A wheel speed sensor and its sensing method

Abstract

A wheel speed sensor and its sensing method, comprising an induction head and a signal processing circuit; the induction head includes: a first induction branch, a second induction branch, a third induction branch and a fourth induction branch, and the processing circuit unit includes but is not limited to an operational amplifier, a digital-to-analog converter, and a digital circuit. Compared with the existing wheel speed sensors based on the Hall principle, the wheel speed sensor based on the magnetoresistive induction principle proposed by the present invention can significantly increase the induction distance and reduce the output signal jitter. At the same time, the innovative induction head design and signal processing circuit proposed by the present invention adopt the differential principle and an optimized signal combination method, and have excellent anti-interference ability and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic sensors, and more specifically, to a wheel speed sensor and its sensing method. Background Art

[0002] Automotive wheel speed sensors are widely used in the anti-lock braking system (ABS), electric power steering system (EPS), and indirect tire pressure monitoring system (iTPMS) of automobiles, and are key sensors related to the driving safety of automobiles.

[0003] Currently, most of the automotive wheel speed sensors on the market are based on the Hall induction principle. However, the wheel speed sensors based on the Hall induction principle have problems such as a small induction airgap and a large output signal jitter. When the installation distance is large or the vehicle travels with large bumps, the output signal will be lost. At the same time, the large jitter also limits its application in the indirect tire pressure monitoring system.

[0004] The magnetoresistive effect refers to the effect that the resistance value of some ferromagnetic metals or semiconductors changes with the change of the external magnetic field. Commonly used magnetoresistive effects generally include semiconductor magnetoresistance (SMR), anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunneling magnetoresistance (TMR). Compared with Hall devices, magnetoresistive devices have higher sensitivity, more stable temperature characteristics, and are insensitive to stress. When using magnetoresistive devices to construct a wheel speed sensor, the induction airgap will increase significantly, and the signal jitter will also be greatly reduced, significantly improving the performance of the wheel speed sensor.

[0005] Aiming at the problems of the wheel speed sensor based on the Hall induction principle, the present invention provides a system and method for a wheel speed sensor based on the magnetoresistive induction principle. Summary of the Invention

[0006] The purpose of the present invention is to provide a wheel speed sensor and its sensing method, which can increase the induction airgap and reduce the output signal jitter.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] A wheel speed sensor includes an induction magnetic head and a signal processing circuit;

[0009] The induction magnetic head includes:

[0010] The first induction branch, the first induction branch includes a first power supply terminal, a second power supply terminal, and a first sensing element of the first branch and a second sensing element of the first branch connected in series between the two power supply terminals; the electrical signal at the first intermediate node between the first sensing element of the first branch and the second sensing element of the first branch is VA;

[0011] The second induction branch, the second induction branch includes a first power supply terminal, a second power supply terminal, and a first sensing element of the second branch and a second sensing element of the second branch connected in series between the two power supply terminals; the electrical signal at the second intermediate node between the first sensing element of the second branch and the second sensing element of the second branch is VM1;

[0012] The third induction branch, the third induction branch includes a first power supply terminal, a second power supply terminal, and a first sensing element of the third branch and a second sensing element of the third branch connected in series between the two power supply terminals; the electrical signal at the third intermediate node between the first sensing element of the third branch and the second sensing element of the third branch is VM2;

[0013] The fourth induction branch, the fourth induction branch includes a first power supply terminal, a second power supply terminal, and a first sensing element of the fourth branch and a second sensing element of the fourth branch connected in series between the two power supply terminals; the electrical signal at the fourth intermediate node between the first sensing element of the fourth branch and the second sensing element of the fourth branch is VB;

[0014] Each sensing element of the induction head is manufactured based on a magnetoresistive unit; the first induction branch, the first sensing element of the first branch and the second sensing element of the first branch it includes have the same resistance magnitude in the absence of a magnetic field, but have magnetoresistive changes in opposite directions for the same magnetic field, so the electrical signal VA at the first intermediate node will generate a signal change deviating from VCC / 2.

