Steering system

Abstract

To provide a steer-by-wire type steering system having high practicality.SOLUTION: A steering system includes a steering device 14 having a steering motor 50 with two systems, i.e., a main system 50a and a sub-system 50b, and steers a wheel by force generated by the steering motor. In the steering system, when normal power supply takes place in which power is supplied to the main system and the sub-system from a main power source 70, the sub-system is operated so as to match the main system; and when backup takes place in which power is supplied to the main system from a backup power source 72, the main system is operated while supply of power to it is limited, or is not operated, and the sub-system is independently controlled. Accordingly, when backup takes place, supply of power from the backup power source can be continued for a relatively long time while force for steering the wheel can be secured.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In a steer-by-wire type steering system, from the viewpoint of fail-safe, for example, as described in the following patent documents, it has been proposed to provide a backup power source or to make the system redundant (duplicate).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When adopting a backup power source, it is possible to improve the practicality of the steering system by considering that the capacity of the backup power source is relatively small. Furthermore, when making the steering system redundant, it is also possible to improve the practicality of the steer-by-wire type steering system by considering the connection mode of the backup power source in the redundant system and the like. The present invention has been made in view of such circumstances, and an object thereof is to provide a highly practical steer-by-wire type steering system.

Means for Solving the Problems

[0005] To solve the above problems, the steering system of the present invention includes a main power source and a backup power source, A steering device having a steering motor divided into a main system and a sub - system, and the wheels are steered by the force generated by the steering motor, A controller for controlling the operation of each of the main system and the sub - system of the steering motor to control the steering device based on a steering request A steer - by - wire type steering system comprising: When the controller is in normal power supply in which the main power supply supplies power to the main system and the sub - system of the steering motor, the sub - system of the steering motor is operated in synchronization with the main system of the steering motor. The sub-system of the steering motor is not powered from the backup power supply and When in backup power supply in which only the backup power supply supplies power to the main system of the steering motor, the main system of the steering motor is operated while restricting power supply thereto, or without being operated, and the sub - system of the steering motor is configured to be independently controlled.

Advantages of the Invention

[0006] For the backup power supply, for example, for emergency use, one with a relatively small capacity (charge capacity) is adopted. Therefore, in the present invention where the steering device is made redundant of the s In the steering system, the backup power supply is configured to supply current only to the main system of the steering motor (hereinafter sometimes referred to as the "steering main system") instead of the main power supply. Also, on the other hand, in view of the small capacity of the backup power supply, in the present invention of the s In the steering system, during backup, power supply to the steering main system is restricted, or, for example, when current can be supplied from the main power supply to the sub - system of the steering motor (hereinafter sometimes referred to as the "steering sub - system"), the operation of the steering main system is stopped without supplying power.

[0007] Also, in the present invention of the sIn the steering system, during normal power supply, that is, when current is supplied from the main power source to both the main steering system and the sub-steering system, considering the smooth operation of the steering device, the operation of the sub-steering system is coordinated with the operation of the main steering system. In other words, so-called "coordinated control" is executed. If coordinated control is performed during backup, the sub-steering system will also be restricted in current supply or its operation will be stopped, just like the main steering system. Therefore, the present invention of the s In the steering system, during backup, instead of by coordinated control, the sub-steering system is independently operated, that is, it is operated in the same way as during normal power supply, so that the force for steering the wheels (hereinafter sometimes referred to as "steering force") is ensured. Aspects of the invention

[0009] The present invention of the s In the steering system, during backup, whether to operate the main steering system while restricting power supply (hereinafter sometimes referred to as "power supply restricted operation") or not to operate it (hereinafter sometimes referred to as "non-operation") can be arbitrarily set or selected according to the vehicle design, the situation where the vehicle is placed, the power supply situation from the main power source to the sub-steering system, etc. In many situations, that is, generally, when the main steering system is operated with power supply restricted, the steering device can generate a greater steering force compared to the non-operation case. On the other hand, as will be described later, during high-speed operation of the steering motor in the power supply restricted operation, etc., the main steering system may operate in a so-called regeneration region and become a resistance to the wheel steering operation. Considering this, when the power supply from the main power source to the sub-steering system is appropriately performed during backup, the main steering system may be set to non-operation.

[0010] In addition, during backup, when appropriate power supply is not provided from the main power source to the steering sub-system, it is desirable not to operate the steering sub-system. In that case, regardless of whether the power supply limit operation of the steering main system is set to operate or not operate when appropriate power supply is provided from the main power source to the steering sub-system, in view of the need to ensure steering force, it is desirable to cause the power supply limit operation. Conversely, during backup, on the premise that the steering main system is made to perform the power supply limit operation when appropriate power supply is not provided from the main power source to the steering sub-system, even when appropriate power supply is provided from the main power source to the steering sub-system, the power supply limit operation may be performed, or it may be made non-operational when appropriate power supply is provided from the main power source to the steering sub-system. Also, as described above, the power supply limit operation and non-operation of the steering main system may be switched according to whether there is resistance to the steering operation of the wheels.

[0011] Regarding the coordinated control between the steering main system and the steering sub-system, for example, when the configurations of the steering main system and the steering sub-system are the same as each other, during normal power supply, it is desirable to control the operations of the two systems so that the steering main system and the steering sub-system generate the same force as each other.

