JP5034178B2 - Tractor 2WD 4WD switching device - Google Patents

Description

  The present invention relates to a 2WD 4WD switching device for a tractor that switches between 2WD (2WD traveling) and 4WD (4WD traveling) according to road surface conditions.

  As shown in Patent Document 1 (slip control in FIG. 10), two-wheel drive and four-wheel drive switching of a tractor comprising a transmission transmission unit capable of switching between 2WD and 4WD transmission systems and a control unit for the transmission and transmission system switching. The device is known. The speed change transmission unit is configured to be able to switch between the transmission system for the 4WD mode for driving both the front and rear wheels for driving the aircraft and the 2WD mode for driving only one of the wheels, and for a plurality of speed ranges. Shifts the driving power of the front and rear wheels. The control unit performs automatic switching control according to a predetermined switching condition for switching the transmission system of the transmission unit.

  The two-wheel drive / four-wheel drive switching device having the above configuration shifts the driving power of the front wheels and the rear wheels, and the transmission configuration is a 4WD configuration according to a predetermined slip ratio set as a switching condition by the transmission system switching control unit. By switching between the 2WD mode and driving the front wheels and / or the rear wheels, the traveling traction force of the tractor is automatically adjusted as necessary.

However, the two-wheel drive / four-wheel drive switching device having the above-described configuration is switched to the 4WD form even in the high-speed road traveling speed range in the same manner as the low-speed field work. Is required, and the transmission system (power shift unit, control curve, clutch flow rate, etc.) is affected by an extreme drop in secondary pressure due to transmission system switching. Since it is necessary to suppress such a sudden change in the secondary pressure, a pressure reducing valve must be provided for each system, including a forward / reverse switching unit, a 4WD transmission switching unit, a Hi-Lo switching unit, etc. It included the problem of cost due to complications.
JP-A-7-266910

  The problem to be solved is a two-wheel-drive four-wheel drive tractor that can simplify the structure of the hydraulic control system by ensuring the driving force by 4WD transmission as required and improving the efficiency of airframe travel. It is to provide a switching device.

The invention according to claim 1 is configured to be switchable between a 4WD configuration for driving both the front wheels and the rear wheels and a 2WD configuration for driving one of the front wheels or the rear wheels, and the slip state of the front and rear wheels is predetermined. In a two-wheel drive / four-wheel drive switching device for a tractor having a control unit that selects a travel in the 2WD form if it is less than the value, and selects a travel in the 4WD form if the predetermined value is exceeded, the tractor includes a plurality of sub-shifts. A shift lever capable of selecting an arbitrary speed range from the speed range is provided, and the control unit determines that the predetermined value is in a 2WD form as the selected speed range becomes higher in a speed range where the main gears do not overlap. Change to a value that makes driving easy to select, and the main gear position of the sub-position for road driving overlaps with part of the main gear position of the high-speed position, and for road driving where this main gear position overlaps Sub An intermediate vehicle speed speed region of Jishon, by comparing the intermediate vehicle speed range position for high speed, as the intermediate wheel speed is high speed, changing the predetermined value to easily value travel is selected by 2WD form It is characterized by.

According to a second aspect of the present invention, when the control unit is selected to travel in the 2WD form , the brake connection sensor that detects the connection of the left and right brake pedals is connected, and the three conditions that the vehicle speed is equal to or higher than a predetermined speed are satisfied. The control process switches to 4WD corresponding to the brake pedal operation, and returns to 2WD when the brake pedal operation is released.
Invention, wherein the control unit sets a off-delay in the detection of the brake coupling sensor, connecting sensors are specified time after off of the control process that holds on determining according to claim 3 And

  With the above configuration, the driving power of the front wheels and the rear wheels is shifted and transmitted for each selected speed range, including the case where the speed ranges overlap, and the drive mode is set according to the speed range by the control unit. According to the switching condition, the 4WD mode and the 2WD mode are switched to drive both front wheels and / or rear wheels.

According to the first aspect of the present invention, the two-wheel drive / four-wheel drive switching device is switched between the 4WD mode and the 2WD mode according to the switching condition depending on the slip state according to the speed range by the control unit, and the slip ratio at the time of high speed traveling is lower than that at low speed traveling. By setting the switching condition to reduce the ratio of 4WD transmission, it is possible to improve the efficiency of airframe traveling on high-speed roads while ensuring the necessary driving force during low-speed work traveling. Wear due to an excessive difference in rotation of the ring can be reduced.
The invention according to claim 2 can ensure 4WD transmission corresponding to the brake operation during traveling by performing control so as not to return to 2WD except under a predetermined condition.
According to the third aspect of the present invention, when the on / off is repeated within a specified time due to the setting of the off-delay, the on-determination is continued, so that the 4WD transmission corresponding to the above brake operation is ensured by the reliable detection of the “connection”. be able to.

