
The function generator 502 is a function that associates the corrected engine speed Ns (hereinafter referred to as the corrected engine speed Ns) according to the travel drive pressure, that is, the pump pressure P detected by the pressure sensor 42 and the corrected engine speed of the engine 1. (Correction speed characteristic) A correction speed Ns determined by L2 is output. According to the function L2, when the pump pressure P is less than or equal to the predetermined value Pa, the corrected rotational speed Ns gradually decreases as the pump pressure P increases, and when the pump pressure P exceeds the predetermined value Pa, the corrected rotational speed Ns is It becomes constant (= 0). The predetermined value Pa is set to the pressure at the start of downhill traveling, that is, P1 in FIG.
[0023]
The function generator 503 outputs a high level signal when the accelerator pedal 22a is operated to a predetermined value or more, for example, when the accelerator pedal 22a is fully operated, and closes the switch 504. In a state where the switch 504 is closed, the subtractor 505 outputs a value obtained by subtracting the corrected rotational speed Ns from the target rotational speed Nt as the target rotational speed command value Ny. In a state where the switch 504 is opened, the subtracter 505 outputs the target rotational speed Nt as it is as the target rotational 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 so that they coincide with each other according to the procedure shown in FIG. Is done.
[0025]
In FIG. 7, first, at step S21, the target rotational speed command value Ny and the control rotational 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 rotational speed difference A, and in step S23, it is determined whether or not | A | ≧ K using a predetermined reference rotational speed difference K. If the determination is affirmative, the routine proceeds to step S24, where it is determined whether or not the rotational speed difference A> 0. If A> 0, the control rotational speed Nθ is greater than the target rotational speed command value Ny, that is, the control rotational speed is the target rotational speed. Therefore, in order to lower the engine speed, a signal instructing motor reverse rotation is output to the pulse motor 53 in step S25. As a result, the pulse motor 53 reverses and the rotational speed of the engine 1 decreases.
[0026]
On the other hand, if A ≦ 0, the control rotational speed Nθ is smaller than the target rotational speed command value Ny, that is, the control rotational speed is lower than the target rotational speed. Therefore, in order to increase the engine rotational speed, a normal motor rotation is commanded in step S26. Output a signal. As a result, the pulse motor 53 rotates forward and the rotational speed of the engine 1 increases. If step S23 is negative, the process proceeds to step S27 to output a motor stop signal, whereby the engine speed is held at a constant value. When steps S25 to S27 are executed, the process returns to the beginning.
[0027]
The operation of the travel control apparatus according to the first embodiment configured as described above will be described more specifically.
(1) Traveling on flat ground, traveling uphill
Since the traveling load is larger when traveling on a flat ground or when traveling uphill, the pump pressure P (traveling drive pressure) detected by the pressure sensor 42 is larger than a predetermined value Pa (P1). Therefore, the corrected rotational speed Ns output from the function generator 502 is 0, and the target rotational speed Nt output from the function generator 501 is equal to 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 rotational speed command value Ny. Thereby, the engine speed N is controlled to the 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 that the pump pressure P detected by the pressure sensor 42 is less than or equal to a predetermined value Pa, causing overtravel of the traveling motor 12. A light load condition is detected. As a result, the corrected rotational speed Ns (> 0) corresponding to the pump pressure P is output from the function generator 502, and the target rotational speed command value Ny is obtained by subtracting the corrected rotational speed Ns from the target rotational speed Nt (= N1). 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 the rated speed N1 is not exceeded even if the engine speed increases due to a decrease in travel load. Therefore, the pump discharge amount can be suppressed below the rated maximum discharge amount, and the overtravel of the traveling motor 12 can be prevented.
[0029]
In this case, as the slope of the slope becomes steeper, the pump pressure P decreases, and the corrected rotational speed Ns from the function generator 502 increases. Therefore, even when the traveling load is remarkably reduced, it is possible to reliably prevent the engine speed from increasing.
