Method for controlling a steering system having two redundant power supplies

Abstract

The present invention relates to a control method for controlling a steering system of an automobile having a power supply device with a first channel (12) and a second channel (12') arranged in parallel, each of which supplies an assist force to the steering system of the vehicle (2) to obtain the sum of two assist forces to be supplied corresponding to a desired total requested assist force (30). The method comprises the steps of: evaluating the channel of the power supply device with the lowest power supply voltage; defining a master channel function for supplying an initial portion of the total requested assist force and a slave channel function for supplying a variable complementary portion of the assist force corresponding to the difference between the initial portion (32) of the actually supplied force and the total requested force (30); associating the master channel function with the channel of the power supply device with the lowest power supply voltage and the slave channel function with the channel of the power supply device with the highest power supply voltage.

Description

[Technical field]

[0001] The present invention relates to a method for controlling a steering system of a motor vehicle, and to a steering system having means for implementing said control method. [Background technology]

[0002] Automobiles generally have a steering system with a motorization that provides an assist force to the steering of the vehicle in response to a total required assist force determined by the torque applied by the driver, measured by a driver intention sensor, to obtain part of the force required to turn the wheels. Hereinafter, the torque applied by the driver to the steering wheel is referred to as steering wheel torque.

[0003] The electric machines used in steering systems are generally of the "brushless" type. These electric machines have a particularly fast dynamic response, high efficiency, low wear and low noise. Furthermore, it is known that these electric machines are characterized by a no-load speed and a block rotor operating torque at a given supply voltage and temperature, between which the possible operating points of the electric machine are determined. A decrease in the supply voltage reduces the no-load speed and, as a result, changes the operating point of the electric machine.

[0004] The "brushless" type electric machine has a first operating mode, a "motor mode", in which the electric machine provides driving force to a rack-type steering member when the rotational speed of the electric machine is less than the no-load speed, at a given supply voltage and temperature.

[0005] The "brushless" type electric machine has a second operating mode, a "generator" mode, in which the electric machine applies a braking torque or force to the rack-type steering member when the rotational speed of the electric machine is greater than the no-load speed, at a given supply voltage and temperature.

[0006] Additionally, automobile manufacturers are currently developing autonomous driving features that allow the car to more or less automate some driving modes, such as automatically parking the car, navigating traffic jams, following the car ahead, and even fully autonomous driving. These various features use the steering system to turn the wheels, without the driver exerting any force to do so.

[0007] Therefore, the safety of operation of the steering system is important for both manual driving assistance functions and automated driving functions.

[0008] In order to meet the requirements of safety and usability of the steering system, it is common practice to arrange two electric machines in parallel, each with its own power supply available for a part of the total assist force required for steering. In particular, the electric machine arrangement has two independent and equivalent channels arranged in parallel with full redundancy, each with its own power supply and with different functions such as receiving signals from the vehicle, controlling the system and controlling the electric machines. Thus, the electric machines may operate independently and / or simultaneously.

[0009] When the electric machines are operated simultaneously, the two assist channels ensure that in normal operating mode they each provide the same assist force and the two channels are connected to the same working shaft, i.e. the rotating shaft of the electric machines, i.e. each channel provides a portion of the total required assist force. In normal operating mode, redundancy of the electric machine arrangement is guaranteed. Summary of the Invention [Problem to be solved by the invention]

[0010] However, in a vehicle with two independent power supply networks, the operating conditions may vary and affect the power supply of the two channels, which have different capabilities in providing assist power. This difference may cause one channel to interfere with the operation of the other. More specifically, the no-load speed of the channel with the lowest power supply voltage will decrease.

[0011] In this way, the electric machine in the channel with the lowest supply voltage may be forced to rotate at a speed greater than its no-load speed by the electric machine in the channel with the highest supply voltage, causing the electric machine to produce a braking torque and operate in generator mode.

[0012] This braking torque increases with the speed of rotation of the steering wheel, creating an unpleasant, even unstable, feeling in the steering wheel and reducing the overall efficiency of the electric machine, which then causes the two channels to operate in a reduced mode.

[0013] In this type of degraded operating mode, it is known to disconnect the electric machine of the channel with the lowest power supply. The electric machine of the channel with the highest power supply then supplies alone an assistance corresponding to the maximum total required assistance force. The driver's sensation then depends on the total power available from this channel alone. Assuming that each channel receives a maximum power of 50% of the total maximum required, there are very few situations during driving where the driver may have an undesirable sensation (a lack of power will be felt during parking maneuvers, even during very dynamic maneuvers). However, this solution leads to a loss of redundancy in the electromechanical device.

