Power steering architecture without mechanical connection between steering wheel and steering mechanism of vehicle

Abstract

The invention relates to a method for controlling a power steering system (1) of a motor vehicle, comprising the steps of: detecting an operating state of a steering actuator (SM1) coupled to a rack (8); providing a torque setpoint (TRQ) to a main motor (M1) of the steering actuator by a first control unit (ECU1) of the steering actuator while the steering actuator is operating; controlling, by a second control unit (ECU3), a brushless auxiliary motor (M2) coupled to the rack, based on measurements of the angular position of the main motor and the angular position (HWA) of the steering wheel (2), when the steering actuator fails but an angular position measurement (SAA) of the main motor is provided; and controlling an assist motor according to an angular position of a steering wheel when the steering actuator is completely failed.

Description

Technical Field

[0001] The invention relates to the field of electric power steering devices for motor vehicles, and more particularly to power steering devices of the SBW (“Steer by Wire”) type, that is to say without mechanical connection between the steering wheel and the steering mechanism of the vehicle. Background Art

[0002] An electric power steering device for a motor vehicle generally comprises mechanical parts, which include a steering wheel connected to a steering pinion meshing with a rack via a steering column and an intermediate shaft, and slidably mounted in a steering housing. The two opposite ends of the rack are connected to the right and left steering wheels of the vehicle via tie rods, respectively. In order to assist the manual action applied to the steering wheel by the driver of the vehicle, an electric auxiliary actuator with two rotation directions is connected to the mechanical steering connection between the steering wheel and the steering column of the vehicle via a reducer, thereby transmitting the motor torque (and possibly also the resistance torque) to assist the steering column. The auxiliary actuator is driven by an on-board electronic computer, which receives and processes various signals from sensors, which in particular include a torque sensor applied to the steering column by the driver of the vehicle.

[0003] In the SBW type electric assist device, the steering wheel is not mechanically coupled to the rack 8, and the steering of the vehicle is controlled by an actuator mechanically coupled to the rack. This steering architecture makes it easier to integrate the steering system into the vehicle. In addition, the angular position of the steering wheel is independent of the angular position of the wheels, which makes it possible to provide a large range of operation at low speeds, especially for parking maneuvers, and thus limits the influence of the rotation of the steering wheel on high-speed steering.

[0004] However, in order to ensure the safety objectives, a certain redundancy is necessary so that in the event of failure of a part of the device, the driver can maintain control of the direction of the vehicle. For this purpose, it has been proposed to place a clutch on the steering column so that in the event of failure of the actuator coupled to the rack, the mechanical connection between the steering wheel and the rack can be reestablished. This solution does not make it possible to eliminate the traditional mechanical connection and its disadvantages and integrate it into the vehicle. It is also proposed to install two redundant rack-actuated motors. Thus, if one of the motors fails, the other takes over. This architecture can be easily integrated into the vehicle, but the safety provided may be considered insufficient, since in fact it cannot overcome the failure of the control electronics of the two motors. Therefore, it is also proposed to adopt two computers, each controlling one motor. However, the cost of this solution is relatively high.

[0005] It is therefore desirable to propose an electric power steering architecture for a SBW type motor vehicle which provides high fault tolerance while having a lower cost compared to prior art solutions. Summary of the invention

[0006] An embodiment relates to a method for controlling a power steering system of a motor vehicle, the method comprising: detecting an operating state of a steering actuator, the steering actuator being mechanically connected to a first steering pinion meshing with a steering rack of the motor vehicle; providing a torque set point to a main motor of the steering actuator through a first control unit of the steering actuator when the steering actuator is operating; when the steering actuator fails but provides an angular position measurement of the main motor, using a closed-loop angle adjustment function to receive the angular position measurement of the main motor and the angular position measurement of a steering wheel of the vehicle, and controlling a brushless auxiliary motor mechanically connected to a second steering pinion meshing with the steering rack through a second control unit; and when the steering actuator completely fails, using an open-loop angle adjustment function to receive the angular position measurement of the steering wheel, and controlling the auxiliary motor through the second control unit.

