Steering system

Abstract

To provide a steer-by-wire type steering system having high practical utility.SOLUTION: A steer-by-wire type steering system includes: an operation member 20 operated by an operator; and a steering device 14 steering wheels 10 as two systems having electric motors 50a, 50b as driving sources. In the system, supply of electric current exceeding an upper limit value to each of the electric motors with two systems is prohibited, and the upper limit value of the electric current supplied to one of the electric motors is raised when steering the wheels by only one of the two systems. The upper limit value of the electric current supplied to the electric motor having another one system is raised even when the wheels are steered by only another one of the two systems of the steering device due to failure of one of the two systems, so that sufficient steering power can be obtained.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a steer-by-wire type steering system mounted on a vehicle. [Background technology]

[0002] For example, in the electric power steering system described in the following patent document, the steering force applied by the driver to the steering wheel is assisted by two assist devices to steer the wheels. If one of the two assist devices fails, the other assists only. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-130007 A Summary of the Invention [Problem to be solved by the invention]

[0004] Steering systems mounted on vehicles include steering systems that have a steering device having an electric motor and steer wheels, not depending on the driver's operating force applied to an operating member such as a steering wheel, i.e., steer-by-wire type steering systems. For example, from the viewpoint of fail-safe, it is considered to provide a two-system steering device for the steer-by-wire type steering system. In the steer-by-wire type steering system, the driver's operating force does not contribute to steering the wheels, so that, for example, when the wheels are steered by only one of the two systems of the steering device, the steering force, which is the force for steering the wheels, may be insufficient. By eliminating or alleviating the insufficiency of the steering force, the practicality of the steer-by-wire type steering system is improved. The present invention has been made in view of such a situation, and an object of the present invention is to provide a highly practical steer-by-wire type steering system. [Means for solving the problem]

[0005] In order to solve the above problems, the steering system of the present invention comprises: An operating member operated by a driver; A steering device that steers the wheels using two systems each having an electric motor as a drive source. , By controlling the current supplied to each of the two electric motors, a controller that realizes steering of the wheels in response to the operation of the operating member; A steer-by-wire type steering system mounted on a vehicle, comprising: The controller controls the supply of a current exceeding an upper limit value to each of the electric motors of the two systems. In addition, when the wheels are steered by only one of the two systems, that one The upper limit value of the current supplied to the electric motor is increased. and configured to prohibit the upper limit value from being increased when the vehicle's traveling speed is equal to or lower than a set speed. do. Effect of the Invention

[0006] An upper limit is usually set for the current supplied to the electric motor to protect the electric motor and the drive circuit (driver) of the electric motor from overheating. According to the steering system of the present invention, even if the wheels are steered only by the other one due to a failure of one of the two systems of the steering device, the upper limit of the current supplied to the electric motor of the other system is raised, so that a sufficient steering force can be obtained. On the other hand, for example, the electric motor and its drive circuit are generally provided with a heat sink shared by the two systems for overheat protection, and even if the upper limit of the current supplied is raised and the wheels are steered only by the other one system, the heat sink can be used only by the other one system, so overheating of the electric motor of the other one system and its drive circuit does not become a major problem. In addition, in the case of a failure of one system, it is difficult to imagine that steering by only the other one system as described above will be performed for a relatively long period of time. Therefore, in this case, when the wheels are steered by a separate system, even if the upper limit of the current supply is increased, overheating of the electric motor and its drive circuit will not be a major problem.

[0007] The steering device of the steering system of the present invention has two systems, and each of the two systems may have two electric motors that are separate from each other, or a single two-system electric motor may be provided corresponding to the two systems. In more detail, an electric motor having one output shaft and two sets of coils corresponding to the two systems may be used.

[0008] When the temperature of the steering system drops to a certain level, the operating resistance of the mechanical structure increases due to a reduction in clearance caused by cooling, an increase in the viscosity of the lubricant, and the like, and a larger steering force is required to steer the wheels. In other words, a larger current needs to be supplied to the electric motor of the steering device. Taking this into consideration, when the temperature of the steering system is below a set temperature, the amount by which the upper limit of the supply current is increased (the amount of increase) may be larger than when the temperature of the steering system is above the set temperature. Conversely, when the temperature of the steering system has not yet dropped to a certain level, not much steering force is required. Taking this into consideration, the upper limit of the supply current may be increased on the condition that the temperature of the steering system is below a set temperature. In other words, as long as the temperature of the steering system is above the set temperature, the upper limit of the supply current may not be increased.

