JP5160367B2 - Work vehicle - Google Patents

Description

  The present invention relates to a work vehicle including a main transmission and a sub-transmission that perform travel shift switching based on a shift command.

A main transmission that performs a multi-stage traveling shift switching based on a shift command, and a sub-transmission that performs at least a high-speed and a low-speed traveling shift switching based on the shift command, the main transmission and the sub-transmission device, 2. Description of the Related Art A work vehicle shown in Patent Document 1 is known which is arranged in series so that power after shifting from one side is input to the other side.
JP 2000-62500 A

However, in the work vehicle of the above document, for example, when switching the running shift from the 4th speed to the 5th speed, the main transmission is switched from the 4th speed to the 1st speed and the subtransmission is switched from the low speed to the high speed. In this case, there is a problem that a shift shock may occur due to inertial power on the transmission downstream side of the auxiliary transmission. On the other hand, simply reducing the speed ratio at the time of shifting from 4th to 5th speed to reduce the above-mentioned shift shock, the maximum speed necessary for the work vehicle may not be ensured in some cases. There are challenges.
The present invention solves the above-described problems and provides a maximum travel speed required for a work vehicle while reducing shift shock in a work vehicle including a main transmission and a sub-transmission that perform travel shift switching based on a shift command. An object is to provide a work vehicle that can be easily secured.

In order to solve the above-described problems, a work vehicle according to the present invention includes a main transmission 13 that switches a plurality of travel shifts based on a shift command, and a sub-transmission that switches at least a high speed and a low speed based on the shift command. 17 in a work vehicle in which the main transmission 13 and the sub-transmission 17 are arranged in series so that power after shifting from one side is input to the other side. Compared to the speed ratio for each speed increase when the speed is increased from the highest speed stage to the lower speed stage than the highest speed stage, the speed ratio for increasing the speed from the lower speed stage to the highest speed stage is lower than the highest speed stage. And the speed ratio when the auxiliary transmission 17 is increased from low speed to high speed as compared to the speed ratio when the main transmission 13 is increased from the lowest speed to the highest speed at a stretch , and From the low speed of the auxiliary transmission 17 to the high speed The value obtained by dividing the speed ratio at the time of the shift change by the speed ratio when the main transmission 13 is increased from the lowest speed to the highest speed at a stretch increases the main transmission 13 from the lowest speed to the highest speed. Of the speed ratio for each one-stage speed increase, or the speed ratio for each one-stage speed increase when the main transmission 13 is accelerated from the lowest speed stage to a speed stage that is one step lower than the highest speed stage. The main transmission 13 and the auxiliary transmission 17 are configured to be smaller than the average value .

  According to the work vehicle of the present invention configured as described above, the subtransmission is increased from a low speed to a high speed as compared with a speed ratio when the main transmission is increased from the lowest speed to the highest speed at a stroke. Because the speed ratio at the time is slightly large, the main transmission is decelerated from the highest speed to the lowest speed, and the auxiliary transmission is accelerated from the low speed to the high speed to change the traveling speed to the speed increase side. While the speed ratio is small, there is an effect that the shift shock is suppressed. On the other hand, each speed ratio for each speed increase when the main transmission is increased from the lowest speed to one speed lower than the highest speed. Compared to the above, since the speed ratio when the speed is increased from the lower speed stage to the highest speed stage is larger than that of the highest speed stage, there is an effect that it becomes easy to secure the maximum speed necessary for the work vehicle.

Embodiments of the present invention will be described below based on the illustrated example.
FIG. 1 is an overall side view of a tractor to which a work vehicle of the present invention is applied. The tractor can be connected to the traveling machine body 3 by a traveling machine body 3 having a pair of left and right front wheels 1, 1 and rear wheels 2, 2 and arranged behind the traveling machine body 3 so as to be driven up and down by a lifting link (link mechanism) 4. And a working machine (not shown) such as a rotary tiller.

  A bonnet 7 that houses the engine 6 (see FIG. 3) is installed in the front half of the traveling machine body 3, and a control unit 8 is provided behind the hood 7 in the traveling machine body 3. By the operation of the operator who has entered the control unit 8, the tractor performs a work such as a tilling work with a work machine while traveling on the field.

