WO2004055482A1

WO2004055482A1 - Very high-resolution position sensor

Info

Publication number: WO2004055482A1
Application number: PCT/FR2003/003670
Authority: WO
Inventors: Olivier Andrieu
Original assignee: Electricfil Automotive
Priority date: 2002-12-11
Filing date: 2003-12-11
Publication date: 2004-07-01
Also published as: FR2848663A1; FR2848663B1; EP1570238A1; AU2003296816A1

Abstract

The invention concerns a sensor comprising a circular magnetic track consisting of a series of elements generating a variable magnetic field, distributed to form P pairs of elements with a mechanical period T equal to 360 DEG /P, the magnetic track being designed to move past 2n detecting cells offset to deliver mutually electrically phase-shifted periodic electric signals (Si). The detecting cells are connected to means for processing the phase-shifted electric signals (Si) comprising: means for providing the difference between two electric signals to obtain n differential analog signals (Sdp) mutually phase-shifted in pairs by T/2n and such that Sdp = Sn+p Sp with p ranging between 1 and n; and means for extracting from each differential signal (Sdp) two pulses spaced by T/2 so as to obtain a digitized signal comprising 2n pulses phase-shifted by T/2n.

Description

VERY HIGH RESOLUTION POSITION SENSOR

The object of the invention relates to the technical field of magnetic sensors, of the type comprising an encoder element moving close to a detection cell and adapted to locate at least one angular position in the general sense. The object of the invention finds a particularly advantageous application in the automotive field where such a sensor can be used, for example, in the context of ignition functions.

It is known, in the preferred field above, to implement a magnetic sensor adapted to measure the change in the intensity of a magnetic field, when an encoder provided with a series of elements generating a variable magnetic field, scrolls past a measurement or detection cell. The detection cell, such as for example a Hall effect or magneto-resistive probe, delivers a periodic electrical signal corresponding to the change in the intensity of the magnetic field generated by the elements. The detection cell is associated with a hysteresis level comparator, such as a Schmitt trigger, in order to obtain frank transitions of the output voltage for distinct values of the magnetic field, depending on whether it varies in increasing or decreasing.

In order to constitute a speed detection sensor, it is known to produce an encoder provided with elements generating a variable magnetic field arranged in a regular manner around a circumference to form a track.

According to a first embodiment, the generating elements consist of elements disturbing a magnetic field created by a fixed magnet placed near such disturbing elements. For example, such disturbing elements are constituted by teeth arranged in a ferromagnetic ring.

According to a second preferred embodiment, the elements generating a variable magnetic field are formed by magnetic poles, regularly spaced at a given pitch. Such an encoder is thus in the form of a multipolar magnetic ring. To make it possible to determine at least one position, corresponding for example to the top dead center of ignition of a cylinder, it is known to make a mark on the magnetic encoder. It is known thus, to delete, for example, two teeth on the ferromagnetic ring. In the variant embodiment using an encoder produced in the form of a multipolar magnetic ring, it can be envisaged either to delete several magnetic poles leaving an empty space, or to replace one or more poles with a sign given by one or more poles of a contrary sign. There is thus produced a given magnetization pole having, between its two adjacent poles of an opposite sign, a different spacing with respect to the spacing pitch of the other poles.

As part of the ignition functions of an automobile, the usual resolution of the sensors is currently 60-2 pulses per revolution. This level of performance is traditionally obtained using an encoder comprising 60-2 pairs of magnetic poles or 60-2 ferromagnetic teeth and associated with a detection cell delivering a pulse per pair of poles or per tooth.

To improve the resolution of such a sensor, it can be envisaged to increase the number of generator elements produced along a circumference. However, there appears to be a technical limitation linked to the production of ferromagnetic teeth or magnetic poles, which must have sufficient dimensions to be detected by the measuring cell. In addition, it does not appear possible, in many applications, for reasons of space, to increase the circumference of such an encoder. Another solution for improving the resolution of such a sensor consists in simultaneously increasing the number of tracks and the number of detection cells, so as to increase the number of events. However, such a solution leads to a sensor having a prohibitive cost.

