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

Abstract

To provide a SBW type electric power steering structure for a motor vehicle, capable of offering high fault tolerance while being low in a cost.SOLUTION: A method for controlling a power steering system of a motor vehicle, includes the steps of: when a steering actuator coupled to a rack of the power steering system of the motor vehicle can be operated, providing a torque set value to a main motor of the steering actuator, by a first control unit of the steering actuator; when the steering actuator is faulty, but provides a measured value of an angular position of the main motor, controlling, by a second control unit, a brushless auxiliary motor coupled to the rack, on the basis of measurement of the angular position of the main motor and an angular position of a steering wheel; and when the steering actuator has completely failed, controlling the auxiliary motor according to the angular position of the steering wheel.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to the field of electric power steering devices for automobiles, and more particularly to steer-by-wire (SBW) type power steering devices in which there is no mechanical connection between the steering wheel and the steering mechanism of the vehicle. [Background technology]

[0002] An electric power steering device for a motor vehicle generally includes a mechanical part with a steering wheel connected via a steering column and an intermediate shaft to a steering pinion that engages with a rack slidably mounted on a steering case. Both ends of the rack are connected to the left and right steered wheels of the vehicle via tie rods, respectively. To assist the force applied manually to the steering wheel by the driver of the vehicle, an electric assist actuator with two directions of rotation is coupled to the mechanical steering connection between the steering column and the steered wheels of the vehicle via a reducer to transmit an assisting motor torque (also considered as a resisting torque) to the steering column. This assist actuator is driven by an on-board computer, which receives and processes various signals from sensors, including in particular a sensor of the torque applied by the driver of the vehicle to the steering column.

[0003] In the SBW type electric power 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 structure makes it easier to integrate the steering system into the vehicle. Furthermore, the angular position of the steering wheel is not correlated with the angular position of the wheels, which makes it possible to provide a large amplitude of operation at low speeds, especially for parking operations, and to limit the effect of the rotation of the steering wheel on the steering at high speeds.

[0004] However, to ensure the achievement of the safety objectives, a certain redundancy is necessary so that the driver can continue to control the direction of the vehicle even if a part of the device fails. For this purpose, it has already been proposed to arrange a clutch in the steering column, making it possible to restore the mechanical connection between the steering wheel and the rack in case of failure of the actuator coupled to the rack. This solution does not allow the elimination of the traditional mechanical connection, which has disadvantages for integration in the vehicle. It has also been proposed to implement two redundant rack drive motors, so that if one of the motors fails, the other motor takes over. This structure, although easily integrated in the vehicle, offers only a safety that can be considered insufficient due to the fact that it is not possible to overcome the failure of the control electronics for the two motors. It has therefore also been proposed to implement two computers, each controlling one motor. However, this solution is relatively expensive.

[0005] It would therefore be desirable to be able to propose an electric power steering architecture for SBW vehicles that offers high fault tolerance whilst being low cost compared to prior art solutions. Summary of the Invention

[0006] An embodiment relates to a method of controlling a power steering system of a motor vehicle, the method including detecting an operational state of a steering actuator mechanically coupled to a first steering pinion engaged to a steering rack of the motor vehicle, providing a torque setpoint to a main motor of the steering actuator by a first control unit of the steering actuator when the steering actuator is operational, controlling by a second control unit a brushless auxiliary motor mechanically coupled to a second steering pinion engaged to the steering rack using a closed loop angle adjustment function that receives a measurement of the angular position of the main motor and a measurement of the angular position of a steering wheel of the motor vehicle when the steering actuator has failed but provides a measurement of the angular position of the main motor, and controlling by the second control unit the auxiliary motor using an open loop angle adjustment function that receives a measurement of the angular position of the steering wheel when the steering actuator has completely failed.

[0007] In this way, the necessary redundancy for vehicle steering control in a SBW power steering system is provided by the brush motor, which requires a much simpler and cheaper power circuit than that of a brushless motor. The use of a brush motor offers the possibility of moving the power circuit away from the brush motor, in particular locating the brush motor in an area away from the rack and therefore away from 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, there is no need to provide a separate control unit for the brush motor. This arrangement does not reduce safety during operation of the power steering, since the control unit of the actuator providing feedback to the force on the steering wheel is less susceptible 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 provided in a force feedback actuator coupled to the steering wheel.

