Patent Description:
Vehicles that travel on preset travel routes include vehicles configured to set a different steering angle for each of a plurality of tires to enable complex movement on the site (see, for example, <CIT> (PTL <NUM>)). Further, <CIT> was found to be of technical relevance but merely provides a teaching that finds a steering angle that reduces the deviation between the travel route information and the current position and travel direction.

In the case where the foregoing vehicle deviates from the travel route for some reason, it is desirable that the vehicle quickly returns to the travel route without performing unnecessary operation. It could therefore be helpful to provide a vehicle that, upon deviating from a travel route, can return to the travel route efficiently.

A vehicle according to an aspect of the present disclosure is a vehicle configured to travel on a preset travel route, comprising: a plurality of tires including a first tire and a second tire, and each configured to be set at a different steering angle; and a processing device configured to set a steering angle of each of the plurality of tires, wherein the processing device is configured to: when the vehicle deviates from the travel route and returns to the travel route, determine a return position on the travel route, and calculate a target position of the first tire and a target position of the second tire that allow the vehicle to travel on the travel route when located at the return position; find a common central point at which a difference between a distance from a current position of the first tire and a distance from the target position of the first tire is within a predetermined range and a difference between a distance from a current position of the second tire and a distance from the target position of the second tire is within a predetermined range; and set the steering angle of each of the plurality of tires so that the tire will be oriented in a direction of a tangent to a clearance circle whose center is the common central point and whose radius is a distance to the common central point or oriented in a direction whose angle difference from the direction of the tangent is within a predetermined range.

It is thus possible to provide a vehicle that, upon deviating from a travel route, can return to the travel route efficiently.

An overview of a vehicle <NUM> according to an embodiment will be described below. <FIG> is a schematic plan view of the vehicle <NUM>. The vehicle <NUM> travels on a preset travel route. The vehicle <NUM> may be configured to travel autonomously on the travel route, or configured to travel partially manually (for example, manually only during acceleration/deceleration and otherwise autonomously) on the travel route.

As illustrated in <FIG>, the vehicle <NUM> includes a vehicle body <NUM>, a plurality of tires <NUM> to <NUM>, a tire drive device <NUM>, a positioning system <NUM>, and a processing device <NUM>.

The vehicle body <NUM> is configured to be able to carry heavy objects. In this embodiment, the vehicle body <NUM> has a substantially rectangular shape in a plan view. When the vehicle <NUM> travels on the travel route, the vehicle <NUM> travels in the longitudinal direction of the vehicle body <NUM> with one longitudinal end of the vehicle body <NUM> in front. In this embodiment, the left end of the vehicle body <NUM> in the drawing is in front, and the vehicle <NUM> travels leftward in the drawing (see the arrow). The use, shape, and direction of travel of the vehicle body <NUM> are not limited to such.

The plurality of tires <NUM> to <NUM> include a first tire <NUM> corresponding to the right front wheel, a second tire <NUM> corresponding to the left front wheel, a third tire <NUM> corresponding to the right rear wheel, and a fourth tire <NUM> corresponding to the left rear wheel. The arrangement of the tires <NUM> to <NUM> is, however, not limited to such. The number of tires included in the vehicle <NUM> is not limited to four.

The tire drive device <NUM> rotates the tires <NUM> to <NUM> and sets their steering angles (i.e. the angles of the tires <NUM> to <NUM> with respect to the vehicle body <NUM>). The tire drive device <NUM> in this embodiment can set a different rotation speed and steering angle for each of the tires <NUM> to <NUM>. The tire drive device <NUM> may rotate the tires <NUM> to <NUM> using an internal combustion engine, or rotate the tires <NUM> to <NUM> using an electric motor. The steering angle of each of the tires <NUM> to <NUM> is feedback-controlled based on the results of detection by a steering angle detection sensor.

