Electric power steering device

Abstract

The electric power steering apparatus of the present application has a function of notifying a parking assist device (2) of a current limit value for the purpose of overheat protection of the electric power steering apparatus (3) and a maximum number of times of parking steering that is calculated based on an estimated motor current in a case where parking steering is used when a steering wheel is turned, and a function of notifying the parking assist device of whether or not the electric power steering apparatus (3) can steer in accordance with a target steering angle (26a) and a target vehicle speed (26b) from the start of parking to the completion of parking, thereby avoiding interruption due to overheat of the electric power steering apparatus (3) during the parking assist.

Description

Technical Field

[0001] The present application relates to an electric power steering device. Background Art

[0002] Known systems for automatic vehicle parking require turning the steering wheel while the vehicle is parked. Parking steering places a heavy load on the EPS (Electric Power Steering), which can easily cause EPS overheating. To prevent damage from overheating, current limiting and overheat protection are required.

[0003] To address this issue, one method estimates the number of parking turns required and notifies the driver before initiating overheat protection, thereby preventing sudden initiation of overheat protection during parking assistance (see Patent Document 1). Another method involves turning the steering wheel in the direction of the turn after a parking turn is made, before the next parking turn is made. This reduces the amount of parking steering required (see Patent Document 2). Furthermore, another method determines the path and amount of parking steering required based on the EPS temperature (see Patent Document 3).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-190531

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-3565

[0008] Patent Document 3: Japanese Patent No. 6079596 Summary of the Invention

[0009] Technical problem to be solved by the invention

[0010] The method disclosed in Patent Document 1 cannot prevent parking assistance from being limited or stopped due to overheat protection.

[0011] In the method disclosed in Patent Document 2, the steering wheel is turned in the next steering direction at an earlier stage than usual after the parking steering is forwarded to reduce the steering angle for the parking steering. However, since the load condition of the steering device is not detected, even if the steering device is sufficient to park the vehicle through the parking steering, parking is performed along a path with a reduced parking steering amount, which may result in an increase in the number of steering wheel turns before parking is completed.

[0012] Furthermore, the method disclosed in Patent Document 3 requires regenerating a path during parking control to determine whether parking steering is being performed at the steering wheel turning point based on EPS temperature. This path differs from the initially set path, increasing the steering amount before parking is complete. Furthermore, this increased steering amount could cause the electric motor to overheat, potentially interrupting automatic parking.

[0013] The present application is completed to solve the above-mentioned problems and provides an electric power steering device that can avoid the interruption of parking assistance and the inability to steer due to overheating of the motor during parking control, and can control parking even when the motor is overheated.

[0014] Technical means for solving technical problems

[0015] The electric power steering device disclosed in the present application is characterized by including: a path generation unit that generates a driving path from the vehicle's position to a target parking position; an instruction calculation unit that calculates a target steering angle instruction for driving according to the path generated by the path generation unit; an automatic steering control unit that calculates a motor current for causing the steering angle to follow the target steering angle instruction; an overheat protection current limiting unit that calculates an overheat protection current limit value based on the motor current; and a parking turn number determination unit that calculates an upper limit on the number of parking turns possible based on the overheat protection current limit value.

[0016] Effects of the Invention

[0017] According to the electric power steering device disclosed in the present application, it is possible to avoid the parking assist being stopped and the steering being disabled due to the motor overheating during parking control, and parking control can be performed even in the motor overheating state. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic configuration diagram of the electric power steering device according to the first embodiment.

[0019] Figure 2 This is a flowchart for explaining the operation of the parking possible steering number determination unit according to the first embodiment.

[0020] Figure 3 This is a schematic configuration diagram of an electric power steering device according to a second embodiment.

[0021] Figure 4 This is a flowchart for explaining the operation of the parking possible steering number determination unit according to the second embodiment.

[0022] Figure 5 This is a schematic configuration diagram of an electric power steering device according to a third embodiment.

[0023] Figure 6 This is another schematic structural diagram of the electric power steering device according to the third embodiment.

[0024] Figure 7 This is an example of a hardware configuration diagram of the electric power steering device according to the first to third embodiments. DETAILED DESCRIPTION

[0025] Below, with reference to the accompanying drawings, a preferred embodiment of the electric power steering device involved in the present application is described. In addition, for the same content and corresponding parts, the same reference numerals are assigned, and their detailed description is omitted. In subsequent embodiments, repeated descriptions of the structures with the same reference numerals are also omitted.

