WO2001001096A1

WO2001001096A1 - Steering column with hall-effect sensor bar

Info

Publication number: WO2001001096A1
Application number: PCT/FR2000/001509
Authority: WO
Inventors: Christophe Nicot; Pascal Desbiolles; Fernand Peilloud
Original assignee: S.N.R. Roulements
Priority date: 1999-06-24
Filing date: 2000-05-31
Publication date: 2001-01-04
Also published as: EP1108201A1; JP2003503695A; FR2795376A1; FR2795376B1

Abstract

The invention concerns a vehicle steering column comprising a manual control member for applying a torque on the column drive shaft, said column being provided with means for measuring the torque applied on said drive shaft, said means for measuring the applied torque comprising means generating magnetic pulses and a device detecting said pulses, wherein the detecting device comprises a plurality of aligned sensing elements.

Description

Hall bar steering column

The invention relates to the technical field of vehicle steering columns.

The term “steering column” conventionally denotes a tubular element, fixed to the vehicle body, under the dashboard, which guides and supports the drive shaft connected to the steering wheel.

This steering wheel is then a manual control member, connected to the steered wheels and used by the driver to steer the vehicle.

The invention also relates to the decoupled steering columns. Unlike conventional steering columns, decoupled steering columns are not associated with a steering box transforming the circular movement of the steering wheel into angular displacement of the hanging rod which causes the steering of the wheels.

On the contrary, for these decoupled directions, there is no direct mechanical connection between the steering wheel and the wheels resting on the ground, whether the vehicle is real or belongs to a simulation system.

This simulation can be a fun object, linked to learning in driving schools or even linked to an interactive driving simulation for the needs of car manufacturers.

In such simulators, the restitution of forces at the steering wheel thanks to a mechanism generating a resistant torque on the steering wheel depending on the type of vehicle to be simulated, whether or not equipped with power steering, must take into account the driving conditions. to recreate.

The measurement of the torque applied to the steering wheel is therefore essential to ensure good simulation, in real time. The measurement of torque on the steering wheel shaft is also very important in power steering or power steering.

The level of assistance depends in particular on the torque applied by the driver to the steering wheel.

The torque meter, or torque sensor, used in power steering transmits a signal indicative of the steering torque exerted by the driver on the steering wheel and therefore on the transmission shaft of the vehicle's steering column.

This signal is conventionally sent to a steering assistance computer which controls the assistance, by controlling for example an electric motor, in the case of an electric power steering.

The invention relates more particularly, but not exclusively, to steering columns comprising a magnetic pulse generator called a “coder” and a functionally associated detection device called a “sensor” of magnetoresistance type or Hall effect probe.

By “Hall effect probe”, we mean here sensors comprising at least one sensitive element, generally a semiconductor in the form of a wafer, such that, when it is traversed by a current I, being also subjected to a induction B making an angle le with the current, it appears in a direction perpendicular to the current I and to the induction B a voltage V equaling V≈KIB sinθ, K being called "Hall constant", and being characteristic of the material and the geometry of the sensitive element, K varying with temperature.

By “magnetoresistance”, one indicates here a varistor sensitive to the intensity of a magnetic field, in other words a resistance in semiconductor material whose ohmic value varies when varies the intensity of a unidirectional magnetic field applied perpendicular to the direction of current flowing through the resistance. Hall probes are considered active sensors, since the information delivered is linked to an electromotive force.

When these Hall probes are used for displacement translation, the magnet which creates the induction is associated with the test body on which the primary value to be measured acts, modifying the secondary measurand, namely conventionally the normal component of l 'induction, measurand to which the probe is directly sensitive.

Devices are known for measuring the torque exerted on a shaft comprising a sensor, for example Hall effect, positioned at an air gap distance from a fast transition magnetic pattern. So that the sensor measures the variation of magnetic induction of the encoder and, by means of cPύri ^" electronic circuit, the torque exerted is then deduced therefrom.