[0030]
When the accelerator pedal 22a is not fully operated during downhill travel, the switch 504 is opened, and the target rotational speed Nt (<N1) from the function generator 501 is output as the target rotational speed command value Ny. In this case as well, the engine speed increases due to a decrease in travel load. However, 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 can be suppressed below the rated maximum discharge amount, and the overtravel of the traveling motor 12 can be prevented. Further, since the engine speed is not reduced more than necessary, good running performance can be exhibited. In order to further reduce the increase in the engine speed during downhill travel, for example, to ensure that the engine speed is equal to or lower than the rated speed N1 during downhill travel, the switch 504 is set before the accelerator pedal 22a is fully operated. The output of the function generator 503 may be adjusted to close.
[0031]
According to the first embodiment described above, the following effects can be obtained.
(1) The travel drive pressure (travel load) P is detected by the pressure sensor 42, and when the travel drive pressure P is less than or equal to a predetermined value Pa, a light load state that causes an excessive rotation of the travel motor 12 is detected, and an engine speed command is issued. The value Ny is reduced from the target rotational speed Nt. As a result, the engine speed can be prevented from exceeding the rated speed N1 during downhill travel, and overtravel of the travel motor 12 can be prevented.
(2) Since the switch 504 is closed to reduce the engine speed command value Ny when the accelerator pedal 22a is fully operated, the engine speed is not reduced more than necessary, and good running performance is achieved. Can be demonstrated.
(3) The function L2 is determined so that the corrected rotational speed Ns increases as the traveling load decreases, and the engine rotational speed command value Ny decreases significantly as the traveling load decreases. As a result, even when the slope of the slope is steep and the engine speed is remarkably increased, the engine speed can be surely made smaller than the rated speed N1, and overtravel of the travel motor 12 can be reliably prevented. Can do.
[0032]
-Second 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 rotation speed is controlled during downhill travel to prevent overtravel of the travel motor 12, but in the second embodiment, the pump maximum tilt amount is controlled. In the following description, 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. In addition, the same code | symbol is attached | subjected to the location same as FIG.
[0034]
As shown in FIG. 8, the torque regulator 110 </ b> A is provided with a torque limiter 110, and the torque limiter 110 includes a spring 113 that biases the piston 112 connected to the pump swash plate 111 to the maximum tilt limiter 114. Is intervening. The pump discharge pressure P is fed back to the torque limiter 110, and the horsepower control described above 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 tilt amount qp is reduced along the P-qp diagram of FIG. On the other hand, in the region where the pump pressure P is P2 or less, the piston 112 is limited by the maximum tilt limiter 114 by the spring force, and the pump tilt becomes the maximum tilt qpmax.
[0035]
Further, a maximum tilt control unit 120 is provided in the regulator 10A. The maximum tilt control unit 120 includes a piston 121 arranged in series with the piston 112, and the piston 121 is biased by a spring 122 in a direction opposite to the piston 112. The maximum tilt 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 side, the pressure oil from the hydraulic source 30 acts on the maximum tilt control unit 120. As a result, the piston 121 moves to the right in the figure against the spring force, and limits the upper limit of the moving range of the piston 112 to a smaller value. As a result, as shown by the dotted line in FIG. 11, the pump maximum tilt amount 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 tilt control unit 120 communicates with the tank as shown in FIG. 8, and the maximum pump tilt amount is qpmax.
[0036]
FIG. 9 is a block diagram of a control circuit of the travel control apparatus according to the second embodiment. In addition, the same code | symbol is attached | subjected to the location same as FIG. 5, and the difference is mainly demonstrated. Connected to the controller 50 are a pressure sensor 41 for detecting the traveling pilot pressure Pt, a rotational speed sensor 43 for detecting the actual rotational speed N of the engine 1, and a potentiometer 54 for detecting the engine control rotational speed Nθ. ing. The controller 50 outputs a control signal to the pulse motor 53 and the electromagnetic proportional pressure reducing valve 31 as follows.
[0037]
FIG. 10 is a conceptual diagram illustrating details of the controller 50 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the location same as FIG. 6, and the difference is mainly demonstrated below. In the second embodiment, the target engine speed Nt corresponding 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 process 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 the engine speed deviation ΔN. 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 with each other. According to the function L3, when the deviation ΔN is 0 or less, the correction tilt amount Δqp = 0, and when the deviation ΔN is greater than 0, the correction tilt amount Δqp decreases proportionally.