[0012] Further, the controller can be configured to have two systems, a main system and a sub-system, corresponding to the main system and the sub-system of the steering motor. The main system of the controller (hereinafter sometimes referred to as the "main control system") and the sub-system of the controller (hereinafter sometimes referred to as the "sub-control system") may be configured to have the same functions as each other. More specifically, each may be configured to be able to determine the current supplied to the corresponding main steering system and sub-steering system based on a steering request, and to be able to supply power to the corresponding main steering system and sub-steering system based on the determined current. In the case of such a configuration, specifically, during normal power supply, in order to perform cooperative control, based on the supply current to the main steering system determined by the main control system, the sub-control system supplies current to the sub-steering system, and during backup, regardless of the supply current to the main steering system determined by the main control system, the sub-control system supplies current to the sub-steering system based on the supply current to the sub-steering system determined by itself.

[0013] Regarding the specific structure of the power source, for example, the main power source may include a storage battery while the backup power source may be configured as a capacitor. Further, the backup power source may be configured to receive power from the main power source and be charged during normal power supply, and to supply power to the main steering system relying on the stored electrical energy during backup.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0015] Hereinafter, as a mode for carrying out the claimable invention, a steering system which is an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art, in addition to the following embodiments and the forms described in the section of 〔Aspects of the Invention〕 above.

Embodiment

[0016] [A] Configuration of Steering System The steering system of the embodiment mounted on a vehicle is a system for steering two wheels (front wheels) 10 which are respectively steered wheels, and is a steer-by-wire type steering system including an operation device 12 and a steering device 14 that are mechanically independent of each other, as schematically shown in FIG. 1.

[0017] The operation device 12 includes: a) a steering wheel 20 as an operation member steered (steering operation) by a driver; b) a steering shaft 22 to which the steering wheel 20 is attached at its tip; c) a steering column 24 that rotatably holds the steering shaft 22 and is supported by an instrument panel reinforcement (not shown); d) a reaction force motor 26 which is an electric motor supported by the steering column 24, and uses the reaction force F (strictly speaking, reaction force torque, but hereinafter, the commonly used term "operation reaction force" will be used) against the steering operation as a power source. CTIt includes a reaction force applying mechanism 28 that applies a reaction force to the steering wheel 20 via the steering shaft 22. Since the reaction force applying mechanism 28 has a general structure including a speed reducer or the like, the description of the specific structure of the reaction force applying mechanism 28 is omitted.

[0018] The reaction force motor 26 is a three-phase brushless DC motor, with magnets attached to the outer periphery of the rotating shaft, and coils arranged in the housing so as to face these magnets. The reaction force 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 force motor 26a and the reaction force motor 26b. Each of the reaction force motors 26a and 26b independently has motor rotation angle sensors 30a and 30b (hereinafter, may be collectively referred to as the "motor rotation angle sensor 30") for detecting the rotation angle ω (which can be considered as the "relative angle" or "phase") within one rotation for the purpose of switching the energized phase in the power supply to itself. Therefore, the present operation device 12 can be considered as a redundant two-system device (hereinafter, may be referred to as the "operation device 12a" and the "operation device 12b").

[0019] 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. Incidentally, when the posture taken by the steering wheel 20 in the straight-ahead state of the vehicle is defined as the neutral posture, the rotation angles (which can be considered as the "absolute angles") in the left and right directions from the neutral posture are the operation angle δ of the steering wheel 20.

[0020] Also, in this steering system, similar to a general so-called power steering system, a torsion bar 34 is incorporated into the steering shaft 22, and based on the amount of twist of the torsion bar 34, the operation torque Tq as the operation force applied to the steering wheel 20 by the driver OIt has operation torque sensors 36a and 36b (hereinafter sometimes collectively referred to as "operation torque sensor 36") for detecting. Two operation torque sensors 36 are provided to correspond to two systems of the operation device 12.

[0021] Each of the wheels 10 is turnably supported on the vehicle body via a steering knuckle 40 which is a component of the suspension device. The steering device 14 integrally steers each of the wheels 10 by rotating the steering knuckle 40. The steering device 14 has, as main components, a steering actuator 42. The steering actuator 42 includes: a) a steering rod (sometimes called a "rack bar") 46 whose both ends are respectively connected to the left and right steering knuckles 40 via link rods 44; b) a housing 48 which movably supports the steering rod 46 left and right and is fixedly held on the vehicle body; and c) a rod moving mechanism 52 for moving the steering rod 46 left and right with a steering motor 50 which is an electric motor as a drive source. The rod moving mechanism 52 mainly includes a ball screw mechanism constituted by a ball groove screwed on the steering rod 46 and a nut which is screwed with the ball groove via a bearing ball and is rotated by the steering motor 50. Since it has a general structure, a detailed description of the rod moving mechanism 52 here is omitted.