For example, in such devices, the encoder is integral with a part of the steering column which, under the action of the torque exerted, moves relative to a substantially unstressed part with which the sensor is associated.

Such devices have the following drawbacks: the sensitivity of the sensor can vary depending on the temperature. Indeed, this takes into account the drift of the sensor and the magnets. Some correction principles consist in using a Hall effect sensor partially compensating for the temperature drift of the magnets or appropriate processing electronics. This principle presents limited performances taking into account the random drift of sensitivity and offset of the sensors; a magnetic shielding device must be used in order to be free from any external magnetic disturbance; the sensitive elements must be positioned finely opposite the magnetic transition in order to minimize the magnetic offset, and the temperature drift from zero that results. The invention relates to a steering column provided with means for measuring the torque based on electromagnetic phenomena which does not have the drawbacks of the devices of the prior art.

To this end, the invention provides a vehicle steering column comprising a manual control member for applying a torque to the transmission shaft of the column, said column being provided with torque measurement means applied to said transmission shaft, the means for measuring the applied torque comprising a magnetic pulse generator means and a device for detecting these pulses, in which the detection device comprises a plurality of aligned sensitive elements chosen from the group comprising the probes to Hall effect, magneto resistors, giant magneto resistors. The sensitive elements being placed equidistant from each other.

The magnetic pulse generating means comprises a number of pairs of magnetic poles with reverse direction of magnetization of a given pole with respect to those which are contiguous to it, capable of providing, to the air gap considered, a sinusoidal magnetic field on the entire measurement area. For example, the number of pairs of magnetic poles is at least two.

The detection device detects the relative movement between the sensitive elements and the magnetic pulse generating means.

In a first embodiment, the detection device comprises an even number 2N sensitive elements. The even number of sensitive elements can be selected by programming type EEPROM, ZENER ZAPPING or equivalent.

The set of 2N sensitive elements is divided into two subsets of N elements, each sensitive element of the first subset being connected to a first adder, each sensitive element of the second subset being connected to a second adder, the output If from the first adder and the output S ₂ from the second adder, via an inverter, are connected to the input 5

of a third adder, the signal COS = Si - S ₂ thus obtained is processed by a circuit, so as to deduce the torque exerted on the steering column.

In another embodiment, the detection device comprises a number of sensitive elements multiple of four.

The set of 4P sensitive elements is divided into four subsets of P elements, each sensitive element of the first subset of P elements being connected to a first adder providing a signal Si; each sensitive element of the second subset of P elements being connected to a second adder providing a signal S ₂ ; each sensitive element of the third subset of P elements being connected to a third adder providing a signal S'i; each sensitive element of the fourth subset of P elements being connected to a fourth adder providing a signal S ₂ ; an adder and inverter circuit providing two signals SIN and COS being respectively: SIN = (Sι - S ₂ ) - (S ^, ι - S ^, ₂ );

These signals SIN and COS being connected to a fifth adder, the signal SCOUPLE = SIN + COS thus obtained being processed by a circuit, so as to deduce the torque exerted on the steering column.

A programmable gain G can be applied to the COS signal and / or to the SIN signal before being connected to the fifth adder, the gain G being programmed so as to obtain a zero SCOUPLE signal when the torque applied to the column is zero.

In a complementary embodiment, the signals from each sensitive element are connected to a maximum intensity detector which, via a regulator and a control device, controls the sensitivity of the sensitive elements, so as to obtain a detection of the torque exerted on the steering column substantially independent of temperature. As a variant, the sensitive elements are integrated on an ASIC type circuit support and the detection device can also be included in a custom integrated ASIC type circuit.

The magnetic pulse generating means are secured to a part of the steering column which deforms under the action of the torque exerted and the detection device is secured to a substantially unstressed part of the steering column.

