Safety devices for work vehicles

Abstract

This system reliably avoids unstable behavior that occurs in high-speed driving ranges, contributing to lower costs and increased productivity of safety mechanisms, as well as miniaturization and simplification of work vehicles. [Solution] The system is equipped with a speed switching means 2, a steering mode switching means 3, and a four-wheel steering controller 4. A switching state detection means 5 is provided to detect the switching state of the speed switching means 2. The four-wheel steering controller 4 is provided with a function that allows the steering mode switching means 3 to switch to four-wheel steering mode MF or two-wheel steering mode MT only when the switching state detection means 5 detects the low-speed side VL, and controls the steering mode switching means 3 to a state where it cannot switch to four-wheel steering mode MF when the switching state detection means 5 detects the high-speed side VH, and controls the steering mode switching means 3 to return to two-wheel steering mode MT when it is in four-wheel steering mode MF.

Description

Technical Field

[0001] The present invention relates to a safety device for a work vehicle including speed switching means capable of switching the traveling speed to at least a high speed side or a low speed side, and steering mode switching means capable of switching to a four-wheel steering mode or a two-wheel steering mode.

Background Art

[0002] Generally, a speed sprayer (work vehicle) for spraying agricultural chemicals in a field such as an orchard is widely known. Since this type of speed sprayer travels by an onboard engine, it has a driver's seat at the front of the vehicle. By the way, when performing operations such as spraying chemical liquid, the speed sprayer needs to move at a relatively low speed, and when traveling on a general road or the like, it needs to move at a relatively high speed. Therefore, it includes speed switching means (sub-speed shift lever) for switching the traveling speed to at least the high speed side or the low speed side, and steering mode switching means (switch) for switching the steering mode to a four-wheel steering mode in which the front and rear wheels are steered or a two-wheel steering mode in which only the front wheels are steered.

[0003] Conventionally, as such a work vehicle, an agricultural work vehicle described in Patent Document 1 and a four-wheel steering work vehicle described in Patent Document 2 are known.

[0004] The agricultural work vehicle of Patent Document 1 is intended to solve the problem that when the sub-speed operation tool is operated to the high speed side, the four-wheel steering mode cannot be selected and the vehicle cannot turn easily even if the actual traveling speed is low. Specifically, it includes an engine and a transmission mechanism mounted on the traveling body, front and rear wheels that support the traveling body and are steerable, a steering switch operating tool for switching the front and rear wheels between the two-wheel steering mode and the four-wheel steering mode, and a controller for control, and also includes a vehicle speed detection member for detecting the traveling speed of the traveling body. The controller is configured to automatically switch to the two-wheel steering mode if the four-wheel steering mode is being executed when the traveling speed detected by the vehicle speed detection member is a predetermined speed or more.

[0005] Furthermore, the four-wheel steering work vehicle described in Patent Document 2 aims to provide a four-wheel steering work vehicle that can improve the impact resistance, water resistance, dust resistance, and foreign body resistance of the steering angle sensor to make it less prone to failure and improve reliability, and can automatically and quickly determine whether or not there is an abnormality in the steering system including the steering angle sensor, and can execute a fail-safe operation when an abnormality occurs, thereby improving control accuracy and steering feel. Specifically, steering angle sensors are provided individually for the front wheels and rear wheels, and the control means is configured to calculate the steering angle that the other front wheel should take based on the steering angle detected by one front wheel, compare this calculated steering angle with the steering angle detected by the other front wheel steering angle sensor, and determine that an abnormality has occurred in the front wheel steering system including the front wheel steering angle sensor when the deviation between them is greater than a predetermined value. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-68830 [Patent Document 2] Japanese Patent Publication No. 2003-63431 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the conventional work vehicles mentioned above had the following problems.

[0008] Firstly, if the auxiliary transmission lever, which switches between high-speed and low-speed modes, is switched to the high-speed mode, and the steering mode switch is accidentally switched to the four-wheel steering mode, or if the auxiliary transmission lever is accidentally switched to the high-speed mode while using the four-wheel steering mode during low-speed driving (work), in either case, there is a risk of unstable driving. However, until now, there has been no means to comprehensively and reliably avoid such unstable behavior due to such errors, and countermeasures have been needed.

