JP2006290009A - Hst travel system of working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an HST travel system of a working machine capable of obtaining speed and traction force suitable for various works without requiring a transmission and a propeller shaft, and without using the transmission. <P>SOLUTION: The capacity of two hydraulic motors 10, 20 of an HST transmission device 30 is equalized each other, the reduction ratio of a reducer 11 of the front wheel side of the travel devices 12, 22 is made to be two times of reduction ratio of the reducer 21 of the rear wheel side, and the reduction ratio of the reducer 11 of the front wheel side and the reducer 21 of the rear wheel side is made to be 2:1. The HST transmission device 30 has a switching valve 41, a selector switch 42, and a controller 43, and can be switched between a low speed four-wheel drive mode driving both travel devices 12, 22 and a high speed two-wheel drive mode driving only the travel device 22 of the rear wheel side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an HST traveling system for work machines, and in particular, hydraulic traveling called HST (Hydro-Static Transmission) in which a hydraulic pump and a traveling motor are connected in a closed circuit, such as a rough terrain lift truck, a wheel loader, a wheeled hydraulic excavator, and the like. The present invention relates to an HST traveling system for a working machine having a circuit.

  In a conventional HST traveling system, for example, as described in Japanese Patent Laid-Open No. 5-306768, one hydraulic pump and one hydraulic motor are connected in a closed circuit, and the traveling device is driven by the one hydraulic motor. Is. In this case, the hydraulic motor is connected to the front and rear wheels via a transmission and a propeller shaft, and simultaneously drives the front and rear wheels by rotating the propeller shaft.

  As another HST traveling system, for example, as described in JP-A-11-166623 and JP-A-11-230333, one hydraulic pump is connected in parallel to two hydraulic motors in a closed circuit, and two hydraulic motors Some also drive the travel device. Also in this case, the two hydraulic motors are connected to the front and rear wheels via a reduction gear and a propeller shaft, and simultaneously drive the front and rear wheels by rotating the propeller shaft. One hydraulic motor is connected to a speed reducer via a clutch, and can be switched between a low speed (high torque) mode (clutch ON) and a high speed mode (clutch OFF) by ON / OFF control of the clutch. The machine is unnecessary.

  On the other hand, as another HST traveling system, one hydraulic pump is connected in parallel to two hydraulic motors in a closed circuit, the two hydraulic motors are connected to the front wheels and the rear wheels, respectively, and the front wheels and the rear wheels are connected by separate hydraulic motors. What drives is known. For example, in Japanese Patent Application Laid-Open No. 2000-1127, in an HST traveling system for a lawn mower, four-wheel drive is performed with high torque at both front and rear wheels at low speeds, low torque at the front wheels and high torque at the rear wheels at high speeds. Thus, the braking force is transmitted hydraulically to the front wheels during traveling, and the two-wheel drive that drives the rear wheels during turning makes it possible to prevent dragging of the front wheels during turning. In order to change the driving torque of the front wheel hydraulic motor, a constant ratio diversion valve is provided at the supply / discharge oil port of the hydraulic pump, a shuttle valve is provided between the main lines on the front wheel side hydraulic motor side, and a high pressure relief is provided on the output side of the shuttle valve. A valve and a low pressure relief valve are connected in parallel.

  In GB2136371A, in an agricultural machinery HST traveling system, one of two hydraulic motors is configured as a small-capacity auxiliary motor, and this auxiliary motor is connected to a front wheel or a rear wheel via a clutch and a speed reducer, and is connected to a hydraulic pump and an auxiliary motor. An on-off valve is provided between the motor and the clutch and the on-off valve are simultaneously switched to connect / disconnect the auxiliary motor and the hydraulic pump or the auxiliary motor and the wheel.

JP-A-5-306768 JP-A-11-166623 JP-A-11-230333 JP 2000-1127 A GB2136371A

  However, the above prior art has the following problems.

  In a general HST traveling system described in JP-A-5-306768, a hydraulic motor is connected to front and rear wheels via a transmission and a propeller shaft, and the front and rear wheels are simultaneously driven by rotating the propeller shaft. For this reason, a transmission and a propeller shaft are indispensable as a traveling device. The transmission and the propeller shaft are located on the lower side of the driving type, and the propeller shaft extends forward and backward under the engine and the driver's seat and is connected to the front and rear wheels. For this reason, it is necessary to install the driver's seat and engine at a position and height that do not interfere with the transmission and the propeller shaft, and the vehicle height (driver's seat height) increases accordingly, making it difficult to see the work equipment part from the driver's seat. There is a problem that workability is lowered. Another problem is that the degree of freedom in the layout of the engine, driver's seat, and other devices is limited by the transmission and the propeller shaft.

  In the HST traveling system using two hydraulic motors described in JP-A-11-166623 and JP-A-11-230333, a transmission is not necessary, but a propeller shaft is necessary. The problem of layout constraints has not been solved.

  In the HST traveling system described in Japanese Patent Application Laid-Open No. 2000-1127 and GB2136371A, the front wheels and the rear wheels are driven by separate hydraulic motors, so a propeller shaft is unnecessary, and there is no problem of vehicle height or layout restrictions due to the propeller shaft. Also, in GB2136371A, it is possible to switch between a four-wheel drive that drives two hydraulic motors simultaneously by a switch operation and a two-wheel drive that drives only one hydraulic motor, and enters a low-speed mode and a high-speed mode without using a transmission. Switching is possible. However, when these conventional techniques are applied to multipurpose work machines such as rough terrain lift trucks, wheel loaders, and wheel-type hydraulic excavators, there is a problem that speeds and traction forces suitable for various work forms cannot be obtained.

