Method for centering the magnetic center of an impulse ring of a bearing unit on the center of rotation of the bearing unit

A method for centering an impulse ring of a bearing unit on the center of rotation of the bearing unit including a first ring and a second ring. The impulse ring provided with a target having pairs of magnetic poles, and with a fixing sleeve. The method provides a) inserting the impulse ring between the first ring and the fixing sleeve, the first ring and the fixing sleeve being configured to maintain the impulse ring in an axial direction of the bearing; b) recording an angular signal over one mechanical turn of the impulse ring, the angular signal being generated by detection configured to cooperate with the pairs of magnetic poles; c) determining a total pitch deviation vector of the impulse ring based on the angular signal; d) shifting the impulse ring in a radial direction of the bearing, and e) securing the impulse ring relative to the first ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application no. 102020206482.2, filed May 25, 2020, the contents of which is fully incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to magnetic sensors comprising bearing units cooperating with detection means, and more particularly to methods for centering impulse rings of such bearing units.

BACKGROUND OF THE INVENTION

Magnetic sensors deliver analogue sine shaped signals related to the rotor angular position. More precisely, such a sensor comprises a rotor formed out of an impulse ring fitted with magnetic poles and a stator fitted with detection means, able to detect the magnetic field of each magnetic pole.

When rotation is applied to the rotor, the magnetic poles pass successively in front of the detections means. A current is induced within the detections means based on its distance to the magnetic poles. The current forms a periodic signal, sine shaped, function of time, wherein the intensity of the signal depends on the distance between the detections means and the magnetic poles. The time dependency can be converted into an angular dependency based on the known geometry of the sensor and the rotation speed. It is therefore possible to link time with angular position of the rotor and to obtain a sine signal linking intensity with angular position.

Such magnetic sensors are commonly used in motor control. In the particular case of belt starter generators, the requirement on sensor output signals accuracy is more and more important, due to the fact that the machine torque needs to be properly controlled with the least amount of noises. Moreover, the level of oscillating current of the battery must remain under a fixed limit in order to not degrade the overall performances of the vehicle.

One of the sources of sensor output inaccuracy is the impulse ring itself as it does not give a perfect image of the rotor position.

Due to misalignment of the different components of the bearing unit, the impulse ring is not perfectly aligned with the detections means so that the induced current is not an accurate picture of the angular position. The magnetic center of the impulse ring and the mechanical center of the rotor do not coincide.

One commonly used solution to reduce the misalignment of the different components is to improve the accuracy of the manufacturing operations in order to produce more accurate components.

However, improving manufacturing operations generally involves to extend manufacturing operation cycle times and to increase costs of production.

There is a need to avoid at least some of the previously-mentioned drawbacks, especially by reducing the misalignment of the impulse ring in the bearing unit without improving the accuracy of the bearing unit components.

SUMMARY OF THE INVENTION

According to an aspect, a method for centering the magnetic center of an impulse ring of a bearing unit on the center of rotation of a bearing of the bearing unit comprising a first ring and a second ring capable of rotating concentrically relative to one another is proposed.

The impulse ring is provided with a target comprising pairs of magnetic poles and with a fixing sleeve fixed to the first ring of the bearing, the method comprises:

a) inserting the impulse ring axially between the first ring and the fixing sleeve, the first ring and the fixing sleeve being configured to maintain the impulse ring in an axial direction of the bearing; a radial gap remaining between the impulse ring and the fixing sleeve,

b) recording an angular signal over one mechanical turn of the impulse ring, the angular signal being generated by detections means configured to cooperate with the pairs of magnetic poles;

c) determining a total pitch deviation vector of the impulse ring based on the angular signal;

d) shifting the impulse ring in a radial direction of the bearing, the amplitude of the shifting and the direction of the shifting being determined from the total pitch deviation vector; and

e) securing the impulse ring relative to the first ring.