[0015] The voltage between the first power supply terminal and the second power supply terminal is VCC.

[0016] Each sensing element of the induction head is manufactured based on a magnetoresistive unit;

[0017] The magnetoresistive unit is one of semiconductor magnetoresistance SMR, anisotropic magnetoresistance AMR, giant magnetoresistance GMR, and tunneling magnetoresistance TMR.

[0018] The signal processing circuit includes three or four processing circuit units;

[0019] The processing circuit unit includes, but is not limited to, operational amplifiers, digital-to-analog converters, and digital circuits.

[0020] A sensing method for a wheel speed sensor, comprising the following steps:

[0021] The electrical signal VA at the first intermediate node and the electrical signal VB at the fourth intermediate node serve as the input terminals of the first operational amplifier of the first processing circuit unit. After differential amplification by the first operational amplifier, they enter the first digital-to-analog converter. The output electrical signal after digital-to-analog conversion is V1, and then it enters the digital circuit for further processing. The electrical signal VM1 at the second intermediate node and the electrical signal VB at the fourth intermediate node serve as the input terminals of the second operational amplifier of the second processing circuit unit. After differential amplification by the second operational amplifier, they enter the second digital-to-analog converter. The output electrical signal after digital-to-analog conversion is V2, and then it enters the digital circuit for further processing. The electrical signal VM2 at the third intermediate node and the electrical signal VA at the first intermediate node serve as the input terminals of the third operational amplifier of the third processing circuit unit. After differential amplification by the third operational amplifier, they enter the third digital-to-analog converter. The output electrical signal after digital-to-analog conversion is V3, and then it enters the digital circuit for further processing. In the digital circuit, the electrical signals V2 and V3 are added to obtain Vsum = V2 + V3.

[0022] When the wheel speed sensor is working, the wheel drives the permanent magnet ring or ferromagnetic gear to rotate. The electrical signals V1 and Vsum exhibit waveforms in an approximately sinusoidal form. When the changing electrical signal V1 passes through its own midpoint, a speed pulse signal of the wheel speed sensor is emitted. According to the phase relationship between the electrical signal Vsum and the electrical signal V1, a steering signal of the wheel speed sensor is obtained and emitted.

[0023] Compared with the existing wheel speed sensors based on the Hall principle, the wheel speed sensor proposed in the present invention based on the magnetoresistive induction principle can significantly increase the induction distance and reduce the output signal jitter. At the same time, the innovative induction head design and signal processing circuit proposed in the present invention adopt the differential principle and optimized signal combination method, and have excellent anti-interference ability and stability. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of a wheel speed sensor according to the first embodiment of the invention.

[0025] Figure 2 It is a schematic structural diagram of the sensing element of a first induction branch according to the first embodiment of the invention.

[0026] Figure 3 It is a schematic structural diagram of the sensing element of a first induction branch according to the first embodiment of the invention.

[0027] Figure 4 It is a schematic structural diagram of the sensing element of a first induction branch according to the first embodiment of the invention.

[0028] Figure 5It is a schematic diagram of the sensing element structure of a first induction branch in the first embodiment of the invention.

[0029] Figure 6(a) is a schematic diagram of a magnetic field with a periodically changing induction direction generated at the induction head during the operation of the wheel speed sensor in the first embodiment of the invention.

[0030] Figure 6(b) is a schematic diagram of periodic electrical signals generated by each intermediate node of the induction head in the first embodiment of the invention along with the periodically changing magnetic field.

[0031] Figure 7 It is a schematic diagram of the waveforms of the electrical signals V1 and Vsum of the wheel speed sensor in the first embodiment of the invention.

[0032] Figure 8 It is a schematic diagram of the speed pulse signal of the wheel speed sensor based on the present invention.

