Steering system

Abstract

To provide a steering system that can suppress a reduction in turning accuracy even when a temperature sensor malfunctions.SOLUTION: The present invention relates to a steer-by-wire type steering system. A control device 5 includes a plurality of calculation units 51 and 54, a plurality of temperature sensors 53 and 56, and a plurality of drive circuits 52 and 55. When a detected temperature difference that is a difference between detected temperatures of any two of the temperature sensors 53 and 56 is larger than a predetermined threshold value, each of the calculation units 51 and 54 individually calculates and sets a current limit value that is an upper limit of a turning current as an individual calculation control based on the detected temperature of each of the temperature sensors 53 and 56 corresponding to the calculation unit itself regardless of the detected temperatures of the temperature sensors 53 and 56 corresponding to the calculation units 51 and 54 other than the calculation unit itself.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a steering system. [Background technology]

[0002] In general, in steering systems, when the temperature of a motor (the driving source) exceeds a threshold, current limiting control is executed to limit the current applied to the motor (hereinafter referred to as the steering current) in order to prevent breakdowns due to heat generation in the motor and motor drive circuit. However, if the motor temperature is not accurately estimated, the steering current may be limited even when the motor is not overheated, resulting in a risk of reduced motor torque. To address this issue, for example, Japanese Patent Application Laid-Open Publication No. 2012-148629 discloses an electric power steering device that, when the difference between the current and previous values of a substrate temperature sensor exceeds a predetermined threshold, stores the previous value as a reference value for motor temperature estimation. In this device, until an abnormality in the substrate temperature sensor is confirmed, the motor temperature is estimated based on the previous value, which is the value before a significant change in the substrate temperature. Therefore, this device can prevent current limiting control from being executed early, before an abnormality in the substrate temperature sensor is confirmed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-148629 Summary of the Invention [Problem to be solved by the invention]

[0004] Current limiting control based on the temperature detected by the temperature sensor is also set in steer-by-wire steering systems in which a steering motor steers the wheels independently of the operating force of an operating member. When current limiting control is executed in a steer-by-wire steering system, the maximum value of the steering current is limited and the driver's operating force does not directly contribute to the steering, so the driver's intended turning may not be achieved.

[0005] The temperature sensor used in a steer-by-wire steering system has the function of detecting a malfunction in which the detected temperature is stuck at the maximum or minimum value. Therefore, when a stuck fault of the temperature sensor is detected, the calculation unit (e.g., a microcomputer or ECU) determines that the detected temperature is an abnormal value and can prohibit current limiting control.

[0006] However, the temperature sensor and the calculation unit do not have the function to detect drift faults, which are when the detected temperature fluctuates between the maximum and minimum values. Therefore, if current limiting control is performed due to drift faults, there is a risk that turning accuracy will decrease at times when current limiting is not actually required. An object of the present invention is to provide a steering system that can suppress a decrease in turning accuracy even when a failure occurs in a temperature sensor. [Means for solving the problem]

[0007] The steering system of the present invention is a steer-by-wire type steering system comprising: a steering device having a steering motor that steers wheels mechanically independently of the operating force of an operating member; and a control device that supplies a steering current to the steering motor in response to a steering request and controls the steering motor, wherein the control device comprises a plurality of calculation units that are communicatively connected to each other and each calculates a current value of the steering current in response to the steering request; a plurality of drive circuits that correspond individually to the plurality of calculation units and supply the steering current to the steering motor under the control of the corresponding calculation unit; and a plurality of temperature sensors that correspond individually to the plurality of calculation units and detect the temperatures of the corresponding calculation unit, wherein each calculation unit is configured, as independent calculation control, to individually calculate and set a current limit value that is an upper limit value of the turning current based on the detected temperature of the temperature sensor corresponding to it, regardless of the detected temperatures of the temperature sensors corresponding to the calculation units other than itself, when a detected temperature difference that is the difference between the temperatures detected by any two of the plurality of temperature sensors is greater than a predetermined threshold. [Effects of the Invention]

[0008] The present invention is based on the premise that the possibility of multiple temperature sensors simultaneously experiencing drift failure is extremely low, and is configured to suppress deterioration of turning accuracy even when one temperature sensor experiences drift failure. Specifically, according to the present invention, a deviation from the normal detected temperature due to a failure (e.g., drift failure) of the detected temperature of one temperature sensor is detected by comparing it with the detected temperatures of other normal temperature sensors. If the detected temperature difference is greater than a predetermined threshold, the control device estimates (determines) that one temperature sensor has failed and performs independent calculation control.

[0009] In independent calculation control, each calculation unit calculates a current limit value based on the temperature detected by its own temperature sensor, regardless of the temperatures detected by the temperature sensors corresponding to the other calculation units. As a result, the calculation unit corresponding to the normal temperature sensor sets a current limit value based on the actual detected temperature, and only the calculation unit corresponding to the faulty temperature sensor calculates a current limit value that is more limited than necessary. In other words, according to the present invention, even if one temperature sensor fails when the actual temperature is not high enough to limit the current, unnecessary reductions in the current limit value are suppressed in the calculation unit corresponding to the normal temperature sensor. Thus, according to the present invention, even if one temperature sensor fails, unnecessary reductions in torque due to steering current limiting are suppressed, thereby suppressing a decrease in turning accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram of a steering system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a configuration diagram of a steering ECU according to the present embodiment. [Figure 3] FIG. 4 is a conceptual diagram showing a limit value map according to the present embodiment. [Figure 4] 5 is a flowchart for explaining cooperative calculation control of the first calculation unit of the present embodiment. [Figure 5] 6 is a flowchart for explaining cooperative calculation control of the second calculation unit of the present embodiment. [Figure 6] 5 is a flowchart for explaining the independent calculation control of the first calculation unit of the present embodiment. [Figure 7] 6 is a flowchart for explaining the independent calculation control of the second calculation unit of the present embodiment. [Figure 8] FIG. 4 is a conceptual diagram showing a limit value map according to the present embodiment. [Figure 9] 4 is a flowchart relating to switching of arithmetic control in the present embodiment. [Figure 10] FIG. 10 is a configuration diagram of a modified embodiment of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A steering system 1 according to an embodiment of the present invention will be described in detail below with reference to the drawings. In addition to the embodiment described below, the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0012] As shown in FIG. 1, steering system 1 of the embodiment includes an operation device 2 and a front wheel steering device (corresponding to a "steering device") 3 that are mechanically independent of each other. Front wheel steering device 3 steers a pair of front wheels 10F. Steering system 1 also includes a steering ECU 5 as a control device that controls front wheel steering device 3 in response to a steering request. Steering system 1 is a steer-by-wire steering system. Note that hereinafter, front wheels 10F and rear wheels 10R may be collectively referred to as wheels 10. The drive wheels are, for example, rear wheels 10R.