  For example, a typical work performed by a rough terrain lift truck is a bucket work. In an HST traveling system, the torque distribution (traction force distribution) of the front and rear wheels is usually set to 1: 1. In this case, in a work machine having a work machine (bucket, etc.) in the front part of the vehicle body, the vehicle weight during bucket operation is only applied to the front wheels, so the tractive force during bucket operation is half of the maximum tractive force for the front and rear wheels combined. The traction force for bucket work is too small. In the HST traveling system described in GB2136371A, it is possible to switch to two-wheel drive that drives only the main hydraulic motor (hydraulic motor that is not an auxiliary motor) during high-speed traveling by a switch operation. However, since the capacity of the main hydraulic motor is larger than the capacity of the auxiliary motor, the rotational speed (vehicle speed) is not twice that of the four-wheel drive state and is insufficient as a vehicle speed for moving the vehicle at high speed.

  An object of the present invention is to provide an HST traveling system for a working machine that does not require a transmission and a propeller shaft and that can obtain speed and traction force suitable for various operations without using a transmission.

  (1) In order to achieve the first object, the present invention provides a hydraulic pump, a first circuit connected to the hydraulic pump in a closed circuit and connected in parallel to each other, and driven by pressure oil discharged from the hydraulic pump. First and second hydraulic motors, a front wheel travel device connected to the first hydraulic motor via a first speed reducer, and a rear wheel travel device connected to the second hydraulic motor via a second speed reducer And a first control means for switching between a low-speed four-wheel drive mode for driving both the front wheel travel device and the rear wheel travel device and a high-speed two-wheel drive mode for driving only the rear wheel travel device. It is assumed that the drive torque of the device is set larger than the drive torque of the rear wheel travel device.

  In the present invention configured as described above, since the front wheel traveling device and the rear wheel traveling device are driven by separate hydraulic motors, a propeller shaft is not required.

  In addition, when the HST traveling system of the present invention is applied to a multi-purpose work machine such as a rough terrain lift truck and the traction work is performed in the low speed four-wheel drive mode, the maximum traction force obtained by the four-wheel drive of the front wheels and the rear wheels is appropriately set. By setting to, the maximum traction force required for traction work can be obtained.

  When bucket work is performed with low-speed four-wheel drive, the driving torque of the front wheel travel device is set to be larger than the drive torque of the rear wheel travel device, so the traction force applied to the front wheel for the bucket work is mostly low-speed four-wheel drive. It becomes larger than half of the maximum traction force of the mode (total traction force of the front and rear wheels), and a traction force suitable for bucket work can be obtained.

  When high-speed traveling is performed in the high-speed two-wheel drive mode, the driving torque of the front wheel traveling device is set to be larger than the driving torque of the rear-wheel traveling device, so that the second hydraulic motor is more than twice that in the low-speed four-wheel driving mode. A larger flow rate acts, and the rotational speed (vehicle speed) becomes larger than twice that in the low-speed four-wheel drive mode, and the vehicle can move at high speed.

  As described above, the present invention provides the maximum traction force required during traction work, the traction force required during bucket operation (front and rear wheel traction force distribution), and the traction force required during high-speed traveling without using a transmission (for example, a two-speed transmission). Can be achieved.

  (2) In the above (1), preferably, the ratio of the driving torque of the front wheel traveling device and the driving torque of the rear wheel traveling device is set in a range of 2 to 3: 1.

  As a result, most of the vehicle weight is 2/3 to 3/4 (67-75%) of the maximum traction force (total traction force of the front and rear wheels) in the low-speed four-wheel drive mode when bucket work is applied to the front wheels. A suitable traction force can be obtained.

  Further, the second hydraulic motor has a flow rate 3 to 4 times that in the low-speed four-wheel drive mode, and the rotational speed (vehicle speed) is 3 to 4 times that in the low-speed four-wheel drive mode. it can.

  (3) In the above (1), more preferably, the ratio of the driving torque of the front wheel traveling device and the driving torque of the rear wheel traveling device is set to 2: 1.

  As a result, most of the vehicle weight is reduced to 2/3 (about 65%) of the maximum traction force (total traction force of the front and rear wheels) in the low-speed four-wheel drive mode. Obtainable.

  Further, a flow rate three times that in the low-speed four-wheel drive mode acts on the second hydraulic motor, and the rotational speed (vehicle speed) becomes three times that in the low-speed four-wheel drive mode, so that the vehicle can move at high speed.

  (4) In order to achieve the above object, the present invention provides a hydraulic pump, a first circuit connected to the hydraulic pump in a closed circuit and connected in parallel to each other, and driven by pressure oil discharged from the hydraulic pump. And a second hydraulic motor, a front wheel travel device connected to the first hydraulic motor via a first speed reducer, and a rear wheel travel device connected to the second hydraulic motor via a second speed reducer, First control means for switching between a low-speed four-wheel drive mode for driving both the front wheel travel device and the rear wheel travel device and a high-speed two-wheel drive mode for driving only the rear wheel travel device; It is assumed that the capacity of the second hydraulic motor is made equal and the reduction ratio of the first reduction gear is made larger than the reduction ratio of the second reduction gear.

  As a result, as described in (1) above, the transmission and the propeller shaft are not required, and the speed and tractive force suitable for various work modes can be achieved without using the transmission.

  Further, by making the first and second hydraulic motors have the same capacity, it is possible to share parts and reduce costs.

  (5) In the above (4), preferably, the ratio of the reduction ratio of the first reduction gear to the reduction ratio of the second reduction gear is set in a range of 2 to 3: 1.

  As a result, most of the vehicle weight is 2/3 to 3/4 (67-75%) of the maximum traction force (total traction force of the front and rear wheels) in the low-speed four-wheel drive mode when bucket work is applied to the front wheels. A suitable traction force can be obtained.

  Further, the second hydraulic motor has a flow rate 3 to 4 times that in the low-speed four-wheel drive mode, and the rotational speed (vehicle speed) is 3 to 4 times that in the low-speed four-wheel drive mode. it can.