[0014] It is also known to reduce the supply voltage of the unaffected channel, i.e. the one with the higher supply voltage, in a reduced operating mode, so as to equalize the power supply of the two channels. This solution maintains the redundancy of the electromechanical device, but reduces the no-load speed of the electric machine and therefore the maximum assist force that the electric machine can provide to steer the vehicle. The total required assist force may not be obtained.

[0015] The present invention aims inter alia to avoid these disadvantages of the prior art. [Means for solving the problem]

[0016] To this end, the present invention comprises: 1. A method for controlling a steering system of a motor vehicle having electric machines with a first channel and a second channel arranged in parallel, each electric machine providing an assist force to a steering of the vehicle, to obtain a sum of two assist forces provided corresponding to a total required assist force, comprising: an evaluation step of evaluating the channel having the lowest power supply voltage of the electric machine; a definition step for defining a master channel function for providing an initial portion of the total requested assist force and a slave channel function for providing a variable complementary portion of the assist force corresponding to the difference between the initial portion of the force actually provided and the total requested force; a combining step of combining the master channel function with the channel having the smallest power supply voltage of the electric machine and combining the slave channel function with the channel having the largest power supply voltage of the electric machine; The present invention provides a control method comprising the steps of:

[0017] In the evaluation step, it is possible to determine which of the first and second channels has the lowest value of the supply voltage of the electric machine, and therefore which of the first or second channels has the lowest no-load speed, in other words, which of the first or second channels is most likely to switch to generator mode.

[0018] Also, the master channel function can be performed by the first channel and by the second channel respectively, and the slave channel function can be performed by the second channel and by the first channel respectively.

[0019] The combining step makes it possible to determine which channels will assume the master channel function and which channels will assume the slave channel function.

[0020] The first and second channels operate simultaneously to enable redundancy of the electromechanical device. More specifically, the first or each second channel performs a master channel function that provides an initial portion of the total requested assist force, and the second or each first channel provides a variable, complementary portion of the assist force to arrive at the total requested assist force based on an estimate or measurement of the force actually provided by the first or each second channel. The electric machines of the first and second channels operate at the same rotational speed, although each provides a different or identical portion of the total requested force.

[0021] In this way, in case of failure of the power supply of the electric machine of the first or second channel, the channel with the failed power supply becomes the master channel. The channel with the failed power supply thus provides an initial portion of the total requested force. This initial portion may be provided in full when the imposed speed is lower than the no-load speed of the master channel, or may correspond to an initial portion to be subtracted from the braking force when the imposed speed is higher than the no-load speed of the master channel. When the imposed speed is lower than the no-load speed of the master channel, the complementary portion provided by the second channel complements the initial portion to provide the entirety of the total requested assist force required, or when the imposed speed is higher than the no-load speed of the master channel, the second channel complements the initial portion by correcting the braking force to provide the entirety of the total requested assist force required.

[0022] Therefore, in the event of a failure in the power supply to a certain channel, redundancy is ensured and a large portion of the total required assist force is supplied.

[0023] The control method according to the present invention may additionally include one or more of the following features, which may be combined with each other.

[0024] The initial portion of the total demand force preferably corresponds to a portion of this total demand force.

[0025] In particular, the initial portion of the total demand force may correspond to the entirety of this total demand force, which simplifies the calculation of the initial portion.

[0026] According to one feature of the invention, the evaluating step is performed by detecting a braking torque corresponding to the path of either electric machine in generator mode.

[0027] According to one aspect of the invention, the evaluating step is performed by comparing the value of the power supply voltage for each channel.

[0028] This comparison allows the voltage deviation between the two channels to be determined.

[0029] According to one feature of the invention, the evaluating step includes determining a deviation threshold.

[0030] To limit the displacement of the master channel function and the slave channel function, a deviation threshold can determine the allowable deviation between the two channels, which deviation threshold may be a predefined fixed value or a variable value depending on the parameters under which the vehicle is running.

[0031] According to one aspect of the invention, the value of the supply voltage of the electric machine of each channel is determined using the power signal actually delivered by each channel.

[0032] According to one aspect of the invention, each channel provides an assist force equal to up to 50% of the total demand force.

[0033] The invention also relates to a steering system comprising means for implementing the method for controlling a steering system according to the invention.

