Patent Publication Number: US-2023159091-A1

Title: Electric power steering device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electric power steering device. 
     BACKGROUND ART 
     In a system that performs automatic parking of a vehicle, it has been known that, when a vehicle stops at a turnabout position and performs turnabout, static steering is performed to turn a steering wheel while the vehicle is stopped. Applying an excessive load on an Electric Power Steering (EPS), the static steering is likely to cause the EPS to be overheated. To prevent overheat damage of the EPS, currents need to be limited and overheat protection needs to be performed. 
     To solve these problems, there is a method of estimating the necessary number of static steering and, so as not to cause overheat protection to start unexpectedly during parking assistance, notifying a driver of the estimated number before the start of overheat protection (see Patent Document 1). Alternatively, after static steering has been performed and then the vehicle has been advanced, the steering direction is changed at a stage slightly earlier than when next static steering is performed. In this way, a static steering amount is reduced (see Patent Document 2). In addition, there is still another method of determining one route including static steering and another route not including static steering, and the static steering amount, depending on the temperature of the EPS (see Patent Document 3). 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-19051 
     Patent Document 2: Japanese Laid-Open Patent Publication No. 2015-3565 
     Patent Document 3: Japanese Patent No. 6079596 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In a method disclosed in Patent Document 1, limitation or cancellation of parking assistance by overheat protection cannot be prevented. 
     In a method disclosed in Patent Document 2, after static steering has been performed and then the vehicle has been advanced, the direction is changed into the next steering direction at the stage earlier than usual, thereby reducing the steering angle for performing static steering. However, since a load state of a steering device is not detected, even if parking involving static steering by the steering device is sufficiently possible, a vehicle is parked through the route for reducing the static steering amount. Thus, the number of turnabouts until the completion of parking may be increased. 
     In a method disclosed in Patent Document 3, presence/absence of static steering is determined at the place for turnabout, on the basis of the temperature of the EPS. Accordingly, another route needs to be regenerated during parking control. The route different from the route initially set is to be used, thereby increasing the amount of steering until the completion of parking. Furthermore, a motor may be overheated due to the increased steering amount, and thus automatic parking may be interrupted. 
     The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide an electric power steering device that can avoid a steering disabled state and cancellation of parking assistance caused by an overheated motor during parking control and that allows parking control even in an overheat condition of the motor. 
     Solution to the Problems 
     An electric power steering device according to the present disclosure includes: route generation means for generating a route for driving from an own vehicle position to a target parking position; calculation command means for calculating a target steering angle command for causing a vehicle to drive along the route generated by the route generation means; an automatic steering control unit for calculating motor current for causing a steering angle to be formed according to the target steering angle command; an overheat protection current limit unit for calculating an overheat protection current limit value from the motor current; and a statically-steerable number determination unit for calculating a statically-steerable upper limit number on the basis of the overheat protection current limit value. 
     Effect of the Invention 
     Such an electric power steering device disclosed in the present disclosure can avoid a steering disabled state and cancellation of parking assistance caused by an overheated motor during parking control, and allows parking control even in an overheat condition of the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram of an electric power steering device according to embodiment 1. 
         FIG.  2    is a flowchart illustrating operation of a statically-steerable number determination unit according to embodiment 1. 
         FIG.  3    is a schematic configuration diagram of an electric power steering device according to embodiment 2. 
         FIG.  4    is a flowchart illustrating behavior of a statically-steerable number determination unit according to embodiment 2. 
         FIG.  5    is a schematic configuration diagram of an electric power steering device according to embodiment 3. 
         FIG.  6    is another schematic configuration diagram of the electric power steering device according to embodiment 3. 
         FIG.  7    is an example of a hardware configuration diagram of the electric power steering device according to each of embodiments 1 to 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an electric power steering device according to preferred embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. In the drawings, the same reference characters denote the same or corresponding parts, and detailed description thereof will be omitted. Also in the subsequent embodiments, repeated description of components denoted by the same reference characters will be omitted in the same manner. 
