JP2010149816A - Working vehicle suspension structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a working vehicle suspension structure for allowing easy work for a fork by correcting the attitude of a vehicle body to set it into a predetermined attitude when a vehicle speed is low during travel. <P>SOLUTION: The working vehicle suspension structure includes a hydraulic cylinder 7 for the suspension of a front wheel 1, a vehicle speed sensor Q, a check valve 13 for checking the operation of the hydraulic cylinder 7, and a hydraulic pump 30 for forcing the telescopic operation of the hydraulic cylinder in the checked condition. When the vehicle speed is changed over to be low, the check valve 13 is operated to be closed and the telescopic operation of the hydraulic cylinder 7 is forced to restore a suspension mechanism into a reference telescopic condition corresponding to the ground parallel attitude of the vehicle body. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a suspension structure in a work vehicle such as a tractor or a construction machine.

In a tractor that is an example of a work vehicle, for example, as disclosed in Patent Document 1, a suspension mechanism composed of a double-acting cylinder (FIG. 1 of FIG. 1 of Patent Document 1) is provided on a front wheel. There is something.
In a work vehicle equipped with a suspension mechanism on the front wheel, there is a demand to stabilize the body height when the pallet is picked up by a fork and transported, or when soil is picked up by an excavator. For this reason, there has been a thing that ensures the stability of the airframe by applying a restraining means for restraining the operation of the suspension mechanism.

  In this case, in the tractor in which the suspension mechanism is configured by a double-acting cylinder as in Patent Document 1, when the brake is operated in a braking state during traveling, the hydraulic oil of the double-acting cylinder is reduced as described above. There has been a structure in which the check means for shutting off the supply / discharge is operated so that the double-acting cylinder cannot expand and contract.

USP 6145859

However, if the brake is operated to the braking state while traveling, the aircraft will be in a forward-lowering state due to inertia, and in this state, as described above, the operation of the suspension mechanism (extension and expansion of the double-acting cylinder) is fixed. If this happens, the aircraft will stop in the front-down state.For example, when scooping up the pallet with a fork, it may be difficult to accurately insert the fork into the specified position on the pallet. It was not good.
Also, it is originally not preferable to move in the forward-downward posture because there is a risk of bringing the bucket or the like into contact with the ground.

  The present invention solves the above-mentioned problems, and in a work vehicle having a suspension mechanism on the front wheels, when the vehicle speed becomes low during traveling, the posture of the fuselage is corrected and set to a predetermined posture to perform fork work etc. An object of the present invention is to provide a suspension structure for a work vehicle that can be more easily performed.

[I]
(Constitution)
The first feature of the present invention is that the suspension structure of a work vehicle is configured as follows.
Front wheel suspension mechanism, vehicle speed detecting means for detecting the vehicle speed, checking means for checking the operation of the suspension mechanism, and forcing the suspension mechanism in a check state checked by the checking means to be able to forcibly extend and contract Stretching means,
When the vehicle speed detected by the vehicle speed detecting means is switched to a low speed state, the restraint means is operated, the forced expansion / contraction means is actuated on the suspension mechanism switched to the restrained state, and the suspension mechanism is grounded to the airframe. Control means for returning to the reference expansion / contraction state corresponding to the parallel posture is provided.

(Function)
According to the first feature of the present invention, when the vehicle speed becomes a low speed state, the restraining means acts to restrain the suspension mechanism from being actuated (blocking the actuation). For example, when the brake is operated during driving (or the HST operation lever is operated to the low speed side), the vehicle is in the front lowering state, the vehicle speed is low, and the check means is activated. The forcible expansion / contraction means is operated, and the suspension mechanism is returned to the reference expansion / contraction state corresponding to the ground parallel posture of the airframe while maintaining the state where the check means is operated.
Accordingly, the suspension mechanism is fixed in the reference expansion / contraction state because the restraining means continues to operate in a state where the forced expansion / contraction means stops operating.

(The invention's effect)
Accordingly, fork work or the like can be performed in a state in which the attitude of the airframe is returned to the ground parallel attitude, workability can be improved, and the airframe can be prevented from moving in a forwardly lowered attitude.

[II]
(Constitution)
The second feature of the present invention is that the work vehicle suspension structure of the first feature of the present invention is configured as follows.
The suspension mechanism is composed of a hydraulic cylinder installed between the front wheel and the airframe that supports the front wheel,
A hydraulic mechanism comprising a hydraulic pump for supplying oil to the hydraulic cylinder via a main oil supply passage and an accumulator connected via a branch oil passage branched from the main oil supply passage;
By allowing hydraulic oil to flow between the hydraulic cylinder and the accumulator via the branch oil passage, the suspension mechanism is configured to perform an expansion / contraction operation corresponding to the front wheel load,
The check means is configured to provide an on-off valve for preventing oil flow in the branch oil passage, and to set the on-off valve in a state for preventing oil flow to check the expansion / contraction operation of the hydraulic cylinder,
The forcible expansion / contraction means is configured to forcibly extend and contract the hydraulic cylinder by forcibly supplying oil to the hydraulic cylinder from the hydraulic pump in a state where the flow is blocked by the on-off valve.