[0009] The temperature of the steering system may be determined based on the detection of a temperature sensor provided in the steering device itself, more specifically, in the housing of the actuator, in the vicinity of the electric motor, in the vicinity of the drive circuit, etc. Alternatively, the temperature may be determined based on the environmental temperature in which the vehicle is placed, or a temperature estimated from the supply of current to the electric motor (current amount, supply time, etc.), etc.

[0010] Taking into consideration the increase in the operating resistance described above, it is desirable to set the set temperature at a temperature below 0° C., for example, −20° C., −10° C., 0° C., etc. Also, taking into consideration that the lower the temperature of the steering system, the greater the steering force required, the greater the allowance for raising the upper limit of the supply current may be increased as the temperature of the steering system decreases, that is, the upper limit of the supply current may be increased.

[0011] On the other hand, when the traveling speed of the vehicle (hereinafter sometimes referred to as "vehicle speed") becomes low to a certain extent, the frictional force between the road surface and the tires becomes influential, and the steering force for steering the wheels becomes considerably large. When the vehicle is stopped, that is, when the vehicle speed is 0, the wheels must be steered in a so-called stationary steering state, which requires a considerably large steering force, and the current supplied to the electric motor becomes excessively large. In consideration of this, when the vehicle speed is equal to or lower than a set speed, the upper limit of the supply current may be prohibited from being increased. It is desirable to set the set speed so as to simulate the vehicle being stopped in order to prohibit the increase of the upper limit in a stationary steering state or a state close to it. Specifically, it may be set to, for example, 2 to 5 km / h.

[0012] When the wheels are steered by both of the two systems of the steering device, it is desirable to make the currents supplied to the steering motors of the two systems equal in order to align the operations of the two systems. In other words, it is desirable to perform control that coordinates the two systems (hereinafter sometimes referred to as "cooperative control"). In this case, in cooperative control, the current to be supplied to the electric motor of one of the two systems is determined, and the determined current is supplied to the electric motor of the other of the two systems. In other words, one of the two systems is designated as a main system and the other as a sub-system, and the main system determines the currents to be supplied to the electric motors of both systems, and the determined current is also supplied to the sub-system. Even in a steering system configured to perform such cooperative control, for example, when the wheels are steered only by the other of the two systems, i.e., the sub-system, the current to be supplied to the other electric motor may be determined independently, and the determined current may be supplied to the other electric motor. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic diagram of an overall configuration of a steering system according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a diagram illustrating a heat sink provided for an electric motor and a controller of the steering device for overheat protection. [Diagram 3] 4 is a flowchart of a basic steering program and a subordinate steering program executed in the steering system of the embodiment. [Figure 4] 13 is a graph showing a high temperature limit map for determining an upper limit of a current supplied to a turning motor, and a graph showing the rotation speed-torque characteristics of the turning motor. [Diagram 5] 5 is a graph showing the relationship between the environmental temperature and the steering force generated by the steering device, and a graph showing a low temperature limit map for determining an upper limit value of a current supplied to a steering motor. [Figure 6] 6 is a flowchart of a current limiting subroutine that constitutes a part of the basic steering program. [Figure 7] 4 is a flowchart of a reaction force application program executed in the steering system of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, as a mode for carrying out the present invention, a steering system according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition to the following embodiment, the present invention can be carried out in various forms including the form described in the above section [Modes of the Invention], and various modifications and improvements based on the knowledge of those skilled in the art. EXAMPLES

[0015] [A] Steering system configuration The steering system of the embodiment mounted on a vehicle is a system for steering two wheels (front wheels) 10, each of which is a steerable wheel, as shown diagrammatically in FIG. 1, and is a steer-by-wire type steering system equipped with an operating device 12 and a steering device 14 which are mechanically independent of each other.

[0016] The operation device 12 includes a) a steering wheel 20 as an operation member that is steered by the driver, b) a steering shaft 22 to the tip of which the steering wheel 20 is attached, c) a steering column 24 that rotatably holds the steering shaft 22 and is supported by an instrument panel reinforcement (not shown), and d) a reaction motor 26 that is an electric motor supported by the steering column 24, and generates a reaction force F (strictly speaking, a reaction torque, but hereinafter the commonly used term "operation reaction force") against the steering operation using a force source of the reaction motor 26. CT to the steering wheel 20 via the steering shaft 22. Since the reaction force imparting mechanism 28 has a general structure including a reducer and the like, a description of the specific structure of the reaction force imparting mechanism 28 will be omitted.