[0022] Note that the steering motor 50 is also a two-channel three-phase brushless DC motor, similar to the reaction force motor 26, and each of the two channels may be referred to as the steering motor 50a and the steering motor 50b. Each of the steering motors 50a and 50b has, for the purpose of switching the energized phase in the power supply to itself, motor rotation angle sensors 54a and 54b (hereinafter may be collectively referred to as the "motor rotation angle sensor 54") for detecting the rotation angle ν (which can be considered as the "relative angle" or "phase") within one rotation. Therefore, the present steering device 14 can be considered as a redundant two-channel device (hereinafter may be referred to as the "steering device 14a" and the "steering device 14b"). Incidentally, the steering motors 50a and 50b each have a current sensor 56a and 56b (hereinafter may be collectively referred to as the "current sensor 56") for detecting the current I S actually supplied to itself.

[0023] Incidentally, the steering device 14 has a steering angle sensor 58 for detecting the steering angle θ as the steering amount of the wheels 10 by detecting the amount of movement of the steering rod 46 from the neutral position (the position where the vehicle is in a straight-ahead state) to the left and right respectively.

[0024] The control of the operating device 12, specifically, the control of the operating reaction force F CT is executed by operation electronic control units (hereinafter may be referred to as "operation ECUs") 60a and 60b as operation controllers, which are respective controllers corresponding to the two channels of the operating device 12. Hereinafter, the operation ECUs 60a and 60b may be collectively referred to as the operation ECU 60. Each operation ECU 60 is composed of a computer having a CPU, ROM, RAM, etc., and an inverter which is a driver (drive circuit) of the reaction force motor 26.

[0025] Similarly, the control of the steering device 14, specifically, the control of the steering angle θ, that is, the control of the steering motor 50 of the steering device 14, is executed by the steering electronic control units (hereinafter sometimes referred to as "steering ECUs") 62a and 62b, which are the respective controllers corresponding to the two systems of the steering device 14. Hereinafter, the steering ECUs 62a and 62b may be collectively referred to as the steering ECU 62. Each steering ECU 62 is composed of a computer having a CPU, ROM, RAM, etc., and an inverter which is a driver (drive circuit) of the steering motor 50, etc.

[0026] The operation device 12a, the steering device 14a, the operation ECU 60a, and the steering ECU 62a constitute one system, and the operation device 12b, the steering device 14b, the operation ECU 60b, and the steering ECU 62b constitute another 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 the "dedicated communication line 64"). In addition, in order to enable communication between the operation devices 12 and the steering devices 14 of different systems, each operation device 12 and steering device 14 are connected to a CAN (car area network or controllable area network) 66 as a common communication line.

[0027] Also, as will be described in detail later, the steering system has a master electronic control unit (hereinafter sometimes referred to as the "master ECU") 68 as a master controller for integrating the two systems of the steering system. The master ECU 68 has a computer as a main component, and the master ECU 68 is also connected to the CAN 66. It can also be considered that one controller of the steering system is constituted by the two operation ECUs 60, the two steering ECUs 62, and the master ECU 68.

[0028] In this steering system, the operation device 12a, the steering device 14a, the operation ECU 60a, and the steering ECU 62a constitute the main system, and the operation device 12b, the steering device 14b, the operation ECU 60b, and the steering ECU 62b constitute the sub-system. The steering device 14a and the steering motor 50a can be considered as the main steering system 14a and the main steering system 50a respectively, and the steering device 14b and the steering motor 50b can be considered as the sub-steering system 14b and the sub-steering system 50b respectively. Similarly, the operation device 12a and the reaction force motor 26a can be considered as the main operation system 12a and the main reaction force system 26a respectively, and the operation device 12b and the reaction force motor 26b can be considered as the sub-operation system 12b and the sub-reaction force system 26a respectively. Also, the operation ECU 60a and the steering ECU 62a can be considered as the main control system 60a and the main control system 62a respectively, and the operation ECU 60b and the steering ECU 62b can be considered as the sub-control system 60b and the sub-control system 62b respectively.

[0029] [B] Power Supply in the Steering System As schematically shown in FIG. 2, the steering system of the embodiment includes a main power supply unit (hereinafter sometimes simply referred to as the "main power supply") 70 as the main power supply and a backup power supply unit (hereinafter sometimes simply referred to as the "backup power supply") 72 as the backup power supply for the operation device 12 and the steering device 14. The main power supply 70 has a DC-DC converter 74 and a storage battery 76. The backup power supply 72 has a capacitor 78. In the figure, the ground lines from the operation device 12 and the operation device 14 are not shown.

[0030] The vehicle equipped with this steering system is a hybrid vehicle, and the DC-DC converter 74 is supplied with power from the drive system power source 80. The DC-DC converter 74 converts the voltage applied from the drive system power source 80 into the drive voltage of the steering system. The storage battery 76 is connected in parallel with the DC-DC converter 74 and stores the electrical energy of the voltage transformed by the DC-DC converter 74. Incidentally, when the vehicle equipped with this steering system is not a hybrid vehicle or an electric vehicle, power may be supplied from, for example, an alternator instead of the drive system power source 80, or the main power source 70 may be configured to include an alternator.

[0031] Power is supplied to the reaction force motor 26b that constitutes the operation sub-system 12b and the steering motor 50b that constitutes the steering sub-system 14b from the main power source 70 via the operation ECU b and the steering ECU b, specifically, via the inverters of these operation ECU b and steering ECU b. On the other hand, power is supplied to the reaction force motor 26a that constitutes the operation main-system 12a and the steering motor 50a that constitutes the steering main-system 14a from the backup power source 72 via the operation ECU a and the steering ECU a, specifically, via the inverters of these operation ECU a and steering ECU a.