The object of the invention aims to remedy the drawbacks stated above by proposing a sensor having a high resolution while presenting an encoder retaining a limited diametral size.

The object of the invention thus aims to propose a sensor delivering an electrical signal whose resolution is much higher than the resolution of the encoder.

To achieve this objective, the object of the invention relates to a sensor comprising at least one rotary magnetic encoder of the type comprising a circular magnetic track formed by a series of elements generating a variable magnetic field, distributed to form P pairs of elements with a period mechanical equal to 360 ° / P, the magnetic track being intended to pass in front of 2n offset detection cells to deliver periodic electrical signals Si (with i varying from 1 to 2n) electrically phase shifted between them by a value equal to l / 2n times the value of the mechanical period and corresponding to the change in the intensity of the magnetic field generated by the elements, the detection cells being connected to means for processing the phase-shifted electrical signals.

According to the invention, the processing means comprise: means for ensuring the difference between two electrical signals in order to obtain n differential analog signals phase shifted between them two by two by T / 2n and such that Sd _p = S _n + _P - S _p with p varying from 1 to n, and means for extracting from each differential signal Sd _p , two pulses spaced from T / 2 in order to obtain a digitized signal comprising 2n pulses phase shifted by T / 2n so that the sensor has a resolution of 360 ° / 2nP. Another object of the invention relates to a sensor, the magnetic track of which comprises elements generating a variable magnetic field, formed by elements disturbing a magnetic field created by a fixed magnet placed nearby.

According to an advantageous characteristic, the sensor track is formed from an elastomeric or plastic ring loaded with magnetized particles to form the magnetic poles, the ring being mounted on a support ring.

According to another characteristic, the sensor comprises a low resolution encoder forming a multipolar magnetic ring comprising a series of elements generating a variable magnetic field having a different spacing to form pairs of irregular elements, the low resolution encoder being intended to scroll in front of a detection cell.

According to another characteristic of the invention, the encoder, and possibly the low resolution encoder, are mounted on a target locked in rotation on a shaft of an engine of a motor vehicle ^" the ^" 2n cells ^"~ die ^" dëtëctîônët évèlTtùèilëmëht ^" the detection cell for the low resolution coder, being mounted in relation to said coders. According to another characteristic of the invention, the target has a peripheral wall and a transverse wall each intended to receive an encoder.

According to another characteristic of the invention, the target forms a drive pulley. According to another characteristic of the invention, the drive pulley is a crankshaft pulley.

According to another characteristic of the invention, the drive pulley is a cam pulley.

According to another characteristic of the invention, the target is rotated by a shaft of the gearbox of a motor vehicle.

According to another characteristic of the invention, the target is mounted inside a support plate of a dynamic seal, mounted in proximity relationship of 2n detection cells, and between the crankshaft and the gearbox of motor vehicle engine speeds. According to another characteristic of the invention, the target is rotated by the crankshaft or the camshaft, while being mounted inside the engine block of a motor vehicle and in proximity relationship of 2n cells detection.

Various characteristics will emerge from the description given below with reference to the accompanying drawings which show, by way of non-limiting examples, embodiments of the subject of the invention.

The fig. 1 is a schematic view showing a first embodiment of a sensor according to the invention.

The fig. 2 shows the shape of the electrical signals obtained and delivered by a position sensor illustrated in FIG. 1.

The fig. 3 shows the form of the electrical signals obtained and delivered by a second embodiment of a sensor according to the invention.

The figs. 4 and 5 are views of examples of mounting an encoder according to the invention. The figs. 6 and 7 are respectively sectional elevation and perspective views of a complete sensor incorporating high resolution and low resolution encoders. The fig. 1 illustrates a first preferred embodiment of a rotary magnetic encoder 1 according to the invention. The encoder 1 comprises a circular magnetic track 2 intended to pass in front of 2n detection or measurement cells 3i with n> 1 and with i varying from 1 to 2n, to form a position sensor 4. In the example illustrated in FIG. . 1, the encoder 1 scrolls past four detection cells, respectively 3χ to 3, (n - 2).