[0009] Secondly, accurately detecting the gear shift state when the sub-gear lever is operated is a crucial element in implementing safety measures. Furthermore, if the detection means could directly utilize existing structures and components, it would be desirable from the perspective of cost reduction and ensuring productivity, as this would allow for the sharing (dual-use) of parts and materials. However, in reality, there have been no suitable detection and control means from this perspective to date.

[0010] The present invention aims to provide a safety device for work vehicles that solves the problems present in the background technology described above. [Means for solving the problem]

[0011] To solve the above-mentioned problems, the present invention provides a safety device 1 for a work vehicle C that includes a speed switching means 2 capable of switching the travel speed to at least the high-speed side VH or the low-speed side VL by operation, a steering mode switching means 3 capable of switching to four-wheel steering mode MF or two-wheel steering mode MT, and a four-wheel steering controller 4 that performs four-wheel steering control. The safety device 1 is characterized by providing a switching state detection means 5 for detecting the switching state of the speed switching means 2, and providing a safety function in the four-wheel steering controller 4 that allows switching to four-wheel steering mode MF or two-wheel steering mode MT by the steering mode switching means 3 only when the switching state detection means 5 detects the low-speed side VL, controls the steering mode switching means 3 to a state where switching to four-wheel steering mode MF is not possible when the switching state detection means 5 detects the high-speed side VH, and controls the steering mode switching means 3 to return to two-wheel steering mode MT when it is in four-wheel steering mode MF.

[0012] In this case, according to a preferred embodiment of the invention, the switching state detection means 5 can be configured with a non-contact sensor 16 that includes a detectable part 15s added to the joint portion 14j of the connecting member 14 that connects the sub-transmission lever 12 and the sub-mission unit 13, and a non-contact detection unit 15d that detects the position of the detectable part 15s. In this case, the non-contact sensor 16 can use a magnet 15sm for the detectable part 15s and a proximity switch 15ds for the non-contact detection unit 15d. On the other hand, the four-wheel steering controller 4 can be controlled to a non-switchable state by switching control of the hydraulic switching valve 17 in the hydraulic circuit that steers the rear wheels 10p and 10q that operate the four-wheel steering mode MF. Furthermore, the four-wheel steering controller 4 can perform control to switch to the two-wheel steering mode MT when the non-contact detection unit 15d fails. In addition, the steering mode switching means 3 can use a changeover switch 18 that switches between the four-wheel steering mode MF and the two-wheel steering mode MT by operation. Furthermore, the work vehicle C is suitable for application to the speed sprayer SS. [Effects of the Invention]

[0013] The safety device 1 for the work vehicle C according to the present invention, having such a configuration, provides the following remarkable effects.

[0014] (1) With the speed switching means 2 such as the sub-transmission lever, even if the sub-transmission lever is switched to the high-speed side VH due to misoperation while the four-wheel steering mode MF is in use (during low-speed driving), or if the steering mode switching means (switching switch) 3 is switched to the four-wheel steering mode MF due to misoperation while the sub-transmission lever is switched to the high-speed side VH, it is possible to completely disable switching to the high-speed side VH in all states in which the four-wheel steering mode MF may function, thereby reliably avoiding unstable behavior that occurs in the high-speed driving range, and thus it can function as an optimal safety device 1 when applied to the speed sprayer SS.

[0015] (2) It is possible to accurately detect switching operations such as erroneous operation of the speed switching means 2 to the high-speed side VH or the low-speed side VL, or switching due to erroneous operation of the steering mode switching means 3. Furthermore, by directly utilizing the existing vehicle body structure, it is possible to share (use together) parts and materials, which contributes to cost reduction and productivity improvement of safety mechanisms including the mechanical and control systems, as well as miniaturization and avoidance of complexity of the work vehicle C.

