Method and apparatus for detecting the direction of crankshaft rotation during a single tooth/slot transition

[0002] The present invention relates to a method of sensing direction of crankshaft rotation and more particularly to a method and apparatus to sense direction of crankshaft rotation from the passage of single tooth edges of an encoder or target wheel with a single, currently used, differential sequential sensor employing either Hall elements or magnetoresistors.

[0003] It is well known in the art that the resistance modulation of Hall elements or magnetoresistors can be employed in position and speed sensors with respect to moving ferromagnetic materials or objects (see for example U.S. Pat. Nos. 4,835,467; 4,926,122; and 4,939,456).

[0004] Increasingly more sophisticated spark timing and emission controls introduced the need for crankshaft sensors capable of providing not only precise position information, but also, during cranking, a direction of rotation signal. Currently, as shown in FIG. 1, direction of rotation, clockwise (CW) 32 or counterclockwise (CCW) 34, is most commonly obtained from an encoder wheel 10, also called a target wheel, having a plurality of teeth 12 and slots 14 of essentially equal length which have a spacing between adjacent teeth or a spacing between adjacent slots of P, called the tooth/slot pitch. The teeth 12 and slots 14 are sensed by SENSOR116 and SENSOR218 in quadrature (i.e. with spacing between sensors equal to one-quarter of the tooth/slot pitch P). Equal lengths of teeth 12 and equal lengths of slots 14 and the one-quarter pitch spacing between sensors are preferred, but not absolutely necessary. The square wave output signals from SENSOR116 and SENSOR218 are fed as a clock input 20 and a data input 22 into a D type FLIP-FLOP 24 whose output 26 provides a direction indication and is either high (H) 28 or low (L) 30 depending on the direction of rotation of the target wheel 10. Due to the large P/4 distance between SENSOR116 and SENSOR218, a major disadvantage of the current method is the inability to detect the change of rotational direction of the target wheel when a single tooth edge, such as tooth edge 36, is oscillating around a single sensor, such as SENSOR116. In this case, SENSOR116 would detect the back and forth oscillating single tooth edge 36 as the rising and falling edges of passing teeth 12. Since the direction indication 26 would remain unchanged, serious position errors would be generated. For this reason, and due to the necessity of adding a second sensor, the conventional method of detecting direction of rotation is not suitable for automotive crankshaft sensors.

[0005] What is needed is a method and apparatus whereby the direction of rotation of an automotive crankshaft can be obtained from the passage of a single tooth edge of a target wheel.

[0006] The present invention provides detection of direction of rotation via the outputs of a differential sequential sensor employing two matched sensing elements, either Hall elements or magnetoresistors (MRs), to extract direction of rotation information from the passage of a single tooth edge of a target wheel. The two matched sensing elements are spaced in close proximity to each other, preferably on the order of about 1 mm to 2 mm apart, in the circumferential direction of the target wheel and generate two identical angularly offset signals from the passage of a single tooth edge of a target wheel which are input to a signal conditioning circuit. Within the signal conditioning circuit, the two sensor signals are differentially amplified to produce a differential signal whereby the polarity of the differential signal enables one of two comparators with respective reference voltages. The output of the enabled comparator is processed and converted into a digital output signal whose voltage level indicates the direction of rotation of the target wheel.

[0007] Accordingly, it is an object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth edge.

[0008] It is an additional object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth-slot edge using two closely spaced sensing elements.

[0009] These, and additional objects, advantages, features, and benefits of the present invention will become apparent from the following specification.

[0010] FIG. 1 shows a combined environmental depiction and circuit schematic of a conventional direction of rotation sensor.

[0011] FIG. 2 depicts an example of a preferred environment of use of the present invention.

[0012] FIG. 3 shows an electronic block diagram of the preferred embodiment of the present invention.

[0013] FIGS. 4athrough 4sshow the wave forms generated from FIG. 3 due to the passage of a rising edge of a tooth of a target wheel rotating in a clockwise (CW) direction.

[0014] FIGS. 5athrough 5sshow the wave forms generated from FIG. 3 due to the passage of a falling edge of a tooth of a target wheel rotating in a clockwise (CW) direction.

[0015] FIGS. 6athrough 6sshow the wave forms generated from FIG. 3 due to the passage of a rising edge of a tooth of a target wheel rotating in a counterclockwise (CCW) direction.