  (6) In the above (4), more preferably, the ratio of the reduction ratio of the first reduction gear to the reduction ratio of the second reduction gear is set to 2: 1.

  As a result, most of the vehicle weight is reduced to 2/3 (about 65%) of the maximum traction force (total traction force of the front and rear wheels) in the low-speed four-wheel drive mode. Obtainable.

  Further, a flow rate three times that in the low-speed four-wheel drive mode acts on the second hydraulic motor, and the rotational speed (vehicle speed) becomes three times that in the low-speed four-wheel drive mode, so that the vehicle can move at high speed.

  (7) Further, in the above (1) or (4), preferably, a switching valve disposed in a closed circuit connecting the hydraulic pump and the first and second hydraulic motors, the front wheel travel device, and the A speed difference with the rear wheel traveling device is detected, and when the speed difference exceeds a predetermined value, the switching valve is switched to switch to the hydraulic motor having the higher rotational speed of the first hydraulic motor and the second hydraulic motor. And a second control means for shutting off the supply of pressure oil.

  As a result, when driving in the low-speed four-wheel drive mode, if any of the front and rear axles is idle due to changes in the road surface conditions during work or the distribution of the axle load of the front and rear wheels, the front or rear wheels that do not run idle It becomes possible to supply pressure oil only to the hydraulic motor on the side, avoiding an open differential state at the time of wheel idling in the low-speed four-wheel drive mode, and improving rough road running performance.

  (8) In the above (1) or (4), preferably, the first control means further includes a medium-speed two-wheel drive mode for driving only the front wheel travel device, and the low-speed four-wheel drive mode. The high-speed two-wheel drive mode and the medium-speed two-wheel drive mode can be switched.

  As a result, in the medium-speed two-wheel drive mode, an approximately intermediate speed and traction force can be obtained between the low-speed four-wheel drive mode and the high-speed two-wheel drive mode, so that an appropriate traveling speed is suitable for a cargo handling operation using a work machine such as a fork. In addition to improving traction, the working efficiency is improved and the engine does not run at high speed, reducing operator fatigue (noise and vibration). In addition, since the working machine such as a fork is located at the front part of the vehicle body, the vehicle weight mainly acts on the front wheels during cargo handling work, and the workability is not impaired.

  According to the present invention, a transmission and a propeller shaft are unnecessary, and a speed and traction force suitable for various operations can be obtained without using a transmission.

  Further, according to the present invention, it is possible to share parts and reduce costs by setting the first and second hydraulic motors to the same capacity.

  In addition, according to the present invention, it is possible to avoid an open differential state at the time of wheel idling in the low-speed four-wheel drive mode, and to improve rough road running performance.

  In addition, according to the present invention, an intermediate speed and traction force between the low-speed four-wheel drive mode and the high-speed two-wheel drive mode can be obtained in the medium-speed two-wheel drive mode. Work efficiency is improved.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a hydraulic configuration diagram showing an HST traveling system for a work machine according to a first embodiment of the present invention.

  In FIG. 1, the HST travel system of the present embodiment includes an HST transmission 30, a front wheel travel device 12, and a rear wheel travel device 22.

  The HST transmission 30 includes a main hydraulic pump 1 driven by the engine 2 and two traveling hydraulic motors 10 and 20 driven by pressure oil discharged from the hydraulic pump 1. And the hydraulic motor 10 are connected in a closed circuit via the main pipelines 3, 4, 5, 6 and the hydraulic pump 2 and the hydraulic motor 20 are connected in a closed circuit via the main pipelines 3, 4, 7, 8 The hydraulic motors 10 and 20 are connected to the hydraulic pump 1 in parallel. A charge pump 33 for replenishment is connected to the main pipelines 7 and 8 via check valves 34 and 35, and the pressure of the main pipeline 7 or 8 is based on the set pressure of the relief valve 37 provided in the discharge passage of the charge pump 33. When the pressure becomes lower, the oil discharged from the charge pump 33 is supplied to the main pipeline 7 or 8.

  The traveling hydraulic motors 10 and 20 are connected to the traveling devices 12 and 22, respectively. The front wheel travel device 12 includes a speed reducer 11 to which a travel hydraulic motor 10 is connected, an axle 13 and a front wheel (wheel) 14 connected to the speed reducer 11, and a rear wheel travel device 22 is a travel hydraulic pressure. A reduction gear 21 to which the motor 20 is connected, an axle 23 and a rear wheel (wheel) 24 connected to the reduction gear 21 are provided, and the driving force is transmitted to the road surface by the wheels 14 and 24, respectively. It is configured to drive the car body.

  In the HST transmission 30, the capacities of the two hydraulic motors 10 and 20 are set equal. Further, in the traveling devices 12 and 22, the front wheel side reduction gear 11 is set to be larger than the rear wheel side reduction gear 21, and specifically, the front wheel side reduction gear 11 is the rear wheel side reduction gear 21. The reduction ratio of the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is 2: 1.

  The ratio of the reduction ratio of 2: 1 is an example (optimal example), and if the reduction ratio of the reduction gear 11 on the front wheel side is larger than the reduction ratio of the reduction gear 21 on the rear wheel side (preferably, the reduction gear on the front wheel side) 11 and the ratio of the reduction ratio of the reduction gear 21 on the rear wheel side is in the range of 2 to 3, and other ratios may be used.

  The HST transmission 30 is also used as a control means for switching between a low-speed four-wheel drive mode for driving both the travel devices 12 and 22 and a high-speed two-wheel drive mode for driving only the rear wheel travel device 22. 6, a two-position switching valve (hereinafter simply referred to as a switching valve) 41, a changeover switch 42 operated by an operator, and a controller 43.