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

[0012] According to one embodiment, the method further includes mechanically coupling the auxiliary motor to the second steering pinion using a clutch when the steering actuator is faulty, and mechanically decoupling the auxiliary motor from the second steering pinion using the clutch when the steering actuator is operable.

[0013] Providing such a clutch makes it possible to prevent the brush motor from rotating when it is not activated, so that the brushes of the brush motor only wear when the brush motor is activated, i.e., during the rare period when the steering actuator fails.

[0014] According to an embodiment, the method further comprises 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 when the steering actuator is operable.

[0015] An embodiment may 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 to 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 to the steering rack, and a second control unit configured to control the auxiliary motor by performing the method described above.

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

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

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

[0019] According to an 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 sized only to enable parking maneuvers of the vehicle.

[0021] The embodiment may relate to a motor vehicle equipped with a power steering system as described above. [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 attached drawings, in which identical reference signs correspond to structurally and / or functionally identical or similar elements, in which: [Figure 1] FIG. 1 is a schematic diagram of a conventional automobile power steering system. [Diagram 2] FIG. 2 is a schematic diagram of a power steering system for a motor vehicle, according to an embodiment. [Diagram 3] FIG. 3 illustrates a schematic diagram of a functional architecture of a computer of a power steering system according to an embodiment. [Figure 4] FIG. 4 shows a schematic diagram of a functional architecture of a computer of a power steering system according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIG. 1 shows a conventional automobile steering system 1a with an electrically-assisted device according to the prior art (see, for example, U.S. Pat. No. 7,900,742). The steer-by-wire (SBW) power steering device 1a includes a steering column 3 coupled to a steering wheel 2 and two redundant actuators SM11 and SM12 mechanically coupled to a rack bar 8. Thus, the two actuators SM11 and SM12 are mechanically coupled to pinion shafts 7b and 7d, respectively. The pinion shafts 7b and 7d are mechanically coupled to pinions 7a and 7c engaged with a rack bar 8 slidably mounted on a steering case 9. Both ends of the rack bar 8 are connected to left and right steered wheels 11 of the vehicle by connecting rods 10, respectively.

[0024] Each actuator SM11, SM12 comprises an electric assist motor M with two directions of rotation, a control circuit DC of the motor M, and a reducer 5. The output shaft of the motor M is mechanically coupled to the pinion shafts 7b, 7d, respectively, via the reducer 5. Each actuator SM11, SM12 also comprises a control unit (on-board computer) ECU, which receives and processes various signals from the sensors, in particular the steering wheel angle sensor 13, and supplies control signals to the control circuit DC of the actuator's motor M. Each reducer 5 can be of the type comprising a worm with a worm shaft and a worm wheel (roue tangente de vis sans fin) fixed to one of the pinion shafts 7b, 7d.

[0025] The power steering system 1a further comprises a third actuator SM13 coupled to the steering column 3 for supplying a resistive or motor torque to the steering wheel 2. 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 assist motor M with two directions of rotation, a control circuit DC for the motor M, a reducer 5 coupled on one side to the motor M and on the other side to the steering column 3 (between the distal bearing of the steering column and the torsion bar 12), and a control unit ECU.

[0026] The control unit ECU of the actuator SM13 is connected to the control units ECUs of the actuators SM11, SM12 and is configured to control the motor M of the actuator SM13 in order to provide force feedback to the steering wheel 2. In particular, the control unit ECU of the actuator SM13 is configured to control the motor M of the actuator SM13 to transmit a resistance torque (which may also be a motor torque) to the steering column 3 that is proportional to the torque provided by the motor M of the actuators SM11, SM12.

[0027] The force feedback provided by the actuator SM13 makes it possible to counteract the driver's movements on the steering wheel, the resistance torque varying inter alia as a function of the vehicle's speed. Thus, for example, at very low speeds, the resistance torque applied to the steering column 3 during a parking maneuver is small. In contrast, at higher speeds, this resistance torque is larger for safety reasons, preventing fast and large amplitude movements of the steering wheel.

