JP2002013561A - Control system for automatic transmission for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems in automatic transmission control system for tractor or the like that the driver's foot is tired with useless pedal operation and gear shift cannot be done in succession. SOLUTION: A vehicle comprises an auxiliary transmission in which a gear shift lever 1 changes over gear positions via a mechanical interlocking member, and a forward/backward changeover device 3 which can turns on and off transmission of revolution power of an engine by driving a clutch piston through hydraulic operation. A gripper of the gear shift lever 1 has an electric switch type operation part 4U (4D), and transmission of the revolution power of the engine is held in off state by the clutch piston over the pressing time of the switch. In addition, the switch also serves as a gearing electric switch and operates the clutch only under a predetermined condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shift control device for a vehicle.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 5-52254, the operation of a shift lever is controlled by a mechanical interlocking member on a tractor for agricultural use. A first transmission (sub-change) for switching gears; a second transmission (main change) for switching gear positions via driving of a hydraulic cylinder by operating a switch of a switch-type shift operation unit for shifting up and shifting down; There is known a clutch having a clutch mechanism (reverse change) capable of turning on and off transmission of rotational power of an engine by driving a clutch actuator.

Further, as disclosed in Japanese Patent Application Laid-Open No. Hei 6-115367, there is known an apparatus in which a shift operation portion of the second transmission is provided on a grip portion (grip portion) of a shift lever for switching the first transmission. Have been. These conventional gears aim at a so-called no-clutch shift which does not require a depressing operation of a clutch pedal by shifting a certain shift range through driving of an actuator.

However, in the above-mentioned conventional technology, only a certain shift range is switched by an actuator in order to suppress the cost. Therefore, the second shift device is moved up or down by a switch-type shift operating portion to shift this shift position. When you reach the highest or lowest speed,
It becomes necessary to manually and mechanically switch the first transmission. At this time, in order to change the lever position, that is, to change gears smoothly, the clutch pedal must be depressed.

For this reason, in particular, when shifting frequently between several upper and lower stages including the highest speed position or the lowest speed position of the second speed change device, there are cases where the depression operation of the clutch pedal is necessary and not necessary. There was annoyance that the useless clutch pedal operation caused tired feet and that the gear shifting operation could not be performed continuously.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a vehicle speed change control device as follows. That is, according to the first aspect of the present invention, a transmission 2 that switches a shift position by operating a shift lever 1 via a mechanical interlocking member;
A clutch mechanism 3 capable of turning on and off the transmission of rotational power of the engine by driving a clutch actuator, wherein a grip portion of the shift lever 1 is provided with a switch-type operation unit 4U (4D); A shift control device for a vehicle, characterized in that control means 5 is provided for keeping the transmission of the rotational power of the engine off by driving the clutch actuator over the switch pressing time.

According to the second aspect of the present invention, the shift lever 1
A first transmission 2 that switches the shift position through a mechanical interlocking member, and a switch-type shift operation section 4F provided for the shift lever 1 for upshifting and downshifting.
By operating the 4R switch, the speed change actuators 7, 8
Transmission 6 that switches the shift position through the drive of
And a clutch mechanism 3 capable of turning on and off the transmission of rotational power of the engine by driving a clutch actuator, wherein a second shift is performed in response to a switch signal of a shift-up switch 4F of the shift lever 1. Apparatus 6a, 6b
Control means for raising the speed change position and maintaining the transmission of the rotational power by driving the clutch actuator for the duration of the switch signal in a state where the speed change position is set to the highest speed position. 5 which is a shift control device for a vehicle.

According to the third aspect of the present invention, the shift lever 1
A first transmission 2 for switching the shift position through a mechanical interlocking member, and switch-type shift operating sections 4F, 4 provided on the shift lever 1 for shifting up and shifting down.
The second transmission 6a, which switches the shift position via the drive of the shift actuators 7, 8 by operating the R switch,
6b and a clutch mechanism 3 capable of turning on and off the transmission of the rotational power of the engine by driving the clutch actuator. When the shift position of the transmission 6 is lowered and the shift position is set to the lowest speed position, the transmission of the rotational power is kept off by driving the clutch actuator for the duration of the switch signal. A shift control device for a vehicle, comprising a control means 5 for controlling the speed of the vehicle.