[0034] In particular, the steering system may have two electric machines, each of which provides an assist force to the steering of the vehicle. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a diagram showing a steering wheel of a vehicle implementing the control method according to the present invention. [Diagram 2] FIG. 2 is a flow chart showing the operation of this control method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The invention will be better understood and other features and advantages will become more apparent from the following description, illustrated in relation to the accompanying drawings, in which:

[0037] FIG. 1 shows a steering box 2 having a rack-type control member arranged transversely on the vehicle and connected at both ends by tie rods 4 to the hubs 6 of the front wheels to pivot the hubs 6 to ensure steering of the vehicle.

[0038] A steering column equipped with a steering wheel 8, connected to the box 2 and operated by the driver, has a sensor of the force applied to the column by the driver, which sensor constitutes a device 10 for measuring the driver's intentions.

[0039] The two electric machines 12, 12' forming the first channel 12 and the second channel 12' each have a power supply and control means for independently applying an assist force to the steering box 2 in order to add all forces to those applied by the driver to the steering wheel 8, either to assist in manual driving or to perform automatic steering in automatic driving of the vehicle.

[0040] Each of the electric machines 12, 12' may comprise an electric motor providing a force, as described below, or alternatively any other electromagnetic means for applying a torque or force, in the form of rotation or translation, to the steering box 2. The action of the electric machines 12, 12' may then be referred to as either a torque or a force.

[0041] The control computer 16 is connected to the driver intent sensor 10 and the electric machines 12, 12' and to their power supplies in order to evaluate the channel with the lowest value of the power supply voltage, define the master channel and slave channel functions, and set the individual torque set points D1, D2 of each motor 12, 12', in particular depending on different parameters received from the outside 14.

[0042] 2 shows a device 10 for measuring the driver's intentions, including a force sensor applied by the driver to the steering column, which sends information to a measurement function 20 of the assist forces actually applied by each electric motor 12, 12'. The applied assist forces may in particular be the torques actually provided by each of the electric machines 12, 12' forming information received from an electric machine group 22 comprising these two electric machines.

[0043] An applied assist force measurement function 20 receives signals of the forces 31 actually provided by each channel of the electromechanical group 22 and sends the information to a total required assist force calculation function 24, where a calculation is performed based in whole or in part on the information provided thereto.

[0044] The total required assist force calculation function 24 sends the total required assist force forming the first signal 30 to a redundant element control function 26 composed of two electric machines 12, 12', determines the channel that will serve as the master channel function and the channel that will serve as the slave channel function, and calculates the assist force target value desired by each of the electric machines included in the electric machine group 22 by supplying them to each of the individual torque setting signals D1, D2.

[0045] The control system of each electric machine 12, 12' receives a respective desired torque set point signal D1, D2 for it and controls the power supply to its electric motor to provide a motor torque corresponding to that set point.

[0046] Each electric motor 12, 12' then sends information to a function 28 that estimates or measures the electric motor's ability to provide a torque corresponding to its respective set point D1, D2. The estimation or measurement function 28 provides the estimate or measurement forming a second signal 32 to the redundant element control function 26.

[0047] In this manner, the redundant element control function 26 has both the total required assist force 30 set by the assist force target calculation function 24 and takes into account an estimate or measurement of a second signal 32 representative of the ability of each electric machine 12 to supply its required torque in order to adjust the individual torque set point signals D1, D2 required from each of these electric machines 12.

[0048] In particular, the redundant element control function 26 incorporates in real time the operating characteristics of each electric machine 12, 12' in response to fluctuations in its condition in order to allocate the individual torque set points D1, D2 between the two electric machines 12, 12' to obtain a sum of supplied torques corresponding to a total required assist force 30.

[0049] The function 26 that controls the redundant elements receives a number of external parameters 14 and calculates individual torque set points D1, D2 with information from functions that estimate or measure the conditions of the electrical network of the vehicle 40, including in particular the voltage, current, and power that can be supplied by the network.

[0050] In this way, the redundant element control function 26 recognizes in real time the possibility that the power supplies of each of these electric machines 12, 12' may differ in the event of an imbalance in the power supply network, establishes channels carrying master channel functions and channels carrying slave channel functions, and sets individual torque set points D1, D2 corresponding to the torques that the electric machines can supply.

[0051] A function for setting a steering set point 42 to facilitate steering input provides a first parameter from the vehicle or an external source to the function 26 controlling the redundant elements.

