JP4136488B2 - Vehicle speed control apparatus and control method for hydraulic drive vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle speed control device for a hydraulic drive vehicle and a control method therefor, and more particularly, to a vehicle speed control device and a control method therefor when a hydraulic drive vehicle traveling with a tire travels down a slope.
[0002]
[Prior art]
In a hydraulic drive vehicle, a variable displacement hydraulic pump and a variable displacement hydraulic motor or a fixed displacement hydraulic motor configured in a closed circuit are generally used.
In particular, tire-type hydraulically driven vehicles use a variable displacement hydraulic pump and a variable displacement hydraulic motor to improve operability and workability. In such tire-type hydraulically driven vehicles, speed control is performed to prevent runaway on flat ground or slopes, etc., and charge pressure is supplied to the closed circuit to prevent cavitation of the hydraulic motor during deceleration traveling or downhill traveling. ing.
[0003]
When speed control is performed with a tire-type hydraulically driven vehicle, the travel speed is detected by a vehicle speed sensor, and the volume of the hydraulic motor is controlled by an electric circuit or a hydraulic circuit so that a predetermined vehicle speed Vrm is obtained.
For example, when a tire-type hydraulically driven vehicle is faster than a predetermined vehicle speed Vrm, control is performed to increase the volume of the hydraulic motor. Conversely, when the tire-type hydraulic drive vehicle is slower than a predetermined vehicle speed Vrm, control is performed to decrease the volume of the hydraulic motor. The vehicle is controlled so as to achieve a predetermined vehicle speed.
[0004]
[Problems to be solved by the invention]
However, in the method of controlling to the above vehicle speed, it is relatively easy to obtain a predetermined vehicle speed by controlling the volume of the hydraulic motor when climbing on a flat ground or a slope, but it is controlled to a predetermined vehicle speed when traveling downhill. There are difficulties to do as described below. During downhill traveling, torque due to the weight of the hydraulically driven vehicle acts on the hydraulic motor from the undercarriage (tire), and therefore, in the vicinity of the predetermined vehicle speed Vrm, hunting of the vehicle speed is likely to occur as shown in FIG. Yes.
[0005]
If the change in the volume of the hydraulic motor is reduced in order to reduce this hunting, the reverse drive torque increases when the slope angle increases, and an overrun condition tends to occur, making it difficult to control to a predetermined vehicle speed.
Thus, since the vehicle speed varies depending on the slope of the slope during downhill travel, there is a problem that it is difficult to control so that hunting does not occur in all slope regions.
[0006]
The present invention has been made paying attention to the above-described problems, and relates to a vehicle speed control device and a control method thereof for a hydraulically driven vehicle, and in particular, a hydraulic pressure corresponding to a vehicle speed difference when going down a hill with a hydraulically driven vehicle traveling with a tire. An object of the present invention is to provide a vehicle speed control device for a hydraulically driven vehicle and a control method thereof with high accuracy and little hunting regardless of the slope of the slope because the motor volume is obtained.
[0007]
[Means, actions and effects for solving the problems]
  In order to achieve the above object, the invention of a vehicle speed control device for a hydraulically driven vehicle according to the present invention is a vehicle speed control device for when a hydraulically driven vehicle goes down a slope,
  A variable displacement hydraulic motor that varies the vehicle speed of the hydraulic drive vehicle, a motor tilt angle control mechanism that varies the volume of the variable displacement hydraulic motor, and a forward / reverse vehicle speed that detects the vehicle speed of the hydraulic drive vehicle The variable displacement hydraulic motor is controlled to a predetermined volume by controlling a sensor, a plurality of speed limits preset for the vehicle speed, a capacity gain set for each speed limit, and the motor tilt angle control mechanism. Control means for controlling,
  When the vehicle speed signal from the forward / reverse vehicle speed sensor is not a waveform signal of a predetermined shape, the control means controls the tilt angle control mechanism for the motor so that the volume of the variable displacement hydraulic motor becomes the maximum capacity. ,
  When the vehicle speed signal from the forward / reverse vehicle speed sensor is a waveform signal of a predetermined shape,Said control meansIsThe capacity gain corresponding to each positive speed difference is integrated with respect to a speed difference obtained by subtracting each of the plurality of speed limits from the detected vehicle speed from the forward / reverse vehicle speed sensor. Value obtainedSum ofThe motor tilt angle control mechanism is controlled accordingly.