[0016] (3) In a preferred embodiment, when configuring the switching state detection means 5, if it is configured with a non-contact sensor 16 that includes a detectable part 15s added to the joint part 14j of the connecting member 14 that connects the sub-transmission lever 12 and the sub-mission unit 13, and a non-contact detection part 15d that detects the position of the detectable part 15s, then some parts can be used (shared) without impairing the original functions of the work vehicle C, such as the sub-transmission lever 12, the sub-mission unit 13, the connecting member 14 and the joint part 14j, and the desired switching state detection means 5 can be implemented easily and at low cost.

[0017] (4) In a preferred embodiment, when configuring the non-contact sensor 16, if a magnet 15sm is used for the detection unit 15s and a proximity switch 15ds is used for the non-contact detection unit 15d, a switching state detection means 5 that is resistant to dust and harsh environments and has excellent waterproofing properties can be configured, thereby providing a highly reliable switching state detection means 5 that can function as an optimal safety device 1 for the work vehicle C.

[0018] (5) In a preferred embodiment, if the four-wheel steering controller 4 is provided with a function to disable switching by controlling the hydraulic switching valve 17 of the hydraulic circuit that steers the rear wheels 10p and 10q which activate the four-wheel steering mode MF, then the safety device 1 can be constructed simply by modifying the control system without adding any new parts, and can be implemented easily and at low cost.

[0019] (6) In a preferred embodiment, if the four-wheel steering controller 4 is provided with a control function to switch to the two-wheel steering mode MT when a failure occurs in the non-contact detection unit 15d, even when a failure occurs in the non-contact sensor 16, the safety device 1 can be switched to the safe side by the fail-safe function.

[0020] (7) In a preferred embodiment, if the steering mode switching means 3 uses a changeover switch 18 to switch to the four-wheel steering mode MF or the two-wheel steering mode MT, the safety function based on the safety device 1 according to the present invention can be accurately implemented by an easy switching function by an operator or the like and a control function by the four-wheel steering controller 4.

Brief Description of the Drawings

[0021] [Figure 1] Mechanical schematic configuration diagram of a speed sprayer equipped with the safety device according to the preferred embodiment of the present invention, [Figure 2] Schematic block configuration diagram of a speed sprayer equipped with the same safety device, [Figure 3] Expanded configuration diagram for explaining the main part structure and operation of the same safety device, [Figure 4] Block system diagram showing the main part of the same safety device, [Figure 5] Configuration diagram corresponding to FIG. 2 showing the structural part excluding the same safety device, [Figure 6] Flowchart for explaining the operation of the same safety device,

Embodiments for Carrying Out the Invention

[0022] Next, preferred embodiments according to the present invention will be given and described in detail based on the drawings.

[0023] First, for the purpose of facilitating the understanding of the safety device 1 according to the present embodiment, the schematic configuration of a speed sprayer SS (working vehicle C) equipped with the same safety device 1 will be described with reference to FIGS. 1 to 5.

[0024] Figure 1 shows the schematic mechanical configuration of the speed sprayer SS as viewed from the planar direction. The dashed line So represents the overall body line of the speed sprayer SS, while the dashed lines 51p and 51q represent the left and right front wheels, and the dashed lines 10p and 10q represent the left and right rear wheels, respectively. The speed sprayer SS is equipped with a driver's seat 55 at the front, a chemical tank (not shown) in the middle, an engine room 56 behind the chemical tank, and a spray unit and blower unit (wind tunnel) 57 at the rear. The driver's seat 55 is equipped with a steering wheel 61, and the driving control unit 56 is located near the steering wheel 61.

[0025] On the other hand, the intermediate section of the Speed ​​Sprayer SS is equipped with a continuously variable transmission (HST) 62 and a sub-transmission unit (auxiliary transmission) 13 located on its output side. The rotational output of this sub-transmission unit 13 is transmitted to the front wheels 51p and 51q via the front propeller shaft 64 and front differential gear 65, and to the rear wheels 10p and 10q via the rear propeller shaft 66 and rear differential gear 67 (Figure 3).

