Steering system

Abstract

The present application provides a steering system that can suppress a decrease in turning accuracy even when a temperature sensor has failed. The present application is a steer-by-wire type steering system, and a control device (5) is provided with a plurality of arithmetic units (51, 54), a plurality of temperature sensors (53, 56), and a plurality of drive circuits (52, 55). Each arithmetic unit (51, 54) is configured to, in a case where a detected temperature difference that is a difference between detected temperatures of any two temperature sensors (53, 56) among the plurality of temperature sensors (53, 56) is greater than a prescribed threshold value, operate and set, as an upper limit value of a steering current, a current limit value that is based on a detected temperature of a temperature sensor (53, 56) corresponding to the arithmetic unit itself independently of a detected temperature of a temperature sensor (53, 56) corresponding to an arithmetic unit other than the arithmetic unit itself.

Description

TECHNICAL FIELD

[0001] The present application relates to a steering system. BACKGROUND

[0002] Generally, in a steering system, in a case where the temperature of a motor as a driving source exceeds a threshold value, in order to suppress a failure caused by heat generation of the motor and a motor driving circuit, current limitation control that limits a current (hereinafter, referred to as a steering current) applied to the motor is executed. However, in a case where the temperature of the motor is not estimated with good precision, the steering current is limited although it is not in a state of overheating, and thus the motor torque can be reduced. Therefore, for example, in Japanese Patent Application Publication No. 2012-148629, an electric power steering device is disclosed in which, in a case where a difference between a present value and a previous value of a substrate temperature sensor is larger than a prescribed threshold value, the previous value is stored as a reference value for estimation of the temperature of the motor. In the device, the temperature of the motor is estimated on the basis of the previous value that is a value before a large change in the substrate temperature, until an abnormal state of the substrate temperature sensor is determined. Therefore, according to the device, it is possible to suppress execution of the current limitation control at an early timing before the abnormality of the substrate temperature sensor is determined.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-148629

[0006] The current limitation control based on the detected temperature of the temperature sensor is also provided in a steer-by-wire type steering system in which a steering motor and an operation force of an operation member are independent of each other to steer a wheel. When the current limitation control is executed in the steer-by-wire type steering system, the maximum value of the steering current is limited and the operation force of the driver does not contribute to direct steering, and thus the turning desired by the driver can not be achieved.

[0007] The temperature sensor used in the steer-by-wire type steering system has a function of detecting a failure in which the detected temperature is fixed at a maximum value or a minimum value. Therefore, when the fixed failure of the temperature sensor is detected, an arithmetic unit (for example, a microcomputer or an ECU (Electronic Control Unit)) can determine that the detected temperature is an abnormal value, and the current limitation control is prohibited. SUMMARY

[0008] However, there is no function of detecting a drift failure in which the detected temperature becomes indefinite between the maximum value and the minimum value in the temperature sensor and the arithmetic unit. Therefore, in a case where the current limit control is executed due to the drift failure, the turning accuracy can be reduced at a timing at which the current limit is not originally required.

[0009] An object of the present application is to provide a steering system in which reduction in turning accuracy is suppressed even in a case where a temperature sensor has failed.

[0010] The steering system of the present application is a steer-by-wire type steering system including a steering device having a steering motor that steers a wheel mechanically independently of an operation force of an operation member, and a control device that supplies a steering current to the steering motor in accordance with a steering request to control the steering motor, wherein the control device includes a plurality of arithmetic units connected to be able to communicate with each other, each of which calculates a current value of the steering current in accordance with the steering request, a plurality of drive circuits corresponding to the plurality of arithmetic units individually, each of which supplies the steering current to the steering motor through control of the corresponding arithmetic unit, and a plurality of temperature sensors corresponding to the plurality of arithmetic units individually, each of which detects a temperature of the corresponding arithmetic unit, and each of the arithmetic units is configured to, in a case where a detected temperature difference as a difference between detected temperatures of any two of the temperature sensors is larger than a prescribed threshold value, perform independent arithmetic control based on the detected temperature of the temperature sensor corresponding to itself independently of the detected temperatures of the temperature sensors corresponding to the arithmetic units other than itself, and set a current limit value as an upper limit value of the steering current.

[0011] Effects of Invention

[0012] The present application assumes that the possibility of a plurality of temperature sensors simultaneously becoming drift failure is extremely low, and is configured to suppress reduction in turning accuracy even in a case where one temperature sensor has failed. Specifically, according to the present application, a case where the detected temperature of one temperature sensor becomes a value deviated from a normal detected temperature due to a failure such as drift failure is detected through comparison with the detected temperature of another normal temperature sensor. The control device determines that one temperature sensor has failed and performs independent arithmetic control in a case where the detected temperature difference is larger than a prescribed threshold value.

[0013] In the independent operation control, each operation section operates the current limit value based on the detected temperature of its own temperature sensor regardless of the detected temperature of the temperature sensor corresponding to the other operation section. Thus, in the operation section corresponding to the normal temperature sensor, the current limit value corresponding to the actual detected temperature is set, and only the operation section corresponding to the temperature sensor that has failed operates the excessively limited current limit value. That is, according to the present application, even if a failure occurs in one temperature sensor, the unnecessary decrease in the current limit value is suppressed in the operation section corresponding to the normal temperature sensor in a state where the actual temperature is not high to the extent that the current is limited. Thus, according to the present application, even if a failure occurs in one temperature sensor, the unnecessary decrease in the torque caused by the limitation of the steering current is suppressed, and thus the decrease in the turning accuracy is suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a configuration diagram of the steering system of the present embodiment.

[0015] Figure 2 is a configuration diagram of the steering ECU of the present embodiment.

[0016] Figure 3 is a conceptual diagram showing the limit value map of the present embodiment.

[0017] Figure 4 is a flowchart for explaining the cooperative operation control of the first operation section of the present embodiment.

[0018] Figure 5 is a flowchart for explaining the cooperative operation control of the second operation section of the present embodiment.

[0019] Figure 6 is a flowchart for explaining the independent operation control of the first operation section of the present embodiment.

[0020] Figure 7 is a flowchart for explaining the independent operation control of the second operation section of the present embodiment.

[0021] Figure 8 is a conceptual diagram showing the limit value map of the present embodiment.

[0022] Figure 9 is a flowchart related to the switching of the operation control of the present embodiment.

[0023] Figure 10 is a configuration diagram of the modified example of the present embodiment.

[0024] EXPLANATION OF REFERENCE NUMERALS:

[0025] 1: Steering system; 3: Front wheel steering device (steering device); 5: Steering ECU (control device); 50: Baseboard; 51: First microcomputer (first arithmetic unit); 52: First drive circuit; 53: First temperature sensor; 54: Second microcomputer (second arithmetic unit); 55: Second drive circuit; 56: Second temperature sensor; 57: Third microcomputer (third arithmetic unit); 58: Third drive circuit; 59: Third temperature sensor. Detailed Implementation

[0026] Hereinafter, the steering system 1, as an embodiment of the present invention, will be described in detail with reference to the accompanying drawings. It should be noted that, in addition to the embodiments described below, the present invention can be implemented through various modifications and improvements based on the knowledge of those skilled in the art.

