This invention relates to position sensors such as throttle position sensors and, in particular, to a method of setting throttle position sensors for use in engine applications. When used in engine applications, throttle position sensors typically require to be set or tuned such that their range of possible outputs correctly correspond to valid engine throttle settings. Typically, the low voltage output end of a throttle position sensor, typically a potentiometer, or "pot", corresponds to one extreme of throttle position settings whilst the high voltage output end of the sensor corresponds to another extreme of throttle position settings. Generally, although not essentially, the low voltage output end corresponds to idle operation throttle settings whilst the high voltage output end corresponds to wide open throttle (WOT) operation settings. Such sensors may, depending on their application and/or working environment, be set once installed on an engine or may be set prior to such installation.

In certain engine applications, the setting of such throttle position sensors is presently a time consuming process in which the pot is attached to the engine and approximate settings for idle and WOT throttle positions are manually set. Using suitable measuring equipment, the voltages corresponding to the approximate idle and WOT throttle positions are then read off. If the values at idle and WOT are acceptable, the throttle sensor or potentiometer is fixed in position on the engine. However, it is more common that several iterations will be required before the pot or sensor may be successfully installed. In this regard, the installation time for the pot may take up to 4-5 minutes and even longer for installations having dual throttle potentiometers which is certainly not desirable, particularly in regard to mass assembly of engines.

In addition, the present method of setting the potentiometer is subject to human error in that the potentiometer setting may be changed by influences such as operator movement upon installation. The setting of the potentiometer is also subject to vibration and other environmental factors. Difficulties may also arise from servicing or repairs to an engine in that the potentiometer is required to be reset if it is removed from the engine.

In certain engine applications, the accuracy of setup of the potentiometer is most important. For example, in certain engine applications which employ the Applicant's direct injected two stroke technology, the throttle position potentiometer is a primary sensor for load control whereas in other more conventional systems it may only be a secondary sensor. For example, some conventional four stroke engines rely on a lambda or oxygen sensor to determine what the level of air-flow to the engine is and hence what the fuelling rate should be. The throttle position sensor on such engines serves as a secondary input, or less critical input, in dictating the overall operation of the engine. With some such systems, the engine may still run satisfactorily if the throttle position sensor failed.

In regard to the Applicant's direct injected engines having fuel based control systems, the level of fuelling to the engine is directly dependent upon the operator demand as indicated by the throttle position. Hence, the throttle position potentiometer in such an application is a primary sensor and critical to the satisfactory operation of the engine.

It is therefore the object of the present invention to provide a method of tuning a sensor, typically a potentiometer, that is less time consuming and subject to less error than previous methods. With this object in view, the present invention provides a method of setting a throttle position sensor in-situ on an engine wherein the engine throttle is in a known position and a signal within the signal range of the sensor corresponding to the known position is generated by the sensor and recorded. A further signal within the signal range of the sensor is then scaled off to correspond with a second known throttle position and recorded.

More particularly, the method comprises setting the throttle position sensor in-situ on the engine wherein the engine throttle is in a first known position at one extreme of throttle position settings, generating a signal at one end of the signal range of the throttle position sensor corresponding to the first known position of the throttle and recording the signal, and scaling off a further signal within the signal range of the sensor to correspond with a second known throttle position and recording said signal. Preferably, the further signal

corresponds to the other end of the sensor signal range and is scaled off to correspond with a second known throttle position at another extreme of the throttle position settings.

The engine throttle may be driven or actuated into the known first position and thereafter a signal at one end of the signal range of the sensor is generated by the sensor and recorded so as to correspond with this first known throttle position.

Preferably, the signal range between the two end points is scaled such that signals which fall within the range correspond to throttle position settings, being typically throttle position settings corresponding to various significant engine operating conditions, which occur between the first known and second known throttle position extremes.

Preferably, the first known throttle position corresponds to idle operation of the engine. Conveniently, the second known throttle position relates to wide open throttle (WOT) operation of the engine. In this regard, the method is readily applicable in the case of a marine engine application wherein typically, the engine is not able to be cranked until the gearbox throttle/shift lever has been returned to the neutral position which corresponds to idle operation of the engine and therefore the idle position for the throttle. That is, there exists a throttle interlock which prevents the engine being started in anything other than an idle condition and hence the first known position of the throttle is readily available for the method of the present invention.

Preferably, the method of setting the throttle position sensor is performed during cranking of the engine when the engine speed is not zero. The operator demand is however zero during this period and it has been found that the throttle position sensor can be easily set within the shortest cranking time conventionally used.