[0017] The reaction motor 26 is a three-phase brushless DC motor, and magnets are attached to the outer periphery of the rotating shaft, and coils are arranged in the housing to face the magnets. The reaction motor 26 is a two-system motor in which two sets of coils are arranged for one magnet. Hereinafter, each of the two systems may be referred to as the reaction motor 26a and the reaction motor 26b. Each of the reaction motors 26a and 26b has its own motor rotation angle sensor 30a, 30b (hereinafter, sometimes collectively referred to as the "motor rotation angle sensor 30") for detecting the rotation angle (which can be considered as the "relative angle" or "phase") ω within one rotation in order to switch the energized phase in the power supply to the reaction motor 26a, 26b. Therefore, the present operating device 12 can be considered as a two-system device (hereinafter, sometimes referred to as the "operating device 12a" and the "operating device 12b") that is a redundant system.

[0018] The operation device 12 has an operation angle sensor 32 that detects the operation angle δ of the steering wheel 20 as the steering operation amount. When the steering wheel 20 is in a neutral position while the vehicle is traveling straight ahead, the rotation angles (which can be considered as "absolute angles") in both the left and right directions from the neutral position are the operation angle δ of the steering wheel 20.

[0019] In addition, in this steering system, as in a general so-called power steering system, a torsion bar 34 is incorporated in the steering shaft 22, and the operation torque Tq as the operation force applied to the steering wheel 20 by the driver is calculated based on the amount of twist of the torsion bar 34. O The operation torque sensors 36a, 36b (hereinafter, may be collectively referred to as "operation torque sensors 36") are provided to detect the torque of the operation device 12. Two operation torque sensors 36 are provided to correspond to the two systems of the operation device 12.

[0020] Each of the wheels 10 is supported on the vehicle body so as to be steerable via a steering knuckle 40, which is one component of a suspension device. The steering device 14 steers each of the wheels 10 integrally by rotating the steering knuckle 40. The steering device 14 has a steering actuator 42 as a main component. The steering actuator 42 is configured to include: a) a steering rod (sometimes called a "rack bar") 46 whose both ends are connected to the left and right steering knuckles 40 via link rods 44, b) a housing 48 that supports the steering rod 46 so that it can move left and right and is fixedly held on the vehicle body, and c) a rod moving mechanism 52 that uses a steering motor 50, which is an electric motor, as a drive source to move the steering rod 46 left and right. Rod moving mechanism 52 is mainly composed of a ball screw mechanism consisting of a ball groove screwed into steering rod 46 and a nut screwed into the ball groove via a bearing ball and rotated by steering motor 50, and has a general structure, so a detailed explanation of rod moving mechanism 52 will be omitted here.

[0021] Like reaction motor 26, steering motor 50 is a two-system three-phase brushless DC motor, and each of the two systems may be referred to as steering motor 50a and steering motor 50b. Each of steering motors 50a and 50b has its own motor rotation angle sensor 54a, 54b (hereinafter sometimes collectively referred to as "motor rotation angle sensor 54") for detecting the rotation angle (which may be considered as the "relative angle" or "phase") ν within one rotation in order to switch the energized phase in the power supply to the steering motor. Therefore, steering device 14 can be considered as a two-system device (hereinafter sometimes referred to as "steering device 14a" and "steering device 14b") that are redundant systems. Incidentally, steering motors 50a and 50b each detect the current (hereinafter sometimes referred to as the "steering current") I that is actually supplied to them. S The power supply 50 also has its own current sensors 56a and 56b (hereinafter, these may be collectively referred to as "current sensor 56") for detecting the current.

[0022] Incidentally, the steering device 14 has a steering angle sensor 58 for detecting the amount of movement of the steering rod 46 to the left and right from a neutral position (the position where the vehicle is located when traveling straight ahead) to detect the steering angle θ as the amount of steering of the wheels 10.

[0023] Control of the operation device 12, in detail, the operation reaction force F CT The control of the reaction force motor 26 of the operation device 12 is executed by operation electronic control units (hereinafter sometimes referred to as "operation ECUs") 60a, 60b as operation controllers that correspond to the two systems of the operation device 12. Hereinafter, the operation ECUs 60a, 60b may be collectively referred to as operation ECU 60. Each operation ECU 60 is composed of a computer having a CPU, ROM, RAM, etc., and an inverter that is a driver (drive circuit) of the reaction force motor 26.

[0024] Similarly, the control of steering device 14, more specifically, the control of steering angle θ, that is, the control of steering motor 50 of steering device 14, is executed by steering electronic control units (hereinafter sometimes referred to as “steering ECUs”) 62a, 62b as steering controllers that are respective controllers corresponding to the two systems of steering device 14. Hereinafter, steering ECUs 62a, 62b may be collectively referred to as steering ECU 62. Each steering ECU 62 is composed of a computer having a CPU, ROM, RAM, etc., and an inverter that is a driver (drive circuit) of steering motor 50.