[0008]
  In this case,The capacity gain value set for each speed limit is set so that the value gradually increases as the speed limit value increases from the low speed limit value to the high speed limit value.Good.
[0009]
  Also,The speed interval between the plurality of speed limits is set to be narrowed as the speed limit becomes lower to higher speed limit.And good.
[0010]
  When the vehicle speed received from the forward / reverse vehicle speed sensor exceeds a maximum speed limit, the control means controls the tilt angle control mechanism for the motor so that the volume of the variable displacement hydraulic motor becomes the maximum capacity. good.
[0011]
  The invention of the vehicle speed control method of the hydraulic drive vehicle according to the present invention is a vehicle speed control method when the hydraulic drive vehicle goes down a slope,
  When the vehicle speed signal detected by the hydraulically driven vehicle is not a waveform signal of a predetermined shape, control is performed so that the volume of the variable displacement hydraulic motor that drives the hydraulically driven vehicle becomes a maximum capacity,
  When the vehicle speed signal detected by the hydraulic drive vehicle is a waveform signal of a predetermined shape, the detectedFrom vehicle speedPresetThe speed difference obtained by subtracting each speed limit is positive.ValueWhile obtaining the speed difference,eachPositiveValueValue obtained by integrating the capacity gain set for each speed limit to the speed differenceSum ofThe volume of the variable displacement hydraulic motor may be controlled according to the above.
[0013]
  According to the above configuration, the hydraulically driven vehicle is traveling at a traveling speed corresponding to the operation amount of the operator. This traveling speed is detected as a vehicle speed signal by a forward / reverse vehicle speed sensor disposed on the output shaft, and is transmitted to the control means as a vehicle speed signal having a predetermined shape. The operation amount of the operator is detected by a potentiometer, and a speed command signal corresponding to the operation amount is transmitted to the control means.
  The control means controls the motor tilt angle control mechanism of the variable displacement motor according to the operation amount of the potentiometer to obtain the volume of the variable displacement motor according to the operation amount, and obtains the rotation speed to drive the hydraulically driven vehicle. I am letting.
  The control means stores a plurality of speed limits set in advance and a capacity gain set for each speed limit,When the vehicle speed signal from the forward / reverse vehicle speed sensor is not a waveform signal having a predetermined shape, the control means controls the motor tilt angle control mechanism so that the volume of the variable displacement hydraulic motor becomes the maximum capacity.
  When the vehicle speed signal from the forward / reverse vehicle speed sensor is a waveform signal of a predetermined shape,Said control meansIsThe capacity gain corresponding to each positive speed difference is integrated with respect to a speed difference obtained by subtracting each of the plurality of speed limits from the detected vehicle speed from the forward / reverse vehicle speed sensor. Value obtainedSum ofThe motor tilt angle control mechanism is controlled accordingly to drive the hydraulically driven vehicle.
[0014]
  controlmeansSaidThe value of the capacity gain set for each speed limit is set so as to increase sequentially from the plurality of speed limits to the speed limit with a lower speed limit.
  When a hydraulically driven vehicle goes down a slope, the hydraulically driven vehicle may receive a driving torque from the undercarriage due to its own weight, and the vehicle speed may increase. However, as mentioned above when a hydraulically driven vehicle goes down a hillPositiveSince a control signal corresponding to the magnitude of the vehicle speed difference is output to the motor tilt angle control mechanism to obtain the volume of the motor, the vehicle can travel accurately at a vehicle speed according to the speed limit, and hunting hardly occurs. .
[0015]
  Since this speed limit is provided with speed limits of a plurality of vehicle speeds, each speed limit range can be narrowed and controlled with a fine control signal P, and the vehicle speed along the speed limit can be easily obtained. In addition, since the vehicle is controlled at a plurality of speed limits, there is no hunting regardless of the slope of the slope, and the hydraulically driven vehicle can be driven with high accuracy.
  In addition, since speed limits are set for a plurality of vehicle speeds and the gains within the speed limits are changed, a suitable gain can be selected even when the gradient increases, so that the vehicle speed can be quickly controlled along the speed limits. be able to. As a result, it is possible to control the hydraulically driven vehicle quickly at the speed limit and with less hunting in all regions regardless of the magnitude of the gradient.
  controlmeansIf the vehicle speed signal from the vehicle speed sensor is a vehicle speed signal that is much faster than the maximum speed, or if it is not a waveform of a predetermined shape, it is judged that an abnormality has occurred in the vehicle speed sensor system, and the variable motor is set to the maximum volume to ensure safety. We are trying to improve.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a vehicle speed control device and a control method for a hydraulically driven vehicle according to the present invention will be described with reference to the drawings.