[0027] like Figure 1 As shown, the steering system 1 of this embodiment includes a mechanically independent operating device 2 and a front wheel steering device (equivalent to "steering device") 3. The front wheel steering device 3 steering a pair of front wheels 10F. Furthermore, the steering system 1 also includes a steering ECU 5 as a control device to control the front wheel steering device 3 according to steering requests. The steering system 1 is a steer-by-wire type steering system. It should be noted that, hereinafter, the front wheels 10F and rear wheels 10R are sometimes collectively referred to as wheels 10. Furthermore, the drive wheel is, for example, the rear wheel 10R.

[0028] (Operating device)

[0029] The operating device 2 includes a steering wheel 21, a steering shaft 22, a steering column 23, a reaction force applying mechanism 24, and an operating angle sensor 25 as operating components. The steering wheel 21 is the operating component for the driver to perform steering operations (steering operations). The steering shaft 22 is a shaft component on which the steering wheel 21 is mounted. The steering column 23 is a component that holds the steering shaft 22 in a rotatable position and supports it to the instrument panel reinforcement (not shown).

[0030] The reaction force applying mechanism 24 uses a reaction force motor 26, which is an electric motor supported on the steering column 23, as a power source to apply the reaction force (hereinafter also referred to as "operation reaction force") to the steering wheel 21 via the steering shaft 22. The reaction force applying mechanism 24 has a general structure including a reducer, etc. A rotation angle sensor 26a is provided in the reaction force motor 26. The operation angle sensor 25 is a sensor that detects the operation angle of the steering wheel 21 to serve as the amount of steering operation.

[0031] Further, in the steering system 1, a torsion bar 27 is assembled to the steering shaft 22 as in a general so-called power steering system. The operation device 2 has an operation torque sensor 28 for detecting an operation torque as an operation force applied by the driver to the steering wheel 21 based on a torsion amount of the torsion bar 27.

[0032] (front wheel steering device)

[0033] Each of the wheels 10 is supported to the vehicle body in a steerable manner via a knuckle 90 as one component of a suspension device. The front wheel steering device 3 steers the pair of front wheels 10F integrally by turning the knuckles 90. The front wheel steering device 3 has a steering actuator 30 as a main component.

[0034] The steering actuator 30 is provided with a steering lever 31, a housing 32, a lever moving mechanism 33, and a steering motor 35. The steering lever 31 (also referred to as "rack lever") is a member whose both ends are linked to the left and right knuckles 90 via links 34, respectively. The housing 32 is a member that supports the steering lever 31 so as to be movable leftward and rightward, and is fixed to the vehicle body.

[0035] The lever moving mechanism 33 is a mechanism for moving the steering lever 31 leftward and rightward with the steering motor 35 as a drive source. The lever moving mechanism 33 is a mechanism that takes a ball screw mechanism as a main body, which is constituted by a ball groove screwed to the steering lever 31 and a nut that is screwed to the ball groove via a bearing ball and is rotated by the steering motor 35. Since it is a general configuration, detailed description of the lever moving mechanism 33 is omitted.

[0036] The steering motor 35 is provided with a rotation angle sensor 35a and a current sensor 35b that detects a current supplied to itself. Further, the front wheel steering device 3 has a steering angle sensor 36 that detects amounts of movement from a neutral position of the steering lever 31 to the left and right, respectively, in order to detect a steering angle (steering amount) of the front wheels 10F. Thus, the front wheel steering device 3 constitutes a steer-by-wire type steering device that steers the front wheels 10F by a force of the steering motor 35 mechanically independently of an operation force of the steering wheel 21.

[0037] The steering ECU 5 is an electronic control unit provided with a CPU (Central Processing Unit) and a memory, and the like. Although the illustration of a communication line is omitted, the steering ECU 5 is communicably connected to each device and each sensor. A CAN (car area network or controllable area network) is used in communication within the vehicle. Further, an automatic driving ECU 9 that performs control related to automatic driving is mounted in the vehicle. Further, various sensors such as a wheel speed sensor 82 are mounted in the vehicle.

[0038] The steering ECU 5 performs steering control for steering the front wheels 10F in accordance with a steering request, that is, an operation angle of the steering wheel 21 at the time of manual driving or an instruction from the automatic driving ECU 9 at the time of automatic driving. The steering ECU 5 acquires the operation angle of the steering wheel 21 based on a rotation angle of the reaction force motor 26 detected by the rotation angle sensor 26a. The steering ECU 5 decides a target front wheel steering angle that becomes a target of a steering angle of the front wheels 10F based on the operation angle.

[0039] The steering ECU 5 decides a target rotation angle that is a target of a rotation angle of the steering motor 35 based on the target front wheel steering angle. The steering ECU 5 detects an actual rotation angle (hereinafter also referred to as "actual rotation angle") of the steering motor 35 via the rotation angle sensor 35a, and decides a rotation angle deviation that is a deviation of the actual rotation angle with respect to the target rotation angle. If a torque generated by the steering motor 35 is referred to as a steering torque, the steering ECU 5 decides a steering torque that should be generated in accordance with a feedback control rule based on the rotation angle deviation.

[0040] If a current supplied to the steering motor 35 is referred to as a steering current, the steering torque is in a substantially proportional relationship with the steering current. In accordance with this relationship, the steering ECU 5 decides a steering current that should be supplied to the steering motor 35 based on the decided steering torque, and supplies the steering current to the steering motor 35.

[0041] The steering system 1 further has a reaction force ECU 4 that performs reaction force control for giving the driver a sense of operation with respect to the steering operation. The reaction force ECU 4 decides an operation reaction force based on two components, that is, a steering load-dependent component FS and an operation force-dependent reduction component FA. The steering load-dependent component FS is a component related to a steering force (steering torque of the steering motor 35) required to steer the front wheels 10F, and is decided based on a steering current supplied to the steering motor 35. Although detailed description is omitted, the higher the current value of the steering current, the more the steering load of the front wheels 10F is considered to be large, and thus the steering load-dependent component FS is decided to be a larger value.

[0042] On the other hand, the reduced component FA of the operating force can be considered as a component that imparts a so-called operating feel to the driver in the power steering system. In a power steering system, generally speaking, an auxiliary torque corresponding to the operating torque is applied to the steering shaft 22. The reaction force ECU4 detects the operating torque via the operating torque sensor 28. Based on the operating reaction force, the reaction force ECU4 determines the reaction force current as the current supplied to the reaction force motor 26, and supplies the determined reaction force current to the reaction force motor 26.

[0043] (Detailed composition of the steering ECU)

[0044] like Figure 2 As shown, the steering ECU 5 mainly includes a first microcomputer 51 as a first arithmetic unit, a first drive circuit 52, a first temperature sensor 53, a second microcomputer 54 as a second arithmetic unit, a second drive circuit 55, and a second temperature sensor 56. The first microcomputer 51 is a microcomputer mounted on the substrate 50 and includes a CPU, memory, etc. The first microcomputer 51 determines the current value of the first steering current supplied to the steering motor 35 via the first drive circuit 52. The first microcomputer 51 controls the first drive circuit 52 by supplying the first steering current to the steering motor 35 (PWM (Pulse-Width Modulation) control).

[0045] The first drive circuit 52 is a motor drive circuit that drives the steering motor 35. It is configured to include multiple switching elements to correspond to the three phases of the steering motor 35. The first drive circuit 52 is disposed on the substrate 50 and is communicatively connected to the first microcomputer 51. The first drive circuit 52 supplies power from a battery (not shown) to the steering motor 35 according to the control of the first microcomputer 51.