The magnetic track 2 comprises a series of generating elements 5 of a variable magnetic field, distributed over the circular track to form P pairs of elements 5, with a mechanical period T equal to 360 ° / P. In the exemplary embodiment illustrated in FIG. 1, the elements generating a variable magnetic field 5 are formed by alternating magnetic poles, so that the magnetic track is constituted by a multipolar magnetic ring. According to this example, the magnetic track of the encoder 1 comprises a series of south poles and north poles arranged to present a regular pitch of spacing between two adjacent poles.

Of course, it can be envisaged to produce the magnetic track 2 with elements generating a variable magnetic field 5, formed by elements disturbing a magnetic field created by a fixed magnet, placed near said magnetic track. For example, the disturbing elements can be formed by means of teeth arranged in a ring made of ferromagnetic material.

According to a preferred embodiment characteristic, the magnetic track 2 comprises at least one generating element, said irregular not shown, having a different spacing with respect to the spacing pitch between the other generating elements 5. For example, the irregular generating element has a double angular pitch compared to the other generating elements 5. The presence of such an irregular generating element constitutes a reference for the magnetic encoder making it possible to determine at least one angular position. Of course, provision can be made for one or more irregular generator elements. The annular magnetic track 2 is intended to pass in front of the 2n fixed detection cells 3i which each deliver a periodic analog electrical signal If corresponding to the evolution of the intensity of the magnetic field delivered by the generating elements 5.

The detection cells 3i are angularly offset between them so that the relative angular offset between the generator elements 5 and the cells 3; is suitable for obtaining 2n electrical signals If electrically phase shifted between them by a value equal to l / 2n times the value of the mechanical period T. The detection cells 3i are thus offset in a direction parallel to a direction perpendicular to the axis of rotation Δ of encoder 1.

In a conventional manner, each detection cell 3j is associated with means, not shown, for processing the phase-shifted electrical signals S, with a view to increasing the resolution of the sensor. In accordance with the invention, and as more specifically shown in FIG. 2, the processing means comprise means for making the difference between two electrical signals Si in order to obtain n differential analog signals Sd _p phase shifted between them two by two by T / 2n and such that Sd _p = S „ _{+ p} - S _p , with p varying from 1 to n.

Thus, in the example illustrated in FIG. 1 where the number of detection cells 3j is equal to 4 (n = 2), there are obtained 4 electrical signals Si, S ₂ , S ₃ , S electrically phase shifted between them by a value equal to 1/4 of the value of the mechanical period T. The processing means ensure in an identical manner the difference between these signals Si to S in order to obtain two differential analog signals Sdi and Sd ₂ such as:

Sdi = S ₃ - If

Sd ₂ - S - S ₂

According to another characteristic of the invention, the processing means comprise means for extracting from each differential signal Sd _p , two pulses spaced from T / 2 in order to obtain a digitized signal S _s comprising 2n pulses phase shifted by T / 2n. In a preferred manner, with a view to improving the precision of the pulses, the extraction means detect the zero crossing of each differential signal Sd _p so that on each zero crossing there corresponds a pulse. It should be understood that such a sensor comprising the processing means described above makes it possible to increase the resolution of the sensor by 2n times without increasing the diametral dimension of the encoder 1. Thus, when the resolution of the encoder is 360 ° / P, the resolution of the associated sensor is 360 ° / 2nP. For example, when the coder 1 comprises 90 pairs of generating elements 5 of a variable magnetic field, the sensor 4 has a resolution of 1 ° by implementing four detection cells 3, (n = 2). Likewise, when the coder 1 comprises 60 pairs of generator elements 5, the sensor has a resolution of 1.5 ° by implementing four detection cells 3 {. Of course, the object of the invention can be implemented for a sensor comprising two detection cells 3; (N = l). According to this variant embodiment illustrated in FIG. 3, the processing means make the difference between the signals Si and S _{2 in} order to obtain a differential signal Sdi = S ₂ - Si. From this differential signal Sdi, the processing means extract two pulses phase shifted by T / 2. When the number P pairs of generator elements 5 is equal to 90 or 60 for example, the sensor has a resolution of 2 ° and 3 ° respectively. Of course, provision can be made for a sensor with a greater number of detection cells, for example 6 or 8.

