JP6033627B2 - Hydraulic drive carrier - Google Patents

Description

  The present invention relates to a hydraulically driven transport vehicle that rotates a wheel by circulating pressure oil between a variable displacement hydraulic pump and a swash plate type hydraulic motor, and in particular, only a braking force when an engine brake is operated depending on the situation. The present invention relates to a hydraulically driven transport vehicle that can accurately decelerate or stop.

  There is a hydraulically driven transport vehicle as one of the carriers that transport heavy objects such as coils and large steel materials mainly in steelworks and shipyards. Some of these hydraulically driven transport vehicles are equipped with a power transmission device called “HST (hydrostatic transmission)”. For example, a transport vehicle using a power transmission device such as a propeller shaft transmits power by mechanical operation. On the other hand, in a hydraulically driven transport vehicle using “HST”, power can be transmitted by supplying and discharging pressure oil flowing in the pipe. Therefore, in the hydraulically driven transport vehicle using “HST”, the number of components for mechanically transmitting power can be reduced, and the arrangement space for engine equipment and the like is excellent. An example of such a hydraulically driven transport vehicle is described in Patent Document 1 below.

  As shown in FIG. 11, a hydraulically driven transport vehicle described in Patent Document 1 below includes a variable displacement hydraulic pump 110 and a hydraulic motor 120 to which pressure oil is supplied from the hydraulic pump 110. The hydraulic pump 110 and the hydraulic motor 120 are connected by a closed circuit 160 including a pair of a feed side pipe 161 and a return side pipe 162. For this reason, when the hydraulic pump 110 is driven by the power of the engine EG to discharge the pressure oil, the hydraulic motor 120 rotates with the pressure oil supplied. As a result, the rotation of the output shaft 120a of the hydraulic motor 120 is transmitted to the wheel 105 via the differential device 190 and the axle 191, and the wheel 105 is rotationally driven.

  Here, a case where the accelerator input amount is decreased in “HST” will be described. When the foot is released from the accelerator pedal to decelerate or stop, the hydraulic pump 110 does not discharge pressure oil to the feed pipe 161, whereas the hydraulic motor 120 connected to the axle 191 rotates due to the inertia of the vehicle body. It is driven to operate like a hydraulic pump and discharges pressure oil to the return side pipe 162. For this reason, the hydraulic pump 110 operates and rotates like a hydraulic motor by the pressure oil supplied from the return side pipe 162, and the driving force that rotates like this hydraulic motor generates a rotational force for the engine EG. give. As a result, a load of rotational resistance is applied to the engine EG, and engine braking occurs.

  In such an engine brake operation, in Patent Document 1 below, control is performed so as to obtain a large braking force. That is, when the accelerator input amount is decreased, the controller 150 performs control so that the motor capacity of the hydraulic motor 120 increases. Here, the motor capacity of the hydraulic motor 120 and the rotational speed of the hydraulic pump 110 are in a proportional relationship, and the rotational speed of the hydraulic pump 110 increases as the motor capacity increases. As a result, as the rotational speed of the hydraulic pump 110 increases, the rotational speed of the engine EG also increases, and a large resistance load acts on the rotation of the engine EG. Thus, in Patent Document 1 described below, a large braking force as an engine brake can be obtained by controlling the motor capacity of the hydraulic motor to be large.

JP 2011-189917 A

  However, the prior art has the following problems. In a hydraulically driven transport vehicle, the braking force obtained by the brake operation is set to a large value for emergency stop, and the start-up may suddenly increase, making fine adjustment difficult. In particular, when a hydraulically driven transport vehicle loads a heavy load of several tens to several hundreds of tons, the braking force obtained by the brake operation causes a sudden forward load to act on the load and balance the load. Otherwise, the load may fall. For this reason, it is desirable to be able to decelerate or stop accurately only with the braking force at the time of engine braking operation, without operating the brake.

  However, in the hydraulically driven transport vehicle of Patent Document 1 described above, the hydraulic motor is reduced due to a decrease in the accelerator input amount even in a situation where a curve is made at a very low speed or a large braking force such as a long distance traveling on a flat road is not required. Therefore, a large braking force as an engine brake is obtained. Therefore, there is a problem that it is difficult to accurately decelerate or stop only with the braking force when the engine brake is operated depending on the situation. Furthermore, the above-mentioned patent document 1 does not describe a specific configuration for controlling the motor capacity of the hydraulic motor to increase, and whether or not the motor capacity of the hydraulic motor can be increased by a simple configuration change. It was not clear.