[0025] The operation device 12a, the steering device 14a, the operation ECU 60a, and the steering ECU 62a constitute one system as a main system, and the operation device 12b, the steering device 14b, the operation ECU 60b, and the steering ECU 62b constitute another system as a sub system, so that the steering system is a two-system steering system. Therefore, the operation device 12a and the steering device 14a are connected by a dedicated communication line 64a, and the operation device 12b and the steering device 14b are connected by a dedicated communication line 64b (hereinafter, the dedicated communication lines 64a and 64b may be collectively referred to as "dedicated communication line 64"). In addition, in order to enable communication between the operation devices 12 and the steering devices 14 of the different systems, each operation device 12 and the steering device 14 is connected to a CAN (car area network or controllable area network) 66 as a common communication line. It is also possible to consider that the two operation ECUs 60 and the two steering ECUs 62 constitute one controller of the steering system.

[0026] The steering force generated by the steering device 14 to steer the wheels 10 can be relatively large, and the steering motor 50, which is an electric motor, is supplied with a relatively large steering current I STherefore, from the viewpoint of overheat protection, a heat sink 70 is provided in steering motor 50, and a heat sink 72 is provided in steering ECUs 62a, 62b having drivers for steering motors 50a, 50b, respectively, as shown in Fig. 2. Both heat sink 70 and heat sink 72 are general-purpose heat sinks, and description of their structures will be omitted.

[0027] As explained above, steering motor 50 is a two-system motor including steering motor 50a and steering motor 50b, and heat sink 70 is shared by steering motor 50a and steering motor 50b. Also, steering ECU 62a and steering ECU 62b are arranged to fit together closely, and heat sink 72 is shared by steering ECU 62a and steering ECU 62b.

[0028] From the viewpoint of overheat protection, the temperature of the steering motor 50, that is, the motor temperature T M , the temperature of the base of the drive circuit of the steering ECU 62, D In order to detect the temperature, a temperature sensor 74 and a temperature sensor 76 are provided for the steering motor 50 and the steering ECU 62, respectively, and temperature detection signals from the temperature sensors 74 and 76 are sent to both the steering ECU 62a and the steering ECU 62b. A In order to detect this, a temperature sensor 78 is also provided in the housing of the steering actuator 42, and a detection signal from the temperature sensor 78 is also sent to both the steering ECU 62a and the steering ECU 62b.

[0029] [B] Steering system control In the following, the control of the present steering system will be described in order, namely, steering control which is the control of the steering device 14, and reaction force control which is the control of the reaction force applying mechanism 28 of the operation device 12.

[0030] (a) Steering control The steering control is a control for steering the wheels 10 in response to a steering request, i.e., in response to the operation angle δ of the steering wheel 20 in the case of manual driving. The steering control is executed by the steering ECU 62. The following describes normal control, which is a control under normal circumstances when none of the two systems has a failure, failure control, which is a control under a failure condition when one of the two systems has a failure, and the steering current I to the steering motor 50 in each control. S This section explains the limitations of .

[0031] i) Normal control The steering ECU 62a and the steering ECU 62b, which are controllers of two systems, are capable of independently executing steering processing, which is processing for steering control. Normally, so-called "cooperative control" is executed for the purpose of smooth operation of the steering device 14, more specifically, the steering actuator 42, and for the main system and the sub-system to generate the same steering force. In this cooperative control, the steering ECU 62a constituting the main system executes "basic steering processing", which is basic steering processing, and the steering ECU 62b constituting the sub-system executes "dependent steering processing" for being subordinate to the main system. Incidentally, the basic steering processing can also be executed by the steering ECU 62b. In the following description, when it does not matter whether it is the main system or the sub-system, or for processing that can be performed by both systems, the suffixes a and b of the symbols of the components will not be used.

[0032] The motor rotation angle ω of reaction force motor 26 and the operation angle δ of steering wheel 20 have a relationship that results in a specified gear ratio, and when the vehicle is started, the motor rotation angle ω is calibrated based on the operation angle δ detected by operation angle sensor 32. In the steering control and reaction force control, the operation ECU 60 obtains the operation angle δ based on the motor rotation angle ω detected via motor rotation angle sensor 30. In the basic steering process, the steering ECU 62 receives information on the operation angle δ from the operation ECU 60 of the same system. The steering ECU 62 calculates the steering gear ratio R set for the operation angle δ obtained by reception according to the following formula: GBy multiplying by this, the target steering angle θ of the wheel 10 is obtained. * Determine. θ * =R G ×δ

[0033] As with the operation angle δ, the steering angle θ of the wheels 10 and the motor rotation angle ν of the steering motor 50 have a relationship that provides a predetermined gear ratio, and when the vehicle is started, the motor rotation angle ν is calibrated based on the steering angle θ detected via the steering angle sensor 58. Control of the steering angle θ of the wheels 10 is performed using the motor rotation angle ν instead of the steering angle θ. Therefore, the steering ECU 62 adjusts the steering angle θ based on the determined target steering angle θ * Based on this, the target motor rotation angle ν * Determine.