[0046] The first temperature sensor 53 is a temperature sensor used to detect the temperature of the first microcomputer 51. The first temperature sensor 53 is disposed inside the first microcomputer 51. The first temperature sensor 53 is connected to the first microcomputer 51 in a communicative manner and sends the detected temperature (detection result) information to the first microcomputer 51. It should be noted that the first temperature sensor 53 can also be disposed on the substrate 50 near (peripherally to) the first microcomputer 51 within the range that can detect (estimate) the temperature of the first microcomputer 51.

[0047] The second microcomputer 54, like the first microcomputer 51, is a microcomputer provided with a CPU, a memory, and the like, which is arranged on the substrate 50. The second microcomputer 54 determines a current value of a second rudder current to be supplied to the rudder motor 35 via the second drive circuit 55. The second microcomputer 54 controls (PWM control) the second drive circuit 55 in such a manner that the second rudder current is supplied to the rudder motor 35. The first microcomputer 51 and the second microcomputer 54 are connected to each other in a communicable manner.

[0048] The second drive circuit 55 is a motor drive circuit that drives the rudder motor 35, and is arranged so as to include a plurality of switching elements corresponding to three phases of the rudder motor 35. The second drive circuit 55 is arranged on the substrate 50, and is connected to the second microcomputer 54 in a communicable manner. The second drive circuit 55 supplies electric power of a battery, which is omitted from illustration, to the rudder motor 35 in accordance with the control of the second microcomputer 54.

[0049] The second temperature sensor 56 is a temperature sensor for detecting a temperature of the second microcomputer 54. The second temperature sensor 56 is arranged inside the second microcomputer 54. The second temperature sensor 56 is connected to the second microcomputer 54 in a communicable manner, and transmits information of a detected temperature (a detection result) to the second microcomputer 54. Note that the second temperature sensor 56 can also be arranged on the substrate 50 in the vicinity (periphery) of the second microcomputer 54 within a range in which the temperature of the second microcomputer 54 can be detected (estimated).

[0050] The rudder motor 35 is an electric motor of a double-winding type provided with a winding 351 connected to the first drive circuit 52 and a winding 352 connected to the second drive circuit 55. That is, the rudder motor 35 is arranged so as to output a rudder torque corresponding to a rudder current (also referred to as a total rudder current) that is a sum of the first rudder current supplied from the first drive circuit 52 and the second rudder current supplied from the second drive circuit 55. The rudder current supplied from the battery via the rudder ECU 5 is the sum of the first rudder current and the second rudder current.

[0051] In order to have redundancy with respect to the drive of the rudder motor 35, the first microcomputer 51 and the second microcomputer 54 of the rudder ECU 5 always implement the same operation as each other. The first microcomputer 51 and the second microcomputer 54 transmit and receive information of an operation result to and from each other. In the case where a failure occurs in one of the operation sections, the rudder motor 35 can be driven by the other operation section. In the present embodiment, the first microcomputer 51 is a master microcomputer, and the second microcomputer 54 is a slave microcomputer.

[0052] (Current limitation against overheating)

[0053] The rudder ECU 5 is arranged so as to be able to execute current limitation control for protecting the ECU from overheating when a detected temperature exceeds a prescribed threshold temperature T thThis control reduces the upper limit of the steering current. For example... Figure 3 As shown, the steering ECU5 stores a limit value mapping diagram representing the current limit value (upper limit value) for the temperature of the ECU or microcomputer. The current limit value is the upper limit (maximum allowed value) of the steering current that the steering ECU5 is allowed to supply to the steering motor 35.

[0054] The steering ECU 5 sets the current limit value based on the temperatures detected by the first temperature sensor 53 and the second temperature sensor 56. When the detected temperature exceeds the threshold temperature T... th At that time, the current limit value gradually decreases to the minimum value I as the temperature rises. min When it reaches a certain temperature, it reaches its lowest value I. min To become constant. Figure 3 In the middle, the highest value I max It is set to the highest current value that can flow through each drive circuit 52, 55. In addition, the lowest value I... min For example, it is the lowest current value that can flow through each drive circuit 52, 55, and it is less than the highest value I. max 50% of the value. Highest value I max The steering current is supplied to the steering motor 35, thereby outputting the maximum steering torque.

[0055] In the steering ECU5 of this embodiment, cooperative operation control and independent operation control are set as the system's operating modes (or steering current operation modes). In other words, the steering ECU5 is configured to execute cooperative operation control and independent operation control at different timings.

[0056] (Collaborative computation control)

[0057] The cooperative operation control is a control (operation mode) in which the first microcomputer 51 and the second microcomputer 54 set current limit values ​​based on the detected temperature T1 of the first temperature sensor 53 and the detected temperature T2 of the second temperature sensor 56, respectively. The cooperative operation control also involves each microcomputer 51 and 54 setting the same current limit value. Furthermore, the cooperative operation control involves each microcomputer 51 and 54 setting the same steering current value.

[0058] In cooperative calculation control, the first microcomputer 51 and the second microcomputer 54 calculate the current limit value based on the higher of the detected temperatures T1 and T2. Cooperative calculation control can be described as the control by which the second microcomputer 54 uses the calculation result of the first microcomputer 51 to calculate the current value of the second steering current. Furthermore, cooperative calculation control can also be described as the control by which multiple computing units collaboratively calculate the steering current.

[0059] More specifically, such as Figure 4As shown, when a steering request is received (the steering wheel 21's operating angle during manual driving or an instruction from the automatic driving ECU 9 during automatic driving), the first microcomputer 51 calculates the current value J1 (S101) corresponding to the steering request. Hereinafter, the current value calculated based on the steering request will also be referred to as the "calculated value". The first microcomputer 51 sets the current limit value I as described later. lim (S102), and then compare the calculated value J1 with the current limit value I. lim Comparison (S103).

[0060] like Figure 5 As shown, similarly to the first microcomputer 51, when the second microcomputer 54 receives a steering request, it calculates the current value J2 of the steering current corresponding to the steering request (S201). The second microcomputer 54 receives the calculated value J1 from the first microcomputer 51. In cooperative operation control, the second microcomputer 54 sets the calculated value J1 of the first microcomputer 51 as the calculated value used in the second microcomputer 54 (S202). That is, in cooperative operation control, the second microcomputer 54 calculates the current value of the second steering current based on the calculated value J1 of the first microcomputer 51 (using calculated value J1). The second microcomputer 54 sets the current limit value I as described later. lim (S203), and then compare the calculated value J1 with the current limit value I. lim Comparison (S204).

[0061] The first microcomputer 51 calculates a current limit value corresponding to the detected temperature T1 of the first temperature sensor 53 based on the limit value mapping map, and uses it as a temporary limit value I1. Similarly, the second microcomputer 54 calculates a current limit value corresponding to the detected temperature T2 of the second temperature sensor 56 based on the limit value mapping map, and uses it as a temporary limit value I2. The first microcomputer 51 and the second microcomputer 54 exchange information about the temporary limit values. In the cooperative operation control, the first microcomputer 51 and the second microcomputer 54 set the lower of the temporary limit values ​​I1 and I2 as the current limit value I1. lim (S102, S203). In other words, in the cooperative operation control, the first microcomputer 51 and the second microcomputer 54 respectively set the current limit value corresponding to the higher value of the detected temperature of the first temperature sensor 53 and the detected temperature of the second temperature sensor 56 as a common current limit value I. lim .