Other objects and advantages of the invention will appear during the following description of an embodiment, which description will be made with reference to the accompanying drawings in which:

- Figure 1 is a partial schematic representation of a pair of poles of an encoder and of the substantially sinusoidal magnetic induction at the working air gap which it delivers;

- Figure 2 shows an embodiment of the detection device according to the invention;

- Figure 3 shows a second embodiment of the detection device according to the invention;

- Figures 4a to 4e represent a vector representation of the evolution of the signals delivered as a function of the torque exerted and / or the incorrect positioning of the sensor in front of the encoder;

- Figure 5 shows a device for overcoming the effect of temperature and air gap variations on the analog signals supplied;

A steering column provided with means for measuring the applied torque comprises a transmission shaft, a means for generating magnetic pulses called “encoder” and a device for detecting these pulses called “sensor”.

In one embodiment, the drive shaft is interrupted by a bending test body. The coder is associated with a part of the test body constrained by the torque exerted and the sensor is associated, at a distance from the airgap of the coder, with a part of the test body which is substantially unstressed. It follows from the torque exerted that the encoder moves in front of the sensor, said movement being a function of the torque exerted on the steering column.

FIG. 1 schematically illustrates a period 1 of a component, for example normal, of said induction B, for a pair of poles 2, 3 of the coder.

The detection device 4 comprises an even number 2N of sensitive elements 5 of the magneto-resistance type or Hall effect probe, placed at equal distance from each other, these elements 5 being substantially arranged along a straight line D, for example the sensitive elements 5 can be arranged on an arc of a circle which can be approximated to a straight line.

In the embodiments shown, twenty-four sensitive elements 5 are provided.

This arrangement defines a strip 6 of sensitive elements 5 of length (2N-1) d.

The detection device also comprises an electronic circuit 7 making it possible to process the analog signals coming from the various sensitive elements 5 in order to obtain information such as, for example, the angular position of a multipolar magnetic piece placed opposite the bar 6.

The detection device can be integrated on a silicon or equivalent substrate, for example AsGa, so as to form an integrated and personalized circuit for specific application, a circuit sometimes designated by the term ASIC to refer to the integrated circuit designed partially or completely according to needs.

When the multipolar magnetic part comprises two pairs of magnetic poles with reverse magnetization direction of a given pole with respect to those which are contiguous to it, the magnetic induction at the air gap can be assimilated to a sinusoidal shape over the whole area measurement and therefore does not present any deformation due to edge effects. Indeed, the presence of two additional poles makes it possible to push back the edge effects outside the measurement area. The magnetic period of the field is then defined as the period of the sine wave delivered to the air gap.

In the embodiments shown, the bar 6 of sensitive elements 5 covers a complete magnetic period.

As a variant, when the strip 6 of sensitive elements 5 detects more than one magnetic period, the length of the strip 6 of sensitive elements 5 can be reduced to 2M elements used on the 2N (M being less than N), by programming, for example of the EEPROM or ZENER ZAPPING type.

By EEPROM, is meant here an electrically erasable reprogrammable memory, each of whose cells is for example formed by a MNOS or DIFMOS transistor or equivalent, with read and write transistors, MNOS transistors (Metal Nitride Oxide Semiconductor), derived from MOS transistors, forming a semiconductor memory.

By Zener zapping, we conventionally designate the Zener adjustment, that is to say a correction of the possible voltage error supplied by a digitizer for a determined binary input word, by selective short-circuiting of diodes. Zener polarized in the opposite direction and supplied by constant current sources of increasing intensity, the total intensity of the circuit thus obtained creating the correction voltage necessary across a resistor.

In the embodiment of FIG. 2, the set of sensitive elements 5 is divided into two subsets 8, 9 of N elements.

Each sensitive element 5 of the first subset 8 is connected to a first adder or addition circuit 10, such as an amplifier, ensuring the summation of the signals Sei, Se ₂ , ..., Se _N , originating from the first N sensitive elements 5.