According to a fourth aspect of the present invention, the clutch mechanism 3 capable of turning on and off the transmission of the rotational power of the engine by driving the clutch actuator according to any one of the first to third aspects is provided by the second transmission device 6. And a shift control device for a vehicle, which also functions as another transmission or a forward / reverse switching device for switching the traveling direction of the vehicle back and forth.

[0010]

According to the shift control device for a vehicle according to the first aspect of the present invention, when the switch-type operating portion of the grip portion of the shift lever is pushed in, the power transmission state of the clutch is kept off during this time. Therefore, the gear can be switched in accordance with the operation time and operational feeling of the operator.

In the second and third aspects of the present invention, the switch-type shift operating portion for shifting up or shifting down is an operating portion for turning off the power transmission state of the clutch, so that the shifting is continuously performed. Alternatively, when the vehicle goes down, the first transmission and the second transmission can be switched while holding the transmission lever, and as described above, there is no need to depress the clutch pedal, and the transmission operation is simplified. Further, the number of components can be reduced as compared with a case where an operation unit is separately provided for disengaging the clutch, and the production cost can be reduced.

Further, according to the present invention, the clutch mechanism capable of turning on and off the transmission of the rotational power of the engine by driving the actuator is provided for switching the traveling direction of the second transmission or another transmission or the vehicle back and forth. Since the switching device also serves as the switching device, the number of parts can be reduced and the production cost can be reduced as compared with the configuration including a separate dedicated clutch, as described above.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to a shift control device for an agricultural tractor (hereinafter, tractor 10) as a work vehicle. First, the overall configuration of the tractor 10 will be described.

As shown in FIG. 1, the tractor 10 has a diesel engine 11 inside a bonnet. The rotational power of the engine 11 is input to various transmissions, which will be described later, and is appropriately decelerated. , 12 to travel.

In front of the cockpit 15, a meter panel 16 provided with various lamps and a liquid crystal monitor serving as display means and a handle post 18 for projecting a steering handle 17 are provided, and an accelerator lever and the like are provided to protrude from the side of the post. ing. A left and right brake pedal, a clutch pedal 19, and the like are provided below the steering handle 17, and a limit switch 20 is provided at a rotation base of the clutch pedal 19 as means for detecting a depression operation of the pedal 19.

A y-shift type shift lever 1 is provided protrudingly on the side of the cockpit 15, and when the lever 1 is rotated, a shift of a sub-transmission 2, which is a first transmission described later, is performed. The position is switched via a mechanical interlocking member such as a rod, a plate, or a link mechanism or a cam mechanism connecting these rod members. As shown in FIG. 2, a pair of upper and lower gears for instructing the first main transmission 6 a and the second main transmission 6 b as second transmissions to shift up or down from the current position is provided on the grip portion of the shift lever 1. A shift operation section (hereinafter, a shift up switch 4U, a shift down switch 4D) composed of a self-return type switch is provided, and a plurality of actuators (first main transmission 6) described later are operated by pressing these shift switches 4U (4D).
b, the clutch piston of the main transmission high-speed clutch 8A and the clutch piston of the main transmission low-speed clutch 8B, the main transmission first hydraulic cylinder 8A and the main transmission for switching the transmission position of the second main transmission 6a. By operating the second hydraulic cylinder 8B), the first and second main transmissions 6a and 6b are switched in cooperation with each other.

A sliding forward / backward changeover switch 21 for switching the forward / backward movement of the vehicle body and a seesaw type working machine lifting / lowering switch for changing the vertical position of a working machine connected to the rear of the vehicle body are provided on the inner surface of the grip portion of the shift lever 1. 22 are provided. Further, a PTO on / off switch 23 for turning on / off the rotation of the PTO shaft is provided outside the shift lever grip portion.

Further, on the side of the cockpit 15 is provided a lever 24 for lifting and lowering the working machine as means for lifting and lowering the working machine, which is separate from the working machine lifting switch 22. A potentiometer for detecting the operating position is provided at the rotation base of the lever 24. 25 are provided. In the vicinity of the guide of the lever 24, there are provided various setting devices such as a raising position adjustment dial 26 as a means for limiting the height of the working machine and a lowering position adjustment dial 27 as a means for limiting the lower limit height of the working machine. ing.