[0033] Among them, 10: induction head; 20: signal processing circuit; 101: first induction branch 101; 105: first power supply terminal; 106: second power supply terminal; 1011: first sensing element of the first branch; 1012: second sensing element of the first branch; 1013: first intermediate node; 102: second induction branch; 1021: first sensing element of the second branch; 1022: second sensing element of the second branch; 1023: second intermediate node; 103: third induction branch; 1031: first sensing element of the third branch; 1032: second sensing element of the third branch; 1033: third intermediate node; 104: fourth induction branch; 1041: first sensing element of the fourth branch; 1042: second sensing element of the fourth branch; 1043: fourth intermediate node; 201: first processing circuit unit; 202: second processing circuit unit; 203: third processing circuit unit; OP1: first operational amplifier; ADC1: first analog-to-digital converter; OP2: second operational amplifier; ADC2: second analog-to-digital converter; OP3: third operational amplifier; ADC3: third analog-to-digital converter; DC: digital circuit. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying Figure 1-8 , and the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] Embodiment 1:

[0036] A wheel speed sensor includes an induction head 10 and a signal processing circuit 20, asFigure 1 as shown;

[0037] The inductive head includes: (a) a first inductive branch 101, the first inductive branch 101 including a first power terminal 105, a second power terminal 106, and a first branch first sensing element 1011 and a first branch second sensing element 1012 connected in series between the two power terminals. The electrical signal at the first intermediate node 1013 between the first branch first sensing element 1011 and the first branch second sensing element 1012 is VA; (b) a second inductive branch 102, the second inductive branch 102 including a first power terminal 105, a second power terminal 106, and a second branch first sensing element 1021 and a second branch second sensing element 1022 connected in series between the two power terminals. The electrical signal at the second intermediate node 1023 between the second branch first sensing element 1021 and the second branch second sensing element 1022 is VM1; (c) a third inductive branch 103, the third inductive branch 103 including a first power terminal 105, a second power terminal 106, and a third branch first sensing element 1031 and a third branch second sensing element 1032 connected in series between the two power terminals. The electrical signal at the third intermediate node 1033 between the third branch first sensing element 1031 and the third branch second sensing element 1032 is VM2; (d) a fourth inductive branch 104, the fourth inductive branch 104 including a first power terminal 105, a second power terminal 106, and a fourth branch first sensing element 1041 and a fourth branch second sensing element 1042 connected in series between the two power terminals. The electrical signal at the fourth intermediate node 1043 between the fourth branch first sensing element 1041 and the fourth branch second sensing element 1042 is VB;

[0038] The voltage between the first power terminal 105 and the second power terminal 106 is VCC;

[0039] Each sensing element of the inductive head 10 is manufactured based on a magnetoresistive unit;

[0040] The magnetoresistive unit is one type of semiconductor magnetoresistance (SMR), anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunneling magnetoresistance (TMR);

[0041] The four inductive branches of the inductive head: the first inductive branch 101, the second inductive branch 102, the third inductive branch 103, and the fourth inductive branch 104 have the same structure and magnetoresistive unit, and the four inductive branches are arranged in sequence;

[0042] Taking the first induction branch 101 as an example, the first branch first sensing element 1011 and the first branch second sensing element 1012 it contains have the same resistance magnitude when there is no magnetic field, but have magnetoresistance changes in opposite directions for the same magnetic field. Then, the electrical signal VA at the first intermediate node 1013 will generate a signal change deviating from VCC / 2.

[0043] As a preferred example, as Figure 2 shown, the first branch first sensing element 1011 contains a number of magnetoresistive units, and the orientation of the magnetoresistive units is +45 degrees (the angle with the X-axis); the first branch second sensing element 1012 also contains a number of magnetoresistive units, and the orientation of the magnetoresistive units is -45 degrees (the angle with the X-axis). Moreover, the magnetoresistive units of the first branch first sensing element 1011 and the magnetoresistive units of the first branch second sensing element 1012 are exactly the same in size and quantity, and the two are at a 90-degree angle to each other in orientation.