Similarly, each sensitive element 5 of the second sub-assembly 9 is connected to a second adder or addition circuit 11, such as an amplifier, ensuring the summation of the signals Se (+ i), S ^β (N + 2), Se _(N +3), ---, Se ₂ N, derived from the N other sensitive elements 5.

Two sum signals are thus obtained:

The output Si of the first adding means and, via an inverter 12, the output S ₂ of the second adding means are connected to the input of a third adding means or adding circuit 13.

In this first embodiment, the bar 6 of sensitive elements 5 is positioned, under zero torque, opposite ^~ the magnetic part and well centered on the magnetic transition so that the phase shift of the signals linked to poor mechanical positioning is no. The signals are then:

Se ₂ = ...

Se _2N = sin (wt- (1/2 + 2N-1) α)

Where α corresponds to the phase shift between two sensitive elements 5 (α = π / 2N.LpO / Lp) with LpO = 2Nd and Lp is the polar length of the sensor which is defined as the length of a magnetic pole measured at the reader radius considered .

At the output of the third adder means 13 then appears a sinusoidal signal: Si - S ₂ (hereinafter called "COS")

The variation of the signal Sι-S ₂ delivered as a function of the movement of the magnetic piece in front of the bar 6 of sensitive elements 5 is then sinusoidal centered on zero (see FIG. 2). By choosing a stiffness of the bending test body appropriate to the torque measurement range, it is thus possible to obtain an almost linear output as a function of the torque exerted on the steering column (see FIG. 2).

The magnetic offset corresponds to a continuous component which is added to the detected signals Si and S ₂ . However, the magnetic offset or the external magnetic disturbances being assumed to be uniform over all of the sensitive elements 5, the subtraction Sι-S ₂ does not include a continuous component linked to the magnetic offset.

As a variant (not shown) of this embodiment, the output Si of the first adding means 10 and the output S ₂ of the second adding means 11 are connected to an additional adding means so as to form the signal SIN = Si + S ₂ .

One way to overcome the precise positioning of the bar 6 of sensitive elements 5 in front of the magnetic part is then to form a linear combination of the SIN and COS signals by amplifying one of these two signals using 'a programmable gain G. This approach is described in detail below in relation to the second embodiment.

However, the signal which is a function of the torque exerted thus obtained is not free from magnetic offset of the encoder or from external disturbances because the signal SIN is obtained by summing Si and S ₂ .

The second embodiment shown in Figure 3 overcomes the precise positioning of the bar 6 of sensitive elements 5 in front of the magnetic part while using a signal depending on the torque exerted which is free of magnetic offset.

The bar 6 of sensitive elements 5 is broken down into four quadrants with P sensitive elements and an electronic circuit based on adding amplifiers makes it possible to obtain the signals Si, S ₂ , S'i and S ' ₂ originating respectively from the first, second, third and fourth sub-assemblies with P sensitive elements of a strip with 4 P sensitive elements.

The analog signals formed using an electronic circuit, for example based on adder amplifiers and inverters, are then as follows: SIN = (S SzHS 'S'a), and COS = (Sι + S ₂ ) - (S'ι + S ' ₂ ).

The expression of the signals SIN and COS is as follows:

SIN = - 4 sin (π / 8.LpQ / Lp) .sin (π4.LpQ / Lp) sin (wt-πLpO / Lp) sin (π / 2 / Lp.Lp0 / 4P)

COS = 2 sin ² (π / 4.LpQ / Lp). cos (wt-πLpO / Lp) sin (π / 2 / Lp.LpO / 4P)

The detection device described in this embodiment delivers two sinusoidal signals SIN and COS in perfect quadrature, this independently of the positioning of the sensor in front of the encoder. These signals are also free of magnetic offset as they are obtained by subtracting quadrants.

By choosing a stiffness of the bending test body appropriate to the torque measurement range, it is thus possible to obtain, with the signal SIN or with the signal COS or with a combination of the two, an almost linear output as a function of the torque exerted. on the steering column.

