JP7656255B2 - Parking assistance device and method - Google Patents

Description

The present invention relates to a parking assistance device and method that assists in parking a vehicle.

Conventionally, there is known a technology (i.e., automatic parking) that controls a vehicle to automatically move to a specified space and stop it there to assist in parking the vehicle. For example, Patent Document 1 discloses a technology in which, when a vehicle comes into contact with a step on the road surface while moving toward a parking space, if the wheel that hits the step is a driven wheel (non-driven wheel), the vehicle is temporarily moved in the opposite direction to the direction in which it should travel, allowing the vehicle to gain a running start and overcome the step.

JP 2020-066329 A

When assisting a vehicle in parking, if there is a step on the road surface, it is desirable to provide parking assistance that ensures the vehicle can quickly overcome relatively low steps, while prohibiting the vehicle from overtaking relatively high steps. The latter is done to prevent the vehicle from going over a wheel stopper or the like. One method for achieving this is to limit the drive torque applied when the vehicle attempts to overcome a step to less than a predetermined limit torque that corresponds to the height of the step that prohibits the vehicle from overtaking (e.g., 70 to 80 mm or more). In other words, a limit torque is set based on the height of the step that prohibits overtaking, and the drive torque is controlled so that the drive torque applied when the vehicle attempts to overcome the step does not exceed this limit torque.

The limit torque applied to the drive torque when going over such a step is desirably set to an appropriate value from the viewpoint of ensuring both the rapid going over of relatively low steps and the prohibition of going over relatively high steps; in other words, it is undesirable to set it to a value that is too large or too small. In particular, the inventors thought that in order to set the limit torque to an appropriate value, the limit torque applied should be changed depending on the wheel (i.e., the drive wheel or the driven wheel) that comes into contact with the step. This is because the drive torque required to go over the step, even if the step is of the same height, differs depending on whether the wheel that goes over the step is a drive wheel or a driven wheel. This difference is thought to be caused by, for example, the load on the drive wheel and the load on the driven wheel, i.e., the front wheel load and the rear wheel load (depending on the front-to-rear weight distribution of the vehicle).

The above-mentioned Patent Document 1 only describes a technology that allows a vehicle to safely overcome a step, but does not state anything about prohibiting a vehicle from overcoming a step.

The present invention has been made to solve the above-mentioned problems, and aims to provide a parking assistance device and method that can, when a wheel comes into contact with a step on the road surface during parking assistance, accurately prohibit the vehicle from climbing over a relatively high step depending on the wheel that comes into contact with the step.

In order to achieve the above object, the present invention is a parking assistance device, comprising: a control unit configured to control the drive torque and braking torque applied to the vehicle to move and stop the vehicle in order to assist in parking the vehicle in a specified space; and a determination unit configured to determine whether the wheel in contact with the step is a drive wheel or a driven wheel when the wheel of the vehicle comes into contact with a step on the road surface while the parking assistance is being provided by the control unit. The control unit is configured to apply a drive torque to the vehicle when the wheel of the vehicle comes into contact with a step on the road surface so that the vehicle overcomes the step, while limiting the drive torque applied to the vehicle to less than a predetermined limit torque so as to prohibit the vehicle from climbing over a step of a height equal to or greater than the limit, and to change the limit torque applied to the drive torque applied to the vehicle depending on whether the wheel in contact with the step is determined to be a drive wheel or a driven wheel by the determination unit.

According to the present invention configured in this way, the control unit changes the limit torque applied to the drive torque applied to the vehicle to make the vehicle overcome the step, depending on whether the wheel in contact with the step is determined by the determination unit to be a drive wheel or a driven wheel. This makes it possible to accurately prohibit the vehicle from overcoming steps of the same limit height or more, regardless of whether the wheel in contact with the step is a drive wheel or a driven wheel. In other words, it is possible to accurately prevent the height of the step that is prohibited from being overtaken in the control from changing depending on whether the wheel in contact with the step is a drive wheel or a driven wheel. Therefore, according to the present invention, when a wheel comes into contact with a step on the road surface during parking assistance, it is possible to accurately prohibit the vehicle from overtaking a step (such as a wheel stopper) of the limit height or more, depending on the wheel in contact with the step.

In the present invention, the control unit is preferably configured to gradually increase the driving torque applied to the vehicle when the wheels of the vehicle come into contact with a step on the road surface so that the vehicle overcomes the step, and when this driving torque reaches a limit torque, to reduce the driving torque applied to the vehicle to prohibit the vehicle from climbing over the step.
According to the present invention configured in this manner, it is possible to accurately balance between allowing a vehicle to quickly overcome a step that is less than the height limit and prohibiting a vehicle from overcoming a step that is equal to or greater than the height limit.

In the present invention, the control unit is preferably configured to change the amount or the speed at which the driving torque is reduced when the driving torque reaches the limit torque, depending on whether the judgment unit judges that the wheel contacting the step is a driving wheel or a driven wheel.
Because the load on the drive wheels and the load on the driven wheels differ depending on the front-rear weight distribution of the vehicle, the ease of passing over the step (possibility of passing over the step) after the drive torque reaches the limit torque changes depending on whether the wheel that comes into contact with the step is a drive wheel or a driven wheel. Therefore, in the present invention, the amount or speed at which the drive torque is reduced after the drive torque reaches the limit torque is changed depending on whether the wheel that comes into contact with the step is a drive wheel or a driven wheel. This makes it possible to reliably prevent the vehicle from passing over a step that is equal to or higher than the limit height.

In the present invention, the limit torque is preferably set based on the radius of the wheels of the vehicle, the limit height of a step that the vehicle is prohibited from crossing, and the front wheel load and rear wheel load of the vehicle.
According to the present invention configured in this manner, it is possible to accurately set the limit torque for the driving wheels and the limit torque for the driven wheels that should be applied to prevent the vehicle from climbing over a step that is equal to or higher than the limit height.

In the present invention, the judgment unit is preferably configured to acquire the wheel speed of each of a plurality of wheels possessed by the vehicle, and to determine whether the wheel contacting the step is a driving wheel or a driven wheel based on the change in the wheel speed of each of the plurality of wheels acquired when the wheel of the vehicle contacts a step on the road surface.
According to the present invention configured as above, it is possible to accurately determine which wheel is in contact with the step.

In another aspect, in order to achieve the above-mentioned object, the present invention is a parking assistance method comprising a control step of controlling a driving torque and a braking torque applied to a vehicle to move and stop the vehicle in order to assist in parking the vehicle in a specified space, and a judgment step of judging whether a wheel of the vehicle contacts a step on a road surface while parking assistance is being performed by the control step, the wheel contacting the step is a driving wheel or a driven wheel, the control step is characterized in that, when a wheel of the vehicle contacts a step on the road surface, a driving torque is applied to the vehicle so that the vehicle overcomes the step, while limiting the driving torque applied to the vehicle to less than a predetermined limit torque to prohibit the vehicle from climbing over a step that is equal to or greater than a limit height, and changing the limit torque applied to the driving torque applied to the vehicle depending on whether the wheel contacting the step is determined to be a driving wheel or a driven wheel by the judgment step.
With the present invention configured in this manner, when a wheel comes into contact with a step on the road surface during parking assistance, the vehicle can be accurately prohibited from climbing over a step (such as a wheel stopper) that is higher than the restricted height, depending on the wheel that comes into contact with the step.