  FIG. 2 is a side sectional view of the transmission case showing the power transmission structure of the tractor. The power of the engine 6 is shifted by a transmission (transmission device, transmission mechanism) 11 in the transmission case 9 and then transmitted to the front and rear wheels 1 and 2 and the work machine.

  The transmission 11 includes a main clutch 12 for connecting / disconnecting power to the traveling transmission system by turning on / off, a main transmission (a main transmission unit, a main transmission mechanism) 13 for changing gears of a plurality of stages (four in the illustrated example), and A forward / reverse switching device (forward / reverse switching unit, forward / reverse switching) that performs forward / reverse switching of the tractor by a forward / reverse switching operation (switching command, shift command) of a switching lever (forward / backward switching operating tool) provided in the control unit 8. Switching mechanism (switching mechanism) 14 and shift switching operation (shift command) of a shift lever (transmission operation tool) provided in the control unit 8 can perform shift switching in multiple stages (low speed, medium speed, and high speed in the illustrated example). A mechanical speed switching device (speed switching unit, speed switching mechanism) 16, a sub-transmission device (sub-transmission unit, sub-transmission mechanism) 17 that performs high-speed and low-speed switching, and intermittent power supply to the front wheels 1 Front-wheel drive switching device that performs shifting ( A wheel drive switching unit, a front wheel drive switching mechanism) 18 and a work machine clutch 19 that is a hydraulic clutch that intermittently turns on and off the power to the PTO shaft (output shaft) S1 that outputs power to the work machine side. Yes.

  The power of the engine 6 is transmitted in the order of the main transmission 13 → the forward / reverse switching device 14 → the speed switching device 16 → the auxiliary transmission device 17. The power input to the auxiliary transmission 17 is shifted and transmitted to the travel drive shaft S2. The power of the travel drive shaft S2 is always transmitted to the rear wheel 2 and is also transmitted to the front wheel 1 via the front wheel drive switching device 18. That is, the main transmission device 13, the forward / reverse switching device 14, the speed switching device 16, the auxiliary transmission device 17, and the front wheel drive switching device 18 are arranged in series on the power transmission path from the engine 6 to the forward / reverse driving 1 and 2. Thus, a travel transmission device (travel transmission mechanism) is configured to perform a total of 24 stages of travel shift switching at 4 × 3 × 2. As described above, the main transmission 13 and the auxiliary transmission 17 are configured such that the power after shifting on one side (the main transmission 13 in the illustrated example) is transmitted to the other side via the forward / reverse switching device 14 and the speed switching device 16. They are arranged in series so as to be input to the auxiliary transmission device 17 (in the illustrated example).

  The main clutch 12 is rotationally driven around the shaft from the engine 6 by the power of the engine 6 and is formed in a cylindrical shape covering the outer periphery of the transmission shaft S3 that transmits power to the work machine clutch 18 side, and is a concentric shaft of the transmission shaft S3. The power transmission to the traveling transmission shaft S4 that is pivotally supported in a freely rotatable state is intermittently turned on and off. The operator turns off the main clutch 12 by a stepping operation of a clutch pedal 21 (see FIG. 1) installed on the floor side of the control unit 8 and turns on the main clutch 12 by releasing the stepping of the clutch pedal 21.

