JP2011149497A - Vehicle speed control structure of work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain work accuracy in rotary plowing work etc. by compensating the fluctuation of power transmission efficiency in a hydrostatic continuously variable transmission arising from a load without causing a complex structure. <P>SOLUTION: A vehicle speed control structure includes: an engine speed detection means 62, which detects engine speed; a change gear ratio setting means D, which sets the change gear ratio of the fluctuation of power transmission 9, a vehicle speed detection means 63, which detects vehicle speed; a change gear ratio changing means C, which changes the change gear ratio of the fluctuation of power transmission 9; and a vehicle speed control means 27B, which controls the operation of the change gear ratio changing means C. The vehicle speed control means 27B is structured to calculate control target vehicle speed based on an output of engine speed detection means 62 and that of change gear ratio setting means D and to control the operation of change gear ratio changing means C so that the output of the vehicle speed detection means 63 matches the calculated control target vehicle speed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a gear ratio setting means for setting a gear ratio of a hydrostatic continuously variable transmission, a gear ratio changing means for changing a gear ratio of the hydrostatic continuously variable transmission, and an operation of the gear ratio changing means. The present invention relates to a vehicle speed control structure of a work vehicle provided with vehicle speed control means for controlling the vehicle.

  As a shift control device for a work vehicle as described above, a shift hydraulic cylinder (corresponding to a gear ratio changing means) that operates a trunnion shaft of a hydrostatic continuously variable transmission, and an operation of the shift hydraulic cylinder are controlled. A control device (corresponding to vehicle speed control means), a potentiometer type speed setting device (corresponding to gear ratio setting means) for detecting the operation amount of the shift lever, and a potentiometer type feedback sensor for detecting the actual rotation amount of the trunnion shaft In some cases, the control device controls the operation of the hydraulic cylinder so that the detected value of the feedback sensor matches the set value by the speed setting device (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-23610 (paragraph number 0012, FIG. 1)

  In the above configuration, the actual rotation amount of the trunnion shaft in the hydrostatic continuously variable transmission can be made to correspond to the operation amount of the shift lever by the control operation of the vehicle speed control means. However, it is known that the hydrostatic continuously variable transmission has a greater hydraulic loss due to oil leaks as the load increases, resulting in lower power transmission efficiency. In addition, even if the actual rotation amount of the trunnion shaft in the hydrostatic continuously variable transmission device matches the operation amount of the shift lever held at a predetermined operation position, if the load fluctuates during traveling, the hydrostatic pressure associated with the variation The transmission ratio of the hydrostatic continuously variable transmission may become unstable due to fluctuations in power transmission efficiency in the type continuously variable transmission, and the vehicle speed may change greatly.

  Therefore, it is common to use motive power from the engine after the shift by the hydrostatic continuously variable transmission, and to work from the engine not shifted by the hydrostatic continuously variable transmission. When the configuration described in Patent Document 1 is employed in a work vehicle, it is desirable to maintain the vehicle speed and the operating speed of the work device in a certain relationship proportional to the engine speed, such as rotary tillage work. In this case, it becomes difficult to maintain the above-mentioned relationship because the vehicle speed largely changes due to fluctuations in power transmission efficiency in the hydrostatic continuously variable transmission, thereby making the work traces by the work device accurate and uniform. It was difficult. In other words, there is room for improvement in improving work accuracy in rotary tillage work and the like.

  An object of the present invention is to compensate for fluctuations in power transmission efficiency in a hydrostatic continuously variable transmission caused by a load without increasing the complexity of the configuration, thereby improving work accuracy in rotary tillage work and the like. There is in doing so.

The first problem solving means of the present invention is:
Engine speed detecting means for detecting the engine speed, speed ratio setting means for setting the speed ratio of the hydrostatic continuously variable transmission, vehicle speed detecting means for detecting the vehicle speed, and the speed ratio of the hydrostatic continuously variable transmission A gear ratio changing means for changing, and a vehicle speed control means for controlling the operation of the gear ratio changing means,
The vehicle speed control means obtains a control target vehicle speed based on the output of the engine speed detection means and the output of the gear ratio setting means, and the output of the vehicle speed detection means matches the obtained control target vehicle speed. The operation of the gear ratio changing means is controlled.

  According to this problem solving means, the vehicle speed control means reads the engine speed from the output of the engine speed detection means, reads the set speed ratio of the hydrostatic continuously variable transmission from the output of the speed ratio setting means, and reads the read engine. A control target vehicle speed is obtained based on the rotational speed and the set gear ratio of the hydrostatic continuously variable transmission. Then, the vehicle speed is read from the output of the vehicle speed detecting means, and the operation of the speed ratio changing means is controlled so that the read vehicle speed matches the control target vehicle speed (the vehicle speed is within the dead zone width of the control target vehicle speed). Change the gear ratio of the continuously variable transmission.

  In other words, the vehicle speed control means performs vehicle speed feedback control that changes the gear ratio of the hydrostatic continuously variable transmission so that the vehicle speed detected by the vehicle speed detection means matches the control target vehicle speed, resulting in an increase or decrease in load. The variation in power transmission efficiency in the hydrostatic continuously variable transmission can be compensated by the control operation of the vehicle speed control means, and the hydrostatic continuously variable transmission regardless of the variation in power transmission efficiency in the hydrostatic continuously variable transmission The gear ratio of the transmission can be stabilized. As a result, gear shifting by the hydrostatic continuously variable transmission can be performed with high accuracy, and the engine speed and the vehicle speed correspond to the gear ratio of the hydrostatic continuously variable transmission set by the gear ratio setting means (for example, The relationship in which the vehicle speed is proportional to the engine speed) can be accurately maintained.

  As a result, in a working vehicle such as a tractor, the power from the engine shifted by the traveling transmission is used for traveling, and the power from the engine not shifted by the traveling transmission is used for work. When carrying out work such as rotary tillage work, where it is desirable to maintain a constant relationship between the vehicle speed and the operating speed of the work device, which is proportional to the engine speed, the relationship can be expressed with a hydrostatic continuously variable transmission. It can be maintained with high accuracy regardless of fluctuations in the power transmission efficiency of the vehicle, and the difference between the vehicle speed and the appropriate vehicle speed with respect to the operating speed of the work device is less likely to occur. In addition, it is possible to improve work accuracy in rotary tillage work and the like.

A second problem solving means of the present invention is the above first problem solving means,
The hydrostatic continuously variable transmission is provided with a variable displacement pump and a variable displacement motor, and the transmission ratio changing means is a pump swash plate angle changing means for changing the swash plate angle of the variable displacement pump steplessly; and The swash plate angle changing means for switching the swash plate angle of the variable capacity motor in a stepped manner is configured.

  According to this problem solving means, the vehicle speed control means ensures that the vehicle speed read from the output of the vehicle speed detection means coincides with the control target vehicle speed obtained based on the output of the engine speed detection means and the output of the gear ratio setting means. The operations of the pump swash plate angle changing means and the motor swash plate angle changing means are controlled.

  In other words, as in the case of swash plate feedback control, the control target swash plate angle of the variable displacement pump corresponding to the set gear ratio that differs depending on the swash plate angle of the variable displacement motor is converted into data, and the set gear ratio and motor swash plate angle are converted into data. The swash plate angle of the variable displacement motor is determined from the operating state of the plate angle changing means, and the control target swash plate angle of the variable displacement pump is set based on the set gear ratio and the determined swash plate angle of the variable displacement motor. As compared with the case where the operation of the swash plate angle changing means for the pump is controlled so that the swash plate angle of the variable displacement pump coincides with the target swash plate angle, the control configuration can be simplified.

According to a third problem solving means of the present invention, in the first or second problem solving means,
When the engine speed is the first set speed set to the engine idling speed or a speed close to the idling speed, the speed ratio of the hydrostatic continuously variable transmission is greater than the minimum speed ratio. When the engine speed is equal to or higher than the second set speed set on the higher speed side than the first set speed, the hydrostatic type Further, when the engine speed is a speed between the first set speed and the second set speed so that the speed ratio of the step transmission is the minimum speed ratio, the engine speed at that time The gear ratio setting means changes the engine speed so that the gear ratio of the hydrostatic continuously variable transmission changes to a larger gear ratio between the first gear ratio and the minimum gear ratio as the number decreases. Based on the output of the detection means, It is arranged to set changes the gear ratio of formula CVT.

  According to this problem solving means, when the engine speed is increased from the idling speed by an accelerator operation and the work vehicle is started, the lower the engine speed is, the lower the speed is close to the first set speed. Since the gear ratio of the continuously variable transmission becomes a large gear ratio on the low speed side and reduces the load on the engine, the gear ratio of the hydrostatic continuously variable transmission is maintained at a small gear ratio on the high speed side with a large load. Compared to starting the work vehicle in a state, it is possible to effectively suppress the decrease in engine speed and the occurrence of engine stall due to overload at the time of start, and smoothly start the work vehicle be able to.

  Further, when the engine speed decreases to a lower speed than the second set speed due to a travel load or work load during travel, the hydrostatic pressure is increased according to the amount of decrease from the second set speed. Since the gear ratio of the continuously variable transmission is a large gear ratio on the low speed side and the load on the engine is reduced, the engine can be made sticky and the engine stall caused by overload is effective Can be suppressed.

  When the engine speed increases to a value equal to or higher than the second set speed, the gear ratio of the hydrostatic continuously variable transmission regardless of fluctuations in power transmission efficiency in the hydrostatic continuously variable transmission due to increase or decrease of the load. Is constant at the minimum speed ratio, so that even if the engine speed increases or decreases due to the accelerator operation or the traveling load or the work load, the relationship in which the vehicle speed is proportional to the engine speed is maintained. As a result, when performing a work in which it is desirable to maintain the vehicle speed and the operating speed of the work device in a certain relationship that is proportional to the engine speed, such as in rotary tillage work, the relationship can be Regardless of fluctuations in power transmission efficiency in the transmission, it can be maintained with high accuracy, and the difference between the vehicle speed and the appropriate vehicle speed with respect to the operating speed of the work device is less likely to occur. Therefore, it is possible to improve work accuracy in rotary tillage work and the like.

  In addition, when the engine speed is between the first set speed and the second set speed, the speed ratio of the hydrostatic continuously variable transmission changes together with the engine speed by the accelerator operation. Since the range of adjustment of the vehicle speed by the accelerator operation is widened, the amount of change in the vehicle speed with respect to the accelerator operation amount is increased, and acceleration / deceleration by the accelerator operation is facilitated, so that traveling can be performed comfortably.

  The vehicle speed control having these functions and effects can be performed by a shift operation of a hydrostatic continuously variable transmission with high shift accuracy.

In the fourth problem solving means of the present invention, in any one of the first to third problem solving means,
A shift speed detection means for detecting a shift speed of the stepped transmission,
The vehicle speed control means obtains the control target vehicle speed in consideration of the gear ratio of the stepped transmission obtained from the output of the gear position detection means, and the output of the vehicle speed detection means coincides with the control target vehicle speed. Thus, the operation of the speed ratio changing means is controlled.

  According to this problem solving means, the engine speed and the vehicle speed correspond to each other between the speed ratio of the hydrostatic continuously variable transmission set by the speed ratio setting means and the speed ratio of the stepped transmission (the engine speed and the vehicle speed). Can be accurately maintained.

  Thereby, even if it is a configuration including a stepped transmission, when performing work such as rotary tillage work, in which it is desirable to maintain a relationship in which the vehicle speed and the operating speed of the work device are proportional to the engine speed, The relationship can be maintained with high accuracy, and the difference between the appropriate vehicle speed and the vehicle speed with respect to the operating speed of the work device is less likely to occur. The work accuracy can be improved.

It is the whole tractor side view. It is a whole top view of a tractor. It is a schematic plan view which shows the transmission structure of a tractor. It is a block diagram which shows a control structure. It is the schematic which shows the structure and operation structure of a main transmission (HST). It is a flowchart of vehicle speed control. It is a flowchart of forward / reverse switching control. It is a flowchart of start stop control. It is a flowchart of braking start stop control. It is a figure which shows the relationship between an engine speed, the gear ratio of a main transmission, and a vehicle speed. It is a flowchart of vehicle speed setting control. It is a flowchart of 1st switching control. It is a flowchart of 2nd switching control. It is a flowchart of 3rd board switching control. It is a front view of a display panel. It is a front view of a liquid crystal display.