[0016] FIGS. 7athrough 7sshow the wave forms generated from FIG. 3 due to the passage of a falling edge of a tooth of a target wheel rotating in a counterclockwise (CCW) direction.

[0017] FIG. 8 is a table summarizing the results of FIGS. 4athrough 7s.

[0018] FIG. 2 is a schematic representation of an exemplar automotive environment of use according to the present invention, wherein a target wheel 10′ is rotating, such as for example in unison with a crankshaft, a drive shaft or a cam shaft, and the rotative direction thereof is to be sensed. Rotative direction of the target wheel 10′ is determined by sensing the passage of either a rising tooth edge 36′ or a falling tooth edge using a single differential sequential sensor 50. A tooth edge 36′ is considered rising or falling depending upon the direction of rotation of the target wheel 10′ with respect to the magnetoresistive sensors MR1 and MR2. The single differential sequential sensor 50 employs two matched magnetoresistor (MR) elements, MR1 and MR2, which are biased by a permanent magnet 56, wherein the magnetic flux 60 and 62 emanating therefrom is represented by the dashed arrows. The magnetic flux 60 and 62 passes from the permanent magnet 56 through the magnetoresistors MR1 and MR2 and through the air gaps 64 and 66 to the target wheel 10′. The target wheel 10′ is made of a magnetic material having teeth 12′ and spacings 14′ therebetween. The spacing L between MR1 and MR2 is between about 1 mm (or less) and about 2 mm (or more) in the circumferential direction of the target wheel 10′ and the target wheel is located near the single differential sequential sensor 50 as indicated in FIG. 2.

[0019] Power is supplied to CURRENT SOURCE172 and CURRENT SOURCE274 through voltage source 70. Power is also supplied to signal conditioning circuit 80 through voltage source 70 but is not shown. CURRENT SOURCE172 supplies current to MR1 thereby providing for an output voltage V_MR1from MRI. CURRENT SOURCE274 supplies current to MR2 thereby providing for an output voltage V_MR2from MR2. Output voltages V_MR1and V_MR2are input into signal conditioning circuit 80 whose output voltage V_OUTis an indication of the direction of rotation of target wheel 10′. It is to be understood that all voltages are measured with respect to ground unless otherwise indicated herein, and that CURRENT SOURCE1 is matched to CURRENT SOURCE2.

[0020] FIG. 3 shows an electronic block diagram of the preferred embodiment of the present invention. It is well known in the art that the resistance of a magnetoresistor will have a larger value when the magnetoresistor is adjacent to a tooth 12′ of a target wheel 10′ of FIG. 2 than when the magnetoresistor is adjacent to a slot 14′ of the target wheel. Thus, when MR1 and MR2 are powered by constant current sources, the output voltages V_MR1and V_MR2will have higher values when the magnetoresistors MR1 and MR2 are adjacent a tooth 12′ of a target wheel 10′ than when MR1 and MR2 are adjacent a slot 14′ of the target wheel. The circuit of FIG. 3 functions as follows.

[0021] As the passage of a tooth edge 36′ is sensed by MR1 and MR2, the two sensor signals V_MR1and V_MR2are input into a differential amplifier 90 to produce a differential signal pulse V_D, which in this case V_Dis taken to be V_MR1−V_MR2.V_Dcould also be taken as V_MR2−V_MR1within the scope of the present invention. During the time that the polarity of V_Dis positive and greater than the reference voltages +ΔV, which is applied to the negative input of comparator C₁, the output of comparator C₁, V_C1, will be high and the output of comparator C₂, V_C2, will be low. Further, during the time that the polarity of V_Dis negative and less than the reference voltage −ΔV, which is applied to the positive input of comparator C₂, the output of comparator C₂, V_C2, will be high and the output of comparator C₁, V_C1, will be low. Hence, the output of C₁, will be a square wave with a positive voltage level or value for V_C2, for V_Dhaving positive values greater than +ΔV, whereas the output of C₂will be a square wave with a positive voltage level or value for V_C2for VD having negative values less than −ΔV.

[0022] The square wave output of either C₁or C₂appears at the output of OR gate G₃as a square wave with a positive voltage for V_G3which is input into the FALLING EDGE SINGLE SHOT block 92. FALLING EDGE SINGLE SHOT block 92 outputs a pulse with a positive voltage for V_SSwhose falling edge is used as the clock input into FLIP-FLOP 94 to latch the output voltage V_OUTof the FLIP-FLOP to the value of the input voltage V_C3to the FLIP-FLOP. The value of V_C3is determined as follows.