Embodiments specifically configured based on the above technical idea will be described below with reference to the drawings.
FIG. 1 is a side view of an agricultural tractor showing an example of a work vehicle according to the present invention.
The agricultural tractor 1 has an engine 4 mounted in a bonnet at the front of an airframe having front wheels 2, 2 and rear wheels 3, 3, and rotational power of the engine 4 is transmitted to a transmission gear transmission 5 a in a mission case 5. The power transmitted and appropriately decelerated by the speed change transmission portion 5a is transmitted to the front wheels 2, 2 and the rear wheels 3, 3, and output to the working machine 6a via the rear PTO shaft 6. Yes.

  In addition, a control seat 7 is provided at the top of the mission case 5 to constitute an operation unit. Specifically, as shown in the operation arrangement (front side) device arrangement configuration diagram of FIG. 2, a monitor 12 that displays a driving state on the front side of the steering handle 11, a forward / reverse switching lever 13 and an accelerator lever for forward / reverse switching on the lower side. 14, a clutch pedal 15 and an accelerator pedal 16, left and right brake pedals 17a and 17b, a speed change lever 18 serving as an operating tool for selecting a speed range are disposed on the side of the cockpit 7, and the like. In the HH position, the control unit c is configured to be capable of automatic shifting according to the conditions of the accelerator pedal 16 and the like. In addition, a work machine lifting / lowering one-touch lever 19c, a parking brake lever 19d, a PTO speed change lever 19e, and the like are disposed in the vicinity of the steering handle 11.

  The transmission transmission unit 5a is a mechanism unit that controls the traveling power and the work machine power, and as shown in the transmission system development diagram of FIG. 3, the forward / reverse switching unit 22 that receives power from the engine 4 via the main clutch 21, A main transmission 23, a sub-transmission 24, and a front-wheel drive clutch for two-wheel drive / four-wheel drive switching control (two-wheel drive / four-wheel drive switching clutch) that receive driving power from the subsequent stage and transmit the driving power to the front wheels 2, 2 and the rear wheels 3, 3. 25, and a PTO reverse clutch 26, a PTO transmission unit 27, and the like for controlling transmission of the work machine power branched by the forward / reverse switching unit 22 to the rear PTO shaft 6. The two-wheel drive / four-wheel drive switching control by the front wheel transmission clutch 25 switches between front and rear wheel drive (4WD) and one front and rear wheel drive (2WD, rear wheel drive in the illustrated example).

  The main transmission unit 23 includes, for example, a first main transmission mechanism capable of switching high and low speed clutches and a second main transmission mechanism capable of switching gears of four speeds connected in series, and in accordance with a command from the control unit c. The sub-transmission unit 24 is configured to be able to select high, middle, and low speed regions by switching the third gear by operating the shift lever 18.

  The gear ratio of all 24 speeds shown in FIG. 4 can be selected by the combination of the main transmission 23 and the sub-transmission 24. The combination is determined by the control unit c in accordance with the lever position for shifting.

  More specifically, the lever position for shifting the sub-transmission unit 24 corresponds to the high, middle and low speed ranges for work travel as shown in the operation unit (side) device arrangement perspective view of FIG. “M” and “L” are set to the lever guide 18g, and an up switch 18u and a down switch 18d for switching the main transmission 23 one step at a time are arranged on the transmission lever 18. Furthermore, an “HH” subposition for traveling on the road is added to the “H” position. This “HH” sub-position limits the main transmission 23 to the 5th to 8th speeds while maintaining the sub-shift “H”, that is, it is possible to switch only the shift position suitable for road travel. In the “HH” sub-position, the main transmission unit 23 is switched by the control unit c according to the accelerator position and the throttle position, and automatic transmission control is performed.

  Further, the switching of the 2WD / 4WD mode by the front wheel transmission clutch 25 is controlled by the control unit c in accordance with a predetermined switching condition, and the switching condition is determined according to the speed range selected by the transmission lever 18 for the auxiliary transmission unit 24. By setting individually, the control part c is comprised so that transmission system switching control may be performed with the switching conditions according to the selected speed range.

  A specific control procedure in the control unit c for the transmission transmission unit 5a having the above-described configuration is read by the shift lever position sensor, the front wheel rotation sensor 2s, the rear wheel rotation sensor 3s, and the like as shown in the transmission control flowchart of FIG. After (S1), by the brake pedal determination process (S2), the control unit c automatically performs the turning control, the two-wheel drive / four-wheel drive switching control, and the shift control (S3 to S5) according to conditions.