[0044] As a preferred example, as Figure 3 shown, the first branch first sensing element 1011 contains a number of magnetoresistive units, and the orientation of the magnetoresistive units is 0 degrees (the angle with the X-axis); the first branch second sensing element 1012 also contains a number of magnetoresistive units, and the orientation of the magnetoresistive units is 90 degrees (the angle with the X-axis). Moreover, the magnetoresistive units of the first branch first sensing element 1011 and the magnetoresistive units of the first branch second sensing element 1012 are exactly the same in size and quantity, and the two are at a 90-degree angle to each other in orientation.

[0045] As a preferred example, as Figure 4 shown, the first branch first sensing element 1011 contains a number of magnetoresistive units; the first branch second sensing element 1012 also contains a number of magnetoresistive units, and the magnetoresistive units of the first branch first sensing element 1011 and the magnetoresistive units of the first branch second sensing element 1012 are exactly the same in size, quantity, and orientation. However, a series of highly conductive conductive metal strips are arranged on the surface of the magnetoresistive units of the first branch first sensing element 1011, and the orientation of the conductive metal strips is +45 degrees (the angle with the X-axis). A series of highly conductive conductive metal strips are arranged on the surface of the magnetoresistive units of the first branch second sensing element 1012, and the orientation of the conductive metal strips is -45 degrees (the angle with the X-axis).

[0046] As a preferred example, as Figure 5As shown, the first sensing element 1011 of the first branch includes a number of magnetoresistive units; the second sensing element 1012 of the first branch also includes a number of magnetoresistive units, and the magnetoresistive units of the first sensing element 1011 of the first branch are exactly the same in size, quantity, and orientation as those of the second sensing element 1012 of the first branch. However, the pinning direction of the pinning layer of the magnetoresistive units of the first sensing element 1011 of the first branch is along the positive Y-axis (as shown by the arrow), and the pinning direction of the pinning layer of the magnetoresistive units of the second sensing element 1012 of the first branch is along the negative Y-axis (as shown by the arrow).

[0047] When there is no external magnetic field, the resistances of the first sensing element 1011 of the first branch and the second sensing element 1012 of the first branch are equal, and the electrical signal VA at the first intermediate node 1013 is near VCC / 2. When an external magnetic field in the induction direction is applied, the magnetoresistance of the first sensing element 1011 of the first branch increases (or decreases), while the magnetoresistance of the second sensing element 1012 of the first branch decreases (or increases). The change directions of the magnetoresistances of the two are opposite, and the electrical signal VA at the first intermediate node 1013 will generate a signal change deviating from VCC / 2.

[0048] If the external magnetic field in the induction direction changes periodically, the electrical signal VA at the first intermediate node 1013 will generate a periodic signal change with VCC / 2 as the central value;

[0049] Similarly, when the external magnetic field in the induction direction changes periodically, the electrical signals VM1 at the second intermediate node 1023, the electrical signal VM2 at the third intermediate node 1033, and the electrical signal VB at the fourth intermediate node 1043 will also generate periodic signal changes with VCC / 2 as the central value.

[0050] As shown in Fig. 6(a), when the wheel speed sensor 1 works, the rotation of the permanent magnet magnetic ring or the ferromagnetic gear driven by the wheel will generate a periodically changing magnetic field in the induction direction at the induction head of the wheel speed sensor. At the same time, since the four induction branches of the induction head: the first induction branch 101, the second induction branch 102, the third induction branch 103, and the fourth induction branch 104 are arranged in sequence and there is a spatial position difference, there will be a phase difference in time for the magnetic field changes sensed by the four induction branches. Furthermore, there is also a phase difference in time for the electrical signals VA at the first intermediate node 1013, the electrical signal VM1 at the second intermediate node 1023, the electrical signal VM2 at the third intermediate node 1033, and the electrical signal VB at the fourth intermediate node 1043, as shown in Fig. 6(b). When the permanent magnet magnetic ring rotates one pair of magnetic poles or the ferromagnetic gear rotates one tooth pitch, the magnetic field in the induction direction at the induction head changes one cycle, and the signals of VA, VM1, VM2, and VB also change one cycle synchronously.