  Therefore, the present invention can increase (change) the motor capacity of the hydraulic motor with a simple configuration change in order to solve the above-described problems, and can appropriately decelerate or stop only with the braking force when the engine brake is operated depending on the situation. An object of the present invention is to provide a hydraulically driven transport vehicle that can perform the above-described operation.

  A hydraulically driven transport vehicle according to the present invention includes a variable displacement hydraulic pump capable of supplying and discharging pressure oil, a swash plate type hydraulic motor that rotates a wheel by the pressure oil supplied from the hydraulic pump, and the hydraulic pump. A first oil passage and a second oil passage for circulating pressure oil to and from the swash plate hydraulic motor; a swash plate tilt mechanism for tilting the swash plate of the swash plate hydraulic motor by the supplied pressure oil; A first control oil passage for branching from one oil passage to supply pressure oil to the swash plate tilt mechanism; and a first control oil passage for branching from the second oil passage to supply pressure oil to the swash plate tilt mechanism. The communication state between the two control oil passages and the first control oil passage is ensured and the communication state between the second control oil passages is released, or the communication state between the first control oil passages is released and the second control oil passage is released. An electromagnetic switching valve that ensures the communication state of the oil passage and the first control during forward acceleration A control device that controls the electromagnetic switching valve so as to ensure the communication state of the road and release the communication state of the second control oil path, and can select a weak brake state or a strong brake state When the accelerator input amount is decreased and the selection unit is selected to be in a weak brake state, the control device ensures the communication state of the first control oil passage and When the electromagnetic switching valve is controlled to release the communication state of the second control oil passage, and the selection portion is selected to be in the strong brake state, the communication state of the first control oil passage is released and the first control oil passage is released. (2) The electromagnetic switching valve is controlled so as to ensure the communication state of the control oil passage.

  According to the hydraulically driven transport vehicle according to the present invention, for example, when traveling forward on a downhill with a heavy object mounted, the driver selects the “strong braking state” at the selection unit. When the driver operates to reduce the accelerator input amount, the electromagnetic switching valve is controlled to release the communication state of the first control oil passage and to secure the communication state of the second control oil passage. . As a result, the pressure oil in a high pressure state in the second oil passage is sent to the swash plate tilting mechanism via the second control oil passage, and the output torque of the swash plate type hydraulic motor is increased. That is, the engine brake can be operated in a “slow gear state” where the swash plate angle of the swash plate hydraulic motor is large. As a result, a large braking force can be obtained as an engine brake, and even in a situation where the vehicle is traveling forward on a downhill with a heavy load mounted, the braking can be accurately and quickly reduced only with the braking force when the engine brake is operated. Or you can stop.

  On the other hand, for example, when turning a curve at a very low speed or when moving on a flat road for a long distance, the driver selects the “weak brake state” at the selection unit. At this time, when the driver operates to decrease the accelerator input amount, the electromagnetic switching valve is controlled to ensure the communication state of the first control oil passage and to release the communication state of the second control oil passage. . As a result, the pressure oil in the low pressure state in the first oil passage is sent to the swash plate tilting mechanism via the first control oil passage, and the output torque of the swash plate type hydraulic motor is reduced. That is, the engine brake can be operated in a “high speed gear state” where the swash plate angle of the swash plate hydraulic motor is small. As a result, in a situation where a large braking force is not required as an engine brake, a braking force that is relatively small and easy to control can be obtained when the engine brake is operated.

  According to the present invention, an electromagnetic switching valve is provided so that a selector is newly provided to the conventional structure so that pressure oil that is in a high pressure state in the second oil passage is sent to the swash plate tilt mechanism when the engine brake is operated. It can be configured by controlling. Therefore, the hydraulically driven transport vehicle according to the present invention can increase (change) the motor capacity of the swash plate type hydraulic motor with a simple configuration change, and decelerate or stop accurately only with the braking force at the time of engine brake operation according to the situation. be able to.

(A) It is a top view of the hydraulic drive conveyance vehicle of this embodiment. (B) It is a side view of a hydraulic drive conveyance vehicle. It is the schematic which showed the power transmission device of the hydraulic drive conveyance vehicle. It is the figure which showed the state of the hydraulic circuit at the time of forward acceleration. It is the figure which showed the state of the hydraulic circuit at the time of reverse acceleration. It is the figure which showed the state of the hydraulic circuit at the time of the engine brake action | operation at the time of a forward drive conventionally. It is the figure which showed the state of the hydraulic circuit at the time of the engine brake action | operation of a strong brake state. It is the figure which showed the state of the hydraulic circuit at the time of engine brake action | operation of a weak brake state. (A) It is the time chart which showed the oil_pressure | hydraulic of sending side piping. (B) It is a time chart which showed the oil pressure of return side piping. (C) It is the time chart which showed the accelerator input amount. (A) It is the time chart which showed the engine speed. (B) It is the time chart which showed the vehicle speed. It is the schematic which showed the power transmission device of the hydraulic drive conveyance vehicle of deformation | transformation embodiment. It is the schematic which showed the power transmission device of the hydraulic drive conveyance vehicle of a prior art.