[0007] In this way, in a SBW type power steering system, the necessary redundancy of the vehicle steering control is provided by a brushed motor which requires a power supply circuit that is much simpler and cheaper than that of a brushless motor. The use of a brushed motor provides the possibility of moving the power supply circuit away from the brushed motor, in particular placing the power supply circuit in an area away from the rack and therefore away from the steering actuator, so as to reduce the risk of simultaneous failure of the steering actuator and the power supply circuit.

[0008] According to one embodiment, the second control unit belongs to a force feedback actuator coupled to the steering wheel.

[0009] Therefore, it is not necessary to provide a specific control unit for the brushed motor. This arrangement does not reduce the operational safety of the power steering because the control unit of the force feedback actuator on the steering wheel is less likely to fail than the steering actuator.

[0010] According to one embodiment, the auxiliary motor is controlled by the second control unit via a power supply circuit installed in a force feedback actuator which is coupled to the steering wheel.

[0011] In this way, the power supply circuit is located in a different area from the steering actuator. This prevents the power supply circuits of the steering actuator and the auxiliary motor from being subject to the same constraints, whether climatic, mechanical or electromagnetic, which could cause these components to fail simultaneously.

[0012] According to one embodiment, the method further comprises: mechanically coupling the auxiliary motor to the second steering pinion using a clutch when the steering actuator fails; and mechanically decoupling the auxiliary motor from the second steering pinion using a clutch when the steering actuator operates.

[0013] The arrangement of this clutch allows to prevent the brushed motor from rotating when not activated. In this way, the brushes of the brushed motor only wear when the brushed motor is activated, that is to say in the rare period when the steering actuator fails.

[0014] According to one embodiment, the method further comprises: when the steering actuator is operated, supplying the torque set value to the auxiliary motor by the second control unit in addition to supplying the torque set value to the main motor of the steering actuator.

[0015] An embodiment also relates to a power steering system for a motor vehicle, the system comprising: a steering actuator including a main motor mechanically connected to a first steering pinion meshing with a steering rack of the motor vehicle, and a first control unit configured to control the main motor; a brushless auxiliary motor mechanically connected to a second steering pinion meshing with the steering rack; and a second control unit configured to control the auxiliary motor by implementing the method previously defined.

[0016] According to one embodiment, the system comprises a force feedback actuator coupled to the steering wheel and comprising a second control unit.

[0017] According to one embodiment, the force feedback actuator comprises a first power supply circuit connected to a second control unit and to a force feedback motor coupled to the steering wheel, the second control unit being configured to control the force feedback motor.

[0018] According to one embodiment, the force feedback actuator comprises a second power supply circuit connected to the second control unit and to the auxiliary motor to allow the second control unit to control the auxiliary motor.

[0019] According to one embodiment, the system comprises a clutch for mechanically coupling the auxiliary motor to the second steering pinion, the clutch being controlled by the second control unit.

[0020] According to one embodiment, the auxiliary motor is dimensioned to allow only parking maneuvers of the vehicle.

[0021] Embodiments may also relate to a motor vehicle comprising a power-assisted steering system as previously defined. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will be better understood with the aid of the following description of exemplary embodiments with reference to the accompanying drawings, in which like reference signs correspond to architecturally and / or functionally identical or similar elements.

[0023] Figure 1 It is a schematic diagram of a traditional power steering system for motor vehicles.

[0024] Figure 2 is a schematic diagram of a power steering system for a motor vehicle according to one embodiment,

[0025] Figure 3 The functional architecture of a computer of a power steering system according to one embodiment is schematically shown.

[0026] Figure 4 The functional architecture of a computer of a power steering system according to another embodiment is schematically shown. DETAILED DESCRIPTION

[0027] Figure 1 A conventional motor vehicle steering system 1a equipped with an electric assist device according to the prior art is shown. The power steering device 1a of the SBW (“steer by wire”) type comprises a steering column 3 connected to a steering wheel 2 and two redundant actuators SM11, SM12 mechanically connected to a rack bar 8. Therefore, the two actuators SM11, SM12 are mechanically connected to pinion shafts 7b, 7d, respectively. The pinion shafts 7b, 7d are mechanically connected to pinions 7a, 7c, respectively, meshing with a rack bar 8 slidably mounted in a bogie 9. The two opposite ends of the rack bar 8 are connected to the right and left steering wheels 11 of the vehicle via connecting rods 10, respectively.

