JP2000158962A - Normal/reverse rotation switching device for tractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax a shock caused by inertia force and to prevent seizure of a clutch even at the time of rapidly switching a reverser operation means for forward-backward switching by an operation mistake or the like. SOLUTION: This normal/reverse rotation switching device for a tractor has a transmission mechanism for shifting an output interlockingly with operation of a main shift operating means 77 and an auxiliary shift operating means 98; and a hydraulic normal/reverse switching means for switching the output interlockingly with operation of a reverser operation means 82. A controller 96 is connected with speed stage detection means 77a, 98a for detecting positions of the shift operating means 77, 98; means 82a, 82b for detecting a position of the reverser operation means 82; and the normal/reverse switching means. When the reverser operation means 82 is switched from 'forward' to 'backward' or from 'backward' to 'forward' within a set time, the controller 96 controls such that pressure does not increase or that the set time is delayed according to detection values of the speed stage detection means 77a, 98a, after switching of the normal/reverse switching means to 'neutral'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydraulic forward / reverse switching means comprising a hydraulic clutch for a reverser for transmitting an output from an engine to an axle transmission system and converting the output between forward and reverse. In a forward / reverse switching device provided in a tractor having a reverser operating means for operating a reverse switching means, a shock generated when the reverser operating means is rapidly switched from forward to reverse or from reverse to forward. The present invention relates to a technique for preventing or dampening, and preventing a burn-in of the forward / reverse switching means.

[0002]

2. Description of the Related Art Conventionally, a reverser hydraulic clutch for transmitting output from an engine to an axle transmission system and converting the output between forward and reverse is provided in the axle transmission system, and a reverser for switching the reverser hydraulic clutch is provided. The technology of agricultural tractors having a configuration provided with a lever is known. This tractor is provided with a reverser lever capable of switching between forward, neutral, and reverse movements in an operation section, and further provided with a forward / reverse switching device that operates a hydraulic clutch for a reverser in conjunction with the reverser lever. By switching the reverser lever, the hydraulic clutch for reverser is disconnected and connected, and the driving direction of the vehicle can be switched to the forward direction or the reverse direction.

Further, in order to buffer a shock caused by switching of the reversing lever, a hydraulic pressure circuit for supplying hydraulic oil to the reversing hydraulic clutch is provided with a delay relief valve,
The technology of a forward / reverse switching device for making connection of a hydraulic clutch for a reverser gradual and smooth is also widely known.

[0004]

However, when the reversing lever is switched in a short time due to an erroneous operation of the operator or the like, the driving direction of the vehicle is rapidly switched without sufficiently obtaining the deceleration by the reversing lever neutral position. The delay relief valve receives a large inertial force because the delay relief valve cannot fully absorb the shock, and the operator feels a strong shock due to the inertial force and feels anxiety and discomfort. Also, when the vehicle is running at high speed,
When the drive direction is switched, an excessive load is applied to the hydraulic clutch for the reverser, and seizure of the clutch occurs, which shortens the life of the clutch. In order to prevent such a shock or an overload of the clutch due to the sudden switching of the reversing lever, various techniques have been developed and are known. For example, a technique as disclosed in JP-A-62-61841 and a technique as disclosed in JP-A-62-62043.

However, it has been desired to develop a technique capable of more effectively solving the above-described problem at the time of sudden switching of the reversing operation means. In addition, there has been a demand for a technique of a forward / reverse switching device that further improves the feeling when operating the reverser operation means and has better operation reliability and stability.

[0006]

The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described. In claim 1, a transmission mechanism for shifting the output from the engine in conjunction with the operation of the main transmission operation means and the sub-transmission operation means, and a hydraulic forward / reverse switching the output in conjunction with the operation of the reversing operation means A forward / reverse rotation switching device provided in a tractor having a switching means, a speed gear detection means for detecting the positions of the main speed change operation means and the sub speed change operation means, a means for detecting a position of the reverser operation means, and the forward / reverse changeover means When the detected value of the speed gear detecting means is equal to or more than the set speed gear and the reverser operating means is switched from forward to reverse or from reverse to forward in less than the set time, In addition, after the switching of the forward / reverse switching means to neutral, control is performed so as not to raise the voltage.