  The main transmission 13 is integrally attached and fixed to the travel transmission shaft S4 and has the same number of shift input gears (first speed input gear, second speed input gear) as the speed of the main transmission 13 that rotates integrally with the travel transmission shaft S4. , 3rd speed input gear, 4th speed input gear) 22A, 22B, 22C, 22D and the same number of shift output gears as the shift stages of the main transmission 13 that always mesh with the corresponding shift input gears 22A, 22B, 22C, 22D. (1st speed output gear, 2nd speed output gear, 3rd speed output gear, 4th speed output gear) 23A, 23B, 23C, 23D, 1st speed output gear 22A and 4th speed output gear 22D can be freely rotated (in the idle state) A first transmission shaft (transmission shaft) S5, a second speed output gear 22B (not shown), and a third speed output gear 22C (not shown) that support the second speed change shaft (speed change) that rotatably support (in the idle state). Axis) S6 (not shown) The first-speed clutch (transmission clutch) 24A, which is a hydraulic clutch that intermittently transmits the power of the first-speed output gear 23A to the first transmission shaft S5 by the operation, and the second-speed output gear 23B by the on / off operation. A second speed clutch (transmission clutch) 24B (see FIG. 3) that is a hydraulic clutch that intermittently transmits to the second and a third speed that is a hydraulic clutch that intermittently transmits the power of the third speed output gear 23C to the second transmission shaft S6 by on / off operation. A clutch (transmission clutch) 24C (see FIG. 3) and a 4-speed clutch (transmission clutch) 24D, which is a hydraulic clutch that intermittently transmits the power of the 4-speed output gear 23D to the first transmission shaft S5 by an on / off operation. Yes.

  Incidentally, the first transmission shaft S5 and the second transmission shaft S6 are arranged in parallel on the left and right, and FIG. 2 shows the second transmission shaft S6, the second speed output gear 23B, the third speed output gear 23C, and the second speed clutch 24B. And the 3rd speed clutch 24C is not shown.

  In this tractor, any one of the four transmission clutches 24A, 24B, 24C, and 24D is turned on and the other three are turned off, so that the main transmission 13 is set to any one of the first to fourth speeds. On the other hand, the power transmission from the engine 6 to the downstream side of the main transmission 13 is cut off by disengaging all the four shift clutches 24A, 24B, 24C, 24D.

  The forward / reverse switching device 14 includes a first speed / fourth speed forward input gear (forward input gear) 26 and a reverse input gear 27 that rotate integrally with the first speed change shaft S5, and an unillustrated 2 that rotates integrally with the second speed change shaft S6. A three-speed forward input gear (forward input gear), a forward / reverse switching shaft S7, and a forward / backward switching shaft S7 are rotatably supported (in a free-wheeling state) and always mesh with the two forward input gears 26. Reverse output from the forward output gear 28, the reverse output gear 29 rotatably supported by the forward / reverse switching shaft S7 (in the idle state), the reverse input gear 27 and the reverse output gear 29 are always meshed with the reverse input gear 27. A reverse gear (not shown) that transmits power to the gear 29, a forward clutch 31 that is a hydraulic clutch that intermittently transmits the power of the forward output gear 28 to the forward / reverse switching shaft S7 by an on / off operation, and a reverse output by an on / off operation Gear 2 And a reverse clutch 32 is a hydraulic clutch for intermittently transmitting the forward-reverse switching axis S7 of power.

  In this tractor, the forward clutch 31 is turned on and the reverse clutch 32 is turned off to switch the forward / reverse switching device 14 (traveling machine body 3) to the forward running state, while the forward clutch 31 is turned off. At the same time, the forward / reverse switching device 14 (the traveling machine body 3) is switched to the reverse traveling state by turning on and operating the reverse clutch 32. In addition, the forward clutch 31 and the reverse clutch 32 are both turned off to move forward and backward from the engine 6. The power transmission to the downstream side of the switching device 14 is interrupted.

  In other words, from the above configuration, the tractor performs a total of four speeds of shifting between the first speed, the second speed, the third speed, and the fourth speed by the main transmission 13 when traveling forward, and the first speed and the fourth speed when traveling backward. Two gears are changed.

  The speed switching device 16 is supported on the forward / reverse switching shaft S7 so as to be freely rotatable (in a free-running state), and a transmission gear 34 that constantly transmits its power to the speed switching shaft S8, and the power from the forward / reverse switching shaft S7. Is continuously transmitted and is rotatably supported by the speed switching shaft S8 (in a free-wheeling state), and the power from the forward / reverse switching shaft S7 to the transmission gear 34 is interrupted by turning on and off. A synchronous mesh (synchromesh type) speed change clutch 38 and a speed change clutch 39 supported by the speed switching shaft S8 are provided.