[0028] Each actuator SM11, SM12 includes an electric auxiliary motor M with two rotation directions, a control circuit DC of the motor M, and a reducer 5. The output shaft of the motor M is mechanically connected to the pinion shafts 7b, 7d respectively via the reducer 5. Each actuator SM11, SM12 also includes a control unit (on-board electronic computer) ECU, which receives and processes various signals from sensors (especially from the sensor steering wheel angle 13) and provides control signals to the control circuit DC of the motor M of the actuator. Each reducer 5 can be a type including a screw, which includes an annular screw shaft and a screw tangential wheel fixed to one of the pinion shafts 7b, 7d.

[0029] The power steering system 1a further comprises a third actuator SM13, which is coupled to the steering column 3 to provide a resistance or motor torque to the steering wheel 2. This resistance or motor torque varies according to different parameters, such as the torque applied to the steering wheel by the driver, the torque applied to the steering pinion 7a or 7c, and the speed of the vehicle. The actuator SM13 comprises an electric auxiliary motor M with two directions of rotation, a control circuit DC of the motor M, a reducer 5, and a control unit ECU, the reducer being coupled to the motor M on one side and to the steering column 3 on the other side (between the distal bearing of the steering column and the torsion bar 12).

[0030] The control unit ECU of the actuator SM13 is connected to the control units ECU of the actuators SM11 and SM12, and is configured to control the motor M of the actuator SM13 so as to provide force feedback on the steering wheel 2. Specifically, the control unit ECU of the actuator SM13 is configured to control the motor M of the actuator SM13 so as to transmit a resistance torque (which may also be a motor torque) proportional to the torque supplied by the motor M of the actuators SM11 and SM12 to the steering column 3.

[0031] The force feedback applied by the actuator SM13 makes it possible to resist the driver's movements on the steering wheel, the resistance torque varying in particular according to the speed of the vehicle. Thus, for example, at very low speeds, during parking maneuvers, the resistance torque applied to the steering column 3 is very low. On the contrary, at higher speeds, for safety reasons, this resistance torque is higher to avoid rapid and large movements of the steering wheel.

[0032] Figure 2 A power steering device 1 according to an embodiment is shown. The device 1 differs from the power steering device 1a in that the actuators SM11, SM12, SM13 are replaced by actuators SM1, SM2, SM3. The actuator SM1 can be the same as the actuator SM11. On the other hand, the actuator SM2 connected to the pinion shaft 7d includes a motor M2. The motor M2 can be connected to the pinion shaft 7d via a reducer 5-2. The actuator SM3 connected to the steering column 3 via the reducer 5-3 includes a control unit ECU3, a motor M3 and a control circuit DC3 allowing the control unit ECU3 to control the motor M3. The actuator SM2 is designed to be activated when the actuator SM1 fails.

[0033] The control unit ECU3 of the actuator SM3 is connected to the control unit ECU1 of the actuator SM1 and transmits to it in particular a measurement of the steering wheel angle HWA relative to the neutral position of the steering wheel 2, redundant with the angle measurement HWA performed by the steering wheel angle sensor 13, directly to the control unit ECU1. The control unit ECU1 transmits to the processing unit ECU3 in particular one of the torque setpoints applied by the electric motor M1 to the pinion 7a.

[0034] According to one embodiment, the motor M2 is of the brushed type, whereas the motors M1, M3 of the actuators SM1 and SM3 are conventional brushless motors. Furthermore, the control unit ECU3 is configured to control the motor M2 via a control circuit DC2, which is remote, for example, in the actuator SM3. To control the brushed motor M2, the circuit DC2 may simply comprise an H-bridge of MOSFET type transistors.