  The switching valve 41 is an electromagnetic switching valve having a solenoid 41a at one end, and is in the illustrated communication position when the electrical signal applied to the solenoid 41a is OFF, and switches from the illustrated position to the shut-off position when the electrical signal is ON. . The circuit state when the switching valve 41 is in the illustrated communication position is referred to as a low-speed four-wheel drive mode, and the circuit state when the switching valve 41 is switched to the shut-off position is referred to as a high-speed two-wheel drive mode.

  The changeover switch 42 can be switched between two positions, low speed and high speed. When the changeover switch 42 is in the low speed position, the controller 43 turns off the electrical signal, and when the changeover switch 42 switches to the high speed position, the controller 43 The signal is turned ON and output to the switching valve 41.

  The hydraulic pump 1 includes a known tilt amount control means (not shown), and increases the tilt amount (capacity) of the hydraulic pump 1 in accordance with an increase in the rotational speed of the engine 2 to smoothly increase the pump discharge flow rate. As the pump discharge flow rate increases, the rotational speeds of the traveling motors 10 and 20 increase, and the vehicle speed increases. The rotational speed of the engine 2 is adjusted by operating an accelerator pedal (not shown).

  The travel motors 10 and 20 are provided with a known tilt amount control means (not shown), which is in a small tilt (small capacity) when the load pressure is lower than the set pressure, and a large tilt (large capacity) when the load pressure is higher than the set pressure. ) Automatically. The set pressure is the same value for the two travel motors 10 and 20.

  FIG. 2 is an external view of a rough terrain lift truck (also referred to as a telescopic handler), which is a typical example of a multipurpose work machine, as an example of a work machine on which the HST traveling system of the present embodiment is mounted.

  In FIG. 2, the rough terrain lift truck includes a vehicle body 41, a cab 42 positioned on the vehicle body 41, an extendable boom 43 attached to the vehicle body 41 so that a side portion of the cab 42 can be raised and lowered, and a boom 43. An attachment mounting portion 44 that is pivotally attached to the tip of the head, and a fork 45 that is a kind of attachment attached to the attachment mounting portion 44 and that is used for a cargo handling operation, and includes a boom 43 and an attachment mounting portion. 44 and fork 45 constitute a working device. Although not shown in the drawing, hydraulic actuators are respectively attached to the boom 43, the attachment attachment portion 44, and the fork 45, and each working member is driven by the respective hydraulic actuator. A front wheel 14 and a rear wheel 24 are attached to the vehicle body 41.

  The imaginary line in FIG. 2 shows a state where the boom 43 is raised and a state where the boom 43 is raised and extended. In this case, even if the boom 43 is raised, the attitude of the fork 45 does not change due to the link action of the attachment mounting portion 44.

  Next, the effect of this Embodiment comprised as mentioned above is demonstrated.

  When the changeover switch 42 is in the low speed position and the changeover valve 41 is in the illustrated communication position, it is in the low speed four-wheel drive mode and pressure oil is supplied from the hydraulic pump 1 to the two hydraulic motors 10 and 20. . In this state, equal driving pressure is generated in the two hydraulic motors 10 and 20, the capacities of the two hydraulic motors 10 and 20 are equal, and the driving torque of the hydraulic motors 10 and 20 is the product of the capacity and the driving pressure. Therefore, the drive torque generated by the hydraulic motors 10 and 20 is the same. However, since the ratio of the reduction ratio of the reduction gear 11 on the wheel side and the reduction gear 21 on the rear wheel side is 2: 1, the torque for driving the vehicle is the front wheel 14 (front wheel travel device 12) on the rear wheel 24 (rear wheel). This is twice that of the traveling device 22). At this time, since the rotational speeds of the front and rear wheels 14 and 24 are the same, a flow rate twice that of the hydraulic motor 20 on the front wheel side acts on the hydraulic motor 10 on the front wheel side. It is possible to run in the state.

  When the changeover switch 42 is operated to the high speed position and the changeover valve 41 is switched from the illustrated position to the shut-off position, the high speed two-wheel drive mode is established, and only the hydraulic motor 20 on the rear wheel side receives pressure oil from the hydraulic pump 1. Supplied. In this state, since all the pressure oil of the hydraulic pump 1 flows into the hydraulic motor 20 on the rear wheel side, a rotation speed (vehicle speed) that is three times that of the low-speed four-wheel drive mode can be obtained. That is, a speed difference three times that of the low-speed four-wheel drive mode is realized without using a transmission.

  At this time, since the main pipelines 5 and 6 of the hydraulic motor 10 on the front wheel side communicate with each other, the hydraulic motor 10 on the front wheel side rotates with the rotation of the front wheel 14. Further, since the traveling drive torque at this time is given only by the rear wheel side hydraulic motor 20, it becomes 1/3 of the drive torque in the low-speed four-wheel drive mode. That is, the traction force in the high-speed two-wheel drive mode is 1/3 of the traction force (maximum traction force) obtained in the low-speed four-wheel drive mode.

  The rough terrain lift truck is a multipurpose work machine, and can perform various operations such as a towing operation, a bucket operation, and a cargo handling operation. The towing operation is an operation in which a towed object such as a trailer is connected to the rear part of the vehicle body and is towed. Bucket work is work that excavates by exchanging the attachment with a bucket and pressing the bucket against an object to be excavated, such as a natural ground, with running force (traction force). After excavation, lift the bucket, move the car body, and dump it on a truck. The cargo handling operation is an operation of placing a load on the fork 45 shown in the drawing and moving it. Moreover, it is necessary to travel at high speed when the vehicle moves.

  In the present embodiment, the towing work is performed in the low-speed four-wheel drive mode, and the vehicle movement at high speed is performed in the high-speed two-wheel drive mode. The cargo handling work is performed in either the low-speed four-wheel drive mode or the high-speed two-wheel drive mode depending on the situation at that time.