The parking assistance device and method according to the present invention can appropriately prohibit the vehicle from climbing over a relatively high step when a wheel comes into contact with a step on the road surface during parking assistance, depending on the wheel that comes into contact with the step.

1 is a block diagram showing a parking assistance system to which a parking assistance device according to an embodiment of the present invention is applied. FIG. 2 is an explanatory diagram of a basic operation of parking assistance according to an embodiment of the present invention. 5 is a time chart showing step-over control executed during parking assistance to allow a vehicle to overcome a step having a height less than a limit in an embodiment of the present invention. 5 is a time chart showing step climbing control executed to prohibit the vehicle from climbing over a step having a height equal to or greater than a limit during parking assistance in an embodiment of the present invention. 7 is an explanatory diagram of a method for setting a limit torque that is applied when a wheel that comes into contact with a step is a drive wheel in the embodiment of the present invention. FIG. 7 is an explanatory diagram of a method for setting a limit torque that is applied when a wheel that comes into contact with a step is a driven wheel in the embodiment of the present invention. FIG. 13 is an explanatory diagram of a method for setting a limit torque that is applied when a wheel that comes into contact with a step is a driven wheel in a modified embodiment of the present invention. FIG. 4 is a flowchart showing an overall process of step clearance control according to an embodiment of the present invention. 10 is a flowchart showing a step handling process according to an embodiment of the present invention. 13 is a flowchart showing an overall process of step clearance control according to a modified example of the embodiment of the present invention.

The parking assistance device and method according to an embodiment of the present invention will be described below with reference to the attached drawings.

[Basic configuration]
First, the basic configuration of the parking assistance device according to the present embodiment will be described with reference to Figures 1 and 2. Figure 1 is a block diagram showing a parking assistance system to which the parking assistance device according to the present embodiment is applied, and Figure 2 is an explanatory diagram of the basic operation of the parking assistance according to the present embodiment.

The parking assistance system 100 shown in FIG. 1 is mounted on the vehicle 1, and as shown in FIG. 2, operates to perform parking assistance (automatic parking) for automatically moving the vehicle 1 to a specified space SP and stopping it. Basically, the parking assistance system 100 performs such parking assistance in response to the operation of the communication terminal 5 by the user U outside the vehicle. In this case, the user U operates the communication terminal 5 to instruct the start of parking assistance (i.e., the start of movement of the vehicle 1), the stop of movement of the vehicle 1, and the restart of movement of the vehicle 1. The communication terminal 5 is, for example, a key fob that locks and unlocks the doors of the vehicle 1, and the user U operates one or more switches (parking switches) related to parking assistance provided on the key fob. Note that the user U is not limited to performing operations for parking assistance using the communication terminal 5 from outside the vehicle in this way, and in another example, the user U may perform operations for parking assistance using a specified switch provided in the vehicle cabin (the communication terminal 5 may be used inside the vehicle).

1, the parking assistance system 100 mainly includes a camera 21, a sonar 22, a wheel speed sensor 23, an acceleration sensor 24, a communication unit 25, a controller 10, an engine control system 31, a brake control system 32, and a steering control system 33. In this parking assistance system 100, the controller 10 outputs control signals to the engine control system 31, the brake control system 32, and the steering control system 33 based on signals input from the camera 21, the sonar 22, the wheel speed sensor 23, the acceleration sensor 24, and the communication unit 25, thereby automatically controlling the movement, steering, and stopping of the vehicle 1, thereby providing assistance in parking the vehicle 1 in the space SP.

The camera 21 includes multiple cameras (front and rear cameras) that capture images in front of and behind the vehicle 1. The camera 21 is also installed facing diagonally downward so that it can capture images of the range including the road surface in front of and behind the vehicle 1. The camera 21 outputs an image signal corresponding to the captured image to the controller 10.

Sonar 22 detects the presence or absence of an object within a predetermined range around vehicle 1 (e.g., relatively close to vehicle 1), and detects the distance from vehicle 1 to the object. For example, sonar 22 is an active ultrasonic sonar, and is disposed at each of the four corners of vehicle 1. Sonar 22 outputs a detection signal related to an object present around vehicle 1 to controller 10. Note that instead of or in addition to sonar 22, a laser (millimeter wave radar or laser radar) may be used to detect the presence or absence of an object around the vehicle and the distance to the object.

The wheel speed sensor 23 detects the rotational speed (wheel speed) of each of the four wheels of the vehicle 1 and outputs the detection signal to the controller 10. For example, the wheel speed sensor 23 includes a rotary encoder and detects the wheel speed from the amount of rotational displacement of the wheel (axle) per unit time. The acceleration sensor 24 detects the acceleration of the vehicle 1 and outputs the detection signal to the controller 10.

The communication unit 25 is a device that communicates with the communication terminal 5 described above. The communication unit 25 receives a signal corresponding to an operation of the user U on the communication terminal 5, in particular a signal (instruction signal) indicating an instruction regarding parking assistance from the user U, from the communication terminal 5. As described above, this instruction signal indicates the start of parking assistance (i.e., the start of movement of the vehicle 1), the stopping of the movement of the vehicle 1, the resumption of movement of the vehicle 1, etc. The communication unit 25 outputs the instruction signal received from the communication terminal 5 to the controller 10.

The engine control system 31 controls the engine (not shown) of the vehicle 1. The engine control system 31 is a component that can adjust the driving torque (engine torque) of the engine, and includes, for example, a spark plug, a fuel injection valve, a throttle valve, and a variable valve mechanism that changes the opening and closing timing of the intake and exhaust valves. When a control signal for accelerating or decelerating the vehicle 1 is input from the controller 10, the engine control system 31 operates to adjust the driving torque of the engine in response to this control signal.

The brake control system 32 controls the brake device (not shown) of the vehicle 1. The brake control system 32 is a component capable of adjusting the braking torque of the brake device, and includes, for example, a hydraulic pump and a valve unit. When a control signal for decelerating the vehicle 1 is input from the controller 10, the brake control system 32 operates to adjust the braking torque of the brake device in response to this control signal. Note that, in addition to the above-mentioned brake devices, the objects to be controlled by the brake control system 32 may also include so-called parking brake devices.

The steering control system 33 controls the steering device (not shown) of the vehicle 1. The steering control system 33 is a component that can adjust the steering angle of the steering device, and includes, for example, an electric motor of an electric power steering system. When a control signal for changing the traveling direction of the vehicle 1 is input from the controller 10, the steering control system 33 operates to change the steering direction by the steering device in response to this control signal.