First, a vehicle speed control apparatus and control method for a hydraulically driven vehicle according to an embodiment will be described with reference to FIGS. 1 is a circuit diagram of a vehicle speed control device 1 for a hydraulically driven vehicle, FIG. 2 is a diagram for explaining a normal waveform shape of a vehicle speed signal, FIG. 3 is a block diagram of the vehicle speed control device 1, and FIG. FIG. 5 is a flowchart of a vehicle speed control method for a hydraulically driven vehicle, FIG. 6 is a diagram for explaining an abnormal waveform shape of a vehicle speed signal, and FIG. 7 is a diagram for explaining the relationship between the vehicle speed signal, control pressure, and variable motor volume. 8 and 8 are diagrams for explaining the relationship between the control pressure and the volume of the variable motor.
[0017]
In FIG. 1, a vehicle speed control device 1 for a hydraulically driven vehicle has a variable displacement pump 4 (hereinafter referred to as a variable pump 4) driven by an engine 3 connected to a variable displacement motor 5 (hereinafter referred to as a variable motor 5). 7 are connected to form a closed circuit.
The variable pump 4 is connected to a pump tilt angle control mechanism 9, and the swash plate of the variable pump 4 is tilted in the forward and reverse directions by the pump tilt angle control mechanism 9. 6 or to the pipe 7 for backward travel. In the following, the pipes 6 and 7 are distinguished from the forward pipe 6 and the reverse pipe 7 by adding f for forward and b for backward.
[0018]
The pump tilt angle control mechanism 9 is formed by a pump tilt angle cylinder 10 (hereinafter referred to as a pump cylinder 10) and a pump switching valve 11. The pump switching valve 11 includes a forward solenoid 12f and a reverse drive. Solenoid for solenoid 12b, forward port 13f and reverse port 13b are provided.
The pump switching valve 11 is connected to a charge pump 15 driven by the engine 3, receives the charge pressure from the charge pump 15, supplies it to the pump cylinder 10 via the cylinder pipes 16f and 16b, and is connected to a slant (not shown). The board is tilted. As a result, the swash plate of the variable pump 4 is tilted in the forward and reverse directions by the pump tilt angle control mechanism 9 to discharge the pressure oil to the forward pipe 6 or the reverse pipe 7.
[0019]
The pump switching valve 11 is connected to the control unit 17 and is switched in response to a forward command or a reverse command from the control unit 17.
The charge pump 15 is connected to the forward pipe 6 by the charge pipe 18f and connected to the reverse pipe 7 by the charge pipe 18b to supply the charge pressure to prevent cavitation. Check valves 19f and 19b with safety valves are provided in the charging pipes 18f and 18b, respectively.
[0020]
The variable motor 5 is connected to a motor tilt angle control mechanism 21, and the swash plate of the variable motor 5 is tilted by the motor tilt angle control mechanism 21, and the volume dm (cc / rev) of the variable motor 5 is increased. Variable.
The motor tilt angle control mechanism 21 includes a motor tilt angle cylinder 24 (hereinafter referred to as a motor cylinder 24), a motor servo valve 25, and an electromagnetic proportional valve 31. The motor tilt angle control mechanism 21 is operated by the motor servo valve 25 receiving the control pressure Pp of the electromagnetic proportional valve 31 and when the motor cylinder 24 is contracted, the swash plate is set to the maximum tilt angle Θmax to the maximum. The volume is set to dmmax, and when the swash plate is extended, the minimum tilt angle Θmin is set to the minimum volume dmmin.
[0021]
The bottom chamber 24 a of the motor cylinder 24 is connected to the motor servo valve 25, and the rod chamber 24 b is connected to the forward piping 6 and the backward piping 7 via the forward / reverse shuttle valve 27. When the cylinder 24 for motor 24 receives pressure oil in the bottom chamber 24a and the rod chamber 24b, the motor cylinder 24 expands due to the difference in area and swings the swash plate in the direction of the minimum tilt angle Θmin to reduce the volume dm.