[0035] Brushed motors are much cheaper to implement than brushless motors. In fact, the control circuit DC2 of the brushed motor M2 is much simpler than the control circuit DC1 of the brushless motor M1 of the actuator SM1. Unlike brushless motors, brushed motors do not require an angular position sensor for their drive. As a result, the connection between the control circuit DC2 and the motor M2 requires only two wires, while the connection between the control circuit DC1 and the motor M1 requires at least five wires. This last advantage makes it possible to move the control circuit DC2 away from the motor M2. Thus, the control circuit DC2 can be installed, for example, in the actuator SM3 or near the steering wheel 2. This reduces the risk of malfunctions of the actuators SM2 and SM1, whose respective control circuits do not use the same technology and are not subject to the same limitations, whether climatic, mechanical or electromagnetic.

[0036] According to one embodiment, the clutch CH is inserted between the reducer 5-2 of the actuator SM2 and the motor M2. When the actuator SM2 is not activated, the clutch CH makes it possible to mechanically separate the motor M2 from the shaft 7d, and conversely, when the actuator SM1 fails, the motor M2 is mechanically coupled to the shaft 7d when the actuator SM2 is activated. The clutch CH can be controlled by the control unit ECU3. Therefore, when the actuator SM2 is not activated, the clutch CH is able to prevent the motor M2 from rotating, and thus avoid increasing the inertia and friction of the system when the motor M2 is not activated, and also limit the wear of the brushes of the motor M2.

[0037] Figure 3 The functions of the control unit ECU3 are shown. The control unit ECU3 includes an open-loop angle adjustment function AOC, a closed-loop angle adjustment function ACC, a torque control function STC and a switching function CM. The functions AOC and ACC receive the angle measurement signal HWA from the steering wheel angle sensor 13. The function ACC also receives the angular position signal from the motor M1 from the control unit ECU1 of the actuator SM1. The function STC receives the set torque value signal TRQ from the control unit ECU1 of the actuator SM1. The TRQ value is proportional to the torque supplied by the motor M1. The switching function CM is controlled by a status signal SAS from the actuator SM1, which is provided by a self-diagnosis function from the actuator SM1. The status signal SAS can indicate any of the following states:

[0038] State 1: Actuator SM1 is fully operational,

[0039] State 2: Actuator SM1 is completely failed, and

[0040] State 3: The actuator SM1 fails, but the angular position of the motor M1 can be reliably provided from the actuator SM1 to the control unit ECU3.

[0041] In state 1, the actuator SM1 is operable and the motor M1 of the actuator activates the steering of the vehicle alone via the pinion 7a. In state 2, only the function AOC is active and the control unit ECU3 controls the motor M2 only based on the angle measurement signal HWA from the steering wheel 2. The motor M2 then activates the steering of the vehicle alone via the pinion 7c. In state 3, only the function ACC is active and the control unit ECU3 controls the motor M2 based on the angle measurement signal HWA and the angular position SAA of the motor M1 controlled by the actuator SM1. In states 2 and 3, the motor M2 activates the steering of the vehicle alone via the pinion 7c. The only purpose of selecting the motor M2 is to stop the vehicle in a safe place as quickly as possible. Therefore, its size can achieve a more limited performance than the motor M1.

[0042] In state 2, actuator SM1 can provide a value for the angular position SAA of motor M1, but this value is not used because it is unreliable.

[0043] In parallel with the functions AOC and ACC, the function STC controls the electric motor M3 to apply a resistance or motor torque to the steering column 3 and therefore a force feedback on the steering column 3, depending on the torque setpoint TRQ supplied by the control unit ECU1 controlling the actuator SM1, as long as this value is available. In this way, the driver can feel the torque when he has to turn the steering wheel of the vehicle.

[0044] according to Figure 4 In one embodiment shown, during certain operation, actuator SM2 is activated to provide additional torque in combination with the torque provided by actuator SM1 in state 1. In this case, control circuit ECU1 is configured to issue a command to this effect to control circuit ECU3. Thus, Figure 4 The functions of the control unit ECU3 are shown. Figure 4 The control unit ECU3 and Figure 3 The control unit in differs in that it also comprises a function STC1 which is activated in state 1 and is configured to control the actuator SM2 so as to provide an additional torque combined with the torque provided by the actuator SM1 during certain operations.