Advantageously, determining a total pitch deviation vector of the impulse ring comprises:

determining a single pitch deviation value for each interval defined as the angular distance between two nearest magnetic poles of the same polarity;

selecting the maximal single pitch deviation value and the minimal single pitch deviation value;

determining a first single pitch deviation vector associated to the maximal single pitch deviation value and a second single pitch deviation vector associated to the minimal single pitch deviation value; and

calculating the vector difference between the first and the second vectors, the total pitch deviation vector being equal to the resulting vector.

Preferably, determining the single pitch deviation value for one interval comprises:

determining the actual period of the angular signal measured by the detections means over the interval;

determining the period of the angular signal over the interval; and

calculating the single pitch deviation as the difference between theoretical period of the angular signal and the actual period of the angular signal as a percentage of theoretical period of the angular signal.

Advantageously, the determination of the amplitude and the direction of the shifting comprises

determining a relation linking the amplitude of the shifting to the module of the total pitch deviation vector,

calculating the amplitude with the relation,

the direction of the shifting being the opposite direction of the total pitch deviation vector.

Preferably, the relation linking the amplitude of the shifting to the module of the total pitch deviation vector is determined mathematically or empirically.

Advantageously, the which steps a), b), c) and d) are executed; steps b) and c) are repeated to determine a new total pitch deviation vector; and step e) is executed if the module of the new total pitch vector is inferior or equal to a threshold.

Preferably, the steps a), b), c) and d) are executed; steps b) and c) are repeated to determine a new total pitch deviation vector; step d) is repeated if the module of the new total pitch vector is superior to a threshold, the amplitude of the shifting and the direction of the shifting being determined from the new total pitch deviation vector; and step e) is executed when the module of the new total pitch vector is inferior or equal to a threshold.

Advantageously, the impulse ring is secured by welding, gluing or clinching.

Preferably, the fixing sleeve is fixed to the inner ring of the bearing.

According to another aspect, a bearing unit is manufactured according to a method as defined above.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made toFIG. 1which represents a longitudinal section of an apparatus1comprises a rotating shaft2, a bearing unit4and detection means5.

The detection means comprises for example a coil.

The shaft2and the bearing unit4are centred on a central axis X1of the apparatus1.

The bearing unit4comprises a bearing6mounted on the shaft2and a magnetic impulse ring7mounted on the bearing6.

The detection means5are associated with the impulse ring7for tracking the rotation of the rotating shaft2.

The bearing6includes a rotating inner ring8and a non-rotating outer ring9centered on axis X1. Bearing6also comprises rolling elements10, for example balls, located between inner ring8and outer ring9.

The inner ring8comprises a cylindrical bore11and a cylindrical groove12made in the bore11. With reference to axis X1, diameter of the cylindrical bore11is smaller than the diameter of the cylindrical groove12.

The impulse ring7includes a target holder13, a target14and a fixing sleeve15.

Going away from central axis X1, the target holder13comprises an inner periphery16, a radial portion17and an outer periphery18. The inner periphery16defines an inner bore of the target holder13, and is fixed to the rotating inner ring8of the bearing6by means of the fixing sleeve15. The radial portion17substantially radially extends from the inner periphery16towards the exterior of the bearing6. The outer periphery18of the radial portion17is located radially beyond the outer ring9.

A gap g17is provided axially between the radial portion17of the target holder13and the lateral face of the outer ring9.

The outer periphery18of the target holder13comprises an outer tubular portion19that axially extends from the radial portion17. The outer tubular portion19extends parallel to axis X1and is located radially above the outer ring9of bearing6.

Target14is held by the outer tubular portion19of the target holder13, beyond outer ring9radially to axis X1.

The target14and the detection means5cooperate for tracking the rotation of the impulse ring7, the target holder13, the inner ring6and the shaft2around central axis X1. A gap g5is provided radially between surface and detection means5.

The target14comprises a succession of magnetic poles of opposed polarity such that the detection means5induce a current when the magnetic poles pass successively in front of the detections means.

As another alternative, the detection means5and the impulse ring7may use any other suitable technology instead of magnetic technology. For example, induction technology or optic technology may be implemented within the bearing unit4of apparatus1.