[0032] The backup power source 72 is supplied with power from the main power source 70, and the capacitor 78 is charged by this power supply. The backup power source 72 realizes the power supply from the main power source 70 to the reaction force motor 26a and the steering motor 50a by charging while passing the power supply from the main power source 70. Therefore, during normal power supply when normal power supply is performed, power is also supplied from the main power source 70 to the reaction force motor 26a and the steering motor 50a that constitute the operation main-system 12a and the steering main-system 14a, and also to the reaction force motor 26b and the steering motor 50b that constitute the operation sub-system 12b and the steering sub-system 14b. Hereinafter, the power supply performed by passing through the backup power source 72 from the main power source 70 will simply be referred to as the power supply from the main power source 70.

[0033] On the other hand, for example, consider a case where the connection between the main power supply 70 and the backup power supply 72 is interrupted at the location indicated by the white arrow in the figure. In this case, power supply to the reaction force motors 26a and the steering motor 50a by the main power supply 70 cannot be performed, and the backup power supply 72 supplies power to the reaction force motors 26a and the steering motor 50a relying on the electrical energy stored in the capacitor 78. That is, the backup power supply 72 has a function of switching the power supply source. More specifically, when the backup power supply 72 is not receiving power from the main power supply 70 at an appropriate voltage, it is configured to supply power from the capacitor 78. Note that the power supply from the capacitor 78 is referred to as the power supply from the backup power supply 72.

[0034] That is, in this steering system, the reaction force motors 26b constituting the operation sub-system 12b and the steering motors 50b constituting the steering sub-system 14b are supplied with power only from the main power supply 70, while the reaction force motors 26a and the steering motors 50a constituting the operation main-system 12a and the steering main-system 14a can be selectively supplied with power from the main power supply 70 and the backup power supply 72. And during backup, the power supply source to the reaction force motors 26a and the steering motors 50a is switched from the main power supply 70 to the backup power supply 72, and the power supply to the reaction force motors 26a and the steering motors 50a is made from the backup power supply 72.

[0035] Since the main power supply 70 includes the storage battery 76, while the backup power supply 72 has only the capacitor 78, the capacity (charge capacity) of the backup power supply 72 is considerably smaller than the capacity of the storage battery 76. Considering this, in this steering system, the backup power supply 72 is configured to supply power only to one of the two systems of each of the operating device 12 and the steering device 14, specifically, to the operation main-system 12a and the steering main-system 14a.

[0036] [C] Control of the Steering System The following describes the control of the present steering system, including the steering control for controlling the steering device 14 and the reaction force control for controlling the reaction force applying mechanism 28 of the operation device 12, in sequence.

[0037] (a) Steering control The steering control is control for steering the wheels 10 in accordance with a steering request, that is, the operation angle δ of the steering wheel 20 in the case of manual operation. The steering control is executed by the steering ECU 62. Specifically, the steering control is classified into two types: independent steering control (sometimes simply referred to as "independent control") performed independently by two systems of controllers, the steering ECU 62a and the steering ECU 62b, and cooperative steering control (sometimes simply referred to as "cooperative control") performed cooperatively by the steering ECU 62a and the steering ECU 62b. The following explains the independent steering control and the cooperative steering control respectively, and then explains the steering control during backup and the flow of control switching.

[0038] i) Independent steering control In independent steering control, the steering ECU 62a that constitutes the control main system controls the steering main system 14a, and the steering ECU 62b that constitutes the control sub-system controls the steering sub-system 14b. That is, the steering ECU 62a and the steering ECU 62b perform the same control in parallel with each other. The following summarizes and explains the steering control of each of the steering ECU 62a and the steering ECU 62b as the control of one system. In the following explanation of the independent steering control, when it is not necessary to distinguish whether it is the main system or the sub-system, the subscripts a and b of the component symbols are not used.

[0039] The motor rotation angle ω of the reaction force motor 26 and the operation angle δ of the steering wheel 20 have a relationship with a predetermined gear ratio. At the start of the vehicle, calibration of the motor rotation angle ω is performed based on the operation angle δ detected by the operation angle sensor 32. The operation ECU 60 acquires the operation angle δ of the steering wheel 20 based on the motor rotation angle ω detected via the motor rotation angle sensor 30 of the reaction force motor 26. In the independent steering control, the steering ECU 62 receives the information of the operation angle δ from the operation ECU 60 of the same system. The steering ECU 62 multiplies the operation angle δ obtained by reception by the set steering gear ratio R G to determine the target steering angle θ * of the wheel 10. θ * =R G ×δ

[0040] The steering angle θ of the wheel 10 and the motor rotation angle ν of the steering motor 50 have a relationship with a predetermined gear ratio. The control of the steering angle θ of the wheel 10 is performed using the motor rotation angle ν instead of the steering angle θ. Therefore, the steering ECU 62 determines the target motor rotation angle ν * which is the target of the motor rotation angle ν of the steering motor 50 based on the determined target steering angle θ * . Incidentally, at the start of the vehicle, calibration of the motor rotation angle ν is performed based on the steering angle θ detected via the steering angle sensor 58.

