JPH0555348B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a two-wheel steering system in which only one of the front and rear wheels is steered in a work vehicle configured such that both the front and rear wheels can be freely steered. The present invention relates to a power steering device for a work vehicle that can switch between a four-wheel steering type and a four-wheel steering type in which the front and rear wheels are steered in opposite directions depending on the size of a target steering angle.

[Conventional technology]

In the power steering system for this type of work vehicle mentioned above, in order to achieve both the good straight-line maneuverability of the two-wheel steering type and the good turning performance of the four-wheel steering type, conventionally, the above-mentioned two-wheel steering type has been used. It is configured so that both the front and rear wheels can be operated with power steering so that it can be used by switching between four-wheel steering types.

By the way, when operating the steering wheel using the above-mentioned four-wheel steering system, if the front and rear wheels start turning off at the same time from the neutral position, the turning performance is good, and the vehicle will turn with a slight steering operation.
Conventionally, the 4-wheel steering system had the disadvantage of making it difficult to operate the vehicle in a straight line.
The 4-wheel steering type mentioned above and the 2-wheel steering type that cannot make sharp turns but have good straight-line maneuverability,
It was designed to be switched manually as necessary.

[Problem that the invention seeks to solve]

However, in actual work, in order to steer the work vehicle so that it goes straight along the work path, to make a turn at the end of the work path, or to quickly correct the direction of the work vehicle in relation to the work path,
It was necessary to make a sharp turn. However, in the above-mentioned conventional configuration, the steering type is changed by manual operation.
During work, it becomes necessary to change the steering type in a complicated manner, and the operation is troublesome.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to achieve both the good straight-line maneuverability of the two-wheel steering system and the good turning performance of the four-wheel steering system, while also switching between them. The object is to be able to automatically switch the steering type so that the state corresponds to the actual steering operation.

[Means for solving problems]

The power steering device for a work vehicle according to the present invention is provided with a steering angle detection means for detecting the actual steering angle of each of the front and rear wheels whose direction can be freely changed, and a target steering angle indicating means for indicating a target steering angle, When the target steering angle is within the set angle range on the neutral side, only one side of the front wheels and rear wheels is later changed in direction according to the target steering angle, and when the target steering angle is outside the set angle range. when the front wheels and the rear wheels are in opposite directions, and the steering actuator is actuated to change the direction of each of the front wheels and the rear wheels separately so that the front wheels and the rear wheels are turned in opposite directions and the directions are changed according to the target steering angle. A control means is provided for controlling the steering angle of the rear wheels for the same amount of steering during a range from when the target steering angle exceeds the set angle range to the maximum steering state. The steering angle is set to be larger than the increasing rate of the steering angle, so that the steering angles of the front wheels and the rear wheels with respect to the neutral position are the same in the maximum steering state.

The functions and effects of this characteristic configuration are as follows.

[Effect]

In other words, when the target steering angle is within the set angle range on the neutral side, a sharp turn is not required, and when the target steering angle is outside the set angle range, it is considered that a sharp turn is necessary. I can do it.

Therefore, when the target steering angle is within the set angle range on the neutral side, a two-wheel steering type with good straight-line maneuverability is used, and when the target steering angle is outside the set angle range, a four-wheel steering type that allows sharp turns is used. By automatically changing the steering type according to the target steering angle so that the steering type is the same as the actual driving condition, the vehicle can be driven with a steering type that corresponds to the actual driving condition.

Furthermore, in order to ensure that the steering angles of the front wheels and rear wheels from the neutral position are the same in the maximum steering state, the steering amount is the same within the range from when the target steering angle exceeds the set angle range to the maximum steering state. The rate of increase in the steering angle of the rear wheels is set to be greater than the rate of increase in the steering angle of the front wheels. becomes the maximum, and the steering angle range can be made extremely wide.