Further, when the bottom chamber 24a is connected to the tank 28 via the motor servo valve 25, the motor cylinder 24 is reduced to the minimum and the swash plate is swung to the maximum tilt angle Θmax so as to have the maximum volume dmmax. Yes.
[0022]
In the motor cylinder 24, a cylinder rod 24 c is connected to a motor servo valve 25 via a spring 30. As the cylinder rod 24c moves, the spool (not shown) of the motor servo valve 25 moves through the spring 30 and stops when the pressure in the bottom chamber 24a and the force acting on the cylinder rod 24c by the rod chamber 24b become equal. Then, the supply of pressure oil through the motor servo valve 25 is cut off.
As a result, the motor cylinder 24 is kept at a position where the cylinder rod 24c is balanced, and the tilt angle of the swash plate is kept constant, and the rotation of the variable motor 5 is maintained at a predetermined rotation speed.
[0023]
  One side of the motor servo valve 25 is connected to the forward piping 6, the backward piping 7 and the tank 28 via the forward / reverse shuttle valve 27. When the motor servo valve 25 is operated, the forward piping 6 and the backward piping 7 are high. Receives pressurized oil from the other pipe.
  The other side is connected to the bottom chamber 24a of the motor cylinder 24, and the hydraulic cylinder 24 is extended by supplying pressure oil from the forward / reverse shuttle valve 27 to the bottom chamber 24a.
  The servo valve for motor 25 has a spring 30 and pilot pressure at one end.Rod chamber 24bThe other end receives the pressure oil that is connected to the charge pump 15 through the electromagnetic proportional valve 31, the forward / reverse shuttle valve 27, and the pump switching valve 11 and is reduced as a pilot pressure. Yes.
[0024]
The motor servo valve 25 is operated by the control pressure Pp of the electromagnetic proportional valve 31 and switches to the M position when receiving a high control pressure Pp, and the pressure of the forward pipe 6 or the reverse pipe 7 via the forward / reverse shuttle valve 27. Oil is supplied to the bottom chamber 24a, and the cylinder rod 24c is extended. As the cylinder rod 24c extends, the cylinder rod 24c stops at the balanced position as described above, and shuts off the supply of pressure oil from the motor servo valve 25 to the bottom chamber 24a.
The forward / reverse shuttle valve 27 is connected on one side to the forward pipe 6, the backward pipe 7, the forward branch pipe 33f from the cylinder pipe 16f, and the reverse branch pipe 33b from the cylinder pipe 16b. On the other side, it is connected to the motor servo valve 25 via the rod chamber 24 b of the motor cylinder 24 and the electromagnetic proportional valve 31.
[0025]
  The forward / reverse shuttle valve 27 receives pressure oil from the forward branch pipe 33f and switches to the Nf position, and supplies the control pressure Pp from the forward port 13f to the motor servo valve 25 via the electromagnetic proportional valve 31. The motor servo valve 25 is switched. The forward / reverse shuttle valve 27 supplies pressure oil from the forward piping 6 to the rod chamber 24b and also to the bottom chamber 24a via the motor servo valve 25, and extends the motor cylinder 24 due to the area difference.
  Similarly, the forward / reverse shuttle valve 27 receives pressure oil from the reverse branch pipe 33b at the other end and switches to the Nr position.13bThe control pressure Pp is supplied to the motor servo valve 25 from the electromagnetic proportional valve 31 to switch the motor servo valve 25.
  The forward / reverse shuttle valve 27 supplies the pressure oil from the reverse piping 7 to the rod chamber 24b and also supplies it to the bottom chamber 24a via the motor servo valve 25, thereby extending the motor cylinder 24 due to the area difference.
[0026]
The electromagnetic proportional valve 31 is connected on one side to the forward / reverse shuttle valve 27 and on the other side to the motor servo valve 25 and the tank 28. The electromagnetic proportional valve 31 operates in response to a control signal P from the control unit 17 to reduce the charge pressure Pmax of the charge pump 15 that has passed through the forward / reverse shuttle valve 27 and supply it to the motor servo valve 25 as the control pressure Pp. .
The electromagnetic proportional valve 31 supplies the control pressure Pp to the motor servo valve 25 for switching, and the pressure oil in the forward pipe 6 or the reverse pipe 7 is transferred from the forward / rearward shuttle valve 27 to the bottom chamber 24a via the motor servo valve 25. The motor cylinder 24 is extended. Accordingly, the motor servo valve 25 is operated by the control pressure Pp output from the electromagnetic proportional valve 31 in accordance with the control signal P of the control unit 17 to control the rotational speed of the variable motor 5.