[0013] (operating device) The operating device 2 includes a steering wheel 21 as an operating member, a steering shaft 22, a steering column 23, a reaction force imparting mechanism 24, and an operating angle sensor 25. The steering wheel 21 is an operating member that is steered by the driver. The steering shaft 22 is a shaft member with the steering wheel 21 attached to its tip. The steering column 23 rotatably holds the steering shaft 22 and is a member that is supported by an instrument panel reinforcement (not shown).

[0014] The reaction force applying mechanism 24 is a mechanism that applies a reaction force against a steering operation (hereinafter also referred to as "operation reaction force") to the steering wheel 21 via the steering shaft 22, using a reaction force motor 26, which is an electric motor supported on the steering column 23, as a power source. The reaction force applying mechanism 24 has a general structure including a reducer and the like. The reaction force motor 26 is provided with a rotation angle sensor 26a. The operation angle sensor 25 is a sensor that detects the operation angle of the steering wheel 21 as the amount of steering operation.

[0015] Furthermore, in the steering system 1, similar to a general so-called power steering system, a torsion bar 27 is incorporated in the steering shaft 22. The operation device 2 has an operation torque sensor 28 for detecting the operation torque as the operation force applied to the steering wheel 21 by the driver based on the amount of twist of the torsion bar 27.

[0016] (front wheel steering device) Each of the wheels 10 is supported on the vehicle body in a steerable manner via a steering knuckle 90, which is one component of a suspension device. The front wheel steering device 3 steers the pair of front wheels 10F together by rotating the steering knuckle 90. The front wheel steering device 3 has a steering actuator 30 as a main component.

[0017] The steering actuator 30 includes a steering rod 31, a housing 32, a rod moving mechanism 33, and a steering motor 35. The steering rod 31 (also called a "rack bar") is a member connected at both ends to left and right steering knuckles 90 via link rods 34. The housing 32 supports the steering rod 31 so that it can move left and right, and is a member that is fixedly held to the vehicle body.

[0018] Rod moving mechanism 33 is a mechanism for moving steering rod 31 left and right using steering motor 35, which is an electric motor, as a drive source. Rod moving mechanism 33 mainly comprises a ball screw mechanism that is made up of a ball groove threaded into steering rod 31 and a nut that threadably engages with the ball groove via a bearing ball and is rotated by steering motor 35. Because it has a common structure, a detailed description of rod moving mechanism 33 will be omitted.

[0019] Steering motor 35 is provided with rotation angle sensor 35a and current sensor 35b that detects the current supplied to it. Front wheel steering device 3 also has steering angle sensors 36 that detect the amount of left and right movement of steering rod 31 from the neutral position in order to detect the steering angle (amount of steering) of front wheels 10F. In this way, front wheel steering device 3 is mechanically independent from the operating force of steering wheel 21, and constitutes a steer-by-wire type steering device that steers front wheels 10F using the force of steering motor 35.

[0020] The steering ECU 5 is an electronic control unit equipped with a CPU, memory, etc. Although communication lines are not shown, the steering ECU 5 is communicatively connected to each device and each sensor. A car area network or controllable area network (CAN) is used for communication within the vehicle. The vehicle is also equipped with an autonomous driving ECU 9 that executes control related to autonomous driving. The vehicle is also equipped with various sensors such as wheel speed sensor 82.

[0021] The steering ECU 5 executes steering control for steering the front wheels 10F in response to a steering request, i.e., the operation angle of the steering wheel 21 during manual driving or a command from the automatic driving ECU 9 during automatic driving. The steering ECU 5 acquires the operation angle of the steering wheel 21 based on the rotation angle of the reaction force motor 26 detected by the rotation angle sensor 26a. The steering ECU 5 determines a target front wheel steering angle, which is a target for the steering angle of the front wheels 10F, based on the operation angle.

[0022] Based on the target front wheel steering angle, steering ECU 5 determines a target rotation angle, which is a target for the rotation angle of steering motor 35. Steering ECU 5 detects the actual rotation angle of steering motor 35 (hereinafter also referred to as "actual rotation angle") via rotation angle sensor 35a, and determines a rotation angle deviation, which is the deviation of the actual rotation angle from the target rotation angle. If the torque generated by steering motor 35 is called steering torque, then steering ECU 5 determines the steering torque to be generated in accordance with a feedback control law based on the rotation angle deviation.

[0023] If the current supplied to steering motor 35 is called the steering current, then there is a roughly proportional relationship between the steering torque and the steering current. In accordance with this relationship, steering ECU 5 determines the steering current to be supplied to steering motor 35 based on the determined steering torque, and supplies that steering current to steering motor 35.

[0024] Steering system 1 further includes reaction force ECU4 that executes reaction force control to give the driver a steering feel. Reaction force ECU4 determines the operation reaction force based on two components: a turning load dependent component FS and an operation force dependent decrease component FA. The turning load dependent component FS is a component related to the turning force (the turning torque of steering motor 35) required to steer front wheels 10F, and is determined based on the turning current supplied to steering motor 35. Although a detailed explanation will be omitted, the higher the current value of the turning current, the greater the turning load on front wheels 10F is recognized to be, and the turning load dependent component FS is determined to be a larger value.

[0025] On the other hand, the operation force dependent decrease component FA can be considered as a component for providing the driver with a so-called operation feeling in a power steering system. In a power steering system, an assist torque corresponding to the operation torque is generally applied to the steering shaft 22. The reaction force ECU 4 detects the operation torque via an operation torque sensor 28. The reaction force ECU 4 determines a reaction force current, which is a current to be supplied to the reaction force motor 26, based on the operation reaction force, and supplies the determined reaction force current to the reaction force motor 26.

[0026] (Detailed configuration of the steering ECU) As shown in Fig. 2, steering ECU 5 mainly includes first microcomputer 51 as a first calculation unit, first drive circuit 52, first temperature sensor 53, second microcomputer 54 as a second calculation unit, second drive circuit 55, and second temperature sensor 56. First microcomputer 51 is a microcomputer that is arranged on substrate 50 and includes a CPU, memory, etc. First microcomputer 51 determines the current value of a first steering current to be supplied to steering motor 35 via first drive circuit 52. First microcomputer 51 controls (PWM control) first drive circuit 52 so that the first steering current is supplied to steering motor 35.

[0027] First drive circuit 52 is a motor drive circuit that drives steering motor 35, and is configured to include a plurality of switching elements corresponding to the three phases of steering motor 35. First drive circuit 52 is arranged on substrate 50, and is connected to be able to communicate with first microcomputer 51. First drive circuit 52 supplies power from a battery (not shown) to steering motor 35 in accordance with the control of first microcomputer 51.

