Power steering architecture without a mechanical link between the steering wheel and the vehicle's steering mechanism

Abstract

The invention relates to a method for controlling a power steering system (1) of a motor vehicle, the method comprising steps of: detecting an operating state of a steering actuator (SM1) coupled to a rack (8); when the steering actuator is operational, providing a torque command (TRQ) to a main motor (M1) of the steering actuator, by a first control unit (ECU1) of the steering actuator; when the steering actuator is faulty, but provides an angular position measurement (SAA) of the main motor, controlling, by a second control unit (ECU3), a brushless auxiliary motor (M2), coupled to the rack, as a function of the angular position measurement of the main motor and an angular position (HWA) of a steering wheel (2); and when the steering actuator is totally faulty, controlling the auxiliary motor as a function of the angular position of the steering wheel.Figure 2.

Description

Title of the invention: Power steering architecture without mechanical connection between the steering wheel and the vehicle steering mechanism Technical field

[0001] The present invention relates to the field of electric power steering for motor vehicles, and more particularly to SBW ("Steer by Wire") type power steering, i.e. without mechanical connection between the steering wheel and the steering mechanism of the vehicle. State of the art

[0002] An electric power steering device for a motor vehicle generally comprises a mechanical part comprising a steering wheel linked via a steering column and an intermediate shaft to a steering pinion meshing with a rack, slidably mounted in a steering casing. The two opposite ends of the rack are respectively linked, via connecting rods, to the right and left steered wheels of the vehicle. To assist the manual force exerted by the driver of the vehicle on the steering wheel, an electric power assistance actuator with two directions of rotation is coupled, via a speed reducer, to the mechanical steering connection between the steering column and the steered wheels of the vehicle, so as to transmit a motor torque (possibly also a resistive torque) of assistance to the steering column.The assistance actuator is controlled by an on-board electronic computer, which receives and processes various signals from sensors including a torque sensor exerted on the steering column by the driver of the vehicle.

[0003] In an SBW type electric assistance device, the steering wheel is not mechanically coupled to the rack 8, the steering of the vehicle being 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 decorrelated from the angular position of the wheels, which makes it possible to offer a large range of maneuver at low speed, in particular for parking maneuvers, and to limit the effects of the rotation of the steering wheel on the steering, at high speed.

[0004] However, in order to ensure safety objectives, a certain redundancy is necessary so that in the event of a failure of a part of the device, the driver can maintain control of the steering of the vehicle. To this end, it has already been proposed to have a clutch on the steering column allowing the mechanical connection between the steering wheel and the rack, in the event of failure of the actuator coupled to the rack. This solution does not allow the removal of the classic mechanical connection with its drawbacks to integrate it into the vehicle. It has also been proposed to implement two redundant motors for actuating the rack. Thus, if one of the motors fails, the other takes over. This architecture can easily be integrated into a vehicle, but offers security that may be considered insufficient because it does not allow overcoming a failure of the control electronics of the two motors. It has therefore also been proposed to implement two computers, each controlling one of the motors. However, this solution is relatively expensive.

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

[0006] Embodiments relate to a method for controlling a power steering system of a motor vehicle, the method comprising steps of: detecting an operating state of a steering actuator mechanically coupled to a first steering pinion engaged with a steering rack of the motor vehicle; when the steering actuator is operational, providing, by a first control unit of the steering actuator, a torque setpoint to a main motor of the steering actuator;when the steering actuator is faulty, but provides an angular position measurement of the main motor, controlling, by a second control unit, a brushless auxiliary motor, mechanically coupled to a second steering pinion meshed with the steering rack, using a closed-loop angle control function receiving the angular position measurement of the main motor and an angular position measurement of a steering wheel of the vehicle; and when the steering actuator is completely faulty, controlling the auxiliary motor by the second control unit, using an open-loop angle control function receiving the angular position measurement of the steering wheel. ;

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

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

[0009] Thus, 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, since the control unit of the force feedback actuator on the steering wheel is less prone to failure than the steering actuator.

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

[0011] In this way, the power circuit is located in a different area from the steering actuator. This prevents the steering actuator and the power circuit of the auxiliary engine from being subjected to the same constraints, whether climatic, mechanical or electromagnetic, which could lead to simultaneous malfunction of these components.