[0027]
The control unit 17 is connected to the potentiometer 34, the vehicle speed sensor 35, the electromagnetic proportional valve 31, and the pump switching valve 11. The control unit 17 receives a signal from the potentiometer 34 corresponding to the operation amount, outputs a control signal P to the electromagnetic proportional valve 31, and controls the volume dm of the variable motor 5 according to the operation amount.
The control unit 17 outputs a control signal P so that the hydraulically driven vehicle travels at a vehicle speed limit speed set in response to the vehicle speed of the hydraulically driven vehicle from the vehicle speed sensor 35. For example, as will be described in detail later, when going down a slope, the vehicle speed from the vehicle speed sensor 35 is compared with the set speed limit of the vehicle speed to obtain the control signal P, and the control signal P is output to the electromagnetic proportional valve 31. Then, the control pressure Pp is supplied to the motor servo valve 25, and the volume dm of the variable motor 5 is controlled by a command from the control unit 17.
Thus, the control unit 17 controls the hydraulically driven vehicle so as to go down the hill at a stable speed limit with less hunting. The controller 17 is formed by a controller, but may be formed by a CPU or a computer.
[0028]
The potentiometer 34 is attached to a vehicle speed setting dial or the like disposed in a driver's seat (not shown), detects its operation amount, and outputs it to the control unit 17 as a speed command signal.
The vehicle speed sensor 35 is attached to the output shaft 5 a such as the variable motor 5, detects the traveling speed of the hydraulically driven vehicle, and outputs it to the control unit 17 as a vehicle speed signal V. As the vehicle speed signal V, a pulse-shaped vehicle speed signal V as shown in FIG. 2 is output as a predetermined signal.
[0029]
FIG. 3 is a block diagram of the vehicle speed control apparatus 1 for a hydraulically driven vehicle having the above-described configuration. In FIG. 3, a vehicle speed signal V having a predetermined shape is transmitted to the control unit 17 from a vehicle speed sensor 35 disposed on the output shaft 5a as the hydraulically driven vehicle travels. Further, a speed command signal corresponding to the operation amount is transmitted from the potentiometer 34 to the control unit 17.
The control unit 17 outputs a control signal P to the electromagnetic proportional valve 31 according to the operation amount of the potentiometer 34, controls the motor tilt angle control mechanism 21 of the variable motor 5 to obtain a rotation speed according to the operation amount, and hydraulic pressure Driving car is running.
[0030]
When the hydraulic drive vehicle goes down a hill, the traveling speed may be increased by receiving a driving force from the undercarriage due to the weight of the hydraulic drive vehicle. The control unit 17 receives the increased traveling speed of the hydraulically driven vehicle as the vehicle speed signal V from the vehicle speed sensor 35, and when the vehicle speed signal V receives the vehicle speed signal V that is much faster than the maximum speed, or when the waveform does not have a predetermined shape. Therefore, it is determined that an abnormality has occurred in the vehicle speed sensor system, and the variable motor 5 is set to the maximum volume dmmax to improve safety and perform vehicle speed control.
When the hydraulically driven vehicle goes down the slope, the control unit 17 compares the set vehicle speed limit speed signal Vc with the vehicle speed signal V to obtain a vehicle speed difference, and generates a control signal P corresponding to the magnitude of the vehicle speed difference. The output is output to the electromagnetic proportional valve 31 so that the hydraulically driven vehicle travels at a speed limit.
At this time, the electromagnetic proportional valve 31 reduces the charge pressure Pmax of the charge pump 15 in accordance with the control signal P output from the control unit 17 and outputs it to the motor tilt angle control mechanism 21 as the control pressure Pp.
[0031]
The motor tilt angle control mechanism 21 makes the volume dm of the variable motor 5 variable according to the control signal P output from the control unit 17 so that the hydraulically driven vehicle runs at a set control speed. At this time, the control unit 17 controls the motor tilt angle control mechanism 21 so as not to cause hunting by outputting a control signal P corresponding to the set speed difference between the speed limit and the vehicle speed to the motor tilt angle control mechanism 21.
For example, the control unit 17 sets the speed limit of the vehicle speed set as shown in FIG. 4 to three stages, and controls and outputs the control signal P in a narrow speed limit range so that the hydraulically driven vehicle moves along the slope in FIG. As shown by the solid line W, there is no hunting, and the hill is descended stably and accurately.