  Hereinafter, an embodiment in which a vehicle speed control structure for a work vehicle according to the present invention is applied to a tractor, which is an example of a work vehicle, will be described with reference to the drawings.

  As shown in FIGS. 1 and 2, the tractor is equipped with a pair of left and right front wheels 1 so as to be steerable and drivable, and a pair of left and right rear wheels 2 are drivably drivable and can be driven independently. It is configured. An engine 3 is mounted on the front side of the tractor, and a transmission case (hereinafter referred to as a T / M case) 4 serving as a body frame is connected to the rear part of the engine 3. On the rear side of the tractor, a steering wheel 5 for driving the front wheels, a driver's seat 6 and the like are provided to form a boarding operation unit 7, and a gate-shaped protective frame 8 is erected.

  As shown in FIGS. 1 and 3, in this tractor, the power from the engine 3 is transmitted to the main transmission 9 for traveling, and the power after the shift by the main transmission 9 is used for traveling. The passing non-shifting power is used for work. The driving power is transmitted to the driving sub-transmission device 10 and branched into front wheel driving and rear wheel driving after shifting by the sub-transmission device 10. The power for driving the front wheels is transmitted to the left and right front wheels 1 via the transmission switching device 11 for the front wheels and the differential device 12 for the front wheels. The power for driving the rear wheels is transmitted to the left and right rear wheels 2 via the rear wheel differential unit 13 and the like. The working power is transmitted to the power take-out PTO shaft 16 via the working clutch 14 and the working transmission 15.

  In other words, this tractor intermittently transmits power to the left and right front wheels 1 and left and right rear wheels 2 as drive wheels and transmits power to the PTO shaft 16 by intermittently transmitting power from the engine 3 to the main transmission 9. It has a clutch-less specification that does not have a main clutch.

  As shown in FIGS. 1 and 2, in the boarding operation unit 7, an accelerator lever 17 configured to be swingable back and forth and to be held at an arbitrary operation position is disposed on the lower right side of the steering wheel 5. An accelerator pedal 18 and a pair of left and right brake pedals 19 are arranged at the right foot portion so as to automatically return to the depression release position by a depression operation type. On the left side of the driver's seat 6 is a main transmission lever 20 configured to be able to hold a position at an arbitrary operation position by swinging back and forth, and being positioned at three positions of swinging back and forth, a low speed position, a high speed position and a high speed movement position. An auxiliary transmission lever 21 configured to be held is provided. On the lower left side of the steering wheel 5, a forward / reverse switching FR lever 22 that is configured to be swingable back and forth and to be held in three positions of a neutral position, a forward position, and a reverse position is provided. A stop pedal 23 configured to automatically return to the stepping release position by a stepping operation type is provided at the left foot portion. A display panel 24 that displays information such as the vehicle speed is disposed in front of and below the steering wheel 5.

  As shown in FIG. 4, the engine 3 has its output rotational speed between the idling rotational speed and the rated rotational speed by the operation of the accelerator cylinder 26 that operates the speed regulating lever 25 of the speed governor (not shown). Can be adjusted steplessly. The accelerator cylinder 26 is an electric cylinder. The operation of the accelerator cylinder 26 is controlled by a control operation of an accelerator control means 27A provided as a control program in an electronic control unit (hereinafter referred to as ECU) 27.

  The ECU 27 is configured using a microcomputer provided with a CPU, an EEPROM, and the like. The ECU 27 includes an output of a lever sensor 28 that detects the operating position of the accelerator lever 17, an output of a pedal sensor 29 that detects the operating position of the accelerator pedal 18, and a lever sensor 30 that detects the operating position of the governing lever 25. Input the output. A rotary potentiometer is used for the lever sensor 28 for the accelerator lever, the pedal sensor 29 for the accelerator pedal, and the lever sensor 30 for the governing lever.

  The accelerator control means 27A determines the operation position of the accelerator lever 17 and the accelerator based on the output of the lever sensor 28 for the accelerator lever, the output of the pedal sensor 29 for the accelerator pedal, and the output of the lever sensor 30 for the governing lever. The operation position of the pedal 18 is compared, and when the operation position of the accelerator pedal 18 is not higher than the operation position of the accelerator lever 17, the operation position of the speed adjusting lever 25 corresponds to the operation position of the accelerator lever 17. The operation of the accelerator cylinder 26 is controlled. When the operation position of the accelerator pedal 18 is higher than the operation position of the accelerator lever 17, the operation of the accelerator cylinder 26 is controlled so that the operation position of the governing lever 25 corresponds to the operation position of the accelerator pedal 18. To do.

  As shown in FIGS. 3 and 5, the main transmission 9 employs a hydrostatic continuously variable transmission (hereinafter referred to as HST). The HST 9 includes an axial plunger type variable displacement pump 31 and a variable displacement motor 32 built in the T / M case 4. The power passing through the HST 9 (non-shift power) is output from the pump shaft 31A of the variable displacement pump 31 for work, and the power after shifting by the HST 9 is output from the motor shaft 32A of the variable displacement motor 32 for travel. The variable displacement pump 31 and the variable displacement motor 32 are connected via a first oil passage 33 and a second oil passage 34 so as to form a closed circuit. The closed circuit is supplied with oil from a charge pump 35 that is operated by power from the engine 3.

  As shown in FIGS. 4 and 5, the variable displacement pump 31 is operated by the operation angle of the pump swash plate 31 </ b> B (inclination of the variable displacement pump 31 by the operation of the pump shift cylinder 36 provided inside the T / M case 4. The plate angle) can be changed steplessly. The transmission cylinder 36 employs a double-acting hydraulic cylinder incorporating a pair of compression springs 37 that return and urge the transmission cylinder 36 to a neutral state where the operation angle of the pump swash plate 31B is zero. The operation of the shift cylinder 36 is controlled by the operation of a forward shift valve 38 and a reverse shift valve 39 configured by using an electromagnetic proportional valve. The operation of these shift valves 38 and 39 is controlled by the control operation of the vehicle speed control means 27B provided in the ECU 27 as a control program.

  That is, the pump swash plate 31B of the variable displacement pump 31 is operated steplessly by the pump shift cylinder 36, the forward shift valve 38, and the reverse shift valve 39 based on the control operation of the vehicle speed control means 27B. Pump swash plate operating means A is constructed.

  The variable displacement motor 32 uses the motor low speed cylinder 40 and the high speed cylinder 41 provided in the T / M case 4 to operate the motor swash plate 32B (the swash plate angle of the variable displacement motor 32) for low speed operation. It is possible to switch between high and low two stages, a low speed stage set to the set angle and a high speed stage set to the set angle for high speed. Single-acting hydraulic cylinders are employed for the low-speed cylinder 40 and the high-speed cylinder 41. The operations of the low-speed cylinder 40 and the high-speed cylinder 41 are controlled by the operation of a shift valve 42 configured using a pilot operated switching valve. The operation of the shift valve 42 is controlled by the operation of a shift operation valve 43 configured using an electromagnetic proportional valve. The operation of the shift operation valve 43 is controlled by the control operation of the vehicle speed control means 27B.

  That is, the motor swash plate 32B of the variable capacity motor 32 is operated in two steps, high and low, by the low speed cylinder 40, the high speed cylinder 41, the speed change valve 42, and the speed change operation valve 43 for the motor based on the control operation of the vehicle speed control means 27B. The motor swash plate operating means B is configured.

  The pump swash plate operating means A and the motor swash plate operating means B constitute gear ratio changing means C for changing the gear ratio of the main transmission 9, and the main transmission 9 is controlled by the vehicle speed control means 27B. By changing the operation angle of the pump swash plate 31B and the motor swash plate 32B by controlling the operation of the gear ratio changing means C, the electronic gear control system can change the gear ratio steplessly and stepwise. It is configured.

  Although not shown, the auxiliary transmission 10 includes a gear-type transmission configured to be capable of shifting in three stages, a low speed stage for low speed work, a high speed stage for high speed work, and a fastest stage for high speed movement. (Stepped transmission) is adopted. When the sub-transmission lever 21 is operated to the low speed position, the gear stage is switched to the low speed stage, and when the sub transmission lever 21 is operated to the high speed position, the gear stage is switched to the high speed stage, and the sub transmission lever 21 is moved to the high speed stage. The sub gear 21 is linked to the sub gear lever 21 via a sub gear mechanical linkage so that the gear position is switched to the fastest gear when operated to the moving position.

  By the way, in this tractor, the engine speed is set to the rated speed, the speed ratio of the main transmission 9 is set to the maximum speed ratio (minimum speed ratio), and the speed stage of the subtransmission 10 is set to the low speed for low speed work. The maximum speed at low speed work obtained when set to the stage is 5 km / h, the engine speed is set to the rated speed, the speed ratio of the main transmission 9 is set to the maximum speed, and the subtransmission The maximum speed at high speed work obtained when 10 speed stages are set to high speed work speed is 12 km / h, the engine speed is set to the rated speed, and the gear ratio of the main transmission 9 is changed. The traveling transmission system is configured so that the maximum speed in high speed movement obtained when the speed ratio of the sub-transmission device 10 is set to the highest speed stage for high speed movement is set to the highest speed gear ratio, and is 30 km / h. .

  As shown in FIG. 3, multi-plate side brakes 44 that brake the corresponding rear wheels 2 are provided on the left and right sides of the rear side of the T / M case 4. The left side brake 44 is applied to the left brake pedal 19, and the right side brake 44 is applied to the right brake pedal 19, and the corresponding rear wheel 2 is braked with a braking force corresponding to the depression amount of the corresponding brake pedal 19. In this way, they are linked via a mechanical linkage mechanism (not shown) for braking.

  With this configuration, for example, when turning while turning the steering wheel 5 in the turning direction, the left or right brake pedal 19 corresponding to the rear wheel 2 on the inside of the turning is operated by being stepped on alone, thereby turning at that time. The state can be switched from the normal turning state by the turning operation of the steering wheel 5 to the braking turning state in which the rear wheel 2 inside the turning is braked in addition to the normal turning state, and the turning radius of the vehicle body can be reduced. it can. In addition, when there is a shift in the direction of travel of the vehicle body due to the influence of the unevenness of the field cultivator during straight running, the brake pedal 19 on the side opposite to the shift direction can be depressed and operated at that time. The state can be switched from the straight traveling state to the one-brake traveling state, whereby the traveling direction of the vehicle body can be corrected while maintaining the steering operation system in the straight traveling state. The left and right side brakes 44 can be used as brakes for deceleration stop by depressing both the left and right brake pedals 19.

  Although not shown, the left and right brake pedals 19 are connected to the left and right brake pedals 19 to prevent the left and right brake pedals 19 from being operated individually, and the left and right brake pedals 19 are released from the left and right sides. It is equipped with a connecting mechanism that can be switched to a connection-released state that enables individual operation of the brake pedal 19. As a result, when the shift stage of the auxiliary transmission 10 is set to a low speed stage or a high speed stage for work, the connection of the left and right brake pedals 19 by the connection mechanism is released, which is a useful piece during work travel. It is possible to switch to a brake running state or a braking turning state. Further, when the shift stage of the auxiliary transmission 10 is set to the fastest stage for high-speed movement, the left and right brake pedals 19 are connected by a connecting mechanism, so that the brake pedal 19 is not damaged during high-speed movement. Thus, it is possible to avoid the possibility that the traveling state is switched to the one-brake traveling state or the braking turning state.

  As shown in FIG. 5, the stop pedal 23 is linked to an unload valve 45 provided in the main transmission 9 via a mechanical linkage mechanism (not shown) for stopping traveling. The unload valve 45 is provided in a return oil passage 46 connected to the first oil passage 33 of the main transmission 9, and the first oil passage is provided when the stop pedal 23 is not depressed to a predetermined depression limit region. The communication state that allows the oil to be discharged from the first oil passage 33 in conjunction with the stop pedal 23 being depressed to the predetermined depression limit region while maintaining the shut-off state that prevents the oil from being discharged from 33 It is comprised so that it may switch to.