[0062] The first microcomputer 51 and the second microcomputer 54 respectively input the calculated value J1 and the current limit value I. lim The lower value in the value is set as the steering current value (hereinafter also referred to as the command value). The first microcomputer 51 and the second microcomputer 54 respectively multiply the command value by 1 / 2 to obtain the value (hereinafter also referred to as the final calculated value). eEach is set to its respective steering current (S104, S205). The first microcomputer 51 calculates the final value I. e The first drive circuit 52 is controlled by supplying the first rudder current to the winding 351 of the rudder motor 35, which is set as the first rudder current. The second microcomputer 54 calculates the final value I. e The second drive circuit 55 is controlled by setting the current value of the second steering current to the winding 352 of the steering motor 35.

[0063] In cooperative control, the first steering current and the second steering current become the same value. The sum of the first steering current and the second steering current becomes the calculated value J1 and the current limit value I. lim The lower value in (min(J1, I) lim Therefore, in cooperative operation control, the current value supplied to the steering motor 35 is either set to the operation value J1 corresponding to the steering request, or the current value is limited to the current limit value I. lim The steering current. In cooperative operation control, when the calculated value J1 is less than the current limit value I... lim In this case, the steering current supplied to the steering motor 35 is set to the calculated value J1, and the calculated value J1 is the current limit value I. lim In the above case, the steering current supplied to the steering motor 35 is set to the current limit value I. lim It should be noted that collaborative operation control can also be referred to as collaborative action mode or first action mode.

[0064] (Independent operation control)

[0065] Independent operation control is a control (operation mode) in which the first microcomputer 51 and the second microcomputer 54 independently calculate the current value of their respective steering currents (first steering current or second steering current). That is, in independent operation control, the first microcomputer 51 calculates the first steering current value independently of the calculation results of the second microcomputer 54, and the second microcomputer 54 calculates the second steering current value independently of the calculation results of the first microcomputer 51. Therefore, in independent operation control, sometimes the final calculated value I is used as the result of the calculation. e The first microcomputer 51 and the second microcomputer 54 differ. Independent operation control means that each microcomputer 51 and 54 can be set with different current limit values. Furthermore, independent operation control means that each microcomputer 51 and 54 can be set with different steering current values.

[0066] like Figure 6As shown, in independent operation control, the first microcomputer 51 calculates the current value (calculated value) J1 of the steering current corresponding to the steering request (S301). The first microcomputer 51 uses the calculated value J1 for the calculation of the first steering current, regardless of the calculated value J2, which is the result of the calculation by the second microcomputer 54.

[0067] The first microcomputer 51 sets the current limit value corresponding to the detection temperature T1 of the first temperature sensor 53 as the first current limit value I based on the limit value mapping map. lim1 (S302). First current limit value I lim1 This is equivalent to the temporary limit value I1 in collaborative operation control. Thus, in independent operation control, the first microcomputer 51 and the second microcomputer 54 calculate the current limit value (hereinafter referred to as the second current limit value I1) based on the detected temperature T2 of the second temperature sensor 56. lim2 Regardless of the temperature T1 detected by the first temperature sensor 53, the current limit value (first current limit value I) is set. lim1 ).

[0068] The first microcomputer 51 compares the calculated value J1 with the first current limit value I. lim1 The first microcomputer 51 compares the calculated value J1 with the first current limit value I (S303). lim1 The value obtained by multiplying the lower value (instruction value) by 1 / 2 is the first final operation value. e1 The current value is set as the first steering current (S304). The first microcomputer 51 controls the first drive circuit 52 in such a way that the set first steering current is supplied to the winding 351 of the steering motor 35.

[0069] like Figure 7 As shown, the second microcomputer 54, like the first microcomputer 51, calculates the current value (calculated value) J2 of the steering current corresponding to the steering request (S401). In independent operation control, the second microcomputer 54 uses the calculated value J2 for the calculation of the second steering current, regardless of the calculated value J1, which is the result of the calculation by the first microcomputer 51. It should be noted that the input steering request is the same in both the first microcomputer 51 and the second microcomputer 54; therefore, the calculated value J1 and the calculated value J2 are usually the same value.

[0070] The second microcomputer 54 sets the current limit value corresponding to the detection temperature T2 of the second temperature sensor 56 as the second current limit value I based on the limit value mapping map. lim2 (S402). Second current limit value I lim2 This is equivalent to the temporary limit value I2 in cooperative operation control. In independent operation control, the second microcomputer 54 and the first current limit value I... lim1 Regardless, the current limit value is set based on the detected temperature T2 of the second temperature sensor 56.

[0071] The second microcomputer 54 compares the operation value J2 with the second current limit value I lim2 (S403). The second microcomputer 54 multiplies the lower value (the instruction value) of the operation value J2 and the second current limit value I lim2 by 1 / 2 to obtain a value (a second final operation value) I e2 (S404). The second microcomputer 54 controls the second drive circuit 55 in such a manner that the second rudder current is supplied to the winding 352 of the rudder motor 35. The first current limit value I lim1 and the second current limit value I lim2 may differ at times. Therefore, in the independent operation control, the current value of the first rudder current and the current value of the second rudder current may differ at times. Note that the independent operation control can also be said to be the independent operation mode, the second operation mode.

[0072] The current value of the rudder current in the independent operation control differs according to the situation as follows. In the case where the operation value J1 is less than the first current limit value I lim1 and the operation value J2 is less than the second current limit value I lim2 , the current value of the rudder current becomes the sum of "J1 x 1 / 2" and "J2 x 1 / 2". In the case where the operation value J1 is the first current limit value I lim1 or more and the operation value J2 is less than the second current limit value I lim2 , the current value of the rudder current becomes the sum of "I lim1 x 1 / 2" and "J2 x 1 / 2". In the case where the operation value J1 is less than the first current limit value I lim1 and the operation value J2 is the second current limit value I lim2 or more, the current value of the rudder current becomes the sum of "J1 x 1 / 2" and "I lim2 x 1 / 2". In the case where the operation value J1 is the first current limit value I lim1 or more and the operation value J2 is the second current limit value I lim2 or more, the current value of the rudder current becomes the sum of "I lim1 x 1 / 2" and "I lim2 x 1 / 2". Note that in the quotation marks here, the former indicates the current value of the first rudder current, and the latter indicates the current value of the second rudder current.

[0073] (Switching of the operation control)

[0074] The first microcomputer 51 and the second microcomputer 54 share their calculation results and temperature detection information through communication. The first microcomputer 51 and the second microcomputer 54 respectively acquire the temperature detection information of the first temperature sensor 53 and the second temperature sensor 56. Whenever the operation mode is switched, the first microcomputer 51 and the second microcomputer 54 respectively calculate the temperature difference ΔT (ΔT=|T1-T2|) which is the difference between the temperature T1 detected by the first temperature sensor 53 and the temperature T2 detected by the second temperature sensor 56.

[0075] When the detected temperature difference ΔT is within the specified threshold ΔT th In the following situations, the first microcomputer 51 and the second microcomputer 54 respectively perform cooperative operation control. On the other hand, when the detected temperature difference ΔT is greater than a predetermined threshold ΔT... th In cases of large temperature differences, the first microcomputer 51 and the second microcomputer 54 perform independent calculations and control. In other words, when the detected temperature difference ΔT is within a specified threshold value... th In the following situations, the steering ECU5 will set the operation mode to cooperative calculation control, when the detected temperature difference ΔT is higher than a specified threshold ΔT. th In large situations, the steering ECU5 will set its operating mode to independent operation and control. For example, when the temperature difference ΔT is greater than a specified threshold ΔT... th If the large temperature difference persists for a specified time, it is determined that the detected temperature difference ΔT is greater than the specified threshold ΔT. th big.

