FR2847525A1 - Displacement control for hydraulic vehicle comprising hydraulic motor and transmission comprises gear ratio control and vehicle speed detection means, control device sending gear change down signal when vehicle speed is almost stopped - Google Patents

Abstract

The displacement control for a hydraulic vehicle comprising a hydraulic displacement motor (13) and a transmission (14) comprises a gear ratio control (16) for the transmission. There are vehicle speed detection means (31) and a control device (30) which sends a gear change down signal to the gear change control when the vehicle speed is detected is almost stopped.

Description

MOVEMENT CONTROL DEVICE FOR MOBILE VEHICLE

HYDRAULIC

  The present invention relates to a movement control device for a hydraulic mobile vehicle.

  Until now, a hydraulic mobile vehicle, which moves by actuating a hydraulic displacement motor with pressurized oil from a hydraulic displacement pump driven by a motor, has included a transmission to improve travel performance. As the transmission mounted in the hydraulic mobile vehicle, which constitutes a work vehicle, must cover a range of speeds from a range of low speeds from neutral for main operation to a normal travel speed for travel on ordinary roads, it usually has multiple gear ratios. When such a hydraulic mobile vehicle is traveling at high speed, a high speed ratio is selected as the transmission speed ratio, and the capacity of the hydraulic displacement motor is minimized for rotation at high speed, so as to allow therefore a displacement

high speed.

  However, when such a hydraulic mobile vehicle stops after having moved at high speed, the speed ratio of the automatic transmission remains the high speed ratio, and the capacity of the displacement motor remains minimal. When the vehicle in such a state stops in the middle of a sloping road, the vehicle moves down the sloping road when the brake is not applied, and the hydraulic displacement motor is driven by the rotation of the wheels. Furthermore, in the explanation which follows, the term "driving in the opposite direction" defines the fact that "the hydraulic displacement motor is driven by the rotation of the wheels due to the downward sliding of the hydraulic mobile vehicle or similar". When operating in reverse, the hydraulic displacement motor operates like a pump, but resistance to the driving force in reverse is low because its capacity is made minimal. Therefore, when the brake is not applied, the vehicle descends the road on a slope, which causes a downward slip of the vehicle to occur.

  product, and that the speed of sliding down at which the vehicle slides down increases rapidly.

  When a circuit connecting an input side and an output side of the hydraulic displacement motor when the hydraulic displacement motor operates in the opposite direction is present to prevent cavitation of the hydraulic displacement motor, the speed of sliding down increases faster because the reverse drive force easily turns the hydraulic displacement motor. The present invention is carried out in the light of the aforementioned drawbacks, and its object is to provide a device for controlling the movement of a hydraulic mobile vehicle capable of maintaining the sliding speed down on a sloping road at

a low value.

  To achieve the above-mentioned object, a first construction of a device for controlling the movement of a hydraulic mobile vehicle according to the present invention is characterized in that a device for controlling the movement of a hydraulic mobile vehicle comprising a motor displacement hydraulics and a transmission the speed ratio of which can be fixed comprises transmission speed changing means, vehicle speed detection means for detecting the vehicle speed of the vehicle

  hydraulic mobile, and a control device which

  channels a downshift signal to the speed change control means to effect a downshift

  to the transmission when it is determined from the detected vehicle speed that the hydraulic mobile vehicle is almost stopped.

  According to this constitution, the transmission reduction ratio is high, even if the wheels try to move in the opposite direction because the hydraulic mobile vehicle tries to slide down on a sloping road. As a result, the reverse drive force of the wheels is reduced by the reduction ratio of the transmission, and the reverse drive force of the hydraulic displacement motor is reduced, and, therefore, the rotational speed of the hydraulic displacement motor decreases, and therefore the downward sliding speed can be maintained in

a lower range.

  A second constitution of the movement control device of the hydraulic mobile vehicle according to the present invention is characterized in that a movement control device of a hydraulic mobile vehicle comprising a hydraulic displacement displacement motor comprises capacity control means motor of the volumetric displacement hydraulic motor, vehicle speed detection means for detecting the vehicle speed of the hydraulic mobile vehicle, and a control device which sends a capacity increase signal to the motor capacity control means to increase the capacity of the hydraulic displacement motor when determined using

  the vehicle speed detected that the hydraulic mobile vehicle is almost stopped.