     Embodiment 1 
       FIG.  1    is a schematic configuration diagram of an electric power steering device according to embodiment 1. The electric power steering device includes, as main components, a surrounding environment sensor group  1 , a parking assistance device  2 , an electric power steering (EPS)  3 , and a steering angle sensor  4 . 
     As the surrounding environment sensor group  1 , a camera and sonar for monitoring the front, rear, or sides of a vehicle, a marker sensor for detecting markers in a parking lot, a GPS device for obtaining GPS information, a reception device for receiving map data in a parking lot, and the like are mounted in a vehicle. These sensors or devices detect condition information of the vehicle itself and surrounding information thereof. The information is transmitted to the parking assistance device  2  through a communication line of the vehicle such as a communication line of a Controller Area Network (CAN). 
     The parking assistance device  2  is a device for performing so-called automatic parking, and for outputting a command for changing vehicle behavior by using various information from the surrounding environment sensor group  1 . 
     The parking assistance device  2  includes: route generation means  23  for receiving information from the surrounding environment sensor group  1 , calculating own vehicle position information  21  and target parking position. information  22 , and generating a route to a target parking position; and calculation command means  24  for calculating a signal for a control command on the basis of output from the route generation means  23 . Output from the calculation command means  24  is outputted to control the electric power steering (EPS)  3 , a braking device  5 , and a driving device  6 . 
     In detail, the route generation means  23  detects, for example, a distance to a vehicle located to the front, rear, or side, lanes, a parking frame line, an obstacle, and the like, on the basis of information from the camera of the surrounding environment sensor group  1 . From among the information, map information in a parking lot, OPS information, and the like, the route generation means  23  selects information necessary for performing parking control. On the basis of the selected information, the route generation means  23  calculates the own vehicle position information  21  and the target parking position information  22 , and generates a route from an own vehicle position to a target parking position. 
     The calculation command means  24  calculates the target steering angle command  25  needed from the own vehicle position to the target parking position, according to route information generated by the route generation means  23 , and outputs the target steering angle command  25  to the electric power steering (EPS)  3 . In addition, the calculation command means  24  calculates and outputs an acceleration and deceleration command to the driving device  6  and a braking command to the braking device  5 . For example, the calculation command means  24  issues commands, such as accelerating so as to travel along a route, steering to cause the vehicle to park between parking vehicles, braking wheels to cause the vehicle to stop at a vehicle stop position according to a route, and the lke. That is, commands for performing vehicle speed control needed until the completion of parking are outputted to the electric power steering (EPS)  3 , the braking device  5 , and the driving device  6 . 
     Furthermore, the calculation command means  24  calculates a target steering angle  26   a  and a target vehicle speed  26   b  needed from an own vehicle position to a target parking position. The difference between the target steering angle command  25  and the target steering angle  26   a  described above is as follows. 
     The target steering angle command  25  is a target steering angle needed for the calculation command means  24  to operate the vehicle according to the route generated by the route generation means  23 , and is a command to be performed in real time. Meanwhile, the target steering angle  26   a  refers to all steering to be performed by the calculation command means  24  until the completion of parking along the route generated by the route generation means. The target steering angle  26   a  refers to all the steering, but also refers to reduced data thereof with contents limited to only specific points, such as the place where turnabout is performed, because the data amount for all the time-series data is enormous. 
     The electric power steering (EPS)  3  includes an automatic steering control unit  31 , an overheat protection current limit unit  32 , a statically-steerable number determination unit  33 , and a motor control unit  34  that outputs motor current according to a target current. 
     The automatic steering control unit  31  receives the target steering angle command  25  from the parking assistance device  2  and steering angle information  41  from the steering angle sensor  4 , and calculates a motor target current needed for steering according to the target steering angle. 
     The overheat protection current limit unit  32  limits the target current by using an overheat protection current limit value Y calculated from a motor current amount of the electric power steering (EPS)  3 , to prevent damage due to overheat of the electric power steering (EPS)  3 . That is, the overheat protection current limit value Y is a maximum current value of current that can flow through the motor at present, to prevent the motor from damaging itself. 