(Function)
According to the second feature of the present invention, the “action” described in the preceding item [I] is provided in the same manner as the first feature of the present invention, and in addition to this, the following “action” is provided.
In other words, in order to operate the suspension mechanism as a suspension mechanism, the hydraulic oil is supplied to the hydraulic cylinder according to the load applied to the front wheel by opening the on-off valve and flowing the hydraulic oil between the hydraulic cylinder and the accumulator. Exhaust operation can be performed, and the hydraulic cylinder expands and contracts to function the suspension.

According to the second feature of the present invention, as described in the preceding item [I], when the vehicle speed decreases, the restraining means operates. This check means can prevent the inflow and outflow of hydraulic oil from the accumulator to the hydraulic cylinder by closing the on-off valve interposed in the branch oil passage that connects the hydraulic cylinder and the accumulator. The mechanism stops its function.
As a result, as described above, the airframe may stop in the forwardly lowered state by the operation of the restraining means.

However, when the check means is activated, the forced expansion / contraction means also acts. When the forced expansion / contraction means is activated, the hydraulic pump can forcibly supply oil to the hydraulic cylinder via the main oil supply passage, and the hydraulic cylinder is expanded and contracted to make the suspension mechanism in a standard expansion / contraction state corresponding to the ground parallel posture of the aircraft Can be restored.
In this case, since the on-off valve interposed in the branch oil passage is maintained in the closed state, the check means is in the operating state, and the suspension mechanism is maintained in the reference expansion / contraction state corresponding to the ground parallel posture of the airframe. ing.

(The invention's effect)
According to the second feature of the present invention, the “effect of the invention” described in the preceding item [I] is provided in the same manner as the first feature of the present invention. In addition, the following “effect of the invention” is provided. ing.
According to the second feature of the present invention, the hydraulic pump and the hydraulic cylinder are connected to each other so that the suspension mechanism can be returned to the reference expansion / contraction state by the forced expansion / contraction means while maintaining the suspension mechanism in the check state. This can be achieved by installing an on-off valve that constitutes a check means in the branch oil passage that branches off from the main oil supply passage, and it is possible to provide a useful suspension mechanism that effectively uses the hydraulic circuit configuration. It was.

[1]
As shown in FIG. 1, a four-wheel drive type agricultural tractor, which is an example of a work vehicle, includes right and left front wheels 1 and right and left rear wheels 2. The right and left rear wheels 2 are not supported by the transmission case 3 at the rear of the fuselage via a suspension mechanism, but are supported in a fixed position.

  As shown in FIGS. 1, 2, and 4, a support frame 5 is connected to a lower portion of the engine 4 disposed at the front of the airframe and extends forward, and a support bracket 6 having a U-shape in side view is formed. Two hydraulic cylinders 7 (in the suspension mechanism) are supported so as to be swingable up and down around the horizontal axis P1 at the rear portion of the support frame 5 and span the front portion of the support frame 5 and the front portion of the support bracket 6. Equivalent) is connected. A front axle case 8 is supported in a freely rolling manner around the front and rear axis P2 of the support bracket 6, and the right and left front wheels 1 are supported on the right and left sides of the front axle case 8.

[2]
Next, the hydraulic circuit structure of the hydraulic cylinder 7 will be described.
As shown in FIG. 3, the hydraulic cylinder 7 is configured as a double-acting type having an oil chamber 7a on the bottom side and an oil chamber 7b on the piston side. An oil passage 9 (corresponding to a branch oil passage) connected to the oil chamber 7a of the hydraulic cylinder 7 is provided with a gas-filled accumulator 11, a pair of pilot operated check valves 13 (corresponding to an on-off valve), and a hydraulic circuit. A protective relief valve 15 is connected, and a switching valve 17 is provided in front of the accumulator 11.

  As shown in FIG. 3, the switching valve 17 has a first position 17 a that does not have a throttling function (or has an orifice portion having a large diameter), and a second position that has an orifice portion that has a medium diameter. 17b, a third position 17c having an orifice portion having a small diameter, and is configured as a pilot operated type. A pilot valve 20 for operating the switching valve 17 is provided. A gas-filled accumulator 12, a pair of pilot operated check valves 14 and a relief valve 16 for protecting the hydraulic circuit are connected to an oil passage 10 connected to the oil chamber 7b of the hydraulic cylinder 7.