〔Effect of the invention〕

Therefore, when sharp turns are not required, the system uses two-wheel steering with good straight-line maneuverability, and when sharp turns are required, it uses four-wheel steering with good turning performance. Since the steering type is changed, there is no need to manually switch the steering type as in the past, and it is also possible to respond to extremely sharp turns with a single steering operation. It was possible to perform sharp turning operations, and it was possible to obtain characteristics of both straight-line operability and turning operability, and the versatility of steering operations was increased.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 4, an engine E is mounted on the front side of the fuselage frame 1 at the bottom of the vehicle body A, a steering handle H and a seat 2 are provided on the rear side, and a pair of left and right front and rear wheels are mounted on the lower side of the fuselage frame 1. 3F,
3R is provided, and a lawn mowing device 4 is suspended from the lower abdomen of the vehicle body A so as to be movable up and down, thereby constructing a work vehicle used for cutting grass and weeds.

To explain the structure of the vehicle body A, as shown in FIG. 3, the pair of left and right front and rear wheels 3F, 3R
Hydraulic cylinders 5F, 5R as steering actuators for separately operating the pair of front and rear wheels 3F, 3R, and control valves 6 for the same.
F and 6R are provided.

Further, a hydraulic continuously variable transmission 7, which can freely switch between forward and reverse directions and can change speeds in both forward and backward directions, is connected to the engine E and is configured to be able to change speeds with a speed change pedal 8.

Further, a potentiometer R ₀ for detecting a target steering angle serves as a target steering angle indicating means for indicating the operation position of the steering wheel H, that is, a target steering angle, and a potentiometer R 0 for detecting a target steering angle serves as a means for detecting an actual steering angle of the front wheels 3F. A steering angle detection potentiometer R ₁ and a rear wheel steering angle detection potentiometer as a steering angle detection means for detecting the actual steering angle of the rear wheel 3R.
Detection signals V ₀ to V ₂ from the potentiometers R ₀ to _{R 2} are input to a control device ₉ constituting a control means for power steering operation of the front and rear wheels 3F and 3R. be.

Since the front and rear wheels 3F and 3R are configured to be able to be steered independently, there is a parallel steering type in which the front and rear wheels 3F and 3R are turned in the same direction and the direction is changed, and there is a parallel steering type in which the front and rear wheels 3F and 3R are turned in the same direction and the direction is changed in the opposite direction. 4-wheel steering type that allows you to make sharp turns.
Further, the two-wheel steering type can be selectively used by changing the direction of only the front wheels 3F.

That is, in the control device 9, the target voltage corresponding to the target steering angle output from the target steering angle detection potentiometer _R0 is
Comparing V ₀ with detection voltages V 1 _and V ₂ corresponding to the actual steering angles output from the steering angle detection potentiometers R ₁ and R ₂ ,
By controlling the operation of the controls 6F and 6R, the power steering is operated so that the direction of the front and rear wheels 3F and 3R is changed in accordance with the selected steering type and the instructed target steering angle. becomes.

However, when the four-wheel steering type is selected, if the target steering angle is within the set angle range from the neutral position (in this embodiment, it is set to approximately ±15 degrees), the two-wheel steering type is automatically selected. Therefore, the steering type is automatically changed according to the magnitude of the target steering angle so that the four-wheel steering type is used outside the set angle range.

Next, while explaining the configuration of the control device 9 based on the circuit diagram shown in FIG. The configuration of the means for changing between the steering type and the four-wheel steering type will be explained.

That is, the target voltage V ₀ corresponding to the target steering angle which is the output signal of the target steering angle detection potentiometer R ₀ and the front wheel steering angle detection potentiometer
A front wheel control valve drive circuit 10F that drives the front wheel control valve 6F until the detection voltage V ₁ output from R ₁ matches within a tolerance, and the target voltage V ₀ as will be described in detail later. The rear wheel control valve 6R is operated until the command voltage Vr generated based on the rear wheel control valve 6R and _the detection voltage _V2 outputted from the rear wheel steering angle detection potentiometer R2 match within a tolerance. Control valve drive circuit 1 for the rear wheels that drives the
0R, and the front and rear wheels 3F and 3R are configured to be operated with power steering separately according to the selected steering type.

Further, when the four-wheel steering type is selected by the steering type selection switch 11, a preset neutral voltage is applied to change the direction of the rear wheels 3F in the opposite direction to the front wheels 3F.
An inverting amplifier 12 is provided to invert the polarity of the target voltage V ₀ with respect to Vn, that is, the steering direction.