The sensor 25 and the setting devices 26, 2
Reference numeral 7 denotes a configuration for connection to various controllers 5 (work equipment lifting / lowering controller 5a, shift controller 5b), which are control means below the cockpit 15. Tractor 10
At the rear of the vehicle body, there is provided a cylinder case in which a hydraulic cylinder 30 for lifting and lowering the working machine is provided, and a lift arm supported on the left and right sides of the case is vertically rotated by the expansion and contraction of the piston of the cylinder 30. Further, a three-point link mechanism 31 including a top link and left and right lower links is provided at a rear portion of the vehicle body, and a working machine 32 is connected to the link mechanism 31. In the illustrated example, the rotary working machine is connected. On one side of the lift arm, a lift arm angle sensor 33 is provided at the rotation base.

Thus, the working machine controller 5a, which will be described later, adjusts the operating angle of the working machine lifting lever 24 to the set angle of the lift arm, or responds to the pressing operation of the working machine lifting / lowering switch 22. The solenoid 35s of the proportional pressure control valve 35 for raising the working machine or the solenoid 36s of the proportional pressure control valve 36 for lowering the working machine
And a position control for raising and lowering the work implement 32 by supplying power to the work implement 32 is performed.

Next, a power transmission configuration and a hydraulic circuit of the tractor 10 will be described with reference to FIGS. The rotational power of the engine 11 is intermittently operated by a main clutch 40 in a clutch housing, and in order, a first main transmission 6a, a forward / reverse switching device 3, a second main transmission 6b, and a subtransmission 2 in a transmission case. Is transmitted.

The first main transmission 6a includes two high and low wet multi-plate clutches (main transmission high speed clutch 8).
A, a so-called power shift type transmission having a main transmission low speed clutch 8B), in which the rotational power shifted by the transmission 6a is transmitted to the forward / reverse switching device 3.
One of the two clutches 8A and 8B is always operated by the first main speed changeover control valve 41, and at normal time, pressure oil is sent to the low speed clutch 8B to operate the internal clutch piston to press the clutch disk. I have.

The forward / reverse switching device 3 is a transmission device including a forward clutch 3F, a reverse clutch 3R and a counter shaft having a canter gear, also in the form of a wet multi-plate. The discs of the forward clutch 3F and the reverse clutch 3R respectively press-fit through the oil passage switching operation of the forward / backward switching control valve 42. The switch 2
When 1 is set to “N (neutral)”, the power transmission of both clutches 3F and 3R is both “disengaged”.

The second main transmission 6b is a synchromesh gear type transmission, and converts the rotational power output from the forward / reverse switching device 3 into four gear sets (in the figure, a fourth-speed gear set from the power upper side, The transmission is transmitted to the auxiliary transmission 2 through any one of a third-speed gear set, a second-speed gear set, and a first-speed gear set. Further, a shifter ring having a synchronizing mechanism is provided between the drive side gears of the fourth speed gear set and the third speed gear set, and this ring is slid forward and backward by the expansion and contraction of the piston of the first hydraulic cylinder 7A for main speed change. It has become. That is, when the piston of the cylinder 7A extends,
The power is transmitted through the high-speed gear set to become "fourth speed", and the power is transmitted through the third-speed gear set to become "third speed" due to the shortening of the piston of the hydraulic cylinder 7A.

Similarly, a shifter ring having a synchronizing mechanism is provided between the driving side gears of the second speed gear set and the first speed gear set, and the ring is slid forward and backward by the expansion and contraction of the piston of the second hydraulic cylinder 7B for main speed change. Configuration. That is, the power is transmitted through the second-speed gear set by the piston extension of the hydraulic cylinder 7B to become “second speed”,
By shortening the piston of the hydraulic cylinder 7B, power is transmitted via the first-speed gear set to be "first-speed". The hydraulic cylinders 7A and 7B are also provided with the hydraulic clutches 3F and 3R.
In the same manner as described above, each of the switching control valves 43 and 44 is operated by switching the oil passage.