Accordingly, upon initial cranking of the engine, the throttle position is known as the driver demand is zero and hence the throttle position sensor is able to be set. Once the relationship between the throttle position sensor output and idle has been established, the resulting signal can simply be scaled to the opposite end of the known signal range for the sensor and this second signal

then becomes equated with WOT operation. Other signal points for the throttle position sensor may then be determined in the knowledge that the idle and WOT positions have been determined. Hence, regardless of the original set-up of the throttle position sensor or potentiometer, the system adapts as required. Further, reset of the potentiometer on every engine start-up enables changing conditions such as time variant characteristics of the potentiometer to be automatically compensated.

The method is also applicable in the case where at least two throttle position sensors are employed in accordance with the system described in the Applicant's copending Australian Provisional Patent Application No. PN 7163 filed on December 15, 1995.

A throttle position sensor may have a number of distinct operating ranges within its overall signal range. Once the output signal corresponding to the engine idle point is known, adaption rules may be used to determine each of the throttle position sensor's operating ranges. Such adaption rules are generally based on the known relationship existing between increasing throttle position sensor output signal values and the actual engine throttle position itself (ie: this relationship is typically a linear one in that between the idle and WOT settings, sensor output signals increase in a ramp fashion corresponding to increased degrees of opening of the engine throttle) together with the known limits of the signal range of the potentiometer. Hence, once a known position corresponding to one point in the sensor signal range is known, the sensor transfer function is applied to determine other points in the sensor signal range. Different operating ranges within the overall signal range may include, for example, an idle operating range, an off-idle manual operating range, and a WOT operating range.

It is however important to note that the relationship between throttle position sensor output signal values and the actual engine throttle position itself may be represented by other transfer functions. This may often be linear in nature, but not necessarily ramping upwards. Nonetheless, the method of the present invention is equally applicable to sensors having such different transfer functions in that the sensors are able to be set in-situ provided a signal within

the signal range (as defined by the transfer function) are able to be generated in correspondence to some first known position of the means, for example, a throttle, that the sensor is associated with.

Conveniently, the idle throttle position signal corresponds to the low or minimum sensor signal output value, typically a voltage or current value, end of the throttle position sensor range, whilst the WOT position signal corresponds to the high or maximum voltage output end of the throttle position sensor. However, it is to be noted that in a multi-throttle position sensor system that utilises twin throttle position sensors such as that described in the Applicant's co-pending Australian Provisional Patent Application No. PN 7163 as previously referred to, it may be the case that the converse of this is true for one of the throttle position sensors. Hence, the control system is required to determine at which end of the signal output range, typically a voltage range, the idle condition is located. Typically, information of this nature would be invariant for a particular engine installation and may be pre-recorded for use by the control system.

Typically, the throttle position sensor is a potentiometer generally capable of delivering a voltage signal in the range of 0 to 5V. However, this is not to say that idle will be set at OV and WOT at 5V. Generally, idle will be set a little above OV and WOT a little below 5V. Further values may then be set as limits to the range for idle and WOT beyond which an abnormal throttle position sensor condition may be flagged by an engine control means as described in the Applicant's copending Australian Provisional Patent Application No. PN 7163 as previously referenced.

The throttle position sensor may be assembled on the engine to make use of the full sweep thereof. For example, a 90° pot may be employed on an engine that has a full angular deviation from idle to WOT of 70°. This 70° would be positioned such that it was in the middle of the 90° angular range, thus allowing some range at either end of the 70° for abnormal conditions to be flagged. This is equally applicable for pots having different angular sweeps. The signal generated by the throttle position sensor may be filtered to remove noise. Further, if a signal is determined to be subject to excessive noise, it may be discarded. The output signal, whilst the engine is in the known

position, for example, idle, may conveniently be sampled a number of times before the final signal value, which may be an average or a steady state signal value, is selected as that corresponding with idle, provided that this signal value lies between predetermined bounds. This may similarly be the case in regard to the final signal value which corresponds with WOT.

Other signal points that may readily be established from the typically linear characteristic of the throttle position sensor are the minimum allowable idle threshold and the maximum allowable WOT threshold. Beyond these boundary values, an abnormal throttle position sensor condition may be flagged and acted upon as required.

The method is equally applicable to throttle systems wherein the throttle means is controlled by a drive-by-wire (DBW) control system as it is to the more conventional mechanical operator controlled throttle means system.