Further, when the four-wheel steering type is selected, if the target steering angle is within the set angle range, the rear wheels 3F are maintained in neutral and the two-wheel steering type is selected;
The instruction voltage Vr input to the control valve drive circuit 10R for the rear wheels is adjusted to the target steering angle so that the steering operation of the rear wheels 3F is started according to the target steering angle as the angle becomes outside the set angle range. When the voltage V ₀ is within the set voltage range, it becomes the neutral voltage Vn, and as it goes outside the set voltage range, it becomes a voltage corresponding to the magnitude of the target voltage V ₀ and the maximum steering angle. In this case, the command voltage Vn input to the rear wheel command voltage control circuit 13 and the rear wheel control valve drive circuit 10R, which are adjusted so as to match the steering angle of the front wheels 3F, is set in parallel. When selecting the steering type, the target voltage angle
V ₀ , and is fixed at the neutral voltage Vn when a two-wheel steering type is selected, and is selected by the steering type selection switch 11 so that it becomes the output of the instruction voltage control circuit 14 when a four-wheel steering type is selected. A steering type switching circuit 14 is provided to switch the type of steering depending on the type of steering.

Next, each of the circuits 10F, 10R, 13, 14
The configuration will be explained in detail.

The control valve drive circuits 10F and 10R have the same configuration, and to explain the structure of the control valve drive circuit 10F for the front wheels, the difference between the input target voltage V ₀ and the detected voltage V ₁ is If the differential amplifier A ₀ that calculates the deviation and the output of the differential amplifier A ₀ deviate from the neutral voltage Vn by more than a tolerance, the control valve 6F is activated in accordance with the direction of the deviation. A pair of comparators A ₁ and A ₁ are provided to output driving signals.

The configuration of the command voltage control circuit 13 will be described as follows: a pair of differential amplifiers A ₄ and A ₅ that add and subtract the output V ₃ of the inverting amplifier 12 and the voltage Vd corresponding to the set angle; output
V ₃ and a pair of reference voltages (Vn±Vd) obtained by adding and subtracting the neutral voltage Vn and the voltage Vd corresponding to the set angle, the inverting amplifier 1
A differential amplifier that adds the output V ₃ of the inverting amplifier 11 and the set voltage Vd when the output V ₃ of the inverting amplifier 11 is less than or equal to a reference voltage (Vn - Vd) obtained by subtracting the set voltage Vd from the neutral voltage Vn. A comparator that outputs a "H" level switching signal _S2 that turns on the first analog switch SW1 that outputs the output voltage ( _V3 + Vd) of _A4 as the instruction voltage Vr to the rear wheel electromagnetic variable drive circuit _10R . _A6 ,
A differential amplifier that subtracts a set voltage Vd from the output V ₃ of the inverting amplifier 12 when the output V ₃ of the inverting amplifier 12 is equal to or higher than a reference voltage (Vn + Vd) which is the sum of the neutral voltage Vn and the set voltage Vd. A comparator that outputs an “H” level switching signal S ₃ that turns on the second analog switch SW ₂ that outputs the output voltage (V ₃ +Vd) of A ₅ as the instruction voltage Vr for the rear wheel solenoid valve drive circuit 10R. A ₇ , the pair of switching signals S ₂ and S ₃ that are the outputs of both the comparators A ₆ and A ₇ are both “L”
level, that is, when the output V ₃ of the inverting amplifier 12 is within the reference voltage (Vn±Vd), the neutral voltage Vn is output as the instruction voltage Vr to the rear wheel solenoid valve drive circuit 10R. A NOR gate _G1 is provided to turn on the third analog switch _SW3 .

To explain the configuration of the steering type switching circuit 14, when the operation position of the steering type selection switch 11 is the two-wheel steering type, the rear wheel electromagnetic Valve drive circuit 1
When the operating position of the analog switch SW ₄ for switching the command voltage Vr for 0R to the neutral voltage Vn and the steering type selection switch 11 is the four-wheel steering type, the command voltage for the rear wheel solenoid valve drive circuit 10R. Vr
is switched to the output of the instruction voltage control circuit 13 so that the voltage is automatically switched between the two-wheel steering type and the four-wheel steering type according to the target steering angle.
When the operation position of SW ₅ and the steering type selection switch 11 is the parallel steering type, the rear wheel 3R is turned in the same direction at the same steering angle as the front wheel 3F. Analog switches SW ₆ are provided for switching the instruction voltage Vr for the wheel electromagnetic valve drive circuit 10R to the output of a potentiometer R ₀ that detects the operating position of the handle H.