The controller 10 is composed of a computer equipped with one or more microprocessors 10a (typically a CPU), memory 10b (ROM, RAM, etc.) that stores various programs, and input/output devices. The controller 10 executes various calculations based on signals input from the camera 21, sonar 22, wheel speed sensor 23, acceleration sensor 24, and communication unit 25, and outputs control signals to the engine control system 31, brake control system 32, and steering control system 33 to appropriately operate the engine, brake device, and steering device, respectively.

In this embodiment, the controller 10 corresponds to an example of the "parking assistance device" of the present invention, and functions as a "control unit" and a "determination unit". That is, the controller 10 is configured to control the driving torque and braking torque applied to the vehicle 1 to move and stop the vehicle 1 in order to assist in parking the vehicle 1 in a specified space SP. Specifically, the controller 10 first identifies the specified space SP in which the vehicle 1 should be parked based on signals from the camera 21, sonar 22, etc. This space SP not only means a relatively wide range in which the vehicle 1 can be parked, but also means here the position (stopping position) within such a range where the vehicle 1 will actually be parked (the same applies below).

The controller 10 then controls the engine control system 31 to apply a driving torque to the vehicle 1 while controlling the steering control system 33 to appropriately adjust the traveling direction of the vehicle 1 in order to move the vehicle 1 to the specified space SP. In this case, the controller 10 controls the brake control system 32 to apply a braking torque to the vehicle 1 in addition to the driving torque. More specifically, the controller 10 controls the engine control system 31 to maintain the driving torque applied to the vehicle 1 constant, while controlling the brake control system 32 to appropriately adjust the braking torque so that the vehicle 1 moves at a predetermined target vehicle speed. In this way, a stable response can be ensured by controlling a braking torque with a small response delay so as to realize the target vehicle speed, and the control configuration can be simplified by limiting the control target to the braking torque. After this, when the movement of the vehicle 1 to the space SP is completed, the controller 10 controls the brake control system 32 to stop the vehicle 1.

In addition, in this embodiment, when the wheels of the vehicle 1 come into contact with a step on the road surface while the controller 10 is performing the parking assistance as described above, the controller 10 applies a driving torque to the vehicle 1 so that the vehicle 1 overcomes the step, while controlling the engine control system 31 to limit the driving torque applied to the vehicle 1 to less than a predetermined limit torque so as to prohibit the vehicle 1 from climbing over a step of a height equal to or greater than a limit (e.g., 70 to 80 mm or more). Specifically, the controller 10 gradually increases the driving torque applied to the vehicle 1 so that the vehicle 1 overcomes the step, and when the driving torque reaches the limit torque, the controller 10 quickly reduces the driving torque applied to the vehicle 1 so as to prohibit the vehicle 1 from climbing over the step.

On the other hand, when the wheels of the vehicle 1 come into contact with a step on the road surface, the controller 10 determines whether the wheel that comes into contact with the step is a driving wheel or a driven wheel. For example, the controller 10 determines whether the wheel that comes into contact with the step is a driving wheel or a driven wheel based on the change in the wheel speed of each of the four wheels (typically, the timing of the decrease in the wheel speed of each of the four wheels, etc.) acquired by the wheel speed sensor 23 when the wheel comes into contact with the step. Then, the controller 10 changes the limit torque applied to the driving torque applied when the vehicle 1 goes over the step as described above, depending on whether the wheel that comes into contact with the step is a driving wheel or a driven wheel. This is because the driving torque required to go over the step differs depending on whether the wheel that goes over the step is a driving wheel or a driven wheel, even if the step is the same height. This is caused by, for example, the load on the driving wheel and the load on the driven wheel, that is, the front wheel load and the rear wheel load (corresponding to the front-rear weight distribution of the vehicle 1).

[Step Overrun Control]
Next, we will explain the control that is performed in this embodiment when the wheels of the vehicle 1 come into contact with a step on the road surface during parking assistance, specifically, the control that allows the vehicle 1 to overcome steps that are less than the limit height while prohibiting the vehicle 1 from overcoming steps that are equal to or greater than the limit height (hereinafter referred to as "step overcoming control" as appropriate).

Figure 3 is a time chart showing an example of step overrunning control executed in this embodiment to allow the vehicle 1 to overcome a step less than the height limit during parking assistance. From top to bottom, Figure 3 shows the time change in vehicle speed (the solid line represents the target vehicle speed, and the dashed line represents the actual vehicle speed), the time change in driving torque, and the time change in braking torque. Note that the driving torque and braking torque indicate the target driving torque and target braking torque to be applied to the vehicle 1 as instructed by the controller 10.

First, at time t11, the user U operates the communication terminal 5 to instruct the start of parking assistance (i.e., the start of movement of the vehicle 1). At this time, the controller 10 increases the set target vehicle speed, and in response to the increase in the target vehicle speed, starts applying a constant driving torque and reduces the applied braking torque. However, in this example, even if the driving torque is applied and the braking torque is reduced, the wheels of the vehicle 1 are in contact with a step on the road surface, so the actual vehicle speed remains 0, that is, the vehicle 1 remains stopped. In this case, at time t12, the controller 10 temporarily reduces the driving torque so that the vehicle 1 continues to be stopped until there is a further instruction from the user U. After that, at time t13, the user U performs a predetermined operation on the communication terminal 5 to instruct the vehicle 1 to resume movement (i.e., to overcome the step). For example, the user U performs another operation on the communication terminal 5 (pressing the button again) or an operation on the communication terminal 5 that continues for a predetermined time (long press operation).

From time t13, the controller 10 gradually increases the driving torque applied to the vehicle 1 so that the vehicle 1 overcomes the step. In this case, the controller 10 maintains the braking torque at the torque reduced as described above and gradually increases the driving torque applied so that the vehicle 1 overcomes the step. As a result, the vehicle 1 moves little by little, and a certain degree of actual vehicle speed is generated. Then, around time t14, the vehicle 1 begins to overcome (start to climb) the step, and the actual vehicle speed increases. From time t15 after time t14, the controller 10 quickly reduces the applied driving torque and temporarily increases the limit torque in order to suppress an increase in the actual vehicle speed after the vehicle 1 overcomes the step.

In the example shown in FIG. 3, the driving torque applied to the vehicle 1 to get over the step does not exceed the above-mentioned limit torque Thr (a limit value applied to the driving torque to prohibit the vehicle 1 from getting over a step that is equal to or greater than the limit height). In other words, the driving torque that is gradually increased so that the vehicle 1 gets over the step does not reach the limit torque Thr before the vehicle 1 gets over the step. Therefore, in the example shown in FIG. 3, the controller 10 does not limit the driving torque applied to the vehicle 1 to get over the step.

Next, FIG. 4 is a time chart showing an example of step-crossing control executed in this embodiment to prohibit the vehicle 1 from crossing a step (e.g., a wheel stopper) that is equal to or greater than a limit height during parking assistance. From top to bottom, FIG. 4 also shows the time change in vehicle speed (the solid line represents the target vehicle speed, and the dashed line represents the actual vehicle speed), the time change in driving torque, and the time change in braking torque. Note that the driving torque and braking torque indicate the target driving torque and target braking torque.