[0028] The first temperature sensor 53 is a temperature sensor for detecting 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 communicably connected to the first microcomputer 51 and transmits information on the detected temperature (detection result) to the first microcomputer 51. The first temperature sensor 53 may be disposed on the substrate 50 near (around) the first microcomputer 51 within a range where the temperature of the first microcomputer 51 can be detected (estimated).

[0029] Like first microcomputer 51, second microcomputer 54 is a microcomputer equipped with a CPU, memory, etc., arranged on substrate 50. Second microcomputer 54 determines the current value of the second steering current to be supplied to steering motor 35 via second drive circuit 55. Second microcomputer 54 controls (PWM control) second drive circuit 55 so that the second steering current is supplied to steering motor 35. First microcomputer 51 and second microcomputer 54 are connected to each other so as to be able to communicate with each other.

[0030] Second drive circuit 55 is a motor drive circuit that drives steering motor 35, and is configured to include a plurality of switching elements corresponding to the three phases of steering motor 35. Second drive circuit 55 is arranged on substrate 50, and is connected to be able to communicate with second microcomputer 54. Second drive circuit 55 supplies power from a battery (not shown) to steering motor 35 in accordance with the control of second microcomputer 54.

[0031] The second temperature sensor 56 is a temperature sensor for detecting the temperature of the second microcomputer 54. The second temperature sensor 56 is disposed inside the second microcomputer 54. The second temperature sensor 56 is communicably connected to the second microcomputer 54 and transmits information on the detected temperature (detection result) to the second microcomputer 54. The second temperature sensor 56 may be disposed on the substrate 50 near (around) the second microcomputer 54 within a range where the temperature of the second microcomputer 54 can be detected (estimated).

[0032] Steering motor 35 is a double-winding electric motor having a winding 351 connected to first drive circuit 52 and a winding 352 connected to second drive circuit 55. In other words, steering motor 35 is configured to output a steering torque corresponding to a total steering current (which may also be called a total steering current) of a first steering current supplied from first drive circuit 52 and a second steering current supplied from second drive circuit 55. The steering current supplied from the battery via steering ECU 5 is the sum of the first turning current and the second turning current.

[0033] To provide redundancy for the drive of steering motor 35, first microcomputer 51 and second microcomputer 54 of steering ECU 5 always perform the same calculations. First microcomputer 51 and second microcomputer 54 exchange information on the calculation results with each other. Even if one calculation unit fails, steering motor 35 can be driven by the other calculation unit. In this embodiment, first microcomputer 51 is a master microcomputer, and second microcomputer 54 is a slave microcomputer.

[0034] (current limiting against overheating) The steering ECU 5 detects that the detected temperature is below a predetermined threshold temperature T th When the steering ECU 5 exceeds this value, the steering ECU 5 is configured to be able to execute current limit control to reduce the upper limit of the steering current. As shown in Fig. 3, a limit value map showing the current limit value (upper limit value) relative to the temperature of the ECU or microcomputer is stored in the steering ECU 5. The current limit value is the upper limit (maximum permitted value) of the current value of the steering current that the steering ECU 5 is permitted to supply to the steering motor 35.

[0035] 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. th When the temperature exceeds 100°C, the current limit drops to the minimum value I min When the temperature exceeds a certain level, it reaches a minimum value I min In Figure 3, the maximum value I max is set to the maximum current value that can be passed through each of the drive circuits 52 and 55. min is the minimum current value that can be applied to each of the drive circuits 52 and 55, and the maximum value I max The maximum value is less than 50% of the value I. max When this steering current is supplied to the steering motor 35, the maximum steering torque is output.

[0036] In the steering ECU 5 of this embodiment, cooperative calculation control and independent calculation control are set as system operation modes (which can also be considered calculation modes of steering currents). In other words, the steering ECU 5 is configured to execute the cooperative calculation control and the independent calculation control at mutually different timings.

[0037] (Cooperative Calculation Control) The cooperative calculation control is a control (operation mode) in which the first microcomputer 51 and the second microcomputer 54 set the current limit value 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 calculation control is a control in which the microcomputers 51 and 54 set the same value of the current limit value. The cooperative calculation control is also a control in which the microcomputers 51 and 54 set the same value of the steering current.

[0038] In the cooperative calculation control, the first microcomputer 51 and the second microcomputer 54 each calculate a current limit value according to the higher value (temperature) of the detected temperatures T1 and T2. The cooperative calculation control can also be said to be a control in which the second microcomputer 54 calculates the current value of the second control current using the calculation result of the first microcomputer 51. The cooperative calculation control can also be said to be a control in which multiple calculation units cooperate to calculate the steering current.

[0039] More specifically, as shown in Fig. 4, when the first microcomputer 51 receives a steering request (the operation angle of the steering wheel 21 during manual driving or a command from the automatic driving ECU 9 during automatic driving), it calculates a current value J1 of the steering current corresponding to the steering request (S101). Hereinafter, the current value calculated in response to the steering request will also be referred to as the "calculated value." The first microcomputer 51 calculates a current limit value I as will be described later. lim (S102), and calculate the value J1 and the current limit value I lim and compare (S103).

[0040] As shown in Fig. 5, similar to the first microcomputer 51, when the second microcomputer 54 receives a steering request, it calculates a current value J2 of the steering current corresponding to the steering request (S201). The second microcomputer 54 receives information on the calculated value J1 from the first microcomputer 51. In the cooperative calculation control, the second microcomputer 54 sets the calculated value J1 of the first microcomputer 51 as the calculated value to be used by the second microcomputer 54 (S202). That is, in the cooperative calculation 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 the calculated value J1). 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 the calculated value J1), as will be described later. lim (S203), and calculate the value J1 and the current limit value I lim and compare (S204).

[0041] The first microcomputer 51 calculates a current limit value corresponding to the temperature T1 detected by the first temperature sensor 53 as a provisional limit value I1 based on the limit value map. Similarly, the second microcomputer 54 calculates a current limit value corresponding to the temperature T2 detected by the second temperature sensor 56 as a provisional limit value I2 based on the limit value map. The first microcomputer 51 and the second microcomputer 54 exchange information on provisional limit values with each other. In the cooperative calculation control, the first microcomputer 51 and the second microcomputer 54 each set the lower of the provisional limit value I1 and the provisional limit value I2 as the current limit value I1. lim In other words, in the cooperative calculation control, the first microcomputer 51 and the second microcomputer 54 respectively set the current limit value corresponding to the higher of the temperatures detected by the first temperature sensor 53 and the second temperature sensor 56 as the common current limit value I lim Set as.

[0042] The first microcomputer 51 and the second microcomputer 54 respectively calculate the calculated value J1 and the current limit value I lim The first microcomputer 51 and the second microcomputer 54 each calculate a value I (hereinafter also referred to as a final calculation value) by multiplying the command value by 1 / 2. e The first microcomputer 51 sets the final calculated value I as the steering current (S104, S205). e as the current value of the first steering current, and controls the first drive circuit 52 so that the first steering current is supplied to the winding 351 of the steering motor 35. The second microcomputer 54 calculates the final calculated value I e as the current value of the second steering current, and controls second drive circuit 55 so that the second steering current is supplied to winding 352 of steering motor 35.