According to a second aspect of the present invention, there is provided a speed change mechanism for shifting the output from the engine in accordance with the operation of the main speed change operation means and the auxiliary speed change operation means, and a hydraulic pressure for switching the output in accordance with the operation of the reverser operation means. A forward / reverse switching device provided in a tractor having a forward / reverse switching device; a speed stage detecting device for detecting the positions of the main shift operating device and the sub-shift operating device; a device for detecting the positions of the reverser operating device; Three of the reverse switching means are connected to the control means, and the detected value of the speed gear detecting means is less than the set speed gear, and the reverser operating means switches from forward to reverse or from reverse to forward in less than the set time. In such a case, control is performed such that the boosting is started with a delay of a set time after the forward / reverse switching means is switched to neutral.

Next, embodiments of the present invention will be described. FIG. 1 is a side view showing an overall configuration of an agricultural tractor according to an embodiment of the present invention, and FIG. 2 is a side view showing an arrangement configuration of a main shift lever, a potentiometer for detecting a position of a main shift lever, and an auxiliary shift lever. FIG. 3 is a side view showing an arrangement configuration of a sub-transmission lever position detection switch, and FIG. 4 is a side sectional development view showing a configuration of a main clutch and a transmission. FIG. 5 is a skeleton diagram showing a power transmission configuration of the tractor, and FIG. 6 is a hydraulic circuit diagram of the tractor.

First, the overall configuration of an agricultural tractor according to one embodiment of the present invention will be described with reference to FIG. That is, in this tractor, a bonnet 6 is disposed at a front portion of a main body that suspends a front wheel 1 and a rear wheel 2 back and forth, and an engine 5 is disposed inside the hood 6. Bonnet 6
Is provided with a steering handle 10 and a reversing lever 82 serving as a reversing operation means is disposed near the steering handle.

The reversing lever 82 is switched in three stages of "forward", "neutral" and "reverse". When the operator operates the reversing lever 82 to the "forward" or "reverse" side, the tractor is driven. The direction is determined to be the forward direction or the reverse direction. Further, a reverser position detecting means for detecting the position of the reverser lever 82 is provided near the reverser lever 82. The reversing position detecting means includes a reversing neutral detecting switch 82a and a reversing reverse detecting switch 82b (both are not shown in FIG. 1), and only when the reversing lever 82 is located at the "neutral" position or the "reverse" position. Switch 8
2a and 82b are configured to be ON.

A seat 11 is arranged behind the steering handle 10. Steering handle 10
And the seat 11 is covered by the cabin 12.

A clutch housing 8 is provided behind the engine 5, a transmission case 9 is connected behind the clutch housing 8, and power from the engine 5 is supplied to the rear wheels 2.
To be driven. However, depending on the operation, a four-wheel drive that transmits the driving force to the front wheels 1 at the same time is also possible.

The driving force of the engine 5 is transmitted to a PTO shaft 15 protruding from the rear end of the transmission case 9 and
Working machine 100 driving TO shaft 15 and connected to the rear end of the machine
(Not shown in FIG. 1).

A clutch pedal 16 for connecting and disconnecting the clutch is tiltably supported at the foot of the operator who operates the tractor. On the side of the seat 11 on which the operator sits, a main shift lever 77 as a main shift operating means and a sub-shift lever 98 as an auxiliary shift operating means for shifting are provided as shown in FIG.

The main shift lever 77 is provided with a one- to four-step shift M1.
-It is possible to switch to a total of five positions: M2, M3, M4 and the neutral position MN, and the vehicle is shifted by operating the main shift lever 77. A potentiometer 77 serving as a speed gear detecting means is provided at a position near the main shift lever 77.
a is arranged and is linked to the main speed change lever 77 to detect the position of the main speed change lever 77.

The auxiliary shift lever 98 has two neutral positions S.
N ・ SN and creep (ultra low speed) SC, low speed SL, medium speed S
M and high-speed SH can be switched to a total of six positions, and the shift of the vehicle is performed by the operator operating the sub-shift lever 98. At a position near the sub-shift lever 98, a sub-shift high-speed detection switch 98a as another speed stage detecting means is disposed as shown in FIG. The sub-shift high-speed detection switch 98a is configured to be turned ON only when the sub-shift lever 98 is at the high speed position SH.

Next, the structure inside the clutch housing 8 and the transmission case 9 will be described with reference to FIGS. That is, the clutch housing 8 is fixedly provided behind the engine 5, and the transmission case 9 is attached to the rear surface of the clutch housing 8. The transmission case 9 is divided into two parts (9a and 9b), and a center plate 13 is sandwiched between the two. Rear axle cases are fixedly provided on the left and right sides of the rear portion of the transmission housing 9b.