  The shift clutch 39 is configured to transmit the power of the transmission gear 36 to the speed switching shaft S8 and to block the power transmission from the transmission gear 37 to the speed switching shaft S8 by fine reciprocation in the axial direction on the speed switching shaft S8. A state in which power of the transmission gear 37 is transmitted to the speed switching shaft S8 and power transmission from the transmission gear 36 to the speed switching shaft S8 is interrupted, and any power of the pair of transmission gears 36, 37 is the speed switching shaft. This is a synchronous mesh clutch that switches between S8 and a non-transmission state.

  In this tractor, the two shift clutches 38 and 39 are operated by the forward / backward swing operation (shift switching operation) of the shift lever, and any one of the three shift gears 34, 36, and 37 is applied to the travel switching shaft S8. It is configured to transmit in three stages, low speed, medium speed and high speed.

  The sub-transmission device 17 is supported by a high-speed input gear 41 and a low-speed input gear 42 that rotate integrally with the speed switching shaft S8, and a travel drive shaft S2 that serves as a sub-transmission shaft. A high-speed output gear 43 that is always meshed with the gear 41, a low-speed output gear 44 that is rotatably supported (in the idle state) on the traveling drive shaft S2 that is the sub-transmission shaft, and is always meshed with the low-speed input gear 42; A high-speed clutch (transmission clutch) 46, which is a hydraulic clutch that intermittently transmits power from the high-speed output gear 43 to the travel drive shaft S2 by operation, and a hydraulic pressure that intermittently transmits power from the low-speed output gear 44 to the travel drive shaft S2 by on / off operation. A low-speed clutch (transmission clutch) 47 that is a clutch is provided.

  The tractor engages and disengages the high-speed clutch 46 and disengages the low-speed clutch 47 to switch the auxiliary transmission 17 (the traveling machine body 3) to a high speed, while disengaging the high-speed clutch 46 and operating the low-speed clutch 47 at low speed. In addition to switching the auxiliary transmission 17 (running vehicle body 3) to low speed by operating the clutch 47, the high speed clutch 46 and the low speed clutch 47 are both operated to disconnect from the engine 6 on the downstream side of the auxiliary transmission 17. It is comprised so that the power transmission to may be interrupted.

  FIG. 3 is a hydraulic circuit diagram of a hydraulic apparatus that supplies / discharges pressure oil to / from hydraulic equipment such as a hydraulic clutch. This tractor is equipped with a hydraulic device 48 that supplies and discharges pressure oil to and from the hydraulic clutches 24A, 24B, 24C, 24D, 31, 32, 47, 46 and the like described above. The hydraulic device 48 includes a hydraulic pump 51 that is driven by the engine 6 and pumps the pressure oil in the hydraulic tank 49.

  The pressure oil from the hydraulic pump 51 is first supplied to the steering unit 54, which is a hydraulic steering device that operates based on the operation of the steering handle 53 (see FIG. 1) provided in the control unit 8 by the diversion valve 52. And the pressure oil to the hydraulic clutches 24A, 24B, 24C, 24D, 31, 32, 46, 47 side. And the pressure oil sent to the hydraulic clutches 24A, 24B, 24C, 24D, 31, 32, 46, 47 side, the first speed clutch 24A, the second speed clutch 24B, the third speed clutch 24C and the fourth speed clutch 24D side, It is supplied to the forward clutch 31 and the reverse clutch 32 side, and to the high speed clutch 46 and the low speed clutch 47 side, respectively.

  The pressure oil sent to the first speed clutch 24A, the second speed clutch 24B, the third speed clutch 24C, and the fourth speed clutch 24D in this way can be adjusted in opening degree so that the first speed clutch 24A is turned on and off by an opening / closing operation. A speed valve (electromagnetic proportional valve, speed change valve) 56A, a speed-adjustable second speed valve (electromagnetic proportional valve, speed change valve) 56B that opens and closes the second speed clutch 24B by opening / closing operation, and a 3-speed clutch by opening / closing action An openable adjustable 3-speed valve (electromagnetic proportional valve, speed change valve) 56C for turning on and off 24C and an openable adjustable 4-speed valve (electromagnetic proportional valve, open / closed for open / close operation of 4-speed clutch 24D) (Transmission valve) 56D.