[0076] The first temperature sensor 53 and the second temperature sensor 56 are disposed within the same ECU (on the same substrate 50), therefore, if normal, it can be presumed that they detect the same temperature. That is, when the first temperature sensor 53 and the second temperature sensor 56 are normal, the detected temperature difference ΔT is small. Therefore, if the first temperature sensor 53 and the second temperature sensor 56 are normal, cooperative operation control is executed, thereby making the current values ​​of the first steering current and the second steering current the same. Under the condition that cooperative operation control is executed, when the detected temperature of at least one of the first temperature sensor 53 and the second temperature sensor 56 exceeds the threshold temperature T... th At that time, through current limit control based on the limit value mapping diagram, the current limit value in the operation of both the first microcomputer 51 and the second microcomputer 54 will be reduced.

[0077] On the other hand, when the detected temperature difference ΔT is greater than the specified threshold ΔT thIn the case where the temperature sensor of one side has a high possibility of malfunction, if the cooperative operation control is continued, the operation of both the current value of the first rudder current and the current value of the second rudder current is set to a common current limit value corresponding to a relatively high detected temperature. Therefore, both the current value of the first rudder current and the current value of the second rudder current are limited by the current limit value set to a low value. Thus, in the case where the temperature sensor of one side has a drift malfunction and the detected temperature is higher than the detected temperature in the normal state, although the actual temperature is not high, the current value of the rudder current is lowered, and thus the turning accuracy can be lowered due to the reduction in torque.

[0078] However, according to the present embodiment, in the case where the detected temperature difference ΔT is higher than the prescribed threshold value ΔT th In the case where the detected temperature difference ΔT is higher than the prescribed threshold value ΔT th , the operation control (the operation mode) of the microcomputer is switched from the cooperative operation control to the independent operation control. Thus, the microcomputer of the other side can set the rudder current by the same current limit value as in the normal state, since the microcomputer of only one side is limited by the detected temperature of the temperature sensor having a malfunction, not corresponding to the actual temperature. That is, at least one microcomputer can operate the rudder current as in the normal state by the execution of the independent operation control, and thus the reduction in the rudder current due to the detection of a temperature different from the actual temperature is suppressed. According to the present embodiment, the reduction in the rudder current in a situation not in accordance with the purpose of the current limit control (protection from overheating) is suppressed, and thus the reduction in the turning accuracy with respect to the rudder request is suppressed.

[0079] As one example, in the case where the detected temperature of only the first temperature sensor 53 is higher than the threshold temperature T th , and the detected temperature difference ΔT is higher than the prescribed threshold value ΔT th , the operation control is switched from the cooperative operation control to the independent operation control. The first microcomputer 51 sets the first current limit value I lim1 , for example, to the lowest value I min , and operates the current value of the first rudder current. On the other hand, the second microcomputer 54 sets the second current limit value I lim2 to the highest value I max , and operates the current value of the second rudder current. Here, in the case where the maximum rudder torque is requested, the current value of the first rudder current becomes a value (I min × 1 / 2) that is half of the lowest value I min of the limited value, and the current value of the second rudder current becomes a value (I max × 1 / 2) that is half of the highest value I max . The highest value I maxhalf of the value of the maximum value of the output of the steering current. That is, according to the independent operation control, even in a scene where the maximum output is requested, the current value of the steering current, which is the sum of the first steering current and the second steering current, is set to a value of 50% or more of the maximum output. If an output of 50% of the maximum output is ensured, torque deficiency does not occur, and thus a decrease in turning accuracy is suppressed. The same effect can be obtained even in a case where only the detected temperature of the second temperature sensor 56 is higher than the threshold temperature T th It should be noted that the probability that both of the temperature sensors 53, 56 become drift faults at the same time is extremely low.

[0080] (Summary of Effects of the Present Embodiment)

[0081] The steering system 1 of the present embodiment is configured such that, in a case where the detected temperature difference AT is greater than the prescribed threshold AT th According to this configuration, a case where the detected temperature of one temperature sensor becomes a value deviating from the normal detected temperature due to a fault (e.g., a drift fault) is detected by comparison with the detected temperature of the other normal temperature sensor. Specifically, the steering ECU 5, in a case where the detected temperature difference is greater than the prescribed threshold, assumes (determines) that a fault has occurred in one temperature sensor, and performs independent operation control. In this way, the steering system 1 of the present embodiment, premised on the extremely low probability that multiple temperature sensors become drift faults at the same time, is configured such that a decrease in turning accuracy is suppressed even in a case where a drift fault has occurred in one temperature sensor.

[0082] In the independent operation control, each microcomputer 51, 54, regardless of the detected temperature of the temperature sensor 53, 56 corresponding to the other microcomputer 51, 54, operates the current limit value based on the detected temperature of its own temperature sensor 53, 56. Thus, in the microcomputers 51, 54 corresponding to the normal temperature sensors 53, 56, current limit values corresponding to the actual detected temperatures are set, and only the microcomputers 51, 54 corresponding to the temperature sensors 53, 56 that have generated faults operate the current limit values. That is, according to the present embodiment, in a situation where the actual temperature is not high enough to limit the current, even in a case where a fault has occurred in one temperature sensor 53, 56, unnecessary decreases in the current limit values are suppressed in the microcomputers 51, 54 corresponding to the normal temperature sensors 53, 56. In this way, according to the present embodiment, even in a case where a fault has occurred in one temperature sensor 53, 56, unnecessary decreases in torque caused by limitation of the steering current are suppressed, and thus a decrease in turning accuracy is suppressed.

[0083] (Addition of Switching Condition)

[0084] As the condition for switching the operation control (the operation mode) from the cooperative operation control to the independent operation control, in addition to detecting that the temperature difference ΔT is larger than the prescribed threshold value ΔT th , the following condition can be added. For example, the second condition is "the calculated current limit value I lim is smaller than the threshold current value I th ". In other words, the second condition is "the temporary limit value I1 or the temporary limit value I2 is smaller than the threshold current value I th ". The threshold current value I th is set to be higher than the minimum value I min and smaller than the maximum value I max (see Figure 8 ). Thus, the switching of the operation control is actually performed after the current limit value is decreased by the current limit control. Therefore, by adding the second condition to the switching condition, in a situation where the current value of the rudder current is actually affected due to the drift fault, the rudder ECU 5 can switch the operation control. By the addition of the second condition, in a situation where the current value of the rudder current is not affected, that is, in a situation where the current limit value is not changed due to the switching of the operation control, the operation control is not switched.

[0085] Likewise, "detecting that the detection temperature T1 or the detection temperature T2 exceeds the prescribed temperature T ps " can be added to the switching condition as the third condition. The prescribed temperature T ps may be set to a value of the threshold temperature T th or more and smaller than the temperature corresponding to the minimum value I min , or to a temperature slightly lower than the threshold temperature T th as shown in Figure 8 . As with the second condition, by the third condition, in a situation where the current value of the rudder current is actually affected, or in a situation where the probability of the effect is high, the rudder ECU 5 can switch the operation control.

[0086] For example, as shown in Figure 9 , the rudder ECU 5 can be set to switch the operation control from the cooperative operation control to the independent operation control in a case where three conditions are satisfied (S501: Yes, S502: Yes, S503: Yes). Thus, the rudder ECU 5 can switch the operation control in a more appropriate situation. As such, it can also be that, in addition to the first condition as the necessary condition, the switching condition of the operation control includes at least one of the second condition and the third condition.