  According to this constitution, even if the wheels try to move in the opposite direction because the hydraulic mobile vehicle tries to slide down on the sloping road, the capacity of the hydraulic displacement motor is maximized. As a result, the hydraulic displacement motor only rotates at a low rotational speed, and, moreover, the resistance to rotation inside the hydraulic displacement motor increases, whereby the sliding speed downwards can

  be kept in a lower range.

  A third constitution of the movement control device of the hydraulic mobile vehicle according to the present invention is characterized in that a movement control device of a hydraulic mobile vehicle comprising a hydraulic displacement displacement motor and a transmission whose speed ratio the possibility of being fixed comprises means for controlling the speed change of the transmission; means for controlling the capacity of the hydraulic displacement displacement motor, vehicle speed detection means for detecting a vehicle speed of the hydraulic mobile vehicle, and a control device which sends a downshift signal to the control means gear change to downshift the transmission and send a signal

  capacity increase to the motor capacity control means to increase a capacity of the hydraulic displacement displacement hydraulic motor when it is determined from the detected vehicle speed that the hydraulic mobile vehicle is almost stopped.

  According to this constitution, the wheels are driven because the hydraulic mobile vehicle tries to slide down on a sloping road, and therefore, the hydraulic displacement motor is driven

  in reverse through the transmission.

  However, since the reduction ratio of the transmission is high, the drive force against the wheels is reduced by the reduction ratio of the transmission, and the force to drive the hydraulic displacement motor is reduced. Consequently, the rotational speed of the hydraulic displacement motor decreases, and the capacity of the hydraulic displacement motor is maximized, whereby the hydraulic displacement motor rotates only at a low rotational speed. Furthermore, the resistance to rotation inside the hydraulic displacement motor increases, whereby the downward sliding speed of the hydraulic mobile vehicle can be maintained.

in a lower range.

  In addition, it is appropriate that, in the movement control device of the hydraulic mobile vehicle, displacement motor throttle valves are arranged in a circuit connecting an input side and an output side of the hydraulic displacement motor. when the hydraulic displacement motor is driven by the rotation of the wheels of the hydraulic mobile vehicle. According to this constitution, pressurized oil from the hydraulic displacement motor passes through the displacement motor throttling valves arranged in the circuit connecting the inlet side and the outlet side of the hydraulic displacement motor due to drive in reverse. As a result, the pressure loss of the pressurized oil occurs, causing the rotational resistance caused by the reverse drive to increase, and therefore the speed

  rotation of the hydraulic displacement motor can be kept in a lower range.

  Therefore, the reverse drive force of the hydraulic displacement motor, which is caused because the work vehicle slides down on the sloping road, becomes maximum and has significant resistance, and, therefore, the sliding speed of the hydraulic mobile vehicle can be maintained at a

sufficiently low speed.

  In addition, it is appropriate that, in the movement control device of the hydraulic mobile vehicle, the control device determines that the hydraulic mobile vehicle is almost stopped when the detected vehicle speed is less than or equal to a predetermined speed for a time. predetermined. According to this constitution, when the detected vehicle speed is less than or equal to the predetermined speed during the predetermined time, it is determined that the hydraulic mobile vehicle is almost stopped, and, therefore,

  it can be determined with certainty that the hydraulic mobile vehicle is almost stopped.

  In addition, it is appropriate that, in the movement control device of the hydraulic mobile vehicle, the control device determines that the hydraulic mobile vehicle is almost stopped also thanks to the detection of the fact that an accelerator pedal is not not pressed. According to this constitution, the control device determines that the hydraulic mobile vehicle is almost stopped also thanks to the detection of the fact that the accelerator pedal is not depressed, and therefore it can be more surely determined that

  the hydraulic mobile vehicle is almost stopped.

  The present invention will be better understood on reading

  of the following detailed description, made with reference

  in the accompanying drawings, in which: FIG. 1 is a general diagram of the system of a movement control device according to an embodiment

of the present invention.

  A movement control device of a hydraulic mobile vehicle according to an embodiment of the present invention will be explained with reference to the drawing. Figure 1 is a general diagram of the system of the device

move control.