  The electromagnetic proportional valves 56A, 56B, 56C, and 56D engage and operate the corresponding hydraulic clutches 24A, 24B, 24C, and 24D to transmit the power of the corresponding transmission output gears 23A, 23B, 23C, and 23D to the corresponding transmission shaft S5. , And the corresponding hydraulic clutches 24A, 24B, 24C, and 24D are turned off, and the corresponding hydraulic clutches 24A, 24B, 24C, and 24D are turned off and the corresponding positions of the hydraulic clutches 24A, 24B, 24C, and 24D are formed. A flow path for discharging pressure oil from the corresponding hydraulic clutches 24A, 24B, 24C, 24D is formed so as to cut off the power from the corresponding shift output gears 23A, 23B, 23C, 23D to the corresponding transmission shafts S5, S6. Cutting position. Then, the solenoid proportional valves 56A, 56B, 56C, and 56D are switched between the on position and the off position by operating a solenoid based on an electrical control signal output from a control unit configured by a microcomputer or the like.

  Since each of the electromagnetic proportional valves 56A, 56B, 56C, 56D is configured to be able to adjust the opening degree based on the duty ratio of the control signal, etc., it is gradually applied to the corresponding hydraulic clutch 24A, 24B, 24C, 24D. It is possible to perform pressure increase control in which pressure oil is supplied to the internal pressure to gradually increase the internal pressure.

  In this tractor, when performing the gear shift switching, the electromagnetic proportional valves 56A, 56B, 56C, 56D for controlling on / off of the hydraulic clutches 24A, 24B, 24C, 24D currently connected in the main transmission 13 are switched to the off position. Thereafter, when the electromagnetic proportional valves 56A, 56B, 56C, and 56D for controlling on / off of the hydraulic clutches 24A, 24B, 24C, and 24D to be connected are switched to the on position, the pressure control is performed to perform the pressure control. 24B, 24C, and 24D are gradually connected to reduce the shift shock when shifting.

  Specifically, for example, when performing the shift switching from the second speed to the third speed of the main transmission, the second speed valve 56B is switched from the on position to the off position, and the second speed gear 23B is switched to the second speed change shaft. When switching from the OFF position to the ON position of the 3rd speed valve 56C after the power transmission to S6 is cut off, the 3rd speed output gear 23C and the 2nd speed gear 2C are connected via the 3rd speed clutch 24 by performing the above boost control. The shift shock is reduced by gradually connecting the transmission shaft S6 to the power transmission.

  In addition, the pressure to the hydraulic clutches 24A, 24B, 24C, 24D from the electromagnetic proportional valves 56A, 56B, 56C, 56D to the corresponding hydraulic clutches 24A, 24B, 24C, 24D, A one-way throttle valve 57 acting only on the oil flow is installed, and the four one-way throttle valves 57 also prevent the hydraulic clutches 24A, 24B, 24C, and 24D from entering and operating instantaneously. The

  The pressure oil sent to the forward clutch 31 and the reverse clutch 32 described above is supplied to a forward / reverse switching valve 58 that is a manual hydraulic valve. This forward / reverse switching valve 58 engages and operates the forward clutch 31 by supplying pressure oil to the inside to transmit the power of the forward output gear 28 to the forward / reverse switching shaft S7 and discharges the hydraulic oil to the hydraulic tank 49 to reverse clutch. The forward clutch 31 is disengaged by the forward position where the pressure oil passage is formed so as to cut off the power transmission from the reverse output gear 29 to the forward / reverse switching shaft S7 and the hydraulic oil discharge to the hydraulic tank 49. The power transmission from the forward output gear 28 to the forward / reverse switching shaft S7 is cut off, and the reverse clutch 32 is turned on and off by the supply of pressure oil to transmit the power of the reverse output gear 29 to the forward / reverse switching shaft S7. The reverse drive position where the pressure oil flow path is formed and the forward clutch 31 and the reverse clutch 31 are turned off by the pressure oil discharge to the hydraulic tank 49, and the forward output gear 28 is turned forward and backward. And a neutral position for forming a pressure oil passage so as to block the power transmission from the shaft S7 and the reverse output gear 29 to the forward-reverse switching axis S7 (neutral position).