  Here, in a working machine such as a rough terrain lift truck, generally, the maximum traction force at the time of towing is set to 90 to 100% in terms of the vehicle body weight ratio, and the traction force at the maximum speed is 20 to 30 by vehicle body weight ratio. % Is set. The conventional HST traveling system uses a transmission (transmission) and a propeller shaft, and simultaneously drives the front and rear wheels by one or two hydraulic motors. In such an HST traveling system, in order to achieve both the maximum traction force at the time of towing and the traction force at the maximum speed, a two-speed transmission with a step ratio (ratio of reduction ratio between high speed and low speed) of 3 to 4 is used. It was. When performing towing work or bucket work, the transmission is switched to a low-speed gear, and the vehicle is moved (running) to switch the transmission to a high-speed gear.

  However, in a working machine such as a rough terrain lift truck, the maximum traction force that can be obtained with a low-speed gear is essential for traction work, but the maximum traction force is excessive for bucket work. In addition, since high-speed traveling is used when moving between work sites, the four-wheel drive system without a center differential for the purpose of improving rough road running performance is inefficient.

  In addition, when the HST traveling system described in Japanese Patent Application Laid-Open No. 2000-1127 and GB2136371A is applied to a work machine such as a rough terrain lift truck, consideration is not given to torque distribution (traction force distribution) of the front and rear wheels. Sufficient traction force cannot be obtained during bucket operation. That is, when the torque distribution of the front and rear wheels (traction force distribution) is not considered, the torque distribution of the front and rear wheels is usually set to 1: 1. In this case, in a working machine having a work machine (bucket etc.) in the front part of the vehicle body, the vehicle weight during bucket operation is only applied to the front wheels, so the traction force during bucket operation is half of the maximum traction force. It is too small.

  In the present embodiment, as described above, in the low-speed four-wheel drive mode, traveling can be performed in a traction force distribution state of 2: 1 in the front-rear direction, so that the necessary maximum traction force can be obtained by the front and rear wheels 14, 24 in the traction operation. Further, in a working machine having a work machine (bucket or the like) in the front part of the vehicle body, the vehicle weight at the time of bucket work is only applied to the front wheels, so it is sufficient that a driving force of about 60% is generated only on the front wheels (rear wheels). It is useless to generate driving force. Since the driving torque of the front wheel 14 by the hydraulic motor 10 is 2/3 of the total driving torque of the front and rear wheels by the two hydraulic motors 10 and 20, the maximum traction force is at least exerted by the front wheel 14 during bucket operation when a considerable portion of the vehicle weight is applied to the front wheel. Thus, a traction force of about 65% of 2/3 of the above can be obtained, and the traction work and the bucket work can be performed with an appropriate traction force.

  Further, in the high-speed two-wheel drive mode, the vehicle can travel at a speed three times that of the low-speed four-wheel drive mode with only the rear wheels 24, and good traveling performance is obtained.

  As described above, according to the present embodiment, the front wheel traveling device 12 and the rear wheel traveling device 22 are driven by the separate hydraulic motors 10 and 20, so that a propeller shaft is not necessary.

  Further, the maximum traction force required for traction work, traction force required for bucket work (front and rear wheel traction force distribution), and traction force required for high-speed traveling can be achieved without using a transmission (for example, a two-speed transmission). .

  Further, by setting the front and rear wheel hydraulic motors 10 and 20 to the same capacity, it is possible to share parts and reduce costs.

  As described above, the ratio of the reduction ratio between the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is not limited to 2: 1. Basically, the reduction ratio of the front wheel reduction gear 11 is the rear wheel. It is sufficient that the reduction ratio of the reduction gear 21 on the side is set larger than that of the reduction gear 21 on the front wheel side. Preferably, the reduction gear 11 on the front wheel side has a reduction ratio two to three times that of the reduction gear 21 on the rear wheel side. The ratio of the reduction ratio of the reduction gear 11 of the rear wheel and the reduction gear 21 on the rear wheel side may be 2 to 3: 1.

  When bucket work is performed in the low-speed four-wheel drive mode by setting the reduction ratio of the front wheel side reduction gear 11 to be larger than the reduction ratio of the reduction gear 21 on the rear wheel side, the driving torque of the front wheel traveling device is the rear wheel traveling. Since it becomes larger than the driving torque of the device, the traction force during the bucket operation where most of the vehicle weight is applied to the front wheels is larger than half of the maximum traction force, and the reduction ratio between the reduction device 11 on the front wheel side and the reduction device 21 on the rear wheel side. Compared with the case where the ratio is 1: 1, the traction force in the bucket operation is optimized. Further, when high-speed traveling is performed in the high-speed two-wheel drive mode, a flow rate larger than twice that in the low-speed four-wheel drive mode acts on the rear wheel side hydraulic motor 20 and the rotational speed (vehicle speed) is low. Compared to the case where the reduction ratio ratio of the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is 1: 1, the vehicle can move at a higher speed than in the wheel drive mode. .

  Further, by setting the ratio of the reduction ratio of the front wheel side reduction gear 11 to the rear wheel side reduction gear 21 to 2 to 3: 1, the traction force during the bucket work on the front wheels is almost low. 2/3 to 3/4 (67 to 75%) of the maximum traction force in the drive mode, compared to the case where the reduction ratio ratio of the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is 1: 1, The traction force for bucket work is optimized. In addition, a flow rate 3 to 4 times that in the low-speed four-wheel drive mode acts on the hydraulic motor 20 on the rear wheel side, and the rotational speed (vehicle speed) is 3 to 4 times that in the low-speed four-wheel drive mode. The vehicle can move at a higher speed than when the ratio of the reduction ratio between the machine 11 and the reduction gear 21 on the rear wheel side is 1: 1.

  As described above, the maximum traction force required for traction work, the traction force required for bucket work (front and rear wheel traction force distribution), and the traction force required for high-speed travel can be achieved without using a transmission (for example, a 2-speed transmission). Can do.

