Parking assistance device and method

Abstract

To precisely prohibit a vehicle from riding over a comparatively high step, on the basis of a wheel rotation amount since the wheel starts the riding-over of the step, when the step exists on a road surface during parking assistance.SOLUTION: A controller 10 of a parking assisting system 100, when a step exists on a road surface during parking assistance, applies drive torque to a vehicle 1 so that a wheel of the vehicle 1 rides over the step, and when the wheel starts the riding-over of the step by the application of the drive torque, lowers the drive torque applied to the vehicle 1 on the basis of a wheel rotation amount since the wheel starts the riding-over of the step. Concretely, the controller 10 lowers the drive torque applied to the vehicle 1 so as to suppress the wheel rotation amount from reaching a limited value R1 by using the limited value R1 set on the basis of the wheel rotation amount when the vehicle 1 rides over a step with the limited height.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a parking assistance device and method for assisting in parking a vehicle. [Background technology]

[0002] Conventionally, there has been known a technology for controlling a vehicle to automatically move to a specified space and stop there (i.e., automatic parking) in order to assist in parking the vehicle. For example, Patent Document 1 discloses a technology for controlling a vehicle to go over a step that exists on a road surface during parking assistance, and for determining whether or not the step can be overcome based on the amount of rotational displacement of the wheels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-066329 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a step is present on the road surface during parking assistance for a vehicle, it is desirable to provide parking assistance that ensures the vehicle to quickly overcome a relatively low step, while prohibiting the vehicle from overcoming a relatively high step, in order to prevent the vehicle from running over a wheel stopper or the like.

[0005] Here, as a result of intensive research, the inventors have come to the conclusion that it is possible to appropriately prohibit a vehicle from climbing over a relatively high step by focusing on the amount of wheel rotation (amount of rotational displacement of the wheel) after the wheels of the vehicle start climbing over the step. The amount of wheel rotation from when the wheels start climbing over the step until they finish climbing over it corresponds to the height of the step. Therefore, the inventors have come to the conclusion that it is possible to realize the prohibition of a vehicle from climbing over a step that is equal to or higher than the limit height by controlling the parking assistance so that the amount of wheel rotation from when the wheels start climbing over the step does not reach the amount of wheel rotation corresponding to the limit height of the step (for example, 70 to 80 mm or more) at which the vehicle should be prohibited from climbing over.

[0006] Another possible method is to prohibit the vehicle from going over a step that is greater than the limit height by limiting the drive torque applied when the vehicle tries to go over the step to less than a predetermined limit torque according to the limit height of the step. However, this method may not be able to properly prohibit the vehicle from going over a step that is greater than the limit height due to the influence of the ground load of the wheels that contact the step. This is because even if the step is the same height, the drive torque required to go over the step varies depending on the ground load of the wheels that contact the step. In other words, if the limit torque is not set appropriately taking such factors into consideration, an excessively large limit torque may be applied, in which case the vehicle may go over a step that is greater than the limit height. The ground load of the wheel that contacts the step also differs depending on whether the wheel is a driving wheel or a driven wheel. This is due to the difference between 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).

[0007] In contrast, the amount of wheel rotation after the wheel starts to go over the step is not affected by the ground load of the wheel that contacts the step, etc. Therefore, according to the above-mentioned method of control based on the amount of wheel rotation devised by the inventor, it is believed that it is possible to more accurately prohibit the vehicle from going over a step that is equal to or higher than the limit height.

[0008] Incidentally, the above-mentioned Patent Document 1 only describes a technique for determining whether or not a vehicle can overcome a step, and does not describe anything about prohibiting a vehicle from overcoming a step.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a parking assistance device and method that, when a step is present on the road surface during parking assistance for a vehicle, can accurately prohibit the vehicle from climbing over a relatively high step based on the amount of wheel rotation after the vehicle's wheels start to climb over the step. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a parking assistance device comprising: a control unit configured to control 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 configured to apply a driving torque to the vehicle so that the wheels of the vehicle overcome the step when a step is present on a road surface in the traveling direction while assisting in parking the vehicle; and a wheel rotation amount acquisition unit that acquires an amount of wheel rotation from when the wheels of the vehicle begin to overcome the step due to the application of the driving torque by the control unit, the wheel rotation amount being acquired by the wheel rotation amount acquisition unit being configured to prevent the wheel rotation amount from reaching a specified limit value by reducing the driving torque applied to the vehicle based on the wheel rotation amount acquired by the wheel rotation amount acquisition unit after the wheels of the vehicle begin to overcome the step, and the limit value is set based on the wheel rotation amount when the vehicle overcomes a step of a limited height so as to prohibit the vehicle from overcoming a step of a height equal to or greater than the limited height.