The situation up to time t23 is the same as in FIG. 3, so a description thereof will be omitted here. In the example of FIG. 4, from time t23, the controller 10 gradually increases the driving torque applied to the vehicle 1 so that the vehicle 1 overcomes the step, and at time t24, this driving torque reaches the limit torque Thr. Therefore, at time t24, the controller 10 quickly reduces the driving torque applied to the vehicle 1. As a result, the vehicle 1 does not overcome the step, that is, the vehicle 1 is prohibited from overcoming the step. In this case, the vehicle 1 descends the step that it had been climbing partway up, generating a negative actual vehicle speed (the actual vehicle speed when traveling in the opposite direction to the direction in which it should travel).

Next, referring to Figures 5 and 6, a specific example of a method for setting the limit torque Thr that is applied to the drive torque when going over a step will be described. This limit torque Thr is a limit value that is applied to the drive torque applied for going over a step in order to prohibit the vehicle 1 from going over a step that is equal to or greater than the limit height. As described above, in this embodiment, the limit torque Thr that is applied is changed depending on whether the wheel that comes into contact with the step is a drive wheel (e.g., a front wheel) or a driven wheel (e.g., a rear wheel).

First, Fig. 5 is an explanatory diagram of a method for setting the limit torque Thr applied in this embodiment when the wheel contacting the step is a driving wheel. Fig. 5 is a side view that typically shows the driving wheel 2 and the driven wheel 3 of the vehicle 1, and the step St contacting the driving wheel 2. First, the driving force _Ff of the driving wheel 2 is expressed as " _Ff = T/r" from the driving torque T applied to the driving wheel 2 and the tire radius r. Also, from the rear wheel load _mr and the acceleration _ax of the vehicle 1, the force Te _f acting on the shaft connecting the driving wheel 2 and the driven wheel 3 is " _{mr ax} = Te _f = 0" when the forces in the front-rear direction are balanced.

5, if angle θ is defined between the contact point between the drive wheel 2 and the tip of the step St and the center point of the drive wheel 2, this angle θ can be expressed as "θ=sin ^-1 {(r-h)/r}" from the tire radius r and the height h of the step St. If it is considered that a drive torque reaction force acts on the center point of the drive wheel 2, the balance of the moment around the center point of the drive wheel 2 can be expressed as "{m _f g cos θ + Te _f cos(π/2-θ)}r = F _f r" using the above angle θ and the front wheel load m _f , etc.

When this formula is rearranged, since " _Tef = 0" as described above, " _Ff = _mfgcosθ " is obtained. Therefore, the driving torque T applied to the driving wheel 2 is "T = _mfgrcosθ " from "T = _Ffr ". This driving torque T is the driving torque when the driving wheel 2 starts to climb the step St, that is, the driving torque required for the driving wheel 2 to overcome the step St. Since "θ" in the formula is determined by the height h of the step St, the driving torque T also becomes a value according to the height h of the step St, that is, the driving torque required for the driving wheel 2 to overcome the step St of height h. Therefore, by determining the height h (restricted height) at which the vehicle 1 should be prohibited from climbing over the step, and then calculating the driving torque T for the step St of this height h, the restricted torque Thr to be applied when the driving wheel 2 tries to climb over the step St can be set from this driving torque T. Specifically, the determined drive torque T or a value slightly smaller than the drive torque T may be set as the limit torque Thr.

Next, Fig. 6 is an explanatory diagram of a method for setting the limit torque Thr applied in this embodiment when the wheel contacting the step is a driven wheel. Fig. 6 is also a side view that shows a schematic representation of the drive wheel 2 and driven wheel 3 of the vehicle 1, and the step St contacting the drive wheel 2. First, the drive force _Ff of the drive wheel 2 is " _Ff = T/r" as in Fig. 5. Furthermore, the force Te _f acting on the shaft connecting the drive wheel 2 and the driven wheel 3 is " _mf a _x = _Ff - Te _f = 0" due to the balance of the drive wheel 2 in the front-rear direction, that is, " _Ff = Te _f ".

The balance of the moment around the center point of the driven wheel 3 is expressed as " _mr grcosθ=Tef _r sinθ". Therefore, " _Tef = _mr gcosθ/sinθ". Therefore, the drive torque T applied to the driving wheel 2 is "T= _Ff r= _Tef r= _mr grcosθ/sinθ". This drive torque T is the drive torque when the driven wheel 3 starts to climb the step St, that is, the drive torque required for the driven wheel 3 to overcome the step St (different from the above-mentioned formula "T= _mf grcosθ" of the drive torque T required for the driving wheel 2 to overcome the step St). Since "θ" in the formula is determined by the height h of the step St, the drive torque T also has a value according to the height h of the step St, that is, it is the drive torque required for the driven wheel 3 to overcome the step St of height h. Therefore, by determining a height h (restricted height) at which the vehicle 1 should be prohibited from climbing over a step, and then calculating the drive torque T for the step St of this height h, it is possible to set the limit torque Thr to be applied when the driven wheels 3 attempt to climb over the step St from this drive torque T. Specifically, the calculated drive torque T or a value slightly smaller than the drive torque T may be set as the limit torque Thr.

Here, an example is taken in which the front wheel load _mf is 927 kg, the rear wheel load _mr is 613 kg, the tire radius r is 0.3425 m, and the limit height h is 70 mm. In this case, the angle θ is about 0.92. The driving torque T required for the driving wheel 2 to overcome the step St of the limit height h is about 1886 Nm from the above formula "T = _mf grcosθ". The driving torque T required for the driven wheel 3 to overcome the step St of the limit height h is about 1566 Nm from the above formula "T = _mr grcosθ/sinθ". Therefore, the limit torque Thr applied when the driving wheel 2 tries to overcome the step St may be set to 1886 Nm or a value slightly smaller than this, and the limit torque Thr applied when the driven wheel 3 tries to overcome the step St may be set to 1566 Nm or a value slightly smaller than this.

Next, referring to Fig. 7, a modified example of the method of setting the limit torque Thr applied when the wheel contacting the step is the driven wheel 3 will be described. This modified example is applied when, for example, the driving wheel 2 has already overcome the step St by driving by the user U (driver), specifically, the driving wheel 2 is on the step St extending in the front-rear direction, and the driven wheel 3 then attempts to overcome the step St during parking assistance. First, the driving force F _f of the driving wheel 2 is "F _f = T/r" as in Figs. 5 and 6. Furthermore, the force Te _f acting on the shaft connecting the driving wheel 2 and the driven wheel 3 is "m _f a _x = F _f - Te _f cos α = 0" due to the balance of the driving wheel 2 in the front-rear direction when the inclination α of this shaft is used, that is, "Te _f = F _f / cos α". If the wheelbase is "L", then the inclination α of the axis is "α=sin ^-1 (h/L)".