  A hydraulically driven transport vehicle according to the present invention will be described below with reference to the drawings. FIG. 1A is a plan view of the hydraulically driven transport vehicle 1 of the present embodiment, and FIG. 1B is a side view of the hydraulically driven transport vehicle 1.

  The hydraulically driven transport vehicle 1 is a carrier that transports heavy objects such as coils and large steel materials mainly in steelworks and shipyards. As shown in FIGS. 1 (A) and 1 (B), the hydraulically driven transport vehicle 1 includes a load platform 2 on which a conveyed product is loaded, and a plurality of load platforms 2 that support the load platform 2 via a suspension bracket 3 and a swing arm 4. The wheel 5 is provided. Further, as shown in FIG. 1B, the loading platform 2 and the swing arm 4 are connected by a hydraulic cylinder 6, and the loading platform 2 can be moved up and down by expansion and contraction of the hydraulic cylinder 6.

  The hydraulically driven transport vehicle 1 has a first cab 7F and a second cab 7R at both ends in the traveling direction. Each cab 7F, 7R has a handle (not shown), an accelerator, respectively. A pedal 8 (see FIG. 2), a brake pedal (not shown), and a forward / reverse selector switch 9 (see FIG. 2) are provided. For this reason, the driver operates the steering wheel, the accelerator pedal 8, the brake pedal, and the forward / reverse switching switch 9 in both the first cab 7F and the second cab 7R, thereby providing a hydraulically driven carrier vehicle. 1 can be steered, accelerated forward and backward, and decelerated and stopped.

  The hydraulically driven transport vehicle 1 includes a power transmission device called “HST (hydrostatic transmission)” so that the power of the engine EG (see FIG. 2) is transmitted to the wheels 5 through the power transmission device. It has become. Here, FIG. 2 is a schematic diagram showing the power transmission device TR of the hydraulically driven transport vehicle 1. As shown in FIG. 2, the power transmission device TR mainly includes a variable displacement hydraulic pump 10, a swash plate hydraulic motor 20, a swash plate tilt mechanism 30, an electromagnetic switching valve 40, and a control device 50. It is configured.

  The hydraulic pump 10 discharges pressure oil toward the swash plate type hydraulic motor 20 and is driven by the rotation of the drive motor 11. The drive motor 11 is connected to the engine EG and can rotate the hydraulic pump 10 forward or backward using the power of the engine EG. Then, by changing the discharge amount of the hydraulic pump 10, the rotational speed of the engine EG can be changed steplessly.

  The hydraulic pump 10 and the swash plate type hydraulic motor 20 are connected in communication by a closed circuit 60 including a feed side pipe (first oil path) 61 and a return side pipe (second oil path) 62, and the pressure oil is The closed circuit 60 is circulated. When the vehicle moves forward, the hydraulic pump 10 discharges pressure oil toward the feed side pipe 61, and the discharged pressure oil returns to the return side pipe 62 by driving the swash plate hydraulic motor 20 to rotate. . On the other hand, when the vehicle travels backward, the hydraulic pump 10 discharges pressure oil toward the return side pipe 62, and the discharged pressure oil returns through the feed side pipe 61 by driving the swash plate hydraulic motor 20 to rotate. .

  The swash plate type hydraulic motor 20 drives the wheel 5 to rotate, and the output shaft 20a is connected to the wheel 5 via a differential device, an axle, or the like (not shown). The swash plate type hydraulic motor 20 changes the motor capacity, that is, the output torque depending on the angle of the swash plate 20b. For this reason, if the angle of the swash plate 20b is small, the motor capacity is reduced, the output shaft 20a is driven at an increased speed, and the output torque is reduced. On the other hand, when the angle of the swash plate is large, the motor capacity is increased, the output shaft 20a is driven at a reduced speed, and the output torque is increased. Here, in this embodiment, a state where the angle of the swash plate 20b is small and the output torque is small is referred to as “temporary high-speed gear state”, and a state where the angle of the swash plate 20b is large and the output torque is large is referred to as “temporary low-speed gear state”. It will be called "gear state".

