Sensing system for vehicle steering capable of measuring torque and multi-turn absolute steering wheel angle

Abstract

The present invention relates to a detection system for a steering mechanism, comprising: - a first angular position sensor (11) that measures the angle of an electric motor (3) and transmits a first signal; - a second angular position sensor (12) that measures the angle of the steering mechanism between a first side of a reduction gear (4) and a torsion bar (7) and transmits a second signal; - a third angular position sensor (13) that measures the angle of the steering mechanism on a second side of the torsion bar (7) and transmits a third signal; and a processing unit (15) that, on the one hand, performs a cursor calculation based on the first signal and the second signal in order to generate a first calculated signal #imgabs0# proportional to an absolute steering wheel angle (θ2) over more than one mechanical rotation and, on the other hand, performs an angular weighted sum of one of the signals obtained from the first signal, the second signal, and the first calculated signal #imgabs1# and the third signal in order to generate a second calculated signal #imgabs2# proportional to a torque (T).

Description

Technical Field

[0001] The invention relates in a general sense to the technical field of detection systems for measuring the torque and the multi-turn absolute steering wheel angle of a steering mechanism of a vehicle.

[0002] A preferred application of the invention relates to a detection system for measuring the torque and the multi-turn absolute steering wheel angle of a power steering mechanism of a vehicle.

[0003] Another application of the invention relates to a detection system for measuring the torque and the multi-turn absolute steering wheel angle of a steering mechanism of a vehicle, wherein the steering wheel is mechanically decoupled from the wheels. Background Art

[0004] Conventionally, power steering includes an electric motor equipped with a reduction gear that applies torque to assist the vehicle's steering mechanism (i.e., steering column or steering rack). The operation of the power steering mechanism requires knowledge of the intensity of the torque applied to the steering mechanism and the steering wheel angle or angle lock.

[0005] Typically, a vehicle's steering wheel is designed to rotate about one and a half turns to the left and right from a neutral point. In other words, the steering wheel can rotate about three turns from the left end to the right end. Therefore, the power steering must be equipped with an angle lock sensor that can detect an angle range greater than or equal to three turns (360 degrees x 3) in order to properly detect the angle lock. In addition, the steering wheel angle is also required for the operation of other functions of the vehicle (for example, electronic stability control, or new driver assistance functions).

[0006] Patent FR2964190 of MMT company proposes a device for magnetic detection of multi-turn absolute steering wheel angle, especially realizing magnet and magnetic sensitive probe. This detection device also needs a system (gear) for converting movement, which makes the detection device expensive.

[0007] Patent application EP3090921 of the company NSK describes a device for detecting the angle lock of a vehicle, the device comprising a vernier calculation section that performs a vernier calculation based on the angle of the steering shaft and the angle of the shaft of the auxiliary electric motor. The device also implements a section for determining a neutral period including a neutral point based on a reference angle calculated by the vernier calculation, and a section for specifying a neutral point that specifies the neutral point based on the neutral period and a stored neutral point value. The device allows determining the angle lock for multiple turns only after a training step, so that the device cannot learn the angle lock from start-up.

[0008] Patent FR2872896 of MMT describes a torque sensor that uses the angular deformation of a torsion bar of known stiffness. This differential angular deformation includes several magnetic concentrators, magnetic targets and Hall effect detection probes. The sensor is complex in design and only measures the angle between the input and output shafts. It does not provide information about the angles of the input and output shafts relative to the vehicle chassis.

[0009] Patent application DE102009039764 from BMW describes a detection system for measuring the torque and multi-turn absolute steering wheel angle of a steering mechanism of a vehicle, wherein the steering wheel is mechanically separated from the wheel. This steering mechanism, called "steer by wire", includes an electrical or hydraulic connection between the steering wheel and the wheel. An electric motor equipped with a reduction gear provides the drag torque to the steering mechanism. The document proposes measuring the steering wheel angle not only based on an angular position sensor, which measures the angle of the electric motor, but also based on an additional Hall effect probe, which detects the leakage magnetic flux of the magnetized target of the (MMT type) torque sensor and is located on the reduction gear side of the torsion bar. The use of conventional torque sensors leads to expensive detection systems, and the robustness of the position sensor measuring the leakage magnetic flux has not yet been proven.

[0010] The purpose of the present invention is to remedy the drawbacks of the prior art and to propose a new detection system for the steering mechanism of a vehicle, allowing the measurement of torque and absolute steering wheel angle over more than one mechanical rotation without adding additional gears and without implementing a training phase, and comprising a simpler and less burdensome position sensor than the prior art. Summary of the invention

[0011] To achieve this aim, the subject of the invention relates to a new detection system for a steering mechanism of a vehicle comprising a torsion bar and equipped with an electric motor provided with a reduction gear, which detection system allows measuring the torque and the absolute steering wheel angle over more than one mechanical rotation.