[0039]
The function generator 513 outputs a high level signal when the accelerator pedal 22a is operated more than a predetermined value, 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 obtain a correction tilt amount Δqp (≦ 0), and when the switch 514 is switched to the contact b side, a correction tilt is output from the setting device 515. A control signal for setting the amount of rotation Δqp = 0 is output. The electromagnetic proportional pressure reducing valve 31 is switched by this control signal, so that the maximum pump tilt amount is reduced by a correction tilt amount Δqp from qpmax.
[0040]
The operation of the traveling control apparatus according to the second embodiment configured as described above will be described more specifically.
(1) Traveling on flat ground, traveling uphill
When traveling on a flat road or traveling uphill, the traveling load is greater than when traveling downhill. For this reason, if the accelerator pedal 22 a is fully operated and the vehicle is traveling on a flat ground or running uphill, the target engine speed Nt (= N1) output from the function generator 501 is greater than the actual engine speed N detected by the engine speed sensor 43. Greater or nearly equal. Accordingly, the correction tilt amount Δqp output from the function generator 512 is 0, and the electromagnetic proportional pressure reducing valve 31 is switched to the position b. Thus, in the regulator 10A, the maximum pump tilt amount control by the tilt amount control unit 120 is not performed, and the pump tilt amount is controlled according to the traveling drive pressure acting on the torque control unit 110 with qpmax as the upper limit.
[0041]
When the vehicle is decelerated by releasing the accelerator pedal 22a during traveling on flat ground, the actual rotational speed N becomes larger than the target rotational 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 pump maximum tilt amount control by the tilt amount control unit 120 is not performed.
[0042]
(2) Downhill driving
When traveling downhill with the accelerator pedal 22a fully operated, the vehicle is accelerated by inertial force when traveling downhill, so the actual rotational speed N becomes larger than the target rotational speed Nt (= N1). As a result, the correction tilt amount Δqp (<0) corresponding to the engine speed deviation ΔN is output from the function generator 512, and the electromagnetic proportional pressure reducing valve 31 is switched to the position A side. As a result, the maximum pump tilt amount is reduced by the correction tilt amount Δqp. Therefore, even when the rotational speed of the engine 1 and the hydraulic pump 10 is increased due to a decrease in travel load, the pump discharge amount is suppressed to the rated maximum discharge amount (N1 × qpmax) or less, and the travel motor 12 is prevented from over-rotating. can do.
[0043]
In this case, as the slope of the slope becomes steeper, the engine speed deviation ΔN increases, and the corrected tilt amount Δqp from the function generator 512 decreases. Therefore, even when the traveling load is remarkably reduced, it is possible to reliably prevent the engine speed from increasing.
[0044]
When the accelerator pedal 22a is not fully operated during downhill travel, the switch 515 is switched to the contact b side, and the pump maximum tilt amount control is not performed. In this case as well, the actual rotational speed N becomes larger than the target rotational speed Nt due to the reduction of the traveling load. However, since the target rotational speed Nt is smaller than the rated rotational speed N1, the pump discharge amount is suppressed to the rated maximum discharge amount or less. In addition, since the pump discharge amount is not reduced more than necessary, good running performance can be exhibited. In order to further reduce the increase in pump discharge during downhill travel, the output of the function generator 513 may be adjusted so that the switch 514 is switched to the contact a side before the accelerator pedal 22a is fully operated.
[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 an overspeed of the traveling motor 12 is detected, and the hydraulic pump The maximum amount of tilt of 10 was reduced. As a result, it is possible to prevent the traveling motor 12 from over-rotating, which can prevent the pump discharge amount from increasing due to an increase in the engine speed during downhill traveling.
(2) When the accelerator pedal 22a is fully operated, the switch 514 is switched to the contact point a side to reduce the maximum pump tilt amount, so that the pump tilt amount is not reduced more than necessary. Good running performance can be exhibited.
(3) Since the pump maximum tilt amount is greatly reduced as the actual rotational speed N becomes larger than the target rotational speed Nt, it is possible to reliably prevent the traveling motor 12 from over-rotating even if the slope of the slope is steep. be able to.