[0023] If C₁outputs a square wave, as previously described, then DUAL SINGLE SHOT196 will output a pulse on the rising and falling edges of the square wave. The rising edge pulse from DUAL SINGLE SHOT196 latches the output voltage, V_SH1, of SAMPLE & HOLD198 to the value of V_MR1at this time. The falling edge pulse from DUAL SINGLE SHOT196 latches the output voltage, V_SH2, of SAMPLE & HOLD2100 to the value of V_MR1at this time.

[0024] On the other hand, if C₂outputs a square wave, as previously described, then DUAL SINGLE SHOT2102 will output a pulse on the rising and falling edges of the square wave. The rising edge pulse from DUAL SINGLE SHOT2102 latches the output voltage, V_SH2, of SAMPLE & HOLD2100 to the value of V_MR1at this time. The falling edge pulse from DUAL SINGLE SHOT2102 latches the output voltage, V_SH1, of SAMPLE & HOLD198 to the value of V_MR1at this time.

[0025] Within the scope of the present invention, V_MR2could be the sampled voltage of SAMPLE & HOLD198 and SAMPLE & HOLD2100 instead of V_MR1. V_SH1is one input into comparator C₃and V_SH2is another input into comparator C₃. If V_SH2is larger than V_SH1then the output of C₃, V_C3, will be a high voltage which will appear as V_OUTwhen a clock pulse is input to FLIP-FLOP 94 as previously described. If V_SH1is larger than V_SH2then the output of C₃, V_C3, will be a low voltage which will appear as V_OUTwhen a clock pulse is input to FLIP-FLOP 94 as previously described. As will be explained in FIGS. 4a through 7s, the value of VOUT is indicative of the direction of rotation of the target wheel. With V_Dtaken to be V_MR1−V_MR2and V_MR1being the sampled voltage of SAMPLE & HOLD198 and SAMPLE & HOLD2100, a high voltage for V_OUTindicates a CW rotation of the target wheel 10′ of FIG. 2 whereas a low voltage for Vout indicates a CCW rotation of the target wheel.

[0026] FIGS. 4athrough 4sshow the wave forms generated from FIG. 3 due to the passage of a rising edge 36′ of a tooth 12′ of a target wheel 10′ rotating in a clockwise (CW) direction. The sensors MR1 and MR2 are initially adjacent to a slot 14′ of the target wheel 10′ which is rotating in a CW direction as shown in FIG. 4aand V_MR1and V_MR2have a low value as depicted in (a) of FIG. 4d.As the target wheel 10′ rotates CW, MR1 becomes adjacent to a tooth 12′ of the target wheel whereas MR2 is still adjacent to a slot 14′ but is approaching the tooth as shown in FIG. 4b.During this time V_MR1, rises quickly to a high level whereas V_MR2starts to rise as MR2 approaches the tooth 12′ as shown in (b) of FIG. 4d.As the target wheel 10′ continues to rotate CW, both MR1 and MR2 become adjacent to a tooth 12′ and V_MR1and V_MR2are at a high level as shown in (c) of FIG. 4d.

[0027] FIG. 4edepicts the differential voltage pulse V_D,which is positive in this case, thereby, producing a square wave output, V_C1, from comparator C₁of FIG. 3, as shown in FIG. 4f,which is then input to DUAL SINGLE SHOT196 of FIG. 3. The DUAL SINGLE SHOT1 of FIG. 3 outputs a pulse V_DSS1(R) of FIG. 4jon the rising edge of V_C1as well as a pulse V_DSS1(F) of FIG. 4kon the falling edge of V_C1.

[0028] V_DSS1(R) is input to OR gate G₁, of FIG. 3 and the output of OR gate G₁, V_G1, shown in FIG. 4nis input to SAMPLE & HOLD198 of FIG. 3. The output of SAMPLE & HOLD198 of FIG. 3, V_SH1, is denoted as V₁, and is depicted in FIGS. 4dand 4q.V₁, in FIG. 4d,is the value of V_MR1at the rising edge of V_C1, of FIG. 4fand is applied to the negative input of comparator C₃of FIG. 3.