[0012] According to the present invention, the detection system comprises:

[0013] a first angular position sensor having N1 polar pairs, wherein N1 is an integer greater than or equal to 1, which first angular position sensor measures the angle of the electric motor and delivers a first signal;

[0014] a second angular position sensor having N2 polar pairs, wherein N2 is an integer greater than or equal to 1, the second angular position sensor measuring the angle of the steering mechanism between the reduction gear and the first side of the torsion bar, the second angular position sensor delivering a second signal;

[0015] a third angular position sensor having N3 polar pairs, wherein N3 is an integer greater than or equal to 1, which measures the angle of the steering mechanism located on a second side of the torsion bar, the second side of the torsion bar being opposite to the first side, and transmits a third signal;

[0016] - and a processing unit which, on the one hand, performs a vernier calculation based at least on the first signal and the second signal to generate a first calculation signal proportional to the absolute steering wheel angle over more than one mechanical rotation, and on the other hand performs an angle-weighted summation of one of the signals obtained from the first signal, the second signal and the first calculation signal with a third signal to generate a second calculation signal proportional to the torque.

[0017] The device according to the invention also comprises one and / or another of the following additional features in combination:

[0018] - the processing unit considers that the first calculated signal corresponds to an absolute steering wheel angle over more than one mechanical rotation and that the second calculated signal corresponds to an applied torque;

[0019] The processing unit performs a cursor calculation to generate a first calculation signal, the first calculation signal being:

[0020]

[0021] Where Θ = f s (p1α1+p2α2)

[0022] And, f S is a mathematical sawtooth function with a slope equal to 1, wherein q1 and q2 are selected as fixed weighting coefficients, and α1 is a signal generated by the first angular position sensor, and α2 is a signal generated by the second angular position sensor;

[0023] And among them, p1, p2 and N turns are numerical coefficients that are selected and must satisfy the following conditions:

[0024]

[0025] where Δθ2 is the peak-to-peak change in absolute steering wheel angle over more than one mechanical revolution, and R red is the reduction ratio of the reduction gear;

[0026] Advantageously, the weighting coefficients q1 and q2 may be chosen to be equal to:

[0027] If N2 <N1R Red ,but

[0028]

[0029] If N2>N1R red ,but

[0030]

[0031] Where σ1 is the typical magnitude of the error of the first angular position sensor, and σ2 is the typical magnitude of the error of the second angular position sensor.

[0032] According to another variant embodiment, the processing unit performs a cursor calculation to generate a first calculation signal The first calculation signal is:

[0033]

[0034] in,

[0035] -

[0036] -

[0037] -

[0038] -

[0039] And, f s is a mathematical sawtooth function with slope equal to 1, where pgcd is the "greatest common denominator" operator, where and is selected as a fixed weighting coefficient, and α1 is a signal generated by the first angular position sensor, α2 is a signal generated by the second angular position sensor, and α3 is a signal generated by the third angular position sensor;

[0040] And among them, c2, c3, and are numerical coefficients that are selected and must satisfy the following conditions:

[0041]

[0042] and where Δθ2 is the peak-to-peak change in absolute steering wheel angle over more than one mechanical revolution, and R red is the reduction ratio of the reduction gear;

[0043] According to a first variant embodiment, the second calculation signal is:

[0044]

[0045] Among them, f Sis a mathematical sawtooth function with a slope equal to 1, α2 is the signal generated by the second angular position sensor, α3 is the signal generated by the third angular position sensor, and G is the stiffness of the torsion bar, and wherein k2, k3 are numerical coefficients that are selected and must satisfy the following conditions:

[0046]

[0047] Among them, Δθ Shift is the peak-to-peak variation in the angular deformation of the torsion bar;

[0048] According to a second variant embodiment, the second calculation signal is:

[0049]

[0050] Among them, f S is a mathematical sawtooth function with a slope equal to 1, α1 is the signal generated by the first angular position sensor, α3 is the signal generated by the third angular position sensor, and G is the stiffness of the torsion bar, and wherein k1, k3 are numerical coefficients that are selected and must satisfy the following conditions:

[0051]

[0052] Among them, Δθ shift is the peak-to-peak variation in the angular deformation of the torsion bar;

[0053] According to a third variant embodiment, the second calculation signal is:

[0054]

[0055] Among them, f s is a mathematical sawtooth function with a slope equal to 1, is the first calculated signal, α3 is the signal generated by the third angular position sensor, and G is the stiffness of the torsion bar, and wherein k3 is a numerical coefficient that is selected and must satisfy the following conditions:

[0056]

[0057] Among them, Δθ shift is the peak-to-peak variation in the angular deformation of the torsion bar;

[0058] - the processing unit verifies whether the set of measured signals and calculated signals belongs to a set of acceptable values, and transmits an alarm signal when the set of values ​​does not belong to the set of acceptable values;

[0059] - the first angular position sensor, the second angular position sensor and / or the third angular position sensor is a Hall effect position sensor, a magnetoresistive sensor, a fluxgate sensor, an inductive sensor, an eddy current sensor or a variable reluctance sensor or a combination of sensors;

[0060] The second angular position sensor and the third angular position sensor are eddy current position sensors comprising a common detection probe comprising a common support plate for the windings of the second angular position sensor and the third angular position sensor.