Of course, the various values stated above, with regard, in particular, to the period and the phase shift between the signals, are considered to be ideal. In practice, it is clear that the manufacturing conditions of the sensor lead to errors which can degrade the precision of the pulses while retaining the target resolution.

According to a preferred embodiment, the magnetic track 2 is formed from an elastomeric or plastic ring loaded with magnetized particles to form the magnetic poles. This elastomer ring can be mounted on a support ring, not shown.

The encoder 1, as described above, is intended to be mounted, being attached or integrated, on a rotating target 6 in the general sense, from which at least one position is determined. The description which follows illustrates various variants for mounting the encoder 1 on a rotating target 6. According to an implementation characteristic, the encoder 1 is intended to be mounted on a drive pulley mounted at the outlet of the engine of a motor vehicle, that is to say on a timing pulley or on one auxiliary pulleys. According to an advantageous characteristic, as shown in FIGS. 4 and 5, the encoder 1 is mounted on the drive pulley 6 located in the axis of the crankshaft, in order to allow detection of the neutral point or of ignition of a cylinder. In the example illustrated, the encoder 1, which consists of a multipolar magnetic ring, is mounted on the internal radial wall or hub 7 (fig. 4) or on the external radial wall 8 (fig. 5) of the pulley d 'drive 6. The magnetic multipole elastomer ring is mounted either directly on the pulley 6 which constitutes, by its radial wall a support ring, or indirectly by its support ring which is fixed, by any suitable means, on the pulley. As is apparent from Figs. 4 and 5, the detection cells 3i, for example Hall effect, are mounted in the clearance defined between the outer 8 and inner 7 radial walls of the pulley.

In the exemplary embodiment illustrated, the position sensor comprises, as a drive pulley, a crankshaft pulley provided with a magnetic ring adapted to locate a single position. It should be noted that the subject of the invention can, possibly, be applied to the production of a sensor comprising a magnetic encoder 1 provided with several irregular poles, making it possible to identify several positions. Advantageously, the magnetic encoder 1 comprises, for example, four irregular poles making it possible to identify the position of the cylinders of an engine. In this case, the encoder 1 is mounted integral with the camshaft of a motor vehicle engine. Of course, the encoder 1 can be mounted on the camshaft by having a single irregular pole.

According to another preferred implementation characteristic, the encoder 1 according to the invention is intended to be mounted inside a support plate of a dynamic seal for a drive shaft between the crankshaft and the gearbox of an engine of a motor vehicle. Encoder 1 is rotated by the drive shaft and is mounted in proximity relationship of 2n cells 3i detection mounted on the gasket support plate, to form a position sensor.

According to another preferred implementation characteristic, the encoder 1 according to the invention is rotated by a shaft of the gearbox of a motor vehicle.

According to another preferred implementation characteristic, the encoder 1 according to the invention is rotated by the crankshaft or the camshaft of an engine of a motor vehicle, while being mounted inside the engine block of such a vehicle, in proximity relation of 2n detection cells 3i, in order to constitute a position sensor.

The sensor 4 according to the invention described above is a so-called high resolution sensor. According to another characteristic of the invention, such a sensor 4 can comprise, in accordance with FIGS. 6, 7, in addition, a low resolution encoder l 'forming a multipolar magnetic ring comprising a series of generating elements 5 of a variable magnetic field having a different spacing to form P pairs of irregular elements. The low resolution encoder 1 'is intended to pass in front of a detection cell V. Of course, the generator elements 5 can be formed, as explained above, by elements disturbing a magnetic field or by magnetic poles. According to a preferred embodiment characteristic, the low resolution encoder is mounted on the target 6 on which is already mounted the high resolution encoder 1. This target, generally constituted in the form of a ring, has a radial or peripheral wall 6ι and a transverse wall 6 ₂ each intended to receive an encoder 1, l '. The invention is not limited to the examples described and shown since various modifications can be made without departing from its scope.