[0046]
In the above, focusing on the phenomenon that the traveling load becomes light and the traveling motor 12 over-rotates during downhill traveling, traveling based on the traveling driving pressure P and the deviation ΔN between the actual engine speed N and the target engine speed Nt. Although the light load state that causes the motor 12 to over-rotate is detected, the light load state may be detected based on another physical quantity correlated with the traveling load. Moreover, you may detect the over-rotation generation | occurrence | production state which causes the over-rotation of the traveling motor 12 irrespective of the traveling load. 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 possibility of over-rotation is high although it is not actually over-rotating.
[0047]
By controlling the engine speed or controlling the maximum amount of tilting of the pump, the over-rotation of the traveling motor 12 is suppressed, but other methods (for example, controlling the amount of tilting of the traveling motor 12, the control valve 11 The over-rotation of the traveling motor 12 may be suppressed by driving control, relief pressure control of the relief valves 15 and 16, and the like. 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 other than the accelerator pedal 22a. In the above, the control valve 11 and the engine speed are controlled according to the operation amount of the accelerator pedal 22a (accelerator control), but only the control valve 11 may be controlled according to 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 rotational 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 driven to travel by the travel 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】
Book According to the invention , Descend It is possible to prevent the traveling motor from being over-rotated by reducing the traveling load during hill traveling.
[Brief description of the drawings]
FIG. 1 is a side view of a wheeled excavator to which the present invention is applied.
FIG. 2 is a hydraulic circuit diagram for travel 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.
4 is a diagram showing the relationship between engine speed and load shown in FIG. 2;
FIG. 5 is a block diagram of a control circuit of the travel control apparatus according to the first embodiment.
6 is a conceptual diagram illustrating details of the controller shown in FIG.
7 is a flowchart showing an example of processing performed by the servo control unit of 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 travel control apparatus according to the second embodiment.
10 is a conceptual diagram illustrating details of the controller shown in FIG. 9;
FIG. 11 is a diagram showing P-qp characteristics of a hydraulic pump according to a second embodiment.
[Explanation of symbols]
1 Engine 10 Hydraulic pump
10A Pump regulator 11 Travel control valve
12 Traveling hydraulic motor 22a Accelerator pedal
31 Electromagnetic proportional pressure reducing valve 41, 42 Pressure sensor
50 Controller 53 Pulse motor
54 Potentiometer

Claims (4)

A variable displacement hydraulic pump driven by a prime mover;
A variable displacement travel motor driven by pressure oil supplied from the hydraulic pump;
A travel control valve that is provided between the hydraulic pump and the travel motor and controls a flow rate of pressure oil supplied from the hydraulic pump to the travel motor;
Operating means for operating the control valve for traveling;
A counter balance valve provided between the variable displacement hydraulic motor and the travel control valve;
A conduit for guiding return oil from the travel control valve to the tank;
A rotational speed detection means for detecting the rotational speed of the prime mover;
Setting means for arbitrarily setting the target rotational speed of the prime mover;
A rotational speed control device for controlling the prime mover to the target rotational speed;
Due to a reduction in the load acting on the prime mover, an excessive rotation occurrence state that causes an excessive rotation of the travel motor is detected when at least the prime rotation speed greater than the target rotational speed is detected by the rotational speed detection means. Rotation detection means;
Wherein the overspeed occurrence is discovered by overspeed detection means, the travel control device for a hydraulically driven vehicle, comprising a motor overspeed prevention means for reducing the tilting amount of the hydraulic pump. The travel control device for a hydraulically driven vehicle according to claim 1,
Further comprising an operation amount detection means for detecting an operation amount of the operation means,
The motor over-rotation preventing means is configured to detect the hydraulic pressure when the engine speed is larger than the target speed by the speed detecting means and the maximum operation of the operating means is detected by the operation amount detecting means. A travel control device for a hydraulically driven vehicle, characterized by reducing a tilting amount of a pump. The travel control apparatus for a hydraulically driven vehicle according to claim 1 or 2,
The motor over-rotation prevention means increases the amount of reduction in pump tilt as the difference between the motor speed detected by the speed detection means and the target speed increases. Travel control device.   A hydraulically driven vehicle comprising the travel control device according to claim 1.

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