  That is, by depressing the stop pedal 23 to a predetermined depression limit region, the oil is discharged from the first oil passage 33 of the main transmission 9 and the hydraulic transmission from the variable displacement pump 31 to the variable displacement motor 32 is interrupted. It is possible to stop or prevent the vehicle body from traveling.

  As a result, when it becomes necessary to stop the vehicle body in a one-brake driving state or a braking turning state in which one of the left and right brake pedals 19 is depressed, the depression pedal 23 is depressed to a predetermined depression limit region. As a result, the vehicle body can be quickly stopped without requiring the trouble of changing the left and right brake pedals 19 from the one-step state to the two-step state.

  As shown in FIGS. 1 and 4, the rear part of the T / M case 2 is provided with a left and a right that enable a lifting / lowering operation of a working device (not shown) such as a rotary tiller or a medicine sprayer connected to the rear of the tractor. A pair of lift arms 47 and a pair of left and right lift cylinders 48 that swing and drive the corresponding lift arms 47 are provided. The left and right lift cylinders 48 are single acting hydraulic cylinders. When a working device such as a rotary tiller that is operated by power from the tractor is connected to the rear portion of the tractor, the power taken out from the PTO shaft 16 is operated via a removable external transmission mechanism (not shown). Can be supplied to the device.

  As shown in FIGS. 2 to 4, the working clutch 14 causes the non-shifting power from the main transmission 9 to pass through the working transmission 15 by the operation of the clutch valve 49 configured using an electromagnetic control valve. Thus, the state is switched between an on state where the power is transmitted to the PTO shaft 16 and a cut state where the transmission is cut off. The operation of the clutch valve 49 is controlled by the control operation of the work power control means 27C provided in the ECU 27 as a control program. The working clutch 14 is a multi-plate hydraulic clutch.

  The ECU 27 is supplied with the output of the PTO switch 50 for setting on / off of transmission to the PTO shaft 16 and the output of the arm sensor 51 for detecting the swing angle of the lift arm 47 as the height of the working device. The work power control means 27C controls the operation of the clutch valve 49 based on the output thereof.

  Specifically, the work power control means 27 </ b> C determines the operation position of the PTO switch 50 based on the output of the PTO switch 50. When the operation position of the PTO switch 50 is the disengaged position, the operation of the clutch valve 49 is controlled so that the working clutch 14 maintains the disengaged state. When the operation position of the PTO switch 50 is the on position, the operation of the clutch valve 49 is controlled so that the working clutch 14 maintains the on state. When the operation position of the PTO switch 50 is an automatic position, while the swing angle of the lift arm 47 reaches the angle region above the set angle above the set angle based on the output of the arm sensor 51 for the lift arm. So that the working clutch 14 is disengaged, and the working clutch 14 is in the engaged state while the swing angle of the lift arm 47 reaches an angle region on the grounding side that is less than the set angle. The operation of the clutch valve 49 is controlled.

  That is, when a grounding work type work device such as a rotary tiller that operates with power from the PTO shaft 16 is connected as the work device, the work device is operated by operating the PTO switch 50 to the automatic position. The working device can be operated in conjunction with the swinging angle of the lift arm 47 being less than the set angle by the lowering operation. In addition, the operation of the working device can be stopped in conjunction with the swing angle of the lift arm 47 being greater than or equal to the set angle by the raising operation of the working device.

  The PTO switch 50 is provided at a position on the right side of the driver seat 6 in the boarding driver 7 (see FIG. 2). The PTO switch 50 employs a dial-type multi-contact switch configured to return to the cutting position by a downward pressing operation by a three-position switching type. The arm sensor 51 for the lift arm employs a rotary potentiometer.

  Although not shown, the work transmission 15 employs a gear-type transmission that is configured to enable forward / reverse switching and four forward rotation. The work transmission 15 is operated so that the operating state is switched in accordance with the operation position of the work shift lever 52 (see FIG. 2) provided on the right side of the driver seat 6 in the boarding operation unit 7. It is linked to the working speed change lever 52 via a mechanical linkage mechanism for use. The work shift lever 52 is configured to be capable of holding a position with a composite swing type that can swing in the front-rear direction and the left-right direction.

  As shown in FIG. 4, the operation of the left and right lift cylinders 48 is controlled by the operation of a lift valve 53 configured using an electromagnetic control valve. The operation of the elevating valve 53 is controlled by a control operation of elevating control means 27D provided in the ECU 27 as a control program.

  The ECU 27 includes an output of a lever sensor 55 that detects the operation position of the height setting lever 54 as a control target height of the work device, and a lever sensor that detects an operation from the neutral position to the ascending position or the descending position of the elevation command lever 56. 57, the output of the upper limit setter 58 that outputs the amount of rotation operation from the reference position as the control target upper limit position of the work device, and the like. The elevation control means 27D is configured to control the height of the working device at an arbitrary height position based on the output thereof, or to raise the working device to the set upper limit position in preference to the height control, Etc.

  In the height control, the swing angle of the lift arm 47 corresponds to the operation position of the height setting lever 54 based on the output of the lever sensor 55 for the height setting lever and the output of the arm sensor 51 for the lift arm. The operation of the lift valve 53 is controlled.

  The elevation control is performed with priority over the height control when the lever sensor 57 detects an operation of the elevation command lever 56 to the elevation position. In the ascent control, the swing angle of the lift arm 47 corresponds to the rotation operation amount from the reference position of the upper limit setter 58 based on the output of the upper limit setter 58 and the output of the arm sensor 51 for the lift arm. The operation of the lift valve 53 is controlled. Then, when the lever sensor 57 detects an operation of the elevation command lever 56 to the lowered position, the priority of the ascending control is canceled and the height control is performed.

  That is, by operating the height setting lever 54, the height of the work device can be changed to an arbitrary height corresponding to the operation position of the height setting lever 54. Further, the height of the working device can be changed to the upper limit position set by the upper limit setting device 58 by swinging the elevation command lever 56 to the raised position. Then, by swinging the elevation command lever 56 to the lowered position, the height of the work device can be returned to an arbitrary height corresponding to the operation position of the height setting lever 54.

  As shown in FIGS. 1 and 2, the height setting lever 54 is arranged on the right side of the driver's seat 6 in the boarding operation unit 7 and is configured to be able to hold a position by swinging back and forth. The raising / lowering command lever 56 is provided at the lower right side of the steering wheel 5 in the boarding operation unit 7, and is configured to be a vertical return type and a neutral return type. The upper limit setter 58 is arranged on the right side of the driver's seat 6 in the boarding driver 7 and is configured as a dial operation type. The lever sensor 55 for the height setting lever and the upper limit setting device 58 employ a rotary potentiometer. The lever sensor 57 for the elevation command lever employs a switch.

  By the way, it is known that HST9 which comprises the main transmission 9 becomes so that the hydraulic load loss by oil leak becomes large and power transmission efficiency falls, so that a load becomes large. Therefore, for example, a swash plate angle sensor for detecting the operation angle of the pump swash plate 31B in the main transmission 9 is provided, and the vehicle speed control means 27B is inclined to the control target operation angle set based on the operation position of the main transmission lever 20. Swash plate feedback control is performed to control the operation of the pump swash plate operating means A so that the outputs of the plate angle sensors coincide (the operation angle of the swash plate angle sensor falls within the dead zone width of the control target operation angle). Then, the operation angle of the pump swash plate 31B can be made to coincide with the control target operation angle by this swash plate feedback control, but the fluctuation of the power transmission efficiency in the main transmission 9 caused by the fluctuation of the load is compensated. Therefore, it is difficult to stabilize the gear ratio of the main transmission 9 due to the fluctuation of the power transmission efficiency, and it is difficult to maintain the relationship in which the vehicle speed is proportional to the engine speed with high accuracy. Kunar.

  As a result, when performing work that desirably maintains the vehicle speed and the operating speed of the work device in a certain relationship proportional to the engine speed, such as rotary tillage work, the relationship is maintained accurately. Inability to do so tends to cause a difference between the appropriate vehicle speed and the vehicle speed with respect to the operating speed of the work device, and easily causes spots on the work device. It becomes difficult.

  Therefore, in the vehicle speed control for controlling the vehicle speed of the tractor, the vehicle speed control means 27B matches the control target vehicle speed set based on the operation position of the main transmission lever 20, etc. (the vehicle speed falls within the dead zone width of the control target vehicle speed). Vehicle speed feedback control is performed to control the operation of the gear ratio changing means C so that the

  The configuration will be described in detail. As shown in FIGS. 3, 4, and 6, the ECU 27 detects the output of the lever sensor 59 that detects the operation position of the main transmission lever 20 and the operation position of the sub transmission lever 21. Controlling the output of the lever sensor 60, the output of the lever sensor 61 for detecting the operation position of the FR lever 22, the output of the engine sensor 62 as engine speed detecting means for detecting the engine speed, and the output speed of the main transmission 9 are controlled. The output of the vehicle speed sensor 63 which is an example of the vehicle speed detection means which detects the upper vehicle speed, the output of the pedal sensor 64 which detects the arrival of the stop pedal 23 to the predetermined depression limit region, and the depression release of the left and right brake pedals 19 The output of the pedal sensor 65 that detects the amount of stepping operation from the position is input. Further, the ECU 27 is provided with vehicle speed setting data indicating the relationship between the engine speed, the gear ratio of the main transmission 9 and the vehicle speed (output speed of the main transmission 9).

  A rotary potentiometer is adopted for the lever sensor 59 for the main transmission lever and the pedal sensor 65 for the brake pedal. Switches are employed for the lever sensor 60 for the auxiliary transmission lever, the lever sensor 61 for the FR lever, and the pedal sensor 64 for the stop pedal. The engine sensor 62 and the vehicle speed sensor 63 are electromagnetic pickup type rotation sensors. Map data and relational expressions can be adopted as the vehicle speed setting data.

  In the vehicle speed feedback control, the vehicle speed control means 27B first sets the gear ratio of the main transmission 9 set by the main transmission lever 20 from the output of the lever sensor 59 for the main transmission lever (hereinafter referred to as a set transmission ratio). Based on the output of the sub-transmission device 10 (hereinafter referred to as “set transmission speed”), the output of the engine sensor 62, and the vehicle speed setting data set by the auxiliary transmission lever 21 from the output of the lever sensor 60 for the auxiliary transmission lever. The control target vehicle speed (control target rotation speed) with respect to the output of the vehicle speed sensor 63 determined by the vehicle speed setting control performed in this manner is read [step # 1], and whether the control target vehicle speed is for forward use from the output of the lever sensor 61 for the FR lever Whether it is for backward use is read [step # 2]. Next, the output of the vehicle speed sensor 63 is read [step # 3], and the control target vehicle speed for forward or reverse travel is compared with the output of the vehicle speed sensor 63 [steps # 4 and # 5]. The output of the vehicle speed sensor 63 coincides with the forward or reverse control target vehicle speed (the vehicle speed on control output by the vehicle speed sensor 63 falls within the dead band width of the forward or reverse control target vehicle speed. If so, constant speed control is performed to control energization of the forward shift valve 38 or the reverse shift valve 39 and the shift operation valve 43 so that the current vehicle speed is maintained [step # 6]. When the output of the vehicle speed sensor 63 is smaller than the forward or reverse control target vehicle speed, the forward shift valve 38 or reverse drive is used so that the output of the vehicle speed sensor 63 matches the forward or reverse control target vehicle speed. The speed increasing control for increasing the speed by controlling the energization to the speed change valve 39 and the speed change operation valve 43 is performed [step # 7]. When the output of the vehicle speed sensor 63 is larger than the control target vehicle speed for forward or reverse travel, the forward shift valve 38 or reverse drive is used so that the output of the vehicle speed sensor 63 matches the forward or reverse control target vehicle speed. The decelerating control for decelerating by controlling energization to the shift valve 39 and the shift operation valve 43 is performed [step # 8].