  The three-position forward / reverse switching valve 58 is mechanically connected to the switching lever, and the forward / backward swing operation (forward / reverse switching operation) of the switching lever switches between the forward position, the neutral position, and the reverse position. Done. In addition, the forward / reverse switching valve 58 is configured to always be temporarily switched to the neutral position when switching from the forward position to the reverse position and from the reverse position to the forward position.

  The pressure oil sent to the above-described high speed clutch 46 and low speed clutch 47 side is supplied to a travel shift switching valve 59 which is an electromagnetic direction switching valve. The travel shift switching valve 59 engages and operates the high-speed clutch 46 by supplying pressure oil to the inside to transmit the power of the high-speed output gear 43 to the travel drive shaft S2 and discharges the pressure oil to the hydraulic tank 49 so that the low-speed clutch 47 And the high speed clutch 46 is cut off by the pressure oil discharge to the hydraulic tank 49 and the high speed position where the pressure oil passage is formed so as to cut off the power transmission from the low speed output gear 44 to the traveling drive shaft S2. Thus, the power transmission from the high speed output gear 43 to the travel drive shaft S2 is interrupted, and the low speed clutch 47 is engaged by the supply of pressure oil to the inside so that the power of the low speed output gear 44 is transmitted to the travel drive shaft S2. The low pressure position forming the oil flow path, the flow path of the pressure oil from the high speed clutch 46 and the flow path of the pressure oil from the low speed clutch 47 are joined together and the joined pressure oil is supplied to the hydraulic tank 4. A neutral position in which the power transmission from the low-speed output gear 44 to the travel drive shaft S2 and from the high-speed output gear 43 to the travel drive shaft S2 is cut off by forming a flow path to be discharged to disconnect the high-speed clutch 46 and the low-speed clutch 47. Neutral position).

  The travel shift switching valve 59 composed of the three positions is switched between a forward position, a neutral position, and a reverse position by a solenoid operated by an electrical control signal output from the control unit. Incidentally, the travel shift switching valve 59 is configured to always be temporarily switched to the neutral position when switching from the high speed position to the low speed position and when switching from the low speed position to the high speed position.

  Then, when switching the travel shift switching valve 59 from the high speed position to the low speed position or from the low speed position to the high speed position, the travel shift switching valve 59 is held at a neutral position for a predetermined time (temporarily, temporarily for the processing speed of the control unit). Thus, synchronization processing (rotation synchronization processing) is performed, inertia power on the downstream side of the auxiliary transmission 17 is suppressed, and a shift shock at the time of shift switching by the auxiliary transmission 17 is reduced.

  In order to perform this synchronization processing, the travel shift switching valve 59 is held at the neutral position for a predetermined time, so that the travel shift switching time becomes longer. However, in order to make this travel shift switching time as short as possible, A throttle valve (throttle) 62 is provided in the flow path (oil discharge path) 61 to the hydraulic tank 49.

  With the above configuration, when the traveling shift switching valve 59 is held at the neutral position when switching from the high speed position to the low speed position or from the low speed position to the high speed position, the hydraulic pressure that is currently connected before switching is selected from among the high speed clutch 46 and the low speed clutch 47. The pressure oil on the clutch 46, 47 side is hardly discharged into the hydraulic tank 49 due to the resistance of the throttle valve 62, and is supplied to the hydraulic clutch 46, 47 side to be connected after switching. Subsequently, when the travel shift switching valve 59 is switched to the low speed position or the high speed position, the hydraulic clutches 46 and 47 to be connected after the switching are charged and supplied, and the hydraulic clutches 46 and 47 are completely connected. At this time, since the predetermined amount of pressure oil is already supplied to the hydraulic clutches 46 and 47 by the operation of the throttle valve 62, the on-time of the hydraulic clutches 46 and 47 (pressure oil filling) Time).