[0029] V_DSS1(F) is input to OR gate G₂of FIG. 3 and the output of OR gate G₂, V_G2, shown in FIG. 4ois input to SAMPLE & HOLD2100 of FIG. 3. The output of SAMPLE & HOLD2100 of FIG. 3, V_SH2, is denoted as V₂and is depicted in FIGS. 4dand 4p.V₂, in FIG. 4d,is the value of V_MR1at the falling edge of V_C1of FIG. 4fand is applied to the positive input of comparator C₃of FIG. 3.

[0030] As can be seen in FIG. 4dand by comparing FIG. 4pto FIG. 4q,V₂is greater than V₁. Thus the output of comparator C₃of FIG. 3, V_C3, will have a high value as shown in FIG. 4r.V_C3in FIG. 3 is input to FLIP-FLOP 94 and is transferred to the output of the FLIP-FLOP where it appears as Vout upon reception of the falling edge of a clock pulse, V_SS, to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT 92.

[0031] The clock pulse, V_SS, is shown in FIG. 4i.V_SSis the output of FALLING EDGE SINGLE SHOT 92 of FIG. 3. The FALLING EDGE SINGLE SHOT 92 of FIG. 3 generates the pulse V_SSupon the falling edge of V_G3of FIG. 4hwhich is obtained from the falling edge of V_C1, via OR gate G₃of FIG. 3. Thus, when the clock pulse, V_SS, is input to FLIP-FLOP 94 of FIG. 3, V_OUTwill have a high value as depicted in FIG. 4sindicating, in this case, a CW rotation of the target wheel 10′ of FIG. 3.

[0032] FIG. 5 shows the wave forms generated from FIG. 3 due to the passage of a falling edge 36′ of a tooth 12′ of a target wheel 10′ rotating in a clockwise (CW) direction. The sensors MR1 and MR2 are initially adjacent to a tooth 12′ of the target wheel 10′ which is rotating in a CW direction as shown in FIG. 5aand V_MR1and V_MR2have a high value as depicted in (a) of FIG. 5d.As the target wheel 10′ rotates CW, MR1 becomes adjacent to a slot 14′ of the target wheel whereas MR2 is still adjacent to a tooth 12′ but is approaching the slot as shown in FIG. 5b.During this time V_MR1falls quickly to a low level whereas V_MR2starts to fall as MR2 approaches the slot 14′ as shown in (b) of FIG. 5d.As the target wheel 10′ continues to rotate CW, both MR1 and MR2 become adjacent to a slot 14′ and V_MR1and V_MR2are at a low level as shown in (c) of FIG. 5d.

[0033] FIG. 5edepicts the differential voltage pulse V_D, which is negative in this case, thereby, producing a square wave output, V_C2, from comparator C₂of FIG. 3, as shown in FIG. 5g,which is then input to DUAL SINGLE SHOT2102 of FIG. 3. The DUAL SINGLE SHOT2102 of FIG. 3 outputs a pulse V_DSS2(R) of FIG. 51 on the rising edge of V_C2as well as a pulse V_DSS2(F) of FIG. 5oon the falling edge of V_C2.

[0034] V_DSS2(R) is input to OR gate G₂of FIG. 3 and the output of OR gate G₂, V_G2, shown in FIG. 5ois input to SAMPLE & HOLD2100 of FIG. 3. The output of SAMPLE & HOLD2100 of FIG. 3, V_SH2, is denoted as V₁, and is depicted in FIGS. 5dand 5p.V₁, in FIG. 5d,is the value of V_MR1at the rising edge of V_C2of FIG. 5gand is applied to the positive input of comparator C₃of FIG. 3.

[0035] V_DSS2(F) is input to OR gate G₁of FIG. 3 and the output of OR gate G₁, V_G1, shown in FIG. 5nis input to SAMPLE & HOLD198 of FIG. 3. The output of SAMPLE & HOLD198 of FIG. 3, V_SH1, is denoted as V₂and is depicted in FIGS. 5dand 5q.V₂, in FIG. 5d,is the value of V_MR1at the falling edge of V_C2of FIG. 5gand is applied to the negative input of comparator C₃of FIG. 3.

[0036] As can be seen in FIG. 5dand by comparing FIG. 5pto FIG. 5q,V₁, is greater than V₂. Thus the output of comparator C₃of FIG. 3, V_C3, will have a high value as shown in FIG. 5r.V_C3in FIG. 3 is input to FLIP-FLOP 94 and is transferred to the output of the FLIP-FLOP where it appears as V_OUTupon reception of the falling edge of a clock pulse, V_SS, to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT 92.