[0011] According to the present invention configured as described above, when a step exists on the road surface while assisting parking, the control unit applies a driving torque to the vehicle so that the wheels of the vehicle overcome the step, and when the wheels begin to overcome the step by applying such driving torque, the control unit reduces the driving torque applied to the vehicle based on the wheel rotation amount after the wheels begin to overcome the step. Specifically, the control unit uses a limit value set based on the wheel rotation amount when the vehicle overcomes the step of the restricted height, and reduces the driving torque applied to the vehicle so as to prevent the wheel rotation amount from reaching this limit value. Here, as described above, in the method according to the comparative example in which the driving torque applied to the vehicle is limited to less than the limit torque according to the restricted height to prohibit the vehicle from overtaking a step of the restricted height or more, the vehicle may not be able to accurately prohibit the vehicle from overtaking a step of the restricted height or more due to the influence of the ground load of the wheels contacting the step. In contrast, the wheel rotation amount used in the control according to the present invention is not influenced by the ground load of the wheels contacting the step. Therefore, according to the present invention, it is possible to more accurately prevent a vehicle from climbing over a step (such as a wheel stopper) that is equal to or higher than a restricted height, without being affected by ground load or the like.

[0012] In the present invention, the control unit is preferably configured to complete the reduction in the driving torque applied to the vehicle at or before the timing when the wheel rotation amount acquired by the wheel rotation amount acquisition unit reaches a predetermined specified value which is smaller than the limit value after the wheels of the vehicle start to climb over the step. According to the present invention configured in this manner, the reduction in driving torque is completed at or before the timing at which a predetermined specified value smaller than the limit value is reached, thereby reliably preventing the wheel rotation amount from reaching the limit value.

[0013] In the present invention, the control unit is preferably configured to reduce the driving torque applied to the vehicle after the wheels of the vehicle start to climb over the step, in accordance with the difference between the wheel rotation amount acquired by the wheel rotation amount acquisition unit and a predetermined specified value smaller than the limit value. According to the present invention configured in this manner, the driving torque is reduced in accordance with the difference between the wheel rotation amount and a specified value smaller than the limit value, thereby reliably preventing the wheel rotation amount from reaching the limit value.

[0014] In a preferred example of the present invention, the above-mentioned specified value is set based on the amount of wheel rotation when the vehicle goes over a step having a maximum height that the vehicle is permitted to go over.

[0015] In the present invention, preferably, when the control unit is providing assistance for parking the vehicle, the control unit further includes a judgment unit configured to judge whether the wheel contacting the step is a drive wheel or a driven wheel when the wheel of the vehicle contacts the step, and the control unit is configured to change the amount or speed at which the drive torque is reduced after the wheel of the vehicle begins to overcome the step depending on whether the judgment unit judges that the wheel contacting the step is a drive 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 with which the wheel overcomes the step after it starts to overcome the step (the possibility of overcoming the step) differs 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 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 overcoming a step that is equal to or higher than the restricted height.

[0016] In the present invention, the control unit is preferably configured to reduce the drive torque applied to the vehicle after the wheels of the vehicle have begun to overcome the step to a drive torque that is applied when stopping the vehicle when providing assistance for parking the vehicle. According to the present invention configured in this manner, the drive torque is reduced to a torque sufficient to stop the vehicle, so that the vehicle can be reliably prevented from climbing over a step that is equal to or higher than the height limit.

[0017] In another aspect, in order to achieve the above object, the present invention provides 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 predetermined space, and a control step of applying a driving torque to the vehicle so that wheels of the vehicle overcome the step when a step is present on a road surface in the traveling direction while assisting in parking the vehicle; and a wheel rotation amount acquisition step of acquiring an amount of wheel rotation from when the wheels of the vehicle start to overcome the step by applying the driving torque by the control step, wherein the control step prevents the wheel rotation amount from reaching a predetermined limit value by reducing the driving torque applied to the vehicle based on the wheel rotation amount acquired by the wheel rotation amount acquisition step after the wheels of the vehicle start to overcome the step, and the limit value is set based on the amount of wheel rotation when the vehicle overcomes a step of a height limit so as to prohibit the vehicle from overcoming a step of a height equal to or greater than the height limit. The present invention thus configured can also reliably prevent a vehicle from climbing over a step (such as a wheel stopper) that is equal to or higher than a restricted height, without being affected by ground load or the like. Effect of the Invention

[0018] According to the parking assistance device and method of the present invention, when a step is present on the road surface during parking assistance for a vehicle, the vehicle can be accurately prohibited from climbing over a relatively high step based on the amount of wheel rotation after the vehicle's wheels begin to climb over the step. [Brief description of the drawings]

[0019] [Figure 1] 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. [Diagram 2] FIG. 2 is an explanatory diagram of a basic operation of parking assistance according to an embodiment of the present invention. [Diagram 3] 4 is a time chart showing an example of step climbing control according to an embodiment of the present invention. [Figure 4]10 is an explanatory diagram of a method for setting a limit value and a specified value applied to a wheel rotation amount in the step overcoming control according to the embodiment of the present invention. FIG. [Diagram 5] 4 is a flowchart showing an overall process of step clearance control according to an embodiment of the present invention. [Figure 6] 10 is a flowchart showing a step handling process according to an embodiment of the present invention. [Figure 7] 13 is a flowchart showing an overall process of step clearance control according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a parking assistance device and method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] [Basic configuration] First, the basic configuration of the parking assistance device according to this 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 this embodiment is applied, and Figure 2 is an explanatory diagram of the basic operation of the parking assistance according to this embodiment.