[0041] The steering ECU 62 detects the actual motor rotation angle ν of the steering motor 50 via the motor rotation angle sensor 54, and determines the motor rotation angle deviation Δν which is the deviation of the motor rotation angle ν with respect to the target motor rotation angle ν * according to the following formula. Δν=ν * -ν

[0042] If the torque generated by the steering motor 50 is called the steering torque Tq S , the steering ECU 62 generates the steering torque Tq SDetermine. Incidentally, the first term, the second term, and the third term of the following formula are the proportional term, the integral term, and the differential term, respectively, and G P , G I , G D are the proportional term gain, the integral term gain, and the differential term gain, respectively. Tq S = G P ×Δν + G I ×∫Δνdt + G D ×dΔν / dt

[0043] If the current supplied to the steering motor 50 is called the steering current I S , the steering torque Tq S and the steering current I S are generally in a proportional relationship. According to this relationship, the steering ECU 62 determines the steering current I S to be supplied to the steering motor 50 based on the determined steering torque Tq S , and supplies the steering current I S to the steering motor 50. Incidentally, as will be described in detail later, in order to utilize the value of the steering current I S in the control of the reaction force applying mechanism 28 of the operation device 12 and in the cooperative steering control, the steering ECU 62 transmits information about the steering current I S .

[0044] The independent steering control described above is performed by the steering ECU 62a and the steering ECU 62b repeatedly executing the basic steering program shown in the flowchart in FIG. 3 at short time intervals (for example, several msec to several tens of msec). Hereinafter, the processing according to the program will be briefly described. Incidentally, the processing of the steering ECU 62a and the steering ECU 62b according to the basic steering program may be hereinafter referred to as "basic steering processing".

[0045] In the basic steering processing, 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 * is determined. In the subsequent S3, the target motor rotation angle ν *Once determined, in S4, the actual motor rotation angle ν is detected. In the next S5, the motor rotation angle deviation Δν is determined, and in S6, based on the motor rotation angle deviation Δν, the steering torque Tq S is determined. Then, in S7, based on the steering torque Tq S , the steering current I, which is the supply current to the steering motor 50 S is determined, and in S8, the steering current I S is supplied to the steering motor 50. Information on the steering current I S is transmitted in S9.

[0046] ii) Cooperative steering control The independent steering control is as described above. However, during normal power supply when power can be supplied from the main power source 70 to the steering main system 14a and the steering sub-system 14b, in this steering system, cooperative steering control is executed. The cooperative steering control is control that takes into account the smooth operation of the steering device 14, specifically the steering actuator 42, and the fact that the steering main system 14a and the steering sub-system 14b generate the same force with each other. In other words, the cooperative steering control is control that operates the steering motor 50b constituting the steering sub-system 14b in synchronization with the steering motor 50a constituting the steering main system 14a.

[0047] In the independent steering control described above, the steering ECU 62a constituting the control main system transmits information about the steering current I S that it supplies to the steering motor 50a to the steering ECU 62b constituting the control sub-system. The steering ECU 62b does not determine the steering current I S that it supplies to the steering motor 50b, but supplies the steering current I S based on the received information to the steering motor 50b.

[0048] On the other hand, the steering ECU 62b repeatedly executes a subordinate steering program whose flowchart is shown in FIG. 3 at a short time pitch (for example, several msec to several tens of msec) instead of the basic steering program. In the process according to this program, at S11, the steering current I to be supplied to the steering ECU 62b is obtained by receiving from the steering ECU 62a. S At the subsequent S12, the steering current I S is supplied to the steering motor 50b, and at S13, information on the steering current I S is transmitted. Note that the processing of the steering ECU 62b according to this subordinate steering program may be referred to as "subordinate steering processing".

[0049] iii) Steering control during backup As described above, the backup power supply 72 includes the capacitor 78 and is configured to have a considerably lower capacitance compared to the main power supply 70. Therefore, when operating the steering main system 14a by receiving power supply from the backup power supply 72 instead of the main power supply 70, a limit is provided for the steering current I supplied to the steering motor 50a in the steering main system 14a. S If the steering current I

[0050] is not limited, the steering motors 50a and 50b have a rotational speed - torque characteristic (N - T characteristic) schematically shown by a solid line in the graph of FIG. 4. Since there is an output peak in those steering motors 50a and 50b, until the motor rotational speed (strictly speaking, the rotational speed per unit time, that is, the "rotational speed", but hereinafter may be simply referred to as "rotational speed") N becomes N S , the steering torque Tq 1 is constant at Tq S . And as the rotational speed N becomes higher beyond N S1 , the steering torque Tq 1 decreases linearly and becomes 0 when the rotational speed N becomes N S and N 2 .

[0051] The steering current I in this steering systemS The restriction, although detailed description thereof is omitted, is carried out by setting a guard for the maximum supply current while making the duty ratio lower than that during normal power supply in the PWM (pulse width modulation) operation of the inverter of the steering ECU 62. Therefore, the rotational speed-torque characteristics as indicated by the one-dot chain line in the graph of FIG. 4 are exhibited. More specifically, until the rotational speed N becomes N 1 ’, the steering torque Tq S is constant at Tq S1 ’ (<Tq S1 ), and as the rotational speed N becomes higher beyond N 1 ’, the steering torque Tq S decreases linearly and becomes 0 when the rotational speed N becomes N 2 ’ (<N 2 ). By such a restriction, even a backup power supply 72 with a small capacity can supply power to the steering motor 50a for a relatively long time.