[0037] The clock pulse, V_ss, is shown in FIG. 5i.V_SSis the output of FALLING EDGE SINGLE SHOT 92 of FIG. 3. The FALLING EDGE SINGLE SHOT 92 of FIG. 3 generates the pulse V_SSupon the falling edge of V_G3of FIG. 5hwhich is obtained from the falling edge of V_C2via OR gate G₃of FIG. 3. Thus, when the clock pulse, V_SS, is input to FLIP-FLOP 94 of FIG. 3, V_OUTwill have a high value as depicted in FIG. 5sindicating, in this case, a CW rotation of the target wheel 10′ of FIG. 3.

[0038] FIG. 6 shows the wave forms generated from FIG. 3 due to the passage of a rising edge 36′ of a tooth 12′ of a target wheel 10′ rotating in a counterclockwise (CCW) direction. The sensors MR1 and MR2 are initially adjacent to a slot 14′ of the target wheel 10′ which is rotating in a CCW direction as shown in FIG. 6aand V_MR1and V_MR2have a low value as depicted in (a) of FIG. 6d.As the target wheel 10′ rotates CCW, MR2 becomes adjacent to a tooth 12′ of the target wheel whereas MR1 is still adjacent to a slot 14′ but is approaching the tooth as shown in FIG. 6b.During this time V_MR2rises quickly to a high level whereas V_MR1starts to rise as MR1 approaches the tooth 12′ as shown in (b) of FIG. 6d.As the target wheel 10′ continues to rotate CCW, both MR1 and MR2 become adjacent to a tooth 12′ and V_MR1and V_MR2are at a high level as shown in (c) of FIG. 6d.

[0039] FIG. 6edepicts the differential voltage pulse V_D,which is negative in this case, thereby, producing a square wave output, V_C2, from comparator C₂of FIG. 3, as shown in FIG. 6g,which is then input to DUAL SINGLE SHOT2102 of FIG. 3. The DUAL SINGLE SHOT2102 of FIG. 3 outputs a pulse V_DSS2(R) of FIG. 61 on the rising edge of V_C2as well as a pulse V_DSS2(F) of FIG. 6mon the falling edge of V_C2.

[0040] V_DSS2(R) is input to OR gate G₂of FIG. 3 and the output of OR gate G₂, V_G2, shown in FIG. 60 is input to SAMPLE & HOLD2100 of FIG. 3. The output of SAMPLE & HOLD2100 of FIG. 3, V_SH2, is denoted as V₁, and is depicted in FIGS. 6dand 6p.V₁, in FIG. 6d,is the value of V_MR1at the rising edge of V_C2of FIG. 6gand is applied to the positive input of comparator C₃of FIG. 3.

[0041] V_DSS2(F) is input to OR gate G₁, of FIG. 3 and the output of OR gate G₁, V_G1, shown in FIG. 6nis input to SAMPLE & HOLD198 of FIG. 3. The output of SAMPLE & HOLD198 of FIG. 3, V_SH1, is denoted as V₂and is depicted in FIGS. 6dand 6q.V₂, in FIG. 6d,is the value of V_MR1at the falling edge of V_C2of FIG. 6gand is applied to the negative input of comparator C₃of FIG. 3.

[0042] As can be seen in FIG. 6dand by comparing FIG. 6pto FIG. 6q,V₂is greater than V₁. Thus the output of comparator C₃of FIG. 3, V_C3, will have a low value as shown in FIG. 6r.V_C3in FIG. 3 is input to FLIP-FLOP 94 and is transferred to the output of the FLIP-FLOP where it appears as V_OUTupon reception of the falling edge of a clock pulse, V_SS, to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT 92.

[0043] The clock pulse, V_SS, is shown in FIG. 6i.V_SSis the output of FALLING EDGE SINGLE SHOT 92 of FIG. 3. The FALLING EDGE SINGLE SHOT 92 of FIG. 3 generates the pulse V_SSupon the falling edge of V_G3of FIG. 6hwhich is obtained from the falling edge of V_C2via OR gate G₃of FIG. 3. Thus, when the clock pulse, V_SS, is input to FLIP-FLOP 94 of FIG. 3, V_OUTwill have a low value as depicted in FIG. 6sindicating, in this case, a CCW rotation of the target wheel 10′ of FIG. 3.