[0022] The parking assistance system 100 shown in FIG. 1 is mounted on a vehicle 1, and operates to perform parking assistance (automatic parking) for automatically moving and stopping the vehicle 1 to a predetermined space SP as shown in FIG. 2. Basically, the parking assistance system 100 performs such parking assistance in response to the operation of the communication terminal 5 by a 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, the restart of movement of the vehicle 1, and the like. The communication terminal 5 is, for example, a key fob for locking and unlocking 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 predetermined switch provided in the vehicle cabin (the communication terminal 5 may be used inside the vehicle).

[0023] 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 the 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 realizing assistance in parking the vehicle 1 in the space SP.

[0024] The camera 21 includes a plurality of cameras (front cameras and rear cameras) that capture images in front of and behind the vehicle 1. The camera 21 is also provided facing diagonally downward so as to capture images of ranges 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.

[0025] The sonar 22 detects the presence or absence of an object present within a predetermined range around the vehicle 1 (for example, relatively close to the vehicle 1), and detects the distance from the vehicle 1 to the object. For example, the sonar 22 is an active ultrasonic sonar, and is disposed at each of the four corners of the vehicle 1. The sonar 22 outputs a detection signal related to an object present around the vehicle 1 to the controller 10. Note that instead of or in addition to the sonar 22, a laser (millimeter wave radar or laser radar) or the like may be used to detect the presence or absence of an object around the vehicle and the distance to the object.

[0026] 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 (amount of wheel rotation) 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.

[0027] The communication unit 25 is a device that communicates with the above-mentioned communication terminal 5. The communication unit 25 receives a signal corresponding to an operation on the communication terminal 5 by the user U, in particular a signal (instruction signal) indicating an instruction related to parking assistance by 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 stop of 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.

[0028] The engine control system 31 controls the engine (not shown) of the vehicle 1. The engine control system 31 is a component capable of adjusting 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 the control signal.

[0029] The brake control system 32 controls a 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 include a so-called parking brake device.

[0030] The steering control system 33 controls a steering device (not shown) of the vehicle 1. The steering control system 33 is a component capable of adjusting 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 the control signal.

[0031] The controller 10 is composed of a computer equipped with one or more microprocessors 10a (typically a CPU), a memory 10b (ROM, RAM, etc.) that stores various programs, and input / output devices, etc. The controller 10 executes various calculations based on signals input from a camera 21, a sonar 22, a wheel speed sensor 23, an acceleration sensor 24, and a communication unit 25, and outputs control signals to an engine control system 31, a brake control system 32, and a steering control system 33 for appropriately operating the engine, the brake device, and the steering device, respectively.

[0032] In this embodiment, the controller 10 corresponds to an example of the "parking assistance device" of the present invention, and functions as a "controller", a "wheel rotation amount acquisition 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 predetermined space SP. Specifically, the controller 10 first identifies the predetermined space SP in which the vehicle 1 should be parked, based on signals from the camera 21, the 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 a position (stopping position) within such a range where the vehicle 1 is actually parked (the same applies hereinafter).

[0033] Then, the controller 10 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.

[0034] In this embodiment, when a step exists on the road surface while the above-mentioned parking assistance is being performed, the controller 10 controls the engine control system 31 to increase the driving torque applied to the vehicle 1 so that the wheels of the vehicle 1 can overcome the step. Then, when the wheels start to overcome the step due to the application of such driving torque, the controller 10 acquires the wheel rotation amount after the wheels start to overcome the step based on the detection signal from the wheel speed sensor 23, and reduces the driving torque based on this wheel rotation amount. Specifically, the controller 10 reduces the driving torque applied to the vehicle 1 so as to prevent the wheel rotation amount from reaching a predetermined limit value (basically, the driving torque is reduced to a level that can reliably prevent the vehicle 1 from overcoming the step). This limit value is set based on the wheel rotation amount when the vehicle 1 overcomes a step with a limit height (for example, 70 to 80 mm). In this way, by reducing the driving torque so as to prevent the wheel rotation amount from reaching the limit value after the wheels start to overcome the step, it is possible to ensure that the vehicle 1 overcomes a step with a height less than the limit height, while prohibiting the vehicle 1 from overcoming a step with a height equal to or greater than the limit height.

[0035] More specifically, after the wheels start to climb over the step, the controller 10 reduces the driving torque applied to the vehicle 1 according to the difference between the acquired wheel rotation amount and a predetermined specified value smaller than the limit value, and completes the reduction of the driving torque applied to the vehicle 1 at the timing when the wheel rotation amount reaches this specified value or before the timing. This specified value is set based on the wheel rotation amount when the vehicle 1 climbs over a step of the maximum height that the vehicle 1 is allowed to climb. By reducing the driving torque based on such a specified value, it is possible to reliably prevent the wheel rotation amount from reaching the limit value. Furthermore, when reducing the driving torque after the wheels start to climb over the step, the controller 10 reduces this driving torque to the driving torque applied when the vehicle 1 is stopped in the parking assistance. This makes it possible to reliably prohibit the vehicle 1 from climbing over a step of a height equal to or greater than the limit height.