[0026] Furthermore, as shown in Figure 2, the front wheels 51p and 51q are equipped with a front wheel steering drive mechanism 76 that variably drives the steering angle of the front wheels 51p and 51q in accordance with the operating angle of the steering 61 using a hydraulic cylinder 75, etc., and the rear wheels 10p and 10q are equipped with a rear wheel steering drive mechanism 78 that variably drives the steering angle of the rear wheels 10p and 10q in accordance with the drive operation of a hydraulic cylinder 77, etc. controlled by a hydraulic switching valve 17 (Figure 4).

[0027] Furthermore, an engine 68 is mounted in the engine room 56. The rotational output of this engine 68 is transmitted to the input side of the distributor 69. The first rotational output of the distributor 69 is transmitted to the input side of the HST 62 via the HST propeller shaft 70, and the second rotational output of the distributor 69 is transmitted via a clutch to the blower fan 72 located in the blower section (wind tunnel) 57. Note that 73 indicates a spray pump that supplies chemical solution to the spray section.

[0028] On the other hand, as shown in Figure 2, the present invention includes a speed switching means 2 that can switch the driving speed to at least the high-speed side VH or the low-speed side VL by operation, and a steering mode switching means 3 that can switch between four-wheel steering mode MF or two-wheel steering mode MT.

[0029] The speed switching means 2 includes a sub-transmission lever 12, and by rotating this sub-transmission lever 12 by a predetermined angle, it can be switched to the high-speed side VH or the low-speed side VL. The amount of displacement corresponding to the switching position of this sub-transmission lever 12 is transmitted to the submission unit 13 via the connecting member 14.

[0030] Furthermore, the steering mode switching means 3 includes a changeover switch 18 that switches between four-wheel steering mode MF and two-wheel steering mode MT by operation. By using such a changeover switch 18, the safety function based on the safety device 1 according to the present invention can be accurately implemented through an easy switching function by an operator and a control function by the four-wheel steering controller 4.

[0031] In Figures 2 and 4, reference numeral 4 denotes a four-wheel steering controller that performs four-wheel steering control and controls the hydraulic switching valve 17. The aforementioned switching switch 18 is connected to this four-wheel steering controller 4. In Figure 2, 81 denotes a travel direction switching means, which can be switched to the forward direction 82f, the reverse direction 82r, or the neutral position 82n by rotating the travel lever 82 over a predetermined angle. The amount of displacement corresponding to the switching position of the travel lever 82 is transmitted to the continuously variable transmission (HST) 62 via the connecting member 83.

[0032] Next, the specific configuration of the safety device 1 according to this embodiment will be described with reference to Figures 1 to 5.

[0033] The safety device 1 according to this embodiment comprises, as a basic configuration, a switching state detection means 5 that detects the switching state of the speed switching means 2, and a four-wheel steering controller 4 that performs control processing to the safety side in response to the detection result of the switching state detection means 5.

[0034] In this case, as shown in Figures 1 and 3, the switching state detection means 5 is configured with a non-contact sensor 16 that includes a detectable part 15s added to the joint portion 14j of the connecting member 14 that connects the sub-transmission lever 12 and the sub-mission unit 13, and a non-contact detection part 15d that detects the position of the detectable part 15s.

[0035] As shown in Figure 1, in the case of the Speed ​​Sprayer SS, the auxiliary shift lever 12 and the sub-mission unit 13 are connected by a connecting member 14. The connecting member 14 that connects to the auxiliary shift lever 12 is a wire member 14w, and the connecting member 14 that protrudes from the sub-mission unit 13 is a rod member (shaft member) 14s. Therefore, when the switching state detection means 5 is not installed, as shown in Figure 5, the rod member 14s and the wire member 14w are connected by a U-shaped bent joint portion 14j.

[0036] Specifically, one end of the joint portion 14j is connected to the tip of the rigid rod member 14s, and the other end of the joint portion 14j is connected to the tip of the flexible wire member 14w. Note that 31 indicates a fastener for connecting the rod member 14s to the joint portion 14j, and 32 indicates a fastener for connecting the tip of the wire member 14w to the joint portion 14j. Thus, the connecting member 14 is composed of the wire member 14w and the rod member 14s.