  As shown in FIG. 3, the check valves 13 and 14 are provided with a pilot valve 19 for supplying and discharging pilot hydraulic oil, and the check valves 13 and 14 are shut off by the pilot valve 19 (accumulators 11 and 12 and And the open state (accumulators 11 and 12 to the oil chambers 7a and 7b of the hydraulic cylinder 7, and the accumulator 11 from the oil chambers 7a and 7b of the hydraulic cylinder 7). , 12 to allow the flow of both hydraulic fluids to.

  As shown in FIG. 3, the hydraulic oil of the pump 30 is supplied to the control valve 18 via the filter 31, the diversion valve 32 and the check valve 33, and the relief valve is provided between the diversion valve 32 and the check valve 33. 34 is connected. An oil passage 21 (corresponding to the main oil supply passage) is connected across the portion between the oil chamber 7 a of the hydraulic cylinder 7 and the check valve 13 in the oil passage 9 and the control valve 18, and the hydraulic cylinder in the oil passage 10 7 is connected to the control valve 18 between the oil chamber 7 b and the check valve 14.

  As shown in FIG. 3, the control valve 18 supplies the operating oil to the oil passage 21 (the oil chamber 7 b of the hydraulic cylinder 7) and the oil passage 22 (the oil chamber 7 b of the hydraulic cylinder 7). A three-position switching type, that is, a lowered position 18D to be supplied and a neutral position 18N, is configured as a pilot operated type, and is provided with a pilot valve 29 for operating the control valve 18.

As shown in FIG. 3, a pilot operated check valve 23 and a throttle portion 25 are provided in the oil passage 21. The oil passage 22 is provided with a pilot operated check valve 24, a check valve 26 (the check valve 24 is on the oil passage 10 side and the check valve 26 is on the control valve 18 side), and a throttle portion 27. A relief valve 28 is connected between the stop valve 24 and the check valve 26 (throttle portion 27).
The pilot valves 19, 20, and 29 are electromagnetically operated, and the pilot valve 19 and the pilot valves 20, 29 are operated by a control device 35 (corresponding to control means) as described in [3] to [7] described later. Then, the check valves 13 and 14, the control valve 18 and the switching valve 17 are operated.

[3]
Next, the operation of the hydraulic cylinder 7 will be described.
When the control valve 18 is operated to the neutral position 18N and the check valves 13 and 14 are operated in the open state as shown in FIG. 3 according to the structure described in the preceding item [2], When the front axle case 8 and the support bracket 6 try to swing up and down around the horizontal axis P1, the hydraulic cylinder 7 expands and contracts and operates between the oil chambers 7a, 7b of the hydraulic cylinder 7 and the accumulators 11, 12. The oil reciprocates, and the hydraulic cylinder 7 operates as a suspension mechanism having a spring constant K1.

In this case, the pressure in the oil chamber 7b and the oil passage 10 of the hydraulic cylinder 7 is maintained at the set pressure MP1 by the relief valve 28. The pressure of the oil chamber 7a of the hydraulic cylinder 7 is PH, the pressure receiving area of the piston of the oil chamber 7a of the hydraulic cylinder 7 is AH, and the pressure receiving area of the piston of the oil chamber 7b of the hydraulic cylinder 7 is AR (for the piston rod, AR is AH If the weight applied to the front part of the airframe (the weight applied to the hydraulic cylinder 7) is M and the gravitational acceleration is g, the following equation (1) is established.
Formula (1) M * g = PH * AH-MP1 * AR

  Accordingly, the pressure MP1 of the oil chamber 7b of the hydraulic cylinder 7, the pressure receiving area AH of the piston of the oil chamber 7a of the hydraulic cylinder 7, and the pressure receiving area AR of the piston of the oil chamber 7b of the hydraulic cylinder 7 are constant. The pressure PH of the oil chamber 7a is higher than the pressure MP1 of the oil chamber 7b of the hydraulic cylinder 7, and varies depending on the weight (weight applied to the hydraulic cylinder 7) M applied to the front of the machine body.

  The spring constant K1 of the hydraulic cylinder 7 is determined by the pressures PH and MP1 of the oil chambers 7a and 7b of the hydraulic cylinder 7, and increases as the pressure PH of the oil chamber 7a of the hydraulic cylinder 7 increases. The pressure PH of the oil chamber 7a of the hydraulic cylinder 7 decreases as the pressure PH decreases. Therefore, the spring constant K1 of the hydraulic cylinder 7 is determined by the weight (weight applied to the hydraulic cylinder 7) M applied to the front portion of the airframe, and the weight applied to the front portion of the airframe (weight applied to the hydraulic cylinder 7) M is large. As it becomes larger, the weight applied to the front part of the airframe (weight applied to the hydraulic cylinder 7) M becomes smaller.

  As shown in FIG. 3, when the control valve 18 is operated to the raised position 18U and the check valves 13 and 14 are operated to be shut off, hydraulic fluid is supplied from the control valve 18 to the oil chamber 7a of the hydraulic cylinder 7. The hydraulic oil is discharged from the oil chamber 7 b of the hydraulic cylinder 7 through the check valve 24 (operated to be opened by the pilot hydraulic oil of the control valve 18) and the relief valve 28. In this case, the pressure in the oil chamber 7b and the oil passage 10 of the hydraulic cylinder 7 is maintained at the set pressure MP1 by the relief valve 28.