[0061] Another subject of the invention relates to a steering mechanism equipped with a detection system according to the invention, which implements a steering command as a function of the absolute steering wheel angle and the applied torque over more than one mechanical rotation. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Various other characteristics will become apparent from the following description given with reference to the accompanying drawings which illustrate, by way of non-limiting example, forms of embodiment of the subject matter of the invention.

[0063] Figure 1 is a diagram showing a detection system according to the invention, which allows measuring the torque of a steering mechanism of a vehicle and the absolute steering wheel angle over more than one mechanical rotation.

[0064] Figures 2 to 4 is a block diagram showing three alternative embodiments for calculating the applied torque.

[0065] Figure 5 The shapes of the signals delivered by the three angular position sensors implemented by the detection system according to the invention are shown as a function of the steering wheel angle (in degrees) and for the maximum torque applied.

[0066] Figure 6 A first calculated signal proportional to the absolute steering wheel angle over more than one mechanical rotation is shown for different torque values

[0067] Figure 7 The second calculated signal proportional to the torque is shown for different values ​​of the steering wheel angle

[0068] Figure 8 and Fig. 9 are diagrams showing two variant embodiments of the second sensor and the third sensor in the form of eddy current position sensors. DETAILED DESCRIPTION

[0069] from Figure 1More precisely, the subject of the invention relates in a general sense to a detection system 1 that allows measuring a torque T and an absolute steering wheel angle θ2 over more than one mechanical rotation of a steering mechanism 2 of a vehicle. According to a preferred exemplary application that will be described in the remainder of the description, the detection system 1 makes it possible to measure a torque and an absolute steering wheel angle over multiple rotations of a power steering mechanism of a vehicle. Of course, the detection system 1 is also suitable for measuring a torque and an absolute steering wheel angle over multiple rotations of a steering mechanism of a vehicle, wherein the steering wheel is mechanically separated from the wheels.

[0070] The steering mechanism 2 includes an electric motor 3 provided with a reduction gear 4, the reduction gear 4 having a reduction ratio R red The electric motor 3 applies torque to the steering mechanism of the vehicle (in the example shown, the steering column 5), which is provided with a steering wheel 6. Conventionally, the steering wheel 6 can be rotated about three times from the left end to the right end. The electric motor 3 applies auxiliary torque to the steering mechanism of the vehicle in the case of power steering, and applies drag torque to the steering mechanism of the vehicle in the case of mechanical separation of the steering wheel and the wheel during steering.

[0071] Of course, the reduction gear 4 may apply assist torque to a steering rack, which is not shown and is used to turn the wheels.

[0072] The steering mechanism 2 also comprises a torsion bar 7 mounted on a steering column 5 in the illustrated example, the steering column 5 being located between the reduction gear 4 and the steering wheel 6. The torsion bar 7 is made in any suitable manner to allow the torque applied to the steering mechanism to be measured by angular deformation. The torque T applied to the torsion bar 7 is the first quantity to be measured.

[0073] According to the invention, the detection system 1 comprises a first angular position sensor 11 having N1 polar pairs, wherein N1 is an integer greater than or equal to 1. The first angular position sensor 11 measures the angle θ1 of the rotor of the electric motor 3 and delivers a first signal α1. It should be noted that the first angular position sensor 11 can generally be used in auxiliary steering mechanisms, since it allows the electric motor 3 of the auxiliary steering mechanism to be controlled.

[0074] The detection system 1 includes a second angular position sensor 12 having N2 poles, where N2 is an integer greater than or equal to 1. The second angular position sensor 12 measures the angle θ2 of the steering mechanism between the reduction gear 4 and the first side of the torsion bar 7 (i.e., the side opposite to the steering wheel 6). The angle θ2 of the steering mechanism is located between the reduction gear 4 and the torsion bar 7, i.e., upstream of the torsion bar. The second angular position sensor 12 transmits a second signal α2. It should be noted that the second angular position sensor 12 measures the angle θ2 of the steering mechanism relative to the vehicle chassis.

[0075] The fact of choosing an integer number N2 of antipodes greater than or equal to 1 allows a simple and inexpensive design of the second sensor. A consequence of this is that the second signal α2 is not absolute over more than one mechanical rotation.