[0037] The connecting member 14, including the joint portion 14j, is configured as shown in Figure 5. In this invention, a non-contact sensor 16, which includes a detected portion 15s and a non-contact detection portion 15d as shown in Figure 3, is attached by directly utilizing this connecting member 14 and the submission unit 13.

[0038] When configuring the switching state detection means 5, if it is configured with a non-contact sensor 16 that includes a detectable part 15s added to the joint part 14j of the connecting member 14 that connects the sub-transmission lever 12 and the sub-mission unit 13, and a non-contact detection part 15d that detects the position of the detectable part 15s, then some parts of the work vehicle C such as the sub-transmission lever 12, sub-mission unit 13, connecting member 14 and joint part 14j can be used (shared) without impairing the original functions of each part, so the desired switching state detection means 5 can be implemented easily and at low cost.

[0039] In this embodiment, when configuring the non-contact sensor 16, a magnet 15sm was used for the detection unit 15s, and a proximity switch 15ds was used for the non-contact detection unit 15d. That is, as shown in Figure 3, the magnet 15sm was fixed at an intermediate position on the outer surface of the joint unit 14j, and the proximity switch 15ds was fixed using a part of the housing 13p of the submission unit 13. In this embodiment, as an example, a mounting member 37 was attached to a part of the housing 13p, and the proximity switch 15ds was fixed to this mounting member 37. As shown in Figure 4, this proximity switch 15ds is connected to the four-wheel steering controller 4 via a 4WS switching relay 33.

[0040] Thus, when configuring the non-contact sensor 16, by using a magnet 15sm for the detection unit 15s and a proximity switch 15ds for the non-contact detection unit 15d, a switching state detection means 5 that is resistant to dust and harsh environments and has excellent waterproofing properties can be configured. As a result, a highly reliable switching state detection means 5 can be obtained, and it can function as an optimal safety device 1 for the work vehicle C.

[0041] In Figure 4, 18 is a changeover switch that constitutes the steering mode switching means 3 and is connected to the four-wheel steering controller 4. This changeover switch 18 is equipped with a mode indicator light 18s that lights up or flashes in accordance with the switching position of the changeover switch 18, and a 4WS buzzer 18b that emits a sound when switched to four-wheel steering mode MF. 35 indicates the potentiometers for the front wheels 51p and 51q, and 36 indicates the potentiometers for the rear wheels 10p and 10q. Also, 17 indicates a hydraulic changeover valve that is driven and controlled by a control signal output from the four-wheel steering controller 4.

[0042] On the other hand, the four-wheel steering controller 4 has a safety function that allows the steering mode switching means 3 to switch to four-wheel steering mode MF or two-wheel steering mode MT only when the switching state detection means 5 detects the low-speed side VL, and when the switching state detection means 5 detects the high-speed side VH, it controls the steering mode switching means 3 to a state where switching to four-wheel steering mode MF is not possible, and when the steering mode switching means 3 is in four-wheel steering mode MF, it controls it to return to two-wheel steering mode MT.

[0043] Next, the specific functions (operations) of the four-wheel steering controller 4 and the specific functions of the switching state detection means 5 will be explained in accordance with the flowchart shown in Figure 6, with reference to each figure.

[0044] Currently, the speed sprayer SS is in a stopped state. Now, let's consider the case where the ignition key is turned ON in this state (step S1). At this time, the driving lever 82 is in the neutral position 82n, the sub-transmission lever 12 is in the high-speed side VH, and the changeover switch 18 is set to the two-wheel steering mode MT.

[0045] As a result, the Speed ​​Sprayer SS can travel at high speeds on public roads, etc. (Step S2). In this state, the non-contact sensor 16 is in the position shown in Figure 3(b) (Step S3). That is, it is separated from the magnet 15sm, and the proximity switch 15ds is in the OFF (not detected) state.

