Electronic position and speed sensing device

Details Electronic position and speed sensing device Electronic position and speed sensing device

1998-05-12

2001-03-27

Oda, Christine (Department: 2862)

Electricity: measuring and testing

Electrical speed measuring

Including speed analog electrical signal generator

C324S207220, C324S207250, C340S672000, C123S406580, C123S617000

Reexamination Certificate

active

06208131

ABSTRACT:

This invention relates to electronic position and speed sensors and, in particular, to position and speed sensors suitable for use in determining the timing for injection and ignition of combustible mixtures, for example, in spark ignited engines.
Conventional position and speed sensor devices for use in multi-cylinder engines, commonly referred to as “encoders”, typically comprise a wheel or disc which rotates at a speed which is a fraction of, or which is synchronous with, the speed of the engine crankshaft. These discs are commonly provided with a plurality of position indicators or markers and specific position indicators on their periphery which, upon passing a sensor, generate a train of pulses which may be analysed to determine the speed and position of the crankshaft and hence pistons in each cylinder of the engine.
The need for accuracy of the position and speed data produced by such sensing devices typically dictates that a large number of markers, usually teeth, notches, magnetic strips or other markers that can readily be detected by a sensor, are required to be provided on the disc. Generally, many equispaced teeth will be distributed around the circumference of an encoder disc to provide good angular resolution with factors of 360° being preferred, for example 15°, 30° or 45°. The teeth, together with the or a number of sensors, will generate the electrical signals that enable determination of speed and position at sufficient accuracy to be useful in the control of the operation of the engine.
It is to be understood that the need for sensing of specific position indicators which identify the top dead centre (TDC) position of each piston in each cylinder of the multi-cylinder engine creates particular problems. The sensing of the correct TDC position for each cylinder is critical to the determination of the appropriate ignition time, and sometimes injection time, to produce the combustible mixture required in each cylinder. Failure to determine the TDC position accurately may give rise to problems of misfiring of the engine and as a consequence, engine performance may be adversely affected.
Such failures are likely unless the sensing device is of a high sophistication because the many variables at play in the operation of the engine may create obstacles to the accurate determination of the TDC position or, indeed, any other pertinent position of the piston in each cylinder. For example, between markers, pulses are positioned using interpolation, usually without taking acceleration into account as this is difficult to measure. As a result, ignition and injection events may be timed incorrectly due to variations in the speed of rotation of the crankshaft in response to acceleration or deceleration causing the signal pulses to not occur at the desired angle and be of a shorter or longer duration. This effect worsens as the number of markers is reduced. In a case where the specific position indicator has only a slightly different angular width from other position indicators, this being a typical case in order to establish an absolute angular position, discrimination of specific position indicators can be difficult. Further, in a two cycle engine that is directly injected, it will be appreciated that an injection event and an ignition event occurs each revolution of the crankshaft rather than every two revolutions as is the case in a four stroke cycle engine. Therefore, sophisticated circuitry is required to ensure that correct control over injection and ignition timing occurs in the lesser time interval than would be available, for example, in a four cycle engine.
A still further problem has been that many prior art systems do not have the capability to provide an indication of rotation of an engine in a direction contrary to that desired. The consequences of incorrect rotation can be highly detrimental to the performance and life of the engine.
U.S. Pat. No. 4,941,445 assigned to Motorola Inc., discloses an electronic position sensor assembly with two sensing elements to provide separate, independent position signals related to multi-cylinder engine cycle control by sensing the angular position of an engine rotated slotted wheel. Specific position indicators of three different angular widths are required whilst a large number of position indicators are provided to generate position and engine speed data of sufficient accuracy for engine control. In addition to the dual sensing elements, a sophisticated control unit is required for analysis of the dual independent train of pulses produced. Needless to say, a two sensor, multi-tooth construction position sensor assembly with specific position indicators of several angular widths, whilst being a complicated arrangement, is also relatively costly to manufacture.
Australian Patent No. 626828 assigned to Caterpillar Inc., discloses an apparatus with a toothed wheel having a plurality of markers, the specific position indicators of which have a different angular extent to the other position indicators. In this case, a single sensor is relied upon to provide the required position and speed data. Again, the multi-tooth construction is relatively costly to manufacture.
A difficulty with each of the above proposals is that manufacture is problematic and accordingly expensive, especially in developing countries. In this regard, encoder wheels or discs of the kind described above require to be cast with very tight tolerances since the spacing of teeth, notches or other types of marker is crucial to the performance of the sensors as discussed above. The combination of these factors creates expense that can reach intolerable levels in developing countries which may not have access to equipment required for undertaking such manufacturing operations. In addition, the market may not be prepared to pay the premium for sensors which are manufactured by this process.
It is the object of the present invention to provide an engine position and speed sensor that reduces or alleviates at least some of the problems referred to above.
With this object in view, the present invention provides a position and speed sensor comprising:
a circular element rotatably driven about an axis thereof, said circular element having two position indicators of different angular width arranged thereon;
a sensor means fixed in position with respect to and adjacent to the circular element, the sensor means having a sensing element for sensing the passage of each of the position indicators past the sensing element and producing in response thereto an electrical signal corresponding to the passage of each of the sensed position indicators and having a duration corresponding to the angular widths of the sensed position indicators; and
means to process the electrical signal to produce information as to the angular position and angular velocity of the circular element.
Preferably, the two position indicators are the only position indicators provided on the circular element.
Preferably, in addition to providing information as to angular position and angular velocity, the means to process the electrical signal may additionally produce information as to the direction of rotation of the circular element.
Conveniently, the position and speed sensor is an electronic position and speed sensor and the circular element is arranged to rotate at a speed which is a fraction or multiple of, or which is synchronous with, the speed of rotation of a crankshaft of an engine. Preferably, the position indicators are sensed in turn by the sensing element such that the sensing of a second position indicator occurs very shortly after the sensing of a first position indicator.
The location of the two position indicators may be arbitrarily selected but should be such that the separation distance therebetween does not cause problems from the point of view of discrimination of one position indicator from the other, particularly so that transient acceleration and deceleration events may be compensated for and the most up-to-date information may be provided on angular velocity and position to ac

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