The inner periphery16of the target holder13is fixed to the rotating inner ring9of the bearing6by means of the fixing sleeve15.

The fixing sleeve15comprises an annular tubular portion20that axially extends parallel to axis X1.

The tubular portion20is fitted in the groove12of the rotating inner ring8.

The fixing sleeve15further comprises a radial collar21that radially outwardly extends from an end of the annular tubular portion20.

The radial collar21is overlapping the inner periphery16of radial extension of the target holder13. The inner periphery16is axially pressed by the radial collar21onto the lateral face of inner ring8so as to prevent any relative rotation between the fixing sleeve15, the target holder13and the inner ring8.

FIG. 2represents schematically an example of an embodiment of the impulse ring7mounted on the shaft2and the detection means5.

The target14comprises for example 8 north magnetic poles named N1to N8alternating with 8 south magnetic poles named S1to S8forming 8 pair of poles denoted Npp.

In another embodiment, the impulse ring7comprises more or less that 8 pair of poles.

The magnetic center of the impulse ring7is named C4and does not coincident with the center of rotation of the bearing6, the center of rotation lying on axis X1, the two centers being separated by a distance e.

The detection means5generate an angular signal SDEcomprising the induced current Iinducedover one mechanical turn of the impulse ring7.

An interval i is defined as the angular distance between two nearest poles Ni, Siof same polarity, i varying from 1 to 8.

When rotation is applied to the rotating shaft2, each pair of poles Si, Niin front of the detections means5induces a current Ireal(i) such that:

The angular signal SDEis for example process by a processing unit PU.

FIG. 3represents a first embodiment of a method for centering the magnetic center C4of the impulse ring7on the center of rotation of the bearing6.

In a step30, the impulse ring7is inserted between the inner ring8and the fixing sleeve15, the inner ring8and the fixing sleeve15being configured to maintain the impulse ring7in the axial direction X1of the bearing6.

As represented onFIG. 4, a radial gap g7remains between the target holder13of the impulse ring7and the fixing sleeve15.

The radial gap g7remains between the fixing sleeve15and the bore of the target holder.

Then, in a step31, the detection means generate the angular signal SDEover one mechanical turn of the impulse ring7.

In step32, the processing unit PU determines a total pitch deviation vector {right arrow over (TPD)} of the impulse ring7based on the angular signal SDE.

First, a single pitch deviation value SPD for each interval i is calculated on the basis of the formula:

PTheo(i): Theoretical period of the angular signal for the interval i

Preal(i): Actual period of the angular signal for the interval i.

It is to be noted that the actual period Preal(i) is to be determined between poles of same sign, i.e. between North poles or between South poles. Similarly, the actual period Preal(i) is to be determined between the same kind of signal edges, i.e. between rising edges or between falling edges.

FIG. 5illustrates the induced current Iinducedcomprising the currents Ireal(i), theoretical period PTheo(i) and the actual period Preal(i) over a mechanical turn, i varying from 1 to 8.

Then, the processing unit PU selects the maximal single pitch deviation value SPDmax and the minimal single pitch deviation value SPDmin, and determines a first single pitch deviation vector {right arrow over (SPD)}max associated to the maximal single pitch deviation value and a second single pitch deviation vector {right arrow over (SPD)}min associated to the minimal single pitch deviation value.

The module of the first single pitch deviation vector {right arrow over (SPD)}max is defined by the maximal single pitch deviation value SPDmax for example equal to 0.16% and the direction of the vector is defined by the angular position of the maximal single pitch deviation value SPDmax in the mechanical turn for example

Similarly, the module of the second single pitch deviation vector {right arrow over (SPD)}min is defined by the minimal single pitch deviation value SPDmin for example equal to −0.13% and the direction of the vector is defined by the angular position of the minimal single pitch deviation value SPDmin in the mechanical turn for example

The processing unit PU calculates the vector difference between the first and the second vectors, the pitch deviation vector {right arrow over (TPD)} being equal to the resulting vector.