[0076] As will be explained in the remainder of the description, the detection system 1 aims at determining a reference steering wheel angle which conventionally corresponds to an absolute steering wheel angle θ2 over more than one mechanical revolution. This multi-turn absolute steering wheel angle θ2 is the second quantity to be measured.

[0077] The detection system 1 comprises a third angular position sensor 13 having N3 poles, wherein N3 is an integer greater than or equal to 1. The third angular position sensor 13 measures the angle θ3 of the steering mechanism located on the second side of the torsion bar 7 (i.e., opposite to the first side of the torsion bar 7). The third angular position sensor 13 is mounted on a portion of the steering column directly associated with the steering wheel 6, and measures the angle of the steering wheel downstream of the torsion bar 7 in a non-absolute manner. The third angular position sensor 13 transmits a third signal α3. It should be noted that the third angular position sensor 13 measures the angle θ3 of the steering relative to the vehicle chassis.

[0078] According to the present invention, a mathematical function f is defined s , which is a mathematical sawtooth function with a slope equal to 1, and when the input data is zero, the value of the function is zero. The mathematical function f s This allows to convert an angle defined in degrees to an angle between -180° and 180° (-180° and 180° are not included):

[0079] f s ∶x→((x+180)mod360)-180

[0080] where mod is the modulus operator that gives the remainder of a division. The function f s is a sawtooth function with slope equal to 1, between -180° and 180° (-180° and 180° are not included), and crosses zero when x is equal to zero. By convention, this document uses angles defined in degrees, but it is possible to define the same function using other angular units. For example, the function f that converts any angle defined in radians to an angle between -π and π (-π and π are not included) is s Defined by:

[0081] f s ∶x→((x+π)mod2π)-π

[0082] Alternatively, when the function f s When defined in terms of angles in radians, the function f s can also be defined in a completely equivalent way by:

[0083] f s ∶x→atan2(sin(x),cos(x))

[0084] Wherein sin and cos are conventional trigonometric functions, and where atan2 is a function that gives the angular coordinates of a point in the Euclidean plane, defined between -π and π (-π and π are not included).

[0085] Of course, other units, such as the number of digits, may be used.

[0086] The angular deformation of the torsion bar 7 is represented by θ shift Angular deformation θ shift The relationship between and torque T is:

[0087]

[0088] Here, G is the stiffness of the torsion bar 7 .

[0089] By convention, the angle θ2 is considered to represent the reference steering wheel angle. According to the previous content, the independent mechanical angles θ2, θ shift The mathematical relationship between and the subordinate mechanical angles θ1, θ3 can be modeled as follows:

[0090] θ1=R red θ2

[0091] θ3=θ2+θ shift

[0092] The reference steering wheel angle θ2 to be measured has a peak-to-peak variation denoted as Δθ2. The torque to be measured has a peak-to-peak variation denoted as ΔT. This means that the angular deformation of the torsion bar 7 to be measured has a peak-to-peak variation denoted as Δθ which is equal to ΔT / G. shift .

[0093] The first signal α1, the second signal α2 and the third signal α3 generated by the first angular position sensor 11, the second angular position sensor 12 and the third angular position sensor 13, respectively, are equal to:

[0094] α1=f s (N1·θ1)

[0095] α2=f s (N2.θ2)

[0096] α3=f s (N3.θ3)

[0097] From the foregoing it follows that each of the signals α1, α2 and α3 is contained in the interval [-180°; 180°], which is generally not the case for the mechanical angles θ1, θ2, θ3.

[0098] It is also important to note that the invention is not limited to the angular position sensors 11, 12, 13 explicitly transmitting the signals α1, α2, α3 to the processing unit 15. Typically, in the context of a physical embodiment, the angular position sensors 11, 12, 13 transmit the information items α1, α2, α3 in coded form in order to facilitate the transmission and optimize the robustness of these signals with respect to noise and any interference sources. For example, the signal α may be transmitted in two signals S sin and S cos The two signals S sin and S cos Defined by the following equation:

[0099]

[0100] Where A is the amplitude of the signal. Of course, the processing unit 15 must then process the signal S sin and S cos Decoding is performed in order to retrieve the signal α. In the previous example, decoding is done as follows:

[0101]

[0102] where atan2 is a function that gives the angular coordinates of a point in the Euclidean plane, defined between -π and π (-π and π are not included).

[0103] According to the present invention, the detection system 1 further comprises a processing unit 15 which receives the first signal α1, the second signal α2 and the third signal α3 and is configured to perform calculations to generate a first calculation signal proportional to the absolute steering wheel angle θ2 over more than one mechanical rotation. and a second calculated signal proportional to the applied torque T The processing unit 15 is implemented by any programmed computer system and configured to perform the processing and computing operations according to the present invention.