[0052] The process of the steering ECU 62a with the restriction on the above-mentioned steering current I S is called “restricted steering process”. Referring to the basic steering program whose flowchart is shown in FIG. 3 for explanation, in that restricted steering process, as shown in parentheses, after the determination of the steering current I S in S7, before the current supply to the steering motor 50a in S8, in S7’, the above-mentioned current restriction is made, and in S8, based on the restricted steering current I S , current is supplied to the steering motor 50a.

[0053] The overall characteristics of the steering motor 50 can be considered as the sum of the specifications of each of the steering motor 50a and the steering motor 50b. The rotational speed-torque characteristics of each of the steering motor 50a and the steering motor 50b when the steering current I S is not restricted are shown in the graph of FIG. 5(a) with the steering current I SIf the rotational speed - torque characteristics of the steering motor 50a when restricted are respectively shown in the graph of Fig. 5(b), during normal power supply, the overall characteristics of the steering motor 50 are as shown in the graph of Fig. 5(c). On the other hand, if cooperative steering control is performed while restricting the steering current I S to the steering motor 50a, the rotational speed - torque characteristics of the steering motor 50b will be the same as those of the steering motor 50a when the steering current I S is restricted, and the overall characteristics of the steering motor 50 will become considerably low as shown in the graph of Fig. 5(d). Simply put, it will become impossible to obtain sufficient steering torque Tq S .

[0054] Therefore, in this steering system, during backup, independent steering control is adopted. The main steering system 14a is operated by restricted steering processing, that is, power supply restriction operation, and the sub - steering system 14b is operated by basic steering processing. By such operation of the main steering system 14a and the sub - steering system 14b, the overall characteristics of the steering motor 50 can be maintained at relatively high characteristics as shown in the graph of Fig. 5(e). The mode of operating the main steering system 14a by restricted steering processing and the sub - steering system 14b by basic steering processing will be called the "restricted operation mode".

[0055] Here, for further detailed explanation, the characteristics of the steering motor 50a by restricted steering processing are, as described above, the characteristics of the dashed - dotted line in Fig. 4. However, in the restricted operation mode, strictly speaking, as shown by the dashed line, when the rotational speed N of the steering motor 50 exceeds N 2 ', it enters the operation of the regeneration region. In the operation of this region, the torque generated by the steering motor 50a becomes a torque in the opposite direction to the steering torque Tq S generated by the steering motor 50b, and cancels out the steering torque Tq S generated by the steering motor 50b. This can lead to a decrease in the overall characteristics of the steering motor 50 in the restricted operation mode.

[0056] Concerned about the deterioration of the overall characteristics of the steering motor 50 in the restricted operation mode, in addition to the restricted operation mode, this steering system has a "non-operation mode", that is, a mode in which the main steering system 14a is not operated and the sub-steering system 14b is operated by basic steering processing. According to this non-operation mode, since only the sub-steering system 14b generates steering torque, the overall characteristics of the steering motor 50 are as shown in the graph of Fig. 5(a). Even with such overall characteristics, during backup, higher characteristics can be obtained than the characteristics when performing cooperative steering control while restricting the power supply operation of the main steering system 14a, that is, the characteristics shown in the graph of Fig. 5(d).

[0057] Furthermore, since the above-mentioned regeneration region is the region where the rotational speed N of the steering motor 50 exceeds N 2 ’, in this steering system, when the rotational speed N of the steering motor 50 is N 2 ’ or less, the steering device 14 is operated in the restricted operation mode, and when the rotational speed N of the steering motor 50 exceeds N 2 ’, a mode in which the steering device 14 is operated in the non-operation mode, that is, a "switching mode" for switching the operation mode according to the rotational speed N, is also prepared.

[0058] Regarding which of the restricted operation mode, non-operation mode, and switching mode to adopt, it may be set by the vehicle manufacturer, sales dealer, etc. according to the type of the vehicle, etc., or it may be arbitrarily set by the driver of the vehicle.

[0059] In the case of a failure of the main power supply 70 or the like, it is also expected that appropriate power supply will not be provided to the steering sub-system 14b during backup. If such a situation is called a "sub-system proper power supply failure situation", in this steering system, in this sub-system proper power supply failure situation, the main steering system 14a is operated with power supply restricted without operating the steering sub-system 14b. More specifically, regardless of which of the above-mentioned restricted operation mode, non-operation mode, and switching mode is adopted, in the sub-system proper power supply failure situation, the main steering system 14a will be operated while the power supply is restricted. Therefore, even in the sub-system proper power supply failure situation, as the overall characteristics of the steering motor 50, although the characteristics are relatively low, the characteristics shown in the graph of FIG. 5(b) are ensured.

[0060] iv) Flow of switching the operation of the main steering system and the sub-steering system The switching of the operations of the main steering system 14a and the sub-steering system 14b, that is, the operations that the main steering system 14a and the sub-steering system 14b should perform respectively during normal power supply and backup, are instructed by the integrated ECU 68. The integrated ECU 68 repeatedly executes an operation switching program whose flowchart is shown in FIG. 6 at a short time pitch (for example, several msec to several tens of msec) for the above-mentioned operation switching. The processing according to the program will be described below.