[0032]
Next, a vehicle speed control method for a hydraulically driven vehicle will be described.
A control method when the hydraulically driven vehicle moves down the slope will be described with reference to the flowchart of FIG.
When the hydraulically driven vehicle goes down the slope in step 1, the operator operates the vehicle speed setting dial to travel at a predetermined speed. The potentiometer 34 attached to the vehicle speed setting dial detects the operation amount and transmits it to the control unit 17 as an operation signal. The control unit 17 receives a signal corresponding to the operation amount, outputs a control signal P to the electromagnetic proportional valve 31, and causes the motor servo valve 25 to output a control pressure Pp corresponding to the operation amount. The motor servo valve 25 extends the motor cylinder 24. For example, the swash plate is largely tilted to reduce the volume dm of the variable motor 5 so that the hydraulically driven vehicle travels at a predetermined speed and goes down the slope.
[0033]
In step 2, the traveling speed of the hydraulically driven vehicle is detected by the vehicle speed sensor 35, and the vehicle speed signal V is transmitted to the control unit 17.
In step 3, the control unit 17 determines whether or not the vehicle speed signal V from the vehicle speed sensor 35 is much larger than the third speed limit signal Vcmax that is the maximum vehicle speed signal (V >> Vcmax). For example, it is determined whether or not the vehicle speed signal V exceeds a vehicle speed that is 1.2 times the third speed limit signal Vcmax that is the maximum vehicle speed signal.
If it is very large in step 3 (YES), it is determined that a vehicle speed sensor system such as the vehicle speed sensor 35 or a harness short circuit has failed, and the process goes to step 4.
[0034]
In step 4, the control unit 17 outputs the third control signal P to the electromagnetic proportional valve 31, connects the electromagnetic proportional valve 31 to the tank 28, and sets the control pressure Pp to the motor servo valve 25 to the minimum control pressure Ppmin.
The motor servo valve 25 connects the bottom chamber 24a of the motor cylinder 24 to the tank 28 and reduces the motor cylinder 24 to make the variable motor 5 have a maximum capacity dmmax, thereby reducing the traveling speed of the hydraulically driven vehicle. .
When it is not very large at step 3 (NO), it goes to step 5 as a normal vehicle speed signal V.
[0035]
  In step 5, it is determined whether or not the vehicle speed signal V is a waveform signal having a predetermined shape.
  When the vehicle speed signal V is not a normal waveform signal as shown in FIG. 2 in step 5 (NO), for example, when the vehicle speed signal V is a constant value as shown in FIG. It is determined that the system has failed, and the process goes to Step 4.
  In step 4, the control unit 5 sends the third control signal P to the motor tilt angle control mechanism 21 as described above.InThe variable motor 5 is output to make the maximum capacity dmmax, and the traveling speed of the hydraulically driven vehicle is reduced.
  If the vehicle speed signal V is a normal waveform signal in step 5 (YES), go to step 6.
[0036]
In step 6, it is determined whether or not the vehicle speed signal V exceeds the first speed limit signal Vcn.
When the vehicle speed signal V does not exceed the first speed limit signal Vcn in step 6 (NO), the process returns to step 1 and the control unit 17 outputs the control signal P to the electromagnetic proportional valve 31 and performs control according to the operation amount. The pressure Pp is output to the motor servo valve 25 to drive the hydraulically driven vehicle according to the operation amount.
If the vehicle speed signal V exceeds the first speed limit signal Vcn in step 6 (YES), the process goes to step 7.
In step 7, it is determined whether or not the vehicle speed signal V exceeds the second speed limit signal Vci.
[0037]
If the vehicle speed signal V does not exceed the second speed limit signal Vci in Step 7 (NO), go to Step 8.
In step 8, the control unit 17 obtains the first control signal Ps from the vehicle speed signal V, the first speed limit signal Vcn, and the first gain Kps using Equation 1, and outputs a command to the electromagnetic proportional valve 31. The electromagnetic proportional valve 31 is operated by the control unit 17 to output the first control signal Ps to the motor servo valve 25 to expand and contract the motor cylinder 24 and control the volume dm of the variable motor 5 so as to reach a predetermined rotational speed. To do.
[0038]
The first control signal Ps is obtained by the following formula 1.