The positioning system <NUM> is a system that measures the current position (which is the center position of the vehicle body <NUM> in this example, but is not limited to such) and orientation of the vehicle body <NUM>. The positioning system <NUM> in this embodiment includes a global navigation satellite system (GNSS) receivers in the front and rear parts of the vehicle body <NUM>, and can measure the detailed positions of the front and rear parts of the vehicle body <NUM>. Based on the positions of the front and rear parts of the vehicle body <NUM>, the positioning system <NUM> calculates the current position and orientation of the vehicle body <NUM>. The positioning system <NUM> may measure the current position and orientation of the vehicle body <NUM> by any method other than the above, such as using a camera. The positioning system <NUM> may include only one receiver that has two antennas. The positioning system <NUM> may include only one receiver, and calculate (obtain) the orientation of the vehicle body <NUM> based on the measured latest position of the vehicle body <NUM> and the position of the vehicle body <NUM> a predetermined time before the latest position.

The processing device <NUM> includes a processor, a volatile memory, a nonvolatile memory, an I/O interface, and the like. The processing device <NUM> is electrically connected to the positioning system <NUM>, and can acquire the current position and orientation of the vehicle body <NUM> from the positioning system <NUM>. The processing device <NUM> is also electrically connected to the tire drive device <NUM>, and can transmit a control signal to the tire drive device <NUM> to control the tire drive device <NUM> and set the rotation speed and steering angle of each of the tires <NUM> to <NUM>.

The nonvolatile memory in the processing device <NUM> stores data of the preset travel route of the vehicle <NUM>, and data of a route return program. The processor in the processing device <NUM> performs computation using the volatile memory based on the route return program. The processing device <NUM> transmits a control signal to the tire drive device <NUM> based on the results of computation in the volatile memory.

The route return program will be described below. <FIG> is a flowchart of the route return program. The route return program is a program for causing the vehicle <NUM> that has deviated from the travel route to return to the travel route, and is executed during travel on the travel route. The process illustrated in <FIG> is executed by the processing device <NUM>.

After the route return program is started, the processing device <NUM> acquires the current position and orientation of the vehicle body <NUM> (step S1). The current position and orientation of the vehicle body <NUM> can be acquired from the positioning system <NUM>.

The processing device <NUM> then calculates the current position of each of the tires <NUM> to <NUM> (step S2). Since the relative position of each of the tires <NUM> to <NUM> with respect to the vehicle body <NUM> is known, the current position of each of the tires <NUM> to <NUM> can be calculated based on the current position and orientation of the vehicle body <NUM>.

The processing device <NUM> then determines the travel speed (hereinafter referred to as "return travel speed") when the vehicle <NUM> returns to the travel route (step S3). The return travel speed is determined based on the travel speed of the vehicle <NUM> during execution of a route travel program and conditions such as the weight of the load on the vehicle body <NUM>. For example, if the load on the vehicle body <NUM> is light, the return travel speed may be set to be high. Alternatively, the return travel speed may be constant. Step S3 can be omitted in this case.

The processing device <NUM> then determines a reference distance (step S4). The reference distance is determined depending on the return travel speed determined in step S3. In this embodiment, the reference distance is determined to be longer when the return travel speed is higher, and shorter when the return travel speed is lower. The relationship between the return travel speed and the reference distance is, however, not limited to such.

The processing device <NUM> then determines the return position (step S5). In this embodiment, the return position is determined based on the reference distance determined in step S4. Specifically, as illustrated in <FIG>, position B that is on travel route R and is reference distance L away from the current position A of the vehicle <NUM> is determined as the return position. The return position B is located ahead of the vehicle <NUM> in the direction of travel of the travel route R.

The processing device <NUM> then calculates the target position of the first tire <NUM> and the target position of the second tire <NUM> (step S6). As illustrated in <FIG>, the target position B <NUM> of the first tire <NUM> is such a position of the first tire <NUM> that allows the vehicle <NUM> to travel on the travel route R when located at the return position B. Likewise, the target position B2 of the second tire <NUM> is such a position of the second tire <NUM> that allows the vehicle <NUM> to travel on the travel route R when located at the return position B.