[0012] According to one embodiment, the method comprises steps of: when the steering actuator is faulty, mechanically coupling the auxiliary motor to the second steering gear using a clutch; and when the steering actuator is operational, mechanically decoupling the auxiliary motor from the second steering gear using the clutch.

[0013] The provision of such a clutch makes it possible to prevent the brushed motor from rotating when it is not activated. In this way, the brushes of the brushed motor only wear out when the latter is activated, that is to say in the rare periods when the steering actuator is faulty.

[0014] According to one embodiment, the method comprises steps consisting of: when the steering actuator is operational, providing, by the second control unit, a torque setpoint to the auxiliary motor in addition to the torque setpoint provided to the main motor of the steering actuator.

[0015] Embodiments may also relate to a power steering system for a motor vehicle, the system comprising: a steering actuator comprising a main motor mechanically coupled to a first steering pinion engaged with a steering rack of the motor vehicle, and a first control unit configured to control the main motor, a brushless auxiliary motor mechanically coupled to a second steering pinion engaged with the steering rack, and a second control unit configured to control the auxiliary motor by implementing the method defined previously.

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

[0017] According to one embodiment, the force feedback actuator comprises a first power circuit connected to the 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 circuit connected to the second control unit and to the auxiliary motor, to enable 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 gear, the clutch being controlled by the second control unit.

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

[0021] Embodiments may also relate to a motor vehicle comprising a power steering system as previously defined. Brief description of the figures

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

[0023] [Fig-1] Figure 1 is a schematic view of a conventional steering system motor vehicle assisted,

[0024] [Fig.2] Figure 2 is a schematic view of a power steering system of motor vehicle, according to one embodiment,

[0025] [Fig.3] Figure 3 schematically represents a functional architecture of a power steering system calculator, according to one embodiment,

[0026] [Fig.4] Figure 4 schematically represents a functional architecture of a power steering system calculator, according to another embodiment. Detailed description

[0027] Figure 1 shows a conventional motor vehicle steering system 1a equipped with an electric power assist device, according to the prior art. The power assisted steering device 1a, of the SBW ("Steer by Wire" type, comprises a steering column 3 coupled to a steering wheel 2, and two redundant actuators SMI 1, SM 12 mechanically coupled to a rack bar 8. Thus, the two actuators SMI 1, SM12 are mechanically coupled respectively to pinion shafts 7b, 7d. The pinion shafts 7b, 7d are mechanically coupled respectively to pinions 7a, 7c, in engagement with a rack bar 8 mounted on the rack bar 8. smoothing in a steering casing 9. The two opposite ends of the rack bar 8 are respectively connected, by means of connecting rods 10, to the right and left steering wheels 11 of the vehicle.

[0028] Each actuator SMI 1, SM12 comprises an electric assistance motor M with two directions of rotation, a DC control circuit of the motor M, and a speed reducer 5. The output shaft of the motor M is mechanically coupled, respectively to the pinion shafts 7b, 7d, via the speed reducer 5. Each actuator SMI 1, SM 12 also comprises a control unit (on-board electronic calculator) ECU which receives and processes various signals from sensors, in particular from a steering wheel angle sensor 13, and provides control signals to the DC control circuit of the motor M of the actuator. Each speed reducer 5 may be of the type comprising a worm screw comprising a worm shaft and a worm tangential wheel secured to one of the pinion shafts 7b, 7d.

[0029] The power steering system 1a further comprises a third actuator SM 13 coupled to the steering column 3 to provide the steering wheel 2 with a resistive or motor torque. This resistive or motor torque varies depending on various 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 power assist motor M with two rotation directions, a DC control circuit for the motor M, a speed reducer 5 coupled on one side to the motor M and on the other side to the steering column 3 (between a distal bearing of the steering column and the torsion bar 12), and an ECU control unit.

[0030] The SM 13 actuator ECU control unit is connected to the control units ECU control of the actuators SMI 1, SM12 and configured to control the motor M of the actuator SM 13 in order to provide force feedback on the steering wheel 2. In particular, the ECU control unit of the actuator SM 13 is configured to control the motor M of the actuator SM13, so as to transmit a resistive torque (possibly also a motor torque) to the steering column 3, proportional to the torque provided by the motors M of the actuators SMI 1, SM12.