  As shown in FIG. 1, a displacement pump 12, which is a hydraulic pump for displacement, is connected to a motor 11, and the displacement pump 12 is driven by the motor 11 and discharges an oil under pressure. The pressurized oil discharged from the displacement pump 12 is supplied to a displacement motor 13, which is a hydraulic motor for displacement, via a displacement control valve 21 and a seal oil pressure swivel 15. The displacement motor 13 is connected to an input shaft of a transmission 14 and drives the transmission 14. A displacement speed detection pump 17 is present for the transmission 14, and it rotates pro15 in proportion to the rotation of an output shaft (not shown) of the transmission 14. Pressurized oil discharged from the displacement speed detection pump 17 is supplied to a displacement speed detection motor 18 through the pivo20 oil pressure seal 15. The displacement pump 12 is a volumetric hydraulic pump, and includes displacement pump capacity control means 12C. The displacement motor 13 is a hydraulic motor

  volumetric, and comprises means for controlling the capacity of the displacement motor 13C.

  Furthermore, a work vehicle (not shown), which constitutes the hydraulic mobile vehicle, comprises lower displacement equipment (not shown) and

  an upper rotating superstructure (not shown).

  The upper rotating superstructure comprises a working accessory (not shown), and the pivoting oil pressure seal 15 is arranged in a connection part of the lower displacement equipment and the upper rotating superstructure. Engine 11 and a

  control device 30 are arranged in the super

  upper rotary structure, and the transmission 14 is

  arranged in the lower displacement equipment.

  The transmission 14 is connected to a speed change valve 16, which constitutes speed change control means, via the pivoting oil pressure seal. The speed change valve 16 delivers pressurized oil from a transmission pump (not shown) to the transmission 14 via the pivoting oil pressure seal. The speed change valve 16 is connected to the control device 30, and sends a pressure signal, in response to a speed change signal

  coming from the control device 30, to the transmission 14.

  The transmission 14 comprises, for example, two speed reports, namely the first and second speed reports. When the transmission 14 is put in the first speed ratio, the transmission 14 is put in the first speed ratio by an oil pressure coming from the speed change valve 16. In addition, when the transmission 14 is put in the second gear ratio, the transmission 14 is put into the second gear ratio by the oil pressure coming from the gear change valve 16, whereby its gear ratio

speed can be set.

  A balancing valve 41 is disposed between a forward travel side circuit 46F and a reverse travel side circuit 46R, which are connected to the displacement motor 13. The forward travel side circuit 46F is provided with a forward travel side non-return valve 42F, and the reverse travel side circuit 46R is provided with a reverse travel side check valve 42R. A circuit diverging from a point between the non-return valve on the side of

  forward travel 42F and the forward motor

  ment 13 is connected to an orifice A of the balancing valve 41. A circuit diverging from a point between the non-return movement check valve in reverse 42R and the displacement motor 13 is connected to an orifice B of the balancing valve 41. The balancing valve 41 has a neutral position 41N, a forward travel side position 41F, and a reverse travel side position 41R, which are shown in the drawing . In the neutral position 21N, a circuit which includes a throttle 41C and which connects the orifice A and the orifice B is present, and it delivers oil from the high pressure side to the low pressure side when the displacement motor 13 is trained in

  reverse, so as to prevent cavitation.

  In the forward travel side position 41F of the balancing valve 41, a circuit which includes a throttle 41FC and which connects the orifice A and an orifice T of the balancing valve 41 is present, and, in the reverse travel side position 41R, a circuit which includes a throttle 41RC and

  which connects the orifice B and the orifice T of the balancing valve 41 is present.

  An end portion of the forward travel side position 41F of the balancing valve 41 and a point between the forward travel side check valve 42F and the travel control valve 21 are connected by a circuit comprising a throttle 44F. An end portion on the side of the reverse travel side position 41R of the balancing valve 41 and a point between the reverse travel side check valve 42F and the movement control valve 21 are connected

  by a circuit comprising a throttle 44R. Therefore, switching between neutral position 41N, po-

  forward travel side position 41F and the reverse travel side position 41R is made by pressurized oil from the displacement pump 12. Non-return valves 45F and 45R are valves allowing prevent return flow of pressurized oil from the forward travel side circuit 46F and the reverse travel side circuit 46R. Port T of the balancing valve 41 is connected to the forward travel side circuit 46F by means of a forward travel check valve 43F, and is connected to the travel side circuit at reverse 46R via a non-return valve

  reverse travel 43R.