Claims

CLAIMS:

1 - Position sensor comprising at least one rotary magnetic encoder (1) of the type comprising a circular magnetic track (2) formed by a series of elements (5) generating a variable magnetic field, distributed to form P pairs of elements with a mechanical period T equal to 360 ° / P, the magnetic track being intended to pass before 2n detection cells (3i) (with i varying from 1 to n) offset to deliver periodic electrical signals (Si) electrically out of phase between them with a value equal to 1/2 times the value of the mechanical period T and corresponding to the change in the intensity of the magnetic field generated by the elements, the detection cells being connected to means for processing the electrical signals phase shifted (Si), characterized in that the processing means comprise: means for ensuring the difference between two electrical signals in order to obtain n different analog signals iels (Sd _p ) phase shifted between them two by two by T / 2n and such that Sd _p = S _{n + p} - S _p with p varying from 1 to n, and means for extracting from each differential signal (Sd _p ) two pulses spaced apart from T / 2 in order to obtain a digitized signal comprising 2n pulses out of phase with T / 2n so that the sensor has a resolution of 360 ° / 2nP.

2 - Position sensor according to claim 1, characterized in that the means for extracting from each differential signal (Sd _p ) two spaced apart pulses, detect the zero crossing of each differential signal (Sd _p ).

3 - Position sensor according to claim 1, characterized in that it comprises two detection cells (3ι, 3 ₂ ).

4 - Position sensor according to claim 1, characterized in that it comprises four detection cells (3ι to 3).

5 - Position sensor according to claim 3 or 4, characterized in that the encoder (1) comprises a number P pairs of generator elements equal to 90 so that the sensor has a resolution equal to 1 ° and 2 ° for respectively four and two detection cells (3). 6 - Position sensor according to claim 3 or 4, characterized in that the encoder (1) comprises a number P pairs of generator elements equal to 60 so that the sensor has a resolution equal to 1.5 ° and 3 ° for respectively four and two detection cells (3. 7 - Position sensor according to claim 1, characterized in that the magnetic track (2) comprises elements generating a variable magnetic field (5), formed by magnetic poles alternated.

8 - Position sensor according to claim 1, characterized in that the magnetic track (2) comprises elements generating a variable magnetic field (5), formed by elements disturbing a magnetic field created by a fixed magnet placed near.

9 - Position sensor according to one of claims 1 to 8, characterized in that the magnetic track (2) comprises at least one generator element called irregular having a different spacing with respect to the spacing pitch between the other generator elements ( 5).

10 - Position sensor according to claim 7, characterized in that the magnetic track (2) is formed from an elastomeric or plastic ring loaded with magnetized particles to form the magnetic poles, the ring being mounted on a support ring. 11 - Position sensor according to one of claims 1 to 10, characterized in that it comprises a low resolution encoder (1 ') forming a multipolar magnetic ring comprising a series of elements (5) generating a magnetic field variable having a different spacing to form P pairs of irregular elements, the low resolution coder (1 ') being intended to pass in front of a detection cell (2').

12 - Position sensor according to one of claims 1 to 11, characterized in that the encoder (1) and possibly the low resolution encoder (1 *), are mounted on a target (6) locked in rotation on a shaft of 'An engine of a motor vehicle, the 2n detection cells (3Î) and possibly the detection cell (2') for the low resolution encoder, being mounted in relation to said encoders. 13 - Position sensor according to claim 12, characterized in that the target (6) has a peripheral wall (6ι) and a transverse wall (6 ₂ ) each intended to receive an encoder (1, l ').

14 - Position sensor according to claims 12 or 13, characterized in that the target (6) forms a drive pulley.

15 - Position sensor according to claim 14, characterized in that the drive pulley is a crankshaft pulley.

16 - Position sensor according to claim 14, characterized in that the drive pulley is a cam pulley. 17 - Position sensor according to claim 12 or 13, characterized in that the target (6) is mounted inside a support plate of a dynamic seal, mounted in proximity relationship of 2n cells detection (3i), and between the crankshaft and the gearbox of an engine of a motor vehicle.

18 - Position sensor according to claim 12 or 13, characterized in that the target (6) is rotated by the crankshaft or the camshaft, being mounted inside the engine block of a vehicle automotive and in proximity relationship of 2n detection cells (3.

19 - Position sensor according to claim 12 or 13, characterized in that the target (6) is rotated by a shaft of the gearbox of a motor vehicle.