[0061] In the processing according to the operation switching program, first, in S21, information about the power supply status of the backup power supply 72, that is, whether it is possible to supply power from the main power supply 70 to the main steering system 14a, is obtained from the backup power supply 72. Although detailed description is omitted, the backup power supply 72 is also connected to the CAN 66, and the information is obtained via the CAN 66. In the subsequent S22, based on the obtained information, it is determined whether it is backup time.

[0062] When it is determined that it is not during backup, that is, during normal power supply, in S23, in order to execute cooperative steering control, an instruction to execute basic steering processing is issued to the steering ECU62a, which is the main control system, and an instruction to execute subordinate steering processing is issued to the steering ECU62b, which is the sub-control system.

[0063] When it is determined that it is during backup, in S24, information about the voltage in the power supply from the main power supply 70 to the steering sub-system 14b is acquired. Incidentally, although detailed explanation is omitted, the steering ECU62b has a voltage sensor for detecting the voltage it receives, and the above information is received by the overall control ECU68 from the steering ECU62b via the CAN66. Based on that information, in S25, it is determined whether it is possible to supply power to the steering sub-system 14b from the main power supply 70 at an appropriate voltage, that is, whether it is a situation where proper power supply to the sub-system is not possible. If it is a situation where proper power supply to the sub-system is not possible, in S26, an instruction to perform restricted steering processing is issued to the steering ECU62a, which is the main control system, and an instruction not to operate the steering sub-system 14b is issued to the steering ECU62b, which is the sub-control system.

[0064] On the other hand, when it is determined in S25 that it is possible to supply power to the steering main system 14b from the main power supply 70 at an appropriate voltage, in S27, it is determined whether the operation mode flag FM is "1". The operation mode flag FM is a flag indicating which of the above-mentioned restricted operation mode, non-operation mode, and switching mode is adopted. It is a flag that is set to "1" when the non-operation mode is adopted, "2" when the restricted operation mode is adopted, and "3" when the switching mode is adopted.

[0065] When the operation mode flag FM is "1", it is recognized as the non-operation mode. In S28, an instruction not to activate the steering main system 14a is issued to the steering ECU 62a, which is the control main system, and an instruction to execute the basic steering process is issued to the steering ECU 62b, which is the control sub-system. When it is determined in S27 that the operation mode flag FM is not "1", it is determined in S29 whether the operation mode flag FM is "2". When the operation mode flag FM is "2", it is recognized as the restricted operation mode. In S30, an instruction to execute the restricted steering process is issued to the steering ECU 62a, which is the control main system, and an instruction to execute the basic steering process is issued to the steering ECU 62b, which is the control sub-system.

[0066] When it is determined in S29 that the operation mode flag FM is not "2", that is, when the operation mode flag FM is "3", it is recognized as the switching mode. In S31, the motor rotation speed N of the steering motor 50 is acquired. Incidentally, although detailed description is omitted, among the steering main system 14a and the steering sub-system 14b, the one that is activated is identifying the rotation speed N based on the motor rotation angle ν detected by the motor rotation angle sensor 54, and information about the identified rotation speed N is transmitted from the one that is activated among the steering main system 14a and the steering sub-system 14b.

[0067] In the subsequent S32, it is determined whether the rotation speed N exceeds the above-mentioned N 2 ’. When the rotation speed N exceeds the above-mentioned N 2 ’, it is determined that the steering motor 50a operates in the regeneration area by the restricted steering process. To operate the steering device 14 in the non-operation mode, in S28, an instruction not to activate the steering main system 14a is issued to the steering ECU 62a, which is the control main system, and an instruction to execute the basic steering process is issued to the steering ECU 62b, which is the control sub-system. On the other hand, when the rotation speed N is N 2When it is determined that it is as follows, in order to operate the steering device 14 in the restricted operation mode, in S30, an instruction to execute the restricted steering process is sent to the steering ECU 62a which is the main control system, and an instruction to execute the basic steering process is sent to the steering ECU 62b which is the sub control system, respectively.

[0068] (b) Reaction force control Reaction force control is control for imparting an operating feeling to the driver with respect to the steering operation. In this steering system, during normal power supply, the main operation system 12a and the sub operation system 12b independently and in parallel apply the same operating reaction force F CT to the steering wheel 20. Hereinafter, the reaction force application processes performed by each of the operation ECU 60a constituting the main control system and the operation ECU 60b constituting the sub control system in the reaction force control will be described unifiedly.

[0069] The operation ECU 60 determines the operating reaction force F CT based on two components, namely, the steering load-dependent component F S and the operation force-dependent reduction component F A according to the following formula. F CT =F S -F A

[0070] The steering load-dependent component F S is a component related to the steering force (the steering torque Tq S ) required to steer the wheels 10, and is determined based on the steering current I S supplied to the steering motor 50. Although detailed description is omitted, it is recognized that the greater the steering current I S , the greater the steering load of the wheels 10, and the steering load-dependent component F S is determined to be a large value. Incidentally, information regarding the steering current I S actually supplied to the steering motor 50 is sent from the steering ECU 62 to the operation ECU 60 of the same system via the dedicated communication line 64.