[0036] [Step-over control] Next, we will explain the control that is performed in this embodiment when a step is present on the road surface in the direction of travel during parking assistance, specifically, the control that allows the vehicle to overcome steps that are less than the limit height while prohibiting the vehicle from overcoming steps that are equal to or greater than the limit height (hereinafter referred to as "step overcoming control" as appropriate).

[0037] Fig. 3 is a time chart showing an example of step-over-step control according to this embodiment. Here, a flow of step-over-step control performed when a step of equal to or greater than the height limit is present on the road surface in the traveling direction during parking assistance will be described. Fig. 3 shows, from the top, the time change in vehicle speed (the solid line indicates the target vehicle speed, and the dashed line indicates the actual vehicle speed), the time change in the wheel rotation amount corresponding to the detection signal from the wheel speed sensor 23, the time change in driving torque, and the time change in braking torque. The driving torque and braking torque indicate the target driving torque and target braking torque to be applied to the vehicle 1, which are instructed by the controller 10.

[0038] 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 applied to the vehicle 1 to a torque T1 for keeping the vehicle 1 stopped until there is a further instruction from the user U. Thereafter, 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 an operation on the communication terminal 5 again (pressing a button again), or performs an operation on the communication terminal 5 that continues for a predetermined period of time (long press operation).

[0039] From such 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, at time t14, the vehicle 1 begins to overcome (start to climb) the step. For example, the controller 10 determines that the vehicle 1 has begun to overcome the step based on the amount of change and the rate of change in the acceleration of the vehicle detected by the acceleration sensor 24. From this time t14, the controller 10 begins to reduce the driving torque that has been increased up until now.

[0040] Specifically, the controller 10 obtains the wheel rotation amount after the wheel starts to go over the step based on the detection signal from the wheel speed sensor 23, and reduces the drive torque based on this wheel rotation amount to prevent the wheel rotation amount from reaching the limit value R1. More specifically, the controller 10 reduces the drive torque applied to the vehicle 1 according to the difference between the wheel rotation amount and the specified value R2 (< limit value R1), so that at time t15 when the wheel rotation amount reaches the specified value R2, that is, at time t15 when the difference between the wheel rotation amount and the specified value R2 becomes 0 (in another example, it may be before time t15), the drive torque applied to the vehicle 1 is reduced to the torque T1 for stopping the vehicle. As a result, after time t15, the wheel rotation amount becomes slightly larger than the specified value R2 due to the inertia of the vehicle 1, but the wheel rotation amount does not exceed the limit value R1, that is, the vehicle 1 does not go over the step. Therefore, the vehicle 1 is prohibited from going over a step that is equal to or greater than the limit height. In this case, the vehicle 1 descends the step that it had been climbing partway up, and a negative actual vehicle speed (actual vehicle speed when traveling in the direction opposite to the direction in which the vehicle should travel) occurs.

[0041] In FIG. 3, the case where the step-over-crossing control according to the present embodiment is applied when a step of a height equal to or greater than the limit exists in the travel direction during parking assistance is illustrated. However, when the step-over-crossing control is applied to a step of a height less than the limit, the following occurs. In the present embodiment, even when a step of a height less than the limit exists, the controller 10 performs the same step-over-crossing control as when a step of a height equal to or greater than the limit exists. That is, the controller 10 performs the same step-over-crossing control regardless of the height of the step. When such step-over-crossing control is performed, if the height of the step is less than the limit, the vehicle 1 finishes over the step while the driving torque is being reduced (between times t14 and t15) after the vehicle 1 starts over the step. This is because the wheel rotation amount that increases while the driving torque is being reduced exceeds the wheel rotation amount corresponding to the step (step of a height less than the limit). In this case, the actual vehicle speed is maintained at the target vehicle speed after it has increased significantly to the target vehicle speed (the actual vehicle speed may slightly exceed the target vehicle speed). On the other hand, if the height of the step is equal to or greater than the limit height, as described above (see FIG. 3), between times t14 and t15, the wheel rotation amount increasing toward the specified value R2 does not exceed the wheel rotation amount corresponding to the step (which is equal to or greater than the limit value R1), and so the vehicle 1 does not climb over the step (in the end, the wheel rotation amount is limited to be less than the limit value R1, including after time t15, so that the wheel rotation amount does not exceed the wheel rotation amount corresponding to the step).

[0042] Next, a specific example of a method for setting the limit value R1 and the specified value R2 applied to the wheel rotation amount in the step overcoming control according to this embodiment will be described with reference to Fig. 4. As described above, the limit value R1 is a value that is set based on the wheel rotation amount when the vehicle 1 goes over a step with a limited height (for example, 70 to 80 mm), and the specified value R2 is a value that is smaller than the limit value R1 and is set based on the wheel rotation amount when the vehicle 1 goes over a step with the maximum height that the vehicle 1 is permitted to go over.