As shown in the flowchart of FIG. 7, the detailed processing procedure example of the above-described two-wheel-drive / four-wheel-drive switching control sets the condition A (S12a) if the road running position is HH by checking the shift lever position (S11), and others. Sets condition B (S12b). Next, the control valve is energized to temporarily control the front wheel transmission clutch 25 under the condition (S13, S14) that the slip ratio detected by the front wheel rotation sensor 2s and the rear wheel rotation sensor 3s is equal to or greater than a predetermined value and the predetermined time has elapsed. Set to 2WD (S15).

  The two-wheel drive / four-wheel drive switching control process according to the above procedure enables the two-wheel drive / four-wheel drive switching control under the switching conditions corresponding to the shift lever position. By doing so, it is possible to perform the 2WD 4WD switching traveling according to the traveling mode. If necessary, the switching conditions may be set individually corresponding to the four shift lever positions.

  Thus, the transmission transmission unit 5a having the above-described configuration transmits the traveling power of the front wheels 2, 2 and the rear wheels 3, 3 for each selected speed range, and the transmission configuration is switched according to the speed range. The 4WD mode and the 2WD mode are switched by the control unit c according to the conditions, and both or one of the front wheels 2 and 2 and the rear wheels 3 and 3 are driven.

  Therefore, since the 4WD mode and the 2WD mode are switched according to the switching condition for each speed range, the shift transmission unit 5a is, for example, 0 when the normal slip ratio is 0.86 or less or 1.15 or more. .76 or less, that is, by setting the road driving switching condition that makes it difficult for the four-wheel-drive to be driven, it is possible to suppress the extreme secondary pressure drop due to the 4WD switching at the time of the conventional automatic road shifting. Therefore, it is possible to ensure operation with a single pressure reducing valve for forward / reverse, indepe, 4WD, Hi-Lo control, etc., and without affecting the power shift part, control curve, clutch flow rate etc. The circuit configuration can be simplified.

In this way, by setting the switching condition so that the slip ratio at the time of high speed traveling by the “HH” sub-position for driving on the road of the sub-transmission unit 24 is smaller than that of the low speed traveling, the low speed work traveling is set. It is possible to improve the efficiency of airframe traveling on a high-speed road while securing the necessary driving force at the time, so that the maximum load capacity of the hydraulic system can be suppressed and the configuration can be simplified. It is possible to avoid wear due to excessive rotation difference.
Incidentally, the speed range different switching conditions, when overlapping with another speed range, such as "HH" sub position, the order of the intermediate wheel speed of the speed range and not include the "HH" sub Position In general, the slip ratio as a switching condition is sequentially set in accordance with the speed order of the speed range.

Next, a processing example of the control unit c that performs automatic switching control in the 2WD 4WD switching traveling will be described.
As an example of associating the two-wheel-drive and four-wheel drive switching with the brake operation, three predetermined conditions, that is, the traveling unit setting is “2WD”, the brake connection sensor that detects the connection of the left and right brake pedals 17a and 17b is “connection”, and the vehicle speed Is set to 4WD corresponding to the brake pedal operation, and the control process of returning to 2WD by releasing the brake pedal operation is configured. By controlling so as not to return to 2WD except for the above three conditions, 4WD transmission can be ensured corresponding to the brake operation during traveling.

  In this case, the control unit c sets an off-delay for the detection of the brake coupling sensor, and a predetermined time (for example, 0.5 to 1 second) after the coupling sensor is turned off holds the on-determination and is a condition Judgment processing. Due to the setting of the off-delay, the on-determination is continued when the on-off is repeated within a specified time, so that the 4WD transmission corresponding to the above brake operation can be ensured by the reliable detection of “connection”.

  Therefore, when driving on rough roads, the condition of “connection” of the brake connection sensor in the above three conditions can be satisfied with respect to on / off (chattering) accompanying mechanical backlash of the brake connection switch. Even when mechanical backlash occurs due to the passage of the general use time, the switching function can be maintained without requiring readjustment of the attachment. In particular, when “connection” is detected by communication data between a plurality of controllers, it is possible to cover a delay in ON detection due to the previous data being held during the communication interval.

  In addition, in the case of a system using the left and right brake pedals 17a and 17b, instead of the above-described brake connection sensor, 4WD is set when both sensors are detected, and both are turned off or off for a specified time. By performing the control process so as to release 4WD when it continues for more than (for example, 0.3 seconds), the same effect as described above can be ensured.