[0034] The steering ECU 62 detects the actual motor rotation angle ν of the steering motor 50 via the motor rotation angle sensor 54, and calculates the target motor rotation angle ν * The motor rotation angle deviation Δν, which is the deviation of the motor rotation angle ν with respect to Δν=ν * -ν

[0035] The torque generated by the steering motor 50 is called steering torque Tq S In other words, the steering ECU 62 determines the steering torque Tq to be generated according to a feedback control rule based on the motor rotation angle deviation Δν, that is, according to the following formula: S By the way, the first, second, and third terms in the following equation are proportional, integral, and differential terms, respectively, and G P ,G I ,G D are the proportional gain, integral gain, and differential gain, respectively. Tq S =G P ×Δν+G I ×∫Δνdt+G D ×dΔν / dt

[0036] The steering current I supplied to the steering motor 50 Sis the steering torque Tq S According to this relationship, the steering ECU 62 determines the steering torque Tq S Based on this, the steering current I to be supplied to the steering motor 50 is S Determine,

[0037] In this steering system, in order to protect the steering device 14 from overheating, the steering current I S The steering ECU 62 sets a limit on the determined steering current I S The steering ECU 62 performs a current limiting process on the steering current I S is supplied to the steering motor 50. In addition, as will be described in detail later, in the control of the reaction force imparting mechanism 28 of the operation device 12 and in the cooperative steering control, the steering current I S In order to utilize the value of S Send information about.

[0038] The basic steering process is performed by the steering ECU 62 repeatedly executing a basic steering program shown in the flowchart of Fig. 3 at short intervals (for example, several msec to several tens of msec). Below, the process according to the program will be briefly described with reference to the flowchart.

[0039] In the process according to the basic steering program, first, in S1, the operation angle δ of the steering wheel 20 is obtained from the operation ECU 60, and in S2, the target steering angle θ * In the next step S3, the target motor rotation angle v * is determined, and the actual motor rotation angle ν is detected in S4. In the next step S5, the motor rotation angle deviation Δν is determined, and in S6, the turning torque Tq S In the next step S7, the steering torque Tq S Based on this, the steering current I Sis determined, and in S8, the determined steering current I S Then, in S9, the current limiting process is performed on the steering current I S is supplied to the steering motor 50, and in S10, the steering current I S The information is sent.

[0040] On the other hand, in the cooperative control, the steering ECU 62b constituting the sub system performs a dependent steering process to be subordinate to the main system as a control process. As described above, the steering ECU 62a constituting the main system supplies the steering current I S The steering ECU 62b transmits information about the steering current I S Instead of determining the steering current I based on the received information, S is supplied to the steering motor 50b.

[0041] The dependent steering process is performed by the steering ECU 62b repeatedly executing a dependent steering program shown in the flowchart of Fig. 3 at short intervals (for example, several msec to several tens of msec). To briefly explain the process according to the program with reference to the flowchart, in this process, in S11, the steering current I to be supplied by the steering ECU 62b is received from the steering ECU 62a. S By the way, the steering current I S In the next step S12, the steering current I S is supplied to the steering motor 50b, and in S13, the steering current I S The information is sent.

[0042] ii) Failure Control When one of the two systems fails, control is performed during the failure. When the failed system is a sub-system, the sub-system is not activated and steering control is performed only by the main system. On the other hand, when the failed system is the main system, the main system is not activated and steering control is performed only by the sub-system, but at that time, the steering ECU 62b constituting the sub-system performs basic steering processing instead of the subordinate steering processing. In other words, the steering ECU 62b executes the basic steering program instead of the subordinate steering program.

[0043] iii) Limiting the current supplied to the steering motor Large steering current I S If the steering motor 50 is supplied with the steering current I for a long period of time, the steering motor 50 and the drive circuit (driver, for example, an inverter) of the steering motor 50 will be overheated. S Specifically, the steering current I supplied to either the steering motor 50a or the steering motor 50b is limited. S For the upper limit I S-LIM Set the upper limit I S-LIM A steering current exceeding I S In other words, the supply of the steering current I determined as described above is prohibited. S is the upper limit I S-LIM When it exceeds this, the steering current I S The upper limit I S-LIM The processing is performed as follows.