[0043] Fig. 4 is a side view showing a wheel 2 of a vehicle 1 and a step St that comes into contact with the wheel 2. In Fig. 4, "r" is the tire radius, "h" is the height of the step St, and "θ" is the angle defined between the contact point between the wheel 2 and the tip of the step St and the center point of the wheel 2. This angle θ is expressed as "θ=sin -1 It is expressed as "{(rh) / r}".

[0044] The amount of wheel rotation when the wheel 2 goes over the step St corresponds to the movement distance D of the center point of the wheel 2 as shown in FIG. 4. The movement distance D is expressed as "D = r (π / 2 - θ)" using the above angle θ. This movement distance D corresponds to the amount of wheel rotation when the wheel 2 goes over the step St. Since "θ" in the formula expressing the movement distance D is determined by the height h of the step St, the movement distance D also has a value according to the height h of the step St, and therefore, from this formula, the amount of wheel rotation required for the wheel 2 to go over the step St of height h can be obtained. Therefore, the height h (restriction height) at which the vehicle 1 should be prohibited from going over the step is determined, and then the movement distance D for the step St of this height h is obtained, and the limit value R1 can be set based on this movement distance D. Basically, the obtained movement distance D can be set as the limit value R1. Furthermore, after determining the maximum height h (a height slightly lower than the above-mentioned restricted height) that the vehicle 1 is permitted to climb over, the travel distance D for the step St of this height h is calculated, and the specified value R2 can be set based on this travel distance D. Basically, the calculated travel distance D can be set as the specified value R2.

[0045] Here, let us take an example in which the tire radius r is 0.3425 m and the limit height h is 70 mm. In this case, the angle θ is approximately 0.920. The travel distance D required for the wheel 2 to get over the step St of this limit height h is approximately 0.223 m according to the formula "D = r (π / 2 - θ)". Therefore, the limit value R1 should be set to 0.223 m. Furthermore, if the maximum height h that the vehicle 1 is allowed to get over is 60 mm, the angle θ is approximately 0.970. The travel distance D required to get over the step St of this maximum height h is approximately 0.206 m, so the specified value R2 should be set to 0.206 m.

[0046] 4 is an example, and the limit value R1 and the specified value R2 may be set using other methods. For example, the limit value R1 and the specified value R2 may be set in consideration of the spring force and the dent when the wheel contacts a step.

[0047] [Control Flow] Next, a process flow (control flow) relating to step overcoming control according to this embodiment will be described with reference to FIGS.

[0048] FIG. 5 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 have already contacted the step (more specifically, in a state where the vehicle 1 is in contact with the step and does not 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 the driving torque constant. On the other hand, FIG. 6 is a flowchart showing a specific process (hereinafter referred to as a "step-over-running process") for dealing with a step on the road surface, which is performed in the overall process of the step-over-running control in FIG. 8. The controller 10 (more specifically, the microprocessor 10a) reads out and executes a program stored in the memory 10b, thereby realizing the processes shown in FIG. 5 and FIG. 6. In addition, these processes are repeatedly executed at a predetermined period.

[0049] 5 is started, the controller 10 acquires various information necessary for the step-over control in step S101. 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).

[0050] Next, in step S102, the controller 10 determines the wheel that contacts the step (hereinafter referred to as a "step-contact wheel" as appropriate), that is, determines (distinguishes) whether the step-contact wheel is a drive wheel or a driven wheel. In one example, the controller 10 determines whether the step-contact wheel is a drive wheel or a driven wheel 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 wheels are drive wheels and the rear wheels are driven wheels (this information is stored in the memory 10b or the like, and the controller 10 reads and uses the information thus stored. The same applies below), when a step is included in the image captured by the camera 21 that captures the front of the vehicle 1, the controller 10 determines that the step-contact wheel is a drive wheel, whereas when a step is included in the image captured by the camera 21 that captures the rear of the vehicle 1, the controller 10 determines that the step-contact wheel is a driven wheel. In another example, the controller 10 uses the sonar 22 instead of or in addition to the camera 21 to determine whether the step-contacting wheel is a driving wheel or a driven wheel in the same manner as when the camera 21 is used. That is, when the front wheels are driving wheels and the rear wheels are driven wheels, the controller 10 determines that the step-contacting wheel is a driving wheel when a step is detected by the sonar 22 covering the front of the vehicle 1, and determines that the step-contacting wheel is a driven wheel when a step is detected by the sonar 22 covering the rear of the vehicle 1. In yet another example, the controller 10 determines whether the step-contacting wheel is a driving wheel or a driven wheel based on the traveling direction of the vehicle 1 (either forward or backward, and basically a step exists in this direction) instructed by the user U using the communication terminal 5. In this example, when the front wheels are driving wheels and the rear wheels are driven wheels, the controller 10 determines that the step-contacting wheels are driving wheels when the user U instructs the vehicle 1 to move forward, and determines that the step-contacting wheels are driven wheels when the user U instructs the vehicle 1 to move backward.

[0051] 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 a vehicle speed that is a lowered target vehicle speed applied during normal driving in parking assistance as a 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. 6 (details will be described later).