  As a result, the hydraulic cylinder 7 expands and contracts and the front part of the airframe rises (corresponding to a state in which the operation of the hydraulic cylinder 7 (suspension mechanism) is changed to the airframe ascending side). Thereafter, when the control valve 18 is operated to the neutral position 18N and the check valves 13 and 14 are opened, the hydraulic cylinder 7 operates as a suspension mechanism as described above with the hydraulic cylinder 7 extending and contracting. To do.

  As shown in FIG. 3, when the control valve 18 is operated to the lowered position 18 </ b> D and the check valves 13, 14 are operated to shut off, the hydraulic oil is supplied from the control valve 18 to the oil chamber 7 b of the hydraulic cylinder 7. The hydraulic oil is discharged from the oil chamber 7 a of the hydraulic cylinder 7 through the check valve 23 (operated to be opened by the pilot pressure of the control valve 18), the throttle portion 25, and the control valve 18. In this case, the pressure in the oil chamber 7b and the oil passage 10 of the hydraulic cylinder 7 is maintained at the set pressure MP1 by the relief valve 28.

  As a result, the hydraulic cylinder 7 is contracted and the front part of the airframe is lowered (corresponding to a state in which the operation of the hydraulic cylinder 7 (suspension mechanism) is changed to the airframe lowering side). Thereafter, when the control valve 18 is operated to the neutral position 18N and the check valves 13 and 14 are operated to the open state, the hydraulic cylinder 7 operates as a suspension mechanism with the hydraulic cylinder 7 contracted as described above. To do.

Further, when the check valves 13 and 14 are operated to the operating state, the oil flow between the hydraulic cylinder 7 and the accumulators 11 and 12 is blocked, and the expansion and contraction operation of the hydraulic cylinder 7 is restrained. In this way, the control valve 18 and the check valves 13 and 14 that restrain the expansion and contraction operation of the hydraulic cylinder 7 are referred to as restraint means.
On the other hand, while the check valves 13 and 14 are kept in the operating state, the control valve 18 is moved to the raised position 18U while the oil flow between the hydraulic cylinder 7 and the accumulators 11 and 12 is checked. When operated, the hydraulic cylinder 7 is supplied with oil from the pump 30, and the hydraulic cylinder 7 expands and contracts. Here, the check valves 13 and 14, the control valve 18, and the pump 30 are referred to as forced expansion / contraction means.

[4]
Next, the operation of the switching valve 17 will be described.
As shown in FIG. 6, a right side brake 38 capable of braking the right rear wheel 2 and a right side brake pedal 39 capable of operating the right side brake 38 in a braking state are provided. A left side brake 38 capable of braking the rear wheel 2 and a left side brake pedal 39 capable of operating the left side brake 38 in a braking state are provided.

As shown in FIG. 6, the right and left side brake pedals 39 are provided on the right side of the floor of the driving unit, and only one of the right and left side brake pedals 39 can be stepped on. It is also possible to operate both the left and right side brake pedals 39 simultaneously. The driver generally depresses only one of the right and left side brake pedals 39 when turning right or left, and brakes the rear wheel 2 on the turning center side when turning right or left. This enables a small turn to the right or left.
This agricultural tractor is a four-wheel drive type, and the right and left front wheels 1 and the right and left rear wheels 2 are connected by a transmission system, so that the right and left side brakes 38 are operated in a braking state and the right When the left rear wheel 2 is braked, the right and left front wheels 1 are also braked.

  As shown in FIG. 6, the right side brake sensor 40 for detecting that the right side brake pedal 39 has been depressed (the braking state of the right side brake 38) and the left side brake pedal 39 have been depressed. (A braking state of the left side brake 38) is provided, and the detection values of the right and left side brake sensors 40 are input to the control device 35.

As shown in FIG. 6, a pressure sensor 36 for detecting the pressure in the oil chamber 7 a of the hydraulic cylinder 7 is provided, and the detection value of the pressure sensor 36 is input to the control device 35. Based on this, a weight (weight applied to the hydraulic cylinder 7) M applied to the front portion of the machine body is calculated.
In this way, even if there is a change in the weight M applied to the front part of the aircraft, the return control as described later is always performed in order to maintain the aircraft in a horizontal orientation to the ground.