  The swash plate tilting mechanism 30 tilts the swash plate 20b of the swash plate type hydraulic motor 20. In the swash plate tilting mechanism 30, the angle of the swash plate 20b is changed by the expansion and contraction of the control piston 31, and the control piston 31 has a direction in which the angle of the swash plate 20b decreases by the return spring 32 (left side in FIG. 2). Is being energized. When the control piston 31 extends to the right in FIG. 2 against the urging force of the return spring 32 according to the hydraulic pressure of the pressure oil supplied to the control port SP, the angle of the swash plate 20b increases.

  The electromagnetic switching valve 40 switches between the case where the pressure oil in the feed side pipe 61 is sent to the control port SP and the case where the pressure oil in the return side pipe 62 is sent to the control port SP. The electromagnetic switching valve 40 is a three-port valve, and has a first input port EP1, a second input port EP2, and an output port OP. The first input port EP1 and the branch portion 61a of the feed side pipe 61 are connected in communication by the first branch pipe 71, and the second input port EP2 and the branch portion 62a of the return side pipe 62 are connected to the second branch pipe. 72 is connected in communication. Further, the output port OP and the control port SP are connected in communication by a control pipe 73.

  Thus, as shown in FIG. 2, the electromagnetic switching valve 40 secures the communication state between the first input port EP1 and the output port OP when the solenoid is not energized, while the second input port EP2 Release the communication state of the output port OP. As a result, the pressure oil in the feed side pipe 61 is sent to the control port SP via the first branch pipe 71, the electromagnetic switching valve 40, and the control pipe 73.

  On the other hand, when the solenoid is energized, the electromagnetic switching valve 40 releases the communication state between the first input port EP1 and the output port OP, while ensuring the communication state between the second input port EP2 and the output port OP. (See FIG. 4). Thereby, the pressure oil in the return side pipe 62 is sent to the control port SP via the second branch pipe 72, the electromagnetic switching valve 40 and the control pipe 73. Here, the first branch pipe 71 and the control pipe 73 of the present embodiment correspond to the first control oil path of the present invention, and the second branch pipe 72 and the control pipe 73 of the present embodiment are the main control oil paths. This corresponds to the second control oil passage of the invention.

  The control device 50 controls switching of the electromagnetic switching valve 40, and can supply a control signal (driving current) c1 to the solenoid of the electromagnetic switching valve 40. And the control apparatus 50 inputs the forward side signal f1 or the reverse side signal r1 from the forward / reverse selector switch 9. The forward / reverse selector switch 9 is for the driver to arbitrarily select forward or reverse of the vehicle, and outputs a forward signal f1 when selected to the front side, and when selected to the rear side. A reverse side signal r1 is output. Thus, the control device 50 does not supply the control signal c1 to the solenoid of the electromagnetic switching valve 40 when the forward signal f1 is input, and the control signal to the solenoid of the electromagnetic switching valve 40 when the reverse signal r1 is input. c1 is supplied.

  Next, in the power transmission device TR configured as described above, the state of the hydraulic circuit during traveling will be described with reference to FIGS. FIG. 3 is a diagram illustrating the state of the hydraulic circuit during forward acceleration, and FIG. 4 is a diagram illustrating the state of the hydraulic circuit during reverse acceleration. FIG. 5 is a diagram showing a state of a hydraulic circuit when the engine brake is operated during forward travel. Here, in FIGS. 3 to 5, a thick line indicates that the hydraulic pressure is high, and a thin line indicates that the hydraulic pressure is low.

<For forward acceleration>
As shown in FIG. 3, the hydraulic pump 10 discharges the pressure oil toward the feed side pipe 61, so that the hydraulic pressure is increased in the feed side pipe 61. Then, the pressure oil is supplied to the swash plate type hydraulic motor 20, and the swash plate type hydraulic motor 20 is rotated forward so that the wheels 5 move forward. Thus, since the flowing pressure oil works in the swash plate type hydraulic motor 20, the hydraulic pressure is low in the return side pipe 62.

  During the forward acceleration, the control device 50 does not output the control signal c1 to the electromagnetic switching valve 40, and the electromagnetic switching valve 40 ensures the communication state between the first input port EP1 and the output port OP. For this reason, the pressure oil in the high pressure state in the feed side pipe 61 is sent to the control port SP via the first branch pipe 71, the electromagnetic switching valve 40 and the control pipe 73, and the angle of the swash plate 20b is controlled. It is increased by the extension of the piston 31. Thus, the motor capacity of the swash plate hydraulic motor 20 is increased, and the vehicle can move forward in the “temporary low-speed gear state” in which the output torque is large. Therefore, when traveling with a heavy load of several tens to hundreds of tons, or when traveling uphill, the vehicle can travel with increased output torque.