Next, the configuration of the rear axle transmission system will be described. That is, a wet multi-plate type main clutch 21 linked to the clutch pedal 16 is disposed in the clutch housing 8, and a driving side shaft 22 of the main clutch 21 is disposed.
, The rotation of the crankshaft of the engine 5 is input. A driven side shaft 23 of the main clutch 21 extends rearward of the fuselage, and a main speed fourth speed gear 34 loosely fitted to the traveling clutch shaft 24 meshes with a gear 23a formed at the rear end thereof. The main transmission fourth speed gear 34 meshes with a transmission gear 44 fixed to the main shaft 25. The main shaft 25 has three transmission gears 41.4.
The main transmission first-speed gear 31 and the main transmission second gear 31, which are loosely fitted to the traveling clutch shaft 24 via the three transmission gears 41, 42, 43, respectively. Power is transmitted to the speed gear 32 and the main transmission third speed gear 33. Therefore, when the driven side shaft 23 of the main clutch 21 rotates, the main speed first speed gear 31, the main speed second speed gear 32, the main speed third speed gear 33, and the main speed fourth speed gear 34 rotate at different rotational speeds. Becomes Then, one of the four hydraulic clutches 51, 52, 53, and 54 is selected and brought into "contact" by a hydraulic control valve interlocked with the main shift lever 77, thereby enabling four-step shifting. The rotation of the main shaft 25 is transmitted to the traveling clutch shaft 24 via the speed change.

The traveling clutch shaft 24 is mounted on the center plate 1.
3 and extend rearward. A forward rotation side gear 26 and a reverse rotation side gear 27 are loosely fitted on the same axis on the extended portions. By operating the hydraulic control valve linked to the reverser lever 82, either the forward-side reverser hydraulic clutch 56 or the reverse-side reverser hydraulic clutch 57 is selected and connected, and the rotation of the traveling clutch shaft 24 is controlled. The power is transmitted to either the forward rotation gear 26 or the reverse rotation gear 27. However, when the reversing lever 82 is in the neutral position, the rotation is not transmitted to both the gears 26 and 27.

The forward rotation gear 26 is non-rotatably connected to the auxiliary transmission shaft 35 and, at the same time, meshes with a transmission gear 37 fixed to the creep transmission shaft 36, and rotates the rotation of the transmission gear 37 between the two shafts 35.
・ Communicate to 36. The reverse rotation gear 27 meshes with a gear 39 formed at one end of a forward / reverse rotation shaft 38, and a gear 40 formed at the other end of the forward / reverse rotation shaft is fixed to a creep speed change shaft 36. The transmission gear 37 meshes. Accordingly, the rotation of the reverse rotation gear 27 causes the creep speed change shaft 36 to rotate in the reverse rotation direction via the forward / reverse rotation shaft 38. Further, the auxiliary transmission shaft 35 connected thereto is rotated in the reverse direction via the forward rotation gear 26 meshing with the transmission gear 37 of the creep transmission shaft 36. That is, by selectively operating the two reverser hydraulic clutches 56 and 57, the engine 5
Can be transformed in the inverse direction. In this sense,
The reversing hydraulic clutches 56 and 57 serve as the above-mentioned forward / reverse switching means.

A sub-transmission second shaft 45 is provided at the rear of the sub-transmission shaft 35.
Are arranged on the same axis so as to be freely rotatable, and a creep speed change gear 46 is loosely fitted to the auxiliary speed change second shaft 45. The creep speed change gear 46 meshes with a gear 47 formed on the creep speed change shaft 36. An input clutch slider 91 is spline-fitted to the sub-transmission second shaft 45 so as to be slidable in the axial direction, and is linked to the above-described sub-transmission lever 98. Therefore, the input clutch slider 91 is meshed with either the auxiliary transmission shaft 35 or the creep transmission gear 46 by operating the auxiliary transmission lever 98, and is capable of transmitting its rotation to the auxiliary transmission second shaft 45. That is, depending on the selection based on the sliding of the input clutch slider 91, either the rotation of the auxiliary transmission shaft 35 or the rotation from the auxiliary transmission shaft 35 through the creep shift by the creep transmission shaft 36 is transmitted to the auxiliary transmission second shaft 45. Is entered.