[0052] Next, in step S105, the controller 10 determines whether or not the vehicle 1 has gone over a step by the step handling 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 higher 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.

[0053] 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 a driving 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 a 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 a predetermined space SP. Then, the controller 10 proceeds to step S107.

[0054] 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 proceeds to step S107 without performing the normal driving control in the above-mentioned step S106.

[0055] 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 the 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 stop. More specifically, when the vehicle 1 has overcome 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 has not overcome the step, the controller 10 forcibly sets the target vehicle speed to 0 regardless of the command related to parking assistance, thereby controlling the vehicle 1 to stop in this manner. In the latter case, the vehicle 1 stops before the step that the vehicle 1 has not overcome. After the above step S107, the controller 10 ends the entire process of the step-over-step control.

[0056] Next, the step response process shown in Fig. 6 will be specifically described. This step response process is a subroutine performed in step S104 in Fig. 5. When the step response process is started, first, in step S201, the controller 10 confirms an instruction to run (move) the vehicle 1. Specifically, the controller 10 confirms the continuation of the driving instruction from the user U (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 certainly exists).

[0057] Next, in step S202, the controller 10 controls the engine control system 31 to apply a driving torque for pressing 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 since 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.

[0058] In step S204, the controller 10 controls the engine control system 31 to increase the driving torque applied to the vehicle 1 so as to allow the vehicle 1 to overcome the step. Specifically, the controller 10 gradually increases the driving torque at a predetermined rate of change that is set in advance.

[0059] Next, in step S205, the controller 10 determines whether the vehicle 1 has started to go over the step. Specifically, the controller 10 determines whether the vehicle 1 has started to go over the 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 the step (step S205: Yes), the controller 10 proceeds to step S206. On the other hand, if the vehicle 1 has not started to go over the step (step S205: No), the controller 10 returns to step S204. In this case, the controller 10 gradually increases the drive torque applied to the vehicle 1 until the vehicle 1 starts to go over the step.

[0060] Next, in step S206, the controller 10 controls the engine control system 31 to reduce the driving torque applied to the vehicle 1. Specifically, the controller 10 acquires the wheel rotation amount (the amount of rotational displacement of the wheel) after the wheel starts to go over the step based on the detection signal from the wheel speed sensor 23, and reduces the driving torque based on this wheel rotation amount, thereby suppressing the wheel rotation amount from reaching the limit value R1. More specifically, the controller 10 gradually reduces the driving torque applied to the vehicle 1 according to the difference between the acquired wheel rotation amount and the specified value R2, thereby reducing the driving torque applied to the vehicle 1 to the torque T1 for stopping the vehicle 1 in parking assistance at or before the timing at which the wheel rotation amount reaches the specified value R2 (i.e., the timing at which the difference becomes 0) (see FIG. 3). After the above step S206, the controller 10 ends the step response process.

[0061] In a preferred example, the controller 10 may change the amount or speed of reducing the drive torque in step S206 depending on whether the step-contact wheel is a drive wheel or a driven wheel (based on the determination result in step S102 in FIG. 5). Specifically, the controller 10 changes the amount or speed of reducing the drive torque depending on whether the step-contact wheel is a drive wheel or a driven wheel, depending on the magnitude relationship between the load on the drive wheel and the load on the driven wheel with respect to the vehicle weight, that is, depending on the magnitude relationship between the front wheel load and the rear wheel load. More specifically, when it is determined based on the magnitude relationship between the front wheel load and the rear wheel load that the load on the step-contact wheel (one of the drive wheel and the driven wheel) is larger than the load on the step-non-contact wheel (the other of the drive wheel and the driven wheel), the controller 10 reduces the amount or speed of reducing the drive torque. In this case, since the load on the step-contacting wheel is relatively large, the possibility that the step-contacting wheel will overcome the step after it starts to overcome the step is low, so the amount or speed of reducing the drive torque is suppressed. On the other hand, when the controller 10 determines that the load on the step-contacting wheel (one of the driving wheel and the driven wheel) is smaller than the load on the step-non-contacting wheel (the other of the driving wheel and the driven wheel) based on the magnitude relationship between the front wheel load and the rear wheel load, the amount or speed of reducing the drive torque is increased. In this case, since the load on the step-contacting wheel is relatively small, there is a possibility that the step-contacting wheel will overcome the step after it starts to overcome the step, so the amount or speed of reducing the drive torque is increased to reliably prohibit the step from being overcome.

[0062] For example, in a vehicle 1 in which the front wheel load is larger than the rear wheel load, when the step-contacting wheel is a front wheel (drive wheel), the controller 10 reduces the amount or speed of reducing the drive torque compared to when the step-contacting wheel is a rear wheel (driven wheel). This is because the load on the front wheel (drive wheel) is relatively large, so the possibility of the front wheel climbing over the step after it starts to climb over the step is low. On the other hand, in a vehicle 1 in which the front wheel load is larger than the rear wheel load, when the step-contacting wheel is a rear wheel (driven wheel), the controller 10 increases the amount or speed of reducing the drive torque compared to when the step-contacting wheel is a front wheel (drive wheel). This is because the load on the rear wheel (driven wheel) is relatively small, so there is a possibility that the rear wheel (driven wheel) will climb over the step after it starts to climb over the step, and therefore the controller 10 reliably prohibits the rear wheel from climbing over the step. Note that in a vehicle 1 in which the front wheel load is smaller than the rear wheel load, the controller 10 performs control opposite to the above-mentioned control.