<During reverse acceleration>
As shown in FIG. 4, since the hydraulic pump 10 discharges the pressure oil toward the return side pipe 62, the hydraulic pressure is increased in the return side pipe 62. Then, the pressure oil is supplied to the swash plate type hydraulic motor 20, and the swash plate type hydraulic motor 20 rotates in reverse so that the wheels 5 are rotated backward. Thus, since the flowing pressure oil works in the swash plate type hydraulic motor 20, the hydraulic pressure is low in the feed side pipe 61.

  During the reverse acceleration, the control device 50 outputs a control signal c1 to the electromagnetic switching valve 40, and the electromagnetic switching valve 40 ensures the communication state between the second input port EP2 and the output port OP. For this reason, the pressure oil in a high pressure state in the return side pipe 62 is sent to the control port SP via the second branch pipe 72, the electromagnetic switching valve 40 and the control pipe 73, and the angle of the swash plate 20b is controlled. It is increased by the extension of the piston 31. Thus, the motor capacity of the swash plate hydraulic motor 20 is increased, and the vehicle can be moved backward in a “temporary low speed gear state” in which the output torque is large.

<Conventionally, when the engine brake is operated during forward travel>
As shown in FIG. 5, when the accelerator pedal 8 is operated so as to reduce the accelerator input amount, the hydraulic pump 10 stops discharging little or no pressure oil toward the feed side pipe 61, and the feed side pipe 61 has a hydraulic pressure. Lower. On the other hand, the swash plate type hydraulic motor 20 connected to the axle or the like is driven to rotate by the inertia of the vehicle body, operates like a hydraulic pump, and discharges pressure oil toward the return side pipe 62. As a result, the hydraulic pressure is low in the feed side pipe 61, but the hydraulic pressure is high in the return side pipe 62. Thus, the hydraulic pump 10 operates and rotates like a hydraulic motor by the pressure oil supplied from the return side pipe 62, and the driving force that rotates like this hydraulic motor gives the engine EG rotational force. . As a result, a load of rotational resistance is applied to the engine EG, and engine braking occurs.

  Conventionally, when the engine brake is operated, the control device 50 maintains a state in which the control signal c1 is not output. Therefore, the electromagnetic switching valve 40 ensures a communication state between the first input port EP1 and the output port OP. . For this reason, the pressure oil in the low pressure state in the feed side pipe 61 is sent to the control port SP, and the angle of the swash plate 20 b is reduced by the contraction of the control piston 31. Thus, the braking force as the engine brake can be obtained in the “temporary high speed gear state” in which the motor capacity of the swash plate type hydraulic motor 20 is reduced and the output torque is small.

  Here, the braking force as the engine brake obtained in the “temporary high-speed gear state” was relatively small. This is because the motor capacity is reduced in the “temporary high-speed gear state”, so that the change in the engine speed is small when the engine brake is operated, and a relatively small resistance load acts on the rotation of the engine EG. For this reason, for example, in a situation where the vehicle travels on a downhill with a heavy load loaded thereon, there is a possibility that the vehicle cannot be accurately decelerated or stopped only by the braking force when the engine brake is operated.

  On the other hand, even if the motor capacity is increased as in the prior art so that the braking force as the engine brake can be obtained in the “temporary low speed gear state”, there are the following problems. That is, in the “temporary low gear state”, the engine speed changes greatly when the engine brake is operated, and a large resistance load acts on the rotation of the engine EG, so that a large braking force is obtained as an engine brake. However, for example, even in a situation where a curve is turned at a very low speed or a situation where a large braking force such as a long distance on a flat road is not required, a large braking force can be obtained by reducing the accelerator input amount. It should be noted that the braking force obtained by the brake operation is set to a large value for emergency stop and is difficult to finely adjust. Therefore, it is desirable to decelerate or stop only with the engine brake.

  Therefore, the inventor has devised a configuration in which the braking force as the engine brake can be adjusted according to the driver's selection and can be accurately decelerated or stopped only by the braking force when the engine brake is operated depending on the situation. And the structure has the characteristics in the point which can solve the above-mentioned problem by simple change, utilizing the conventional structure. Hereinafter, the configuration will be described.