An output shaft 48 is supported in parallel with the auxiliary transmission second shaft 45. The output shaft 48 has two transmission gears 49
50 is fixed. The transmission gears 49 and 50 mesh with two transmission gears 59 and 60 loosely fitted on the auxiliary transmission second shaft 45. An output clutch slider 92 is spline-fitted to the sub-transmission second shaft 45 so as to be slidable in the axial direction. The output clutch slider 92 is linked to the sub-shift lever 98 described above. Therefore, the output clutch slider 92 is slid by the operation of the auxiliary transmission lever 98 and meshes with one of the two transmission gears 59 and 60 to rotate the auxiliary transmission second shaft 45 to the two transmission gears 59. -It is possible to transmit to any one of 60. Therefore, by the selection based on the sliding of the output clutch slider 92, the sub-transmission second shaft 4
The rotation of No. 5 is output through a two-stage shift and input to the output shaft 48.

A rear wheel differential portion 66b is arranged at the rear portion 9b of the transmission housing, and the rotation of the output shaft 48 is input to the rear wheel differential portion 66b via the bevel gear 20 formed at the rear end of the rear wheel differential portion 66b. The rear wheel 2 is driven via an internal axle, a transmission gear, and the like.

Next, the PTO transmission system will be described. That is, a PTO clutch shaft 29 is arranged in the transmission housing front portion 9a in parallel with the main shaft 25,
The O clutch shaft 29 has four PTO transmission gears, ie, PT
The first O gear 61, the second PTO gear 62, the third PTO gear 63, and the fourth PTO gear 64 are loosely fitted. The PTO transmission gears 61, 62, 63, and 64 are four transmission gears 41, 42, 43, 44 fixed or formed on the main shaft 25.
, And the rotation of the main shaft 25 causes the PTO transmission gears 61, 62, 63, and 64 to rotate at different rotational speeds. The PTO clutch shaft 29 has a PTO reverse gear 6
5 is loosely fitted, and the PTO reverse rotation gear 65 meshes with the above-mentioned main speed first speed gear 31 loosely fitted on the traveling clutch shaft 24. That is, the main speed first gear 31 also functions as an idle gear of the PTO reverse rotation imparting mechanism.

The PTO clutch shaft has two PTOs.
Clutch sliders 93 and 94 are spline-fitted slidably in the axial direction. Also, the PTO clutch slider 93
94 is linked to a PTO shift lever (not shown).
Therefore, by the selection based on the sliding of the two PTO clutch sliders 93 and 94, the rotation of the main shaft is transmitted to the PTO shaft after passing through the four-stage shift. Also, the main transmission first speed gear 31,
The rotation of the main shaft 25 is forward / reverse converted via the PTO reverse rotation gear 65 and transmitted to the PTO clutch shaft 29. In other words, the fourth forward speed and the first reverse speed are shifted between the two shafts 25 and 29. The PTO clutch shaft 29 is connected to the PTO shaft 15 so as not to rotate relatively. The PTO shaft 15 extends rearward and drives a work machine 100 connected to the rear end of the tractor.

Next, the front axle transmission system will be described. That is, a pipe-shaped front wheel input shaft 55 is rotatably fitted to the PTO shaft 15, and the front wheel clutch shaft 30 is supported in parallel with the front wheel input shaft 55. An input gear 67 is fixed to the front wheel input shaft 55, and the input gear 67 is connected to the output shaft 4.
8 is engaged with one of the two transmission gears 49 fixed to the transmission gear 8. The front wheel input shaft 55 further includes two transmission gears 1.
8 and 19 are fixedly mounted, and the transmission gear is a front wheel clutch shaft 30.
The two gears, ie, the four-wheel drive-side gear 68 and the front-wheel double-speed gear 69, which are loosely fitted to the gears, respectively mesh with each other.

Then, one of the two hydraulic clutches 78 and 79 is selected and connected by operating a hydraulic control valve that is interlocked with a 4WD / front wheel double speed changeover switch (not shown).
The rotation of the front wheel input shaft 55 is transmitted to the front wheel clutch shaft 30 at approximately double speed or approximately constant speed. Front wheel clutch shaft 30
Is input to the front wheel side differential portion 66a via a front wheel transmission shaft 14 connected to the front end, a universal joint and the like, and drives the front wheel 1 via an axle, a transmission gear and the like in the front axle case.