  A displacement motor capacity control valve 26 delivers the pressurized oil from the transmission pump I to the displacement motor capacity control means 13C via the oil pressure swivel joint 15. The displacement motor capa20 control valve 26 is connected to the control device 30, and controls the capacity of the motor

  displacement 13 in response to a displacement motor capacity control signal from the controller 30.

  A vehicle speed detection device 35 for producing a vehicle speed signal is disposed on an output shaft of the vehicle speed detection motor 18, and it rotates under the actuation of the vehicle speed detection motor 18 For example, a predetermined number of teeth, slots, and protrusions and cavities are formed on an outer circumference of the vehicle speed detection device 35. A vehicle speed detection sensor 31 is disposed in close proximity of the outer circumference of the positive vehicle speed detection device 35, and outputs there a pulse, which occurs, for example, when the predetermined number of teeth on the outer circumference of the vehicle speed detection device 35 pass through a signal detection portion of the vehicle speed detection sensor 31, under the

form of an electrical signal.

  The vehicle speed detection sensor 31, acting as vehicle speed detection means, is connected to the control device 30 and sends a vehicle speed signal to the control device in the form of an electrical signal. The controller 30 performs operational processing of the vehicle speed signal to calculate the vehicle speed. A main safety valve 24 is disposed in a discharge circuit of the displacement pump 12, and releases the pressurized oil to an oil tank when the pressure of the pressurized oil discharged from the displacement pump 12 is greater than or

  equal to a predetermined value.

  The displacement control valve 21 is switched from a neutral position N to a forward displacement position F or to a reverse displacement position R, and controls the direction of the pressurized oil discharged from the displacement pump 12 so as to send it to the displacement motor 13. The displacement control valve 21 is switched from the neutral position N to the forward movement position F or to the reverse position R by receiving a pilot displacement pressure, constituting a pilot pressure, from a forward and reverse motion switching valve 22, in a forward side displacement pressure receiving portion 21F or a reverse travel side pressure receiving portion 21R of the travel control valve 21. The forward and reverse travel switching valve 22 is switched to a forward travel position FK in response to a forward travel signal from the controller 30, and switched to a reverse travel position RK in response to a forward travel signal back. An accelerator pedal 23A is depressed to actuate a displacement pilot pressure valve 23 so as to cause it to generate a displacement pilot pressure. The pilot displacement pressure, which constitutes means for detecting the extent to which the accelerator pedal 23A is depressed, changes as a function of the extent to which the accelerator pedal 23A is depressed, and increases at a predetermined speed. when the depth of depression of the accelerator pedal 23A increases. A displacement pilot pressure sensor 32 is disposed in a circuit between the displacement pilot pressure valve 23 and the forward and reverse displacement switching valve 22, and the displacement pilot pressure sensor 32 sends a signal pilot pressure

  displacement detected at control device 30.

  A forward travel pressure sensor 36 is disposed in a circuit between the forward and reverse travel switching valve 22 and the forward travel side pressure receiving portion 21F, and a sensor of reverse travel pressure 37 is disposed in a circuit between the forward travel and reverse travel switching valve 22 and the reverse travel side pressure receiving portion 21R. The forward travel pressure sensor 36 sends a forward travel signal to the controller 30 when its internal switch is actuated by the pilot travel pressure, and the reverse travel pressure sensor 37 sends a reverse movement signal to the control device 30 when its internal switch is put into operation by the pilot displacement pressure. A forward and reverse motion switch 34 is connected to the controller 30, and sends a forward motion control signal or a forward motion control signal

  back to control 30.

  Upon receiving the vehicle speed signal as the electrical signal from the vehicle speed detection sensor 31, the controller 30 sends a signal to reduce the capacity of the travel motor 13 to the control valve of displacement motor capacity 26 so that the capacity of displacement motor 13 can be reduced, so as to allow displacement at a higher speed depending on the speed of the vehicle, for example depending on the fact that the speed of the vehicle increases. In response to this signal, the displacement motor capacity control valve 26 actuates the displacement motor capacity control means 13C so as to reduce the capacity of the displacement motor 13. Upon reception of the pressure signal displacement pilot detected by the displacement pilot pressure sensor 32, the control device 30 calculates the amount of depression of the accelerator pedal 23A as a function of the magnitude

  of the displacement pilot pressure signal.