[Control of switching valve]
As shown in FIG. 7, based on the detection value of the pressure sensor 36, a weight (weight applied to the hydraulic cylinder 7) M applied to the front portion of the airframe is calculated (step S1).
The load applied to the hydraulic cylinder 7 varies depending on the work device attached to the machine body. That is, when the weight applied to the front part of the aircraft (weight applied to the hydraulic cylinder 7) M becomes medium (for example, the state where the earth and sand have been discharged by the front loader, (When loaded and unloaded), the spring constant K1 of the hydraulic cylinder 7 becomes small (see [3] in the previous section). Accordingly, the switching valve 17 is operated to the first position 17a, and the damping force of the hydraulic cylinder 7 becomes small. (Steps S1 to S3).

  As shown in FIG. 7, when the weight applied to the front part of the machine body (weight applied to the hydraulic cylinder 7) M is increased by the working device attached to the front part of the machine body (for example, scooping up (loading) earth and sand with a front loader). (Step S2), the spring constant K1 of the hydraulic cylinder 7 is increased (see [3] in the previous section). Accordingly, the switching valve 17 is operated to the second position 17b. As a result, the damping force of the hydraulic cylinder 7 increases (steps S1, S2, S4).

As shown in FIG. 7, when the weight applied to the front part of the aircraft (weight applied to the hydraulic cylinder 7) M is reduced by the working device attached to the rear part of the aircraft (for example, a backhoe is attached to the rear part of the aircraft and the backhoe is raised. In this state, the spring constant K1 of the hydraulic cylinder 7 becomes extremely small. Accordingly, the switching valve 17 is operated to the third position 17c (step S5), and the damping force of the hydraulic cylinder 7 is expanded.
Once the switching valve 17 has been set, a return control is performed to return the suspension mechanism to the reference telescopic state corresponding to the ground parallel posture of the aircraft (step S6).

[5]
Next, return control of the hydraulic cylinder 7 will be described with reference to FIGS.
As shown in FIGS. 9 and 10, an operation position sensor 37 for detecting the operation position L (actual length) of the hydraulic cylinder 7 is provided, and a detection value of the operation position sensor 37 is input to the control device 35, and control is performed. In the device 35, the operating position L of the hydraulic cylinder 7 is stored. In this case, the telescopic operating position sensor 37 is directly attached to the hydraulic cylinder 7 to detect the operating position L of the hydraulic cylinder 7, or the rotary operating position sensor 37 is positioned at the position of the horizontal axis P1 shown in FIG. The operating position L of the hydraulic cylinder 7 is detected by mounting and detecting the angle of the support bracket 6 with respect to the support frame 5.

Here, when performing the return control, the control sensitivity is set according to the vehicle speed V of the airframe. This is because if the vehicle speed V of the airframe is high and the control sensitivity is too sensitive, control instability will be caused. The reason why the control sensitivity is made sensitive when the vehicle speed V is low has been described in the section of the effect according to the third aspect.
As shown in FIG. 8, when the control is started, the control valve 18 is operated to the neutral position 18N and the check valves 13 and 14 are opened (the hydraulic cylinder 7 operates as a suspension mechanism). (Step S7). Then, the vehicle speed V is detected by a vehicle speed sensor Q as a vehicle speed detecting means (step S8). If the detected vehicle speed V is low, the check means C is operated (steps 9 and 10). Here, the check means C means that the check valves 13 and 14 are operated (closed state). Thereafter, the control sensitivity of the return control is set to “sensitive” (step S11). If the detected vehicle speed V is high, the control sensitivity of the return control is set to “insensitive” (step S12).

[6]
[When the control sensitivity of return control is insensitive]
The control here is based on the following knowledge as described in the section of action. In other words, the suspension mechanism constantly fluctuates while the aircraft is traveling. Therefore, since it is difficult to accurately grasp the operating position L of the suspension mechanism at a certain point in time, the average operating position L of the suspension mechanism is determined based on time series data of the operating position L over a certain time. Estimation is performed, and return control is performed based on the estimated value.

As shown in FIG. 5, when the central position of the operation of the hydraulic cylinder 7 is set in the control device 35 and the operation position L of the hydraulic cylinder 7 is the central position, the airframe is substantially parallel (substantially horizontal) to the ground. It becomes.
Here, the reference telescopic state of the suspension mechanism corresponding to the ground parallel posture of the airframe corresponds to the center position of the hydraulic cylinder 7. A second target range H2 having a certain range on the aircraft ascending side and the aircraft descending side with respect to the central position is set in the control device 35.

  An integration number N obtained by integrating the number of units to be described later is set in the control device 35. First, the integration number N is set to “0” (step S13). Counting of the control cycle T12 is started (step S14), and the operating position L of the hydraulic cylinder 7 is detected and stored (step S15).

  When the control cycle T12 elapses (step S16) (see time point T2 in FIG. 5), from the operating positions L of all the hydraulic cylinders 7 past the set time T11 from time point T2 (see time point T2 to time point T1 in FIG. 5), The maximum position A1 and the minimum position A2 of the operation of the hydraulic cylinder 7 are detected (step S17), and the intermediate position B1 between the maximum and minimum positions A1, A2 (the central position between the maximum and minimum positions A1, A2). Is detected (step S18).