The configuration of the hydraulic circuit provided in the tractor having the above configuration will be described with reference to FIG. That is, the hydraulic oil in the oil tank (mission case) 71 is branched in two directions via a suction strainer 73, and one of the oil is pumped to a power steering unit 74 by a traveling hydraulic pump 72. The power steering unit 74 is provided to reduce the torque required to operate the steering handle 10, and is provided with a switching valve 75 interlocked with the steering handle 10 to be connected to a double-acting front steering device. The cylinder 76 is driven to give a steering angle to the front wheels 1.

The hydraulic oil that has passed through the power steering unit 74 is branched into three, and one of the four hydraulic clutches 51, 52, 53, 54 is operated by a main transmission control valve 80 that is linked to a main transmission lever 77. Is operated to perform the main shift. The other goes through the proportional pressure reducing valve 81,
The two hydraulic clutches 56 for the reverser are operated by the reverser control valve 83 linked to the reverser lever 82.
One of the wheels 57 is operated to switch the tractor between forward and reverse. The proportional pressure reducing valve 81 is constituted by an ON / OFF switching valve formed of an electromagnetic valve, and plays a role of adjusting the hydraulic pressure supplied to the above-described hydraulic clutches 56 and 57 for the reverser. Also, by switching the proportional pressure reducing valve 81 to drain the pump port of the reverser control valve 83 to make the pressure zero, the hydraulic clutch 56 for the reverser can be used regardless of the position of the reverser lever 82.
-It is also possible not to operate any of 57. The rest passes through an electromagnetic control valve 95 to operate one of the two hydraulic clutches 78 and 79 to switch between front wheel acceleration or four-wheel drive. At the time of increasing the front wheel speed, one of the braking devices 84 and 85 provided on the left and right of the rear wheel is operated to turn the inside of the turning device to reduce the turning radius when turning.

Next, the hydraulic circuit of the work machine control system will be described. From the oil tank 71 to the suction strainer 7
The hydraulic oil branched through 3 is a working machine hydraulic pump 86
As a result, it is pressure-fed to the working machine control unit 88 via the external hydraulic pressure take-out part 87. And the working machine lifting cylinder 8
9 and the work machine horizontal control cylinder 90 are appropriately operated to perform elevation and level control of the work machine 100 connected to the rear end of the tractor.

Next, the hydraulic clutch for reverser 56
Control of the proportional pressure reducing valve 81 that supplies pressure oil to 57 will be described with reference to FIGS. 7 to 11. FIG. 7 is a configuration diagram of a control device of the proportional pressure reducing valve. FIG. 8 is a diagram showing a control flow of the control device. 9 is a diagram showing a pressure waveform of the proportional pressure reducing valve at the time of normal switching of the reverser, FIG. 10 is a diagram showing a pressure waveform of the proportional pressure reducing valve when the reverser is rapidly switched in the low speed state, and FIG. FIG. 4 is a diagram showing a pressure waveform of a proportional pressure reducing valve when a reverser is suddenly switched in a state. The symbols “F”, “N”, and “R” shown in FIGS. 9 to 11 mean “forward”, “neutral”, and “reverse” of the reverser lever 82, respectively.

That is, the proportional pressure reducing valve 81 shown in FIGS.
Is an electromagnetic switching type, and a control device 9 as a control means.
The pressure (duty ratio) is controlled by a signal sent from the control device 96. still,
Reference numeral 97 denotes a battery that supplies power to the control device 96.

The potentiometer 77a for detecting the position of the main shift lever 77 and the auxiliary shift high speed detection switch 98a for detecting the high speed position of the auxiliary shift lever 98.
Are electrically connected to the control device 96. Then, information about the resistance value of the potentiometer 77a and the state of the sub-shift high-speed detection switch 98a is input to the control device 96, and the control device 96 uses the main shift lever 77 and the sub-shift lever 98 based on the information. It is determined whether or not the determined speed stage is in a high speed state. Specifically, for example, if the sub-shift high-speed detection switch 98a is ON,
This means that the sub-shift lever 98 is at the high-speed position SH. Therefore, if the position of the main shift lever 77 is at a certain position (for example, the position of the third speed M3 or the position of the fourth speed M4),
For example, it is determined that the speed stage is in the high speed state.