[0026] Implementation method 1.

[0027] Figure 1 This is a schematic configuration diagram of an electric power steering device according to the first embodiment, which mainly includes a peripheral environment sensor group 1 , a parking assist device 2 , a steering system (EPS) 3 , and a steering angle sensor 4 .

[0028] The vehicle is equipped with a surrounding environment sensor set 1, which includes cameras and sonars that monitor the front, rear, and sides of the vehicle, a sign sensor that detects parking lot signs, a GPS device for acquiring GPS information, and a receiver for receiving parking lot map data. These sensors and devices detect the vehicle's own status and surrounding information. This information is transmitted to the parking assistance device 2 via the vehicle's communication lines, such as CAN (Controller Area Network) lines.

[0029] The parking assist device 2 is a device for executing so-called automatic parking and is a device for outputting an instruction to change the behavior of the vehicle based on various information from the surrounding environment sensor group 1 .

[0030] Therefore, parking assist device 2 includes a path generation unit 23 that receives information from surrounding environment sensor group 1 and calculates vehicle position information 21 and target parking position information 22 to generate a path to the target parking position, and a calculation and instruction unit 24 that calculates a signal for control instruction based on the output of path generation unit 23. The output of calculation and instruction unit 24 is output to control steering system (EPS) 3, braking system 5, and driving system 6.

[0031] Specifically, the path generation unit 23 uses information from the cameras of the surrounding environment sensor group 1 to detect, for example, vehicle distances to vehicles ahead, behind, or to the sides, lanes, parking area lines, and obstacles. It selects information necessary for parking control from this information, along with parking lot map information and GPS information. Based on this selected information, it calculates the vehicle's position information 21 and the target parking position information 22, generating a path from the vehicle's position to the target parking position.

[0032] Based on the route information generated by the route generation unit 23, the calculation and instruction unit 24 calculates the target steering angle instruction 25 required to travel from the vehicle's position to the target parking position and outputs it to the steering system (EPS) 3. Furthermore, the calculated acceleration and deceleration instructions are output to the drive system 6, and the calculated braking instructions are output to the brake system 5. For example, instructions may be given for accelerating along the route, steering to stop the vehicle between parked vehicles, or applying the brakes to the wheels to stop at the vehicle's stopped position according to the route. In other words, instructions are output to the steering system (EPS) 3, the brake system 5, and the drive system 6 for controlling the vehicle speed required to complete parking.

[0033] Furthermore, the calculation instruction unit 24 calculates a target steering angle 26a and a target vehicle speed 26b required to move the vehicle from its own vehicle position to the target parking position. The difference between the target steering angle instruction 25 and the target steering angle 26a is as follows.

[0034] The target steering angle instruction 25 is the target steering angle required by the calculation and instruction unit 24 to operate the vehicle according to the route from the route generation unit 23, and is an instruction issued in real time. In contrast, the target steering angle 26a indicates all steering angles that the calculation and instruction unit 24 plans to perform along the route from the route generation unit until parking is complete. While this refers to all steering angles, due to the enormous volume of total time-series data, this includes data reduction by focusing on specific points, such as steering wheel turning locations.

[0035] The power steering system (EPS) 3 includes an automatic steering control unit 31 , an overheat protection current limiter 32 , a parking steering number determination unit 33 , and a motor control unit 34 that outputs a motor current corresponding to a target current.

[0036] The automatic steering control unit 31 receives the target steering angle instruction 25 from the parking assist device 2 and the steering angle information 41 from the steering angle sensor 4 and calculates a target electric motor current required for steering according to the target steering angle.

[0037] The thermal current limiting unit 32 limits the target current based on a thermal current limit value Y calculated from the motor current of the power steering system (EPS) 3, thereby preventing damage to the power steering system (EPS) 3 due to overheating. Specifically, the thermal current limit value Y is the maximum current that can flow through the motor to prevent damage to the motor.

[0038] Reference Figure 2 The operation of the parking possible steering number determination unit 33 of the first embodiment will be described with reference to the flowchart of FIG.

