The invention relates to the technical domain of bearings provided with a rotating means generating pulses, and referred to as an xe2x80x9cencoderxe2x80x9d, a detection device, referred to as a xe2x80x9csensorxe2x80x9d, make it possible to obtain information, such as for example, the speed of rotation, the angular position and the direction of rotation of a bush comprising such a bearing with built-in encoder.
Such bushes may, for example, be employed for the wheels of motor vehicles provided with a wheel anti-lock system.
The invention relates more particularly, but not exclusively, to bearings with built-in magnetic encoder, the functionally associated sensor being of magnetoresistor or Hall-effect probe type.
The expression xe2x80x9cHall-effect probexe2x80x9d here designates sensors comprising at least one sensitive element, generally a semiconductor in wafer form, such that, when a current I flows through it, whilst being subjected moreover to an induction B making an angle xcex8 with the current, a voltage V equal to V=K.I.B. sinxcex8 appears in a direction perpendicular to the current I and to the induction B, K being referred to as the xe2x80x9cHall constantxe2x80x9d, and being characteristic of the material and of the geometry of the sensitive element, K varying with temperature.
The expression xe2x80x9cmagnetoresistorxe2x80x9d here designates a varistor sensitive to the intensity of a magnetic field, or in other words a resistor made of a semiconductor material whose ohmic value varies alongside a variation in the intensity of a unidirectional magnetic field applied perpendicularly to the direction of the current flowing through the resistor.
Hall probes are regarded as active sensors, insofar as the information delivered is related to the electromotive force.
When these Hall probes are used for conveying position or displacement, the magnet which creates the induction is the test body on which the primary value to be measured acts, modifying the secondary measureand, namely conventionally the normal component of the induction, to which measurand the probe is directly sensitive.
Numerous designs of bearings with built-in magnetic encoder and sensors of Hall-effect probe or magnetoresistor type are already known in the prior art.
Reference may be made for example to the following documents:
French patent applications 2 667 947, 2 669 432, 2 669 728, 2 671 633, 2 678 691, 2 678 692, 2 690 989, 2 693 272, 2 694 082, 2 702 567, 2 710 985, 2 718 499;
European patent applications 375 019, 420 040, 420 041, 438 624, 487 405, 488 853, 498 298, 518 157, 521 789, 522 933, 531 924, 557 931, 557 932, 647 851, 693 689, 701 132, 701 133, 714 029, 745 857, 751 311, 753 679, 767 385.
Reference may be made, likewise by way of example, to the following documents emanating from the applicant:
French patent applications 2 639 689, 2 640 706, 2 645 924, 2 730 283, 2 732 458, 2 717 266, 2 701 298;
European patent applications 371 836, 376 771, 484 195, 394 083, 607 719, 616 219, 619 438, 631 140, 652 438, 671 628, 725 281, 735 348.
When one wishes to ascertain both the speed of rotation of the inner race or of the outer race of the bearing and also the direction of rotation of this race, it is known practice to utilize two signals electrically out of phase by 90xc2x0 to define the direction of rotation.
For the sake of clarity, it is recalled here that two sinusoidal signals of like frequency are said to be in quadrature when the signals are out of phase by xcfx80/2 or 90xc2x0, i.e. a quarter of a cycle, that is to say when one of the signals is at its peak value while the other is passing through zero.
Thus, for example, the document FR-A-2 599 794, emanating from the applicant, describes a bush or bearing with information sensor comprising a fixed element supporting, in one embodiment, two Hall sensors or magnetoresistors angularly offset by an interval of n+0.5n, in which n is the length of a magnet.
The document EP-A-395 783 describes a bush with a sensor for measuring the speed of rotation and/or the angle of rotation, comprising one or more Hall-effect sensors.
In the devices of the type mentioned above, the out-of-phase signals emanate from two Hall-effect sensitive elements or magnetoresistors, placed on a substrate or implanted directly on silicon with a defined and fixed distance between them, this distance being dependent on the encoder.
Given the inter-element distance fixed by the very principle of the sensor, in the case where the polar distance is not suitable, the digital signals emanating from the sensitive elements are not in quadrature.