[0063] Next, another overall process of the step-over-step control will be described with reference to FIG. 7. FIG. 7 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. 7 is different from the overall process shown in FIG. 5 and 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. 7 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.

[0064] 7 is started, the controller 10 acquires various information necessary for the step-over control in step S301. 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).

[0065] Next, 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, whereas if it is not judged 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.

[0066] Next, in step S303, the controller 10 judges the step-contacting wheel, that is, judges (discriminates) whether the step-contacting wheel is a driving wheel or a driven wheel. In one example, the controller 10 judges whether the step-contacting wheel is a driving wheel or a driven wheel based on the change in the wheel speed of each of the four wheels detected by the wheel speed sensor 23 when it is judged that a step exists (i.e., when a wheel comes into contact with a 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 and the rear wheels are driven wheels, the controller 10 judges that the step-contacting wheel is a driving wheel 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 judges that the step-contacting wheel is a driven wheel 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, similar to step S102 in FIG. 5, the controller 10 may determine whether the step-contacting wheel is a driving wheel or a driven wheel 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.

[0067] 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 of deceleration of the vehicle 1 is determined according to the height of the relatively high step that the vehicle 1 is prevented from going over due to the inertial force of the vehicle 1. To explain the process of step S304 more specifically, 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 so as to realize the 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 performs control so as to appropriately adjust the braking torque according to the target vehicle speed while maintaining the driving torque constant.

[0068] Next, in step S305, the controller 10 determines whether or not 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 higher 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.

[0069] 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 a driving 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 a 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 predetermined space SP.

[0070] 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 braking torque so that the vehicle 1 continues to be 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 process of the step-crossing control.

[0071] On the other hand, when 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 the vehicle 1 descends the step. This is to avoid an unstable state in which the vehicle 1 stops 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. Then, the controller 10 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.

[0072] Next, the controller 10 proceeds to step S309. The processes of the following steps S309, S310, S311, S306, and S307 are similar to the processes of steps S103, S104, S105, S106, and S107 in Fig. 5, respectively, and therefore description thereof will be omitted.

[0073] [Action and Effects] Next, the operation and effects of the parking assistance device according to the embodiment of the present invention will be described.

[0074] In this embodiment, when a step exists on the road surface while assisting parking, the controller 10 applies a driving torque to the vehicle 1 so that the wheels of the vehicle 1 overcome the step, and when the wheels begin to overcome the step by applying such driving torque, the controller 10 acquires the wheel rotation amount after the wheels begin to overcome the step, and reduces the driving torque based on this wheel rotation amount. Specifically, the controller 10 uses a limit value set based on the wheel rotation amount when the vehicle 1 overcomes a step of the restricted height, and reduces the driving torque applied to the vehicle 1 so as to prevent the wheel rotation amount from reaching this limit value. Here, as described above, in the method according to the comparative example in which the vehicle 1 is prohibited from overtaking a step of the restricted height or more by limiting the driving torque applied to the vehicle 1 to less than the limit torque according to the restricted height, it may not be possible to accurately prohibit the vehicle 1 from overtaking a step of the restricted height or more due to the influence of the ground load of the wheels contacting the step. In contrast, the wheel rotation amount used in the control according to this embodiment is not affected by the ground load of the wheels contacting the step. Therefore, according to this embodiment, it is possible to reliably prevent the vehicle 1 from climbing over a step (such as a wheel stopper) that is equal to or higher than a restricted height, without being affected by the ground load or the like.

[0075] Furthermore, in this embodiment, the controller 10 completes the reduction in the driving torque applied to the vehicle 1 at or before the timing at which the wheel rotation amount after the wheel starts to climb over the step reaches a specified value R2 which is smaller than the limit value R1, thereby reliably preventing the wheel rotation amount from reaching the limit value R1.

[0076] Furthermore, in this embodiment, the controller 10 reduces the driving torque applied to the vehicle 1 in accordance with the difference between the amount of wheel rotation after the wheel starts to climb over the step and a specified value R2 that is smaller than the limit value R1, thereby reliably preventing the amount of wheel rotation from reaching the limit value R1.

[0077] In addition, in this embodiment, the controller 10 changes the amount or speed of reducing the drive torque after the wheel starts to go over the step, depending on whether the wheel that contacts the step is a drive wheel or a driven wheel. Since the load on the drive wheel and the load on the driven wheel differ due to the front-rear weight distribution of the vehicle 1, the possibility of the wheel going over the step changes depending on whether the wheel that contacts the step is a drive wheel or a driven wheel. Therefore, the amount or speed of reducing the drive torque after the wheel starts to go over the step is changed depending on whether the wheel that contacts the step is a drive wheel or a driven wheel. This makes it possible to reliably prevent the vehicle 1 from going over a step that is equal to or greater than the restricted height.