  As a result, only the fluctuation of the power transmission efficiency in the main transmission (HST) 9 caused by the hydraulic loss that fluctuates as the load increases or decreases can be compensated by the control operation of the vehicle speed control means 27B. 9 can be accurately performed. As a result, when it is desired to maintain the vehicle speed and the operating speed of the work device in a certain relationship that is proportional to the engine speed, as in rotary tillage work, the relationship is used as the main transmission. 9 can be maintained with high accuracy regardless of fluctuations in power transmission efficiency, and the difference between the appropriate vehicle speed and the vehicle speed with respect to the operating speed of the work device is less likely to occur. be able to.

  As shown in FIGS. 4 and 7, the vehicle speed control means 27B performs forward / reverse switching control based on the operation of the FR lever 22 when the operation of the FR lever 22 is detected from the output of the lever sensor 61 for the FR lever. It is constituted as follows.

  The forward / reverse switching control will be described based on the flowchart of FIG. 7. When the vehicle speed control unit 27B detects the operation of the FR lever 22 from the output of the lever sensor 61 for the FR lever, the FR after the operation is performed. The operation position of the lever 22 is determined [steps # 1, # 2]. When the operated position of the FR lever 22 after the operation is the neutral position, the power supply to the forward shift valve 38 and the reverse shift valve 39 is stopped [step # 3]. Thereby, the operation angle of the pump swash plate 31B can be made zero and the main transmission 9 can be made neutral, and the output of the vehicle speed sensor 63 can be made zero regardless of the control target vehicle speed determined by the vehicle speed setting control. it can. When the operation position of the FR lever 22 after the operation is the forward movement position or the reverse movement position, it is determined whether or not a predetermined traveling condition is satisfied by the operation to the forward movement position or the reverse movement position at this time [step # 4, # 5] If the predetermined traveling condition is satisfied, the routine proceeds to vehicle speed feedback control [step # 6]. If the predetermined traveling condition is not satisfied, the energization stop of the forward shift valve 38 and the reverse shift valve 39 is continued [step # 7].

  The state where the predetermined traveling condition is satisfied means that the FR lever 22 sensor 61 detects that the operation position of the FR lever 22 is the forward position or the reverse position, and the predetermined depression limit of the stop pedal 23 is reached. The pedal sensor 64 for the stop pedal does not detect the arrival to the area, and the pedal sensor 65 for the brake pedal detects that the operation position of both the left and right brake pedals 19 is within the brake release area. State.

  As shown in FIGS. 4 and 8, the vehicle speed control means 27B performs start / stop control based on the operation of the stop pedal 23 when the operation of the stop pedal 23 is detected from the output of the pedal sensor 64 for the stop pedal. It is configured.

  The start / stop control will be described with reference to the flowchart of FIG. 8. When the vehicle speed control means 27B detects the operation of the stop pedal 23 from the output of the pedal sensor 64 for the stop pedal, it determines the operation position of the stop pedal 23 after the operation. [Step # 1]. Then, when the operation position of the stop pedal 23 after the operation is within a predetermined depression limit region, the energization to the forward shift valve 38 and the reverse shift valve 39 is stopped [step # 2]. Thereby, the operation angle of the pump swash plate 31B can be made zero and the main transmission 9 can be made neutral, and the output of the vehicle speed sensor 63 can be made zero regardless of the control target vehicle speed determined by the vehicle speed setting control. it can. When the operation position of the stop pedal 23 after the operation is outside the depression limit region, it is determined whether or not a predetermined traveling condition is satisfied by this operation [step # 3]. When the predetermined traveling condition is satisfied, the unload valve 45 is switched from the communication state to the shut-off state in conjunction with the operation of the stop pedal 23 to the outside of the depressing limit region, and the circuit pressure of the main transmission 9 reaches the set value. It is determined whether or not a set time required to rise has elapsed [step # 4]. Then, the process proceeds to vehicle speed feedback control as the set time elapses [step # 5]. If the predetermined traveling condition is not satisfied in step # 3, the energization stop of the forward shift valve 38 and the reverse shift valve 39 is continued [step # 6].

  The state in which the predetermined traveling condition in the start / stop control is satisfied is the same state as the state in which the predetermined traveling condition in the forward / reverse switching control described above is satisfied.

  As shown in FIGS. 4 and 9, the vehicle speed control means 27 </ b> B detects that the left and right brake pedals 19 are both stepped on when the left and right brake pedals 19 are detected from the output of the brake pedal pedal sensor 65. The brake start / stop control based on the above is performed.

  The braking start / stop control will be described with reference to the flowchart of FIG. 9. When the vehicle speed control means 27B detects the depressing operation of the left and right brake pedals 19 from the output of the pedal sensor 65 for the brake pedal, first, predetermined running conditions are set. Is determined [Step # 1]. If the predetermined traveling condition is satisfied, the position of the pedals for both the left and right brake pedals 19 is determined from the output of the pedal sensor 65 for the brake pedal [Steps # 2 and # 3], and the left and right brake pedals are determined. If the both-step operation position of 19 is within the braking release region, the vehicle speed feedback control is continued [step # 4]. If the stepping operation position of the left and right brake pedals 19 is within the braking shift area following the braking release area, the control target vehicle speed determined by the vehicle speed setting control is read [step # 5], and the lever sensor 61 for the FR lever is read. Whether the control target vehicle speed is for forward movement or reverse movement is read from the output (step # 6), and the output of the vehicle speed sensor 63 is for forward movement or as the amount of both stepping operations of the left and right brake pedals 19 in the braking shift region increases. Braking shift control is performed in which the operation angle of the pump swash plate 31B is changed by controlling the energization of the forward shift valve 38 or the reverse shift valve 39 so as to approach zero from the reverse control target vehicle speed. # 7]. When the position of both the left and right brake pedals 19 is within the stop braking region following the braking shift region, the energization of the forward shift valve 38 and the reverse shift valve 39 is stopped [step # 8]. Thereby, the operation angle of the pump swash plate 31B can be made zero and the main transmission 9 can be made neutral, and the output of the vehicle speed sensor 63 can be made zero regardless of the control target vehicle speed determined by the vehicle speed setting control. it can. If the predetermined traveling condition is not satisfied in step # 1, it is determined whether or not a double stepping operation from the stop braking region to the braking shift region of the left and right brake pedals 19 has been detected [step # 9]. Then, when a both stepping operation from the stop braking region to the braking shift region of the left and right brake pedals 19 is detected, it is determined whether or not a predetermined traveling condition is satisfied by this operation [Step # 10], If the traveling condition is satisfied, the process proceeds to step # 2. As a result, the brake shift control is performed while both the stepping operation positions of the left and right brake pedals 19 are within the brake shift region, and the vehicle speed feedback control is performed as the left and right brake pedals 19 return to the brake release region. It will be. If no stepping operation from the stop braking region to the braking shift region of the left and right brake pedals 19 is detected in step # 9, and if the predetermined traveling condition is not satisfied in step # 10, The energization stop to the shift valve 38 and the reverse shift valve 39 is continued [step # 11].

  The state in which the predetermined traveling condition in the braking start / stop control is satisfied is the same state as the state in which the predetermined traveling condition in the forward / reverse switching control and the start / stop control described above is satisfied.

  Although illustration is omitted, the work power control means 27C detects the operation position of the PTO switch 50 when the operation of the stop pedal 23 to the predetermined depression limit region is detected based on the output of the pedal sensor 64 for the stop pedal. The state of the working clutch 14 is determined based on the output of the arm sensor 51 for the lift arm. If the working clutch 14 is in the disengaged state, this state is maintained. If the working clutch 14 is in the engaged state, the unload valve 45 is switched to the communication state based on the depression operation of the stop pedal 23. Thus, the working clutch 14 is switched to the disengaged state after a set time has elapsed since the operation of the stop pedal 23 to the predetermined depression limit region is detected so that the working device stops operating after the vehicle body stops traveling.

  Further, when the operation of the stop pedal 23 to the depressing limit region is not detected and the establishment of a predetermined traveling condition is detected, the operation position is determined from the operation position of the PTO switch 50 or the output of the arm sensor 51 for the lift arm. It is determined whether or not a condition for switching the clutch 14 from the disengaged state to the engaged state (hereinafter referred to as a work start condition) is satisfied. If the work start condition is satisfied, the work clutch 14 is switched to the engaged state, and if the work start condition is not satisfied, the work clutch 14 is maintained in the disengaged state.

  When the work power control means 27C detects the movement of the left and right brake pedals 19 to the work stop area provided on the depressing limit side of the stop brake area based on the output of the pedal sensor 65 for the brake pedal, the PTO switch The state of the working clutch 14 is determined based on the operation position of 50, the output of the arm sensor 51 for the lift arm, and the like. If the working clutch 14 is in the disengaged state, this state is maintained, and if the working clutch 14 is in the engaged state, the state is switched to the disengaged state.

  When the movement of the left and right brake pedals 19 from the work stop area to the stop brake area outside the work stop area is detected, the predetermined travel condition is established by the subsequent movement of the left and right brake pedals 19 to the brake release area. If the predetermined travel condition is satisfied, it is determined whether the work start condition is satisfied. If the work start condition is satisfied, the work clutch 14 is engaged. When the work start condition is not satisfied, the work clutch 14 is kept in the disengaged state.

  By the control operation of the vehicle speed control means 27B and the work power control means 27C described above, the stop pedal 23 is depressed or both the left and right brake pedals 19 are depressed while the clutchless specification is not provided with the main clutch. As a result, the transmission to the left and right front wheels 1 and the left and right rear wheels 2 as drive wheels can be intermittently transmitted to the PTO shaft 16. When the travel of the vehicle body and the operation of the work device are controlled by depressing the stop pedal 23 or both the left and right brake pedals 19, the work device stops operating after the travel of the vehicle body is stopped. After the operation of the device starts, the vehicle body starts to travel. As a result, appropriate work can be reliably performed at the stop position or start position of the vehicle body, and in particular, when a rotary tiller is provided as a work device, occurrence of residual tillage or the like at the stop position or start position of the vehicle body Can be prevented.

  Although illustration is omitted, the pedal sensor 65 for the brake pedal is linked to the left and right brake pedals 19 via a mechanical linkage mechanism (not shown) for detecting the amount of both stepping operations. The mechanical linkage mechanism for detecting the amount of stepping operation includes a moving member that is spring-biased so as to be displaced in the pedal depression direction in conjunction with the stepping operation of the left and right brake pedals 19, and either left or right brake When the pedal 19 is operated with one step, the following displacement of the moving member with respect to the one brake pedal 19 is prevented by the contact between the moving member and the other brake pedal 19, and the left and right brake pedals 19 are operated with both steps. Only in this case, the moving member is configured to follow and displace with respect to the left and right brake pedals 19 and transmit the amount of both stepping operations of the left and right brake pedals 19 to the pedal sensor 65 for the brake pedal.

  As shown in FIG. 10, the vehicle speed setting data provided in the ECU 27 includes first vehicle speed setting data for work travel (see FIG. 10A) and second vehicle speed setting data for high speed movement (( B) see]. In each vehicle speed setting data, the engine speed, the gear ratio of the main transmission 9 and the vehicle speed (the output of the vehicle speed sensor 63) are based on the fastest speed ratio of the main transmission 9 corresponding to the fastest position of the main transmission lever 20. The relationship is set.

  More specifically, each vehicle speed setting data is basically set as follows in common with the first and second vehicle speed setting data. When the engine speed is the first set speed N1 set to the idling speed, the speed ratio of the main transmission 9 becomes the first speed ratio set to a large speed ratio on the low speed side and the vehicle speed is preset. It is set to be a low speed. When the engine speed is the speed in the high speed range NH that is equal to or higher than the second set speed N2 set on the higher speed side than the first set speed N1, the speed ratio of the main transmission 9 is the fastest speed ratio. The vehicle speed is set to be proportional to the engine speed. When the engine speed is a speed in the middle speed range NM between the first set speed N1 and the second set speed N2, the lower the engine speed at that time, the lower the shift of the main transmission 9. The ratio is changed to a large gear ratio on the low speed side between the first gear ratio and the fastest gear ratio, and the vehicle speed is proportional to the engine speed and the gear ratio of the main transmission 9 (the rate of change of the vehicle speed is high). The rate of change is larger than the rate of change in the region NH, and the rate of change is constant). When the engine speed is the speed in the low speed range NL that is equal to or lower than the first set speed N1, the main transmission 9 is not neutral and the vehicle speed is not the engine speed if the engine speed is greater than zero. The gear ratio of the main transmission 9 is changed in accordance with the engine speed so as not to become zero (so that the change rate of the vehicle speed becomes constant at a change rate smaller than the change rate in the high rotation speed region NH). It is set.