  As shown in FIG. 2, in the present embodiment, a selection switch (selection unit) 80 for allowing the driver to arbitrarily select a “weak brake state” or a “strong brake state” is newly added to the conventional structure. Is provided. The selection switch 80 outputs an on signal to the control device 50 when the driver selects the “strong brake state”, and outputs an off signal to the control device 50 when the driver selects the “weak brake state”. It is like that. The configuration of the selection switch 80 can be changed as appropriate, such as a button type, a lever type, or a contact type incorporated in the touch panel.

  The control device 50 sequentially inputs an on signal or an off signal from the selection switch 80 and also inputs an accelerator input amount a1 from the accelerator amount detection sensor 81 (for example, every 5 msec). The accelerator amount detection sensor 81 detects an accelerator input amount a1 that is the amount by which the accelerator pedal 8 is depressed. Then, when the on-signal is input when the control device 50 moves forward (when the forward-side signal f1 is input from the forward / reverse selector switch 9) and when the accelerator input amount a1 is decreased, the control device 50 controls the electromagnetic switching valve 40. When the c1 is output and the off signal is input, the control signal c1 is not output to the electromagnetic switching valve 40.

  In the power transmission device TR of the present embodiment configured as described above, the state of the hydraulic circuit at the time of forward movement and when the engine brake is operated will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing a state of the hydraulic circuit when the engine brake is operated in the strong brake state, and FIG. 7 is a diagram showing a state of the hydraulic circuit when the engine brake is operated in the weak brake state. 6 and 7, the thick line indicates that the hydraulic pressure is high, and the thin line indicates that the hydraulic pressure is low.

<When the engine brake is operating in the strong brake state>
In a situation where a large braking force is required as an engine brake, such as a situation where the vehicle is traveling on a downhill with a heavy load loaded, as shown in FIG. select. When the driver operates the accelerator pedal 8 so that the accelerator input amount a1 decreases, the control device 50 outputs a control signal c1 to the electromagnetic switching valve 40. Thereby, the electromagnetic switching valve 40 ensures the communication state of 2nd input port EP2 and output port OP.

  Here, when the engine brake is operated, the hydraulic pressure is increased in the return side pipe 62 and the hydraulic pressure is reduced in the feed side pipe 61 as described above. For this reason, in this embodiment, the high pressure oil in the return side pipe 62 is used, and the high pressure oil is sent to the control port SP via the electromagnetic switching valve 40. As a result, the angle of the swash plate 20b can be increased, and a “temporary low-speed gear state” with a large motor capacity can be achieved. As a result, the engine speed changes greatly when the engine brake is operated, and a large braking force can be obtained as an engine brake.

<When the engine brake is operating in a weak brake state>
On the other hand, in a situation where a curve is made at a very low speed, or a situation where a relatively small braking force is sufficient as an engine brake, such as a situation where the vehicle travels a long distance on a flat road, the driver selects as shown in FIG. The switch 80 selects “weak brake state”. At this time, even if the driver operates the accelerator pedal 8 so that the accelerator input amount a <b> 1 decreases, the control device 50 does not output the control signal c <b> 1 to the electromagnetic switching valve 40. For this reason, the electromagnetic switching valve 40 ensures the communication state of the first input port EP1 and the output port OP.

  Therefore, as in the conventional case (see FIG. 5), in this case, the low pressure oil in the feed side pipe 61 is fed into the control port SP. As a result, the angle of the swash plate 20b is reduced and the motor capacity is reduced to a “temporary high speed state”. As a result, the engine speed changes little when the engine brake is operated, and a relatively small braking force can be obtained as an engine brake.

  Next, a case where the vehicle is stopped by the engine brake in the weak brake state and a case where the vehicle is stopped by the engine brake in the strong brake state during the forward movement will be described with reference to FIGS. 8 and 9. FIG. 8A is a time chart showing the hydraulic pressure of the feed-side piping 61, and FIG. 8B is a time chart showing the hydraulic pressure of the return-side piping 62. FIG. 8C is a time chart showing the accelerator input amount a1. FIG. 9A is a time chart showing the engine speed, and FIG. 9B is a time chart showing the vehicle speed. The time from time A to time E is about 10 seconds.

  As shown in FIG. 8 (C), when the accelerator input amount a1 is increased from 0 to x1 at time A, as shown in FIG. 8 (A), the hydraulic pressure of the feed side pipe 61 increases from time A, As shown in FIG. 9A, the engine speed increases from the idling speed (about 500 rpm). Then, as shown in FIG. 9B, the vehicle speed of the hydraulically driven transport vehicle 1 increases from 0 and accelerates forward from time B. Thus, during forward acceleration, the pressure oil in the feed side pipe 61 is in a high pressure state (see FIG. 8A), whereas the pressure oil in the return side pipe 62 is in a low pressure state (FIG. 8B). See).

