Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2003-03-10
2004-08-17
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06776058
ABSTRACT:
TECHNICAL FIELD
The present invention relates to magnetosensitive or galvanomagnetic devices (e.g. Hall generators, magnetoresistors, etc.) arranged in arrays for use as digital torque sensors.
BACKGROUND OF THE INVENTION
Only analog sensors are available or known for use as torque sensors in automotive applications such as electronic power steering (EPS), engine control systems, etc. The majority of torque sensors use strain gages attached to a rotating shaft whose signal is transmitted through slip rings. In some cases, inductive coupling, infrared, or radio frequency methods are utilized for transmission instead of slip rings. These types of sensors arc highly accurate, but they are not suitable for in-vehicle applications due to the fragile nature of strain gages and the way they have to be attached to the shaft surface.
Presently, the torque sensor selected for EPS is of the resistive film type, which works in conjunction with a torsion bar. Essentially, it is a potentiometer translating the angle of the torsion bar twist into an electrical resistance value. It requires slip rings for signal transmission and, at least in principle, might have limited life due to localized film wear-out caused by extensive dithering.
Noncontacting compliant torque sensors utilizing a torsion bar to convert a twist of the torsion bar into torque by measuring the angular offset between the ends of the torsion bar are also known in the art. These torque sensors utilize various analog measurement techniques.
The use of magnetosensitive or galvanomagnetic devices, such as magnetoresistors (MRs) and Hall devices, as non-contacting position and angle sensors is well known in the art. For example, a magnetically biased differential magnetoresistive sensor may be used to sense angular position of a rotating toothed wheel, as for example exemplified by U.S. Pat. Nos. 4,835,467, 5,731,702, and 5,754,042.
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 moving 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 moving target wheel is adjacent to the MR than when a slot of the moving target wheel is adjacent to the MR.
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. No. 5,570,016.
Single element magnetic field sensors composed of, for example, an indium antimonide or indium arsenide epitaxial film strip supported on, for example, a monocrystalline elemental semiconductor substrate, are also known. The indium antimonide or indium arsenide film is, for example, deposited either directly on the elemental semiconductor substrate or on an intermediate film that has a higher resistivity than that of silicon. A conductive contact is located at either end of the epitaxial film, and a plurality of metallic (gold) shorting bars are on, and regularly spaced along, the epitaxial film. U.S. Pat. Nos. 5,153,557, 5,184,106 and 5,491,461 exemplify examples thereof.
Many kinds of measurements require high accuracy and high resolution, and, as such, cannot easily be performed with common magnetic sensors comprising a single sensing element or dual sensing elements. Improved accuracy and resolution measurements can be achieved, however, using an array. The most common magnetic sensing element, the Hall effect element or device, does not quite fit the requirements for an array. Being a 4-terminal device complicates the array connections. Furthermore, its low output signal mandates the use of an integrated amplifier for each sensing element increasing the die size and its cost. Nonetheless, appropriately configured Hall sensors can be incorporated into Hall arrays.
However, compound semiconductor MRs, such as those manufactured from InSb, InAs, etc. are simply two-terminal resistors with a high magnetic sensitivity. Thus, compound semiconductor MRs are very suitable for the construction of single die MR array geometries for use as large range angular position sensors. In most cases, one terminal of all the MR elements can be common.
Ultimately, such MR arrays could be integrated on the same die with appropriate processing circuitry. For example, if the MR array were fabricated on a Si substrate then the processing circuitry would be also Si based. For higher operating temperatures, silicon-on-insulator (SOI) fabrication could be used. A potentially lower cost alternative to the SOI approach would be to take advantage of the fact that MRs are currently fabricated on GaAs, a high temperature semiconductor. In this regard, the integrated processing circuitry is fabricated on GaAs (or related InP) using HBT (Heterojunction Bipolar Transistor) or HEMT (High Electron Mobility Transistor) structures. This technology is now easily available and inexpensive through the explosive growth of the cellular phone industry.
Accordingly, what is needed is a compact and inexpensive die having at least two arrays of magnetosensitive elements and configured so as to produce an array geometry suitable for torque sensing schemes in which the output signals are capable of being directly coupled to digital signal processing electronics, such as a digital signal processor or microprocessor, whereby appropriate algorithms can provide, for example, target torque information, target position information, direction of target rotation, and target rotational speed information.
SUMMARY OF THE INVENTION
The present invention is a compact, inexpensive, high accuracy, non-contacting digital torque sensor employing a torsion bar, a target wheel at each end thereof, and at least two magnetosensitive (galvanomagnetic) sensors, in the form of magnetosensor device arrays (one for each target wheel, respectively), to precisely determine the angle of twist of the torsion bar (unlike present art compliant analog torque sensors employing a torsion bar and utilizing analog measuring techniques). The present invention also provides target wheel rotation speed, position and rotational direction information, is capable of self-compensation over wide temperature ranges and air gaps, including tilts, does not require tight assembly tolerances and has a theoretically infinite life due to its non-contact nature. The present invention can also be smaller than the present resistive film type torsion sensor and can meet anticipated future reduced size requirements.
The present invention employs two identical target wheels, having peripherally disposed magnetic irregularities preferably consisting of teeth and slots, fixedly attached to opposing ends of a torsion bar. By “fixedly attached” is meant that both target wheels must rotate in unison with twist of the torsion bar at its respective attachment location. The teeth and slots of the target wheels do not have to be aligned in any particular way with respect to each other.
The teeth and slots of each target wheel are sensed by its respective magnetosensitive sensor, each being composed of an array of several magnetosensitive (galvanomagnetic) elements preferably manufactured on a single die to secure extremely accurate spacing between the elements. The arrays do not need to be placed at the same angular positions of the torsion bar or target wheels. The arrays may be located anywhere around the periphery of their respective target wheel provided that the array elements are aligned with the direction of target wheel rotation.
When the torque sensor is initially installed, each array is rapidly scanned by a micropr
Delphi Technologies Inc.
Funke Jimmy L.
Noori Max
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