[0044] Steering current I from the viewpoint of overheat protection S If the limit is called an overheat protection limit, then as the overheat protection limit, the steering ECU 62 sets the motor temperature T M ,substrate temperature T D Based on this, the upper limit I S-LIM According to this high temperature limit map, the motor temperature T M ,substrate temperature T D However, the temperature T that needs to be monitored is set to a relatively high temperature. HIf the motor temperature T M ,substrate temperature T D As the value increases, the upper limit I S-LIM In the description of this embodiment, in order to facilitate understanding, the high temperature limit map is set to a value that is smaller than the motor temperature T M ,substrate temperature T D Although the same map is used for the upper limit I S-LIM The lower of the two is adopted. Also, the high temperature limit map has an upper limit I S-LIM Although only the temperature T is shown, it is necessary to monitor the temperature. H Below the motor temperature T M ,substrate temperature T D is constant whatever the temperature.

[0045] One characteristic of the steering motor 50, specifically, the number of rotations (strictly speaking, the "rotation speed") N of the steering motor 50 and the steering torque Tq S With reference to the graph in FIG. 4(b), the rotational speed-torque characteristic (hereinafter sometimes referred to as the "NT characteristic") showing the relationship between the steering current I S The upper limit I set for S-LIM Therefore, the steering torque Tq S There is an upper limit to the torque Tq S - LIM In other words, the steering device 14 has an upper limit torque Tq S - LIM Therefore, it can only generate a steering force that corresponds to the steering force.

[0046] In normal operation when neither of the two systems is malfunctioning, the steering torque Tq shown by the solid line in the graph of Fig. 4(b) is S Up to twice the steering torque Tq S However, when one of the two systems fails, the steering torque Tq shown by the solid line in Figure 4(b) SIn other words, the steering force is halved. Therefore, when the steering torque Tq S In other words, the upper limit torque Tq S - LIM The upper limit torque Tq S - LIM ', so that the steering current I S Upper limit of I S-LIM It is designed to raise the

[0047] Here, the environmental temperature T A The relationship between the environmental temperature T and the steering force that the steering device 14 needs to generate when performing a specific steering operation will be described with reference to the graph of FIG. A When the temperature of the suspension system, specifically the environmental temperature T A However, the set temperature T is set to a relatively low temperature. L (For example, -10°C) or lower, the steering current I S Upper limit of I S-LIM It is desirable to raise the environmental temperature T A The lower the temperature, the greater the resistance increase. A The lower the upper limit I S-LIM Increase the allowance for raising the upper limit I S-LIM It is desirable to set it higher.

[0048] In consideration of the above, in the present steering system, in the above-mentioned current limiting process, the steering ECU 62 limits the steering current I S Upper limit of I S-LIMIn this steering system, two modes are prepared for this upper limit raising. One is a "standard raising mode" in which the upper limit is raised on the condition that the wheels 10 are turned by only one of the two systems, and the other is a "standard raising mode" in which the upper limit is raised on the condition that the wheels 10 are turned by only one of the two systems and the environmental temperature T A is the set temperature T L The "temperature-dependent increase mode" increases the upper limit under the following conditions. The mode in which the upper limit is increased is selected in advance at the time of manufacture depending on the vehicle model, specifications, etc.

[0049] More specifically, the steering ECU 62 controls the steering current I S Upper limit of I S-LIM In normal operation, the upper limit I S-LIM However, the standard value I S-N In contrast, when the upper limit is raised in the standard raising mode in the event of a failure, the environmental temperature T A is the set temperature T L Even if it exceeds the upper limit I S-LIM is the increase amount ΔI S-LIM The ambient temperature T A is the set temperature T L If the upper limit I S-LIM However, the environmental temperature T A As the amount of lifting ΔI S-LIM On the other hand, when the upper limit is raised in the temperature-dependent raising mode, the environmental temperature T A is the set temperature T L If it exceeds the upper limit I S-LIM is not raised, and the environmental temperature T A is the set temperature T L If the upper limit I S-LIM However, the environmental temperature T A As the amount of lifting ΔI S-LIM is determined to be large.