For example, as illustrated in <FIG>, in the case where the travel route R is straight, the respective positions of the first tire <NUM> and the second tire <NUM> when the vehicle body <NUM> is located at the return position B and the longitudinal direction (front-back direction) of the vehicle body <NUM> is parallel to the travel route R are the target position B1 of the first tire <NUM> and the target position B2 of the second tire <NUM>.

For example, as illustrated in <FIG>, in the case where the travel route R is curved, the respective positions of the first tire <NUM> and the second tire <NUM> when the vehicle body <NUM> is located at the return position B and the longitudinal direction of the vehicle body <NUM> is parallel to the tangent to the travel route R are the target position B1 of the first tire <NUM> and the target position B2 of the second tire <NUM>.

The processing device <NUM> then finds a common central point (step S7). As illustrated in <FIG>, the common central point X is a point at which the distance from the current position A1 of the first tire <NUM> and the distance from the target position B1 of the first tire <NUM> are the same and the distance from the current position A2 of the second tire <NUM> and the distance from the target position B2 of the second tire <NUM> are the same. That is, the common central point X is the intersection point of the perpendicular bisector of the straight line connecting the current position A1 and the target position B1 of the first tire <NUM> and the perpendicular bisector of the straight line connecting the current position A2 and the target position B2 of the second tire <NUM>.

The processing device <NUM> then sets the steering angle of each of the tires <NUM> to <NUM> (step S8). Specifically, as illustrated in <FIG>, the steering angle of the first tire <NUM> is set so that the first tire <NUM> will be oriented in the direction of the tangent to a clearance circle C1 whose center is the common central point X obtained in step S7 and whose radius is the distance from the current position A1 of the first tire <NUM> to the common central point X. Likewise, the steering angle of each of the tires <NUM> to <NUM> other than the first tire <NUM> is set so that the tire will be oriented in the direction of the tangent to a corresponding one of clearance circles C2 to C4 whose center is the common central point X and whose radius is the distance from the current position of the tire to the common central point X.

The processing device <NUM> then rotates the tires <NUM> to <NUM> toward the travel route of the vehicle <NUM> (step S9). The processing device <NUM> may rotate each of the tires <NUM> to <NUM> at the same rotation speed, or at a different rotation speed depending on the distance from the current position to the target position of the tire. For example, a tire for which the distance from the current position to the target position is long may be rotated at a higher rotation speed than a tire for which the distance from the current position to the target position is short.

After step S9, the processing device <NUM> returns to step S1, and repeats steps S1 to S9 until the vehicle <NUM> returns to the travel route. Thus, the processing device <NUM> constantly updates the return position (step S5) and constantly updates the set steering angle of each of the tires <NUM> to <NUM> according to the updated return position (step S8) until the vehicle <NUM> that has deviated from the travel route returns to the travel route. Steps S1 to S8 may be executed while rotating the tires <NUM> to <NUM> (i.e. during execution of step S9). In such a case, as the vehicle <NUM> approaches the travel route, the steering angle of each of the tires <NUM> to <NUM> is corrected so that the tire will be oriented in the direction along the travel route. Consequently, upon reaching the return position, the vehicle <NUM> can immediately travel on the travel route.

Alternatively, the set steering angle of each of the tires <NUM> to <NUM> may be maintained until the vehicle <NUM> returns to the travel route, without repeating steps S1 to S9. Even in this case, by adjusting the steering angle of each of the tires <NUM> to <NUM> so that the tire will be oriented in the direction of travel of the travel route after the vehicle <NUM> reaches the return position, the vehicle <NUM> can immediately travel on the travel route. That is, the vehicle <NUM> can quickly return to the travel route.