  The controller 30 performs operational processing of the vehicle speed signal, which constitutes the electrical signal detected by the vehicle speed detection sensor 31, to calculate the vehicle speed. The control device 30 then performs operational processing of a variation over time

  vehicle speed, and when the vehicle speed

  cule is less than or equal to a predetermined speed (for example 2 km / h or less) for a predetermined time (for example, for one second), it determines that the vehicle is stopped or almost stopped. The control device 30 then outputs a downshift signal at the speed change valve 16, and outputs a capacity increase signal, for example a capacity increase signal to maximize the capacity of the engine. displacement 13, to the displacement motor capacity control valve 26. Furthermore, when it is determined that the vehicle is stopped, as required, the control device 30 can i) output the downshift signal to the speed change valve 16, ii) output the capacity increase signal to the displacement motor capacity control valve 26, or iii) output the downshift signal to the speed change valve 16 and output the capacity increase signal to the motor capacity control valve

displacement 26.

  In addition, as required, the controller can add a state in which the accelerator pedal 23A is not depressed in the determinants. More typically, when i) the displacement pressure signal pi25 lote detected by the displacement pilot pressure sensor 32 is less than or equal to a predetermined pressure, or when the forward displacement pilot pressure switch 36 and the reverse travel pilot pressure switch 37 are both out of service, and the accelerator pedal 23A is not depressed, and that ii) the vehicle speed of the vehicle is less than or equal to the predetermined speed, as described above, the

  command 30 can determine that the vehicle is stopped.

  In this case, the control device 30 can i) output the downshift signal to the speed change valve 16, ii) output the capacity increase signal to the displacement motor capacity control valve 26, or iii) output the speed downshift signal to the speed change valve 16, and output the signal

  capacity increase at displacement motor capacity control valve 26.

  Next, an operation of the movement control device of the hydraulic mobile vehicle according to the present invention will be explained. When an operator switches the forward and reverse travel switch 34 on the forward travel side, the forward and reverse travel switching valve 22 is switched to the forward travel position FK . When the operator depresses the accelerator pedal 23A, the displacement pilot pressure is exerted on the forward travel side pressure receiving part 21F of the displacement control valve 21, and therefore the valve movement control 21 is switched from the neutral position N to the forward movement position F. The forward movement pressure sensor 36 sends the forward movement signal to the control device 30 when its switch

  internal is put into service by the pilot displacement pressure.

  The controller 30 firstly sends a first forward speed signal, which is a speed change signal, to the speed change valve 16, by virtue of the forward movement control signal of the switch forward and reverse 34 and to a speed ratio signal established by a speed ratio lever (not shown), for example, the first gear. The speed change valve 16 sends a pressure signal

  of oil from the first speed forward to the transmission 14 in order to put the transmission 14 in the first gear ratio in forward.

  The displacement control valve 21 delivers the pressurized oil discharged from the displacement pump 12 to a forward displacement side port 13F on the input side of the displacement motor 13 via the pivoting seal of oil pressure 15. The pressurized oil from the forward travel side circuit 46F enters the end portion on the side of the forward travel side position 41F of the balancing valve 41 through l 'Intermediate throttle 44F, so as to switch the balancing valve 41 from the neutral position 41N to the forward travel side position 41F. Oil pressure escaping from a reverse travel side port 13R on the output side of the travel motor 13 enters port A of the balancing valve 41 from the travel side circuit in reverse 46R, and returns to the oil tank 25 via the throttle 41FC, the orifice T, the non-return valve 43, the pressure swivel joint

  oil 15, and the displacement control valve 21.

  The displacement motor 21 then rotates in a direction of displacement in forward motion and drives the transmission 14, so that the work vehicle is

moves forward.

  When the speed of the vehicle increases, and the operator selects the second speed using the gear ratio lever for traveling at high speed, the control device 30 sends a second speed signal in forward direction as of the speed change signal to the speed change valve 16. The speed change valve 16 sends an oil pressure signal of the second speed forward to the transmission 14 so as to put the transmission 14 in the second forward gear. Upon detecting that the vehicle speed becomes high due to a vehicle speed signal from the vehicle speed sensor 31, the controller 30 sends a signal to minimize the capacity of the travel motor 13 at the valve displacement motor capacity control valve 26. The displacement motor capacity control valve 26 actuates the displacement motor capacity control means 13C of

  so as to minimize the capacity of the displacement motor 13.