  As shown in FIG. 8 (C), since the accelerator input amount a1 is maintained at x1 from the time A to the time D, the engine speed is about 2000 rpm at the time C as shown in FIG. 9 (A). A state of reaching about 2000 rpm is maintained until time D. As shown in FIG. 9B, in order to adjust the vehicle speed to about 20 km / h, as shown in FIG. 8C, the accelerator input amount a1 is slightly decreased from x1 to x2 at the time D. Thus, as shown in FIG. 9A, the engine speed is slightly reduced from about 2000 rpm.

  Thus, after traveling at a constant speed from the point D, as shown in FIG. 8C, when the accelerator input amount a1 is decreased from x2 to 0 at the point E, as shown in FIG. As shown in FIG. 8B, the hydraulic pressure of the return side pipe 62 increases greatly from the time point E. Therefore, in the present embodiment, the pressure oil in the return side pipe 62 becomes a high pressure state when the accelerator input amount a1 is reduced (see the Y portion in FIG. 8B). The pressure oil in the state is sent to the control port SP through the electromagnetic switching valve 40. As a result, the motor capacity of the swash plate hydraulic motor 20 is increased to obtain a large braking force as an engine brake.

  That is, in FIG. 9 (A) and FIG. 9 (B), after time E, the thin solid line sends the pressure oil in the low pressure state in the feed side pipe 61 to the control port SP, and the braking force as a small engine brake. The thin broken line shows the case where the high pressure oil in the return side pipe 62 is sent to the control port SP to obtain a large braking force as an engine brake. As is apparent from FIGS. 9A and 9B, the broken line indicates that the degree of decrease in the engine speed and the decrease in the vehicle speed are large compared to the solid line. Thus, in this embodiment, the driver can easily change the braking force as the engine brake by switching the “weak brake state” and the “strong brake state” with the selection switch 80.

The effects of the hydraulically driven transport vehicle 1 of this embodiment will be described.
When traveling forward on a downhill with a heavy object mounted, the driver selects the “strong braking state” with the selection switch 80. When the driver operates to decrease the accelerator input amount a1, as shown in FIG. 6, the control device 50 outputs a control signal c1 to the electromagnetic switching valve 40, and the electromagnetic switching valve 40 is connected to the second input port. The communication state between EP2 and the output port OP is secured. As a result, the pressure oil in the high pressure state in the return side pipe 62 is sent to the control port SP, and the engine brake can be operated in the “temporary low speed gear state” in which the angle of the swash plate 20b is large. As a result, a large braking force can be obtained as an engine brake, and even in a situation where the vehicle is traveling forward on a downhill with a heavy load mounted, the braking can be accurately and quickly reduced only with the braking force when the engine brake is operated. Or you can stop.

  On the other hand, when turning a curve at a low speed or when moving on a flat road for a long distance, the driver selects the “weak brake state” with the selection switch 80. At this time, if the driver operates to decrease the accelerator input amount a1, the control device 50 does not output the control signal c1 to the electromagnetic switching valve 40 as shown in FIG. A communication state between the port EP1 and the output port OP is secured. Thereby, the pressure oil in the low pressure state in the feed side pipe 61 is sent to the control port SP, and the engine brake can be operated in the “temporary high speed gear state” in which the angle of the swash plate 20b is small. As a result, in a situation where a large braking force is not required as an engine brake, a braking force that is relatively small and easy to control can be obtained when the engine brake is operated.

  Furthermore, according to the hydraulically driven transport vehicle 1 of the present embodiment, a selection switch 80 is newly provided with respect to the conventional structure, and the pressure oil in the high-pressure state in the return side pipe 62 is controlled when the engine brake is operated. It can be configured by controlling the electromagnetic switching valve 40 so as to send it to the SP. Accordingly, the hydraulically driven transport vehicle 1 can increase (change) the motor capacity of the swash plate hydraulic motor 20 with a simple configuration change, and can accurately decelerate or stop only with the braking force when the engine brake is operated depending on the situation. Can do.