[0043] In the cooperative calculation control, the first turning current and the second turning current have the same current value. The sum of the first turning current and the second turning current is calculated as J1 and the current limit value I lim The lower value (min(J1,I limTherefore, in the cooperative calculation control, the steering motor 35 is supplied with a steering current whose current value is set to the calculated value J1 according to the steering request, or a current whose current value is set to the current limit value I lim In the cooperative calculation control, the current value of the steering current supplied to the steering motor 35 is set to a value when the calculated value J1 is equal to the current limit value I lim If it is less than the current limit value I, it is set to the calculated value J1. lim If it is greater than or equal to the current limit value I lim The cooperative calculation control can also be called a cooperative operation mode or a first operation mode.

[0044] (Independent calculation control) Independent calculation control is a control (operation mode) in which first microcomputer 51 and second microcomputer 54 independently calculate the current value of each turning current (first turning current or second turning current). That is, in independent calculation control, first microcomputer 51 independently calculates the current value of the first turning current regardless of the calculation result of second microcomputer 54, and second microcomputer 54 independently calculates the current value of the second turning current regardless of the calculation result of first microcomputer 51. Therefore, in independent calculation control, the calculation result, which is the final calculation value I e may differ between the first microcomputer 51 and the second microcomputer 54. Independent calculation control is control in which each microcomputer 51, 54 can set a different current limit value. Moreover, cooperative calculation control is control in which each microcomputer 51, 54 can set a different steering current value.

[0045] 6, in the independent calculation control, first microcomputer 51 calculates a current value (calculated value) J1 of a steering current corresponding to a steering request (S301). First microcomputer 51 uses calculated value J1 to calculate the first steering current, regardless of calculated value J2, which is the calculation result of second microcomputer 54.

[0046] The first microcomputer 51 sets the current limit value corresponding to the temperature T1 detected by the first temperature sensor 53 as the first current limit value I lim1 (S302) The first current limit value I lim1is a value corresponding to the provisional limit value I1 in the cooperative calculation control. In this way, in the independent calculation control, the first microcomputer 51 calculates the current limit value (second current limit value I2 to be described later) calculated by the second microcomputer 54 based on the detected temperature T2 of the second temperature sensor 56. lim2 ), the current limit value (first current limit value I lim1 ) to set the

[0047] The first microcomputer 51 calculates the calculated value J1 and the first current limit value I lim1 The first microcomputer 51 compares the calculated value J1 with the first current limit value I lim1 The lower of these values (command value) is multiplied by 1 / 2 (first final calculation value) e1 as the current value of the first steering current (S304). First microcomputer 51 controls first drive circuit 52 so that the set first steering current is supplied to winding 351 of steering motor 35.

[0048] 7, second microcomputer 54, like first microcomputer 51, calculates a current value (calculated value) J2 of a steering current corresponding to a steering request (S401). In the independent calculation control, second microcomputer 54 uses calculated value J2 to calculate a second steering current, regardless of calculated value J1, which is the calculation result of first microcomputer 51. Note that since the input steering request is the same for first microcomputer 51 and second microcomputer 54, calculated value J1 and calculated value J2 are usually the same value.

[0049] The second microcomputer 54 sets the current limit value corresponding to the temperature T2 detected by the second temperature sensor 56 as the second current limit value I lim2 (S402) The second current limit value I lim2 is a value corresponding to the provisional limit value I2 in the cooperative calculation control. In the independent calculation control, the second microcomputer 54 calculates the first current limit value I lim1 Regardless of this, the current limit value is set based on the temperature T2 detected by the second temperature sensor 56.

[0050] The second microcomputer 54 calculates the calculated value J2 and the second current limit value I lim2The second microcomputer 54 compares the calculated value J2 with the second current limit value I lim2 The lower of these values (command value) is multiplied by 1 / 2 (second final calculation value) e2 is set as the current value of the second steering current (S404). Second microcomputer 54 controls second drive circuit 55 so that the set second steering current is supplied to winding 352 of steering motor 35. Since there may be cases where the detected temperatures of first temperature sensor 53 and second temperature sensor 56 differ, first current limit value I lim1 and the second current limit value I lim2 Therefore, in the independent calculation control, the current value of the first turning current and the current value of the second turning current may differ. Note that the independent calculation control can also be called an independent operation mode or a second operation mode.

[0051] The current value of the steering current in the independent calculation control differs depending on the case as follows: lim1 and the calculated value J2 is less than the second current limit value I lim2 If the calculated value J1 is less than the first current limit value I lim1 and the calculated value J2 is equal to or greater than the second current limit value I lim2 If the current value of the steering current is less than "I lim1 The calculated value J1 is the sum of "J1 × 1 / 2" and "J2 × 1 / 2". The calculated value J1 is the first current limit value I lim1 and the calculated value J2 is less than the second current limit value I lim2 If this is the case, the current value of the steering current is "J1×1 / 2" and "I lim2 The calculated value J1 is the sum of the first current limit value I lim1 and the calculated value J2 is equal to or greater than the second current limit value I lim2 If this is the case, the current value of the steering current is "I lim1 ×1 / 2" and "I lim2 × 1 / 2". Note that the former in parentheses indicates the current value of the first turning current, and the latter in parentheses indicates the current value of the second turning current.

[0052] (Switching of calculation control) The first microcomputer 51 and the second microcomputer 54 share calculation results and detected temperature information with each other through communication. The first microcomputer 51 and the second microcomputer 54 acquire information on the detected temperatures of the first temperature sensor 53 and the second temperature sensor 56, respectively. When switching the operating mode, the first temperature sensor 51 and the second microcomputer 54 each calculate a detected temperature difference ΔT, which is the difference between the detected temperature T1 of the first temperature sensor 53 and the detected temperature T2 of the second temperature sensor 56 (ΔT = |T1 - T2|).

[0053] The first microcomputer 51 and the second microcomputer 54 detect the temperature difference ΔT as a predetermined threshold ΔT th If the detected temperature difference ΔT is equal to or less than the predetermined threshold ΔT, the cooperative calculation control is executed. th If the detected temperature difference ΔT is greater than the predetermined threshold ΔT, the first microcomputer 51 and the second microcomputer 54 each execute independent calculation control. th If the temperature difference ΔT is equal to or less than the predetermined threshold ΔT, the operation mode is set to cooperative calculation control. th If the detected temperature difference ΔT is greater than or equal to a predetermined threshold ΔT, the steering ECU 5 sets the operation mode to independent calculation control. th If the detected temperature difference ΔT is greater than the threshold ΔT, the temperature difference ΔT will exceed the threshold ΔT. th is judged to be greater than

[0054] Since the first temperature sensor 53 and the second temperature sensor 56 are arranged in the same ECU (on the same board 50), it can be assumed that they detect the same temperature if they are normal. In other words, if 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, the cooperative calculation control is executed, and the current value of the first turning current and the current value of the second turning current are the same. When the cooperative calculation control is executed, if the detected temperature of at least one of the first temperature sensor 53 and the second temperature sensor 56 is lower than the threshold temperature T th If the current limit value exceeds this limit, the current limit value calculated by both the first microcomputer 51 and the second microcomputer 54 is reduced by current limit control based on the limit value map.