  It is assumed that the work vehicle is traveling at a high speed, and that, when moving on an uphill road, the operator releases the accelerator pedal 23A and applies the brake (not shown) to stop the work vehicle in the middle of the sloping road. When the brake is released for another movement, the speed ratio of the transmission 14 is that of the second speed, and the capacity of the displacement motor 13 is made minimal. In addition, since the accelerator pedal 23A is not depressed, the pilot displacement pressure does not occur, and the displacement control valve 21 is in the neutral position N, whereby the oil under pressure n is not supplied to the displacement motor 13. Consequently, the displacement motor control valve 41 is in the position

neutral 41N.

  Meanwhile, the controller 30 detects a state in which "the displacement pilot pressure signal produced by depressing the accelerator pedal 23A and detected by the displacement pilot pressure sensor 32" is less than or equal at a predetermined pressure, or, in other words, the accelerator pedal 23A is not depressed. In addition, the controller performs operational processing of the vehicle speed signal, which constitutes the electrical signal detected by the vehicle speed detection sensor 31, so as to calculate the vehicle speed. When, in the state in which the displacement pilot pressure signal is less than or equal to the predetermined pressure and the accelerator pedal 23A is not depressed, an operational processing of the variation over time of the speed of the vehicle is performed, and as a result, the vehicle speed is less than or equal to the predetermined speed (for example, 2 km / h or less) for the predetermined time (for example, for one second), the command 30 determines that the vehicle is stopped. The control device 30 then outputs the downshift signal to the speed control valve 16, and outputs the capacity increase signal, for example the capacity increase signal to maximize the capacity of the engine. displacement 13, at the capacity control valve

displacement motor 26.

  The speed change valve 16 which has received the downshift signal sends the oil pressure signal from the first gear to the transmission 14 to downshift the transmission 14 to the first gear ratio. The displacement motor capacity control valve 26 which has received the capacity increase signal actuates the displacement motor capacity control means 13 to maximize the capacity of the motor

displacement 13.

  The work vehicle tries to slide down on the sloping road, which causes its wheels to be driven, and therefore, the displacement motor 13 is driven in the opposite direction via the transmission 14. However, the reduction ratio of the transmission 14 is increased because of the downshift, and in this case it is maximized because the transmission 14 is put in the first gear ratio. Therefore, the reverse drive force of the wheels is reduced by the reduction ratio of the trans5 mission 14, and the capacity of the displacement motor 13 is maximized, whereby the rotational speed of the displacement motor is in a lower range. In addition, due to the drive in the opposite direction, the oil pressure from the displacement motor 13 passes through the displacement motor throttle valve 41C in the neutral position 41N of the balancing valve 41 connecting the side. input and output side of the displacement motor 13. Consequently, a loss of pressure in the oil pressure occurs, which increases the resistance to rotation caused by the reverse drive, and therefore the reverse rotation speed of the displacement motor 13 can be maintained in a lower range. Consequently, the reverse drive force of the traveling motor 13, which is caused by the fact that the working vehicle slides down on the sloping road, becomes maximum, and undergoes significant resistance, and, through

  Therefore, the downward sliding speed of the work vehicle can be maintained at a sufficiently low speed.

  When determining that the accelerator pedal 23A is not depressed and that the work vehicle is stopped, the control device 30 can only output the downshift signal to the speed change valve 16. In this case, the reduction ratio of the transmission is maximized, even if the wheels try to produce a drive in the opposite direction because the work vehicle tries to slide down on the sloping road, and, therefore, the reverse drive force of the wheels is reduced by the reduction ratio of the transmission, and the reverse drive force of the traveling motor is reduced. Therefore, the rotational speed of the displacement motor decreases, and therefore, the downward sliding speed can be maintained in a lower range. In addition, the control device 30 can output only the capacity increase signal to the displacement motor capacity control valve 26. Also, in this case, the wheels try to produce a drive in the opposite direction because as the work vehicle attempts to slide down on the sloping road, but, as the capacity of the displacement motor 13 is maximized, the displacement motor 13 only rotates at a low speed of rotation, and, by moreover, the resistance to rotation inside the displacement motor 13 increases, thanks to

  what the downward sliding speed can be kept in a lower range.