[0028] FIG. 2 shows a power steering device 1 according to an embodiment. This 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 may be identical to the actuator SM11. On the other hand, the actuator SM2 coupled to the pinion shaft 7d comprises a motor M2. The motor M2 may be coupled to the pinion shaft 7d via a reducer 5-2. The actuator SM3 coupled to the steering column 3 via a reducer 5-3 comprises a control unit ECU3, a motor M3 and a control circuit DC3 that enables the control unit ECU3 to control the motor M3. The actuator SM2 is designed to be activated in case of failure of the actuator SM1.

[0029] The control unit ECU3 of the actuator SM3 is connected to the control unit ECU1 of the actuator SM1, and thereby transmits to the control unit ECU1, inter alia, the measured value HWA of the steering wheel angle relative to the neutral position of the steering wheel 2. This is done in addition to the angle measured value HWA obtained by the steering wheel angle sensor 13 and transmitted directly to the control unit ECU1, thereby obtaining redundancy. The control unit ECU1 transmits to the processing unit ECU3, inter alia, one of the setpoint values ​​of the torque applied by the motor M1 to the pinion 7a.

[0030] According to an embodiment, the motors M1, M3 of the actuators SM1 and SM3 are brushless motors, as is conventional, while the motor M2 is of the brushed type. Furthermore, the control unit ECU3 is arranged to control the motor M2 by means of a remote control circuit DC2, for example in the actuator SM3. For the control of the brush motor M2, the circuit DC2 may simply comprise an H-bridge circuit of MOSFET type transistors.

[0031] The implementation of a brush motor is much cheaper than that of a brushless motor. In fact, the control circuit DC2 of the brush motor M2 is much simpler than the control circuit DC1 of the brushless motor M1 of the actuator SM1. Unlike a brushless motor, the brush motor does not need 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, whereas 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 provided, for example, in the actuator SM3, i.e. close to the steering wheel 2. This reduces the risk of failure of the actuators SM2 and SM1, since the respective control circuits of the actuators SM2 and SM1 do not use the same technology and are not subject to the same constraints, whether climatic, mechanical or electromagnetic.

[0032] According to an embodiment, a clutch CH is interposed between the motor M2 of the actuator SM2 and the reducer 5-2. 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, to mechanically couple the motor M2 to the shaft 7d when the actuator SM2 is activated when the actuator SM1 is at fault. The clutch CH can be controlled by the control unit ECU3. The clutch CH thus prevents the motor M2 from rotating when the actuator SM2 is not activated, thus making it possible to prevent an increase in the inertia and friction of the system when the motor M2 is inactive and also to limit wear of the brushes of the motor M2.

[0033] Figure 3 shows the functions of the control unit ECU3. The control unit ECU3 comprises an open loop angle regulation function AOC, a closed loop angle regulation function ACC, a torque control function STC and a switching function CM. The functions AOC and ACC receive an angle measurement signal HWA from the steering wheel angle sensor 13. The function ACC also receives an angular position signal from the control unit ECU1 of the actuator SM1 from the actuator SM1. The function STC receives a set torque value signal TRQ from the control unit ECU1 of the actuator SM1. The value TRQ is proportional to the torque provided 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 of the actuator SM1. The status signal SAS is: State 1: Actuator SM1 is fully operational; State 2: Actuator SM1 has completely failed, and State 3: The actuator SM1 has failed but the actuator SM1 still reliably provides the angular position of the motor M1 to the control unit ECU3. The status may be any of the following:

[0034] In state 1, the actuator SM1 is operable and the motor M1 of the actuator SM1 alone steers the vehicle via the pinion 7a. In state 2, only the function AOC is active and the control unit ECU3 controls the motor M2 solely on the basis of the angle measurement signal HWA from the steering wheel 2. The motor M2 alone steers the vehicle via the pinion 7c. In state 3, only the function ACC is active and the control unit ECU3 controls the motor M2 solely on the basis of the angle measurement signal HWA and the angular position SAA of the motor M1 from the actuator SM1. In states 2 and 3, the motor M2 alone steers the vehicle via the pinion 7c. The motor M2 can be selected for the sole purpose of making it possible to park the vehicle as quickly as possible in a safe place. The motor M2 can therefore be dimensioned to achieve a much more limited performance than the motor M1.

[0035] In state 2, actuator SM1 may provide a value for the angular position SAA of motor M1, but this value is not used because it is unreliable.