The invention may be more fully understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of an engine in which a throttle position sensor is calibrated in accordance with the method of the invention; and

Figure 2 is a characteristic of voltage signal-wiper angle for the throttle position sensor calibrated in accordance with the method of the invention.

Referring now to Figure 1 of the drawings, there is shown a three cylinder engine 8 including an air intake manifold 7 and an exhaust manifold 10. The intake manifold 7 is in communication with an air intake passage 1 1. Mounted in the air intake passage 1 1 is an operator controlled throttle valve 12. The engine 8 can be considered to be representative of a marine engine in which the throttle valve 12 is manually actuated by way of an operator controlled throttle lever 14. It is to be appreciated that the marine engine 8 is such that, as in many conventional marine engines, the engine is not able to be cranked until the throttle level 14, which also typically controls gear selection, has been returned to the neutral position which corresponds to idle operation of the engine 8. It will be further appreciated that the present invention is not limited in its application to marine engines.

In operation, as the operator actuates the throttle level 14 from an idle position, the throttle position sensor or potentiometer 15 will provide a signal to the control means, typically an Electronic Control Unit (ECU) 17, of the engine 8 indicating the load demand thereof. The potentiometer 15 may be of any known type and may conveniently be of a kind in which a wiper contact wipes over an electric resistance providing a voltage signal corresponding to a particular position of throttle valve 12. The ECU 17, which is provided with an appropriate look-up map, will determine therefrom the fuelling rate required by the engine 8 and the necessary air flow into the engine 8 to achieve the desired air/fuel ratio in the combustion chambers thereof. Hence, it will be understood from the foregoing that the throttle position setting is of great importance to establishment of a correct air/fuel ratio and optimal control of operation of the engine 8.

Accordingly, it follows from this that calibration of the throttle pot 15 is important to appropriate setting of the throttle position for conditions throughout the operating range of the engine 8. It is additionally to be observed that the above described arrangement is a system where the throttle position sensor 15 is a primary sensor so accuracy is of heightened importance.

The throttle position sensor or potentiometer 15 may be mounted on a shaft 13 directly connected to the throttle means 12, the shaft 13 being directly driven from the manually actuated throttle lever 14. Thus, in operation, the throttle lever 14 will be moved by the operator to a desired position and hence move the shaft 13 acting to open and close the throttle means 12. It is of course to be appreciated that the throttle position sensor 15 may be located at other suitable locations. For example, the sensor 15 could be arranged adjacent or in working relation to the throttle lever 14 such that different positions of the lever 14 correspond to different engine fuelling rates. Alternatively, the sensor 15 could be located on an independent cam means actuated by the throttle lever 14 and which in turn actuates the throttle means 12.

In regard to the present embodiment, movement of the throttle 12 will cause a voltage signal to be generated by the throttle pot 15 which may be employed by the ECU 17 as a measure of driver demand. The signal may be input to a look-up map which provides a particular fuel per cycle (FPC) setting

for the given driver demand. Although the throttle position indication could be used as a sole input to the FPC look-up map, this may be a compromised system. Advantageously, driver demand and engine speed are to be input to the look-up map to provide the desired FPC for the engine 8. Further description of such an air/fuel ratio control strategy may be found in the applicant's co-pending Australian Patent Application No. 34862/93, the contents of which are hereby incorporated by reference. It will also be understood that the above description relates in the main to a fuel based control system, however, there is no reason, in principle, why air per cycle (APC) cannot be set first. In accordance with output FPC, appropriate APC is set to establish the required air/fuel ratio of the engine 8. If an air based control system were employed, appropriate FPC would subsequently be set.

As alluded to hereinbefore, when the engine 8 is cranked, the cranking typically occurs in a neutral position whereat engine speed is non-zero but driver demand is equal to zero. As this neutral position also corresponds to idle operation of the engine 8, throttle position at idle is known and the potentiometer voltage corresponding to idle may readily be recorded. Generally, the recorded voltage may correspond to the low or minimum voltage output end of the throttle position sensor range, but this is not necessarily the case as will be described hereinbelow.

The desired voltage corresponding with wide open throttle (WOT) may then be scaled and recorded, if desired, by operation of the engine at WOT conditions. It could also be calculated by reference to an adaption rule found, for example, to provide accuracy of say ±1 % for a given potentiometer type, though any other acceptable rule may be employed.