  Next, a modified embodiment will be described with reference to FIG. FIG. 10 is a schematic view showing a power transmission device TR1 of a hydraulically driven transport vehicle according to a modified embodiment. As shown in FIG. 10, in this modified embodiment, unlike the above-described embodiment (see FIG. 2), the power transmission device TR1 is a first electromagnetic switching valve 41 and a second electromagnetic switching valve that are two electromagnetic switching valves. 42. The first electromagnetic switching valve 41 and the second electromagnetic switching valve 42 are two-port valves, the first electromagnetic switching valve 41 has a first input port EP1 and a first output port OP1, and the second electromagnetic switching valve 42 is It has a second input port EP2 and a second output port OP2.

  The first output port OP1 and the first control port SP1 are connected in communication by the first control pipe 74, and the second output port OP2 and the second control port SP2 are connected to the second control pipe 74. 75 is connected in communication. In the modified embodiment, the first branch pipe 71 and the first control pipe 74 correspond to the first control oil passage of the present invention, and the second branch pipe 72 and the second control pipe 75 of the present invention. This corresponds to the second control oil passage.

  The control device 50 does not output the first control signal (driving current) d1 to the first electromagnetic switching valve 41 when the “weak brake state” is selected by the selection switch 80, whereas the second electromagnetic switching valve 42 Is configured to output a second control signal (drive current) d2. Thus, when the driver selects the “weak brake state”, the communication state between the first branch pipe 71 and the first control pipe 74 is ensured when the engine brake is operated, whereas the second branch pipe 72 is secured. As a result, the communication state of the second control pipe 75 is cut off.

  On the other hand, the control device 50 outputs the first control signal d1 to the first electromagnetic switching valve 41 when the “strong braking state” is selected by the selection switch 80, while the second electromagnetic switching valve 42 2 is configured not to output the control signal d2. Thus, when the driver selects the “strong brake state”, the communication state between the first branch pipe 71 and the first control pipe 74 is cut off when the engine brake is operated, whereas the second branch pipe 72 is cut off. As a result, the communication state of the second control pipe 75 is ensured.

  Since other configurations of the modified embodiment are the same as the configurations of the above-described embodiment, the description thereof is omitted. Moreover, since the effect of modification embodiment is the same as the effect of embodiment mentioned above, the description is abbreviate | omitted.

Although the hydraulic drive vehicle according to the present invention has been described above, the present invention is not limited to this, and various modifications can be made without departing from the spirit of the present invention.
In the present embodiment and its modified embodiments, the power transmission devices TR and TR1, which are “HST”, are configured to include one hydraulic pump 10 and a swash plate hydraulic motor 20, but the hydraulic pump 10 and the swash plate hydraulic motor are included. The number of can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Hydraulic drive vehicle 5 Wheel 8 Accelerator pedal 9 Forward / reverse changeover switch 10 Hydraulic pump 11 Drive motor 20 Swash plate type hydraulic motor 20b Swash plate 30 Swash plate tilt mechanism 40 Electromagnetic switching valve 50 Controller 60 Closed circuit 61 Feed side piping 62 Return Side piping 63 Control piping 71 First branch piping 72 Second branch piping 80 Selection switch 81 Acceleration amount detection sensor TR, TR1 Power transmission device EG Engine

Claims (1)

A variable displacement hydraulic pump capable of supplying and discharging pressure oil;
A swash plate type hydraulic motor for rotating the wheel by pressure oil supplied from the hydraulic pump;
A second oil passage is a first oil passage, and the return-side pipe is a feed pipe which constitutes a closed circuit for circulating the hydraulic oil between the swash plate type hydraulic motor and the hydraulic pump,
A swash plate tilting mechanism for tilting the swash plate of the swash plate type hydraulic motor by the supplied pressure oil;
A first control oil passage for branching from the first oil passage and supplying pressure oil to the swash plate tilting mechanism;
A second control oil passage branched from the second oil passage to supply pressure oil to the swash plate tilting mechanism;
The communication state of the first control oil passage is secured and the communication state of the second control oil passage is released, or the communication state of the first control oil passage is released and the communication state of the second control oil passage is changed. An electromagnetic switching valve to be secured;
A hydraulically driven transport vehicle comprising: a control device that controls the electromagnetic switching valve so as to ensure the communication state of the first control oil passage during forward acceleration and to release the communication state of the second control oil passage;
There is a selection part that can select the weak brake state or the strong brake state,
The control device is at the time of a decrease in the accelerator input amount,
When the selection unit is selected to be in a weak brake state, the electromagnetic switching valve is controlled to ensure the communication state of the first control oil passage and to release the communication state of the second control oil passage,
Controlling the electromagnetic switching valve to release the communication state of the first control oil passage and to secure the communication state of the second control oil passage when the selection unit is selected to be in a strong brake state. Features a hydraulically driven transport vehicle.