The vectorial representation of the evolution of these two signals as a function of the torque exerted and / or the incorrect positioning of the sensor in front of the encoder is given in FIGS. 4a to 4e.

In these figures, the detection axis corresponds to the Ox axis and the measurement corresponds to the vector projection on this axis. FIGS. 4a and 4b correspond to the case where the bar 6 of sensitive elements 5 has been positioned, under zero torque, opposite the sensor.

Under zero torque, the component along the detection axis of the signal SCOUPLE = SIN + COS is zero (see Figure 4a). The rest angle θ ₀ measured between the axis Ox and the vector representation of the signal SIN is then equal to 45 °.

When a torque is applied to the steering column, the encoder then moves relative to the sensor, which results in the vector representation of the signals SIN and COS rotating by an angle β (see Figure 4b). The component along the axis of detection of the SCOUPLE signal is then no longer zero and is a function of the torque exerted on the steering column.

In the case of a bad positioning of the sensor in front of the encoder, the vector representation of the signals SIN and COS the rest angle θ ₀ is equal to a value θ different from 45 ° which corresponds to this bad positioning. It then appears that the component along the detection axis of the SCOUPLE signal is no longer zero under zero torque (see FIG. 4c). This situation corresponds to a zero offset of the sensor.

One way to overcome this problem is to amplify the SIN signal and / or the COS signal using a programmable gain G, then to establish, using an adder means, the sum of these amplified signals.

For example, in the case where only the COS signal is amplified, the signal used to measure the torque exerted is then SCOUPLE = SIN + G. COS.

The gain G is programmed as a function of the angle θ, under zero torque, so that the component along the detection axis of the SCOUPLE signal is zero (see FIG. 4d).

When a torque is applied to the steering column, the encoder then moves relative to the sensor, which means that the vector representation of the signals SIN and COS rotates by an angle β (see Figure 4e). The component along the detection axis of the SCOUPLE signal is then no longer zero and is a function of the torque exerted on the steering column.

Zero adjustment can then be achieved by roughly positioning, for example around a position corresponding to an electrical angle of 45 °, the bar 6 of sensitive elements 5 in front of the magnetic part and then adjusting the gain G by programming so that the detected component of the signal SCOUPLE = SIN + G.COS is zero under zero torque.

As a variant of the two embodiments described above, the torque sensor associated with the steering column provides an analog signal independent of the temperature.

Indeed, when the temperature changes, the amplitude of the field delivered by the encoder varies by 20% for every 100 ° C in the case of ferrite, consequently the sensitivity of the sensor is modified.

In order to overcome these temperature drifts, the signals from each sensitive element 5 are connected to a detection means 14 which makes it possible to select the maximum signal (see FIG. 5). The maximum of the magnetic field is known with an accuracy which depends on the distance between elements d. On the other hand, whatever the position of the sensor facing the encoder, there is always a sensitive element 5 capable of delivering the maximum of magnetic field.

The amplitude of the magnetic field read by the bar 6 is then regulated by using a loop for regulating the current injected into the sensitive elements 5, comprising for example a regulator 15 and a means 16 for controlling the injected current. The signals delivered by each of the sensitive elements 5 then correspond to a portion of sinusoid, the amplitude of which is maintained at the constant and known reference value.

The sensor output signal is then a sinusoidal signal whose amplitude is constant and therefore insensitive to temperature. More generally, the device described above makes it possible to obtain at the output of the sensor a signal independent of the air gap variations.

Claims

1. Vehicle steering column comprising a manual control member for applying a torque to the transmission shaft of the column, said column being provided with torque measurement means applied to said transmission shaft, the means for measurement of the applied torque comprising a means for generating magnetic pulses and a device for detecting these pulses, characterized in that the detection device (4) comprises a plurality of aligned sensitive elements (5).