With the foregoing route return program, the common central point is a point at which the distance from the current position of the first tire <NUM> and the distance from the target position of the first tire <NUM> are the same and the distance from the current position of the second tire <NUM> and the distance from the target position of the second tire <NUM> are the same (step S7). Alternatively, the common central point may be determined in consideration of the slippage, etc. of each of the tires <NUM> to <NUM>. That is, the common central point may be a point at which the difference between the distance from the current position of the first tire <NUM> and the distance from the target position of the first tire <NUM> is within a predetermined range and the difference between the distance from the current position of the second tire <NUM> and the distance from the target position of the second tire <NUM> is within a predetermined range.

With the foregoing route return program, the steering angle of each of the tires <NUM> to <NUM> is set so that the tire will be oriented in the direction of the tangent to a clearance circle whose center is the common central point and whose radius is the distance from the tire to the common central point (Step S8). Alternatively, the steering angle of each of the tires <NUM> to <NUM> may be set so that the tire will be oriented in a direction whose angle difference from the direction of the tangent to the clearance circle whose center is the common central point and whose radius is the distance from the tire to the common central point is within a predetermined range.

With the foregoing route return program, the common central point is determined based on the current position and the target position of each of two tires, i.e. the first tire <NUM> and the second tire <NUM> (step S7, <FIG>). Alternatively, the common central point may be determined based on the current position and the target position of each of three or more tires.

As described above, the vehicle according to this embodiment is a vehicle configured to travel on a preset travel route, comprising: a plurality of tires including a first tire and a second tire, and each configured to be set at a different steering angle; and a processing device configured to set a steering angle of each of the plurality of tires, wherein the processing device is configured to: when the vehicle deviates from the travel route and returns to the travel route, determine a return position on the travel route, and calculate a target position of the first tire and a target position of the second tire that allow the vehicle to travel on the travel route when located at the return position; find a common central point at which a difference between a distance from a current position of the first tire and a distance from the target position of the first tire is within a predetermined range and a difference between a distance from a current position of the second tire and a distance from the target position of the second tire is within a predetermined range; and set the steering angle of each of the plurality of tires so that the tire will be oriented in a direction of a tangent to a clearance circle whose center is the common central point and whose radius is a distance to the common central point or oriented in a direction whose angle difference from the direction of the tangent is within a predetermined range.

Thus, the vehicle according to this embodiment can quickly locate each tire at such a position that allows the vehicle to travel on the travel route, and therefore can return to the travel route efficiently.

In the vehicle according to this embodiment, when determining the return position, the processing device is configured to determine a reference distance depending on a travel speed when the vehicle returns to the travel route, and determine the return position so that a distance from a current position of the vehicle to the return position will be the reference distance.

Thus, the vehicle according to this embodiment can appropriately determine the return position depending on the travel speed.

In the vehicle according to this embodiment, the processing device is configured to constantly update the return position and constantly update the set steering angle of each of the plurality of tires according to the updated return position until the vehicle that has deviated from the travel route returns to the travel route.

Claim 1:
A vehicle (<NUM>) configured to travel on a preset travel route, the vehicle comprising:
a plurality of tires (<NUM> - <NUM>) including a first tire (<NUM>) and a second tire (<NUM>), and each configured to be set at a different steering angle; and
a processing device (<NUM>) configured to set a steering angle of each of the plurality of tires (<NUM> - <NUM>),
wherein the processing device (<NUM>) is configured to:
when the vehicle (<NUM>) deviates from the travel route and returns to the travel route, determine a return position on the travel route, and calculate a target position of the first tire (<NUM>) and a target position of the second tire (<NUM>) that allow the vehicle (<NUM>) to travel on the travel route when located at the return position;
find a common central point at which a difference between a distance from a current position of the first tire (<NUM>) and a distance from the target position of the first tire (<NUM>) is within a predetermined range and a difference between a distance from a current position of the second tire (<NUM>) and a distance from the target position of the second tire (<NUM>) is within a predetermined range; and
set the steering angle of each of the plurality of tires (<NUM> - <NUM>) so that the tire will be oriented in a direction of a tangent to a clearance circle whose center is the common central point and whose radius is a distance to the common central point or oriented in a direction whose angle difference from the direction of the tangent is within a predetermined range.