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

[0032] Figure 2 shows a power steering device 1, according to one embodiment. The device 1 differs from the power steering device 1a in that the ac- donors SM11, SM12, SM13 are replaced by actuators SMI, SM2, SM3. The SMI actuator can be identical to the SMI actuator 1. On the other hand, the SM2 actuator which is coupled to the pinion shaft 7d comprises a motor M2. The motor M2 can be coupled to the pinion shaft 7d via a speed reducer 5-2. The SM3 actuator which is coupled to the steering column 3 via a reducer 5-3 comprises a control unit ECU3, a motor M3 and a control circuit DC3 allowing the control unit ECU3 to control the motor M3. The SM2 actuator is intended to be activated in the event of a failure of the SMI actuator.

[0033] The control unit ECU3 of the actuator SM3 is connected to the control unit ECU1 of the actuator SMI in particular to transmit to the latter measurement values ​​of a steering wheel angle HWA relative to a neutral position of the steering wheel 2, in redundancy with an angle measurement HWA carried out by the steering wheel angle sensor 13, directly transmitted to the control unit ECU1. The control unit ECU1 transmits to the processing unit ECU3 in particular one of the torque setpoint values ​​applied by the motor M1 to the pinion 7a.

[0034] According to one embodiment, the motor M2 is of the brush type, while the motors M1, M3 of the actuators SMI and SM3 are conventionally brushless motors. In addition, 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. For controlling the brushed motor M2, the circuit DC2 may simply comprise an H-bridge of MOSFET-type transistors.

[0035] Implementing a brushed motor is much less expensive than a brushless motor. Indeed, the control circuit DC2 of the brushed motor M2 is much less complex than the control circuit DC1 of the brushless motor M1 of the actuator SMI. Unlike brushless motors, a brushed motor does not require an angular position sensor to drive it. 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, for example, be installed in the actuator SM3 or near the steering wheel 2.This results in a reduction in the risk of malfunction of the SM2 and SMI actuators, as their respective control circuits do not use the same technologies and are not subject to the same constraints, whether climatic, mechanical or electromagnetic.

[0036] According to one embodiment, a clutch CH is interposed between the motor M2 and the speed reducer 5-2 of the actuator SM2. The clutch CH makes it possible to mechanically decouple the motor M2 from the shaft 7d when the actuator SM2 is not activated, and conversely mechanically couple the M2 motor to the 7d shaft upon activation of the SM2 actuator when the SMI actuator is faulty. The CH clutch can be controlled by the ECU3 control unit. Thus, the CH clutch prevents the M2 motor from rotating when the SM2 actuator is not activated, and therefore avoids increasing the inertia and friction of the system when the M2 motor is inactive, and also limits the wear of the M2 motor brushes.

[0037] Figure 3 shows functions of the control unit ECU3. The control unit ECU3 includes an open-loop angle control function AOC, a closed-loop angle control function ACC, a torque control function STC, and a CM switching function. The AOC and ACC functions receive the angle measurement signal HWA from the steering wheel angle sensor 13. The ACC function also receives an angular position signal of the ML motor from the control unit ECU1 of the SMI actuator. The STC function receives a target torque value signal TRQ from the control unit ECU1 of the SMI actuator. The TRQ value is proportional to the torque supplied by the ML motor. The CM switching function is controlled by a status signal SAS of the SMI actuator supplied by a self-diagnostic function of the SMI actuator. The status signal SAS can indicate one of the following states: State 1: The SMI actuator is fully operational, State 2: The SMI actuator is completely faulty, and State 3: The SMI actuator is faulty but reliably provides the angular position of the SMI actuator motor Ml to the ECU3 control unit.

[0038] In state 1, the SMI actuator is operational, and the motor M1 of the latter alone actuates the steering of the vehicle via the pinion 7a. In state 2, only the AOC function is active and the control unit ECU3 controls the motor M2 on the basis of the angle measurement signal HWA of the steering wheel 2 alone. The motor M2 then alone actuates the steering of the vehicle via the pinion 7c. In state 3, only the ACC function is active and the control unit ECU3 controls the motor M2 on the basis of the angle measurement signal HWA and the angular position SAA of the motor M1 by the SMI actuator. In states 2 and 3, the motor M2 alone actuates the steering of the vehicle via the pinion 7c. The motor M2 can be chosen with the sole objective of allowing the vehicle to be parked as quickly as possible in a safe place. It can therefore be sized to achieve much more limited performance than the ML engine

[0039] In state 2, the SMI actuator can provide a value of the angular position SAA of the motor M1, but this value is not used because it is not reliable.