[0036] In parallel with the functions AOC and ACC, the function STC controls the motor M3 to apply a resistive or motor torque to the steering column 3 depending on the torque setpoint TRQ given by the control unit ECU1 of the control actuator SM1, as long as the torque setpoint TRQ is available, and thus a force feedback to the steering column 3. In this way, the driver can feel a torque when he has to turn the steered wheels of the vehicle.

[0037] According to an embodiment shown in Fig. 4, the actuator SM2 is activated to provide an additional torque during the specific maneuver in combination with the torque provided by the actuator SM1 in state 1. In this case, the control circuit ECU1 is configured to issue commands for this purpose to the control circuit ECU3. Fig. 4 thus represents the functionality of the control unit ECU3. The control unit ECU3 of Fig. 4 differs from the control unit ECU3 of Fig. 3 in that it further comprises a function STC1, activated in state 1 and configured to control the actuator SM2, to provide this additional torque in combination with the torque provided by the actuator SM1 during the specific maneuver.

[0038] It is clear to a person skilled in the art that the present invention can be modified in many different ways and applied in many different ways. In particular, the present invention is not limited to the implementation of the control function of the auxiliary motor M2 in the control unit ECU3 of the force feedback actuator SM3. In fact, a specific control unit can be implemented for the control of the motor M2.

[0039] Providing the power circuit DC2 within the force feedback actuator SM3 provides additional safety, but this configuration is not required. Additionally, this power circuit may be located external to the actuator SM3, near the steering wheel.

[0040] Furthermore, the inclusion of the clutch CH makes it possible to easily extend the operating time of the motor M2 without the need to replace the brushes. If the operating time of the motor M2 without replacing the brushes is longer than the average period of use of the vehicle, it may be unnecessary to include the clutch CH.

Claims

1. A method for controlling a power steering system (1) of a motor vehicle, comprising the steps of: The method comprises: Detecting an operating state of a steering actuator (SM1) mechanically coupled to a first steering pinion (7a) engaged with a steering rack (8) of the vehicle; providing a torque setpoint (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 operable; controlling, by a second control unit (ECU3), a brushless auxiliary motor (M2) mechanically coupled to a second steering pinion (7c) engaged to the steering rack, using a closed loop angle adjustment function (ACC) receiving the angular position measurement of the main motor and an angular position measurement of a steering wheel (2) of the vehicle (HWA) when the steering actuator has failed but provides an angular position measurement of the main motor (SAA); controlling the auxiliary motor by the second control unit using an open loop angular control function (AOC) that receives a measurement of the angular position of the steering wheel when the steering actuator has completely failed; The method includes:

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

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

4. using a clutch (CH) to mechanically couple the auxiliary motor (M2) to the second steering pinion (7c) when the steering actuator (SM1) fails; mechanically decoupling the assist motor from the second steering pinion using the clutch when the steering actuator is operable; The method of any one of claims 1-3, further comprising:

5. 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 (M1) of the steering actuator (SM1) when the steering actuator (SM1) is operable; The method of any one of claims 1-4, further comprising:

6. A power steering system for an automobile, comprising: The power steering system includes: a steering actuator (SM1) comprising a main motor (M1) mechanically coupled to a first steering pinion (7a) engaged with a steering rack (8) of the 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; a second control unit (ECU3) configured to control the auxiliary motor by carrying out the method according to any one of claims 1 to 5. Power steering system.

7. a force feedback actuator (SM3) coupled to the steering wheel (2) and having the second control unit (ECU3); 7. The power steering system of claim 6.

8. 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 is configured to control the force feedback motor; 8. The power steering system of claim 7.

9. the force feedback actuator (SM3) comprises a second power circuit (DC2) connected to the second control unit (ECU3) and to the auxiliary motor (M2), enabling the second control unit to control the auxiliary motor; 9. A power steering system according to claim 7 or 8.

10. a clutch (CH) for mechanically connecting the auxiliary motor (M2) to the second steering pinion (7c); The clutch is controlled by the second control unit (ECU3). A power steering system according to any one of claims 6 to 9.

11. The auxiliary motor (M2) is sized only to enable parking operations of the vehicle. A power steering system according to any one of claims 6 to 10.

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

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