[0055] On the other hand, the detected temperature difference ΔT is equal to the predetermined threshold ΔT th If the detected temperature is higher than the first temperature sensor value, it is highly likely that one of the temperature sensors is faulty. In this case, if the cooperative calculation control continues to be executed, a common current limit value corresponding to the relatively higher detected temperature is set for both the calculation of the current value of the first turning current and the current value of the second turning current. Therefore, the current value of the first turning current and the current value of the second turning current are both limited by the current limit value set to a lower value. As a result, if a drift failure occurs in one of the temperature sensors and the detected temperature becomes higher than normal, the current value of the turning current will be lower even though the actual temperature is not high, which could reduce torque and result in reduced turning accuracy.

[0056] However, according to this embodiment, the detected temperature difference ΔT is equal to or greater than the predetermined threshold ΔT th If the detected temperature is greater than the actual temperature, the microcomputer's calculation control (operation mode) switches from cooperative calculation control to independent calculation control. As a result, only one microcomputer is subject to a limit that does not correspond to the actual temperature due to the temperature detected by the faulty temperature sensor, while the other microcomputer can set the steering current using the same current limit value as in normal operation. In other words, by executing independent calculation control, at least one microcomputer can calculate the steering current in the same way as in normal operation, and a decrease in steering current due to a detected temperature different from the actual temperature is suppressed. According to this embodiment, a decrease in steering current is suppressed in situations that do not meet the purpose of current limit control (protection from overheating), and a decrease in turning accuracy in response to a steering request is suppressed.

[0057] As an example, the temperature detected by the first temperature sensor 53 is equal to or lower than the threshold temperature T th The detected temperature difference ΔT becomes higher than the predetermined threshold ΔT th If the first current limit value I is larger than the first current limit value I , the first microcomputer 51 switches from cooperative control to independent control. lim1 For example, the lowest value I min On the other hand, the second microcomputer 54 sets the second current limit value I lim2The highest value I max and calculate the current value of the second steering current. Here, when the maximum steering torque is required, the current value of the first steering current is set to the limited minimum value I min It is half the value of (I min ×1 / 2), the current value of the second steering current is the maximum value I max It is half the value of (I max ×1 / 2). Maximum value I max Half of this value is half (50%) of the maximum value of the steering current that can be output. In other words, according to the independent calculation control, even in situations where maximum output is required, the current value of the steering current, which is the sum of the first and second steering currents, is set to a value that is 50% or more of the maximum output. If an output that is 50% of the maximum output is ensured, there will be no shortage of torque and a decrease in turning accuracy will be suppressed. Only the temperature detected by the second temperature sensor 56 is above the threshold temperature T th Even if the temperature is higher than this, the same effect can be obtained. It should be noted that the possibility of both the temperature sensors 53 and 56 suffering from drift failure at the same time is extremely low.

[0058] (Summary of Effects of the Present Embodiment) In the steering system 1 of this embodiment, the detected temperature difference ΔT is a predetermined threshold ΔT th If the difference is greater than the predetermined threshold, first microcomputer 51 and second microcomputer 54 are configured to each execute independent calculation control. With this configuration, it is possible to detect that the detected temperature of one temperature sensor has deviated from the normal detected temperature due to a malfunction (e.g., drift malfunction) by comparing it with the detected temperatures of the other normal temperature sensors. Specifically, if the detected temperature difference is greater than a predetermined threshold, steering ECU 5 estimates (determines) that one temperature sensor has failed, and executes independent calculation control. In this way, steering system 1 of this embodiment is configured to suppress a decrease in turning accuracy even if one temperature sensor experiences drift malfunction, assuming that the possibility of multiple temperature sensors simultaneously experiencing drift malfunction is extremely low.

[0059] In the independent calculation control, each microcomputer 51, 54 calculates a current limit value based on the detected temperature of its own temperature sensor 53, 56, regardless of the detected temperatures of the temperature sensors 53, 56 corresponding to the other microcomputers 51, 54. As a result, the microcomputers 51, 54 corresponding to the normal temperature sensors 53, 56 set a current limit value based on the actual detected temperature, and only the microcomputers 51, 54 corresponding to the faulty temperature sensors 53, 56 calculate a current limit value that is more limited than necessary. In other words, according to this embodiment, even if one of the temperature sensors 53, 56 fails when the actual temperature is not high enough to limit the current, the microcomputers 51, 54 corresponding to the normal temperature sensors 53, 56 are prevented from unnecessary reductions in the current limit value. As such, according to this embodiment, even if one of the temperature sensors 53, 56 fails, unnecessary reductions in torque due to steering current limitation are prevented, thereby preventing a decrease in turning accuracy.

[0060] (Add switching conditions) The condition for switching the operation mode from cooperative to independent is to determine whether the detected temperature difference ΔT exceeds a predetermined threshold ΔT th In addition to the first condition that the calculated current limit value I is greater than the first condition, the following condition may be added. For example, the second condition may be that the calculated current limit value I is greater than the first condition. lim is the threshold current value I th In other words, the second condition is that the provisional limit value I1 or the provisional limit value I2 is less than the threshold current value I th The threshold current I th is the minimum value I min Higher Maximum Value I max is set to less than (see FIG. 8). As a result, the switching of the calculation control is performed after the current limit value has actually been reduced by the current limit control. Therefore, by adding the second condition to the switching conditions, the turning ECU 5 can switch the calculation control in a situation where the current value of the turning current is actually affected by a drift fault. By adding the second condition, the calculation control will not be switched in a situation where the current value of the turning current is not affected, that is, in a situation where the current limit value does not change due to the switching of the calculation control.

[0061] Similarly, as the third condition, "the detected temperature T1 or the detected temperature T2 is equal to or lower than the predetermined temperature T ps The switching condition may be added as "exceeding a predetermined temperature T ps is set in the limit value map, for example, at the threshold temperature T th Above minimum value I min or a value less than the temperature corresponding to the threshold temperature T th As with the second condition, the third condition also enables the steering ECU 5 to switch the calculation control in a situation where the current value of the steering current is actually affected or where there is a high probability that the current value will be affected.