[0104] The processing unit 15 performs a cursor calculation based on at least the first signal α1 and the second signal α2 to generate a first calculation signal proportional to the absolute steering wheel angle over more than one mechanical rotation. On the other hand, the first signal α1, the second signal α2 and the first calculated signal One of the signals obtained in the above method is angle-weighted summed with the third signal α3 to generate a second calculated signal proportional to the torque T.

[0105] According to a first variant embodiment, the processing unit 15 performs a cursor calculation to generate a first calculation signal The first calculated signal for

[0106]

[0107] in,

[0108] -Θ=f s (p1α1+p2α2)

[0109] -f s is the mathematical function defined previously,

[0110] -q1 and q2 are fixed weighting coefficients that the designer can choose to minimize sensor errors. The simplest choice (q1=0, q2=0) defines a signal that is not always the best in terms of suppressing noise and measurement errors. There are many other possible choices, such as (q1 = 0, q2 = 1 / (N2N turns )) or (q1=1 / (N1R red N turns ), q2=0). In general, the best choice of coefficients q1 and q2 depends on the accuracy of the two angular position sensors 11, 12 used for the Vernier effect.

[0111] α1 is a signal generated by the first angular position sensor 11, α2 is a signal generated by the second angular position sensor 12;

[0112] Parameters p1, p2, and N turns are numerical coefficients that are chosen by the designer and must satisfy the following conditions:

[0113]

[0114] where Δθ2 is the peak-to-peak change in absolute steering wheel angle over more than one mechanical revolution, and R red is the reduction ratio of the reduction gear 4.

[0115] It should be noted that the parameter N turns has a physical meaning. It corresponds to the first calculated signal On it will be a bijection of the number of mechanical steering wheel turns. Therefore, there is a constraint N turns ≥Δθ2 / 360, which means that the first calculated signal The linear peak-to-peak variation in must be at least as large as the peak-to-peak variation in the measurand defined by the applicable specification. In addition, N turns Does not have to be an integer.

[0116] It should be understood that the subject matter of the present invention uses the Vernier effect technique to construct a first calculated signal of the steering wheel angle

[0117] Another important point to note is that to have multiple mechanical turns (N turns >1)) The sensor for the absolute steering wheel angle must have a non-integer reduction ratio R red This can be understood using the constraints already defined above:

[0118] Among them, N1, p1, N2, p2 are integers when N turns > 1, it can be seen that the only way to satisfy this constraint is to have a non-integer reduction ratio R red This is usually the case in power steering. In order to remain absolute over several steering wheel turns (once the system is powered on), current steering wheel angle sensors use gears to be able to distinguish mechanical turns. These additional gears are expensive. Thanks to the proposed invention, it is possible to manufacture a multi-turn sensor without adding any gears, since the subject of the invention reuses the gears of the reduction gear 4 of the electric motor 3 that are already available.

[0119] According to an advantageous variant, the optimal values ​​of the weighting coefficients q1 and q2 are as follows:

[0120] If N2 <N1R red ,but

[0121]

[0122] If N2>N1R red ,but

[0123]

[0124] Where σ1 is the typical magnitude of the error of the first angular position sensor, and σ2 is the typical magnitude of the error of the second angular position sensor.

[0125] According to a second variant embodiment, the first signal is calculated based on the signals α1, α2 and α3. As shown below. First, calculate the intermediate signal As shown below:

[0126]

[0127] in,

[0128]

[0129] Where pgcd is the "greatest common denominator". Parameters c2 and c3 are numerical coefficients chosen by the designer and must satisfy the following conditions:

[0130]

[0131] It can be shown that the intermediate signal has the same absolute measurement error (in geometric degrees) as signal α2, but has a smaller periodicity (equal to N2) than that of signal α2. 23 ). In other words, the use of signal α3 makes it possible to reduce the relative measurement error (in electrical degrees) of α2, since its periodicity is reduced. Thanks to this improvement, it is actually simpler in the second step to compare α1 with Instead of combining with α2 to obtain This calculation is defined as follows:

[0132]

[0133] in,

[0134]

[0135] in, and are fixed weighting factors that the designer can choose to minimize the sensor error. The simplest option is Defines signals that are not always optimal in terms of rejecting noise and measurement errors Function. Parameters and is a numerical coefficient chosen by the designer and must satisfy the following conditions:

[0136]

[0137] where Δθ2 is the peak-to-peak change in absolute steering wheel angle over more than one mechanical revolution, and R red is the reduction ratio of the reduction gear 4.

[0138] When all of the above conditions are met for a given embodiment, for the closest measurement error and the closest slope sign, it can be shown that the first calculated signal is equal to the absolute steering wheel angle θ2 over one mechanical rotation, i.e.