Further, a reverser neutral detection switch 82a and a reverser reverse detection switch 82b for detecting the position of the reverser lever 82 are connected to the control device 96. Then, information on the states of both switches 82a and 82b is input to the control device 96, and based on the information, the control device 96 determines whether the reverser lever 82 is currently "forward" or "neutral".
It is determined which position of "reverse".

The control unit 96 controls the proportional pressure reducing valve 81 as follows based on the result of the determination. That is,
As shown in FIG. 8, the control device 96 first determines whether or not the current speed stage is in the high speed state based on the detection values of the speed stage detection means 77a and 98a. When the current speed stage is in the high speed state, the time (t shown in FIGS. 9 to 11) required for the reverser lever 82 to pass through the “neutral” position is measured. When the passing time t is less than the predetermined value, the control device 96 controls the reversing lever 8
It is determined that 2 has been rapidly switched from forward to reverse or from reverse to forward (hereinafter, this rapid switching operation is defined as "rapid operation"). In this case, since the vehicle is running at high speed, the control device 96 sends a signal to maintain the pressure of the proportional pressure reducing valve 81 at 0 as shown in FIG. Drain the pump port of valve 83 to zero pressure. Therefore, even if the reversing lever 82 is in the forward or reverse position, no hydraulic pressure is supplied to the reversing control valve, and neither of the two reversing hydraulic clutches 56, 57 is operated. 57 is protected from overload.

On the other hand, when the passing time t is equal to or longer than the predetermined value, the control device 96 judges that the reversing lever 82 has not been suddenly operated and, as usual, that is, A of FIG. The pressure of the proportional pressure reducing valve 81 is increased as shown in a waveform. That is,
In this case, since the reverser lever is in the neutral position for a long time, the speed is sufficiently reduced during that time. Therefore, the hydraulic clutches 56 and 57 for the reverser
, The shock felt by the operator is small, and the problem of seizing of the clutches 56 and 57 does not occur.
Is to be activated.

On the other hand, when the current speed stage is not in the high speed state (ie, in the low speed state or the medium speed state), the control device 9
6 measures the time t required for the reverser lever 82 to pass through the "neutral" position. When the passing time t is less than the predetermined value, the control device 96 controls the reversing lever 8
2 is determined to have been suddenly operated. In this case, in order to alleviate the shock due to the inertial force, the proportional pressure reducing valve 81 is raised in pressure as shown in the waveform B of FIG. That is, in this case, the deceleration is insufficient because the time during which the reverser lever 82 is in the neutral position is short, and when the hydraulic clutches 56 and 57 for the reverser are operated as in the normal state, a large inertia force is generated and the operator is instructed. Because it gives a strong shock, the hydraulic clutch for reverser 56
The operation of 57 is to be delayed, during which time deceleration is sufficiently performed.

On the other hand, when the passing time t is equal to or longer than the predetermined value, the control device 96 determines that the reversing lever 82 has not been suddenly operated, and as usual, that is, A of FIG. The pressure of the proportional pressure reducing valve 81 is increased as shown in a waveform. That is,
In this case, since the deceleration is sufficiently performed because the time in the neutral position is long, the generated inertial force is small, and the generated shock is within an allowable range. Is to be activated.

[0038]

The present invention is configured as described above.
The following effects are obtained. That is, as set forth in claim 1, a speed change mechanism that changes the output from the engine in conjunction with the operation of the main speed change operation means and the auxiliary speed change operation means,
A forward / reverse switching device provided in a tractor having a hydraulic forward / reverse switching means for switching the output in conjunction with the operation of the reversing means; The speed detecting means, the means for detecting the position of the reverser operating means, and the forward / reverse switching means are connected to the control means, and the detected value of the speed gear detecting means is equal to or higher than the set speed gear, and the reverser operating means When the reverser is switched from forward to reverse or from reverse to forward for less than the set time, the forward / reverse switching means is switched to neutral and then controlled so as not to boost the voltage. Since the supply of hydraulic pressure is cut off after the forward / reverse switching means becomes neutral, the forward / reverse switching means does not operate even if the reverser operating means is in the forward or reverse position, and the engine Output is not transmitted to the axle. Therefore, even when the reverser operating means is suddenly switched due to an erroneous operation of the operator, the switching means does not operate, so that the axle is not suddenly driven in the opposite direction, and as a result, the operator feels a strong shock due to the inertial force. Is prevented.