  A second embodiment of the present invention will be described with reference to FIGS. In FIG. 3, the same members as those in FIG.

  In FIG. 3, the HST travel system of the present embodiment includes an HST transmission 30 </ b> A, a front wheel travel device 12, and a rear wheel travel device 22.

  In the HST transmission 30A, the capacities of the two hydraulic motors 10 and 20 are set equal. Further, in the traveling devices 12 and 22, the front wheel side reduction gear 11 is set to be larger than the rear wheel side reduction gear 21, and specifically, the front wheel side reduction gear 11 is the rear wheel side reduction gear 21. The reduction ratio of the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is 2: 1. Also in this case, the reduction ratio ratio is such that the reduction ratio of the reduction gear 11 on the front wheel side is larger than the reduction ratio of the reduction gear 21 on the rear wheel side (preferably, the reduction gear 11 on the front wheel side and the reduction gear 21 on the rear wheel side. If the ratio of the reduction ratio is in the range of 2 to 3: 1), other ratios may be used.

  The HST transmission 30A includes a main pipeline 3a on the hydraulic pump 1 side and separate main pipelines 3b and 3c on the main pipelines 5 and 7 side instead of the main pipeline 3 in FIG. 1 are provided between the main pipelines 3a, 4a, 4b and the main pipelines 3b, 3c, instead of the switching valve 41 of FIG. A three-position switching valve (hereinafter simply referred to as a switching valve) 41A is provided.

  The HST transmission 30A includes a changeover switch 42A and a controller 43A in place of the changeover switch 42 and the controller 43 of FIG. 1, and detects the rotational speeds (axle speeds) of the axles 13 and 23 of the traveling devices 12 and 22. The rotation speed sensors 51 and 52 are provided, and the detection signals of the rotation speed sensors 51 and 52 are input to the controller 43A.

  The switching valve 41A is an electromagnetic switching valve having solenoids 41Aa and 41Ab at both ends. When both electrical signals applied to the solenoids 41Aa and 41Ab are OFF, the switching valve 41A is at the first position A and is applied to the right solenoid 41Aa. When the electrical signal to be turned on is switched to the second position B on the right side of the figure from the position shown in the figure, and when the electrical signal applied to the solenoid 41Ab on the left side of the figure is turned on, the position is switched from the position to the third position C on the left side of the figure. . When the switching valve 41A is in the first position A, the main pipeline 3a communicates with the main pipelines 3b and 3c, and the oil discharged from the hydraulic pump 1 is supplied to the two hydraulic motors 10 and 20, and the two hydraulic motors 10 are supplied. , 10 rotate, and both the front wheel 14 and the rear wheel 24 are driven. That is, the low-speed four-wheel drive mode is set. When the switching valve 41A is switched to the second position B, the main pipeline 3a and the main pipeline 3c communicate with each other, the main pipeline 4a and the main pipeline 3b communicate with each other, and only the hydraulic motor 20 on the rear wheel side is connected to the hydraulic pump 1 The hydraulic oil 10 on the front wheel side rotates with the rotation of the front wheel 14 because the main pipelines 5 and 6 communicate with each other. That is, the high-speed two-wheel drive mode is set. When the switching valve 41A is switched to the third position C, the main pipeline 3a and the main pipeline 3b communicate with each other, the main pipeline 4b and the main pipeline 3c communicate with each other, and only the hydraulic motor 10 on the front wheel side is connected to the hydraulic pump 1 Pressure oil is supplied, only the front wheel 14 is driven, and the hydraulic motor 20 on the rear wheel side rotates with the rotation of the rear wheel 24 because the main pipelines 7 and 8 are in communication. This state is called a medium speed two-wheel drive mode.

  The changeover switch 42A can be changed over to three positions of low speed, high speed, and medium speed, and the controller 43A controls the changeover of the changeover valve 41A based on the signal of the changeover switch 42A and the detection signals of the rotational speed sensors 51 and 52.

  FIG. 4 is a flowchart showing the processing contents of the controller 43A.

  The controller 43A determines the position of the changeover switch 42A based on the signal from the changeover switch 42A (step S10). When the changeover switch 42A is in the low speed position, the controller 43A performs a low speed control process (step S20). When the changeover switch 42A is switched to the high speed position, the electrical signal applied to the solenoid 41Aa of the changeover valve 41A is turned ON to switch the changeover valve 41A to the second position B (step S30), and the changeover switch 42A is switched to the medium speed position. Then, the electric signal applied to the solenoid 41Ab of the switching valve 41A is turned ON to switch the switching valve 41A to the third position C (step S40). In the low speed control process when the changeover switch 42A is in the low speed position, a speed difference between the axle 13 of the front wheel travel device 12 and the axle 23 of the rear wheel travel device 22 is detected based on signals from the rotational speed sensors 51 and 52. When this speed difference is less than or equal to a predetermined value, both electrical signals applied to the solenoids 41Aa and 41b of the switching valve 41A are turned OFF, and when the speed difference exceeds a predetermined value, an electrical signal applied to either the solenoids 41Aa and 41b. The switching valve 41A is switched to either the second position B or the third position C so as to cut off the supply of pressure oil to the hydraulic motor having the higher rotational speed among the hydraulic motors 10 and 20.

  FIG. 5 is a flowchart showing details of the low speed control process.