[0139]

[0140] The processing unit 15 obtains the angle-weighted sum of the different available signals to generate a second calculated signal proportional to the torque T The angle-weighted sum of the signals is a linear combination of the signals, wherein the final result is placed in the interval [-180; 180°] (or in the interval [-π; π] depending on the choice of the angular unit).

[0141] The processing unit 15 obtains the third signal α3 and the first signal α1, the second signal α2 and the first calculated signal Angle-weighted summation of one of the signals obtained in .

[0142] according to Figure 2 In the first variant embodiment shown, the second calculation signal is calculated based on the third signal α3 and the first signal α1. The second calculated signal for:

[0143]

[0144] Among them, f s is the aforementioned mathematical sawtooth function with a slope equal to 1, α1 is the signal generated by the first angular position sensor 11, α3 is the signal generated by the third angular position sensor 13, and G is the stiffness of the torsion bar 7, and wherein k1, k3 are numerical coefficients selected by the designer and must satisfy the following conditions:

[0145]

[0146] Among them, Δθ shift is the peak-to-peak variation in the angular deformation of the torsion bar 7 .

[0147] according to Figure 3 In the second variant embodiment shown, the second calculated signal is calculated based on the third signal α3 and the second signal α2. The second calculated signal for:

[0148]

[0149] Among them, f s is the aforementioned mathematical sawtooth function with a slope equal to 1, α2 is the signal generated by the second angular position sensor 12, α3 is the signal generated by the third angular position sensor 13, and G is the stiffness of the torsion bar 7, and wherein k2, k3 are numerical coefficients selected by the designer and must satisfy the following conditions:

[0150]

[0151] Among them, Δθ shift is the peak-to-peak variation in the angular deformation of the torsion bar 7 .

[0152] according to Figure 4The third variant embodiment shown is based on the third signal α3 and the first calculation signal To calculate the second calculation signal The second calculated signal for:

[0153]

[0154] Among them, f s is the aforementioned mathematical sawtooth function with a slope equal to 1, is the first calculated signal, α3 is the signal generated by the third angular position sensor 13, and G is the stiffness of the torsion bar 7, and wherein k3 is a numerical coefficient selected by the designer and must satisfy the following conditions:

[0155]

[0156] Among them, Δθ shift is the peak-to-peak variation in the angular deformation of the torsion bar 7 .

[0157] When all the above conditions are met (for a given variant embodiment), for the closest measurement error and the closest slope sign, it can be shown that the second calculated signal is equal to the applied torque, or:

[0158]

[0159] It is obvious from the foregoing description that the torque and the reference steering wheel angle are determined by "physical" sensors of the torque and steering wheel angle. Specifically, the absolute steering wheel angle θ2 over more than one mechanical rotation is determined based on the first signal α1 generated by the first angular position sensor 11 and the second signal α2 generated by the second angular position sensor 12, while the absolute steering wheel angle θ2 over more than one mechanical rotation is determined based on the third signal α3 generated by the third angular position sensor 13 and the first signal α1, the second signal α2 and the first calculated signal α2. The applied torque T is determined by one of the signals obtained in .

[0160] The first angular position sensor 11, the second angular position sensor 12 and the third angular position sensor 13 are any type of angular position sensors known per se having Ni polar pairs (Ni is an integer greater than or equal to 1). For example, the first angular position sensor 11, the second angular position sensor 12 and / or the third angular position sensor 13 are Hall effect position sensors, magnetoresistive sensors, fluxgate sensors, inductive sensors, eddy current sensors or variable magnetoresistive sensors or a combination of sensors.

[0161] The complex and expensive sensor of the prior art is replaced by a much simpler angular position sensor and a specific signal processing. This replacement has been made possible by the judicious reuse of the first signal of the first angular position sensor 11, which is already available on most power steerings, and which ensures the control of the electric motor 3 of the power steering mechanism, and also by the judicious reuse of the reduction gear of the electric motor, which is already available on all power steerings. Furthermore, the detection system 1 according to the invention does not require any initialization at start-up and does not require any continuous control system. As soon as the angular position sensor is powered on, the first calculated signal and the second calculated signal are available. The two calculated signals can be obtained without first moving the steering mechanism.

[0162] Figures 5 to 7 The subject matter of the invention is illustrated by performing numerical calculations according to the above principles using the following dimensions: Δθ2 = 1000° mec, ΔT = 21 N.m, G = 3 N.m / °, R red =61 / 3,N1=1,N2=10,N3=20,p1=1,p2=-2,N turns =3, k2 = -2, k3 = 1, q1 = 0, q2 = 0. The second variant embodiment has been used for the calculation of the torque.

