Low cost binary encoded crankshaft position sensor

Details Low cost binary encoded crankshaft position sensor Low cost binary encoded crankshaft position sensor

1999-02-17

2001-07-31

Strecker, Gerard R. (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207210, C123S406580, C341S015000

Reexamination Certificate

active

06268721

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of sensing precise angular positions of a rotating object and more particularly to a method and apparatus to sense crankshaft rotational position utilizing a single track target wheel with a single dual element sensor employing either Hall elements or magnetoresistors.
BACKGROUND OF THE INVENTION
It is well known in the art that the resistance modulation of magnetoresistors can be employed in position and speed sensors with respect to moving magnetic materials or objects (see for example U.S. Pat. Nos. 4,835,467, 4,926,122, and 4,939,456). In such applications, the magnetoresistor (MR) is biased with a magnetic field and electrically excited, typically, with a constant current source or a constant voltage source. A magnetic (i.e., ferromagnetic) object rotating relative and in close proximity to the MR, such as a toothed wheel, produces a varying magnetic flux density through the MR, which, in turn, varies the resistance of the MR. The MR will have a higher magnetic flux density and a higher resistance when a tooth of the rotating target wheel is adjacent to the MR than when a slot of the rotating target wheel is adjacent to the MR. The use of a constant current excitation source provides an output voltage from the MR that varies as the resistance of the MR varies.
Increasingly more sophisticated spark timing and emission controls introduced the need for crankshaft sensors capable of providing precise position information during cranking. Various combinations of magnetoresistors and single and dual track toothed or slotted wheels (also known as encoder wheels and target wheels) have been used to obtain this information (see for example U.S. Pat. Nos. 5,570,016, 5,731,702, and 5,754,042).
A target wheel of interest in this regard, is the 24X target wheel (see for example U.S. Pat. No. 5,570,016). This wheel and its associated sensor utilize analog signals which are converted into a 24 bit digital signal that is repeated every 360 degrees of rotation of the wheel. Each bit represents a particular position of the wheel and adjacent bits are angularly separated by 15 degrees. Prior art uses of this wheel have utilized a single sensor incorporating two matched MRs with a dual track wheel or a dual sensor, each sensor incorporating two matched MRs, with a single track wheel.
What is needed is a method and apparatus whereby the position of the crankshaft can be obtained via bit encoding utilizing one sensor incorporating two matched MRs in conjunction with a simple single track target wheel that can be inexpensively manufactured as an integral part of the crankshaft or as a separate item to be installed later.
SUMMARY OF THE INVENTION
The present invention provides detection of position of rotation via the outputs of a differential sensor employing two matched MRs to extract bit position of rotation information from a simple single track target wheel that can be inexpensively manufactured as an integral part of the crankshaft or as a separate item to be installed later.
The target wheel is toothed with wide and narrow slots between teeth circumferentially such that, preferentially but not exclusively, 24 zones are created wherein each zone occupies 15 degrees circumferentially measured from the center of one slot to the center of an adjacent slot. Within the context of the present invention, the target wheel may also be toothed with wide and narrow teeth circumferentially such that, preferentially but not exclusively, 24 zones are created wherein each zone occupies 15 degrees circumferentially measured from the center of one tooth to the center of an adjacent tooth.
The two matched MRs of the sensor, having matched magnetic biasing and powered by matched current sources, are aligned in the circumferential direction of the target wheel and generate two angularly offset signals (first and second voltages, respectively) from the passage of a single slot of the target wheel which are input to a signal conditioning circuit. Within the signal conditioning circuit, the two sensor signals (first and second voltages) are differentially amplified to produce a differential signal whereby the width of the slot is used to encode a binary position pulse. For example, a wide slot may be encoded as a binary “0” while a narrow slot may be encoded as a binary “1” although the reverse binary assignments could also be used.
Empirical testing and/or theoretical modeling is required to determine the optimal width of an arbitrary slot with respect to the spacing between the MRs such that the magnetic symmetry, the matched MR elements, and the matched current sources cause a magnetic flux density to be sensed by the MRs when they are equidistant from the center of the slot such that the output resistances of the two MRs and, thus, their output signals become equal (crossover) in the middle of the slot whereby the crossover occurs at a value of resistance (or output signal) equal to the average value or midpoint value, to be further exemplified later, of the highest and lowest resistance (or output signal) taken at the peak value of the differential resistance (or output signal) between the two MRs during the passage of the slot. For example, crossover occurs at the midpoint level if the slot width is equal to the MR spacing plus, approximately, 1.2 mm.
Empirical testing and/or theoretical modeling is also required to determine the optimal width of an arbitrary tooth with respect to the spacing between the MRs such that the magnetic symmetry, the matched MR elements, and the matched current sources cause a magnetic flux density to be sensed by the MRs when they are equidistant from the center of the tooth such that the output resistances of the two MRs and, thus, their output signals become equal (crossover) in the middle of the tooth whereby the crossover occurs at a value of resistance (or output signal) equal to the average value or midpoint value of the highest and lowest resistance (or output signal) taken at the peak value of the differential resistance (or output signal) between the two MRs during the passage of the tooth. For example, crossover occurs at the midpoint level if the tooth width is equal to the MR spacing minus, approximately, 1.2 mm.
Empirical testing and/or theoretical modeling is required to determine the optimal width of a wide or narrow slot with respect to the spacing between the MRs such that the magnetic symmetry, the matched MR elements, and the matched current sources cause a magnetic flux density to be sensed by the MRs when they are equidistant from the center of the slot such that the output resistances of the two MRs and, thus, their output signals become equal (crossover) in the middle of the slot whereby, for a wide slot, crossover occurs at a value of resistance (or output signal) less than the average value or midpoint value of the highest and lowest resistance (or output signal) taken at the peak value of the differential resistance (or output signal) between the two MRs during the passage of the wide slot and, for a narrow slot, crossover occurs at a value of resistance (or output signal) greater than the average value or midpoint value of the highest and lowest resistance (or output signal) taken at the peak value of the differential resistance (or output signal) between the two MRs during the passage of the narrow slot. For example, the width of a narrow slot is equal to the width of a slot at which crossover occurs at the midpoint level (as calculated above) minus, approximately, 1.8 mm whereas the width of a wide slot is equal to the width of a slot at which crossover occurs at the midpoint level (as calculated above) plus, approximately, 1.6 mm. The low level signal from a wide slot is assigned the binary value of “0” while the high level signal is assigned the binary value of “1” although the reverse assignments of binary values could also be used.
Alternatively, the present invention could be implemented by width encoded teeth instead of slots whereby empirical testing and/or theoretical modeling is req

Affiliated with

Also associated with

Rating

Low cost binary encoded crankshaft position sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Low cost binary encoded crankshaft position sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low cost binary encoded crankshaft position sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2519398