Using the above-mentioned values, the pitch deviation vector {right arrow over (TPD)} is defined by its module TPD equal to 0.20% and by the angular position DTPDequal to −85.55°.

Then, in step33(FIG. 3), the impulse ring7is shifted in a radial direction of the bearing6

The amplitude ASHof the shifting and the direction DSHof the shifting is determined from the total pitch deviation vector {right arrow over (TPD)}, the shifting being represented by the shifting vector {right arrow over (SH)} characterized by the amplitude ASHand the direction DSH

A relation named Flinklinks the amplitude ASHof the shifting to the module of the total pitch deviation vector {right arrow over (TPD)}, and the direction DSHof the shifting is opposed to the direction of the vector {right arrow over (TPD)}.

The relation Flinkis determined empirically or mathematically.

Now is exposed a method to determine mathematically the relation Flink.

FIG. 6illustrates schematically the magnetic center C4and the mechanical center X1separated by the distance e.

The circumference C1of the impulse ring7is equal to the diameter D of the impulse ring7in front of the detection means5multiply by π.

One electric degree is equal to the circumference C1divided by 360 multiply by the number of pair of magnetic poles NPP.

As illustrated onFIG. 6, a shift of amplitude equal to the distance e of the mechanical center X1relative to the magnetic center C4creates a magnet sector angle amplitude of an angle α multiply by 2, approximate by a position amplitude of the distance e multiply by 2.

The relation Flinkis equal to:

the amplitude ASHand the circumference being in millimetre, and the module TPD being in percentage.

For example, it is assumed that the diameter D is equal to 63 mm.

As the module TPD is equal to 0.2%, the amplitude ASHof the shifting is equal to 0.025 mm.

The shifting vector {right arrow over (SH)} is defined by the amplitude ASHequal to 0.025 mm and the direction DSHequal to 94.45° (−85.55° plus 180°).

FIG. 7represents the first single pitch deviation vector {right arrow over (SPD)}max, the second single pitch deviation vector {right arrow over (SPD)}min, the pitch deviation vector {right arrow over (TPD)} and the shifting vector {right arrow over (SH)}.

Then in step34(FIG. 3), the impulse ring7is locked in the radial direction so that the impulse ring is fixed radially and axially to the inner ring9of the bearing6.

The impulse ring7is locked for example by welding, gluing or clinching.

FIG. 8represents a second embodiment of the method for centering the magnetic center C4of the impulse ring7on the center of rotation of the bearing6.

If the steps30,31and32are executed for the first time (step35), then step33is executed and then steps31and32are repeated to determine a new total pitch deviation vector.

When the new total pitch deviation vector is determined, the module of the new total pitch deviation vector is compared to a threshold (step36). The value of the threshold is for example equal to 0.30%.

If the module of the new total pitch deviation vector is inferior or equal to the threshold, step34is executed.

If the module of the new total pitch deviation vector is superior to the threshold, step33is executed to determine the shifting vector, the amplitude of the shifting and the direction of the shifting being determined from the new total pitch deviation vector.

The method permits to compensate the misalignment of the different components of the bearing unit2by adjusting the impulse ring7according to the values of the total pitch deviation vector TPD without improving the accuracy of the bearing unit components so that the magnetic center of the impulse ring and the mechanical center of the bearing unit substantially coincident in order to improve the quality of the detection of the angular position of the rotor.

In the illustrated example, the sensor bearing unit is provided with a rolling bearing comprising one row of rolling elements. Alternatively, the rolling bearing may comprise at least two rows of rolling elements. In the illustrated example, the rolling elements are balls. Alternatively, the rolling bearing may comprise other types of rolling elements, for example rollers. In another variant, the rolling bearing may also be provided with a sliding bearing having no rolling elements.

Otherwise, in this illustrated example, the first ring of the rolling bearing is the inner ring8whereas the second ring is the outer ring9. As an alternative, it could be possible to provide a reversed arrangement with the first ring forming the outer ring and the second ring forming the inner ring. In this case, the impulse ring is secured to the outer ring.