  When determining that the work vehicle is stopped without determining that the accelerator pedal 23A is not depressed, the control device 30 i) can output only the downshift signal to the valve. gear change 16, ii) can output only the capacity increase signal to the displacement motor capacity control valve 26, or iii) can output the downshift signal to the gear change valve speed 16 and output the capacity increase signal to the displacement motor capacity control valve 26. In all cases, it is possible to obtain the

same effects as above.

  Furthermore, an explanation is made with the transmission 14 comprising two speed reports, the first and second speed reports, by way of example,

  but a transmission comprising three life reports

  tesse, the first, second and third gear ratios, or a transmission having a plurality of gear ratios greater than this, for example a transmission with four gear ratios, further comprising the fourth gear ratio, or a transmission with five speed ratios, further comprising the fifth speed ratio, is also usable. The previously mentioned downshift, carried out when it is determined that the work vehicle is stopped, can be a downshift from the gear ratio to the current state of a gear ratio (for example, from third gear to second gear ), or can be a direct downshift from third gear to first gear,

  in which the maximum reduction ratio is obtained.

  The hydraulic mobile vehicle can be a vehicle without an upper rotating superstructure, and the present invention can also be applied, for example, to a wheel loader, a forklift, or other work vehicles. Furthermore, when the movement control device according to the present invention is applied to the vehicle without the upper rotating superstructure, it is appropriate to remove the swivel joint from

oil pressure 15.

Claims (6)

  1. Movement control device for a mobile hydraulic vehicle, comprising a hydraulic displacement motor (13) and a transmission (14) whose speed port rap5 can be fixed, characterized in that it comprises: speed change control means (16) of said transmission (14); vehicle speed detection means (31) for detecting a vehicle speed of said hydraulic mobile vehicle; and a controller (30) which sends a downshift signal to said gear change control means so as to downshift the said transmission (14) when it is determined by the   vehicle speed detected that said hydraulic hydraulic mobile vehicle is almost stopped.   2. A displacement control device for a mobile hydraulic vehicle, comprising a hydraulic displacement displacement motor (13), characterized in that it comprises: motor capacity control means (13C) of said volumetric displacement hydraulic motor (13C) 13); vehicle speed detection means (31) for detecting a vehicle speed of said hydraulic mobile vehicle; and a controller (30) which sends a capacity increase signal to said motor capacity control means (13C) to increase a capacity of said   volumetric displacement hydraulic motor (13) when it is determined from the detected vehicle speed that said hydraulic mobile vehicle is almost stopped.   3. Movement control device for a hydraulic mobile vehicle, comprising a hydraulic displacement displacement motor (13) and a transmission (14) whose speed ratio can be fixed, characterized in that it comprises : speed change control means (16) of said transmission (14); motor capacity control means (13C) of said hydraulic displacement motor (13); vehicle speed detecting means (31) for detecting a vehicle speed of said hydraulic motor vehicle; and a controller (30) which sends a downshift signal to said shift control means to cause a downshift to be effected on said transmission (14), and which sends a capacity increase signal to said shift control means motor capacity (13C) so as to increase a capacity of said hydraulic displacement motor (13) when it is   determined by the detected vehicle speed that said hydraulic mobile vehicle is almost stopped.   4. Movement control device for a hydraulic mobile vehicle according to any one of claims 1 to 3, characterized in that:   displacement motor throttle valves are disposed in a circuit connecting an input side and an output side of said hydraulic displacement motor (13) when said hydraulic displacement motor (13) is driven by the rotation of the wheels of said vehicle hydraulic mobile.   5. A movement control device for a mobile hydraulic vehicle according to any one of claims 1 to 4, characterized in that:   said control device (30) determines that said hydraulic mobile vehicle is almost stopped when the detected vehicle speed is less than or equal to a   predetermined speed for a predetermined time.   6. Movement control device for a hydraulic mobile vehicle according to any one of claims 1 to 5, characterized in that:   said control device (30) determines that said hydraulic mobile vehicle is almost stopped also by detecting that an accelerator pedal (23A) is not pressed. i