  Specifically, in the first vehicle speed setting data, the first set speed N1 is set to the idling speed as described above, and the second set speed N2 is set to the speed at which the engine 3 exhibits the maximum torque. It is set. Then, the relationship between the engine speed, the transmission ratio of the main transmission 9 and the vehicle speed is set such that in the high rotation speed region NH, the vehicle speed is the engine speed so that the vehicle speed corresponds to the engine speed at the highest speed transmission ratio of the main transmission 9. The relationship is proportional to the rotational speed. In the middle engine speed range NM, when the engine speed reaches the first set engine speed (idling engine speed) N1, the vehicle speed becomes a very low set speed, and the engine engine speed is the second that exhibits the maximum torque. When the set rotational speed N2 is reached, the vehicle speed is set to be proportional to the engine rotational speed and the speed ratio of the main transmission 9 so that the vehicle speed corresponds to the engine speed at the fastest speed ratio of the main transmission 9. It is. In the low engine speed region NL, the vehicle speed is set to a relationship corresponding to the engine speed with the gear ratio of the main transmission 9 that is inversely proportional to the engine speed so that the vehicle speed becomes constant at an extremely low set speed. See FIG. 10A].

  On the other hand, in the second vehicle speed setting data, the first set speed N1 is set to the idling speed as described above, and the second set speed N2 is set to a speed slightly lower than the rated speed of the engine 3. It is. Then, the relationship between the engine speed, the transmission ratio of the main transmission 9 and the vehicle speed is set such that in the high rotation speed region NH, the vehicle speed is the engine speed so that the vehicle speed corresponds to the engine speed at the highest speed transmission ratio of the main transmission 9. The relationship is proportional to the rotational speed. In the middle speed range NM, when the engine speed reaches the first set speed (idling speed) N1, the vehicle speed is set to a low speed, and the engine speed is slightly lower than the rated speed. When the second set rotational speed N2 close to the rotational speed is reached, the vehicle speed corresponds to the engine rotational speed at the maximum speed transmission ratio of the main transmission 9 and the vehicle speed corresponds to the engine rotational speed and the transmission gear ratio of the main transmission 9. Is set to be proportional to In the low speed range NL, the main transmission 9 is set when the engine speed reaches the first set speed (idling speed) N1 and the vehicle speed becomes a low speed and when the engine speed is zero. So that the vehicle speed becomes zero and the vehicle speed is set to a relationship corresponding to the engine speed with the speed ratio of the main transmission 9 that is proportional to the engine speed (see FIG. 10B). .

  Note that the alternate long and short dash line in FIG. 10 assumes a state in which the speed ratio of the main transmission 9 is maintained at the highest speed ratio in the low speed range NL and the medium speed range NM.

  Also, the broken line shown in FIG. 10B shows the pump displacement of the variable displacement pump 31 in proportion to the engine speed changing from zero to the rated speed with the variable displacement motor 32 maintained at the low speed stage. This assumes the gear ratio of the main transmission 9 obtained when the operation angle of the plate 31B is changed from zero to the operation limit angle. That is, the transmission ratio of the main transmission 9 in the low rotation speed region NL of the second vehicle speed setting data is proportional to the engine rotation speed while the variable displacement motor 32 is set to the low speed stage. This is the gear ratio that can be obtained in the low rotation speed region NL by changing the operation angle of the plate 31B.

  The vehicle speed control means 27B changes the vehicle speed setting data to be employed based on the output of the lever sensor 60 for the auxiliary transmission lever that functions as a transmission stage detection means for detecting the transmission stage of the auxiliary transmission (stepped transmission) 10. . Specifically, if the shift stage of the auxiliary transmission 10 read based on the output of the lever sensor 60 for the auxiliary transmission lever is the low speed stage for low speed work or the high speed stage for high speed work, the first vehicle speed setting data is stored. Adopting the second vehicle speed setting data if it is the fastest stage for high-speed movement.

  The ECU 27 corrects each vehicle speed setting data set based on the fastest speed ratio of the main transmission 9 to a reference based on a set speed ratio corresponding to the operation position of the main speed change lever 20 set arbitrarily. Has a gain of.

  The vehicle speed control means 27B reads the gain corresponding to the operation position of the main transmission lever 20 from the output of the lever sensor 59 for the main transmission lever, multiplies the adopted vehicle speed setting data by the read gain, and uses the adopted vehicle speed setting data. It is automatically corrected to an appropriate one based on the set gear ratio corresponding to the operation position of the main transmission lever 20.

  For example, as an example, if the operation position of the main transmission lever 20 is 50% of the fastest position of the main transmission lever 20, the adopted vehicle speed setting data is multiplied by 0.5, and the adopted vehicle speed setting data is The entire range is automatically corrected to an appropriate value based on a speed ratio of 50% with respect to the fastest speed ratio of the main transmission 9 (where a relationship indicated by a virtual line (two-dot chain line in FIG. 10 is obtained)). Further, if the operation position of the main transmission lever 20 is the fastest position, the adopted vehicle speed setting data is multiplied by 1.0, and the adopted vehicle speed setting data is based on the fastest speed ratio of the main transmission 9 over the entire area. It is automatically corrected to an appropriate one (a relationship indicated by a solid line in FIG. 10 is obtained).

  Thus, as shown in FIG. 10A, in the first vehicle speed setting data after optimization, the relationship between the engine speed, the speed ratio of the main transmission 9 and the vehicle speed is as follows: The vehicle speed is proportional to the engine speed so that the vehicle speed corresponds to the engine speed at the corrected maximum speed gear ratio (set speed ratio) of the main transmission 9 corresponding to the operation position of the main transmission lever 20. Further, in the middle engine speed region NM, when the engine speed reaches the first set engine speed (idling engine speed) N1, the vehicle speed becomes an extremely low set speed after correction based on the operation position of the main transmission lever 20. In addition, when the engine speed reaches the second set speed N2 at which the maximum torque is exhibited, the vehicle speed corresponds to the engine speed at the speed ratio of the corrected main transmission 9 described above. The relationship is proportional to the engine speed and the gear ratio of the main transmission 9. In the low rotation speed region NL, the relationship between the vehicle speed and the engine speed is the speed ratio of the main transmission 9 that is inversely proportional to the engine speed so that the vehicle speed becomes constant at the corrected extremely low speed set as described above. Become.

  On the other hand, as shown in FIG. 10B, in the second vehicle speed setting data after optimization, the relationship between the engine speed, the gear ratio of the main transmission 9 and the vehicle speed is The vehicle speed is proportional to the engine speed so that the speed corresponds to the engine speed at the corrected fastest speed ratio (set speed ratio) of the main transmission 9 corresponding to the operation position of the main transmission lever 20. Further, in the middle rotational speed region NM, when the engine rotational speed reaches the first set rotational speed (idling rotational speed) N1, the vehicle speed becomes a low speed set speed after correction based on the operation position of the main transmission lever 20, In addition, when the engine speed reaches the second set speed N2 that is slightly lower than the rated speed, the vehicle speed corresponds to the engine speed at the speed ratio of the corrected main transmission 9 described above. Is proportional to the engine speed and the gear ratio of the main transmission 9. In the low engine speed region NL, when the engine speed reaches the first set engine speed (idling engine speed) N1, the vehicle speed becomes the above-described corrected low speed and the engine engine speed is zero. In order for the main transmission 9 to become neutral and the vehicle speed to become zero, the vehicle speed is in a relationship corresponding to the engine speed with the gear ratio of the main transmission 9 that is proportional to the engine speed.

  Then, control is performed based on the optimized vehicle speed setting data and the output of the engine sensor 62 so that the relationship between the engine speed in the optimized vehicle speed setting data, the gear ratio of the main transmission 9 and the vehicle speed is established. Set the target vehicle speed.

  The vehicle speed setting control will be described with reference to the flowchart of FIG. 11. The vehicle speed control means 27B determines the gear position of the auxiliary transmission 10 from the output of the lever sensor 60 for the auxiliary transmission lever [Step # 1], When the stage is a low speed stage for low speed work or a high speed stage for high speed work, the first vehicle speed setting data for work travel is adopted as the vehicle speed setting data [Step # 2], and the gear stage is the fastest stage for high speed movement. In this case, the second vehicle speed setting data for high speed movement is adopted as the vehicle speed setting data [Step # 3]. Next, a gain for the vehicle speed setting data is read from the output of the lever sensor 59 for the main transmission lever [steps # 4 and # 5], and the vehicle speed setting data obtained by using this gain is multiplied by the vehicle speed setting data to be output from the main transmission lever 20 Optimization of the vehicle speed setting data that is automatically corrected to an appropriate one based on the set speed ratio corresponding to the operation position (the highest speed speed ratio of the main transmission 9 set by the main speed change lever 20) is performed [Step #. 6, # 7]. Then, the engine speed is read from the output of the engine sensor 62 [Steps # 8, # 9], and the control target vehicle speed for the output of the vehicle speed sensor 63 is determined based on the optimized vehicle speed setting data and the read engine speed. [Steps # 10 and # 11].

  Then, the control target vehicle speed determined by the vehicle speed setting control is set to forward or reverse from the output of the lever sensor 61 for the FR lever, and the output of the vehicle speed sensor 63 is set to the set forward or reverse control target vehicle speed. The operation of the gear ratio changing means C is controlled so as to match (the output of the vehicle speed sensor 63 falls within the dead zone width of the forward or reverse control target vehicle speed), and the pump swash plate 31B and the motor swash plate 32B are operated. Vehicle speed feedback control is performed to change the gear ratio of the main transmission 9 by changing the angle.

  From the above configuration, for example, when the accelerator operation is performed by the accelerator lever 17 or the accelerator pedal 18 in a state where the main transmission lever 20 is operated from the zero speed position to an arbitrary operation position and a predetermined traveling condition is established. While the engine speed is in the middle speed range NM, the engine speed is increased or decreased by the accelerator operation, and the speed ratio of the main transmission 9 is changed in proportion to the increased or decreased engine speed, so that the vehicle speed is increased. It changes at a constant change rate larger than the change rate in the high rotational speed region NH.

  As a result, when the engine speed is gradually increased from the idling speed by the accelerator operation and the vehicle body is started, the gear ratio of the main transmission 9 becomes larger as the engine speed is closer to the idling speed. Since the load applied to the engine 3 is reduced, the vehicle body is started in a state where the transmission gear ratio of the main transmission 9 is maintained at the set transmission gear ratio corresponding to the operation position of the main transmission lever 20. Thus, it is possible to effectively suppress the decrease in the engine speed and the occurrence of the engine stall due to the overload at the time of starting, and the vehicle body can be started smoothly.

  In addition, when performing traveling over a fence that causes the vehicle body to enter and exit the field or loading and unloading operation that uses a step board to load and unload the vehicle body onto a truck bed, the engine speed is brought closer to the idling speed by operating the accelerator. As the gear ratio of the main transmission 9 becomes a large gear ratio on the low speed side, the load applied to the engine 3 is reduced and the vehicle speed is greatly reduced. Can do. In particular, if the auxiliary speed change lever 21 is operated to the low speed position or the high speed position and the first vehicle speed setting data is adopted, the speed stage of the auxiliary transmission 10 can be set to a low speed stage or a high speed stage with high torque. Can be set to a very low speed, so that overrunning and unloading can be performed better at a very low speed with high torque.