[0071] One, the operation force-dependent reduction component F A can be considered as a component for imparting an operating feeling to the driver in a so-called power steering system. In a power steering system, generally, an assist torque corresponding to the operation torque Tq O is applied to the steering shaft 22. Modeling the assist torque, the operation force-dependent reduction component F A is determined according to the following formula. F A =β×Tq O Incidentally, β is a gain for determining the operation force-dependent reduction component F A , and the operation ECU 60 detects the operation torque Tq O via the operation torque sensor 36.

[0072] Based on the operation reaction force F CT determined as described above, the operation ECU 60 determines the reaction force current I C , which is the current supplied to the reaction force motor 26, according to the following formula, and supplies the determined reaction force current I C to the reaction force motor 26. I C =α×F CT Incidentally, α is a set current determination coefficient.

[0073] Each of the operation ECUs 60a and 60b performs the above-described reaction force application process by repeatedly executing, at a short time pitch (for example, several msec to several tens of msec), a reaction force application program whose flowchart is shown in FIG. 7 by a computer included in each of them. Briefly explaining the process according to the program, first, in S41, the steering current I S is acquired, and in S42, based on the steering current I S , the steering load-dependent component F S is determined. In the next S43, the operation torque Tq O is detected, and in S44, based on the operation torque Tq O , the operation force-dependent reduction component F Ais determined. In subsequent S45, the steering load-dependent component F S and the operation force-dependent decreasing component F A are used to determine the operation reaction force F CT . In S46, based on the operation reaction force F CT , the reaction force current I C to be supplied to the reaction force motor 26 is determined. Then, in S47, based on the reaction force current I C , current is supplied to the reaction force motor 26.

[0074] Regarding the reaction force control during backup, briefly explained, since power is only supplied to the operation main system 12a from the backup power supply 72, as long as the voltage of the power supply to the operation sub-system 12b is appropriate, the above reaction force application process is only executed for the operation sub-system 12b. When the voltage of the power supply to the operation sub-system 12b is not appropriate, the above reaction force application process is only executed for the operation main system 12a.

Explanation of Symbols

[0075] 10: Wheel 12, 12a, 12b: Operating device 14: Steering device 14a: Steering main system 14b: Steering sub-system 20: Steering wheel [operating member] 26: Reaction force motor 28: Reaction force application mechanism 30: Motor rotation angle sensor 42: Steering actuator 50: Steering motor 50a [steering main system] 50b [steering sub-system] 54, 54a, 54b: Motor rotation angle sensors 60: Operation electronic control unit (operation ECU) [controller] 62: Steering electronic control unit (steering ECU) [controller] 62a [control main system], 62b [control sub-system] 68: Integrated electronic control unit (integrated ECU) [controller] 70: Main power supply unit [main power supply] 72: Backup power supply unit [backup power supply] 74: DC-DC converter 76: Battery 78: Capacitor

Claims

1. A main power supply, a backup power supply, a steering device having a steering motor divided into two systems, a main system and a sub-system, and the wheels are steered by the force generated by the steering motor; a controller for controlling the operation of each of the main system and the sub-system of the steering motor so as to control the steering device based on a steering request, A steer-by-wire type steering system comprising: when the controller is normally powered from the main power supply to the main system and the sub-system of the steering motor, the sub-system of the steering motor is operated in synchronization with the main system of the steering motor, and the sub-system of the steering motor is not powered from the backup power supply. When in backup mode, only the backup power supply powers the main system of the steering motor. The main system of the steering motor is operated while restricting power supply thereto, or not operated, and the sub-system of the steering motor is configured to be independently controlled.

2. The controller, The steering system according to claim 1, wherein, during normal power supply, the operations of the main system and the sub-system of the steering motor are controlled such that the main system and the sub-system of the steering motor generate the same force with respect to each other.

3. The controller, The steering system according to claim 1 or 2, wherein, during backup mode, when appropriate power supply from the main power supply to the sub-system of the steering motor is not performed, the sub-system of the steering motor is not operated, and the main system of the steering motor is operated while restricting power supply thereto.

4. The controller, The steering system according to claim 1 or 2, wherein, during backup mode, when appropriate power supply from the main power supply to the sub-system of the steering motor is being performed, the main system of the steering motor is operated while restricting power supply thereto.

5. The controller, The steering system according to claim 1 or 2, wherein, during backup mode, when appropriate power supply from the main power supply to the sub-system of the steering motor is being performed, the main system of the steering motor is configured not to be operated.

6. The controller, corresponding to the main system and the sub-system of the steering motor, has two systems, a main system and a sub-system, During the normal power supply, based on the supply current to the main system of the steering motor determined by the main system, the sub-system supplies power to the sub-system of the steering motor. The steering system according to any one of claims 1 to 5, wherein during the backup, the sub-system is configured to supply power to the sub-system of the steering motor based on the supply current to the sub-system of the steering motor determined by itself, regardless of the supply current to the main system of the steering motor determined by the main system. **Claim 7** The steering system according to any one of claims 1 to 6, wherein the main power supply includes a storage battery, while the backup power supply is a capacitor. **Claim 8** The backup power supply is The steering system according to any one of claims 1 to 7, wherein during the normal power supply, it receives power from the main power supply and is charged, and during the backup, it is configured to supply power to the main system of the steering motor depending on the stored electrical energy.

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