[0046] The detection result that the proximity switch 15ds is turned OFF is transmitted to the four-wheel steering controller 4, and the four-wheel steering controller 4 performs control to enable the switchable state. Specifically, it controls the system to enable the switchable state by switching the hydraulic switching valve 17 in the hydraulic circuit that steers the rear wheels 10p and 10q, which enable the four-wheel steering mode MF (step S4).

[0047] Thus, by providing the four-wheel steering controller 4 with a function to disable the four-wheel steering mode MF by controlling the hydraulic switching valve 17 of the hydraulic circuit that steers the rear wheels 10p and 10q, the safety device 1 can be constructed simply by modifying the control system without adding any new parts, making it easy and inexpensive to implement.

[0048] On the other hand, consider the case where the sub-transmission lever 12 is operated to switch from the high-speed side VH to the low-speed side VL (step S5). As a result, the speed sprayer SS will operate at a low speed (step S6).

[0049] Furthermore, by switching the sub-transmission lever 12, the position of the magnet 15sm is displaced to the position shown in Figure 3(a), and the proximity switch 15ds enters the ON (detection) state (step S7). The detection result that the proximity switch 15ds is ON is transmitted to the four-wheel steering controller 4, and the four-wheel steering controller 4 is released from the switchable state (step S8). That is, the switching operation of the steering mode switching means 3 becomes effective, and either the four-wheel steering mode MF or the two-wheel steering mode MT can be selected.

[0050] Furthermore, consider the case where the sub-transmission lever 12 is operated to switch from the low-speed side VL to the high-speed side VH (step S9). Due to the switching of the sub-transmission lever 12, the position of the magnet 15sm is displaced to the position shown in Figure 3(b), and the proximity switch 15ds becomes OFF (not detected) (step S10). In Figure 3, the symbol Lm indicates the amount of displacement of the magnet 15sm when switching between the high-speed side VH and the low-speed side VL.

[0051] The detection result that the proximity switch 15ds is OFF is sent to the four-wheel steering controller 4, which forcibly cancels the four-wheel steering mode MF and forcibly switches to the two-wheel steering mode MT (step S11). This enables high-speed driving (steps S12, S13, S2…). To stop driving, the ignition key is turned OFF (step S14).

[0052] Furthermore, the four-wheel steering controller 4 is equipped with a control function that switches to two-wheel steering mode MT in the event of a failure of the non-contact detection unit 15d. This makes it possible to switch the safety device 1 to the safe side by the fail-safe function even if a failure occurs in the non-contact sensor 16.

[0053] Therefore, according to the safety device 1 of this embodiment, the basic configuration includes a switching state detection means 5 for detecting the switching state of the speed switching means 2, and the four-wheel steering controller 4 is provided with a function that allows switching to four-wheel steering mode MF or two-wheel steering mode MT by the steering mode switching means 3 only when the switching state detection means 5 detects the low-speed side VL, and when the switching state detection means 5 detects the high-speed side VH, it controls the steering mode switching means 3 to a state where switching to four-wheel steering mode MF is not possible, and when the steering mode switching means 3 is in four-wheel steering mode MF, it controls the system to return to two-wheel steering mode MT, thus providing a sub-transmission The speed switching means 2, such as a lever, ensures that even if the sub-transmission lever is switched to the high-speed side VH due to misoperation while using the four-wheel steering mode MF (during low-speed driving), or if the steering mode switching means (switch) 3 is switched to the four-wheel steering mode MF due to misoperation while the sub-transmission lever is switched to the high-speed side VH, switching to the high-speed side VH is completely disabled in all states where the four-wheel steering mode MF may function. This ensures that unstable behavior occurring in the high-speed driving range is reliably avoided, and thus it can function as an optimal safety device 1 when applied to the speed sprayer SS.

[0054] Furthermore, it is possible to accurately detect switching operations due to erroneous operation of the speed switching means 2 to the high-speed side VH or the low-speed side VL, or switching due to erroneous operation of the steering mode switching means 3. In addition, by directly utilizing the existing vehicle body structure, it is possible to share (use together) parts and materials, which contributes to cost reduction and productivity improvement of safety mechanisms, including the mechanical and control systems, as well as miniaturization and avoidance of complexity of the work vehicle C.