Hence, the devices known from the prior art have the following drawbacks:
the polar length span, and therefore the encoder span which can be used with a dual sensor (that is to say having two sensitive elements), whose polar length is fixed, is limited by the tolerance in the quadrature of the digital output signals;
for a polar length corresponding to the inter-element distance, the tolerance in the output signals is dependent on the technology of the sensor and on the accuracy of placement of the sensitive elements;
in the case of a dual sensor delivering analog signals associated with an interpolation principle such as described in the document WO-97/01660 or in the document FR-97/12033, the accuracy required with regard to the quadrature of the analog signals limits the use of such a sensor to magnetic encoders whose polar distance corresponds accurately to the inter-element distance.
The invention relates to a device for detecting the direction of rotation of an outer race or of an inner race of a bearing, this device also allowing the detection of the angular position and of the speed of rotation of the said race, the said device allowing adaptation to various polar lengths and cancellation of the magnetic offset.
For this purpose, the subject of the invention is a bearing provided with an annular means generating magnetic pulses and with a device for detecting these pulses, the detection device comprising a plurality of aligned sensitive elements.
The aligned sensitive elements are, for example, chosen from among the group comprising Hall-effect probes, magnetoresistors, giant magnetoresistors and are placed equidistantly from one another.
According to one embodiment, the pulse generating means is an annular member 15 which is made of a synthetic material laden with ferrite particles and is formed by a plurality of contiguous domains 18 having reversed direction of magnetization of a given domain with respect to the two domains which are contiguous with it, as shown in FIG. 4.
In a first embodiment, the detection device comprises an even number 2N of sensitive elements, for example divided into two subassemblies of N elements, each sensitive element of the first subassembly being connected to a first adder, each sensitive element of the second subassembly being connected to a second adder, the two sums S1, S2 emanating from the first and second adders being connected to the input of a third adder, the output S1 of the first adder and, via an inverter, the output S1 of the second adder being connected to the input of a fourth adder, the signals SIN=S1+S2 and COS=S1xe2x88x92S2 emanating from the third and fourth adders being processed by a circuit so as to deduce the direction of rotation and/or the speed or rotation and/or the position of the pulse generating means with respect to the detection device.
In a first variant, the polar length Lp of the encoder is substantially equal to the product of the number 2N of sensitive elements times the distance d between sensitive elements, the signals SIN and COS then being in substantially perfect quadrature and of substantially like amplitude.
In a second variant, the polar length Lp of the encoder is less than the product of the number 2N of sensitive elements times the distance d between sensitive elements.
In a third variant, the polar length Lp of the encoder is greater than the product of the number 2N of sensitive elements times the distance d between sensitive elements.
By programming an even number 2M of sensitive elements, less than the total number 2N of these elements is employed to form two subassemblies of M elements, each sensitive element of the first subassembly being connected to a first adder, each sensitive element of the second subassembly being connected to a second adder, the two sums emanating from the first and second adders being connected to the input of a third adder, the output of the first adder and, via an inverter, the output of the second adder being connected to the input of a fourth adder, the signals emanating from the third and fourth adders being processed by a circuit so as to deduce the direction of rotation and/or the speed or rotation and/or the position of the pulse generating means with respect to the detection device, the said signals being in substantially perfect quadrature.
The programming can be carried out by EEPROM or by Zener Zapping.
In one envisageable subvariant, an amplifier circuit is able to re-establish an identical amplitude for the signals emanating from the third and fourth adders.
In a second embodiment, the detection device comprises a number of sensitive elements which is a multiple of four, for example divided into four subassemblies of P elements,
each sensitive element of the first subassembly with P elements being connected to a first adder supplying a signal S1;
each sensitive element of the second subassembly with P elements being connected to a second adder supplying a signal S2;
each sensitive element of the third subassembly with P elements being connected to a third adder supplying a signal Sxe2x80x21;
each sensitive element of the fourth subassembly with P elements being connected to a fourth adder supplying a signal Sxe2x80x22;
a circuit of adders and of inverters supplying two signals SIN and COS respectively equal to:
SIN=(S1xe2x88x92S2)xe2x88x92(Sxe2x80x21xe2x88x92Sxe2x80x22); 
COS=(S1+S2)xe2x88x92(Sxe2x80x21+Sxe2x80x22);
these signals SIN and COS being devoid of magnetic offset.
As a variant, the detection device comprises an interpolator increasing the resolution of these output signals.
In another embodiment, the sensitive elements are integrated on an ASIC type circuit support, the detection device is incorporated within an ASIC type customized integrated circuit.
According to one embodiment, the pulse generating means is integrated into a preassembled assembly forming a seal, the detection device being secured in a possibly removable manner to the fixed race.