Therefore, when the four-wheel steering type is selected, the instruction voltage Vr to the rear wheel solenoid valve drive circuit 10R, that is, the actual steering angle of the rear wheel 3R, is determined by the target steering as shown by the broken line in FIG. If the angle is within the set angle (±15 degrees) with respect to the neutral angle, the neutral angle is maintained and only the front wheel 3F is steered. 15 degrees), the steering operation is started at a larger steering angle than the front wheel 3F, and at the maximum steering angle, the steering angle is controlled to be the same as the front wheel 3F, and the steering operation is controlled in the opposite direction to the front wheel 3F. The steering type is automatically switched according to the size of the target steering angle, and the steering operation is performed so that the four-wheel steering type is used for the target steering angle.

[Another example]

In the above embodiment, when the 4-wheel steering type is selected, the steering operation range in the 2-wheel steering type is set to an angular range (±
15 degrees), but it may also be configured to be variable so that the angle range can be set artificially, or may be configured to vary depending on the traveling speed, for example. .

Further, in the above embodiment, when the 4-wheel steering type is selected, only the rear wheels 3R are switched between the 2-wheel steering type and the 4-wheel steering type depending on the target steering angle. For example, when moving forward, the steering type of the rear wheels 3R is changed as in the above embodiment, and when moving backward, the steering type of the rear wheels 3R is operated to match the target steering angle, and the steering type of the front wheels 3F is changed to the target steering angle. It may be possible to switch depending on the situation.

Furthermore, in the above embodiment, the case where the target steering angle is instructed by manually operating the steering wheel is exemplified. The present invention can also be applied to cases where a target steering angle is set based on information detected by various sensors, such as in an automatic driving work vehicle. Further, the specific configuration of each part of the working vehicle can be changed in various ways depending on the configuration of the working vehicle to which the present invention is applied, and the present invention is not limited to the above embodiments.

[Brief explanation of the drawing]

The drawings show an embodiment of the power steering device for a working vehicle according to the present invention, FIG. 1 is a circuit diagram showing the configuration of the control device, FIG. 2 is a characteristic diagram of the steering angle, and FIG. 3 is a schematic configuration of the control system. FIG. 4 is an overall side view of the working vehicle. _V0 ...Target steering angle, _V1 , _V2 ...Actual steering angle, _R0 ...Target steering angle indicating means, _R1 , _R2 ...Steering angle detection means, 3F...Front wheels, 3R... Rear wheel, 6F,
6R... Steering actuator, 9... Control means.

Claims (1)

[Claims] 1. Steering angle detection means R ₁ and R ₂ that detect the actual steering angles V ₁ and V ₂ of the front wheels 3F and rear wheels 3R, respectively, which can change direction, and target steering angle instruction means R that indicates the target steering angle V _{0 0} and the target steering angle
When V ₀ is within the setting angle range on the neutral side,
Only one side of the front wheels 3F and rear wheels 3R is changed in direction according to the target steering angle V ₀ , and when the target steering angle V ₀ is outside the set angle range, the front wheels 3F
and steering actuators 6F and 6R that respectively change the direction of the front wheel 3F and the rear wheel 3R so that the rear wheel 3R faces in the opposite direction and changes the direction in accordance with the target steering angle _V0 . A control means 9 for controlling the operation is provided, and
During the range from when the target steering angle V ₀ exceeds the set angle range to the maximum steering state, the rear wheels 3R for the same steering amount
The rate of increase in the steering angle of the front wheels 3F is set to be greater than the rate of increase in the steering angle of the front wheels 3F.
A power steering device for a work vehicle configured such that the steering angles of the rear wheels 3R and 3R with respect to the neutral position are the same in the maximum steering state.