The balance of the moment around the center point of the driven wheel 3 is expressed as " _mr grcosθ=Tef _r sin(θ+α)". Therefore, " _Tef = _mr gcosθ/sin(θ+α)". Therefore, the drive torque T applied to the driving wheel 2 is "T= _Ffr =Tef _rcosα = _mr grcosθcosα/sin(θ+α)". This drive torque T is the drive torque required for the driven wheel 3 to overcome the step St when the driving wheel 2 is on the step St. Since "θ" and "α" in the formula are determined by the height h of the step St, the drive torque T also has a value according to the height h of the step St, that is, it is the drive torque required for the driven wheel 3 to overcome the step St of height h. Therefore, by determining a height h (restricted height) at which the vehicle 1 should be prohibited from climbing over a step, and then calculating the drive torque T for the step St of this height h, it is possible to set the limit torque Thr to be applied when the driven wheels 3 attempt to climb over the step St from this drive torque T. Specifically, the calculated drive torque T or a value slightly smaller than the drive torque T may be set as the limit torque Thr.

Here, let us take an example in which the front wheel load _mf is 927 kg, the rear wheel load _mr is 613 kg, the tire radius r is 0.3425 m, the wheelbase L is 2.75 m, and the limit height h is 70 mm. In this case, the angle θ is about 0.92, and the inclination α is about 0.0255. When the driving wheel 2 is already on the step St, the driving torque T required for the driven wheel 3 to get over the step St of the limit height h is about 1536 Nm from the above formula "T = _mr grcosθcosα/sin(θ+α)". Therefore, the limit torque Thr applied when the driven wheel 3 tries to get over the step St may be set to 1536 Nm or a value slightly smaller than this.

Note that the method for setting the limit torque Thr described in Figures 5 to 7 is one example, and the limit torque Thr may be set using other methods. In another example, the limit torque Thr may be set taking into account the spring force and dent when the wheel contacts a step. In yet another example, the limit torque Thr may be set taking into account the gradient of the road surface (road surface gradient) on which the step exists. In this example, the limit torque Thr may be set to be larger on an upward gradient than on a flat road, and smaller on a downward gradient than on a flat road. In yet another example, the limit torque Thr may be set taking into account wheel air pressure information. This is because the wheel stiffness and amount of distortion change depending on the wheel air pressure, and these affect the vehicle 1's ability to overcome steps.

[Control Flow]
Next, a process flow (control flow) relating to step overcoming control according to this embodiment will be described with reference to FIG. 8 and FIG.

Figure 8 is a flowchart showing the overall process of the step-over-running control according to this embodiment. In particular, this overall process of the step-over-running control is started when the user U operates the communication terminal 5 to move the vehicle 1 in a state where the wheels of the vehicle 1 are already in contact with a step (more specifically, in a state where the vehicle 1 is in contact with a step and cannot move). At the start of this process, the controller 10 performs control to appropriately adjust the braking torque so that the vehicle 1 moves at a predetermined target vehicle speed while maintaining a constant driving torque. On the other hand, Figure 9 is a flowchart showing specific processing (hereinafter referred to as "step-over-running processing") for dealing with steps on the road surface, which is performed in the overall process of the step-over-running control in Figure 8. The controller 10 (more specifically, the microprocessor 10a) reads out and executes a program stored in the memory 10b, thereby realizing the processing shown in Figures 8 and 9. In addition, these processing are repeatedly executed at a predetermined period.

First, when the overall process of the step-crossing control in FIG. 8 is started, in step S101, the controller 10 acquires various information necessary for step-crossing control. Specifically, the controller 10 acquires at least signals input from the camera 21, the sonar 22, the wheel speed sensor 23, the acceleration sensor 24, and the communication unit 25 (see FIG. 1).

Next, in step S102, the controller 10 determines the wheel that contacts the step (hereinafter referred to as the "step-contact wheel"), that is, determines (distinguishes) whether the step-contact wheel is a driving wheel 2 or a driven wheel 3. In one example, the controller 10 determines whether the step-contact wheel is a driving wheel 2 or a driven wheel 3 based on an image captured by the camera 21 that captures an area including the road surface in front of and behind the vehicle 1. In this example, if the front wheel is a driving wheel 2 and the rear wheel is a driven wheel 3 (this information is stored in the memory 10b or the like, and the controller 10 reads out and uses the information thus stored. The same applies below), when the image captured by the camera 21 that captures the front of the vehicle 1 includes a step, the controller 10 determines that the step-contact wheel is a driving wheel 2, while when the image captured by the camera 21 that captures the rear of the vehicle 1 includes a step, the controller 10 determines that the step-contact wheel is a driven wheel 3. In another example, instead of using the camera 21, or in addition to using the camera 21, the controller 10 uses the sonar 22 to determine whether the step-contacting wheel is the driving wheel 2 or the driven wheel 3 in the same manner as in the case of using the camera 21. That is, in the case where the front wheels are the driving wheels 2 and the rear wheels are the driven wheels 3, when a step is detected by the sonar 22 covering the front of the vehicle 1, the controller 10 determines that the step-contacting wheel is the driving wheel 2, while when a step is detected by the sonar 22 covering the rear of the vehicle 1, the controller 10 determines that the step-contacting wheel is the driven wheel 3. In yet another example, the controller 10 determines whether the step-contacting wheel is the driving wheel 2 or the driven wheel 3 based on the traveling direction of the vehicle 1 (either forward or backward, and basically a step exists ahead in this direction) instructed by the user U using the communication terminal 5. In this example, if the front wheels are driving wheels 2 and the rear wheels are driven wheels 3, when the user U instructs the vehicle 1 to move forward, the controller 10 determines that the step-contacting wheels are driving wheels 2, but when the user U instructs the vehicle 1 to move backward, the controller 10 determines that the step-contacting wheels are driven wheels 3.

Next, in step S103, in order to deal with the step on the road surface, specifically before performing the next step response process (step S104), the controller 10 sets the target vehicle speed, which is a reduced vehicle speed applied during normal driving in parking assistance, as the target vehicle speed to be applied during the step response process. Then, in step S104, the controller 10 performs the step response process shown in FIG. 9 (details will be described later).

Next, in step S105, the controller 10 determines whether the vehicle 1 has gone over a step by the step response process in step S104. Specifically, when the actual vehicle speed of the vehicle 1 corresponding to the wheel speed detected by the wheel speed sensor 23 becomes equal to or greater than a predetermined speed, the controller 10 determines that the vehicle 1 has gone over a step (step S105: Yes) and proceeds to step S106.

In step S106, since the vehicle 1 has overcome the step, the controller 10 starts normal driving control that is performed when no step exists in parking assistance. Specifically, the controller 10 controls the engine control system 31 to apply the drive torque that is applied during normal driving in parking assistance, while controlling the brake control system 32 to appropriately adjust the braking torque so that the vehicle 1 moves at the target speed that is applied during normal driving in parking assistance. In this case, the controller 10 performs such normal driving control until the vehicle 1 reaches the specified space SP. Then, the controller 10 proceeds to step S107.