Ps = Pmax−Kps (V−Vcn) (Formula 1)
here,
Ps: first control signal
Pmax: Maximum control pressure (maximum control pressure signal of an electromagnetic proportional valve)
V: Vehicle speed signal
Vcn: first speed limit signal
Kps: 1st gain (experimental value)
It is.
[0039]
In step 8, for example, as shown in FIG. 7, when the vehicle speed signal Va of the hydraulically driven vehicle going down the hill exceeds the first speed limit signal Vcn and is equal to or lower than the second speed limit signal Vci, the vehicle speed is indicated as indicated by a dotted line. The first control signal Ps is obtained from the relationship line Ls between the vehicle speed signal V drawn from the signal Va using the first gain Kps and the control pressure Pp.
Next, the motor servo 25 is controlled by the line Qs using the relationship between the control pressure Pp and the volume dm shown in FIG. 8 from the obtained first control signal Ps, and as shown by the dotted line in FIG. The volume dma of the variable motor 5 is obtained so as to go down the slope at a predetermined traveling speed.
At this time, the interval between the first speed limit signal Vcn and the second speed limit signal Vci is appropriately selected, and the speed limit range can be narrowed by controlling more than the second speed limit signal Vci. The driving vehicle can prevent hunting from occurring and can travel at a stable speed limit with high accuracy.
[0040]
  If the vehicle speed signal V exceeds the second speed limit signal Vci in step 7, the process goes to step 9.
  In step 9, it is determined whether or not the vehicle speed signal V exceeds the third speed limit signal Vcmax.
  If the vehicle speed signal V does not exceed the third speed limit signal Vcmax in step 9 (NO) Go to step 10.
  In step 10, the control unit 17 obtains the second control signal Pr using Formula 2 from the vehicle speed signal V, the first speed limit signal Vcn, the first gain Kps, the second speed limit signal Vci, and the second gain Kpr. A command is output to the electromagnetic proportional valve 31. The electromagnetic proportional valve 31 is actuated by the control unit 17 to output a second control signal Pr to the motor servo valve 25 to expand and contract the motor cylinder 24 and control the volume dm of the variable motor 5 so as to reach a predetermined rotational speed. To do.
[0041]
The second control signal Pr is obtained by the following formula 2.
Pr = Pmax−Kps (V−Vcn) −Kpr (V−Vci) (Formula 2)
here,
Pr: second control signal
Pmax: Maximum control pressure (maximum control pressure signal of an electromagnetic proportional valve)
V: Vehicle speed signal
Vcn: first speed limit signal
Vci: second speed limit signal
Kps: 1st gain (experimental value)
Kpr: first gain (experimental value greater than first gain)
It is.
[0042]
In step 10, for example, as shown in FIG. 7, when the vehicle speed signal Vb of the hydraulically driven vehicle going down the hill exceeds the second speed limit signal Vci and is equal to or lower than the third speed limit signal Vcmax, A second control signal Pr is obtained from a relationship line Lr between the vehicle speed signal V and the control pressure Pp drawn from the vehicle speed signal Vb using the first gain Kps and the second gain Kpr.
Next, the motor servo 25 is controlled by using the relationship line Qr between the control pressure Pp and the volume dm from the obtained second control signal Pr, and the hydraulically driven vehicle is moved to a predetermined traveling speed as shown by a one-dot chain line in FIG. The volume dmb of the variable motor 5 is obtained so as to go down the slope. At this time, when the vehicle travels at a steep slope or at a high speed, the second control signal Pr is controlled within a narrow range between the second speed limit signal Vci and the third speed limit signal Vcmax, and the volume dm is greatly changed. Thus, hunting is prevented from occurring and a predetermined speed is quickly obtained.
If the vehicle speed signal V exceeds the third speed limit signal Vcmax in step 9, the process goes to step 4. In step 4, the variable motor 5 is set to the maximum volume dmmax as described above to reduce the traveling speed of the hydraulically driven vehicle.
[0043]
In the above embodiment, the variable pump 4 and the variable motor 5 are connected in a closed circuit, but may be connected in an open circuit. Although the vehicle speed control device 1 has been described as being applied to a vehicle using a tire-type hydraulic drive vehicle, it may be applied to a vehicle using an endless track. Although the control speed is controlled in three stages, it can be controlled in more stages. The electromagnetic proportional valve 31 receives the charge pressure oil from the charge pump 15 via the forward / reverse shuttle valve 27 and sets the control pressure Pp. However, the electromagnetic proportional valve 31 may directly receive the pressure oil from the charge pump 15 and set the control pressure Pp.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a vehicle speed control device for a hydraulically driven vehicle according to the present invention.