2. Vehicle steering column according to claim 1, characterized in that the sensitive elements (5) aligned are chosen from the group comprising Hall effect probes, magnetoresistors, giant magnetoresistors.

3. Vehicle steering column according to claim 1 or 2, characterized in that the sensitive elements (5) are placed equidistant from each other.

4. Vehicle steering column according to any one of claims 1 to 3, characterized in that the magnetic pulse generating means comprises a number of pairs of magnetic poles with reverse direction of magnetization of a given pole with respect to to those adjacent to it, capable of providing, at the air gap considered, a sinusoidal magnetic field over the entire measurement area.

5. Vehicle steering column according to claim 4, characterized in that the number of pairs of magnetic poles is at least equal to two.

6. Vehicle steering column according to any one of claims 1 to 5, characterized in that the detection device (4) detects the relative movement between the sensitive elements (5) and the means generating magnetic pulses.

7. Vehicle steering column according to any one of claims 1 to 6, characterized in that the detection device (4) comprises an even number 2N sensitive elements.

8. Vehicle steering column according to claim 7, characterized in that the even number of sensitive elements (5) is selected by programming of type EEPROM, ZENER ZAPPING or equivalent.

9. Vehicle steering column according to claim 7 or 8, characterized in that the set of 2N sensitive elements (5) is divided into two subsets (8, 9) of N elements, each sensitive element (5) of the first sub-assembly (8) being connected to a first adder (10), each sensitive element (5) of the second sub-assembly (9) being connected to a second adder (11), the output Si coming from the first adder ( 10) and the output S ₂ from the second adder (11), via an inverter (12), are connected to the input of a third adder (13), the signal COS = Si - S ₂ thus obtained is processed by a circuit, so as to deduce the torque exerted on the steering column.

10. Vehicle steering column according to any one of claims 1 to 9, characterized in that the detection device (4) comprises a number of sensitive elements (5) multiples of four.

11. Vehicle steering column according to claim 10, characterized in that the set of 4P sensitive elements is divided into four subsets of P elements, each sensitive element of the first subset of P elements being connected to a first adder providing a signal Si; each sensitive element of the second subset of P elements being connected to a second adder providing a signal S ₂ ; each sensitive element of the third subset of P elements being connected to a third adder providing a signal S'i; each sensitive element of the fourth subset of P elements being connected to a fourth adder providing a signal S '₂; an adders and inverters circuit providing two signals SIN and COS being respectively: SIN = (S ₁ - S ₂ ) - (S ' ₁ - S' ₂ ); COS = (S ₁ - S ₂ ) - (S ^, ₁ + S ' ₂ ); These signals SIN and COS being connected to a fifth adder, the signal SCOUPLE = SIN + COS thus obtained being processed by a circuit, so as to deduce the torque exerted on the steering column.

12. Vehicle steering column according to claim 11, characterized in that a programmable gain G is applied to the signal COS and / or to the signal SIN before being connected to the fifth adder.

13. Vehicle steering column according to claim 12, characterized in that the gain G is programmed so as to obtain a zero SCOUPLE signal when the torque applied to the column is zero.

14. Steering column according to any one of claims 1 to 13, characterized in that the signals from each sensitive element (5) are connected to a maximum intensity detector (14) which, via a regulator (15 ) and a control device (16) controls the sensitivity of the sensitive elements, so as to obtain a detection of the torque exerted on the steering column that is substantially independent of the temperature.

15. Vehicle steering column according to any one of claims 1 to 14, characterized in that the sensitive elements (5) are integrated on an ASIC type circuit support.

16. Vehicle steering column according to claim 15, characterized in that the detection device (4) is included in a personalized integrated circuit type ASIC.

17. Vehicle steering column according to any one of claims 1 to 16, characterized in that the magnetic pulse generating means are integral with a part of the steering column which deforms under the action of the torque exerted .

18. Vehicle steering column according to claim 17, characterized in that the detection device (4) is integral with a substantially unstressed part of the steering column.