Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-08-14
2004-06-08
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207160, C324S207170, C324S207220, C324S207250
Reexamination Certificate
active
06747448
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to sensing devices and sensing techniques thereof. The present invention also relates to magnetic sensors. Additionally, the present invention relates to rotary position sensors. The present invention is also related to cam and crank applications, such as camshaft and crankshaft devices.
BACKGROUND OF THE INVENTION
A variety of techniques are utilized for angular position sensing. Optical, resistive, electrical, and electrostatic and magnetic fields have all been utilized with sensing devices to measure position. There are many known devices that utilize optical, resistive, electrical, magnetic and other such energies for sensing. Examples of such sensing devices include resistive contacting sensors, inductively coupled ratio detectors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors utilizing the Faraday effect, photo-activated ratio detectors, radio wave directional comparators, and electrostatic ratio detectors. In addition, there are many other sensors/detectors that are not mentioned herein.
Each of these detection methods offers much value for one or more applications, but none meet all application requirements for all position sensing applications. The limitations may be due to cost, sensitivity to particular energies and fields, resistance to contamination and environment, stability, ruggedness, linearity, precision, or other similar factors. Transportation applications generally, and specifically automotive applications, are very demanding.
In mechanical and/or electromechanical systems, such as for example, automotive applications, motion can be initiated and controlled by rotating a member such as a shaft (e.g., camshaft, crankshaft, and so forth). The angular motion of the shaft is then translated into some other motion, such as linear displacement, rotation of a pump or fan, or the angular rotation of some other intermediate part at a different angular velocity or spatial orientation. Numerous mechanical means such as gears, cams, pulleys, and belts are commonly employed in translating the angular motion of an input shaft to drive an output device. Camshaft and crankshaft mechanisms, for example, are well known in the mechanical transportation arts. Thus, a need exists for sensors that can properly monitor motion and position in such mechanical systems.
In engine cam and crank applications, for example, recently manufactured cars require precision rotary sensors for high performance and fuel economy. In particular, some of the new camless engines require precision rotary sensors. Such engines utilize electrical-mechanical solenoids to control the engine valves. The opening and closing of such valves are not controlled by a fixed cam but can be controlled by a microprocessor that receive inputs from precision rotary sensors regarding the crank, speed, torque, load, exhaust gas mixture, oxygen content, and so forth. In this manner, an engine can be achieved that is both efficient and high performing.
Thus, a critical need exists for high performance camshaft and crankshaft position sensors. Major automakers worldwide are presently working, for example, on camless four-stroke engines because of potential performance advantages and reduction in mechanical components subject to wear. A number of development hurdles must be overcome before such mechanical systems can be widely deployed. Cost will limit the camless engine to high-performance cars for some time. Obviously, camless engines do not require a camshaft sensor. On the other hand, valve position sensors will very likely be needed. Developers are presently faced with the challenge of creating cost-effective solutions now, in anticipation of this emerging need. As transport systems develop in their complexity and performance, a need has emerged for non-contact rotary position sensors, which offer significant durability enhancements, lower cost, and improved performance.
Rotary position sensors play a particularly critical role in crankshaft applications used in automotive and other transport systems (e.g., trucking, aerospace, etc.), because the U.S. government requires misfire detection as part of the On-Board Diagnostics incorporated in the engine control system to detect failures of any components of the system. Such failures could result in emissions not being controlled within the proper limits. The misfire event must be identified down to a specific cylinder except at low loads and high rpm. A “misfire” is generally known as an absence of combustion in one or more cylinders, either occurring singly or multiple times. It can be caused by a failure of the ignition system to provide spark or by a failure in the fuel injection system resulting in fuel not being provided to a cylinder. It differs from “knock”, which is spontaneous ignition of the fuel-air mixture. Knock can result in engine damage and is a function of several parameters of both the engine and the fuel used. Engines expected to operate on a variety of fuels usually incorporate a knock detection and prevention function in the engine control system. Misfires typically do not result in engine damage but may cause failure of the catalytic converter if it has to cope with unburned gases.
Each time ignition occurs, the resulting power stroke accelerates the crankshaft and it then decelerates at a rate determined by the load on the engine. The basic equation governing crankshaft angular acceleration/deceleration is as follows: &agr;=d
&ohgr;
/dt=d
2
&thgr;/dt
2
=(T
P
−T
L
)/I, where T
P
=Torque produced by engine, T
L
=Load torque, and I=Moment of inertia of drive train.
A four-stroke engine, for example, produces N/2 torque pulses per crankshaft revolution, where N=number of cylinders. For a constant load torque, the crankshaft accelerates each time a combustion event occurs, followed by a deceleration due to the load torque. By measuring these speed fluctuations, misfires can be detected since a larger deceleration will occur if one or more firing pulses are missed. For a fixed engine displacement, each power pulse becomes smaller as the number of cylinders increases, reducing the magnitude of the speed fluctuations. Likewise, as the load on the engine decreases, the engine decelerates less between power pulses. A variation in load torque due to a bump in the road may also result in a crankshaft speed fluctuation and possibly be confused with a misfire. The misfire detection algorithm is disabled when load torque fluctuations occur, either by an accelerometer signal or by monitoring wheel speed fluctuations. The crankshaft speed fluctuation method is the most widely used approach since most engines already incorporate a crankshaft position sensor.
To be usable for misfire detection by the crankshaft speed fluctuation method, a sensor must have excellent repeatability. Repeatability is affected primarily by the sensor's sensitivity to dynamic radial and axial run-out of the target and by the signal-to-noise ratio of the sensor. Generally, a target can be made wide enough so that axial run-out does not result in any error. The error due to dynamic radial run-out is proportional to the error as a function of air gap so that a sensor with minimum error as a function of air gap is preferred. Typical gear tooth sensors have three main error sources: air gap error, speed error, and temperature error. In general, auto manufacturers desire precision rotary sensors for gearshift levers (e.g., P, R, N, 1, 2, 3, DR). In addition, new automobiles require an absolute rotary position at startup and cannot wait for one or more revolutions of the crank to find the top dead center (TDC) as with gear tooth rotary sensors.
Thus, it can be appreciated that it is very desirable to monitor the position of various mechanical parts within a mechanical system. In many cases, however, due to space restrictions or other physical characteristics, it is inconvenient or impossible to directly monitor the position of a particular pa
Fredrick Kris T.
Kinder Darrell
Lopez Kermit D.
Ortiz Louis M.
Patidar Jay
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