[0039] The parking maneuver count determination unit 33 estimates the target steering amount for each steering turn based on the target steering angle 26a and target vehicle speed 26b required to move from the vehicle's position to the target parking position, which are input from the calculation and instruction unit 24 of the parking assist device 2 (step S1). The input target steering angle 26a does not need to be data for the entire time series until parking assist is completed; it may also be data on the timing of steering turns when the target steering angle changes significantly.

[0040] Based on the target vehicle speed 26b, it is determined whether the vehicle is in a parking turn. The current required for steering the vehicle can be estimated based on the change in the target steering angle 26a, i.e., the target steering amount (step S2). Based on the estimated current, the pre-set estimated motor current for each steering turn is corrected (step S3). Based on the corrected estimated motor current and the aforementioned overheat current limit value Y, an overheat current limit value X is calculated until parking assistance is completed (step S4). This calculation is performed using the same method as the overheat current limit value Y calculated based on the motor current in the overheat current limiter 32, except that the corrected estimated motor current is used instead of the motor current. Specifically, the maximum current value calculated based on the estimated current until parking is completed causes the motor to overheat if it flows. Therefore, the overheat current limit value X until parking assistance is completed is a value that is gradually reduced based on the corrected estimated motor current.

[0041] When the overheat protection current limit value X until parking assistance is completed exceeds the predetermined steering determination current limit threshold (the minimum motor current value required for parking completion) (step S5), the fact that steering can be performed at the input target steering angle 26a is output as the judgment result of the parking determination 35b (step S6).

[0042] On the other hand, if the overheat protection current limit value X is below the threshold, the result of the parking determination 35b indicating that steering at the input target steering angle is not possible is output (step S7). Based on the overheat protection current limit value Y and the pre-set change in the estimated overheat protection current limit value for each steering turn during parking steering, the number of steering turns required for parking steering, i.e., the upper limit 35a of the number of steering turns required for parking steering, is calculated (step S8) and output to the path generation unit 23 of the parking assist device 2 (step S9).

[0043] At this time, the upper limit 35a of the number of parking steering operations can be obtained from a map generated based on the relationship between the overheat protection current limit value Y, a preset parking steering determination current limit threshold, and the estimated change in the overheat protection current limit value for each steering wheel turn including the parking steering operation.

[0044] Alternatively, the value may be calculated by adding a gain corresponding to a previously input target steering angle change amount to the estimated overheat protection current limit value change amount per steering wheel turning of a preset parking steering.

[0045] This allows confirmation of whether the load on the steering system (EPS) 3 in the path generated by the path generation unit 23 is within the permissible range, thereby preventing interruption of the automatic parking control due to a high load on the steering system (EPS) 3. Furthermore, even if a steering error is determined to be impossible, the path generation unit 23 can generate a new path with a higher probability of success by outputting the upper limit 35a of the number of possible parking maneuvers to the path generation unit 23.

[0046] As described above, according to this embodiment, whether parking assistance can be performed for the steering system (EPS) 3 that would cause an overheat condition is determined. Furthermore, even when the steering system (EPS) 3 is overheated, the number of possible parking turns is determined by taking into account the load on the steering system (EPS) 3. This allows the parking assistance system to be notified of the information necessary to calculate a feasible parking path. Consequently, even when the motor is overheated, a shorter parking path than that achieved without parking turns can be calculated.

[0047] Implementation method 2.

[0048] The structure of the electric power steering device in the second embodiment is basically the same as that in the first embodiment, but the input and output signals of the parking assist device 2 and the steering device (EPS) 3 are different. Figure 3: is a schematic configuration diagram of an electric power steering device according to Embodiment 2. That is, in Embodiment 1, control is performed in a state where the upcoming steering is known in advance, but in Embodiment 2, control is performed in a state where the upcoming steering is not known in advance.

[0049] Due to the aforementioned difference in the control precondition, the output of the target steering angle 26a and target vehicle speed 26b required for the vehicle to reach the target parking position from the calculation instruction unit 24 to the parking maneuver number determination unit 33 in the first embodiment is no longer necessary in the second embodiment. Furthermore, the parking availability determination 35b output from the parking maneuver number determination unit 33 in the first embodiment is no longer necessary.