     With reference to a flowchart in  FIG.  2   , behavior of the statically-steerable number determination unit  33  of embodiment  1  will be described. 
     The statically-steerable number determination unit  33  estimates a target steering amount for each turnabout, from the target steering angle  26   a  and the target vehicle speed  26   b  inputted from the calculation command means  24  of the parking assistance device  2  and needed from an own vehicle position to a target parking position (step S 1 ). Here, the target steering angle  26   a  to be inputted need not be all time-series data until the completion of parking assistance, and may be data only at each timing of performing turnabout with great change to the target steering angle. 
     On the basis of the target vehicle speed  26   b , whether or not operation is static steering can be determined, and thus, the current amount necessary for turnabout can be estimated from the target steering amount, which is a variation amount of the target steering angle  26   a  (step S 2 ). A predetermined estimated motor current amount per turnabout is corrected by using the estimated current amount (step S 3 ). An overheat protection current limit value X to be used until the completion of parking assistance is calculated, from the corrected estimated motor current amount and the above overheat protection current limit value Y (step S 4 ). This calculation is the same as that for the overheat protection current limit value Y to be calculated from the motor current amount in the overheat protection current limit unit  32 , but is performed using the corrected estimated motor current amount instead of the motor current amount. That is, the overheat protection current limit value X to be used until the completion of parking assistance is a maximum current value of current that can flow through the motor, calculated from the estimated current amount until the completion of parking. Since the motor is overheated when the current flows, the overheat protection current limit value X is a value that basically decreases depending on the corrected estimated motor current amount. 
     When the overheat protection current limit value X until the completion of parking assistance exceeds a predetermined steerable determination current limit threshold (a minimum motor current value needed until parking has been completed) (step S 5 ), a fact that steering can be performed at the inputted target steering angle  26   a  is outputted as a determination result of a parking possibility determination  35   b  (step S 6 ). 
     On the other hand, when the overheat protection current limit value X is not greater than the steerable determination current limit threshold, a fact that steering cannot be performed at the inputted target steering angle is our as a result of the parking possibility determination  35   b  (step S 7 ). Then, a statically-steerable upper limit number  35   a  is calculated, from the overheat protection current limit value Y and a predetermined estimated overheat protection current limit value variation amount per turnabout with static steering (step S 8 ). Here, the statically-steerable upper limit number  35   a  is the number of times of turnabouts with static steering allowable until a predetermined statically-steerable determination current limit threshold is reached. The statically-steerable upper limit number  35   a  is outputted to the route generation means  23  of the parking assistance device  2  (step S 9 ). 
     In this case, the statically-steerable upper limit number  35   a  may be obtained through a map generated from a relationship between the overheat protection current limit value Y, the predetermined statically-steerable determination current limit threshold, and the estimated overheat protection current limit value variation amount per turnabout with static steering. 
     Alternatively, a gain depending on the target steering angle variation amount inputted in advance is added to the predetermined estimated overheat protection current limit value variation amount per turnabout with static steering, and the obtained value may be used for the calculation as well. 
     In this case, whether or not a load of the electric power steering (EPS)  3  in the route generated by the route generation means  23  is within an acceptable range can be checked, thereby preventing automatic parking control from being interrupted during automatic parking control due to the electric power steering (EPS)  3  being in a high-load condition. Furthermore, even if it is determined that steering cannot be performed, the statically-steerable upper limit number  35   a  is outputted to the route generation means  23 , and thus the route generation means  23  can add the statically-steerable upper limit number  35   a  as a condition to regenerate a more feasible route. 
     According to the present embodiment, as described above, whether or not the electric power steering (EPS)  3  is in an overheat condition and whether or not the scheduled parking assistance can be performed are determined. Even when the electric power steering (EPS)  3  is in an overheat condition, the statically-steerable number is determined in consideration of a load of the electric power steering (EPS)  3 , and thus the parking assistance device can be notified of information necessary for calculation of a feasible parking route. Therefore, a shorter route in which parking is performed than a parking route in which static steering is not performed can be calculated, even when the motor is in an overheat condition. 