  Furthermore, in the control process for automatically switching between 2WD and 4WD with 4WD traveling straight and turning 2WD, control processing is performed to maintain 4WD during turning under conditions of high speed driving (vehicle speed, sub-shift position, etc.). Thus, it is possible to avoid a strange behavior (behavior of the traveling portion when shifting to 2WD) associated with the turning of the vehicle during high-speed traveling and to perform safe turning.

Next, the configuration of the hydraulic drive system of the automatic transmission tractor will be described.
For automatic transmission tractors of various specifications, if the valve body is designed individually as in the past, the machining cost will increase, which will increase the valve cost and increase the cost of the tractor. Rising funds such as jigs and tools are also required.

  In order to solve this problem, as shown in the hydraulic circuit diagram of FIG. 8, as a sub-control valve for changing the tread, a diversion valve 31 that divides the divided flow rate of the horizontal circuit by remodeling the electromagnetic sub-conversion (two stations). The left and right tread changing cylinders 32c and 32c are supplied to the valves 32v and 32v, respectively.

  Thus, by sharing the valve material and machining, machining jigs and tools can be used, no setup is required, and the cost is low. In addition, rising funds for machining jigs, tools, etc. are suppressed.

  Further, the control flow rate 33e (for example, 7.5 ml / min) from the horizontal control by the horizontal cylinder 33 is turned to tread control, and this control flow rate 31e is supplied to the three-speed / four-speed switching clutch 34 and the Hi-Ho switching clutch 35. Supply as lubricating oil. With this configuration, it is not necessary to take the lubricating oil for the hydraulic clutch from the pressure reducing valve circuit through the orifice, and as a result, the problem that the secondary pressure is reduced due to the release of the lubricating oil can be solved.

It is a side view of the agricultural tractor which shows the example of application of the 2WD 4WD switching apparatus which concerns on this invention. It is an operation part (front side) apparatus arrangement block diagram. It is a transmission system expansion | deployment figure of a transmission transmission part. 4 is a shift combination table of the transmission of FIG. 3. It is an operation part (side part) apparatus arrangement | positioning perspective view. It is a flowchart of transmission control. It is a detailed processing procedure of 2WD 4WD switching control. It is a hydraulic circuit diagram of an automatic transmission tractor.

DESCRIPTION OF SYMBOLS 1 Agricultural tractor 2 Front wheel 3 Rear wheel 5 Transmission case 5a Shift transmission part 13 Forward / reverse switching lever 14 Acceleration lever 16 Accelerator pedal 17a, 17b Brake pedal 18 Shift lever 22 Forward / reverse switching part 23 Main transmission part 24 Subtransmission part 25 Front wheel transmission Clutch A, B switching condition HH Road running position

Claims (3)

The front wheel (2) and the rear wheel (3) are both configured to be switched to a 4WD mode and the front wheel (2) or the rear wheel (3) is driven to a 2WD mode. In a two-wheel drive / four-wheel drive switching device for a tractor including a control unit (c) that selects traveling in the 2WD form if the slip state is equal to or less than a predetermined value, and selects traveling in the 4WD form if the predetermined value is exceeded,
The tractor is provided with a shift lever (18) capable of selecting an arbitrary speed range from a plurality of sub-speed ranges.
The control unit (c), the main gear in the stage speed range that does not overlap, as the speed range of the selected becomes fast, by changing the predetermined value to easily value is selected running by 2WD mode,
The main gear position of the sub-position (HH) for road running is overlapped with a part of the main gear position of the high-speed position (H),
The intermediate vehicle speed range of the main gear is a sub position for road overlapping (HH), is compared with the intermediate vehicle speed speed range position for high-speed (H), as the intermediate wheel speed is high speed The two-wheel-drive / four-wheel-drive switching device for a tractor, wherein the predetermined value is changed to a value at which traveling in the 2WD form is easily selected. When the control unit (c) is selected to travel in the 2WD form , the brake connection sensor for detecting the connection of the left and right brake pedals (17a, 17b) is connected, and the three conditions satisfying the vehicle speed equal to or higher than the predetermined speed are satisfied. 2. The two-wheel-drive / four-wheel-drive switching device for a tractor according to claim 1, wherein control processing is performed to switch to 4WD in response to a brake pedal operation and to return to 2WD by releasing the brake pedal operation. Wherein the control unit (c) sets a off-delay in the detection of the brake coupling sensor, claim connecting sensors are specified time after the off, characterized in that the control process for holding the ON determination 2 2WD 4WD switching device for tractors as described in 1.

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