[0163] Figure 5 Shown are the forms of the first signal α1 , the second signal α2 and the third signal α3 respectively generated by the three angular position sensors 11 , 12 , 13 as a function of the reference steering wheel angle in an ideal situation without noise and measurement errors.

[0164] Figure 6 shows a first calculated signal proportional to the absolute steering wheel angle over more than one mechanical rotation for different torque values The first calculated signal It depends linearly on the absolute steering wheel angle θ2 over more than one mechanical revolution and is completely insensitive to torque.

[0165] Figure 7 shows the second calculated signal proportional to the torque for different values ​​of the steering wheel angle The second calculated signal Depends linearly on the applied torque T and is completely insensitive to the steering wheel angle.

[0166] This numerical model makes it possible to demonstrate that the first calculated signal and the second calculated angle correspond to the absolute steering wheel angle θ2 and the applied torque T, respectively, over more than one mechanical revolution.

[0167] It should be noted that these figures show simulations performed in the absence of noise. Other simulations have been performed in the presence of noise. These simulations have shown that the present invention is robust to such noise, including at mechanical angles where the first sawtooth signal α1, the second sawtooth signal α2, and the third sawtooth signal α3 have discontinuities. That is, the noise present at the input is transmitted at the output without being substantially amplified. With a judicious choice of the weighting coefficients q1 and q2, the use of the vernier effect can even greatly improve the signal-to-noise ratio at the output.

[0168] It should be understood that the detection system according to the invention is designed based on input data from the specification for each envisaged application. Thus, the peak-to-peak variations Δθ2 and ΔT of the steering wheel angle and torque correspond to the range of the measurement system required by the specification. Of course, these input data may have different values ​​depending on the desired application.

[0169] According to a particularly advantageous embodiment, the processing unit 15 verifies whether the set of measured and calculated signals belongs to a set of acceptable values. If this is not the case, the processing unit 15 transmits an alarm signal when the set of measured and calculated signals does not belong to the set of acceptable values. This approach makes it possible to detect abnormally large measurement errors of certain categories. For example, the processing unit can calculate the following signal D:

[0170]

[0171] Based on the design parameters, the following threshold D can be defined lim :

[0172]

[0173] Where λ is a fixed coefficient between 0 and 1, chosen by the designer, and allows the severity of the diagnostic system to be adjusted. Thus, if the processing unit detects the following events at any time:

[0174] D>D lim

[0175] The processing unit 15 then transmits an alarm signal.

[0176] According to a variant embodiment, the second angular position sensor 12 and the third angular position sensor 13 are eddy current position sensors. Figure 8 The second angular position sensor 12 and the third angular position sensor 13 are exemplarily shown as being arranged on either side of the torsion bar 7. Each angular position sensor 12, 13 comprises, on the one hand, a target piece 121, 131 respectively firmly mounted on each side of the torsion bar 7, and a detection probe 122, 132 respectively placed outwardly relative to the torsion bar 7 in relation to the corresponding target piece.

[0177] according to Fig. 9 In the advantageous variant embodiment shown, the second eddy current angular position sensor 12 and the third eddy current angular position sensor 13 have a common detection probe 23 placed between the targets 121, 131 of the two sensors, i.e. at the level of the torsion bar 7. This common detection probe 23 comprises a common support plate for the windings of the second angular position sensor 12 and the third angular position sensor 13. The production of the windings of the two angular position sensors 12, 13 makes it possible to reduce the manufacturing costs by adopting a single circuit backing. The crosstalk between the two angular position sensors can be eliminated using a different number of N2 polarizers than N3, or by inserting a conductive and / or magnetic material between the windings to allow the magnetic fields of the two sensors to be decoupled.

[0178] The invention is not limited to the examples described and represented, since various modifications can be made thereto without departing from its scope.

Claims

1. A detection system for a steering mechanism (2) of a vehicle, the detection system allowing the measurement of a torque (T) and an absolute steering wheel angle (θ2) over more than one mechanical rotation, the steering mechanism comprising a torsion bar (7) and equipped with an electric motor (3), the electric motor (3) being provided with a reduction gear (4), the detection system comprising: A first angular position sensor (11) having N1 pairs of poles, wherein N1 is an integer greater than or equal to 1, the first angular position sensor (11) measuring the angle of the electric motor (3) and transmitting a first signal (α1); a second angular position sensor (12) having N2 poles, wherein N2 is an integer greater than or equal to 1, the second angular position sensor (12) measuring an angle of the steering mechanism between the reduction gear (4) and the first side of the torsion bar (7), the second angular position sensor transmitting a second signal (α2); a third angular position sensor (13) having N3 poles, wherein N3 is an integer greater than or equal to 1, the third angular position sensor (13) measuring the angle of the steering mechanism on a second side of the torsion bar (7) opposite to the first side and transmitting a third signal (α3); and A processing unit (15), on the one hand, the processing unit (15) performs a cursor calculation based on at least the first signal (α1) and the second signal (α2) to generate a first calculation signal proportional to the absolute steering wheel angle (θ2) over the more than one mechanical rotation On the other hand, the processing unit (15) combines the third signal (α3) with the first signal (α1), the second signal (α2) and the first calculated signal One of the signals obtained in the above method is angle-weighted summed to generate a second calculated signal proportional to the torque (T) 2. A system according to the preceding claim, wherein: The processing unit (15) considers that the first calculation signal corresponds to the absolute steering wheel angle (θ2) over the more than one mechanical rotation, and the second calculated signal Corresponds to the applied torque (T).