  In addition, in the middle engine speed range NM, the vehicle speed adjustment range by the accelerator operation is wider than the configuration in which the engine speed is increased or decreased by the accelerator operation, and the amount of change in the vehicle speed with respect to the accelerator operation amount is increased. Since acceleration / deceleration by the accelerator operation is facilitated, it is possible to comfortably perform traveling traveling using the intermediate rotation speed region NM. In particular, in the high-speed movement state in which the auxiliary transmission lever 21 is operated to the high-speed movement position, the second vehicle speed setting data in which the second set speed N2 is set to a speed slightly lower than the rated speed of the engine 3 is employed. As a result, acceleration / deceleration by the accelerator operation can be easily performed in substantially the entire region from the idling speed to the rated speed, so that traveling at high speed can be performed comfortably.

  On the other hand, while the engine rotational speed is in the high rotational speed region NH, the gear ratio of the main transmission 9 remains at the operating position of the main transmission lever 20 even if the engine rotational speed changes due to accelerator operation, travel load, or work load. Since the corresponding set gear ratio is constant, the relationship in which the vehicle speed is proportional to the engine speed can be maintained. In particular, the first vehicle speed setting data in which the rotation speed at which the engine 3 exhibits the maximum torque is set to the second setting rotation speed N2 is employed in the working traveling state in which the auxiliary transmission lever 21 is operated to the low speed position or the high speed position. Thus, the high engine speed region NH becomes a wide region from the second set engine speed N2 at which the engine 3 exhibits the maximum torque to the rated engine speed, and the vehicle speed is proportional to the engine engine speed in the wide engine speed region NH. A relationship can be maintained. As a result, when a work device such as a rotary tiller that operates with non-shift power from the engine 3 taken out from the PTO shaft 16 is connected to the rear portion of the vehicle body, the sub-shift lever 21 is moved to a low speed position or a high speed. If it is operated to the position, the vehicle speed and the operating speed of the work device are set to the engine speed in a wide high speed range NH ranging from the second set speed N2 where the engine 3 exhibits the maximum torque to the rated speed. A proportional relationship can be maintained. As a result, it is possible to prevent spots from being generated on the work track by the work device due to the inability to maintain a constant relationship between the vehicle speed and the operating speed of the work device. It can be finished in a good condition with uniform work. In particular, when a rotary cultivator is connected to the rear part of the vehicle body to perform the cultivating work, it is possible to finish in a good cultivated state where the cultivated traces by the rotary cultivator are uniformly cultivated.

  When the engine speed decreases from the high engine speed region NH to the medium engine speed region NM due to travel load, work load, etc., the main transmission is reduced along with a decrease in the engine engine speed in the medium engine speed region NM. The gear ratio of 9 becomes a large gear ratio on the low speed side and the load on the engine 3 is reduced. Therefore, the engine 3 can be made to be sticky, and the engine speed and engine stall can be reduced due to overload. It can be effectively suppressed. In addition, this makes it possible to release the left and right brake pedals 19 or the stop pedal 23 when the engine speed is maintained in the high engine speed range NH, or to swing the FR lever 22 from the neutral position to the forward or reverse position. When the vehicle body is started by operation, even if the engine speed decreases due to the traveling load or work load at that time, the engine 3 can be made sticky if it decreases to the middle speed range NM. Thus, the reduction in engine speed and the occurrence of engine stall due to overload can be effectively suppressed, so that the vehicle body can be started smoothly using the left and right brake pedals 19, the stop pedal 23, or the FR lever 22.

  Furthermore, when the engine speed decreases to the low speed range NL due to travel load or work load, the vehicle speed becomes constant at the extremely low set speed in the first vehicle speed setting data adopted during work travel. In addition, since the second vehicle speed setting data employed during high-speed movement is set so that the vehicle speed becomes zero when the engine speed is zero, the main speed change until the engine speed decreases to zero. The device 9 never becomes neutral, which makes the driver feel uncomfortable that the main transmission 9 becomes neutral and the vehicle body stops running due to a decrease in the engine speed even though the engine 3 is operating. Occurrence of a phenomenon that may be remembered can be prevented.

  In addition, since the low-speed or extremely low-speed running state is maintained in the low-speed region NL, the engine 3 can be given a certain degree of stickiness even in the low-speed region NL. By recognizing that an excessive load is applied to the engine 3 in the low engine speed region NL, it is possible to prompt some action such as a deceleration operation of the main transmission lever 20 to reduce the load. If no action is taken, an engine stall due to overload occurs, and the driver can be made to recognize again that an excessive load is applied to the engine 3 in the low engine speed range NL.

  In this embodiment, the main transmission device includes the main transmission lever 20, the auxiliary transmission lever 21, the vehicle speed control means 27B, the main transmission lever lever sensor 59, the auxiliary transmission lever sensor 60, and the vehicle speed setting data. (HST) Gear ratio setting means D for setting the gear ratio of 9 is configured.

  Incidentally, as a configuration related to the vehicle speed control, instead of the above configuration, a combination of the transmission ratio of the main transmission 9 and the transmission ratio of the auxiliary transmission 10 is used as the transmission ratio of the traveling transmission, and vehicle speed setting data is used. , Which uses the relationship between the engine speed, the transmission gear ratio of the traveling transmission and the vehicle speed (the output rotational speed of the auxiliary transmission 10), and detects the output rotational speed of the auxiliary transmission 10 as the vehicle speed for control. It is good also as a structure provided with the vehicle speed sensor to do. Further, the transmission ratio of the main transmission 9, the transmission ratio of the auxiliary transmission 10, and the final reduction ratio of the rear-wheel differential device 13 and the like are combined as the rear-wheel transmission system, and the vehicle speed. A configuration may be adopted in which the setting data indicates the relationship between the engine speed, the transmission ratio of the rear wheel transmission system, and the vehicle speed.

  As shown in FIGS. 4 and 12 to 13, the vehicle speed control means 27 </ b> B has a gear ratio determination that determines the gear ratio of the main transmission 9 that is set based on the operation position of the main transmission lever 20, the engine speed, and the like. Means 27Ba, reduction amount detection means 27Bb for detecting a reduction amount (hereinafter referred to as engine drop amount) of the engine speed from the set rotational speed, and the output of the variable displacement motor 32 based on the output of the lever sensor 59 for the main transmission lever. The first switching control means 27Bc for switching the gear position, the second switching control means 27Bd for switching the gear position of the variable displacement motor 32 based on the determination of the gear ratio determination means 27Ba, and the variable based on the output of the decrease amount detection means 27Bb. 3rd switching control means 27Be which switches the gear stage of the capacity | capacitance motor 32 is provided.

  Then, the vehicle speed control means 27B is configured to switch the control operation related to switching of the shift stage of the variable displacement motor 32 in accordance with the shift stage of the sub-transmission device 10 read from the output of the lever sensor 60 for the sub-shift lever. It is. Specifically, the vehicle speed control means 27B operates the first switching control means 27Bc when the shift speed of the sub-transmission device 10 is a low-speed operation speed range, and the sub-transmission device 10 shift speed is for the high-speed operation time. The first switching control means 27Bc and the third switching control means 27Be are actuated when the speed is the high speed stage, and the second switching control means 27Bd and the second switching control means 27Bd are operated when the speed stage of the auxiliary transmission 10 is the fastest speed stage for high speed movement. 3 switch control means 27Be is operated.

  The gear ratio determination means 27Ba is a control target set based on the adopted vehicle speed setting data after optimization (vehicle speed setting data corrected based on the operation position of the main transmission lever 20) and the output of the engine sensor 62. By determining whether or not the vehicle speed exceeds the limit value of the speed that can be obtained at the low speed stage of the variable capacity motor 32, the main speed set based on the operation position of the main transmission lever 20, the engine speed, etc. It is configured to determine whether or not the gear ratio of the transmission 9 is a gear ratio that can be obtained at the low speed stage of the variable displacement motor 32.

  The decrease amount detection means 27Bb reads the set rotation speed of the engine 3 set by the accelerator lever 17 or the accelerator pedal 18 based on the output of the lever sensor 30 for the speed control lever, and reads the set rotation speed of the engine 3 and the engine The engine drop amount is calculated based on the output of the sensor 62.

  The first switching control for switching the shift stage of the variable displacement motor 32 by the control operation of the first switching control means 27Bc will be described based on the flowchart of FIG. 12. The first switching control means 27Bc is a lever sensor 59 for the main transmission lever. The operation position of the main transmission lever 20 is determined based on the output of [No. # 1, # 2]. When the operation position of the main speed change lever 20 is in the low speed setting region including the zero speed position, the energization stop of the speed change operation valve 43 is continued so that the speed stage of the variable displacement motor 32 is maintained at the low speed stage. [Step # 3]. When the operation position of the main shift lever 20 is within the high speed setting region including the fastest position, the energization to the shift operation valve 43 is continued so that the shift stage of the variable displacement motor 32 is maintained at the high speed stage [Step # 4]. When the operation position of the main shift lever 20 is within the medium speed setting area between the low speed setting area and the high speed setting area, the operation process to the medium speed setting area is determined [Step # 5], and the operation from the low speed setting area is determined. If the variable displacement motor 32 is located in the medium speed setting area, the variable speed motor 32 is maintained at the low speed, and if the operation is performed from the high speed setting area, the variable capacity motor 32 is located. Is controlled so that the speed change gear is maintained at a high speed (steps # 3 and # 4). When the speed of the variable displacement motor 32 is a low speed, it is determined whether or not there is an operation from the medium speed setting area to the high speed setting area of the main transmission lever 20 based on the output of the lever sensor 59 for the main transmission lever. [Step # 6] When the operation to the high speed setting region is detected, energization of the speed change operation valve 43 is started so that the speed of the variable displacement motor 32 is switched from the low speed to the high speed. # 7] The pump swash plate 31B of the variable displacement pump 31 is operated with an operation amount set so as to compensate for the increase in the gear ratio of the main transmission 9 that changes by switching the variable displacement motor 32 from the low speed stage to the high speed stage. Energization of the forward shift valve 38 or the reverse shift valve 39 is controlled so as to be decelerated [step # 8]. When the speed of the variable displacement motor 32 is a high speed, the presence or absence of an operation from the medium speed setting area to the low speed setting area of the main transmission lever 20 is determined based on the output of the lever sensor 59 for the main transmission lever. Step # 9] When the operation to the low speed setting region is detected, energization of the speed change operation valve 43 is stopped so that the gear position of the variable displacement motor 32 is switched from the high speed stage to the low speed stage [Step # 10]. ] The pump swash plate 31B of the variable displacement pump 31 is operated to increase the speed by an operation amount set so as to compensate for the deceleration of the transmission ratio of the main transmission 9 that changes by switching the variable displacement motor 32 from the high speed stage to the low speed stage. Thus, the power supply to the forward shift valve 38 or the reverse shift valve 39 is controlled [step # 11].

  The second switching control for switching the shift stage of the variable displacement motor 32 by the control operation of the second switching control means 27Bd will be described based on the flowchart of FIG. 13. The second switching control means 27Bd determines the speed ratio determining means 27Ba. Whether the control target vehicle speed determined based on the optimized vehicle speed setting data adopted and the output of the engine sensor 62 exceeds the limit value of the speed that can be obtained at the low speed stage of the variable displacement motor 32. It is determined whether or not [Step # 1]. If the control target vehicle speed does not exceed the limit value, it is determined whether or not the control target vehicle speed exceeds the speed limit value [Step # 2]. If the speed limit value is not exceeded, the variable displacement motor The energization stop to the shift operation valve 43 is continued so that the 32 shift stages are maintained at the low speed [step # 3]. When the control target vehicle speed exceeds the limit value, energization to the shift operation valve 43 is started so that the shift stage of the variable displacement motor 32 is switched from the low speed stage to the high speed stage [Step # 4], and the variable capacity motor The pump swash plate 31B of the variable displacement pump 31 is advanced by a decelerating operation with an operation amount set so as to compensate for the increase in the gear ratio of the main transmission 9 that changes by switching from 32 low speed stages to high speed stages. The energization of the transmission shift valve 38 or the reverse shift valve 39 is controlled [step # 5]. When the control target vehicle speed exceeds the speed limit value in step # 1, it is determined whether or not the control target vehicle speed has decreased below the speed limit value [step # 6]. Then, energization of the shift operation valve 43 is continued so that the shift stage of the variable capacity motor 32 is maintained at a high speed [step # 7]. When the control target vehicle speed falls below the limit value, the energization to the shift operation valve 43 is stopped so that the shift stage of the variable displacement motor 32 is switched from the high speed stage to the low speed stage [Step # 8], and the variable capacity The pump swash plate 31B of the variable displacement pump 31 is speed-up operated with an operation amount set so as to compensate for the reduction of the speed ratio of the main transmission 9 that changes by switching the motor 32 from the high speed stage to the low speed stage. Energization of the forward shift valve 38 or the reverse shift valve 39 is controlled [step # 9].