[0051] The signal processing circuit includes three processing circuit units. The signal processing circuit further processes the electrical signals VA, VM1, VM2, and VB of the induction head to generate the speed pulse signal and the steering signal of the wheel speed sensor;

[0052] The processing circuit unit includes, but is not limited to, operational amplifiers, digital-to-analog converters, and digital circuits;

[0053] The electrical signal VA at the first intermediate node 1013 and the electrical signal VB at the fourth intermediate node 1043 serve as the input terminals of the first operational amplifier OP1 of the first processing circuit unit 201. After differential amplification by the first operational amplifier OP1, it enters the first digital-to-analog converter ADC1. The output electrical signal after digital-to-analog conversion is V1, and then it enters the digital circuit DC for further processing; The electrical signal VM1 at the second intermediate node 1023 and the electrical signal VB at the fourth intermediate node 1043 serve as the input terminals of the second operational amplifier OP2 of the second processing circuit unit 202. After differential amplification by the second operational amplifier OP2, it enters the second digital-to-analog converter ADC2. The output electrical signal after digital-to-analog conversion is V2, and then it enters the digital circuit DC for further processing; The electrical signal VM2 at the third intermediate node 1033 and the electrical signal VA at the first intermediate node 1013 serve as the input terminals of the third operational amplifier OP3 of the third processing circuit unit 203. After differential amplification by the third operational amplifier OP3, it enters the third digital-to-analog converter ADC3. The output electrical signal after digital-to-analog conversion is V3, and then it enters the digital circuit DC for further processing; In the digital circuit DC, the electrical signals V2 and V3 are added to obtain Vsum = V2 + V3.

[0054] When the wheel speed sensor is working, the wheel drives the permanent magnet ring or the ferromagnetic gear to rotate, generating a periodically changing magnetic field in the induction direction at the induction head, thereby generating periodically changing electrical signals VA, VM1, VM2, and VB. Then, the electrical signals V1 and Vsum obtained through signal processing exhibit a periodic waveform similar to a sine form. When the permanent magnet ring rotates a pair of magnetic poles or the ferromagnetic gear rotates a tooth pitch, the signals of V1 and Vsum also synchronously change a period. When the periodically changing electrical signal V1 passes through its own midpoint, the speed pulse signal of the wheel speed sensor is emitted. According to the phase relationship between the electrical signal Vsum and the electrical signal V1, the steering signal of the wheel speed sensor is obtained and emitted. For example, when the phase of Vsum leads V1, it is forward rotation, and when the phase of Vsum lags behind V1, it is reverse rotation, as Figure 7 shown.

[0055] In the first embodiment above, when the wheel speed sensor is working, the wheel drives the permanent magnet ring or ferromagnetic gear to rotate, generating a periodically changing magnetic field in the induction direction at the induction head. When the permanent magnet ring rotates by a pair of magnetic poles or the ferromagnetic gear rotates by a tooth pitch, the electrical signals output by the four induction branches and the V1 / Vdiff_0 / Vdiff_1 and Vsum / Vsum_0 / Vsum_1 signals obtained through signal processing also synchronously change by one cycle. The wheel speed sensor in the present invention can generate a speed pulse signal and a steering signal. Combining the three output protocols (standard protocol, PWM protocol, and AK protocol) of the wheel speed sensor, corresponding output speed pulse waveforms are generated, as Figure 8 shown, where the steering signal is respectively reflected in the pulse width of the PWM protocol and the direction data bit of the AK protocol.

[0056] The wheel speed sensor based on the magnetoresistive induction principle proposed by the present invention innovatively adopts four induction branches to generate four periodic electrical signals with a phase difference in a periodically changing magnetic field. In the signal processing circuit, the differential principle and the optimized signal combination method are adopted to generate stable and reliable speed pulse signals and steering signals, and resist the interference of the external common-mode magnetic field, having excellent stability and anti-interference performance. At the same time, taking advantage of the high sensitivity of the magnetoresistive element, compared with the wheel speed sensor based on the Hall principle, it has a larger induction spacing and smaller output signal jitter, which can significantly improve the performance of the wheel speed sensor, expand the wide application of the wheel speed sensor in the passive tire pressure monitoring system and the automatic parking field, and will produce good economic and social benefits.