[0050] Motor temperature T M ,substrate temperature T D However, the temperature T that needs to be monitored is set to a relatively high temperature. H If the upper limit value I is exceeded, the overheat protection limit described above takes precedence over the upper limit increase described above, but the overheat protection limit is related to the upper limit increase. In more detail, during normal operation or in the temperature-dependent increase mode, the steering ECU 62 references the solid line in the high temperature limit map to set the upper limit value I S-LIM is the standard value I S-N From the motor temperature T M ,substrate temperature T D In contrast, in the standard pull-up mode, the steering ECU 62 determines the upper limit value I S-LIM is the standard value I S-N From the lift amount ΔI S-LIM The motor temperature T M ,substrate temperature T D is determined to decrease as

[0051] In the event of a failure, only one of the two systems will have steering current I S Upper limit of I S-LIM Since the temperature is raised, it is conceivable that the heat generation amount of the steering motor 50 of one system and the steering ECU 62 including the drive circuit will increase. However, since the heat sink 70 and the heat sink 72 are both shared by the two systems under normal circumstances but are dedicated to the one system in the event of a failure, the temperature rise of the steering motor 50 and the steering ECU 62 will be suppressed accordingly.

[0052] When the vehicle speed v is low, specifically, when the vehicle is stopped or when the vehicle speed v is low enough to be assumed to be stopped, the wheels 10 are steered in a so-called stationary steering state or in a state close to stationary steering. In these states, the steering current I Sbecomes considerably large, and the possibility of overheating of the steering motor 50 and the steering ECU 62 becomes high. On the other hand, when the vehicle starts to move and the vehicle speed v becomes high, the above-mentioned state is overcome, and the possibility of overheating of the steering motor 50 and the steering ECU 62 becomes low. Taking these things into consideration, the steering ECU 62 sets the vehicle speed v at a considerably low set speed v TH The above-mentioned upper limit is not raised in the following cases: Incidentally, the steering ECU 62 obtains information relating to the vehicle speed v via the CAN 66 from a brake system (not shown).

[0053] The current limitation described above is performed by the steering ECU 62 executing a current limitation subroutine shown in the flowchart of Fig. 6 in S8 of the basic steering program. In the process according to the subroutine, first, in S21, the motor temperatures T M ,substrate temperature T D ,Environmental temperature T A is acquired, and in S22, the vehicle speed v of the vehicle is acquired from the brake system.

[0054] In the next step S23, it is determined whether or not the other system has failed, that is, whether or not the wheels 10 must be steered using only the own system. If the other system has not failed, the above-mentioned steering current I S Upper limit of I S-LIM In other words, the upper limit is not raised, and in S24, the solid line of the high temperature limit map shown in FIG. 4(a) and the solid line of the low temperature limit map shown in FIG. 5(b) are referenced to determine the upper limit value I S-LIM is determined.

[0055] If the other system is faulty, in S25, the vehicle speed v is set to the set speed v TH It is determined whether the vehicle speed v is equal to or less than the set speed v TH If it is equal to or less than this, the upper limit is not raised, and in S24, the solid line of the high temperature limit map and the solid line of the low temperature limit map are referenced to set the upper limit value I S-LIM On the other hand, when the vehicle speed v is set to the set speed v THIf so, it is determined in S26 whether the mode is a temperature-based raising mode for upper limit raising.

[0056] If the temperature-based pull mode is not selected, i.e., if the standard pull mode is selected, the environmental temperature T A In order to raise the upper limit regardless of the above, in S27, the broken lines of the high temperature limit map and the low temperature limit map are referenced, and the upper limit value I S-LIM On the other hand, if the temperature-based boost mode is selected, the environmental temperature T A is the set temperature T L It is determined whether or not the following is true:

[0057] In temperature-based boost mode, the ambient temperature T A is the set temperature T L If it exceeds, the upper limit is not raised, and in S24, the solid line of the high temperature limit map and the solid line of the low temperature limit map are referenced to set the upper limit value I S-LIM is determined. Meanwhile, the environmental temperature T A is the set temperature T L If it is equal to or less than the upper limit I S-LIM is determined.

[0058] In this way, the upper limit I S-LIM After being determined, in S30, the upper limit I S-LIM Based on this, the steering current I S However, the upper limit I S-LIM It is judged whether the steering current I S However, the upper limit I S-LIM If it exceeds the steering current I S is the upper limit I S-LIM On the other hand, the steering current I S is the upper limit I S-LIM If it is less than or equal to the steering current I S The value of is maintained.

[0059] (b) Reaction Force Control The reaction force control is a control for giving the driver a feeling of operation in response to the steering operation. In the present steering system, under normal circumstances, the main system operation device 12a and the sub system operation device 12b generate the same operation reaction force F independently and in parallel with each other. CT is applied to the steering wheel 20. In the following, the reaction force application processes performed by the operation ECU 60a constituting the main system and the operation ECU 60b constituting the sub system in the reaction force control will be described in a unified manner.