Further, an excessive load generated at the time of rapid switching of the reverser during high-speed running is prevented from acting on the forward / reverse switching means, and the seizure of the clutch does not occur.
The life of components used for the forward / reverse switching means can be extended.

According to a second aspect of the present invention, there is provided a speed change mechanism for shifting the output from the engine in accordance with the operation of the main speed change operation means and the auxiliary speed change operation means, and switching the output in accordance with the operation of the reverser operation means. A forward / reverse switching device provided in a tractor having hydraulic forward / reverse switching means, wherein a speed gear detecting means for detecting the positions of the main shift operating means and the sub-shift operating means, a means for detecting the positions of the reverser operating means, and The forward / reverse switching means is connected to the control means, and the value detected by the speed gear detecting means is less than the set speed gear, and the reverser operating means switches from forward to reverse or from reverse to forward in less than the set time. In such a case, the control is performed such that the boosting is started with a delay of a set time after the forward / reverse switching means is switched to neutral, so that even when the reverser is rapidly switched, the forward / reverse switching means is controlled. Time constant from when neutral does not operate, since the start to operate with a delay said time, it is possible to achieve some reduction in the meantime. Therefore, the inertia force generated at the time of switching the reverser can be reduced, the shock felt by the operator is reduced, and the operator is less likely to feel uneasy or uncomfortable during driving. That is, it is possible to provide a tractor with high reliability and stability and a good operation feeling for the operator.

[Brief description of the drawings]

FIG. 1 is a side view showing the overall configuration of an agricultural tractor according to one embodiment of the present invention.

FIG. 2 is a side view showing an arrangement of a main shift lever, a potentiometer for detecting a position of a main shift lever, and an auxiliary shift lever.

FIG. 3 is a side view showing an arrangement configuration of a sub-transmission lever position detection switch.

FIG. 4 is a side sectional development view showing a configuration of a main clutch and a transmission.

FIG. 5 is a skeleton diagram showing a power transmission configuration of the tractor.

FIG. 6 is a hydraulic circuit diagram of the tractor.

FIG. 7 is a configuration diagram of a control device of the proportional pressure reducing valve.

FIG. 8 is a diagram showing a control flow of the control device.

FIG. 9 is a diagram showing a pressure waveform of a proportional pressure reducing valve when a reverser is normally switched.

FIG. 10 is a diagram showing a pressure waveform of a proportional pressure reducing valve when the reverser is rapidly switched in a low speed state.

FIG. 11 is a diagram showing a pressure waveform of a proportional pressure reducing valve when a reverser is rapidly switched in a high-speed state.

[Explanation of symbols]

 Reference Signs List 5 engine 16 clutch pedal 21 main clutch 56/57 hydraulic clutch for reverser (forward / reverse switching means) 77 main shift lever (main shift operating means) 77a potentiometer (speed gear detecting means) 81 proportional pressure reducing valve 82 reverser lever (reverser operating means) 83) Reverser control valve 96 Control device (control means) 98 Sub-shift lever (sub-shift operation means) 98a Sub-shift high speed detection switch (speed gear detection means)

Claims (2)

[Claims] A speed change mechanism for shifting an output from an engine in conjunction with an operation of a main speed change operation means and a sub speed change operation means;
A forward / reverse switching device provided in a tractor having a hydraulic forward / reverse switching means for switching the output in conjunction with the operation of the reversing means; The speed detecting means, the means for detecting the position of the reversing means, and the forward / reverse switching means are connected to the control means, and the detected value of the speed detecting means is greater than or equal to the set speed step, and A tractor forward / reverse switching device characterized in that when the vehicle is switched from forward to reverse or from reverse to forward for less than a set time, the forward / reverse switching means is switched to neutral and then controlled so as not to boost the voltage. A speed change mechanism for shifting an output from the engine in conjunction with an operation of a main speed change operation means and a sub speed change operation means;
A forward / reverse switching device provided in a tractor having a hydraulic forward / reverse switching means for switching the output in conjunction with the operation of the reversing means; The speed detecting means, the means for detecting the position of the reverser operating means, and the forward / reverse switching means are connected to the control means, and the detected value of the speed gear detecting means is less than the set speed gear, and the reverser operating means When the tractor is switched from forward to reverse or from reverse to forward in less than the set time, the forward / reverse switching means is switched to neutral and then controlled to start boosting with a set time delay. Forward / reverse switching device.