[0087] (Variation)

[0088] The present application is not limited to the above-described disclosure. For example, the steering ECU 5 can also have three or more microcomputers. Three or more sets of microcomputers, temperature sensors, and drive circuits can also be provided in the steering ECU 5. For example, as shown in FIG. 6, in addition to the configuration of the above-described embodiment, the steering ECU 5 is provided with a third microcomputer 57, a third drive circuit 58, and a third temperature sensor 59. In this case, for example, the first microcomputer 51 becomes a master microcomputer, and the second microcomputer 54 and the third microcomputer 57 become slave microcomputers. The third microcomputer 57 operates in the same manner as the second microcomputer 54 of the above-described embodiment. The third temperature sensor 59 is provided in the third microcomputer 57. Figure 10

[0089] The third microcomputer 57 calculates the current value of the third steering current. In the cooperative calculation control, the second microcomputer 54 and the third microcomputer 57 use the calculation value J1 of the first microcomputer 51 for the calculation of the steering current, and do not use their own calculation values for the calculation of the steering current. The third microcomputer 57 calculates a temporary limit value I3 corresponding to the detection temperature T3 of the third temperature sensor 59 based on the limit value map.

[0090] In the cooperative calculation control, the current limit values set by the respective microcomputers 51, 54, 57 are set to the lowest value (min(I1, I2, I3)) of the temporary limit values I1, I2, I3. In other words, the respective microcomputers 51, 54, 57 set the current limit value corresponding to the highest value of the detection temperatures T1, T2, T3. The respective microcomputers 51, 54, 57 set the lower value of the calculation value J1 and the current limit value min(I1, I2, I3) as the command value. The current value of the steering current supplied to the steering motor 35 becomes the sum of the first steering current, the second steering current, and the third steering current. Therefore, the current value of the steering current calculated by the respective microcomputers 51, 54, 57 becomes a value obtained by multiplying the command value by 1 / 3 (command value x 1 / 3).

[0091] In the independent calculation control, the third microcomputer 57 also independently calculates the current value of the third steering current in the same manner as the first microcomputer 51 and the second microcomputer 54. The third microcomputer 57 calculates a calculation value J3 in accordance with the steering request. The third microcomputer 57 sets a current limit value corresponding to the detection temperature T3 of the third temperature sensor 59 as a third current limit value I lim3 . The third microcomputer 57 sets the lower value of the calculation value J3 and the third current limit value I lim3 as the command value. The third microcomputer 57 sets a value obtained by multiplying the command value by 1 / 3 (third final calculation value) as the current value of the third steering current. The third microcomputer 57 controls the third drive circuit 58 in such a manner that the third steering current is supplied to the third winding 353 of the steering motor 35.

[0092] ​The switching condition of the operation control (first condition) is that the first detected temperature difference ΔT1, the second detected temperature difference ΔT2, or the third detected temperature difference ΔT3 is greater than a prescribed threshold value ΔT th (ΔT1 > ΔT th , ΔT2 > ΔT th , or ΔT3 > ΔT th ), where the first detected temperature difference ΔT1 is the difference between the detected temperature T1 and the detected temperature T2, the second detected temperature difference ΔT2 is the difference between the detected temperature T2 and the detected temperature T3, and the third detected temperature difference ΔT3 is the difference between the detected temperature T3 and the detected temperature T1. With this configuration, the same effects as in the above-described embodiment are also exerted.

[0093] Further, a second condition and / or a third condition can also be added to the switching condition. The second condition is, for example, that any one of the temporary limit values I1, I2, I3 is less than the threshold current value I th . The third condition is, for example, that any one of the detected temperatures T1, T2, T3 is higher than the prescribed temperature T ps With this configuration, the switching of the operation control can also be performed in a more appropriate condition, i.e., a condition in which the setting of the current limit value is affected due to the drift failure.

[0094] (Summary of the Configuration of the Present Embodiment)

[0095] The steering system 1 of the present embodiment is a steer-by-wire type steering system that includes a front wheel steering device 3 having a steering motor 35 that mechanically independently steers the front wheel 10F from the operation force of the steering wheel 21, and a steering ECU 5 as a control device that supplies a steering current to the steering motor 35 in accordance with a steering request to control the steering motor 35. The steering ECU 5 includes a plurality of microcomputers 51, 54 as a plurality of operation sections that are connected to be able to communicate with each other and individually operate a current value of the steering current in accordance with the steering request, a plurality of drive circuits 52, 55 that individually correspond to the plurality of microcomputers 51, 54 and supply the steering current to the steering motor 35 through the control of the corresponding microcomputer 51, 54, and a plurality of temperature sensors 53, 56 that individually correspond to the plurality of microcomputers 51, 54 and individually detect the temperature of the corresponding microcomputer 51, 54. Each microcomputer 51, 54 is configured to execute independent operation control when a detected temperature difference that is the difference between the detected temperatures of the plurality of temperature sensors 53, 56 is greater than a prescribed threshold value. In the independent operation control, each microcomputer 51, 54 individually (independently of the other microcomputers) operates and sets a current limit value that is an upper limit value of the steering current based on the detected temperature of the temperature sensor 53, 56 that corresponds to itself, regardless of the detected temperatures of the temperature sensors 53, 56 that correspond to the microcomputers 51, 54 other than itself.

[0096] In addition, when the detected temperature difference is below a specified threshold, each microcomputer 51 and 54, as a cooperative calculation control, calculates and sets a common current limit value based on the highest value among the detected temperatures of all temperature sensors 53 and 56.

[0097] Furthermore, each microcomputer 51, 54 is configured to: under the condition that "the detected temperature difference is greater than a specified threshold (first condition)," and when "the current limit value corresponding to the detected temperature of at least one of the multiple temperature sensors 53, 56 is less than a specified threshold current value I..." th "Condition 2" and / or "At least one of the multiple temperature sensors 53, 56 detects a temperature higher than the specified temperature T". ps Under the condition of “the third condition”, independent operation control is performed.

[0098] Furthermore, in this embodiment, each microcomputer 51, 54 is a microcomputer equipped with a CPU and memory. Multiple microcomputers 51, 54 are configured within the same electronic control unit 5 (within the housing) and / or on the same substrate 50. In other words, multiple microcomputers 51, 54 are configured within a common electronic control unit 5 (within the housing) and / or on a common substrate 50. A limit value mapping map representing the relationship between the temperature detected by the temperature sensor and the current limit value is pre-stored in the steering ECU 5, and each microcomputer 51, 54 is configured to calculate the current limit value based on the limit value mapping map.

[0099] (The control device has a configuration with two arithmetic units)

[0100] In the configuration described in the above "Summary of the Configuration of this Embodiment", the "multiple arithmetic units" can be composed of a first microcomputer 51 and a second microcomputer 54. The first microcomputer 51 calculates the current value of the first steering current, and the second microcomputer 54 calculates the current value of the second steering current. In this case, the "multiple temperature sensors" include a first temperature sensor 53 and a second temperature sensor 56. The first temperature sensor 53 detects the temperature of the first microcomputer 51, and the second temperature sensor 56 detects the temperature of the second microcomputer 54. Furthermore, the "multiple drive circuits" are composed of a first drive circuit 52 and a second drive circuit 55. The first drive circuit 52 supplies the first steering current to the steering motor 35 under the control of the first microcomputer 51, and the second drive circuit 55 supplies the second steering current to the steering motor 35 under the control of the second microcomputer 54. Moreover, each microcomputer 51 and 54 is configured such that the detected temperature difference ΔT, which is the difference between the detected temperature of the first temperature sensor 53 and the detected temperature of the second temperature sensor 56, is greater than a predetermined threshold ΔT. thIn the case of the large, independent operation control is executed. In the independent operation control, the first microcomputer 51 operates a current limit value (first current limit value I lim1 ) that limits the first rudder current, based on the detected temperature of the first temperature sensor 53, regardless of the detected temperature of the second temperature sensor 56. Further, in the independent operation control, the second microcomputer 54 operates a current limit value (second current limit value I lim2 ) that limits the second rudder current, based on the detected temperature of the second temperature sensor 56, regardless of the detected temperature of the first temperature sensor 53.