[0060] The operation ECU 60 detects the operation reaction force F CT The steering load dependent component F S , the reduction component F A Based on this, it is determined according to the following formula: F CT =F S -F A

[0061] Steering load dependent component F S is the steering force required to steer the wheels 10 (the steering torque Tq of the steering motor 50) S ) and the steering current I S It is determined based on the steering current I S The larger the steering load on the wheel 10, the larger the steering load is recognized. S is determined to be a large value. Incidentally, the steering current I S The information relating to the above is sent from the steering ECU 62 via a dedicated communication line 64 to the operation ECU 60 of the same system.

[0062] On the other hand, the reduction component F A can be considered as a component that gives the driver a feeling of operation in the so-called power steering system. In a power steering system, the operation torque Tq OThe assist torque corresponding to the steering force is applied to the steering shaft 22. The operation force-dependent reduction component F A is determined according to the following formula: F A =β×Tq O By the way, β is the reduction component F A The operation ECU 60 receives the operation torque Tq via the operation torque sensor 36. O Detect.

[0063] The reaction force F determined in the above manner CT Based on this, the operation ECU 60 determines the reaction force current I C is determined according to the following formula, and the reaction current I C is supplied to the reaction motor 26. I C = α × F CT Incidentally, α is a current determination coefficient that is set.

[0064] Each of the operation ECUs 60a and 60b performs the reaction force application process by repeatedly executing a reaction force application program, the flow chart of which is shown in FIG. 7, at short intervals (for example, several msec to several tens of msec). To briefly explain the process according to the program, first, in S41, the steering current I S is acquired, and in S42, the steering current I S Based on the steering load dependent component F S In the next step S43, the operation torque Tq O is detected, and in S44, the operation torque Tq O Based on the operation force dependent reduction component F A In the next step S45, the steering load dependent component F S and the reduction component F A Based on this, the reaction force F CT is determined, and in S46, the operation reaction force F CTBased on this, the reaction current I to be supplied to the reaction motor 26 is C Then, in S47, the reaction current I C Based on this, a current is supplied to the reaction motor 26.

[0065] To briefly explain the reaction force control in the event of a malfunction, the reaction force control is executed only in the one of the main system and the sub-system that is not malfunctioning. In other words, only the operation ECU 60 in the one that is not malfunctioning executes the reaction force application process. [Explanation of symbols]

[0066] 10: Wheel 12, 12a, 12b: Operation device 14, 14a, 14b: Steering device 20: Steering wheel (operation member) 26: Reaction motor 42: Steering actuator 50, 50a, 50b: Steering motor (electric motor) 60, 60a, 60b: Operation electronic control unit (operation ECU) (controller) 62, 62a, 62b: Steering electronic control unit (steering ECU) (controller) 70: Heat sink 72: Heat sink

Claims

1. An operating member operated by a driver; A steering device that steers the wheels and is provided in two systems, each of which has an electric motor as a drive source; a controller that realizes steering of the wheels in response to the operation of the operation member by the steering device by controlling a current supplied to each of the electric motors of the two systems; A steer-by-wire type steering system mounted on a vehicle, comprising: a steering system in which the controller is configured to prohibit the supply of current exceeding an upper limit to each of the electric motors of the two systems, and to raise the upper limit of the current supplied to one of the electric motors when the wheels are steered by only one of the two systems, and to prohibit raising the upper limit when the vehicle's traveling speed is equal to or lower than a set speed.

2. The controller:

2. The steering system according to claim 1, wherein the upper limit value is increased by a larger amount when the temperature of the steering system is equal to or lower than a set temperature.

3. The controller:

2. The steering system according to claim 1, wherein the upper limit is increased on condition that the temperature of the steering system is equal to or lower than a set temperature.

4. 4. The steering system according to claim 2, wherein the set temperature is set to a temperature of 0° C. or lower.

5. 5. The steering system according to claim 2, wherein the controller is configured to increase the upper limit value by a larger amount as the temperature of the steering system decreases.

6. 2. The steering system according to claim 1, wherein the set speed is a speed set to simulate that the vehicle is stationary.

7. The controller: a current supplying device configured to supply a current to one of the electric motors of the two systems when the wheels are steered by both of the two systems of the steering device to the electric motors of the other of the two systems; 7. A steering system according to claim 1, configured to determine, when the wheels are steered by only the other of the two systems of the steering device, a current to be supplied to the other electric motor, and to supply the determined current to the other electric motor.

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