  That is, the traveling shift is performed in a state in which the drained oil from the side of the hydraulic clutches 46 and 47 that are in the connected state before the gear change is applied to fill the pressure clutches 46 and 47 that are in the connected state after the gear change. Since the above-described synchronization processing is performed by holding the switching valve 59 for a predetermined time, the time during which the power is shut off by the shift switching is shortened as much as possible while reducing the shift shock at the shift switching of the sub-transmission device 17 and smooth shifting. Switching can be performed.

  FIG. 4 is a list of travel speeds of the main transmission and the auxiliary transmission. In this tractor, when a shift-up switch (accelerating operation tool) and a shift-down switch (deceleration operating tool) provided on the grip of the shift lever are pressed, they are converted into electrical operation signals and input to the control unit. . The control unit outputs an electrical control signal (shift command) to the four electromagnetic proportional valves 56A, 56B, 56C, 56D and the electromagnetic direction switching valve 59 based on the input operation signal, and the main transmission device. 13 and the subtransmission device 17 perform a total of 8 shifts at 4 × 2 for shifting.

  Specifically, as shown in the table of the figure, by holding the auxiliary transmission 17 in a low speed state, the main transmission 13 is increased from 1st speed → 2nd speed → 3rd speed → 4th speed. The traveling speed of the main transmission 13 and the sub-transmission 17 is increased from 1st speed → 2nd speed → 3rd speed → 4th speed, and the main transmission 13 is held at the 1st speed by holding the sub transmission 17 in a high speed state. By increasing the speed from the second speed, the third speed, and the fourth speed, the driving gear stages of the main transmission 13 and the sub transmission 17 are increased from the fifth speed, the sixth speed, the seventh speed, and the eighth speed. By switching the transmission 17 from the low speed to the high speed and the main transmission 13 from the 4th speed to the 1st speed, the main gear 13 and the auxiliary transmission 17 are switched from the 4th speed to the 5th speed. On the other hand, by carrying out the process opposite to the above-described process, the travel speed of the main transmission 13 and the auxiliary transmission 17 is changed from the 8th speed → the 7th speed → the 6th speed → the 5th speed → the 4th speed → the 3rd speed → the 2nd speed → the 1st speed. To slow down.

  In the traveling transmission described above, when the speed switching device 16 is at a low speed, the main transmission 13 and the sub-transmission device 17 perform the gear switching to any one of the first to eighth gears to change the speed. When the speed of the device 16 is medium, the main transmission device 13 and the sub-transmission device 17 perform gear shift switching to any gear number between 9th speed and 16th speed. And the sub-transmission device 17 performs the shift switching to any gear stage number between the 17th speed and the 24th speed.

  In this tractor, the speed ratio from the first speed (lowest speed) to the second speed (1.194 in this example) and the second speed to the third speed (speed lower by one speed than the highest speed) in the main transmission 13. Of the main transmission 13 so that the speed ratio (1.409 in this example) of the third speed to the fourth speed in the main transmission 13 is larger than each of the speed ratios (1.208 in this example). The number of teeth of each shift input gear 22A, 22B, 22C, 22D and each shift output gear 23A, 23B, 23C, 23D is set. By the way, the speed ratio is a value indicating how many times the speed after the shift change is compared with the speed before the shift change. For example, if the speed ratio is 2.000, the rotational speed of the engine 6 is In the same case, it means that the speed after the shift becomes twice the speed before the shift.

  Also, the sub-transmission device is switched from low speed to high speed as compared with the speed ratio (2.034 in this example) when the main transmission device 13 is shifted from the first speed to the fourth speed (highest speed) at a stroke. The number of teeth of each of the transmission input gears 22A, 22B, 22C, 22D and each of the transmission output gears 23A, 23B, 23C, 23D of the main transmission 13 so that the speed ratio (2.118) in the case is slightly increased, The number of teeth of the high speed input gear 41, the low speed input gear 42, the high speed output gear 43 and the low speed output gear 44 of the auxiliary transmission 17 is set.