[0101] Each of the microcomputers 51, 54 is configured to execute the cooperative operation control in the case where the detected temperature difference ΔT is a prescribed threshold value ΔT th The cooperative operation control is executed in the following case. In the cooperative operation control, each of the microcomputers 51, 54 operates a common current limit value based on the higher one of the detected temperature of the first temperature sensor 53 and the detected temperature of the second temperature sensor 56.

[0102] (Configuration in which the control device has three operation sections)

[0103] In the configuration described in the above "Summary of the Configuration of the Present Embodiment", the "multiple operation sections" can also be constituted by a first microcomputer 51 that operates the current value of the first rudder current, a second microcomputer 54 that operates the current value of the second rudder current, and a third microcomputer 57 that operates the current value of the third rudder current. In this case, the "multiple temperature sensors" include a first temperature sensor 53 that detects the temperature of the first microcomputer 51, a second temperature sensor 56 that detects the temperature of the second microcomputer 54, and a third temperature sensor 59 that detects the temperature of the third microcomputer 57. Further, the "multiple drive circuits" are constituted by a first drive circuit 52 that supplies the first rudder current to the rudder motor 35 under the control of the first microcomputer 51, a second drive circuit 55 that supplies the second rudder current to the rudder motor 35 under the control of the second microcomputer 54, and a third drive circuit 58 that supplies the third rudder current to the rudder motor 35 under the control of the third microcomputer 57. Also, each of the microcomputers 51, 54, 57 is configured to execute independent operation control in a case where a first detected temperature difference, a second detected temperature difference, or a third detected temperature difference is greater than a prescribed threshold value, where the first detected temperature difference is the difference between the detected temperature of the first temperature sensor 53 and the detected temperature of the second temperature sensor 56, the second detected temperature difference is the difference between the detected temperature of the second temperature sensor 56 and the detected temperature of the third temperature sensor 59, and the third detected temperature difference is the difference between the detected temperature of the third temperature sensor 59 and the detected temperature of the first temperature sensor 53. Each of the microcomputers 51, 54, 57 is configured to execute independent operation control in a case where a detected temperature difference that is the difference between the detected temperature of any two of the multiple temperature sensors 53, 56, 59 is greater than a prescribed threshold value. In the independent operation control, each of the microcomputers 51, 54, 57 operates and sets a current limit value that is the upper limit value of the rudder current, based on the detected temperature of the temperature sensor 53, 56, 59 corresponding to itself, independently of the detected temperature of the temperature sensor 53, 56, 59 corresponding to the microcomputers 51, 54, 57 other than itself.

[0104] In the independent operation control, the first microcomputer 51 operates the current limit value that limits the first rudder current (the first current limit value I lim1). In the independent operation control, the second microcomputer 54 operates the current limit value (second current limit value I lim2 ) that limits the second steering current, based on the detected temperature of the second temperature sensor 56, independently of the detected temperature of the first temperature sensor 53 and the detected temperature of the third temperature sensor 59. lim3 ).

[0105] Further, each of the microcomputers 51, 54, 57 is configured to execute the cooperative operation control when all of the first detected temperature difference, the second detected temperature difference, and the third detected temperature difference are the prescribed threshold value AT th The cooperative operation control is executed in the following case. In the cooperative operation control, each of the microcomputers 51, 54, 57 operates the common current limit value based on the highest value among the detected temperature of the first temperature sensor 53, the detected temperature of the second temperature sensor 56, and the detected temperature of the third temperature sensor 59.

[0106] (Other)

[0107] The "operation section" is not limited to a microcomputer, and can be, for example, an ECU. That is, the control device can also be constituted by a plurality of ECUs. For example, the steering system 1 can also be provided with a first ECU as the first operation section, a first temperature sensor that detects the temperature of the first ECU, a first drive circuit that is provided in the first ECU, a second ECU as the second operation section, a second temperature sensor that detects the temperature of the second ECU, and a second drive circuit that is provided in the second ECU. In this case, the first temperature sensor and the second temperature sensor can also not be provided on the same substrate, and can also not be provided in the same ECU (electronic control unit). However, as long as it is a case where the first ECU is provided in the vicinity (for example, side by side) of the second ECU, and the like, a configuration state in which a difference does not easily occur in the detected temperature of each temperature sensor at normal times will exert the same effect as in the case of being provided in the same ECU or on the same substrate. Further, in a case where a difference occurs in the detected temperature of each temperature sensor at normal times due to the positions at which the first ECU and the second ECU are provided, a certain degree of effect is exerted by setting the prescribed threshold value taking the difference into account. However, from the viewpoint of the easiness of setting of the threshold value and the like, it is preferable that the plurality of temperature sensors be configured such that the difference in the detected temperature at normal times of each other falls within a prescribed range.

[0108] Further, in the steering system 1, the steering motor that is a drive source of the steering actuator 30 can also not be one, and for example, a plurality of steering motors corresponding to the number of the arithmetic units (for example, microcomputers) can also be provided. Further, a plurality of temperature sensors can also be arranged in the microcomputer, and in this case, for example, the microcomputer can use the average value of the detected temperatures as the detected temperature of the microcomputer for the arithmetic. Further, the control of the present embodiment can also be applied to the steering control of the rear wheel 10R. Further, the detailed parts in the various arithmetics can also be an arithmetic method other than the above-described embodiments as long as the technical idea of the present disclosure is not deviated from. Further, the limit value map can also be set to be different from Figure 3 , Figure 8 .

[0109] The present embodiment can also be described as follows. That is, the steering system 1 is a steer-by-wire type steering system that includes a steering device having a steering motor that steers a wheel mechanically independently of an operation force of an operation member, and a control device that controls the steering motor by supplying a first steering current and a second steering current to the steering motor in accordance with a steering request, wherein the control device includes a first arithmetic unit that performs an arithmetic of a current value of the first steering current, a first temperature sensor that detects a temperature of the first arithmetic unit, a second arithmetic unit that is communicably connected to the first arithmetic unit and performs an arithmetic of a current value of the second steering current, and a second temperature sensor that detects a temperature of the second arithmetic unit, and is configured to execute, in a case where a detected temperature difference that is a difference between the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor is larger than a prescribed threshold value, independent arithmetic control that is control of arithmetically calculating a first current limit value that is an upper limit value of the first steering current based on the detected temperature of the first temperature sensor regardless of the detected temperature of the second temperature sensor and arithmetically calculating a second current limit value that is an upper limit value of the second steering current based on the detected temperature of the second temperature sensor regardless of the detected temperature of the first temperature sensor. Further, the control device is configured to execute, in a case where the detected temperature difference is equal to or less than the prescribed threshold value, cooperative arithmetic control that is control of setting the first current limit value and the second current limit value to a common value based on the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor. The same can also be described in a case where the number of the arithmetic units is three or more. The microcomputer can also be referred to as a microcontroller.