     Embodiment 2 
     A configuration of an electric power steering device according to embodiment 2 is basically not different from that of embodiment 1, but input and output signals for the parking assistance device  2  and the electric power steering (EPS)  3  are different.  FIG.  3    is a schematic configuration diagram of the electric power steering device according to embodiment 2. That is, in embodiment 1, control is performed in a state in which steering to be performed has been recognized in advance, whereas in embodiment 2, control is performed in a state in which steering to be performed has not been recognized in advance. 
     With such difference between the states to be a precondition for control, the target steering angle  26   a  and the target vehicle speed  26   b  needed from an own vehicle position to a target parking position, which are outputted from the calculation command means  24  to the statically-steerable number determination unit  33  in embodiment 1, need not be outputted in embodiment 2. Furthermore, the parking possibility determination  35   b  which is outputted from the statically-steerable number determination unit  33  in embodiment 1 need not be outputted in embodiment 2. 
     In embodiment 2, route generation means  23  detects, for example, a distance to a vehicle located to the front, rear, or side, lanes, a parking frame line, an obstacle, and the like, on the basis of information from a camera of a surrounding environment sensor group  1 . From among the information, map information in a parking lot, GPS information, and the like, the route generation means  23  selects information necessary for performing parking control. 
     Furthermore, on the basis of the selected information, the route generation means  23  calculates own vehicle position information  21  and target parking position information  22 . A statically-steerable upper limit number  35   a , which is outputted from the electric power steering (EPS)  3 , is added as a condition, and as a route from an own vehicle position to a target parking position, a parking route in which static steering is performed within the statically-steerable upper limit number  35   a  is generated. In this case, turnabout in which static steering is not performed may be included. 
     Calculation command means  24  calculates a target steering angle command  25  needed from the own vehicle position to the target parking position, according to information, generated by the route generation means  23 , on a parking route in which static steering is performed, and outputs the target steering angle command  25  to the electric power steering (EPS)  3 . In addition, the calculation command means  24  calculates and outputs an acceleration and deceleration command to a driving device  6  and a braking command to a braking device  5 . For example, the calculation command means  24  issues commands, such as accelerating so as to travel along a route, steering to cause the vehicle to park between parking vehicles, braking wheels to cause the vehicle to stop at a vehicle stop position according to a route, and the like. 
     As shown in a flowchart illustrated in  FIG.  4   , a statically-steerable number determination unit  33  calculates a statically-steerable upper limit number  35   a , from an overheat protection current limit value Y calculated from a motor current amount of the electric power steering (EPS)  3  in an overheat protection current limit unit  32 , and a predetermined estimated overheat protection current limit value variation amount per turnabout with static steering (step S 10 ). Here, the statically-steerable upper limit number  35   a  is the number of times of turnabout with static steering allowable until a predetermined statically-steerable determination current limit threshold is reached. The statically-steerable upper limit number  35   a  is outputted to the route generation means  23  of a parking assistance device  2  (step S 11 ). 
     In this case, the statically-steerable upper limit number  35   a  may be obtained through a map generated from a relationship between the overheat protection current limit value Y, the predetermined statically-steerable determination current limit threshold, and the estimated overheat protection current limit value variation amount per turnabout with static steering. 
     In embodiment 2, a load condition of the electric power steering (EPS)  3  using a motor is not used at the time of generation of a route or calculation of commands, such as a target steering angle command, an acceleration and deceleration command, a braking command, and the like, each of which is processing of the parking assistance device  2 . That is, since steering to be performed has not been recognized in advance, a load condition cannot be considered. Therefore, if the electric power steering (EPS)  3  falls into a steering disabled state during parking assistance due to overheat protection, it is necessary for a driver to take over the steering halfway through parking control. However, being in a high-load condition, the electric power steering (EPS)  3  cannot sufficiently perform steering assistance, that is, assistance to a driver&#39;s steering to be usually performed. 