[0062] For example, as shown in Fig. 9, the steering ECU 5 may be set to switch the calculation control from the cooperative calculation control to the independent calculation control when three conditions are satisfied (S501: Yes, S502: Yes, S503: Yes). This allows the steering ECU 5 to switch the calculation control in a more appropriate situation. In this way, the conditions for switching the calculation control may include at least one of the second condition and the third condition in addition to the first condition as a necessary condition.

[0063] (Transformation mode) The present invention is not limited to the above disclosure. For example, the steering ECU 5 may include three or more microcomputers. The steering ECU 5 may be provided with three or more sets of microcomputers, temperature sensors, and drive circuits. For example, as shown in FIG. 10, the steering ECU 5 may include a third microcomputer 57, a third drive circuit 58, and a third temperature sensor 59 in addition to the configuration of the above embodiment. In this case, for example, the first microcomputer 51 serves as the master microcomputer, and the second microcomputer 54 and the third microcomputer 57 serve as slave microcomputers. The third microcomputer 57 operates in the same manner as the second microcomputer 54 in the above embodiment. The third temperature sensor 59 is provided within the third microcomputer 57.

[0064] Third microcomputer 57 calculates the current value of the third turning current. In cooperative calculation control, second microcomputer 54 and third microcomputer 57 use the calculation value J1 of first microcomputer 51, rather than their own calculation value, to calculate the turning current. Third microcomputer 57 calculates a temporary limit value I3 corresponding to the detected temperature T3 of third temperature sensor 59 based on the limit value map.

[0065] The current limit value set by each microcomputer 51, 54, 57 is set to the smallest value among temporary limit values I1, I2, I3 (min(I1, I2, I3)). In other words, each microcomputer 51, 54, 57 sets the current limit value so as to correspond to the smallest value among detected temperatures T1, T2, T3. Each microcomputer 51, 54, 57 sets the lower of calculated value J1 and current limit value min(I1, I2, I3) as the command value. The current value of the turning current supplied to steering motor 35 is the sum of the first turning current, the second turning current, and the third turning current. Therefore, the current value of the turning current calculated by each microcomputer 51, 54, 57 is the command value multiplied by 1 / 3 (command value × 1 / 3).

[0066] In the independent calculation control, the third microcomputer 57 also independently calculates the current value of the third steering current, similar to the first microcomputer 51 and the second microcomputer 54. The third microcomputer 57 calculates the calculated value J3 in response to a steering request. The third microcomputer 57 calculates the current limit value corresponding to the detected temperature T3 of the third temperature sensor 59 as the third current limit value I lim3 The third microcomputer 57 sets the calculated value J3 and the third current limit value Ilim3 The third microcomputer 57 sets the lower of these values as the command value. The third microcomputer 57 sets the value (third final calculated value) obtained by multiplying the command value by 1 / 3 as the current value of the third turning current. The third microcomputer 57 controls the third drive circuit 58 so that the third turning current is supplied to the third winding 353 of the turning motor 35.

[0067] The switching condition (first condition) of the calculation control is whether a first detected temperature difference ΔT1, which is the difference between the detected temperature T1 and the detected temperature T2, a second detected temperature difference ΔT2, which is the difference between the detected temperature T2 and the detected temperature T3, or a third detected temperature difference ΔT3, which is the difference between the detected temperature T3 and the detected temperature T1, is equal to or exceeds a predetermined threshold ΔTth is greater than (ΔT1>ΔT th , ΔT2>ΔT th , or ΔT3>ΔT th This configuration also provides the same effects as the above embodiment.

[0068] Further, a second condition and / or a third condition may be added to the switching conditions. The second condition is, for example, when any one of the provisional limit values I1, I2, and I3 is equal to or greater than the threshold current value I th The third condition is, for example, that any one of the detected temperatures T1, T2, and T3 is less than a predetermined temperature T ps This configuration also allows for a changeover of the operational control in more appropriate situations, i.e., situations where drift faults affect the setting of the current limit value.

[0069] (Summary of the configuration of this embodiment) Steering system 1 of this embodiment is a steer-by-wire type steering system that includes front wheel steering device 3 having steering motor 35 and that steers front wheels 10F mechanically independently of the operating force of steering wheel 21, and steering ECU 5 as a control device that supplies a steering current to steering motor 35 in response to a steering request and controls steering motor 35. Steering ECU 5 includes a plurality of microcomputers 51, 54 that are connected to each other so as to be able to communicate with each other and that serve as a plurality of calculation units that calculate a current value of the steering current in response to the steering request, a plurality of drive circuits 52, 55 that correspond individually to the plurality of microcomputers 51, 54 and supply the steering current to steering motor 35 under the control of the corresponding microcomputers 51, 54, and a plurality of temperature sensors 53, 56 that correspond individually to the plurality of microcomputers 51, 54 and detect the temperature of the corresponding microcomputer 51, 54. Each microcomputer 51, 54 is configured to execute independent calculation control when a detected temperature difference, which is the difference between temperatures detected by any two of the plurality of temperature sensors 53, 56, is greater than a predetermined threshold. In the independent calculation control, each microcomputer 51, 54 individually (independently from the other microcomputers) calculates and sets a current limit value, which is the upper limit of the steering current, based on the detected temperature of the temperature sensor 53, 56 corresponding to itself, regardless of the detected temperatures of the temperature sensors 53, 56 corresponding to the microcomputers 51, 54 other than itself.

[0070] Furthermore, when the detected temperature difference is equal to or less than a predetermined threshold, each of the microcomputers 51, 54 performs cooperative calculation control by calculating and setting a common current limit value based on the highest value of the temperatures detected by all of the temperature sensors 53, 56.

[0071] Further, each of the microcomputers 51 and 54 determines whether the current limit value corresponding to the detected temperature of at least one of the plurality of temperature sensors 53, 56, and 59 is equal to or exceeds the predetermined threshold current value I th (second condition)” and / or “when the temperature detected by at least one of the plurality of temperature sensors 53, 56, 59 is less than the predetermined temperature T ps If the difference is higher than the reference voltage (third condition), the independent calculation control is executed.

[0072] In this embodiment, each of the microcomputers 51, 54 is a microcomputer equipped with a CPU and a memory. The multiple microcomputers 51, 54 are arranged in the same electronic control unit 5 (inside a case) and / or on the same board 50. In other words, the multiple microcomputers 51, 54 are arranged in one common electronic control unit 5 (inside a case) and / or on one common board 50. A limit value map showing the relationship between the temperature detected by the temperature sensor and the current limit value is stored in advance in the steering ECU 5, and each of the microcomputers 51, 54 is configured to calculate the current limit value based on the limit value map.