[0045] It will be clear to those skilled in the art that the present invention is capable of various modifications and applications. In particular, the present invention is not limited to implementing the control function of the auxiliary motor M2 in the control unit ECU3 of the force feedback actuator SM3. In practice, a specific control unit may be implemented to control the motor M2.

[0046] Although installing the power supply circuit DC2 in the force feedback actuator SM3 provides more safety, this arrangement is not essential. In addition, the power supply circuit can be arranged near the steering wheel outside the actuator SM3.

[0047] Furthermore, the provision of the clutch CH simply allows the operating time of the motor M2 to be increased without replacing the brushes. If the duration of operation of the motor M2 without replacing the brushes is greater than the average use time of the vehicle, this provision may be useless.

Claims

1. A method for controlling a power steering system (1) of a motor vehicle, the method comprising: detecting an operating state of a steering actuator (SM1) mechanically coupled to a first steering pinion (7a) meshing with a steering rack (8) of the motor vehicle; When the steering actuator is in operation, a torque set point (TRQ) is provided to a main motor (M1) of the steering actuator via a first control unit (ECU1) of the steering actuator; When the steering actuator fails but provides an angular position measurement (SAA) of the main motor, using a closed loop angle adjustment function (ACC) to receive the angular position measurement of the main motor and the angular position measurement (HWA) of the steering wheel (2) of the vehicle, control a brushless auxiliary motor (M2) mechanically coupled to a second steering pinion (7c) meshing with the steering rack via a second control unit (ECU3); and When the steering actuator fails completely, the auxiliary motor is controlled by the second control unit using an open loop angle control function (AOC) to receive angular position measurements of the steering wheel.

2. The method according to claim 1, wherein: The second control unit (ECU3) belongs to a force feedback actuator (SM3) coupled to the steering wheel (2).

3. The method according to claim 1 or 2, wherein: The auxiliary motor (M2) is controlled by the second control unit (ECU3) via a power supply circuit (DC2) installed in the force feedback actuator (SM3), which is coupled to the steering wheel (2).

4. The method according to any one of claims 1 to 3, further comprising: When the steering actuator (SM1) fails, the auxiliary motor (M2) is mechanically coupled to the second steering pinion (7c) using a clutch (CH); and When the steering actuator is operated, the auxiliary motor is mechanically decoupled from the second steering pinion using the clutch.

5. The method according to any one of claims 1 to 4, further comprising: When the steering actuator (SM1) is operated, in addition to supplying a torque setting value (TRQ) to the main motor (M1) of the steering actuator, the torque setting value is also supplied to the auxiliary motor (M2) through the second control unit (ECU3).

6. A power steering system for a motor vehicle, the system comprising: A steering actuator (SM1) comprising: a main motor (M1) mechanically coupled to a first steering pinion (7a) meshing with a steering rack (8) of a motor vehicle, and a first control unit (ECU1) configured to control the main motor, a brushless auxiliary motor (M2) mechanically coupled to a second steering pinion (7c) meshing with the steering rack, and A second control unit (ECU 3 ) configured to control the auxiliary motor by implementing the method according to any one of claims 1 to 5 .

7. System according to claim 6, comprising a force feedback actuator (SM3) coupled to the steering wheel (2) and comprising the second control unit (ECU3).

8. The system according to claim 7, wherein: The force feedback actuator (SM3) comprises a first power supply circuit (DC3), which is connected to the second control unit (ECU3) and to a force feedback motor (M3), which is coupled to the steering wheel (2), and the second control unit is configured to control the force feedback motor.

9. The system according to any one of claims 7 and 8, wherein: The force feedback actuator (SM3) comprises a second power supply circuit (DC2) connected to the second control unit (ECU3) and to the auxiliary motor (M2) to allow the second control unit to control the auxiliary motor.

10. System according to any one of claims 6 to 9, comprising a clutch (CH) for mechanically coupling the auxiliary motor (M2) to the second steering pinion (7c), the clutch being controlled by the second control unit (ECU3).

11. A system according to any one of claims 6 to 10, wherein: The auxiliary motor (M2) is dimensioned to allow only parking maneuvers of the vehicle.

12. A motor vehicle comprising a power-assisted steering system (1) according to any one of claims 6 to 11.

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