On the other hand, if the controller 10 does not determine in step S105 that the vehicle 1 has gone over the step (step S105: No), specifically, if the actual vehicle speed of the vehicle 1 has not reached or exceeded the predetermined speed, the controller 10 does not perform the normal driving control of step S106 described above, and proceeds to step S107.

In step S107, the controller 10 stops the vehicle 1. Specifically, the controller 10 controls the engine control system 31 to end the application of drive torque to the vehicle 1, and controls the brake control system 32 to apply a braking torque so that the vehicle 1 continues to be stopped. More specifically, when the vehicle 1 overcomes the step, the controller 10 sets the target vehicle speed to 0 in accordance with a command related to parking assistance, thereby controlling the vehicle 1 to stop in this manner, while when the vehicle 1 fails to overcome the step, the controller 10 forcibly sets the target vehicle speed to 0 regardless of a command related to parking assistance, thereby controlling the vehicle 1 to stop in this manner. In the latter case, the vehicle 1 will stop before the step that the vehicle 1 was unable to overcome. After step S107, the controller 10 ends the overall processing of the step-over-step control.

Next, the step handling process shown in FIG. 9 will be described in detail. This step handling process is a subroutine performed in step S104 in FIG. 8. When the step handling process is started, first, in step S201, the controller 10 confirms an instruction to drive (move) the vehicle 1. Specifically, the controller 10 confirms that the user U has continued the driving instruction (i.e., confirms the user U's intention to overcome the step), and confirms that the vehicle 1 is not moving despite the driving instruction (i.e., confirms that a step is indeed present).

Next, in step S202, the controller 10 controls the engine control system 31 to apply a driving torque to press the wheels of the vehicle 1 against the step in order to confirm that the vehicle 1 is in contact with the step. Then, the process proceeds to step S203, where the controller 10 determines whether the vehicle 1 is not moving, that is, whether pressing the wheels against the step is complete. As a result, if the vehicle 1 is not moving (step S203: Yes), the controller 10 proceeds to step S204 because pressing the wheels against the step is complete. On the other hand, if the vehicle 1 is moving (step S203: No), pressing the wheels against the step is not complete, so the controller 10 returns to step S202. In this case, the controller 10 repeats steps S202 and S203 until the vehicle 1 stops moving.

In step S204, the controller 10 sets the limit torque Thr according to the step-contact wheel determined in step S102 of FIG. 8. That is, the controller 10 sets the limit torque Thr for the driving wheels when it is determined that the step-contact wheel is the driving wheel 2, and sets the limit torque Thr for the driven wheels when it is determined that the step-contact wheel is the driven wheel 3. The limit torques Thr for the driving wheels and the driven wheels are set and stored in advance, for example, by the method described in FIG. 5 and FIG. 6, and the controller 10 reads out and applies the limit torque Thr thus stored.

Next, in step S205, the controller 10 determines whether the drive torque currently being applied to the vehicle 1 via the engine control system 31 is less than the limit torque Thr set in step S204. As a result, if the drive torque currently being applied to the vehicle 1 is less than the limit torque Thr (step S205: Yes), the controller 10 proceeds to step S206. In step S206, the controller 10 controls the engine control system 31 to increase the drive torque applied to the vehicle 1 in order to allow the vehicle 1 to overcome the step. Specifically, the controller 10 gradually increases the drive torque at a predetermined rate of change set in advance.

Next, in step S207, the controller 10 determines whether the vehicle 1 has started to go over a step. Specifically, the controller 10 determines whether the vehicle 1 has started to go over a step based on the amount of change and the rate of change in the acceleration of the vehicle 1 detected by the acceleration sensor 24. As a result, if the vehicle 1 has started to go over a step (step S207: Yes), the controller 10 proceeds to step S208. In this case, since the vehicle 1 has started to go over a step, the controller 10 controls the engine control system 31 to maintain the current drive torque (step S208). Then, after step S208, the controller 10 ends the step response process. Note that in another example, the controller 10 may control the engine control system 31 to reduce the drive torque instead of maintaining it when the vehicle 1 starts to go over a step in this way.

In response to this, if the vehicle 1 has not started to go over the step (step S207: No), the controller 10 returns to step S205 and performs the processes from step S205 onwards again. That is, as long as the driving torque applied to the vehicle 1 is less than the limit torque Thr (step S205: Yes), if the vehicle 1 has not started to go over the step (step S207: No), the controller 10 gradually increases the driving torque applied to the vehicle 1 (step S206). In this way, the vehicle 1 is allowed to go over a step that is less than the limit height.

On the other hand, if the driving torque currently applied to the vehicle 1 is not less than the limit torque Thr (step S205: No), that is, if the driving torque reaches the limit torque Thr, the controller 10 proceeds to step S209. In this case, the controller 10 controls the engine control system 31 to quickly reduce the driving torque applied to the vehicle 1 in order to prohibit the vehicle 1 from climbing over a step that is equal to or greater than the limit height (step S209). In addition, the controller 10 changes the amount or speed at which the driving torque is reduced when the step-contact wheel is the driving wheel 2 or the driven wheel 3. Specifically, the controller 10 changes the amount or speed at which the driving torque is reduced when the step-contact wheel is the driving wheel 2 or the driven wheel 3, depending on the magnitude relationship between the load on the driving wheel 2 and the load on the driven wheel 3 in relation to the vehicle weight, that is, the magnitude relationship between the front wheel load and the rear wheel load. More specifically, when the controller 10 determines that the load applied to the step-contacting wheel (one of the driving wheel 2 and the driven wheel 3) is greater than the load applied to the step-non-contacting wheel (the other of the driving wheel 2 and the driven wheel 3) based on the magnitude relationship between the front wheel load and the rear wheel load, the controller 10 reduces the amount or speed of reducing the drive torque. In this case, since the load applied to the step-contacting wheel is relatively large, it is unlikely that the step-contacting wheel will overcome the step after the drive torque reaches the limit torque Thr, so the controller 10 suppresses the amount or speed of reducing the drive torque. On the other hand, when the controller 10 determines that the load applied to the step-contacting wheel (one of the driving wheel 2 and the driven wheel 3) is less than the load applied to the step-non-contacting wheel (the other of the driving wheel 2 and the driven wheel 3) based on the magnitude relationship between the front wheel load and the rear wheel load, the controller 10 increases the amount or speed of reducing the drive torque. In this case, since the load on the step contact wheel is relatively small, there is a possibility that the step contact wheel will overcome the step after the drive torque reaches the limit torque Thr, so the amount or speed at which the drive torque is reduced is increased to reliably prevent the step from being overcome.

For example, in a vehicle 1 in which the front wheel load is greater than the rear wheel load, when the step-contact wheel is the front wheel (drive wheel 2), the controller 10 reduces the amount or speed of reducing the drive torque compared to when the step-contact wheel is the rear wheel (driven wheel 3). This is because the load on the front wheel (drive wheel 2) is relatively large, so the front wheel is less likely to overcome the step after the drive torque reaches the limit torque Thr. On the other hand, in a vehicle 1 in which the front wheel load is greater than the rear wheel load, when the step-contact wheel is the rear wheel (driven wheel 3), the controller 10 increases the amount or speed of reducing the drive torque compared to when the step-contact wheel is the front wheel (drive wheel 2). This is because the load on the rear wheel (driven wheel 3) is relatively small, so there is a possibility that the rear wheel (driven wheel 3) will overcome the step after the drive torque reaches the limit torque Thr, and therefore the rear wheel is reliably prohibited from overcoming the step. In addition, in a vehicle 1 in which the front wheel load is smaller than the rear wheel load, the controller 10 performs the opposite control to the above control. After step S209, the controller 10 ends the step response process.