As a result, the second main transmission 6b is configured to have four shift positions. The auxiliary transmission 2
This is a constant mesh gear type transmission device which is switched via the mechanical interlocking member by manual operation of the transmission lever 1. In detail, from the upper side in the figure, the first counter shaft 45, an auxiliary transmission output shaft 46 provided with three transmission gears of "H speed", "M speed", and "L speed", and a rear end of the auxiliary transmission output shaft 46. A second counter shaft 47 is provided in parallel with the rotatable reduction gear 50.

When the shift lever 1 is rotated outward and forward along the y-shaped guide, the shifter 48 is slid forward, and the shifter 48 is driven through the "H" gear transmitted from the second main transmission 6b. Directly connected to the speed change output shaft 46, the speed becomes "H speed", and when rotated outward and rearward, the shifter 48 is slid rearward, and the first counter shaft 45, the "M speed" gear, the sub speed change output shaft 46 and the rotational power are rotated. Is transmitted to become "M speed".

When the shift lever 1 is rotated inward and rearward along a guide, the shifter 49 is slid forward, and the rotational power is supplied to the first counter shaft 45, the reduction gear 50,
The second counter shaft 47 is transmitted to the “L speed” gear and
Speed ". As a result, the auxiliary transmission 31 has a configuration having three shift positions.

As described above, the tractor 10 is constructed by combining the respective gear sets of the first main transmission 6a, the second main transmission 6b, and the sub transmission 2, as shown in FIG.
24 forward gears and 24 reverse gears are obtained, and the gears are shifted from 1 gear to 8 gears, 9 gears to 16 gears, and 17 gears to 24 gears by operating the gear shift switches 4U and 4D. It has become.

Reference numeral 51 in FIG. 3 indicates a front wheel drive device having a four-wheel drive clutch and a front wheel drive clutch for driving the front wheel 13 at an increased speed during turning, and reference numeral 53 indicates the PT.
According to the switching of the O ON / OFF switch 23, the PTO shaft 52
1 shows a PTO on / off clutch for turning on / off power transmission to a vehicle.

Next, a control system of the tractor 10 will be described with reference to FIG. The controller 5 of the tractor 10 includes a working machine lifting controller 5a for processing information related to the working machine lifting mechanism, and a traveling controller 5b for processing information related to shift control. A CPU for processing signals;
It has a RAM for temporarily storing these signal information, an EEPROM for storing various control programs, and a timer. These controllers are configured to transmit and receive each other's sensor information and output information via a communication line.

The work implement elevating controller 5a is provided with a potentiometer 2 of the work implement elevating lever 24 at this input portion.
5, a lift arm angle sensor 33, a raising position adjusting dial 26, a lowering position adjusting dial 27, etc. are connected and provided, and an output portion is connected to an oil passage to the hydraulic cylinder for lifting and lowering the working machine. Solenoid 35 for valve 35
s, and a solenoid 36s of the pressure proportional control valve 36 for lowering the work implement are connected and provided.

On the other hand, the traveling controller 5b includes a forward / reverse selector switch 21, a limit switch 20 at the base of the clutch pedal, a work implement elevating switch 22,
Shift up switch 4U, Shift down switch 4D, P
A TO on / off switch 23 and a main shift position sensor for detecting the operating position of the main shift hydraulic cylinder are connected and provided. The output unit is provided with hydraulic oil to press the forward clutch 3F and the reverse clutch 3R. Switching control valve 42 for switching
Solenoids 42s, 41s of the switching control valves 41, 43, 44 for operating a plurality of shift actuators of the first and second main transmissions 6a, 6b.
43a, 43b, 44a, 44b, etc. are connected and provided.

In the tractor 10 configured as described above,
The shift control is executed as in the flowchart showing the outline of the shift control program shown in FIG. First, when the power of the tractor 10 is turned on and the engine is started, the traveling controller 5b reads the states of various sensors and switches in STEP1. Then, in STEP2, it is determined whether or not the shift down switch 4D is pressed.
In the case of ES, it is determined in STEP 3 whether the current shift position is the lowest speed, that is, the first speed. And this is also YE
In the case of S, the process proceeds to STEP4, in which the power supply to the switching control valve 42 is stopped for a time period during which the signal of the shift down switch 4D is detected, and the forward / reverse clutches 3F, 3R
In the neutral position.