[0057] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the invention and do not limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

[0058] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the same elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A wheel speed sensor, characterized in that It includes an induction head and a signal processing circuit; The induction head includes: A first induction branch, which includes a first power supply terminal, a second power supply terminal, and a first sensing element of the first branch and a second sensing element of the first branch connected in series between these two power supply terminals; the electrical signal at the first intermediate node between the first sensing element of the first branch and the second sensing element of the first branch is VA; A second induction branch, which includes a first power supply terminal, a second power supply terminal, and a first sensing element of the second branch and a second sensing element of the second branch connected in series between these two power supply terminals; the electrical signal at the second intermediate node between the first sensing element of the second branch and the second sensing element of the second branch is VM1; A third induction branch, which includes a first power supply terminal, a second power supply terminal, and a first sensing element of the third branch and a second sensing element of the third branch connected in series between these two power supply terminals; the electrical signal at the third intermediate node between the first sensing element of the third branch and the second sensing element of the third branch is VM2; A fourth induction branch, which includes a first power supply terminal, a second power supply terminal, and a first sensing element of the fourth branch and a second sensing element of the fourth branch connected in series between these two power supply terminals; the electrical signal at the fourth intermediate node between the first sensing element of the fourth branch and the second sensing element of the fourth branch is VB; The four induction branches of the induction head have the same structure and magnetoresistive units, and these four induction branches are arranged in sequence; The first sensing elements and the second sensing elements of the four induction branches have the same resistance magnitude in the absence of a magnetic field, but have magnetoresistive changes in opposite directions for the same magnetic field; The signal processing circuit includes three or four processing circuit units; The processing circuit unit includes, but is not limited to, an operational amplifier, an analog-to-digital converter ADC, and a digital circuit; The electrical signal VA at the first intermediate node and the electrical signal VB at the fourth intermediate node are used as the input terminals of the operational amplifier of the first processing circuit unit. After differential amplification by the operational amplifier, it enters the ADC, and then the output electrical signal after analog-to-digital conversion is V1, and then it enters the digital circuit for further processing; the electrical signal VM1 at the second intermediate node and the electrical signal VB at the fourth intermediate node are used as the input terminals of the operational amplifier of the second processing circuit unit. After differential amplification by the operational amplifier, it enters the ADC, and then the output electrical signal after analog-to-digital conversion is V2, and then it enters the digital circuit for further processing; the electrical signal VM2 at the third intermediate node and the electrical signal VA at the first intermediate node are used as the input terminals of the operational amplifier of the third processing circuit unit. After differential amplification by the operational amplifier, it enters the ADC, and then the output electrical signal after analog-to-digital conversion is V3, and then it enters the digital circuit for further processing; in the digital circuit, the electrical signals V2 and V3 are added to obtain Vsum = V2 + V3; When the wheel speed sensor is working, the wheel drives the permanent magnet magnetic ring or the ferromagnetic gear to rotate, and the electrical signals V1 and Vsum show waveforms in an approximate sine form. When the changing electrical signal V1 passes through its own midpoint, a speed pulse signal of the wheel speed sensor is emitted. According to the phase relationship between the electrical signal Vsum and the electrical signal V1, a steering signal of the wheel speed sensor is obtained and emitted.

2. The wheel speed sensor according to claim 1, wherein The voltage between the first power terminal and the second power terminal is VCC.

3. The wheel speed sensor according to claim 1, wherein Each sensing element of the induction head is manufactured based on a magnetoresistive unit; The magnetoresistive unit is one of semiconductor magnetoresistance SMR, anisotropic magnetoresistance AMR, giant magnetoresistance GMR, and tunneling magnetoresistance TMR.

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