  As shown in FIG. 5, the maximum position A1 is a position where the operating position L of the hydraulic cylinder 7 is displaced to the body ascending side and then displaced to the body descending side (a position where the hydraulic cylinder 7 is switched from the expansion / contraction operation to the contracting operation). is there. The minimum position A2 is a position where the operating position of the hydraulic cylinder 7 is displaced to the airframe descending side and then displaced to the airframe ascending side (a position where the hydraulic cylinder 7 is switched from the contraction operation to the expansion / contraction operation).

  In this case, the operating position L of the hydraulic cylinder 7 between the elapse of the previous control cycle T12 and the elapse of the current control cycle T12 (see time T2 in FIG. 5) is the new operating position L of the hydraulic cylinder 7. The operation position L of the hydraulic cylinder 7 in the past from the time T1 in the past by the set time T11 from the time T2 is erased, and the hydraulic pressure stored in the control device 35 every time the control cycle T12 elapses. A part of the operating position L of the cylinder 7 is updated.

  If the set time T11 is set to be slightly longer than one cycle of the resonance frequency of the hydraulic cylinder 7 (suspension mechanism) in steps S17 and S18, one maximum position A1 and one minimum are set during the set time T11. The position A2 is detected, and in this case, the intermediate position B1 is detected from one maximum and minimum position A1, A2 (step S18).

  In steps S17 and S18, if the set time T11 is set to be somewhat long, a plurality of maximum positions A1 and a plurality of minimum positions A2 are detected during the set time T11. In this case, the maximum maximum position A1 of the plurality of maximum positions A1 is detected, the minimum minimum position A2 of the plurality of minimum positions A2 is detected, and the maximum maximum position A1 and the minimum maximum position A2 are detected. An intermediate position B1 is detected from the minimum position A2 (step S18).

  When the intermediate position B1 is detected, the intermediate position B1 is compared with the second target range H2 (step S19), and the intermediate position B1 is moved from the second target range H2 to the aircraft lowering side (the hydraulic cylinder 7 is in the contracted state). If it deviates, “1” as a unit number is subtracted from the cumulative number N (step S20), and the intermediate position B1 deviates from the second target range H2 to the aircraft ascending side (the hydraulic cylinder 7 is in the extended state). Then, “1” as a unit number is added to the cumulative number N (step S21). When the intermediate position B1 is within the second target range H2, addition and subtraction to the integration number N are not performed. In this case, the process then proceeds to step S14, where steps S14 to S21 are performed, and the detection of the intermediate position B1, the comparison between the intermediate position B1 and the second target range H2, and the addition and subtraction of the number of integrations N are performed. Steps S14 to S21 are repeated.

[7]
Furthermore, control of the hydraulic cylinder 7 will be described with reference to FIG.
The accumulated number N is compared with the descending set number ND1 and the ascending set number NU1, and when the accumulated number N reaches (decreases) the descending set number ND1 (step S22), the front part of the fuselage is lowered, and the fuselage Is determined to be in a forward-lowering state with respect to the ground, the control valve 18 is operated to the ascending position 18U, and the check valves 13 and 14 are operated (closed) (step S24).

As a result, as described in [3] above, the hydraulic cylinder 7 expands and the fuselage is in a state where the pressure in the oil chamber 7b and the oil passage 10 of the hydraulic cylinder 7 is maintained at the set pressure MP1 by the relief valve 28. The front of the rises. Here, when the hydraulic cylinder 7 is activated once, the maximum position A1 and the minimum position A2 are detected based on the previous operation position L of the hydraulic cylinder 7 for the set time T13 with reference to the operation start time of the hydraulic cylinder 7. (Step S26), the intermediate position B2 is detected from the detected value (step 27), and the operation of the hydraulic cylinder 7 is stopped when the intermediate position B2 enters the second target range H2 (steps S28, 29). ). If it does not fall within the second target range H2, the set time T13 is set again, and the processing from step 26 to step 28 is repeated to confirm that it has entered the second target position H2, and the hydraulic cylinder 7 Is stopped (step 29).
Thereafter, the process proceeds to step S1.

  The accumulated number N is compared with the descending set number ND1 and the ascending set number NU1, and when the accumulated number N reaches the ascending set number NU1 (exceeds) (step S23), the front part of the aircraft rises and the fuselage Is determined to be in the forwardly rising state with respect to the ground, the control valve 18 is operated to the lowered position 18D, and the check valves 13 and 14 are operated to the operating state (step S24).

As a result, as described in [3] above, the hydraulic cylinder 7 contracts and the fuselage is operated while the pressure in the oil chamber 7b and the oil passage 10 of the hydraulic cylinder 7 is maintained at the set pressure MP1 by the relief valve 28. The front part of the descent.
Here, when the hydraulic cylinder 7 is activated once, as described above, steps S26 to S28 are performed to stop the hydraulic cylinder 7 (step S29). If it does not fall within the second target range H2, the set time T13 is set again, and the processing from step 26 to step 28 is repeated to confirm that it has entered the second target position H2, and the hydraulic cylinder 7 To stop.
Thereafter, the process proceeds to step S1.