Generally, the potentiometer 15 will produce a signal in the range 0 to 5 V, but this will be understood to be preferred only. In addition, the signals corresponding to idle and WOT conditions need not necessarily, or even advantageously, be set at OV or 5V. Typically, there will be an "out of bounds" range at either or both ends of the voltage range in which a fault in the potentiometer 15 may be flagged should a signal in the "out of bounds" range be detected during operation of the engine 8. Incidentally, while voltage is a

conventional, convenient and typical output, it is not intended to exclude signals of other kinds, e.g. current or derivatives of voltage.

It is unlikely that the engine 8 will have a single operating range between idle and WOT conditions. Typically, the engine 8 and hence the throttle position potentiometer 15 will have a number of distinct operating ranges within the overall signal range. Accordingly, voltage signals corresponding to each of the desired operating points throughout the operating range may be scaled in accordance with adaption rules. Operating points of significance may include an idle operating range, an off-idle operating range and a WOT operating range. The voltage signals corresponding to the limits of the ranges may readily be calibrated using such adaption rules.

The adaption rules may be as desired by the manufacturer of an engine. However, it is typically convenient for a linear characteristic between voltage output of the sensor and wiper or potentiometer angle, 0, to be employed during calibration. Nevertheless, a polynomial or other characteristic may be employed, if desired. As the sensor's limit of travel or wiper contact range, in the case of a 90° pot for example will generally be of the order of 70° of rotation, this range may be divided into the various operating ranges as required and shown in Figure 2. The adaption rules may take account of typical 0 and typical voltage outputs for the limits of the various operating ranges of the potentiometer 15 and iterate, if necessary, to establish the desired voltage and 0. The adaption rules may also take account of potentiometer characteristics.

Although a single voltage value could be employed when calibrating the throttle position potentiometer 15, this is not essential. Rather a number of voltage values may be sampled, at 1 to 10 ms intervals for example, with an average or steady state value being utilised, though an absolute value may be utilised on cranking. In the case of a steady state value, voltage may be that at which variance between readings is less than a certain value, say 0.01 volts. If a reading varies by more than a predetermined limit from the average or trend value, it may be discarded in a filtering routine designed to reduce or eliminate the effect of noise.

In regard to Figure 2, the idle point is determined from an average number of samples with signal filtering being employed. The additional break¬ points which define the various operating ranges can be determined by applying the idle point with prior system knowledge. For example, "wot min" equals the idle point plus almost the full range of sensor deflection and "wot max" equals the idle point plus the full range of sensor deflection. It is, however, appreciated that other methods for determining operating range break-points may be applied.

The prior knowledge is determined from stacked tolerances of the sensor 15 itself (linearity etc) and its interaction with the throttle system hardware (linkages etc). The values would be chosen such that it could be ensured that all engines would re-enter idle after initially leaving it, as well as indicating when the throttle blades were fully open (WOT).

Additionally, rules exist for accepting the initial idle point. The stacked tolerance of the sensor installation on the engine 8 generates a range of possible sampled idle points that would be expected. If the measured idle point does not fall within the expected region then the ECU can be informed of a suspected bad sensor and take any necessary pre-cautionary measures. For example, in a dual sensor installation as described hereinafter, the ECU may rely on the remaining sensor. This region can be sub-divided into smaller regions that may flag either warnings or serious errors.

For enhanced fault tolerance, two throttle position potentiometers 15 may conveniently be employed in the marine engine 8 as is described in the Applicant's co-pending Australian Provisional Patent Application No. PN 7163 filed on December, 15, 1995. These may be calibrated together, if desired. It may be appropriate for the potentiometers 15 to be counter-rotating in which case the idle voltage signal for one of the potentiometers 15 may be desired to be at the high or maximum end of the voltage range in contrast to the calibration above described. The associated adaption rule may then remain linear but with negative slope.

Variations from the invention may be apparent to those skilled in the art upon reading of the disclosure. All such variations are considered to be within

the scope of the present invention. In particular, the method of the invention is not restricted to calibration of potentiometers for marine engines and the method may equally well be used for cars, motorcycles or any other vehicle.

The method of the invention may further be applicable to any kind of potentiometer, particularly where one known position of operation, and particularly where one known extreme of position of operation is known at the start of operation. For example, an exhaust or EGR valve may start operation in a fully open position from which the working range of the valve may be determined in a similar manner to the above described method. In this case, there is provided a method of tuning a sensor for sensing the setting of an engine element in-situ on an engine wherein the sensed element is in a known setting and a signal within the signal range of the sensor corresponding to the known position is generated by the sensor and recorded. A further signal within the signal range of the sensor is then scaled off to correspond with a second known setting of the engine element.