[0050] In this embodiment, the path generation unit 23 detects the distance to the vehicle ahead, behind, or to the side, lanes, parking space lines, obstacles, and the like, using information from, for example, the camera of the surrounding environment sensor group 1. The information required for executing parking control is selected from this information, parking lot map information, GPS information, and the like.

[0051] Then, based on the selected information, the vehicle position information 21 and the target parking position information 22 are calculated. The path from the vehicle position to the target parking position is then combined with the maximum number of parking maneuvers 35a output from the steering system (EPS) 3 to generate a parking path that allows the vehicle to perform parking maneuvers within the maximum number of parking maneuvers 35a. In this case, the path may also include steering without performing parking maneuvers.

[0052] Based on the parking path information for parking steering generated by the path generation unit 23, the calculation and instruction unit 24 calculates a target steering angle instruction 25 required to move from the vehicle's position to the target parking position, and outputs it to the steering system (EPS) 3. Furthermore, the calculation and instruction unit 24 outputs the calculated acceleration and deceleration instructions to the drive system 6 and the calculated braking instructions to the braking system 5. For example, instructions may be given for accelerating along the path, for steering to stop the vehicle between parked vehicles, or for applying the brakes to the wheels to stop the vehicle at the stopped position along the path.

[0053] like Figure 4 As shown in the flowchart shown, the parking steering number determination unit 33 calculates the parking steering number that can be performed before reaching a preset parking steering determination current limit threshold value, i.e., the parking steering number upper limit 35a, based on the overheat protection current limit value Y calculated by the overheat protection current limiting unit 32 based on the motor current of the steering system (EPS) 3 and the estimated overheat protection current limit value change for each steering wheel turning according to the preset parking steering (step S10), and outputs the calculated value to the path generation unit 23 in the parking assist device 2 (step S11).

[0054] At this time, the upper limit 35a of the number of times the steering wheel can be turned again can also be obtained from a mapping generated based on the relationship between the overheating protection current limit value Y, the pre-set current limit threshold for determining whether the steering wheel can be turned again, and the estimated change in the overheating protection current limit value for each steering wheel turn including parking steering.

[0055] In the second embodiment, the load status of the electric steering system (EPS) 3, which uses an electric motor, is not considered during the path generation and calculations of instructions such as target steering angle, acceleration / deceleration, and braking instructions performed by the parking assistance system 2. In other words, the load status cannot be considered because the upcoming steering is unknown in advance. Consequently, the EPS 3 may become unable to steer due to overheat protection during parking assistance, forcing the driver to take over the steering operation. In this case, because the EPS 3 is under a high load, it cannot provide the full steering assistance it normally provides to the driver.

[0056] Therefore, the effectiveness of driving assistance can be ensured by transmitting the upper limit 35a of the number of possible parking maneuvers from the steering system (EPS) 3 to the path generation unit 23. The steering system (EPS) 3 outputs information on the number of steering wheel turns that can be made during parking maneuvers, which increases the load on the steering system (EPS) 3, from the possible parking maneuver number determination unit 33 to the path generation unit 23.

[0057] In this case, the path generation unit 23 is notified of the upper limit 35a of the number of parking maneuvers possible by the steering system (EPS) 3 and calculates the path before parking begins. This allows the generation of a path with a shorter vehicle travel distance compared to a case where a steering wheel turn other than a parking turn is performed after detecting a high load on the steering system (EPS) 3. For example, in parallel parking control where the steering system (EPS) 3 is highly loaded and only two parking turns are possible, the first non-parking turn is performed, and in parallel parking, the final steering turn is performed to adjust the parking direction between vehicles with limited maneuverability. This allows the generation of a path with a shorter final vehicle travel distance.

[0058] Implementation method 3.

[0059] based on Figure 5 and Figure 6 Embodiment 3 will be described. The steering system (EPS) 3 in Embodiment 3 differs from Embodiment 1 or 2 in that it includes an EPS temperature detection unit and a method for calculating an overheat protection current limit value by an overheat protection current limiter 32 .

[0060] While the thermal current limit value for overheat protection is calculated based solely on the motor current in the first and second embodiments, the thermal current limiter 32 of the steering system (EPS) 3 in this embodiment calculates the thermal current limit value based on the EPS temperature and motor current from the EPS temperature detection unit 36. This EPS temperature may also include the temperatures of heat-generating components of the steering system (EPS) 3, such as the motor of the steering system (EPS) 3 and FETs (Field Effect Transistors) in the ECU (Electrical Control Unit) of the steering system (EPS) 3.