[0078] Furthermore, in this embodiment, after the wheels start to climb over the step, the controller 10 reduces the driving torque applied to the vehicle 1 to the driving torque applied when stopping the vehicle 1 in case of performing parking assistance, thereby reliably preventing the vehicle 1 from climbing over a step that is equal to or higher than the restricted height.

[0079] [Variations] In the above embodiment, an example was shown in which the present invention is applied to a 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 vehicles and hybrid vehicles). In addition, in the above embodiment, a braking torque is applied to the vehicle 1 by a brake device (brake control system 32), but in other examples, a braking torque may be applied to the vehicle by regeneration of an electric motor.

[0080] In the above embodiment, the controller 10 obtains the wheel rotation amount based on a detection signal from the wheel speed sensor 23, but in another example, the controller 10 may obtain (derive) the wheel rotation amount based on the rotation speed of the power transmission shaft of the vehicle 1 and / or the rotation speed of the power source (engine or motor) of the vehicle 1, instead of or in addition to the wheel speed sensor 23. This makes it possible to use an accurate wheel rotation amount in the step overcoming control. [Explanation of symbols]

[0081] 1 vehicle 5. Communication terminals 10 Controller 21 Camera 22 Sonar 23 Wheel speed sensor 24 Acceleration Sensor 25 Communications Department 31 Engine Control System 32 Brake Control System 33 Steering control system 100 Parking Assist System

Claims

1. A parking assistance device, a control unit configured to control a driving torque and a braking torque to be applied to the vehicle so as to move and stop the vehicle in order to provide assistance for parking the vehicle in a predetermined space, the control unit being configured to apply the driving torque to the vehicle so that wheels of the vehicle overcome the step when a step exists on a road surface in a traveling direction while providing assistance for parking the vehicle; a wheel rotation amount acquisition unit that acquires, when a wheel of the vehicle starts to go over a step due to application of the driving torque by the control unit, a wheel rotation amount from when the wheel starts to go over the step; having the control unit is configured to reduce the drive torque applied to the vehicle based on the wheel rotation amount acquired by the wheel rotation amount acquisition unit after the wheels of the vehicle start to climb over a step, thereby suppressing the wheel rotation amount from reaching a predetermined limit value; the limit value is set based on a wheel rotation amount when the vehicle goes over a step having a height limit or more, so as to prohibit the vehicle from going over a step having a height limit or more. A parking assistance device comprising:

2. 2. The parking assistance device according to claim 1, wherein the control unit is configured to complete the reduction of the drive torque applied to the vehicle at or before a timing at which the wheel rotation amount acquired by the wheel rotation amount acquisition unit reaches a predetermined specified value that is smaller than the limit value after the wheels of the vehicle start to climb over a step.

3. 3. The parking assistance device according to claim 1, wherein the control unit is configured to reduce the driving torque applied to the vehicle in accordance with a difference between the wheel rotation amount acquired by the wheel rotation amount acquisition unit and a predetermined specified value that is smaller than the limit value after the wheels of the vehicle start to climb over a step.

4. 4. The parking assistance device according to claim 2, wherein the specified value is set based on an amount of wheel rotation when the vehicle goes over a step having a maximum height that the vehicle is permitted to go over.

5. A determination unit is further configured to determine whether a wheel of the vehicle contacting the step is a drive wheel or a driven wheel when the wheel of the vehicle contacts the step while the control unit is providing assistance for parking the vehicle, The control unit is configured to change the amount or speed of reducing the drive torque after the wheel of the vehicle starts to overcome the step, depending on whether the wheel that contacts the step is determined by the determination unit to be a drive wheel or a driven wheel. A parking assistance device according to any one of claims 1 to 4.

6. 6. The parking assistance device according to claim 1, wherein the control unit is configured to reduce the drive torque applied to the vehicle after wheels of the vehicle start to climb over a step to a drive torque applied when stopping the vehicle in a case where assistance is provided for parking the vehicle.

7. A parking assistance method, comprising: a control process for controlling a driving torque and a braking torque to be applied to the vehicle so as to move and stop the vehicle in order to provide assistance for parking the vehicle in a predetermined space, the control process being for applying the driving torque to the vehicle so that wheels of the vehicle overcome the step when a step is present on a road surface in a traveling direction while providing assistance for parking the vehicle; a wheel rotation amount acquisition step of acquiring, when the wheel of the vehicle starts to go over a step due to the application of the driving torque by the control step, a wheel rotation amount from when the wheel starts to go over the step; having the control step includes reducing the drive torque applied to the vehicle based on the wheel rotation amount acquired in the wheel rotation amount acquisition step after the wheels of the vehicle start to climb over a step, thereby preventing the wheel rotation amount from reaching a predetermined limit value; the limit value is set based on a wheel rotation amount when the vehicle goes over a step having a height limit or more, so as to prohibit the vehicle from going over a step having a height limit or more. A parking assistance method comprising:

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