  As described above, even if steps S14 to S21 are repeatedly performed, the integration number N does not reach (below) the lower side set number ND1 (step S22), and the upward side integration number NU is set to the upper side. If the number of times NU1 is not reached (if it does not exceed) (step S23), the control valve 18 is operated to the neutral position 18N, and the check valves 13 and 14 are opened (the hydraulic cylinder 7 operates as a suspension mechanism). Is maintained, and the process returns to step 14.

[8]
[When control sensitivity of return control is sensitive]
The reason why the control sensitivity is made sensitive has been described in the section of the operational effect according to the third aspect, but in addition, the following can be said. When transporting a pallet or the like, when the fork is inserted into a predetermined position of the pallet and lifted, it is desirable that the suspension mechanism does not operate, and when inserting the fork into the pallet, it is desirable to work in a stopped state. . Therefore, when approaching the work position, the vehicle speed V is reduced, but the checking means C is operated in order to check the timing when the vehicle speed V decreases and to check the operation of the suspension mechanism. Specifically, the check valves 13 and 14 are switched to the operating state (closed state).

  When the speed is reduced, since the both side brakes 38 are depressed, the aircraft tends to be lowered forward. Since the restraining means C operates in the state of the front lowering posture, the front lowering posture is maintained. Since it is difficult to insert and lift the pallet in the forward-downward posture, it is necessary to return the posture to the parallel posture.

  In this case, since the airframe that receives the action of the restraining means C maintains the forwardly lowered posture, the operating position L of the hydraulic cylinder 7 is constant, and the operating position L of the hydraulic cylinder 7 is within the first target range. It is on the aircraft lowering side than H1. Therefore, only by switching the control sensitivity from the insensitive side to the sensitive side, it is determined whether or not the current operation position L of the hydraulic cylinder 7 is within the second target range H2, and the control is started.

  Further, in the insensitive mode of the return control described above, since the suspension mechanism is constantly fluctuating, there is a surface where the operation position L cannot be accurately grasped, and the above-described control form has to be taken. Then, as described above, since the check means C is operating, the operating position L of the suspension mechanism can be accurately grasped, and the return control for returning to the reference posture of the airframe using the information of the current operating position L. I do.

  Specifically, as shown in FIG. 10, the operating position L of the hydraulic cylinder 7 is detected (step S30), and the operating position L is lower than the first target range H1 based on the detection result (the hydraulic cylinder 7 is If it is shorter than the reference length), the control valve 18 is switched to the raised position U, the check valves 13 and 14 are maintained in the operating state, the forced expansion / contraction means E is automatically operated, and the hydraulic pump 30 is supplied to the hydraulic cylinder 7 to expand and contract the hydraulic cylinder 7 (step 32). When the operating position L of the hydraulic cylinder 7 falls within the first target range H1, the hydraulic cylinder 7 stops (step 34). .

If the operating position L is higher than the first target range H1 based on the detection result (the hydraulic cylinder 7 is longer than the reference length), the control valve 18 is switched to the lowered position D and the check valve 13 is switched. , 14 is kept in the operating state, the oil is discharged from the hydraulic cylinder 7, the hydraulic cylinder 7 is shortened (step 33), and the operating position L of the hydraulic cylinder 7 falls within the first target range H1, The hydraulic cylinder 7 stops (step 34).
Thereafter, the process proceeds to step S1.

  In the above-described mode in which the control mode of the return control is set to the sensitive mode and the control is performed, the case where the restraint means C acts while the suspension mechanism is shortened is handled. However, the restraint means C acts when the speed is increased. Even when the suspension mechanism is assumed to move while being fixed, the control is operated effectively to correct the posture, and the body moves with the suspension mechanism extended. This can be suppressed.

[First Alternative Embodiment of the Invention]
In steps S17, S18, and S26 of FIG. 9 of the above-mentioned [Best Mode for Carrying Out the Invention], the set times T11 and T13 are set a little longer, and a plurality of maximum positions A1 and a plurality of minimum positions A2 are set. When configured to detect, the intermediate position B1 in step S18 in FIG. 9 and the intermediate position B2 in step S27 may be detected as follows.

(1) In a plurality of maximum positions A1 and a plurality of minimum positions A2, one maximum position A1 and one minimum position A2 are set as one set, and a plurality of sets of maximum and minimum positions A1 and A2 are obtained. Separately, a plurality of intermediate positions B1 and B2 are detected by detecting the intermediate positions B1 and B2 in each group, and the average value of the plurality of intermediate positions B1 and B2 is determined as the intermediate position in step S18 of FIG. B1, an intermediate position B2 of step S26.