On the other hand, if the determination in STEP 3 is NO, power is supplied to the solenoids of the switching control valves of the main shift so that the gears are shifted to the normal shift, that is, the shift position one speed below the current position. At this time, the switch 4D
There is a method of lowering the current position by one speed every time the switch is turned on, and a method of lowering the current position by one speed in accordance with the duration of time when the switch 4D is pressed.

Similarly, when the shift up switch 4U is depressed, it is determined in STEP7 whether the current shift position is the highest speed, that is, the eighth speed. If the answer is YES, the process proceeds to STEP 8, and the power supply to the switching control valve 42 for operating the clutches 3F and 3R of the forward / reverse switching device 3 is stopped during the time when the signal of the shift up switch 4U is detected. Then, both clutches 3F and 3R are held at the neutral position.

When the main transmissions 6a and 6b are switched by the speed change switches 4U and 4D, the front and rear clutches 3F and 3R of the forward / reverse switching device 3 are set to the neutral position. The clutch is automatically crimped again based on the detection information. When the sub-transmission 2 is switched to the high-speed side, the main transmission is automatically shifted to the low-speed side (for example, the first speed), and when the sub-transmission 2 is switched to the low-speed side, the main transmission is automatically shifted to the high-speed side (for example, the eighth speed). It is configured to be able to be switched dynamically.

The shift control device for the tractor 10 configured as described above, when the shift up switch 4U or the shift down switch 4D of the gripping portion of the shift lever 1 is depressed,
During this time, the power transmission state of the forward / reverse clutches 3F and 3R is kept off, so that the gear can be switched in accordance with the operation time and the operational feeling of the operator.

Further, the shift-up switch 4U and the shift-down switch 4D are used as an operating portion for turning off the power transmission state of the clutches 3F and 3R without providing a separate operating portion for disengaging the clutch, thereby reducing the number of parts. In addition, the production cost can be reduced, and when shifting up or down continuously, the sub-transmission and the main transmission can be switched while holding the shift lever 1, and the depression operation of the clutch pedal 19 is performed as described above. Is unnecessary, and the shifting operation is simplified.

Further, here, without separately providing a clutch mechanism capable of turning on and off the transmission of the rotational power of the engine 11,
Since the clutches 3F and 3R of the forward / reverse switching device 3 are used, the number of parts can be reduced and the production cost can be reduced as described above. This clutch mechanism may be a method using the second main transmission 6b, or if another transmission is provided, the transmission may be provided with an actuator to turn off the power transmission.

Next, the shift control will be described in detail. The flowchart shown in FIG. 8 is a control flow performed when the tractor 10 starts or starts the engine.
Here, after reading the state of various sensors and switches in STEP1, the shift-up switch 4U in STEP2,
Alternatively, it is determined whether or not the shift down switch 4D is pressed, and whether or not the clutch pedal 19 is depressed in STEP3.
In EP4, the shift position is shifted up or down by one speed at every ON continuation time of the switch 4U (4D). If the determination in STEP 3 is NO, the processing in STEP 4 is jumped to restrict the operation, and one operation is performed for each switch ON.
It is configured to increase or decrease speed by speed.

Thus, when the operator attempts to operate the tractor 10 by himself / herself, that is, when the depression of the clutch pedal 19 is detected, the switch 4
The target vehicle speed can be quickly set without the need to push the U and 4D, and the speed change operation can be improved.

Next, a description will be given of the control of the work implement elevating controller 5a, in particular, processing by operating the work implement elevating switch 22. The work machine elevating switch 22
Are provided with two-stage switches for raising and lowering the working machine, respectively, and when the pushing operation of the switch is shallow, that is, when the working machine 32 is slightly raised and lowered, and when the pushing operation is deep, That is, the operation for raising and lowering the working machine 32 to the highest position or the lowest position at a stretch is distinguished.
The elevating speed is obtained by appropriately reading the position of the operating lift arm, and according to the difference from the target value, the proportional pressure control valve 35,
The configuration is such that the amount of energization to the 36 solenoids 35s and 36s is changed.