  Based on the signals from the rotational speed sensors 51 and 52, the controller 43A determines a speed difference ΔS between the rotational speed of the axle 13 of the front wheel travel device 12 and the rotational speed of the axle 23 of the rear wheel travel device 22 (ΔS = front wheel axle speed− (Rear wheel axle speed) is calculated (step S100), and if the speed difference ΔS is equal to or smaller than a predetermined value, the process is terminated (step S120), and the electrical signals applied to the solenoids 41Aa and 41b of the switching valve 41A are both OFF. To do. If the speed difference ΔS exceeds a predetermined value, it is further determined whether the speed difference ΔS is a negative value (that is, whether the rear wheel axle speed is larger than the front wheel axle speed) (step S130). If the rear wheel axle speed is greater than the front wheel axle speed (ie, the electrical signal applied to the solenoid 41Ab of the switching valve 41A is turned ON to switch the switching valve 41A to the third position C (step S140), In other words, if the front wheel axle speed is greater than the rear wheel axle speed, the electrical signal applied to the solenoid 41Aa of the switching valve 41A is turned on to switch the switching valve 41A to the second position B (step S150). In step S110, an appropriate value close to 0 is set as the predetermined value in consideration of the speed fluctuation of the front and rear wheels during normal driving.

  In the present embodiment configured as described above, the operator can select the medium-speed two-wheel drive mode in addition to the low-speed four-wheel drive mode and the high-speed two-wheel drive mode by operating the changeover switch 42A to the medium-speed position. It is.

  That is, when the changeover switch 42A is in the low speed position and the changeover valve 41A is in the first position A shown in the figure, the low speed four-wheel drive mode is set, the changeover switch 42A is operated to the high speed position, and the changeover valve 41A is moved from the position shown in the figure. When switched to the second position B, the high-speed two-wheel drive mode is set. When the changeover switch 42A is operated to the medium-speed position and the switching valve 41A is switched from the illustrated position to the third position C, the medium-speed two-wheel drive mode is set. .

  In the low-speed four-wheel drive mode, as described above, the ratio of the reduction ratio between the front wheel side reduction gear 11 and the rear wheel side reduction gear 21 is 2: 1. As a result, the vehicle can travel in a traction force distribution state of 2: 1 in the front-rear direction. In the high-speed two-wheel drive mode, all the pressure oil from the hydraulic pump 1 flows into the hydraulic motor 20 on the rear wheel side, so that the rotation speed (vehicle speed) is three times that of the four-wheel drive state in the low-speed four-wheel drive mode. can get.

  In the medium-speed two-wheel drive mode, all the hydraulic oil from the hydraulic pump 1 flows into the front-wheel hydraulic motor 10, and therefore 1.5 (3/2) times that of the low-speed four-wheel drive mode. A half rotation speed (vehicle speed) can be obtained. Further, since the traveling drive torque at this time is given only by the hydraulic motor 10 on the front wheel side, it becomes 2/3 of the drive torque in the low-speed four-wheel drive mode. That is, the tractive force in the medium speed two-wheel drive mode is 2/3 of the tractive force (maximum tractive force) obtained in the low speed four-wheel drive mode.

  As described above, the rough terrain lift truck has various operations such as a towing operation, a bucket operation, and a cargo handling operation. When the HST traveling system of this embodiment is applied to a rough terrain lift truck, the towing operation is performed in the low-speed four-wheel drive mode, the vehicle movement at high speed is performed in the high-speed two-wheel drive mode, and the cargo handling operation is performed in the medium-speed two-wheel drive mode. Perform in drive mode. In this case, in traction work, bucket work, and vehicle movement at a high speed, an appropriate traction force and vehicle speed can be obtained as described in the first embodiment.

  Further, in a conventional HST traveling system using a two-speed transmission (transmission), when carrying out cargo handling work, the transmission must be selected from either a low speed gear or a high speed gear. However, when the low-speed gear was selected, the gear ratio focused on the traction force for heavy traction work, the speed was insufficient, and the efficiency was poor because the engine operated at high speed. In addition, when the high-speed gear was selected, the maximum speed was emphasized and the traction force was insufficient. Therefore, the speed and traction force for driving the machine efficiently could not be obtained.

  In the present embodiment, in the medium-speed two-wheel drive mode in which only the front wheels 14 are driven, the speed and tractive force approximately halfway between the low-speed four-wheel drive mode and the high-speed two-wheel drive mode (3/2 times the low-speed four-wheel drive mode, Rotational speed (vehicle speed) that is 1/2 that of the high-speed two-wheel drive mode, 2/3 that of the low-speed four-wheel drive mode, and double traction force that is twice that of the high-speed two-wheel drive mode. Operator fatigue (noise, vibration) can also be reduced. In addition, since the working machine such as a fork is located at the front part of the vehicle body, the vehicle weight mainly acts on the front wheels during cargo handling work, and the workability is not impaired.

  Further, in the present embodiment, when traveling in the low-speed four-wheel drive mode, when either the front or rear axle is in an idle state due to a change in road surface conditions during work or a change in the axle load distribution of the front and rear wheels, the rotational speed sensor 51 , 52 receives the information from the controller 52, judges the differential state, drives the switching valve 41A, and supplies the pressure oil only to the front-wheel or rear-wheel hydraulic motor where no idling occurs. By such switching control of the switching valve 41A, it is possible to avoid an open differential state at the time of wheel idling in the low-speed four-wheel drive mode, and to improve rough road running performance.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and the intermediate speed between the low-speed four-wheel drive mode and the high-speed two-wheel drive mode in the medium-speed two-wheel drive mode can be obtained. Since traction force can be obtained, an appropriate traveling speed and traction force can be obtained in cargo handling work and the like, and effects such as improvement in work efficiency can be obtained.

  Further, it is possible to avoid an open differential state when the wheels are idling in the low-speed four-wheel drive mode, and to improve rough road running performance.