[0044] FIG. 7 shows the wave forms generated from FIG. 3 due to the passage of a falling edge 36′ of a tooth 12′ of a target wheel 10′ rotating in a counterclockwise (CCW) direction. The sensors MR1 and MR2 are initially adjacent to a tooth 12′ of the target wheel 10′ which is rotating in a CCW direction as shown in FIG. 7aand V_MR1and V_MR2have a high value as depicted in (a) of FIG. 7d.As the target wheel 10′ rotates CCW, MR2 becomes adjacent to a slot 14′ of the target wheel whereas MR1 is still adjacent to a tooth 12′ but is approaching the slot as shown in FIG. 7b.During this time V_MR2falls quickly to a low level whereas V_MR1starts to fall as MR1 approaches the slot 14′ as shown in (b) of FIG. 7d.As the target wheel 10′ continues to rotate CCW, both MR1 and MR2 become adjacent to a slot 14′ and V_MR1and V_MR2are at a low level as shown in (c) of FIG. 7d.

[0045] FIG. 7edepicts the differential voltage pulse V_D, which is positive in this case, thereby, producing a square wave output, V_C1, from comparator C₁of FIG. 3, as shown in FIG. 7f,which is then input to DUAL SINGLE SHOT196 of FIG. 3. The DUAL SINGLE SHOT1 of FIG. 3 outputs a pulse V_DSS1(R) of FIG. 7jon the rising edge of V_C1as well as a pulse V_DSS1(F) of FIG. 7kon the falling edge of V_C1.

[0046] V_DSS1(R) is input to OR gate G₁of FIG. 3 and the output of OR gate G₁, V_G1, shown in FIG. 7nis input to SAMPLE & HOLD198 of FIG. 3. The output of SAMPLE & HOLD198 of FIG. 3, V_SH1, is denoted as V₁, and is depicted in FIGS. 7dand 7q.V₁, in FIG. 7d,is the value of V_MR1at the rising edge of V_C1, of FIG. 7fand is applied to the negative input of comparator C₃of FIG. 3.

[0047] V_DSS1(F) is input to OR gate G₂of FIG. 3 and the output of OR gate G₂, V_G2, shown in FIG. 7ois input to SAMPLE & HOLD2100 of FIG. 3. The output of SAMPLE & HOLD2100 of FIG. 3, V_SH2, is denoted as V₂and is depicted in FIGS. 7dand 7p.V₂, in FIG. 7d,is the value of V_MR1at the falling edge of V_C1, of FIG. 7fand is applied to the positive input of comparator C₃of FIG. 3.

[0048] As can be seen in FIG. 7dand by comparing FIG. 7pto FIG. 7q,V₁, is greater than V₂. Thus the output of comparator C₃of FIG. 3, V_C3, will have a low value as shown in FIG. 7r.V_C3in FIG. 3 is input to FLIP-FLOP 94 and is transferred to the output of the FLIP-FLOP where it appears as V_OUTupon reception of the falling edge of a clock pulse, V_SS, to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT 92.

[0049] The clock pulse, V_SS, is shown in FIG. 7i.V_SSis the output of FALLING EDGE SINGLE SHOT 92 of FIG. 3. The FALLING EDGE SINGLE SHOT 92 of FIG. 3 generates the pulse V_SSupon the falling edge of V_G3of FIG. 7hwhich is obtained from the falling edge of V_C1via OR gate G₃of FIG. 3. Thus, when the clock pulse, V_SS, is input to FLIP-FLOP 94 of FIG. 3, V_OUTwill have a low value as depicted in FIG. 7sindicating, in this case, a CCW rotation of the target wheel 10′ of FIG. 3.

[0050] The Table of FIG. 8 summarizes how the direction of rotation is obtained from a single tooth edge 36′ from a knowledge of the polarity of the differential signal pulse, V_D, and whether the output signal, in this example, V_MR1, is rising or falling within the differential pulse interval. It is understood by those knowledgeable in the art that V_MR2or a combination of V_MR1and V_MR2could also be used as the output signal within the differential pulse interval within the scope of the present invention.

[0051] It is to be understood that while magnetoresistors (MRs) were exemplified in the foregoing detailed description of a preferred embodiment of the present invention, other analogous sensing elements, such as hall elements my be utilized, the class of such sensors being inclusively denoted as magnetostatic elements.

[0052] To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.