[0055] Although preferred embodiments have been described in detail above, the present invention is not limited to these embodiments, and the details of the configuration, shape, materials, quantity, numerical values, etc. can be arbitrarily changed, added, or deleted without departing from the spirit of the present invention.

[0056] For example, the switching state detection means 5 is optimally configured with a non-contact sensor 16 that includes a detectable part 15s added to the joint portion 14j of the connecting member 14 that connects the sub-transmission lever 12 and the sub-mission unit 13, and a non-contact detection part 15d that detects the position of the detectable part 15s. However, this does not preclude the configuration of a non-contact sensor 16 attached to other parts. Furthermore, while it is desirable to use a magnet 15sm and a proximity switch 15ds as the non-contact sensor 16, other components capable of forming a similar non-contact sensor may also be used. In addition, as a means of controlling to a non-switchable state, an example was shown in which a four-wheel steering controller 4 is used to switch and control the hydraulic switching valve 17 in the hydraulic circuit that steers the rear wheels 10p and 10q that activate the four-wheel steering mode MF. However, the non-switchable state may be controlled by other means. [Industrial applicability]

[0057] The safety device according to the present invention can be used in various work vehicles such as speed sprayers equipped with a four-wheel steering controller that performs four-wheel steering control. [Explanation of Symbols]

[0058] 1: Safety device, 2: Speed ​​switching means, 3: Steering mode switching means, 4: Four-wheel steering controller, 5: Switching state detection means, 10p: Rear wheel, 10q: Rear wheel, 12: Sub-transmission lever, 13: Submission unit, 14: Connecting member, 14j: Joint part, 15s: Detected part, 15d: Non-contact detection part, 15sm: Magnet, 15ds: Proximity switch, 16: Non-contact sensor, 17: Hydraulic switching valve, 18: Switching switch, C: Work vehicle, SS: Speed ​​sprayer, VH: High speed side, VL: Low speed side, MF: Four-wheel steering mode, MT: Two-wheel steering mode

Claims

1. A safety device for a work vehicle comprising a speed switching means capable of switching the driving speed to at least a high speed or a low speed by operation, and a steering mode switching means capable of switching between a four-wheel steering mode and a two-wheel steering mode, and a four-wheel steering controller that performs four-wheel steering control, wherein a switching state detection means is provided to detect the switching state of the speed switching means, and the four-wheel steering controller is provided with a safety function that allows the steering mode switching means to switch to a four-wheel steering mode or a two-wheel steering mode only when the switching state detection means detects the low speed, controls the steering mode switching means to a state where switching to a four-wheel steering mode is not possible when the switching state detection means detects the high speed, and controls the steering mode switching means to return to a two-wheel steering mode when it is in four-wheel steering mode.

2. The safety device for a work vehicle according to claim 1, characterized in that the switching state detection means is composed of a non-contact sensor comprising a detection unit added to a joint portion of a connecting member connecting the sub-transmission lever and the sub-transmission unit, and a non-contact detection unit for detecting the position of the detection unit.

3. The safety device for a work vehicle according to claim 2, characterized in that the non-contact sensor uses a magnet in the detection unit and a proximity switch in the non-contact detection unit.

4. The safety device for a work vehicle according to claim 1, characterized in that the four-wheel steering controller controls the switching state by switching a hydraulic switching valve in a hydraulic circuit that steers the rear wheels to enable the four-wheel steering mode.

5. The safety device for a work vehicle according to claim 2, characterized in that the four-wheel steering controller performs control to switch to two-wheel steering mode when the non-contact detection unit fails.

6. The safety device for a work vehicle according to claim 1, characterized in that the steering mode switching means includes a changeover switch that switches between a four-wheel steering mode and a two-wheel steering mode by operation.

7. The safety device for a work vehicle according to claim 1, characterized in that it is applied to a speed sprayer as the aforementioned work vehicle.

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