  By the way, it is preferable that the speed ratio when the main transmission 13 is shifted from the first speed to the fourth speed at a stretch is larger than 2 and not more than 2.05. In addition, the value obtained by dividing the speed ratio when the sub-transmission device 17 is switched from low speed to high speed is divided by the speed ratio when the main transmission device 13 is shifted from the first speed to the fourth speed at once. When the speed is increased from the first speed to the fourth speed, the average of the respective speed ratios for each one-stage speed increase (in this example, 1.270) or when the main transmission 13 is increased from the first speed to the third speed It is set to be a value close to 1 which is smaller than the average of the respective speed ratios for each speed increase (1.201 in this example), and is 1.041 in this example.

  FIG. 5 is a characteristic graph showing the speed ratio of the travel transmission. With the above-described configuration, when the main transmission 13 and the sub-transmission 17 are shifted from the fourth speed to the fifth speed or from the fifth speed to the fourth speed in the travel gear stage (from the 20th speed to the 21st speed of the travel transmission in the figure). Since the difference in rotational speed when the transmission upstream side and the downstream side of the subtransmission device 17 are compared with each other is smaller than that of the conventional tractor, the shift shock is reduced.

  In addition, when the operation signal for switching the traveling gear stage of the main transmission 13 and the auxiliary transmission 17 from the 4th speed to the 5th speed is input to the control unit by the upshift switch at the time of the high speed switching of the speed switching device 16, the control unit After the 4th speed valve 56D is fully opened and switched to the off position and the travel shift switching valve 59 is switched to the neutral position, the downstream side and upstream side synchronous processing of the auxiliary transmission 17 described above is performed, and then the pressure switch or the like The detection means waits until the power transmission state of the auxiliary transmission 17 is detected.

  When the state is detected, the control unit switches the first speed valve 56A to the on position with the opening fully opened, then switches to the off position side after a predetermined time (instantly), and then the travel shift switching valve 59 To the high speed position. By the on / off operation of the first speed clutch 24A by the first speed valve 56A, the main transmission 13 is in a power connection state for a predetermined time (for a moment), and synchronization processing (rotation synchronization processing) on the downstream side and upstream side of the main transmission 13 is performed. ) Is performed. Then, when the control unit detects the power connection state of the sub-transmission device 17 by the detection means, the control unit performs pressure increase control of the first-speed clutch 24A by the first-speed valve 56A, and gradually brings the main transmission 13 into the power connection state. As described above, the tractor reduces the shift shock at the traveling shift stage.

1 is an overall side view of a tractor to which a work vehicle of the present invention is applied. It is a sectional side view of the mission case which shows the power transmission structure of this tractor. It is a hydraulic circuit diagram of a hydraulic device that supplies and discharges pressure oil to and from hydraulic equipment such as a hydraulic clutch. It is a table | surface of the driving gear stage of a main transmission and an auxiliary transmission. It is a characteristic graph which shows the speed ratio of a travel transmission.

Explanation of symbols

13 Main transmission (main transmission unit, main transmission mechanism)
17 Subtransmission (subtransmission unit, subtransmission mechanism)

Claims (1)

A main transmission (13) for switching a plurality of travel shifts based on a shift command; and a sub-transmission (17) for switching at least a high speed and a low speed based on a shift command. 13) In the work vehicle in which the auxiliary transmission (17) is arranged in series so that power after shifting from one side is input to the other side, the main transmission (13) is moved from the lowest speed to the highest speed. Compared to each speed ratio for each speed increase when increasing to a gear position that is one step lower than the speed step, the speed ratio when increasing from the lower speed step to the highest speed step is higher than the highest speed step. The speed ratio for increasing the auxiliary transmission (17) from low speed to high speed is larger than the speed ratio for increasing the main transmission (13) from the lowest speed to the highest speed at a stroke , and , Shifting of the auxiliary transmission (17) from low speed to high speed Divided by the speed ratio when the main transmission (13) is increased from the lowest speed to the highest speed at a stretch, the main transmission (13) is increased from the lowest speed to the highest speed. Or smaller than the average value of the speed ratios for each one-stage speed increase, or when the main transmission (13) is increased from the lowest speed stage to a gear position that is one stage lower than the highest speed stage. A work vehicle in which the main transmission (13) and the auxiliary transmission (17) are configured to be smaller than the average value of the speed ratio .

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