FIG. 2 is a diagram illustrating a normal waveform shape of a vehicle speed signal.
FIG. 3 is a block diagram of a vehicle speed control method for a hydraulically driven vehicle according to the present invention.
FIG. 4 is a diagram illustrating a vehicle speed limit speed according to the present invention.
FIG. 5 is a flowchart of a vehicle speed control method for a hydraulically driven vehicle according to the present invention.
FIG. 6 is a diagram for explaining an abnormal waveform shape of a vehicle speed signal.
FIG. 7 is a diagram for explaining a relationship among a vehicle speed signal, a control pressure, and a volume of a variable motor.
FIG. 8 is a diagram for explaining a relationship between a control pressure and a volume of a variable motor.
FIG. 9 is a diagram for explaining a vehicle speed of a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Vehicle speed control apparatus of hydraulic drive vehicle, 3 ... Engine, 4 ... Variable displacement pump, 5 ... Variable displacement motor, 9 ... Pump tilt angle control mechanism, 10 ... Pump tilt angle cylinder, 11 ... Pump Switch valve, 15 ... charge pump, 17 ... control unit, 21 ... motor tilt angle control mechanism, 24 ... motor tilt angle cylinder, 25 ... motor servo valve, 27 ... forward / reverse shuttle valve, 27 ... tank 31 ... Proportional solenoid valve, 34 ... Potentiometer, 35 ... Vehicle speed sensor.

Claims (5)

A vehicle speed control device for a hydraulically driven vehicle going down a slope,
A variable displacement hydraulic motor that varies the vehicle speed of the hydraulically driven vehicle;
A motor tilt angle control mechanism for changing the volume of the variable displacement hydraulic motor;
A forward / reverse vehicle speed sensor for detecting a vehicle speed of the hydraulically driven vehicle;
A plurality of speed limits preset for the vehicle speed;
Capacity gain set for each speed limit,
Control means for controlling the motor tilt angle control mechanism and controlling the variable displacement hydraulic motor to a predetermined volume;
With
When the vehicle speed signal from the forward / reverse vehicle speed sensor is not a waveform signal of a predetermined shape, the control means controls the tilt angle control mechanism for the motor so that the volume of the variable displacement hydraulic motor becomes the maximum capacity. ,
When the vehicle speed signal from the forward / reverse vehicle speed sensor is a waveform signal having a predetermined shape, the control means has a positive speed difference obtained by subtracting each of the plurality of speed limits from the detected vehicle speed from the forward / rearward vehicle speed sensor. The motor tilt angle control mechanism is controlled according to the sum of the values obtained by integrating the capacity gains corresponding to the positive speed differences. A vehicle speed control device for hydraulically driven vehicles.   The capacity gain value set for each of the speed limits is set so as to increase sequentially as the speed limit becomes lower to higher speed among the plurality of speed limits. The vehicle speed control device for a hydraulically driven vehicle according to claim 1.   3. The hydraulic drive according to claim 1, wherein the speed interval between the plurality of speed limit speeds is set to be narrowed as the speed limit is low and the speed limit is high. Vehicle speed control device.   When the vehicle speed received from the forward / reverse vehicle speed sensor exceeds the maximum speed limit, the control means controls the tilt angle control mechanism for the motor so that the volume of the variable displacement hydraulic motor becomes the maximum capacity. The vehicle speed control device for a hydraulically driven vehicle according to any one of claims 1 to 3. A vehicle speed control method when a hydraulically driven vehicle goes down a slope,
When the vehicle speed signal detected by the hydraulically driven vehicle is not a waveform signal of a predetermined shape, control is performed so that the volume of the variable displacement hydraulic motor that drives the hydraulically driven vehicle becomes a maximum capacity,
When the vehicle speed signal detected by the hydraulic drive vehicle is a waveform signal of a predetermined shape, a speed difference obtained by subtracting a plurality of preset speed limits from the detected vehicle speed is a positive value, and hydraulic characterized by comprising controlling the volume of the variable displacement hydraulic motor in accordance with the sum of values obtained by integrating the capacity gain set for the respective speed limit speed difference became the positive value Vehicle speed control method for driving vehicle.

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