3. The system according to claim 1, wherein: The processing unit (15) performs cursor calculation to generate the first calculation signal The first calculated signal for: where Θ = f s (p1α1 + p2α2) And, f s is a mathematical sawtooth function with a slope equal to 1, wherein q1 and q2 are selected as fixed weighting coefficients, and α1 is a signal generated by the first angular position sensor (11), and α2 is a signal generated by the second angular position sensor (12); And among them, p1, p2 and N turns are numerical coefficients that are chosen and must satisfy the following conditions: where Δθ2 is the peak-to-peak change in absolute steering wheel angle over the more than one mechanical rotation, and R red is the reduction ratio of the reduction gear (4).

4. The system according to claim 3, wherein: The weighting coefficients q1 and q2 are as follows: If N2 <N1R red ,but If N2>N1R red ,but Wherein, σ1 is the typical magnitude of the error of the first angular position sensor, and σ2 is the typical magnitude of the error of the second angular position sensor.

5. The system according to claim 1, wherein: The processing unit (15) performs cursor calculation to generate the first calculation signal The first calculated signal for: in, And, f s is a mathematical sawtooth function with slope equal to 1, where pgcd is the "greatest common denominator" operator, where and is selected as a fixed weighting coefficient, and α1 is a signal generated by the first angular position sensor (11), α2 is a signal generated by the second angular position sensor (12), and α3 is a signal generated by the third angular position sensor (13); And among them, c2, c3, and is a numerical coefficient that is chosen and must satisfy the following conditions: where Δθ2 is the peak-to-peak change in absolute steering wheel angle over the more than one mechanical rotation, and R red is the reduction ratio of the reduction gear (4).

6. The system according to claim 1, wherein: The second calculated signal for: Among them, f s is a mathematical sawtooth function with a slope equal to 1, α2 is the signal generated by the second angular position sensor (12), α3 is the signal generated by the third angular position sensor (13), and G is the stiffness of the torsion bar (7), and wherein k2, k3 are numerical coefficients that are selected and must satisfy the following conditions: Among them, Δθ shift is the peak-to-peak variation of the angular deformation of the torsion bar.

7. The system according to claim 1, wherein: The second calculated signal for: Among them, f s is a mathematical sawtooth function with a slope equal to 1, α1 is the signal generated by the first angular position sensor (11), α3 is the signal generated by the third angular position sensor (13), and G is the stiffness of the torsion bar (7), and wherein k1, k3 are numerical coefficients that are selected and must satisfy the following conditions: Among them, Δθ shift is the peak-to-peak variation of the angular deformation of the torsion bar.

8. The system according to claim 1, wherein: The second calculated signal for: Among them, f s is a mathematical sawtooth function with a slope equal to 1, is the first calculated signal, α3 is the signal generated by the third angular position sensor (13), and G is the stiffness of the torsion bar (7), and wherein k3 is a numerical coefficient that is selected and must satisfy the following conditions: Among them, Δθ shift is the peak-to-peak variation of the angular deformation of the torsion bar (7).

9. The system according to claim 1, wherein: The processing unit (15) verifies whether the set of measured signals and calculated signals belongs to a set of acceptable values, and transmits an alarm signal when the set of values ​​does not belong to the set of acceptable values.

10. The system according to claim 1, characterized in that The first angular position sensor (11), the second angular position sensor (12) and / or the third angular position sensor (13) are Hall effect position sensors, magnetoresistive sensors, fluxgate sensors, inductive sensors, eddy current sensors or variable magnetoresistive sensors.

11. The system according to claim 1, characterized in that The second angular position sensor (12) and the third angular position sensor (13) are eddy current position sensors or a combination of sensors comprising a common detection probe (23), wherein the common detection probe (23) comprises a common support plate for the windings of the second angular position sensor (12) and the third angular position sensor (13).

12. A steering mechanism equipped with a detection system (1) according to claim 1, which implements a steering command as a function of the absolute steering wheel angle (θ2) and the applied torque (T) over said more than one mechanical rotation.

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