Next, another overall process of the step-over-step control will be described with reference to FIG. 10. FIG. 10 is a flowchart showing the overall process of the step-over-step control according to a modified example of this embodiment. The overall process of the step-over-step control shown in FIG. 10 differs from the overall process shown in FIG. 8 in that it is executed when the wheels of the vehicle 1 are not in contact with a step, that is, during normal driving with parking assistance. In this case, there is a possibility that the vehicle 1 may come into contact with a step while moving with parking assistance. The overall process shown in FIG. 10 is realized by the controller 10 (more specifically, the microprocessor 10a) reading and executing a program stored in the memory 10b. This process is also executed repeatedly at a predetermined cycle.

First, when the overall process of the step-crossing control in FIG. 10 is started, in step S301, the controller 10 acquires various information necessary for step-crossing control. Specifically, the controller 10 acquires at least signals input from the camera 21, the sonar 22, the wheel speed sensor 23, the acceleration sensor 24, and the communication unit 25 (see FIG. 1).

Then, the controller 10 judges whether or not a step on the road surface has been detected, specifically, whether or not the wheels of the vehicle 1 have come into contact with the step. In one example, the controller 10 judges that a step exists on the road surface when the amount of change and/or the rate of change of the running resistance of the vehicle 1 is equal to or greater than a predetermined value. This running resistance can be obtained from the driving torque and braking torque applied to the vehicle 1 by an observer model that indicates the equation of motion of the vehicle 1. In another example, the controller 10 judges that a step exists on the road surface when the difference between the target acceleration of the vehicle 1 and the actual acceleration detected by the acceleration sensor 24 is equal to or greater than a predetermined value. If the controller 10 judges that a step exists in this way (step S302: Yes), it proceeds to step S303. On the other hand, if the controller 10 does not judge that a step exists (step S302: No), it ends the entire process of the step overcoming control. In the latter case, the controller 10 continues the normal driving control in the parking assistance.

Next, in step S303, the controller 10 determines whether the step-contact wheel is a driving wheel 2 or a driven wheel 3. In one example, the controller 10 determines whether the step-contact wheel is a driving wheel 2 or a driven wheel 3 based on the change in the wheel speed of each of the four wheels detected by the wheel speed sensor 23 when it is determined that a step exists (i.e., when the wheel contacts the step), particularly based on the timing of the decrease in the wheel speed of each of the four wheels. In this example, when the front wheels are driving wheels 2 and the rear wheels are driven wheels 3, the controller 10 determines that the step-contact wheel is a driving wheel 2 when the timing of the decrease in the wheel speed of the front wheels is earlier than the timing of the decrease in the wheel speed of the rear wheels, whereas it determines that the step-contact wheel is a driven wheel 3 when the timing of the decrease in the wheel speed of the rear wheels is earlier than the timing of the decrease in the wheel speed of the front wheels. In another example, the controller 10 may determine whether the step-contacting wheel is a driving wheel 2 or a driven wheel 3 based on the image captured by the camera 21, the detection results of the sonar 22, the traveling direction of the vehicle 1 (not limited to the traveling direction indicated by the user U using the communication terminal 5, but may be the current traveling direction of the vehicle 1), etc., similar to step S102 in FIG. 8.

Next, in step S304, the controller 10 decelerates the vehicle 1. This prevents the vehicle 1 from going over a relatively high step due to inertial force. Therefore, the degree to which the vehicle 1 is decelerated is determined according to the height of the relatively high step that is to be prevented from being gone over by the inertial force of the vehicle 1. To explain the processing of step S304 in more detail, first, the controller 10 reduces the set target vehicle speed, and controls the engine control system 31 to reduce the driving torque to idle torque to achieve this target vehicle speed, while controlling the brake control system 32 to increase the braking torque. Then, when the actual vehicle speed is decelerated to a constant vehicle speed, the controller 10 returns to normal control. That is, the controller 10 controls the braking torque to be appropriately adjusted according to the target vehicle speed while maintaining the driving torque constant.

Next, in step S305, the controller 10 determines whether the vehicle 1 has gone over a step. Specifically, when the actual vehicle speed of the vehicle 1 corresponding to the wheel speed detected by the wheel speed sensor 23 is equal to or greater than a predetermined speed, the controller 10 determines that the vehicle 1 has gone over a step (step S305: Yes) and proceeds to step S306.

In step S306, since the vehicle 1 has overcome the step, the controller 10 starts normal driving control that is performed when no step exists in parking assistance. Specifically, the controller 10 controls the engine control system 31 to apply the drive torque that is applied during normal driving in parking assistance, while controlling the brake control system 32 to appropriately adjust the braking torque so that the vehicle 1 moves at the target speed that is applied during normal driving in parking assistance. In this case, the controller 10 performs such normal driving control until the vehicle 1 reaches the specified space SP.

Next, in step S307, the controller 10 stops the vehicle 1. Specifically, the controller 10 controls the engine control system 31 to end the application of drive torque to the vehicle 1, and controls the brake control system 32 to apply a braking torque so that the vehicle 1 remains stopped. More specifically, the controller 10 sets the target vehicle speed to 0 in accordance with a command related to parking assistance, and thus performs control to stop the vehicle 1. After step S307, the controller 10 ends the entire processing of the step-crossing control.

On the other hand, if the controller 10 does not determine in step S305 that the vehicle 1 has gone over the step (step S305: No), the process proceeds to step S308. In step S308, the controller 10 stops the vehicle 1 when it descends the step. This is to avoid an unstable state in which the vehicle 1 is stopped halfway over the step. Specifically, the controller 10 first determines that the vehicle 1 has descended the step when the actual acceleration detected by the acceleration sensor 24 switches from negative acceleration to positive acceleration. The controller 10 then controls the engine control system 31 to restore the drive torque, while controlling the brake control system 32 to increase the braking torque in order to hold the vehicle 1 in a stopped state after decelerating it.

The controller 10 then proceeds to step S309. The subsequent steps S309, S310, S311, S306, and S307 are similar to the steps S103, S104, S105, S106, and S107 in FIG. 8, respectively, and therefore will not be described further.

[Action and Effects]
Next, the operation and effects of the parking assistance device according to the embodiment of the present invention will be described.