[0040] In parallel with the AOC and ACC functions, the STC function controls the motor M3 to apply a resistive or motor torque to the steering column 3 and thus exert a force feedback on the steering column 3, depending on the torque setpoint value TRQ provided by the control unit ECU1 of the SMI control actuator, as long as this value is available. In this way, the driver can feel a torque when he has to turn the vehicle's steered wheels.

[0041] According to an embodiment illustrated by Figure 4, the actuator SM2 is activated to provide additional torque in combination with the torque provided by the actuator SMI in state 1 during specific maneuvers. In this case, the control circuit ECU1 is configured to issue a command to this effect to the control circuit ECU3. Thus, Figure 4 represents the functions of the control unit ECU3. The control unit ECU3 of Figure 4 differs from that of Figure 3 in that it further comprises a function STC1 which is activated in state 1 and which is configured to control the actuator SM2, in order to provide this additional torque in combination with the torque provided by the actuator SMI during specific maneuvers.

[0042] It will be clear to those skilled in the art that the present invention is susceptible to various variant embodiments and various applications. In particular, the invention is not limited to the realization of the control functions of the auxiliary motor M2 in the control unit ECU3 of the force feedback actuator SM3. Indeed, a specific control unit can be implemented to control the motor M2.

[0043] Although the installation of the power circuit DC2 in the force feedback actuator SM3 provides greater safety, this arrangement is not necessary. Furthermore, the power circuit can be arranged near the steering wheel outside the actuator SM3.

[0044] Furthermore, the provision of the CH clutch simply makes it possible to increase the operating time of the M2 motor without having to change the brushes. This arrangement may be useless if the operating time of the M2 motor without changing the brushes is greater than the average duration of use of the vehicle.

Claims

Claims

1. 1. A method for controlling a power steering system (1) of a motor vehicle, the method comprising steps consisting of: detecting an operating state of a steering actuator (SMI) mechanically coupled to a first steering pinion (7a) engaged with a steering rack (8) of the motor vehicle; when the steering actuator is operational, providing, by a first control unit (ECU1) of the steering actuator, a torque setpoint (TRQ) to a main motor (Ml) of the steering actuator;when the steering actuator is faulty, but provides an angular position measurement (SAA) of the main motor, controlling, by a second control unit (ECU3), a brushless auxiliary motor (M2), mechanically coupled to a second steering pinion (7c) meshed with the steering rack, using a closed-loop angle regulation function (ACC) receiving the angular position measurement of the main motor and an angular position measurement (HWA) of a steering wheel (2) of the vehicle; and when the steering actuator is completely faulty, controlling the auxiliary motor by the second control unit, using an open-loop angle regulation function (AOC) receiving the angular position measurement of the steering wheel.;

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

4. 4. Method according to one of claims 1 to 3, comprising steps consisting of: when the steering actuator (SMI) is faulty, mechanically coupling the auxiliary motor (M2) to the second steering pinion (7c) using a clutch (CH); and when the steering actuator is operational, mechanically decoupling the auxiliary motor from the second steering pinion using the clutch.

5. 5. Method according to one of claims 1 to 4, comprising steps consisting of: when the steering actuator (SMI) is operational, providing, by the second control unit (ECU3), a torque setpoint to the auxiliary motor (M2) in addition to the torque setpoint (TRQ) provided to the main motor (Ml) of the steering actuator.

6. 6. Power steering system for a motor vehicle, the system comprising: a steering actuator (SMI) comprising a main motor (Ml) mechanically coupled to a first steering pinion (7a) engaged with a steering rack (8) of the 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) engaged with the steering rack, and a second control unit (ECU3) configured to control the auxiliary motor by implementing the method according to one of claims 1 to 5.

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

9. System according to one of claims 7 and 8, in which the force feedback actuator (SM3) comprises a second power 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 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. System according to one of claims 6 to 10, in which the motor auxiliary (M2) is sized to only allow parking maneuvers of the vehicle.

12. Motor vehicle comprising a power steering system (1) according to one of claims 6 to 11.

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