Claims

1. A steering system of a steer-by-wire type, comprising: a steering device having a steering motor that steers a wheel independently of an operation force of an operation member; and a control device that supplies a steering current to the steering motor in accordance with a steering request to control the steering motor, the control device comprising: a plurality of arithmetic units connected to communicate with each other and each calculating a current value of the steering current in accordance with the steering request; a plurality of drive circuits individually corresponding to the plurality of arithmetic units and each supplying the steering current to the steering motor under control of the corresponding arithmetic unit; and a plurality of temperature sensors individually corresponding to the plurality of arithmetic units and each detecting a temperature of the corresponding arithmetic unit, each of the arithmetic units being configured to, in a case where a detected temperature difference as a difference between detected temperatures of any two of the temperature sensors is greater than a prescribed threshold, independently calculate and set a current limit value as an upper limit value of the steering current based on a detected temperature of the temperature sensor corresponding to the arithmetic unit itself, regardless of detected temperatures of the temperature sensors corresponding to the arithmetic units other than the arithmetic unit itself.

2. The steering system according to claim 1, wherein each of the arithmetic units is configured to, in a case where the detected temperature difference is equal to or less than the prescribed threshold, cooperatively calculate and set a common current limit value based on a highest value among detected temperatures of all of the temperature sensors.

3. The steering system according to claim 1 or 2, wherein each of the arithmetic units is configured to, in a case where the detected temperature difference is greater than the prescribed threshold, and in a case where the current limit value corresponding to a detected temperature of at least one of the temperature sensors is less than a prescribed threshold current value, perform the independent calculation control. wherein 4. The steering system according to claim 1 or 2, wherein each of the arithmetic units is configured to, in a case where the detected temperature difference is greater than the prescribed threshold, and in a case where a detected temperature of at least one of the temperature sensors is higher than a prescribed temperature, perform the independent calculation control.

5. The steering system according to claim 1 or 2, wherein each of the arithmetic units is configured to, in a case where the detected temperature difference is greater than the prescribed threshold, in a case where the current limit value corresponding to a detected temperature of at least one of the temperature sensors is less than a prescribed threshold current value, and in a case where a detected temperature of at least one of the temperature sensors is higher than a prescribed temperature, perform the independent calculation control.

6. The steering system according to any one of claims 1 to 5, wherein each of the arithmetic units is a microcomputer, and the plurality of arithmetic units and the plurality of temperature sensors are disposed in the same electronic control unit.

7. The steering system according to any one of claims 1 to 6, wherein each of the arithmetic units is a microcomputer, and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ A plurality of the operation sections and a plurality of the temperature sensors are arranged on the same substrate.

8. The steering system according to any one of claims 1 to 7, wherein a limit value map indicating a relationship between a detection temperature of the temperature sensor and the current limit value is stored in advance in the control device, each of the operation sections is configured to operate the current limit value based on the limit value map.

9. The steering system according to any one of claims 1 to 8, wherein the plurality of operation sections is composed of a first operation section that operates a current value of a first steering current and a second operation section that operates a current value of a second steering current, the plurality of temperature sensors includes a first temperature sensor that detects a temperature of the first operation section and a second temperature sensor that detects a temperature of the second operation section, the plurality of drive circuits is composed of a first drive circuit that supplies the first steering current to the steering motor under control of the first operation section and a second drive circuit that supplies the second steering current to the steering motor under control of the second operation section, the first operation section and the second operation section are configured to perform the independent operation control, respectively, in a case where the detection temperature difference, which is a difference between the detection temperature of the first temperature sensor and the detection temperature of the second temperature sensor, is larger than the prescribed threshold value, in the independent operation control, the first operation section operates the current limit value that limits the first steering current based on the detection temperature of the first temperature sensor regardless of the detection temperature of the second temperature sensor, in the independent operation control, the second operation section operates the current limit value that limits the second steering current based on the detection temperature of the second temperature sensor regardless of the detection temperature of the first temperature sensor.

10. The steering system according to claim 9, wherein the first operation section and the second operation section are configured to operate a common current limit value based on a higher one of the detection temperature of the first temperature sensor and the detection temperature of the second temperature sensor as a cooperative operation control in a case where the detection temperature difference is equal to or lower than the prescribed threshold value.

11. The steering system according to any one of claims 1 to 8, wherein the plurality of operation sections is composed of a first operation section that operates a current value of a first steering current, a second operation section that operates a current value of a second steering current, and a third operation section that operates a current value of a third steering current, the plurality of temperature sensors includes a first temperature sensor that detects a temperature of the first operation section, a second temperature sensor that detects a temperature of the second operation section, and a third temperature sensor that detects a temperature of the third operation section, the plurality of drive circuits is composed of a first drive circuit that supplies the first steering current to the steering motor under control of the first operation section, a second drive circuit that supplies the second steering current to the steering motor under control of the second operation section, and a third drive circuit that supplies the third steering current to the steering motor under control of the third operation section, the first operation section, the second operation section, and the third operation section are configured to perform the independent operation control, respectively, in a case where a detection temperature difference, which is a difference between the detection temperature of the first temperature sensor and the detection temperature of the second temperature sensor, is larger than a prescribed threshold value, The plurality of temperature sensors include a first temperature sensor that detects a temperature of the first arithmetic portion, a second temperature sensor that detects a temperature of the second arithmetic portion, and a third temperature sensor that detects a temperature of the third arithmetic portion, The plurality of drive circuits include a first drive circuit that supplies the first rudder current to the rudder motor under control of the first arithmetic portion, a second drive circuit that supplies the second rudder current to the rudder motor under control of the second arithmetic portion, and a third drive circuit that supplies the third rudder current to the rudder motor under control of the third arithmetic portion, The first arithmetic portion, the second arithmetic portion, and the third arithmetic portion are configured to: in a case where a first detected temperature difference, a second detected temperature difference, or a third detected temperature difference is greater than the prescribed threshold value, respectively perform the independent arithmetic control, wherein the first detected temperature difference is a difference between a detected temperature of the first temperature sensor and a detected temperature of the second temperature sensor, the second detected temperature difference is a difference between the detected temperature of the second temperature sensor and a detected temperature of the third temperature sensor, and the third detected temperature difference is a difference between the detected temperature of the third temperature sensor and the detected temperature of the first temperature sensor; in the independent arithmetic control, the first arithmetic portion operates the current limit value that limits the first rudder current based on the detected temperature of the first temperature sensor regardless of the detected temperature of the second temperature sensor and the detected temperature of the third temperature sensor; in the independent arithmetic control, the second arithmetic portion operates the current limit value that limits the second rudder current based on the detected temperature of the second temperature sensor regardless of the detected temperature of the first temperature sensor and the detected temperature of the third temperature sensor; and in the independent arithmetic control, the third arithmetic portion operates the current limit value that limits the third rudder current based on the detected temperature of the third temperature sensor regardless of the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor.

12. The steering system according to claim 11, wherein the first arithmetic portion, the second arithmetic portion, and the third arithmetic portion are configured to, in a case where the first detected temperature difference, the second detected temperature difference, and the third detected temperature difference are all below the prescribed threshold value, operate the common current limit value based on a highest one of the detected temperature of the first temperature sensor, the detected temperature of the second temperature sensor, and the detected temperature of the third temperature sensor as the cooperative arithmetic control.

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