As described above, since the operating portion for raising and lowering the work implement is provided on the grip portion of the shift lever 1, the operation for lifting and lowering the work implement 32 can be performed at the same time as the shift operation, so that the work can be performed quickly. In addition, since the switch 22 is configured to be pushed in two stages, in the field of a conventional work machine lifting device,
Compared to a configuration in which the fine lifting operation of the work machine and the operation of raising and lowering to a preset target position by a large amount are operated by separate operation members, the lifting operation can be continuously changed even when the situation changes. Operability can be improved.

[Brief description of the drawings]

FIG. 1 is an overall side view of a tractor.

FIG. 2 is a perspective view of a shift lever.

FIG. 3 is a transmission mechanism diagram of a tractor.

FIG. 4 is a diagram showing combinations of shift positions.

FIG. 5 is a partial hydraulic circuit diagram of the tractor.

FIG. 6 is a diagram showing a connection state of a controller.

FIG. 7 is a flowchart (1) showing an outline of a shift control.

FIG. 8 is a flowchart (2) showing an outline of a shift control.

FIG. 9 is a flowchart (1) showing an outline of position control.

FIG. 10 is a flowchart (2) showing an outline of position control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shift lever 2 Subtransmission 3 Forward / reverse switching device 4U Upshift switch 4D Downshift switch 5 Controller 6 Main transmission 7A First hydraulic cylinder for main transmission 7B Second hydraulic cylinder for main transmission 8A High speed clutch for main transmission 8B Main Low speed clutch for shifting 10 tractor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // F16H 59:12 F16D 25/14 640Q 640F (72) Inventor Yutaka Kashino Yatsukura, Tobe-cho, Iyo-gun, Ehime Prefecture. No. 1 Iseki Agricultural Machinery Co., Ltd. Engineering Department F-term (reference) RA04 RA07 SB09 SB10 UA03 UA04 VA62Z VA76W VD17W

Claims (4)

[Claims] An automatic transmission includes a transmission device for switching a shift position of a shift lever via a mechanical interlocking member, and a clutch mechanism capable of turning on and off transmission of rotational power of an engine by driving a clutch actuator. Vehicle
The grip portion of the shift lever 1 has a switch-type operation unit 4U.
(4D) A shift control device for a vehicle, further comprising control means 5 for keeping the transmission of the rotational power of the engine off by driving the clutch actuator over the switch pressing time. 2. A first transmission 2 for switching the operation of a shift lever 1 through a mechanical interlocking member to change a shift position; and a switch-type shift operating section 4F provided on the shift lever 1 for shifting up and shifting down. , 4R, the second transmission 6 for switching the shift position through the drive of the shift actuators 7, 8 and the clutch mechanism 3 capable of turning on and off the transmission of the rotational power of the engine by the drive of the clutch actuator. A state in which the shift positions of the second transmissions 6a and 6b are increased according to a switch signal of a shift-up switch 4F of the shift lever 1 and the shift position is set to the highest speed position. In the control means 5, the transmission of the rotational power is kept off by driving the clutch actuator for the duration of the switch signal. Shift control device for a vehicle, characterized in that it includes. 3. A first transmission 2 for switching the operation of a shift lever 1 through a mechanical interlocking member to shift positions, and a switch-type shift operating section 4F provided on the shift lever 1 for shifting up and shifting down. , 4R, the second transmissions 6a, 6b for switching the shift position via the drive of the shift actuators 7, 8 and the clutch mechanism 3 capable of turning on and off the transmission of the rotational power of the engine by the drive of the clutch actuator. In a state in which the shift position of the second transmission 6 is lowered according to a switch signal of the shift down switch 4D of the shift lever 1 and the shift position is set to the lowest speed position. Then
A shift control device for a vehicle, comprising: a control unit (5) for keeping the transmission of the rotational power off by driving the clutch actuator for the duration of the switch signal. 4. A clutch mechanism 3 capable of turning on and off the transmission of rotational power of an engine by driving a clutch actuator according to claim 1 to 3, said second transmission 6, another transmission, or a vehicle. A shift control device for a vehicle, wherein the shift control device also serves as a forward / reverse switching device that switches the traveling direction of the vehicle forward and backward.