  In the embodiment described above, the capacities of the two hydraulic motors 10 and 20 are made equal, and the reduction ratio of the reduction gear 11 on the front wheel side is larger than the reduction ratio of the reduction gear 21 on the rear wheel side (preferably 2 to 3). : 1, more preferably 2: 1), because the purpose is to obtain an appropriate traction distribution of the front and rear wheels by the hydraulic motor and the speed reducer, the driving torque of the front wheel traveling device is set to the rear wheel traveling device. Other configurations may be adopted as long as the driving torque can be set to be larger than the above. For example, the reduction ratio of the reduction gear 11 on the front wheel side and the reduction ratio of the reduction gear 21 on the rear wheel side are the same (reduction ratio ratio is 1: 1), and the capacity of the hydraulic motor 10 on the front wheel side is the hydraulic motor on the rear wheel side. It may be larger than 20 capacity (or the reduction ratio ratio is preferably set to 2-3: 1, more preferably 2: 1), or the combination of the selection of the reduction ratio and the selection of the capacity, The driving torque of the front wheel traveling device may be larger than the driving torque of the rear wheel traveling device.

  Further, in the second embodiment, when the changeover switch 42A has three positions of low speed, high speed, and medium speed, a switching valve 41A is provided to avoid an open differential state at the time of wheel idling in the low speed four-wheel drive mode. However, such control may be applied in the first embodiment. In this case, the switching valve 41 and the controller 43 in FIG. 1 of the first embodiment are replaced with the switching valve 41A and the controller 43A in FIG. 3, and when the selector switch 42 is in the low speed position by the controller 43A, the low speed control shown in FIG. What is necessary is just to process.

  In the first and second embodiments, the front wheel side hydraulic motor 10 and the speed reducer 11 are directly connected. However, a clutch is provided between the front wheel side hydraulic motor 10 and the speed reducer 11 to provide a switching valve. 41, 41A may be switched to a position (disengagement position or second position B) where the hydraulic pump 1 and the hydraulic motor 10 are disconnected, and the clutch may be turned off at the same time, so that the hydraulic motor 10 during traveling in the high-speed two-wheel drive mode Since there is no accompaniment, traveling load is reduced and energy loss can be reduced.

1 is a hydraulic configuration diagram of an HST traveling system according to a first embodiment of the present invention. FIG. It is a figure which shows the external appearance of a rough terrain lift truck as an example of the working machine with which the HST traveling system of this invention is mounted. 1 is a hydraulic configuration diagram of an HST traveling system according to a first embodiment of the present invention. FIG. It is a flowchart which shows the processing content of a controller. It is a flowchart which shows the processing content (low speed control process) of a controller when a changeover switch exists in a low speed position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Engine 3, 4, 5, 6, 7, 8 Main pipe line 3a, 3b, 3c, 4a, 4b Main pipe line 10 (front wheel side) Hydraulic motor 11 Reduction gear 12 Traveling device 13 Axle 14 Front wheel 20 (Rear wheel) Side) Hydraulic motor 21 Reducer 22 Traveling device 23 Axle 24 Rear wheel 30 HST transmission 41 Switching valve 41A Switching valve 42 Switching switch 42A Switching switch 43 Controller 43A Controller 51, 52 Rotational speed sensor

Claims (8)

A hydraulic pump;
First and second hydraulic motors connected to the hydraulic pump in a closed circuit and connected in parallel to each other and driven by pressure oil discharged from the hydraulic pump;
A front wheel travel device connected to the first hydraulic motor via a first speed reducer;
A rear wheel travel device connected to the second hydraulic motor via a second speed reducer;
First control means for switching between a low-speed four-wheel drive mode for driving both the front wheel travel device and the rear wheel travel device and a high-speed two-wheel drive mode for driving only the rear wheel travel device;
An HST traveling system for a work machine, wherein a driving torque of the front wheel traveling device is set larger than a driving torque of the rear wheel traveling device. In the HST traveling system of the working machine according to claim 1,
A working machine HST traveling system, wherein a ratio of a driving torque of the front wheel traveling device and a driving torque of the rear wheel traveling device is set in a range of 2 to 3: 1. In the HST traveling system of the working machine according to claim 1,
An HST traveling system for a working machine, wherein a ratio of a driving torque of the front wheel traveling device and a driving torque of the rear wheel traveling device is set to 2: 1. A hydraulic pump;
First and second hydraulic motors connected to the hydraulic pump in a closed circuit and connected in parallel to each other and driven by pressure oil discharged from the hydraulic pump;
A front wheel travel device connected to the first hydraulic motor via a first speed reducer;
A rear wheel travel device connected to the second hydraulic motor via a second speed reducer;
First control means for switching between a low-speed four-wheel drive mode for driving both the front wheel travel device and the rear wheel travel device and a high-speed two-wheel drive mode for driving only the rear wheel travel device;
An HST traveling system for a working machine, wherein the capacities of the first and second hydraulic motors are made equal, and a reduction ratio of the first reduction gear is made larger than a reduction ratio of the second reduction gear. In the HST traveling system of the working machine according to claim 4,
A working machine HST travel system, wherein a ratio of a reduction ratio of the first reduction gear to a reduction ratio of the second reduction gear is set in a range of 2 to 3: 1. In the HST traveling system of the working machine according to claim 4,
A working machine HST travel system, wherein a ratio of a reduction ratio of the first reduction gear to a reduction ratio of the second reduction gear is set to 2: 1. In the HST traveling system of the working machine according to claim 1 or 4,
A switching valve disposed in a closed circuit connecting the hydraulic pump and the first and second hydraulic motors;
A speed difference between the front wheel traveling device and the rear wheel traveling device is detected, and when the speed difference exceeds a predetermined value, the switching valve is switched to increase the rotational speed of the first hydraulic motor and the second hydraulic motor. And a second control means for shutting off the supply of the pressure oil to the side hydraulic motor. In the HST traveling system of the working machine according to claim 1 or 4,
The first control means further has a medium-speed two-wheel drive mode for driving only the front wheel travel device, and switches to any one of the low-speed four-wheel drive mode, the high-speed two-wheel drive mode, and the medium-speed two-wheel drive mode. An HST traveling system for a work machine, which is possible.

Images