In this embodiment, when a wheel of the vehicle 1 comes into contact with a step on the road surface, the controller 10 applies a driving torque to the vehicle 1 so that the vehicle 1 overcomes the step, while limiting the driving torque applied to the vehicle 1 to less than a predetermined limit torque Thr to prohibit the vehicle 1 from climbing over a step of a height equal to or greater than the limit. The controller 10 changes the limit torque Thr applied to the driving torque applied to the vehicle 1 depending on whether the wheel in contact with the step is the driving wheel 2 or the driven wheel 3. This makes it possible to accurately prohibit the vehicle 1 from climbing over a step of the same height equal to or greater than the limit, regardless of whether the wheel in contact with the step is the driving wheel 2 or the driven wheel 3. In other words, it is possible to accurately prevent the height of the step that is prohibited from being controlled from changing depending on whether the wheel in contact with the step is the driving wheel 2 or the driven wheel 3.

In addition, in this embodiment, when the wheels of the vehicle 1 come into contact with a step on the road surface, the controller 10 gradually increases the drive torque applied to the vehicle 1 so that the vehicle 1 overcomes the step, and when this drive torque reaches the limit torque Thr, the controller 10 reduces the drive torque applied to the vehicle 1 so as to prohibit the vehicle 1 from climbing over the step. This makes it possible to accurately balance between the vehicle 1 quickly climbing over steps that are less than the limit height and the vehicle 1 being prohibited from climbing over steps that are equal to or greater than the limit height.

In addition, in this embodiment, the controller 10 changes the amount or speed at which the drive torque is reduced when the drive torque reaches the limit torque Thr, depending on whether the wheel in contact with the step is the drive wheel 2 or the driven wheel 3. Because the load on the drive wheel 2 and the driven wheel 3 differ due to the front-rear weight distribution of the vehicle 1, the possibility that the wheel will overcome the step after the drive torque reaches the limit torque Thr changes depending on whether the wheel in contact with the step is the drive wheel 2 or the driven wheel 3. Therefore, the amount or speed at which the drive torque is reduced after the drive torque reaches the limit torque Thr is changed depending on whether the wheel in contact with the step is the drive wheel 2 or the driven wheel 3. This makes it possible to reliably prevent the vehicle 1 from climbing over a step that is equal to or greater than the limit height.

In addition, in this embodiment, the limit torque Thr is set based on the tire radius, the step height limit, and the front and rear wheel loads of the vehicle 1. This allows the limit torque Thr for the driving wheels and the limit torque Thr for the driven wheels to be accurately set in order to prohibit the vehicle 1 from climbing over a step that is equal to or greater than the step height limit.

In addition, in this embodiment, the controller 10 determines whether the wheel that comes into contact with the step is a drive wheel or a driven wheel based on the change in wheel speed of each of the four wheels acquired when the wheel comes into contact with the step on the road surface. This makes it possible to accurately determine which wheel comes into contact with the step.

[Modification]
In the above embodiment, an example is shown in which the present invention is applied to the vehicle 1 using an engine as a drive source, but the present invention can also be applied to vehicles using an electric motor as a drive source (electric automobiles and hybrid automobiles). In addition, in the above embodiment, the braking torque is applied to the vehicle 1 by the brake device (brake control system 32), but in other examples, the braking torque may be applied to the vehicle by regenerating the electric motor.

In the above embodiment, the limit torque Thr is changed according to the determination result of whether the step-contacting wheel is the driving wheel 2 or the driven wheel 3. In another example, in addition to the determination result of whether the step-contacting wheel is the driving wheel 2 or the driven wheel 3, it may be determined whether the step-contacting wheel is two wheels or one wheel (i.e., it is determined whether both wheels of the driving wheel 2 or the driven wheel 3 are in contact with the step or only one wheel is in contact with the step), and the limit torque Thr may be changed according to this determination result. In this example, when there is one step-contacting wheel, it is easier to overcome the step than when there are two step-contacting wheels, so the limit torque Thr may be made smaller. Whether there are two or one step-contacting wheels can be determined based on the image captured by the camera 21 and the change in the wheel speed detected by the wheel speed sensor 23.

REFERENCE SIGNS LIST 1 vehicle 2 driving wheel 3 driven wheel 5 communication terminal 10 controller 21 camera 22 sonar 23 wheel speed sensor 24 acceleration sensor 25 communication unit 31 engine control system 32 brake control system 33 steering control system 100 parking assistance system

Claims (6)

A parking assistance device,
A control unit configured to control a driving torque and a braking torque applied to the vehicle to move and stop the vehicle in order to assist in parking the vehicle in a predetermined space;
a determination unit configured to determine whether a wheel of the vehicle that comes into contact with a step on a road surface is a drive wheel or a driven wheel when the wheel comes into contact with the step while the parking assistance is being performed by the control unit;
having
The control unit is
When a wheel of the vehicle comes into contact with a step on a road surface, the driving torque is applied to the vehicle so that the vehicle overcomes the step, while the driving torque applied to the vehicle is limited to less than a predetermined limit torque in order to prohibit the vehicle from climbing over a step having a height equal to or greater than a limit; and
The limit torque applied to the drive torque applied to the vehicle is changed depending on whether the wheel that contacts the step is determined to be a drive wheel or a driven wheel by the determination unit.
A parking assistance device comprising: The parking assistance device according to claim 1, wherein the control unit is configured to gradually increase the driving torque applied to the vehicle when the wheels of the vehicle come into contact with a step on a road surface so that the vehicle overcomes the step, and to reduce the driving torque applied to the vehicle when the driving torque reaches the limit torque so as to prohibit the vehicle from overcoming the step. The parking assistance device according to claim 2, wherein the control unit is configured to change the amount or speed at which the drive torque is reduced when the drive torque reaches the limit torque, depending on whether the wheel that contacts the step is determined by the determination unit to be a drive wheel or a driven wheel. The parking assistance device according to any one of claims 1 to 3, wherein the limit torque is set based on the radius of the wheels of the vehicle, the limit height of the step that the vehicle is prohibited from crossing, and the front and rear wheel loads of the vehicle. The parking assistance device according to any one of claims 1 to 4, wherein the determination unit is configured to acquire the wheel speed of each of a plurality of wheels of the vehicle, and determine whether the wheel that contacts the step is a driving wheel or a driven wheel based on the change in the wheel speed of each of the plurality of wheels acquired when the wheel of the vehicle contacts the step on the road surface. A parking assistance method, comprising:
a control process for controlling a driving torque and a braking torque applied to the vehicle so as to move and stop the vehicle in order to assist in parking the vehicle in a predetermined space;
a determination step of determining whether a wheel of the vehicle that comes into contact with a step on a road surface is a drive wheel or a driven wheel when the parking assistance is being performed by the control step;
having
The control step includes:
When a wheel of the vehicle comes into contact with a step on a road surface, the driving torque is applied to the vehicle so that the vehicle overcomes the step, while limiting the driving torque applied to the vehicle to less than a predetermined limit torque in order to prohibit the vehicle from climbing over a step having a height equal to or greater than a limit; and
changing the limit torque applied to the drive torque applied to the vehicle depending on whether the wheel that comes into contact with the step is determined to be a drive wheel or a driven wheel in the determination step;
A parking assistance method comprising:

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