[0073] (The control device has two calculation units.) In the above configuration, the "plurality of calculation units" may be constituted by a first microcomputer 51 that calculates the current value of the first turning current, and a second microcomputer 54 that calculates the current value of the second turning current. In this case, the "plurality of temperature sensors" include a first temperature sensor 53 that detects the temperature of first microcomputer 51, and a second temperature sensor 56 that detects the temperature of second microcomputer 54. The "plurality of drive circuits" are constituted by a first drive circuit 52 that supplies the first turning current to steering motor 35 under the control of first microcomputer 51, and a second drive circuit 55 that supplies the second turning current to steering motor 35 under the control of second microcomputer 54. Each of microcomputers 51, 54 then calculates a detected temperature difference ΔT, which is the difference between the temperature detected by first temperature sensor 53 and the temperature detected by second temperature sensor 56, and calculates a detected temperature difference ΔT. th When the first microcomputer 51 determines that the first steering current is greater than the first current limit value I, the first microcomputer 51 executes the independent calculation control. lim1 ) based on the temperature detected by the first temperature sensor 53, regardless of the temperature detected by the second temperature sensor 56. In addition, the second microcomputer 54, in the independent calculation control, calculates a current limit value (second current limit value I lim2 ) is calculated based on the temperature detected by the second temperature sensor 56, regardless of the temperature detected by the first temperature sensor 53.

[0074] Each microcomputer 51, 54 detects the temperature difference ΔT as a predetermined threshold ΔT th In the cooperative calculation control, each of the microcomputers 51 and 54 calculates a common current limit value based on the higher of the temperature detected by the first temperature sensor 53 and the temperature detected by the second temperature sensor 56.

[0075] (The control device has three calculation units) In the above configuration, the "plurality of calculation units" may be made up of first microcomputer 51 that calculates the current value of the first turning current, second microcomputer 54 that calculates the current value of the second turning current, and third microcomputer 57 that calculates the current value of the third turning current. In this case, the "plurality of temperature sensors" include first temperature sensor 53 that detects the temperature of first microcomputer 51, second temperature sensor 56 that detects the temperature of second microcomputer 54, and third temperature sensor 59 that detects the temperature of third microcomputer 57. Also, the "plurality of drive circuits" are made up of first drive circuit 52 that supplies the first turning current to steering motor 35 under the control of first microcomputer 51, second drive circuit 55 that supplies the second turning current to steering motor 35 under the control of second microcomputer 54, and third drive circuit 58 that supplies the third turning current to steering motor 35 under the control of third microcomputer 57. Each microcomputer 51, 54, 57 is configured to execute independent calculation control when the first detected temperature difference, which 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, which is the difference between the detected temperature of the second temperature sensor 56 and the detected temperature of the third temperature sensor 59, or the third detected temperature difference, which is the difference between the detected temperature of the third temperature sensor 59 and the detected temperature of the first temperature sensor 53, is greater than a predetermined threshold value.

[0076] The first microcomputer 51, in the independent calculation control, determines a current limit value (first current limit value I lim1 ) based on the temperature detected by the first temperature sensor 53, regardless of the temperatures detected by the second temperature sensor 56 and the third temperature sensor 59. In the independent calculation control, the second microcomputer 54 calculates a current limit value (second current limit value I lim2) based on the temperature detected by the second temperature sensor 56, regardless of the temperature detected by the first temperature sensor 53 and the temperature detected by the third temperature sensor 59. The third microcomputer 57, in the independent calculation control, calculates a current limit value (third current limit value I lim3 ) is calculated based on the temperature detected by the third temperature sensor 59, regardless of the temperatures detected by the first temperature sensor 53 and the second temperature sensor 56.

[0077] Furthermore, each of the microcomputers 51, 54, 57 detects the first detected temperature difference, the second detected temperature difference, and the third detected temperature difference all at a predetermined threshold value ΔT th In the cooperative calculation control, each of the microcomputers 51, 54, and 57 calculates a common current limit value based on the highest value among the temperatures detected by the first temperature sensor 53, the second temperature sensor 56, and the third temperature sensor 59.

[0078] (others) The "calculating unit" is not limited to a microcomputer and may be, for example, an ECU. In other words, the control device may be composed of multiple ECUs. For example, the steering system 1 may include a first ECU as a first calculating unit, a first temperature sensor that detects the temperature of the first ECU, a first drive circuit disposed within the first ECU, a second ECU as a second calculating unit, a second temperature sensor that detects the temperature of the second ECU, and a second drive circuit disposed within the second ECU. In this case, the first and second temperature sensors are not disposed on the same circuit board, nor are they disposed within the same ECU (electronic control unit). However, if the first ECU is disposed near the second ECU (for example, side by side), or if the temperature sensors are disposed in a manner that minimizes differences in the normal detected temperatures, the same effect as when the temperature sensors are disposed within the same ECU or on the same circuit board can be achieved. Furthermore, if the normal detected temperatures of the temperature sensors differ depending on the locations of the first and second ECUs, a certain degree of effect can be achieved by setting a predetermined threshold value that takes into account the difference. However, from the viewpoint of ease of setting threshold values and the like, it is preferable that the plurality of temperature sensors be arranged so that the difference between the detected temperatures in normal times falls within a predetermined range.

[0079] Furthermore, in steering system 1, the steering motor serving as the drive source for steering actuator 30 does not have to be one; for example, a plurality of steering motors corresponding to the number of calculation units (e.g., microcomputers) may be provided. Also, a plurality of temperature sensors may be arranged within the microcomputer. In this case, for example, the microcomputer may use an average value of detected temperatures as the detected temperature of the microcomputer for calculation. Also, the control of this embodiment may be applied to the steering control of rear wheel 10R. Furthermore, the details of the various calculations may be calculation methods other than those of the above embodiment, as long as they do not deviate from the technical concept of the present disclosure. Also, the limit value map may be set differently from that shown in FIGS. 3 and 8.

[0080] This embodiment can also be described as follows: That is, steering system 1 is a steer-by-wire steering system including: a steering device having a steering motor that steers wheels mechanically independently of the operating force of an operating member; and a control device that supplies a first turning current and a second turning current to the steering motor in response to a steering request and controls the steering motor, the control device including: a first calculation unit that calculates a current value of the first turning current, a first temperature sensor that detects the temperature of the first calculation unit, a second calculation unit that is communicatively connected to the first calculation unit and calculates a current value of the second turning current, and a second temperature sensor that detects the temperature of the second calculation unit, and is configured to perform independent calculation control to calculate a first current limit value that is an upper limit of the first turning current based on the temperature detected by the first temperature sensor regardless of the temperature detected by the second temperature sensor when a detected temperature difference that is a difference between the temperatures detected by the first temperature sensor and the second temperature sensor is greater than a predetermined threshold value, and to calculate a second current limit value that is an upper limit of the second turning current based on the temperature detected by the second temperature sensor regardless of the temperature detected by the first temperature sensor. Furthermore, the control device is configured to execute cooperative calculation control to set the first current limit value and the second current limit value to a common value based on the temperatures detected by the first temperature sensor and the second temperature sensor when the detected temperature difference is equal to or less than a predetermined threshold. [Explanation of symbols]

[0081] 1: Steering system, 3: Front wheel steering device (steering device), 5: Steering ECU (control device), 50: Circuit board, 51: First microcomputer (first calculation unit), 52: First drive circuit, 53: First temperature sensor, 54: Second microcomputer (second calculation unit), 55: Second drive circuit, 56: Second temperature sensor, 57: Third microcomputer (third calculation unit), 58: Third drive circuit, 59: Third temperature sensor.