  The third switching control for switching the shift stage of the variable displacement motor 32 by the control operation of the third switching control means 27Be will be described based on the flowchart of FIG. The gear position of the variable capacity motor 32 is determined [step # 1]. When the gear stage is a high speed stage, the engine drop amount is monitored from the output of the reduction amount detection means 27Bb [Step # 2], and the engine drop amount is set to a set amount (for example, a value of 20% of the set rotational speed). [Step # 3], and when the engine drop amount reaches the set amount, the shift operation valve 43 is connected to the shift operation valve 43 so that the shift stage of the variable displacement motor 32 is switched from the high speed stage to the low speed stage. The energization is stopped [Step # 4]. Thereafter, it is determined whether or not the engine drop amount has recovered to within a predetermined allowable range [Step # 5], and when the engine drop amount has recovered to within the predetermined allowable range, the shift stage of the variable displacement motor 32 is changed from the high speed stage to the low speed stage. Energization of the shift operation valve 43 is started so as to switch to [Step # 6].

  From the above configuration, a higher torque is required in order to perform heavy load work more comfortably in the low speed operation state where the gear position of the auxiliary transmission 10 is set to the low speed stage or the high speed operation state where the speed stage is set to the high speed stage. When the main speed change lever 20 is positioned from the low speed setting area or the low speed setting area to the medium speed setting area, the speed stage of the variable displacement motor 32 can be set to the low speed stage and higher torque can be secured. Can be secured. This makes it possible to smoothly start and run the vehicle body during heavy load work, etc., and to perform heavy load work and the like more comfortably.

  In the low-speed operation state in which the speed stage of the auxiliary transmission 10 is set to the low speed stage, a high torque is secured by the speed stage, so that a decrease in engine speed and engine stall due to overload are unlikely to occur. Therefore, the switching of the variable displacement motor 32 in the main transmission 9 can be performed only by operating the main transmission lever 20 according to the driver's intention. Thus, even when the variable displacement motor 32 of the main transmission 9 is switched to the high speed stage in order to improve the work efficiency in the low speed working state, the shift stage of the variable displacement motor 32 is reduced due to the decrease in the engine speed. If the engine speed is not in the high speed range NH without unexpectedly switching from the high speed stage to the low speed stage, the main transmission lever 20, the accelerator lever 17 or the accelerator pedal 18 based on the driver's intention in consideration of the work. The gear ratio of the main transmission 9 set by the above operation can be maintained. When the engine speed is significantly reduced, the variable displacement motor 32 of the main transmission 9 can be switched to the low speed stage by operating the main transmission lever 20 at the driver's intention, thereby suppressing the engine speed reduction. Alternatively, it can be prevented. As a result, it is possible to satisfactorily perform an operation in which it is desirable to maintain the vehicle speed and the operating speed of the work device in a certain relationship proportional to the engine speed, such as a rotary tillage work.

  Further, in the high-speed operation state in which the shift stage of the auxiliary transmission 10 is set to the high speed stage, although a relatively high torque is secured by the shift stage, the engine caused by the overload compared to the low speed stage. Since the reduction of the rotation speed and engine stall are likely to occur, the switching of the variable displacement motor 32 in the main transmission 9 is automatically performed based not only on the operation of the main transmission lever 20 by the driver's intention but also on the engine drop amount. It is supposed to be done. Accordingly, it is possible to prevent the engine stall due to the overload while enabling the variable transmission motor 32 to be switched between high and low in the main transmission 9 based on the driver's intention according to the work.

  Furthermore, in both the low-speed operation state and the high-speed operation state, the variable displacement motor 32 is set to a low speed during the low-speed traveling when the speed ratio of the main transmission 9 is set to a large speed ratio on the low speed side. As the operating angle of the pump swash plate 31B in the variable displacement pump 31, a large angle on the high speed side with high hydraulic transmission efficiency can be adopted, and as a result, the vehicle speed during low speed traveling can be stabilized.

  In addition, since the hysteresis is provided in the medium speed setting region, it is possible to prevent the variable displacement motor 32 from being frequently switched between high and low by the operation of the main transmission lever 20.

  On the other hand, in the high-speed movement state in which the shift speed of the auxiliary transmission 10 is set to the highest speed, the torque is reduced by the shift speed, so that the control target vehicle speed can be obtained at the low speed of the variable displacement motor 32. As long as the speed is maintained, the gear stage of the variable displacement motor 32 is maintained at a low speed stage to ensure a high torque. This effectively suppresses the decrease in engine speed and the occurrence of engine stall caused by an overload during the start of the vehicle body or during traveling in the high speed movement state where the speed stage of the auxiliary transmission 10 is set to the highest speed stage. be able to. Further, by maintaining the variable displacement motor 32 in the low speed stage as much as possible, a large angle with high hydraulic transmission efficiency can be used as an operation angle of the pump swash plate 31B in a wider speed change region. It is possible to improve the hydraulic transmission efficiency in the main transmission 9 at the time of starting in the high speed movement state or traveling while setting the 10 speed stages to the fastest speed, and at the time of starting the vehicle in the high speed movement state or during traveling It is possible to more effectively suppress the decrease in engine speed and the occurrence of engine stall due to overload.

  In addition, when the shift stage of the variable displacement motor 32 is switched by the control operation of the first switching control means 27Bc or the second switching control means 27Bd, the change in the gear ratio of the main transmission 9 that changes due to the switching is compensated. Since the pump swash plate 31B is operated with the operation amount set to the variable displacement motor 32, the speed change operation for changing the speed ratio of the main transmission 9 by operating the main transmission lever 20, the accelerator lever 17 or the accelerator pedal 18 is performed. Even when the gears are switched, the steps can be smoothly performed in a stepless manner.

  Then, the shift stage of the variable displacement motor 32 suitable for each of the low speed operation state in which the speed stage of the auxiliary transmission 10 is set to the low speed stage, the high speed operation state in which the high speed stage is set, and the high speed movement state in which the maximum speed stage is set. The selection of the control operation related to switching can be automatically performed together with the switching of the gear position of the auxiliary transmission 10 by the auxiliary transmission lever 21.

  Incidentally, the medium speed setting region of the main speed change lever 20 is the main speed change lever 20 in which the speed change ratio of the main speed change device 9 that can be obtained when the speed change stage of the variable displacement motor 32 is switched between the low speed and the high speed. This is an area that can be set. The speed that can be obtained at the low speed stage of the variable capacity motor 32 means that the operating angle of the pump swash plate 31B of the variable capacity pump 31 is operated from zero with the speed stage of the variable capacity motor 32 set to the low speed stage. The speed that can be obtained by changing to the limit angle and the engine speed corresponding to the speed ratio in the second vehicle speed setting data, and the limit value of the speed is a variable capacity motor. The fastest speed ratio at the low speed stage that can be obtained by changing the operation angle of the pump swash plate 31B of the variable displacement pump 31 to the operation limit angle with the 32 speed stages set to the low speed stage, and the fastest speed ratio And the engine speed corresponding to the second vehicle speed setting data.

  In the control operation of the first switching control means 27Bc, the first switching control means 27Bc changes from the low speed setting area of the main transmission lever 20 to the medium speed setting area based on the output of the lever sensor 59 for the main transmission lever. Is detected, the energization of the shift operation valve 43 is started so that the shift stage of the variable displacement motor 32 is switched from the low speed stage to the high speed stage, and the variable capacity motor 32 is switched from the low speed stage to the high speed stage. The forward shift valve 38 or the reverse drive valve is operated so that the pump swash plate 31B of the variable displacement pump 31 is decelerated by an operation amount set so as to compensate for an increase in the speed ratio of the main transmission 9 that changes by switching. When the operation from the middle speed setting area to the high speed setting area of the main speed change lever 20 is detected by controlling energization to the speed change valve 39, the speed change is performed so that the speed of the variable displacement motor 32 is maintained at the high speed. When energization to the valve operating 43 is controlled and an operation of the main speed change lever 20 from the high speed setting area to the medium speed setting area is detected, the speed of the variable displacement motor 32 is switched from the high speed to the low speed. The variable displacement pump is operated with an operation amount that is set so as to compensate for the reduction of the gear ratio of the main transmission 9 that changes when the variable displacement motor 32 is switched from the high speed stage to the low speed stage. The energization of the forward shift valve 38 or the reverse shift valve 39 is controlled so that the pump swash plate 31B of the 31 is increased in speed, and the operation from the medium speed setting area to the low speed setting area of the main transmission lever 20 is controlled. May be configured to stop energization of the speed change operation valve 43 so that the speed of the variable displacement motor 32 is maintained at a low speed.

  As shown in FIGS. 4, 15 and 16, the display panel 24 includes a tachometer 66 for displaying the engine speed, a liquid crystal display 67 for displaying the vehicle speed, and the like. The liquid crystal display 67 has a vehicle speed display portion 67A for displaying the vehicle speed in characters, a main gear position display portion 67B for displaying the gear position of the main transmission 9 and a motor gear stage display for displaying the gear position of the variable capacity motor 32 in characters. 67C, a sub-speed stage display unit 67D that displays the shift speed of the sub-transmission device 10 and a set vehicle speed display unit 67E that displays an arbitrarily set vehicle speed. The operation of the liquid crystal display 67 is controlled by the control operation of display control means 27E provided in the ECU 27 as a control program.

  The vehicle speed display portion 67 </ b> A is arranged on the right side portion of the lower part of the middle stage in the liquid crystal display 67. The main gear stage display part 67B is arranged on the left side of the upper stage of the liquid crystal display 67 so as to be separated from the vehicle speed display part 67A. The motor gear stage display unit 67C is disposed on the left side portion of the upper middle stage of the liquid crystal display 67 so as to be positioned between the vehicle speed display unit 67A and the main gear stage display unit 67B. The auxiliary shift speed display portion 67D is disposed adjacent to the left side of the main shift speed display portion 67B in the liquid crystal display 67. The set vehicle speed display portion 67E is arranged on the lower right portion of the liquid crystal display 67 so as to be positioned below the vehicle speed display portion 67A.

  The display control means 27E outputs the output rotational speed of the main transmission 9 output from the vehicle speed sensor 63, the gear ratio at the set speed of the auxiliary transmission 10 read from the output of the lever sensor 60 for the auxiliary transmission lever, and the vehicle speed. The vehicle speed calculation unit 27Ea that calculates the actual vehicle speed (hereinafter referred to as the actual vehicle speed) based on the final reduction ratio by the differential device 13 for the rear wheels and the length of the outer periphery of the rear wheel 2, which are fixed data relating to the calculation of The actual vehicle speed output by the vehicle speed calculation unit 27Ea is displayed on the vehicle speed display unit 67A.

  The display control means 27E is vehicle speed setting data (set speed ratio of the main transmission 9) optimized by the control operation of the vehicle speed control means 27B based on the rated speed of the engine 3 and the output of the lever sensor 59 for the main transmission lever. The engine in a speed change state arbitrarily set by the main speed change lever 20 and the sub speed change lever 21 on the basis of the speed ratio at the set speed of the sub-transmission device 10, the final reduction ratio, and the outer circumference of the rear wheel 2. A rated vehicle speed calculation unit 27Eb that calculates a rated vehicle speed, which is a theoretical vehicle speed obtained when the rotation speed reaches the rated rotation number, is provided, and the rated vehicle speed output by the rated vehicle speed calculation unit 27Eb is used as a shift of the main transmission 9. The speed is displayed on the main shift speed display section 67B without a unit.