[0061] By providing the EPS temperature detection unit 36 ​​, the overheat protection current limit value can be calculated more accurately according to the temperature characteristics of each EPS component.

[0062] exist Figure 7 An example of the hardware structure mounted on the parking assist device 2 and the steering system (EPS) 3 is shown in FIG. It is composed of a processor 100 and a storage device 200. Although not shown in the figure, the storage device includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk may be provided instead of the flash memory. The processor 100 performs processing such as the path generation unit 23, the calculation instruction unit 24, the automatic steering control unit 31, or the parking steering number determination unit 33 by executing the program input from the storage device 200. In this case, the program is input from the auxiliary storage device to the processor 100 via the volatile storage device. In addition, the processor 100 can output data such as the calculation results to the volatile storage device of the storage device 200, and can also save the data to the auxiliary storage device via the volatile storage device. In addition, there may be multiple processors 100 and storage devices 200.

[0063] Although this application describes various exemplary embodiments and examples, the various features, methods, and functions described in one or more embodiments are not limited to the application of specific embodiments and can be applied to the embodiments individually or in various combinations. Therefore, it can be considered that countless variations not illustrated are also included in the technical scope disclosed in this application specification. For example, it is set to include the case where at least one component is deformed, added, or omitted, and the case where at least one component is extracted and combined with the components of other embodiments.

[0064] Label Description

[0065] 1: Surrounding environment sensor group, 2: Parking assist system, 3: Steering system (EPS), 4: Steering angle sensor, 23: Path generation unit, 24: Calculation indication unit, 25: Target steering angle indication, 26a: Target steering angle, 26b: Target vehicle speed, 31: Automatic steering control unit, 32: Overheat protection current limiting unit, 33: Number of possible parking turns determination unit, 34: Electric motor control unit, 35a: Upper limit of the number of possible parking turns, 35b: Parking determination, 36: EPS temperature detection unit, 41: Steering angle information.

Claims

1. An electric power steering device, characterized in that: include: a path generation unit for generating a driving path from the vehicle position to the target parking position; a calculation and indication unit for calculating a target steering angle indication for traveling along the path generated by the path generation unit; an automatic steering control unit for calculating a motor current for causing the steering angle to follow the target steering angle instruction; an overheat protection current limiting unit that calculates a first overheat protection current limit value based on the motor current; as well as a parking steering number determining unit for calculating an upper limit of the parking steering number based on the first overheat protection current limit value; The calculation instruction unit calculates a target steering angle and a target vehicle speed from the vehicle position to the target parking position. The parking steering number determination unit calculates the current amount when the steering wheel is turned based on the change in the target steering angle, corrects a preset estimated motor current amount for each steering wheel turn based on the current amount, and calculates a second overheat protection current limit value until the parking assist is completed based on the corrected estimated motor current amount and the first overheat protection current limit value. When the second overheat protection current limit value until the parking assist is completed is below a preset steering determination current limit threshold, the upper limit of the number of parking steering times that can be performed before reaching the preset parking steering determination current limit threshold is calculated based on the first overheat protection current limit value and the preset change in the estimated overheat protection current limit value for each steering wheel turn.

2. The electric power steering device according to claim 1, wherein When the second overheat protection current limit value until the parking assist is completed exceeds the pre-set steering determination current limit threshold, a steering determination result is output; when the second overheat protection current limit value until the parking assist is completed is below the threshold, a steering determination result is output.

3. The electric power steering device according to claim 2, wherein: The upper limit of the number of possible parking steering operations is obtained based on a map generated from a relationship between the first thermal protection current limit value and an estimated amount of change in the thermal protection current limit value per steering wheel turning of the preset parking steering operation.

4. The electric power steering device according to claim 1, wherein The upper limit of the number of possible parking steering operations is obtained based on a map generated from a relationship between the first thermal protection current limit value and an estimated amount of change in the thermal protection current limit value per steering wheel turning of the preset parking steering operation.

5. The electric power steering device according to any one of claims 1 to 4, characterized in that: The calculation of the first overheat protection current limit value includes the EPS temperature detected by the EPS temperature detection unit.

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