Claims

1. a steering device having a steering motor and steering the wheels mechanically independent of the operating force of an operating member; a control device that supplies a steering current to the steering motor in response to a steering request and controls the steering motor; A steer-by-wire type steering system comprising: The control device a plurality of calculation units that are communicably connected to each other and that calculate the current value of the steering current in response to the steering request; a plurality of drive circuits respectively corresponding to the plurality of calculation units, and supplying the steering current to the steering motor under control of the corresponding calculation unit; a plurality of temperature sensors respectively corresponding to the plurality of calculation units and detecting temperatures of the corresponding calculation units; Equipped with each of the calculation units is configured to, when a detected temperature difference, which is a difference between detected temperatures of any two of the plurality of temperature sensors, is greater than a predetermined threshold, perform independent calculation control to individually calculate and set a current limit value, which is an upper limit value of the steering current, based on the detected temperature of the temperature sensor corresponding to itself, regardless of the detected temperatures of the temperature sensors corresponding to the calculation units other than itself; Steering system.

2. When the detected temperature difference is equal to or less than the predetermined threshold, each of the calculation units is configured to perform cooperative calculation control to calculate and set a common current limit value based on the highest value of the detected temperatures of all of the temperature sensors. The steering system of claim 1 .

3. each of the calculation units is configured to execute the independent calculation control when the detected temperature difference is greater than the predetermined threshold value and when the current limit value corresponding to the detected temperature of at least one of the plurality of temperature sensors is less than a predetermined threshold current value; 3. A steering system according to claim 1 or 2.

4. each of the calculation units is configured to execute the independent calculation control when the detected temperature difference is greater than the predetermined threshold value and when the detected temperature of at least one of the plurality of temperature sensors is higher than a predetermined temperature; 3. A steering system according to claim 1 or 2.

5. each of the calculation units is configured to execute the independent calculation control when the detected temperature difference is greater than the predetermined threshold value, when the current limit value corresponding to the detected temperature of at least one of the plurality of temperature sensors is less than a predetermined threshold current value, and when the detected temperature of at least one of the plurality of temperature sensors is higher than a predetermined temperature.

3. A steering system according to claim 1 or 2.

6. Each of the computing units is a microcomputer, the plurality of calculation units and the plurality of temperature sensors are arranged in the same electronic control unit; A steering system according to any one of claims 1 to 5.

7. Each of the computing units is a microcomputer, the plurality of calculation units and the plurality of temperature sensors are arranged on the same substrate; A steering system according to any one of claims 1 to 6.

8. The control device stores in advance a limit value map that represents a relationship between the temperature detected by the temperature sensor and the current limit value, Each of the calculation units is configured to calculate the current limit value based on the limit value map. A steering system according to any one of claims 1 to 7.

9. the plurality of calculation units are configured by a first calculation unit that calculates a current value of a first turning current and a second calculation unit that calculates a current value of a second turning current, the plurality of temperature sensors include a first temperature sensor that detects the temperature of the first calculation unit and a second temperature sensor that detects the temperature of the second calculation unit; the plurality of drive circuits are configured by a first drive circuit that supplies the first turning current to the steering motor under the control of the first calculation unit, and a second drive circuit that supplies the second turning current to the steering motor under the control of the second calculation unit, the first calculation unit and the second calculation unit are configured to respectively execute the independent calculation control when the detected temperature difference, which is a difference between the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor, is greater than the predetermined threshold value; the first calculation unit, in the independent calculation control, calculates the current limit value that limits the first turning current based on the detected temperature of the first temperature sensor regardless of the detected temperature of the second temperature sensor, the second calculation unit, in the independent calculation control, calculates the current limit value that limits the second turning current based on the detected temperature of the second temperature sensor regardless of the detected temperature of the first temperature sensor. A steering system according to any one of claims 1 to 8.

10. the first calculation unit and the second calculation unit are configured to, when the detected temperature difference is equal to or less than the predetermined threshold, calculate a common current limit value based on a higher value of the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor as cooperative calculation control.

10. The steering system of claim 9.

11. the plurality of calculation units are configured by a first calculation unit that calculates a current value of a first turning current, a second calculation unit that calculates a current value of a second turning current, and a third calculation unit that calculates a current value of a third turning current, the plurality of temperature sensors include a first temperature sensor that detects the temperature of the first calculation unit, a second temperature sensor that detects the temperature of the second calculation unit, and a third temperature sensor that detects the temperature of the third calculation unit; the plurality of drive circuits are comprised of a first drive circuit that supplies the first turning current to the steering motor under the control of the first calculation unit, a second drive circuit that supplies the second turning current to the steering motor under the control of the second calculation unit, and a third drive circuit that supplies the third turning current to the steering motor under the control of the third calculation unit, The first calculation unit, the second calculation unit, and the third calculation unit the independent calculation control is executed when a first detected temperature difference, which is a difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor, a second detected temperature difference, which is a difference between the temperature detected by the second temperature sensor and the temperature detected by the third temperature sensor, or a third detected temperature difference, which is a difference between the temperature detected by the third temperature sensor and the temperature detected by the first temperature sensor, is greater than the predetermined threshold; the first calculation unit, in the independent calculation control, calculates the current limit value that limits the first turning current based on the detected temperature of the first temperature sensor, regardless of the detected temperatures of the second temperature sensor and the third temperature sensor, the second calculation unit, in the independent calculation control, calculates the current limit value that limits the second turning current based on the detected temperature of the second temperature sensor, regardless of the detected temperatures of the first temperature sensor and the third temperature sensor, the third calculation unit, in the independent calculation control, calculates the current limit value that limits the third turning current based on the detected temperature of the third temperature sensor, regardless of the detected temperatures of the first temperature sensor and the second temperature sensor. A steering system according to any one of claims 1 to 8.

12. the first calculation unit, the second calculation unit, and the third calculation unit are configured to, when all of the first detected temperature difference, the second detected temperature difference, and the third detected temperature difference are equal to or less than the predetermined threshold, respectively, calculate the common current limit value based on the highest value among the detected temperatures of the first temperature sensor, the second temperature sensor, and the third temperature sensor, as cooperative calculation control.

12. The steering system of claim 11.

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