     In this case, the statically steerable upper limit number  35   a  is sent from the electric power steering (EPS)  3  to the route generation means  23 , whereby feasibility of driving assistance can be ensured. The electric power steering (EPS)  3  outputs, from the statically-steerable number determination unit  33 , information on the number of times that the vehicle can perform turnabout with static steering during which the electric power steering (EPS)  3  may fall into a high-load condition, to the route generation means  23 . 
     In this case, since the electric power steering (EPS)  3  notifies the route generation means  23  of the statically-steerable upper limit number  35   a  and a route is calculated before the start of parking operation, a route with a shorter vehicle movement distance can be generated, compared to a case where turnabout without static steering is performed after the electric power steering (EPS)  3  is detected to be in a high-load condition. For example, during parallel parking control in which a vehicle can perform static steering only twice due to the electric power steering (EPS)  3  being in a high load condition, steering without static steering is performed first, and then turning back with static steering is performed when a vehicle is driven between a front vehicle and a rear vehicle in parallel parking and when final turnabout is performed so as to align a parking direction between the vehicles within a limited vehicle-movable space. Thus, a route with a consequently shorter vehicle movement distance can be generated. 
     Embodiment 3 
     Embodiment 3 will be described with reference to  FIG.  5    or  FIG.  6   . An electric power steering (EPS)  3  in embodiment 3 is different from embodiment 1 or embodiment 2 in that the electric power steering (EPS)  3  in embodiment 3 includes EPS temperature detection means, and a method for calculating an overheat protection current limit value in an overheat protection current limit unit  32  is also different as below. 
     In embodiment 1 or embodiment 2, the overheat protection current limit value is calculated solely from the motor current amount. However, the overheat protection current limit unit  32  of the electric power steering (EPS) according to embodiment 3 calculates the overheat protection current limit value from an EPS temperature from an EPS temperature detection means  36 , and a motor current amount. This EPS temperature may indicate any of temperatures of heat generation components, such as a motor of the electric power steering (EPS)  3 , a Field Effect Transistor (FET) mounted in. an Electric Control Unit (ECU) of the electric power steering (EPS)  3 , and the like, constituting the electric power steering (EPS)  3 . 
     The EPS temperature detection means  36  enables more accurate calculation of the overheat protection current limit value according to temperature characteristics for each EPS component. 
     In  FIG.  7   , an example of a hardware configuration mounted in a parking assistance device  2  and the electric power steering (EPS)  3  is shown. The parking assistance device  2  and the electric power steering (EPS)  3  include a processor  100  and a storage device  200 . Although not shown, 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. The storage device  200  may also include an auxiliary storage device of a hard disk instead of the flash memory. The processor  100  executes a program inputted from the storage device  200  to perform processing of, for example, the route generation means  23 , the calculation command means  24 , the automatic steering control unit  31 , the statically-steerable number determination unit  33 , or the like. In this case, the program is inputted into the processor  100  from the auxiliary storage device via the volatile storage device. Tne processor  100  may also output data such as a calculation result to the volatile storage device of the storage device  200 , or may store data into the auxiliary storage device via the volatile storage device. A plurality of the processors  100  and the storage devices  200  may be provided. 
     Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations to one or more of the embodiments of the disclosure. It is therefore understood that numerous modifications which have not been exemplified can be devised without departing from the scope of the present disclosure. For example, at least one of the constituent components may be modified, added, or eliminated. At least one of the constituent components mentioned in at least one of the preferred embodiments may be selected and combined with the constituent components mentioned in another preferred embodiment. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
       1  surrounding environment sensor group 
       2  parking assistance device 
       3  electric power steering (EPS) 
       4  steering angle sensor 
       23  route generation means 
       24  calculation command means 
       25  target steering angle command 
       26   a  target steering angle 
       26   b  target vehicle speed 
       31  automatic steering control unit 
       32  overheat protection current limit unit 
       33  statically-steerable number determination unit 
       34  motor control unit 
       35   a  statically-steerable upper limit number 
       35   b  parking possibility determination 
       36  EPS temperature detection means 
       41  steering angle information