  The display control means 27E reads the shift stage of the variable displacement motor 32 from the control operation of the vehicle speed control means 27B and displays it on the motor shift stage display section 67C. Further, the shift speed of the sub-transmission device 10 is read from the output of the lever sensor 60 for the sub-shift lever and displayed on the sub-shift speed display section 67D.

  The display control means 27E is determined from the set rotation speed of the engine 3 read from the output of the lever sensor 30 for the speed control lever, the set rotation speed, and the vehicle speed setting data after optimization adopted by the vehicle speed control means 27B. Based on the transmission ratio of the main transmission 9, the transmission ratio at the set speed of the auxiliary transmission 10, the final reduction ratio, and the length of the outer periphery of the rear wheel 2, the main transmission lever 20 and the auxiliary transmission lever 21 can arbitrarily Is provided with a set vehicle speed calculation unit 27Ec that calculates a set vehicle speed that is a theoretical vehicle speed obtained when the engine speed reaches a set rotation number that is arbitrarily set. The set vehicle speed to be output is displayed on the set vehicle speed display section 67E.

  Specifically, the display on each of the display units 67A to 67E is “10.0 km” if the calculated vehicle speed is 10 km / h, and “4.5 km” if the calculated vehicle speed is 4.5 km / h. It is displayed on 67A. If the calculated rated vehicle speed is 12 km / h, “12.0” is displayed on the main gear stage display section 67B as the gear stage of the main transmission 9 if “62.0 / h”. When the speed of the variable displacement motor 32 read from the control operation of the vehicle speed control means 27B is a low speed, “L” is displayed on the motor speed stage display section 67C. If the shift stage of the sub-transmission device 10 read from the output of the lever sensor 60 for the sub-shift lever is a low speed stage for work, “low” is set for a high speed stage for work, and “high” is for high speed movement. If it is the fastest speed, “high speed” is displayed on the sub-speed stage display section 67D. If the calculated set vehicle speed is 10 km / h, “10.0 km” is displayed on the set vehicle speed display section 67E, and if it is 4.5 km / h, “4.5 km” is displayed. The display on the set vehicle speed display section 67E is an interrupt display that displays the set vehicle speed at that time only for a set time (for example, 5 seconds) when an operation for changing the vehicle speed is performed.

  Incidentally, the operation for changing the vehicle speed (operation for changing the vehicle speed) referred to here is an operation of the accelerator lever 17, an operation of the accelerator pedal 18, a both-step operation of the left and right brake pedals 19, an operation of the main transmission lever 20, and an auxiliary transmission lever. 21 operation, FR lever 22 operation, and stop pedal 23 operation.

  With the above configuration, when the main transmission lever 20 is operated to change the set gear ratio of the main transmission 9, the shift stage of the main transmission 9 displayed on the main shift stage display portion 67B is the operation position of the main transmission lever 20. Therefore, the transmission gear ratio of the main transmission 9 can be easily set by the main transmission lever 20. The shift speed of the main transmission 9 displayed on the main shift speed display section 67B matches the maximum speed obtained when the accelerator operation is maximized in the shift state set by the main shift lever 20 and the sub shift lever 21. Therefore, the vehicle speed can be easily set according to the working conditions without using a vehicle speed table that describes the maximum speed in each shift state. Further, when the shift stage of the sub-transmission apparatus 10 is changed because the shift stage of the main transmission 9 displayed on the main shift stage display portion 67B is the rated vehicle speed, the shift stage of the sub-transmission apparatus 10 is changed according to the changed shift stage. Since the display range on the main gear stage display section 67B is automatically switched, it becomes easy to set the vehicle speed according to the working conditions including the switching of the gear stage of the auxiliary transmission 10, and the main gear stage display section. Since 67B and the sub-speed display portion 67D are located adjacent to each other on the left and right, it is easy to grasp the relationship between the speed of the main transmission 9 and the speed of the sub-transmission 10. In addition, a main shift speed display section 67B is disposed at a position away from the vehicle speed display section 67A, and a motor shift speed display section 67C is disposed between the vehicle speed display section 67A and the main shift speed display section 67B. The main transmission device displayed on the main gear stage display unit 67B and the actual vehicle speed displayed on the vehicle speed display unit 67B by maximizing the accelerator operation by not attaching a unit to the display on the main gear stage display unit 67B. Even if the 9 gears have the same value, their display contents can be easily distinguished.

  In the set vehicle speed display section 67E, when the vehicle speed setting operation is performed by the accelerator lever 17, the main transmission lever 20, or the like, the operation position of the accelerator lever 17 or the accelerator pedal 18, the operation position of the main transmission lever 20 and the sub transmission lever 21 are displayed. The set vehicle speed determined by (the estimated vehicle speed expected from the vehicle speed setting operation) is displayed immediately, and the displayed set vehicle speed continuously changes according to the vehicle speed setting operation. For example, any engine speed and It is possible to easily and quickly set the vehicle speed when working at a vehicle speed, regardless of whether the vehicle is traveling or stopped. The display on the set vehicle speed display unit 67E is an interrupt display when an operation for changing the vehicle speed is performed, so that the driver can clearly recognize the meaning of the display on the set vehicle speed display unit 67E. In addition, since the vehicle speed displayed on the vehicle speed display unit 67A and the set vehicle speed displayed on the set vehicle speed display unit 67E are the same at the set vehicle speed, the display on the set vehicle speed display unit 67E is not performed. In the liquid crystal display 67, it is possible to prevent the same value (speed) from being displayed wastefully side by side.

  Further, by displaying the shift speed of the variable displacement motor 32 on the motor shift speed display portion 67C, the driver can easily recognize the shift speed of the variable displacement motor 32 that is switched by operating the main shift lever 20 or increasing or decreasing the vehicle speed. Can be made.

    [Another embodiment]

[1] The work vehicle may be an agricultural work vehicle such as a riding rice transplanter or a combiner, a riding mower, or a construction work vehicle such as a wheel loader.

[2] The work vehicle is configured not to include the stepped transmission 10 and configured to include a pair of left and right hydrostatic continuously variable transmissions 9 that shift the left and right rear wheels 2 independently. It may be configured to include a main clutch, or configured to include a forward / reverse switching mechanism dedicated to forward / reverse switching.

[3] As the hydrostatic continuously variable transmission 9, the variable displacement motor 32 is configured to be capable of shifting to three or more stages, the variable displacement motor 32 is provided with a constant capacity motor, or a hydromechanical continuously variable transmission is combined with a planetary gear. A transmission device (HMT) may be used.

[4] The configuration of the pump swash plate angle changing means A and the motor swash plate angle changing means B can be variously modified. For example, an electric actuator such as an electric motor or an electromagnetic cylinder is adopted. Also good.

[5] The stepped transmission 10 may be configured to be capable of two-stage shifting, that is, a low speed stage for work and a high speed stage for movement.

[6] The step detection means 60 for stepped transmission may be configured to detect the operation position of the shift member for shifting step provided in the stepped transmission 10.

[7] The structure of the gear ratio changing means C can be variously changed according to the hydrostatic continuously variable transmission 9 employed. For example, the hydrostatic continuously variable transmission 9 is provided with a constant capacity motor. Is adopted, the gear ratio changing means C includes only the pump swash plate operating means A.

[8] Various changes can be made to the configuration of the gear ratio setting means D. For example, if the vehicle speed control means 27B is configured to set the gear ratio of the HST 9 based only on the output of the main gear shift lever sensor 59 that detects the operation position of the main gear shift lever 20, the gear ratio setting means D is used. The main transmission lever 20 and the lever sensor 59 for the main transmission lever can be used. In the vehicle speed feedback control with this configuration, the vehicle speed control means 27B is configured so that the output of the engine speed detection means (engine sensor) 62, the main speed change lever 20 and the main speed change lever lever sensor 59 are set. The control target vehicle speed is obtained based on the output of the means D, and the operation of the gear ratio changing means C is controlled so that the output of the vehicle speed detecting means (vehicle speed sensor) 63 matches the obtained control target vehicle speed. That is, the method for obtaining the control target vehicle speed by the vehicle speed control means 27B is also changed according to the configuration of the gear ratio setting means D.

[9] The vehicle speed detecting means 63 may be configured to detect the output rotational speed of the auxiliary transmission (stepped transmission) 10, and the output of the rear wheel differential unit 13. A pair of left and right rear axles may be provided so as to detect the rotational speed. The method of obtaining the control target vehicle speed for the output of the vehicle speed detection means 63 by the vehicle speed control means 27B is also changed according to the configuration of the vehicle speed detection means 63.

[10] The first set rotational speed in the vehicle speed setting data may be set to a rotational speed close to the idling rotational speed. Further, the second set rotational speed in the first vehicle speed setting data may be set to a rotational speed close to the rotational speed at which the engine 3 exhibits the maximum torque. Furthermore, you may comprise so that the 1st speed ratio and 2nd setting rotation speed in vehicle speed setting data may be changed according to the kind of work vehicle, or the working apparatus with which it is equipped.

[11] Vehicle speed setting data dedicated to low speed work and vehicle speed setting data dedicated to high speed work may be provided.

  A vehicle speed control structure for a work vehicle according to the present invention includes a gear ratio setting unit that sets a gear ratio of a hydrostatic continuously variable transmission, a gear ratio changing unit that changes a gear ratio of a hydrostatic continuously variable transmission, and The present invention can be applied to a tractor, a riding mower, a riding rice transplanter, a combiner, a wheel loader and the like provided with a vehicle speed control means for controlling the operation of the speed ratio changing means.

DESCRIPTION OF SYMBOLS 3 Engine 9 Hydrostatic continuously variable transmission 10 Stepped transmission 27B Vehicle speed control means 31 Variable capacity pump 32 Variable capacity motor 60 Shift speed detection means 62 Engine speed detection means 63 Vehicle speed detection means A Pump swash plate angle change means B Motor swash plate angle changing means C Gear ratio changing means D Gear ratio setting means

Claims (4)

Engine speed detecting means for detecting the engine speed, speed ratio setting means for setting the speed ratio of the hydrostatic continuously variable transmission, vehicle speed detecting means for detecting the vehicle speed, and the speed ratio of the hydrostatic continuously variable transmission A gear ratio changing means for changing, and a vehicle speed control means for controlling the operation of the gear ratio changing means,
The vehicle speed control means obtains a control target vehicle speed based on the output of the engine speed detection means and the output of the gear ratio setting means, and the output of the vehicle speed detection means matches the obtained control target vehicle speed. A vehicle speed control structure for a work vehicle configured to control the operation of the speed ratio changing means.   The hydrostatic continuously variable transmission is provided with a variable displacement pump and a variable displacement motor, and the transmission ratio changing means is a pump swash plate angle changing means for changing the swash plate angle of the variable displacement pump steplessly; and 2. The vehicle speed control structure for a work vehicle according to claim 1, wherein the swash plate angle of the variable capacity motor is changed by a stepped motor swash plate angle changing means.   When the engine speed is the first set speed set to the engine idling speed or a speed close to the idling speed, the speed ratio of the hydrostatic continuously variable transmission is greater than the minimum speed ratio. When the engine speed is equal to or higher than the second set speed set on the higher speed side than the first set speed, the hydrostatic type Further, when the engine speed is a speed between the first set speed and the second set speed so that the speed ratio of the step transmission is the minimum speed ratio, the engine speed at that time The gear ratio setting means changes the engine speed so that the gear ratio of the hydrostatic continuously variable transmission changes to a larger gear ratio between the first gear ratio and the minimum gear ratio as the number decreases. The still oil based on the output of the detection means Work vehicle speed control structure according to claim 1 or 2 is arranged to set changes the gear ratio of formula CVT. A shift speed detection means for detecting a shift speed of the stepped transmission,
The vehicle speed control means obtains the control target vehicle speed in consideration of the gear ratio of the stepped transmission obtained from the output of the gear position detection means, and the output of the vehicle speed detection means coincides with the control target vehicle speed. The vehicle speed control structure for a work vehicle according to any one of claims 1 to 3, wherein the operation of the speed ratio changing means is controlled as described above.

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