[0052] A function 44 measuring the dynamic situation of the vehicle, for example a function measuring the vehicle's speed, the vehicle's lateral, longitudinal or vertical acceleration, or the vehicle's drift angle, supplies a second parameter to the function 26 controlling the redundant element.

[0053] The steps of the control method according to the present invention are as follows.

[0054] During the evaluation step, the redundant element functional part 26 determines the channel in which the supply voltage of the electric machine has the minimum value by detecting the braking torque corresponding to the path of one of the electric machines in generator mode and / or by comparing the value of the supply voltage of each channel with a predetermined deviation threshold value.

[0055] If the deviation in the values ​​of the power supply voltages of each electric machine is less than a predefined deviation threshold, it may be desirable to periodically reverse the functions performed by the electric machines, for example after each start-up in the vehicle, in order to use the two electric machines in the same way, thereby allowing for equal wear.

[0056] If the deviation in the values ​​of the power supply voltages of each electric machine is greater than a predetermined deviation threshold, the redundant element function 26 pairs the master channel function with the channel having the smallest power supply voltage of the electric machine and pairs the slave channel function with the channel having the largest power supply voltage of the electric machine.

[0057] Next, for example, the channel with the minimum power supply voltage of the electric machine is designated as the first channel 12.

[0058] Thus, in this example, the master channel functions are performed by the first channel and the slave channel functions are performed by the second channel.

[0059] In the following description, reference numbers are made to the embodiments.

[0060] The redundant element function 26 determines an individual torque set point D1 for the master channel 12 corresponding to an initial portion of the total requested assist force 30 and an individual torque set point D2 for the slave channel 12' corresponding to a complementary portion of the assist force corresponding to the difference between the initial portion of the force actually delivered and the total requested force.

[0061] When the rotational speed imposed on the master channel 12 is less than the no-load speed, the master channel 12 supplies an initial portion D1 corresponding to a predefined percentage of the total demand. In particular, this initial portion D1 may constitute a large portion of the total demanded assist force. The complementary portion D2 of the slave channel 12' is set taking into account a second signal 32 that includes the ability of the master channel 12 to supply its demanded torque. In this case, redundancy of the electromechanical device is ensured and the total demanded force is supplied.

[0062] When the rotational speed imposed on the master channel 12 is greater than the no-load speed, the master channel 12 is in generator mode. In generator mode the master channel supplies the initial part D1 and the braking torque. The complementary part D2 of the slave channel 12' is set taking into account the capacity of the master channel 12 to supply the requested torque and the generated braking torque. In this case, the redundancy of the electromechanical device is ensured and the supplied force is equal to the total requested force subtracted from the braking torque.

[0063] The two electric machines 12, 12' operate in a complementary manner to each other, so that unequal forces are required, without the need for synchronization between them.

[0064] In general, the method may operate with only one electric machine, or with two electric machines 12, 12' operating in complement to each other, provided that the supply voltages of the two channels are substantially equal.

[0065] In the case of operation with a single electric machine, the individual torque set point D1 of the master channel 12 is equal to the total demand force and the slave channel 12' remains unchanged with its set point D2 controlled at a low or zero value so as to instantly supply a variable complementary portion of the assist force which is automatically detected when the torque supply by the master channel 12 is insufficient.

[0066] The complementary action of the two electric machines can be used to provide the high power required by the driver, for example during high-speed maneuvers. In these rare driving situations, imperfections in the control of the electric machines, for example resulting in small perceptible vibrations, do not affect vehicle comfort.

Claims

[Claim 1] A control method for a steering system of an automobile having two electric motors (12, 12') arranged in parallel and supplying an assist force to a steering box (2), the method comprising the steps of: controlling the two electric motors (12, 12') as a first channel and a second channel, respectively, the method comprising the steps of: an evaluation step for evaluating which of the first and second channels has the smallest power supply voltage for the electric motor when the dynamic state or operating conditions of the vehicle change and a difference occurs between the power supply voltages of the first and second channels; a definition step for defining a master channel function for supplying an initial portion of the total requested assist force to be determined and a slave channel function for supplying a variable complementary portion of the assist force corresponding to the difference between the initial portion (32) of the force actually supplied and the total requested force (30); a combining step of combining the master channel function unit with the channel having the smallest power supply voltage for the electric motor among the first channel and the second channel, and combining the slave channel function unit with the channel having the largest power supply voltage for the electric motor among the first channel and the second channel; A control method comprising the steps of:

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