(2) The average value of the maximum position A1 is detected at the plurality of maximum positions A1, the average value of the minimum position A2 is detected at the plurality of minimum positions A2, and the intermediate position is determined from the average value of the maximum and minimum positions A1 and A2. B1 and B2 are detected and set as an intermediate position B1 in step S18 and an intermediate position B2 in step S26 in FIG.

[Second Embodiment of the Invention]
In the above-mentioned [Best Mode for Carrying Out the Invention] [First Alternative Embodiment], the intermediate positions B1 and B2 are not set at the center position between the maximum and minimum positions A1 and A2. The intermediate position B1, B2 is slightly raised from the center position between the maximum and minimum positions A1, A2 based on the presence / absence and type of work device (for example, front loader) to be mounted on the front part of the body, the work mode, etc. Set to the position on the side (the expansion / contraction side of the hydraulic cylinder 7), or the intermediate positions B1, B2 slightly from the center position between the maximum and minimum positions A1, A2 on the lower side of the body (the contraction side of the hydraulic cylinder 7) Or may be set to
For example, when a work device (for example, a front loader) is attached to the front of the machine body, the intermediate positions B1 and B2 are slightly raised from the center position between the maximum and minimum positions A1 and A2 (the expansion and contraction side of the hydraulic cylinder 7). By setting this position, the aircraft should be raised slightly forward relative to the ground.

[Third Another Embodiment of the Invention]
The maximum position in the set times T11 and T13 may be used instead of the maximum position A1, and the minimum position in the set times T11 and T13 may be used instead of the minimum position A2. This is because the maximum position A1 and the minimum position A2 may not appear during the set times T11 and T13.

[Fourth Embodiment of the Invention]
(1) As an on-off valve provided in the branch oil passage 9, a normal gate valve may be provided instead of the check valves 13 and 14.
(2) The suspension mechanism includes a hydraulic cylinder 7 provided with an oil damper or the like.
(3) The vehicle speed detecting means may be a means for detecting the rotational speed of the axle or a means for detecting the ground speed of the airframe in a rotational contact type or a non-contact type such as an optical type.
(4) The present invention can also be applied to a work vehicle in which the right and left rear wheels 2 are also provided with a suspension mechanism using a hydraulic cylinder 7 or the like, and a rear two-wheel drive type work vehicle.

Whole side view of agricultural tractor Side view of the front axle case, support bracket, and hydraulic cylinder Diagram showing hydraulic circuit structure of hydraulic cylinder Perspective view of support bracket The figure which shows the state of the operation position (extension position) of a hydraulic cylinder Diagram showing the relationship between the control device and the pilot valve Diagram showing operation flow of switching valve Diagram showing the first half of the flow of hydraulic cylinder return control The figure which shows the flow when the control sensitivity of the return control of the hydraulic cylinder is insensitive The figure which shows the flow when the control sensitivity of the return control of the hydraulic cylinder is sensitive

Explanation of symbols

1 front wheel
7 Hydraulic cylinder (suspension mechanism)
DESCRIPTION OF SYMBOLS 9 Branch oil path 11 Accumulator 13 On-off valve 21 Main oil supply path 30 Hydraulic pump 35 Control apparatus (control means)
C Checking means E Forced expansion / contraction means H1 First target range Q Vehicle speed detection means V Vehicle speed

Claims (2)

Front wheel suspension mechanism, vehicle speed detecting means for detecting the vehicle speed, checking means for checking the operation of the suspension mechanism, and forcing that allows the suspension mechanism to be forcibly expanded and contracted in the checking state checked by the checking means Expansion and contraction means,
When the detected vehicle speed of the vehicle speed detecting means is switched to a low speed state, the restraining means is operated, the forced expansion / contraction means is actuated on the suspension mechanism switched to the restraining state, and the suspension mechanism is A suspension structure for a work vehicle equipped with a control means for returning to a reference expansion / contraction state corresponding to a ground parallel posture. The suspension mechanism is constituted by a hydraulic cylinder installed between the front wheel and the airframe that supports the front wheel,
A hydraulic mechanism comprising a hydraulic pump for supplying oil to the hydraulic cylinder via a main oil supply passage and an accumulator connected via a branch oil passage branched from the main oil supply passage;
By allowing hydraulic oil to flow between the hydraulic cylinder and the accumulator via the branch oil passage, the suspension mechanism is configured to extend and contract according to the load of the front wheel,
The check means is configured to provide an on-off valve for preventing oil flow in the branch oil passage, and to set the on-off valve in a state for preventing oil flow to check the expansion / contraction operation of the hydraulic cylinder,
2. The forced expansion / contraction means is configured to forcibly extend and contract the hydraulic cylinder by forcibly supplying oil to the hydraulic cylinder from the hydraulic pump in a state where flow is blocked by the on-off valve. The suspension structure of a working vehicle.

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