AN IMPROVED METHOD AND APPARATUS FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE

FIELD OF INVENTION

This invention relates to an improved method of controlling an internal combustion engine with load estimation based on a crank position sensor signal.

BACKGROUND OF INVENTION

Vehicles with an internal combustion engine allow the rider to control the engine output power by varying a throttle position. The throttle position determines the quantity and quality of air-fuel mixture allowed into the intake manifold of a petrol engine. Under high engine load conditions, the rider varies the throttle position to supply more quantity of the air-fuel mixture and thereby increase the engine power. Throttle position is thus an indication of engine load. Optimum control of any internal combustion engine to meet performance, exhaust emissions and fuel efficiency requirements, needs throttle position measurement.

In Spark Ignition Internal Combustion Engines, the air-fuel mixture sucked into the combustion chamber during the suction stroke is compressed and ignited by means of an electric arc discharge. The ignition is timed to occur a few degrees before the piston reaching Top Dead Centre (TDC). The exact ignition angle depends on the engine speed, engine load, engine coolant temperature and other engine operating parameters. The compressed air-fuel mixture is ignited before the piston reaching TDC so that sufficient time is allowed for the combustion process to complete and produce maximum power during the power stroke. Hence ignition timing has to be advanced as the engine speed increases. With increase in engine load, the air-fuel mixture quantity is increased, .and also some times the mixture is enriched resulting in combustion flame propagation speed increase. Hence ignition timing has to be retarded with increase in engine load. During cold weather conditions, condensation of air-fuel mixture in the intake manifold is more pronounced and a rich air-fuel mixture is required to ensure engine starting ability. The ignition timing might also require modification during these cold weather conditions. In . low cost engine control systems, the ignition timing is a three-dimensional map with engine speed, throttle position and ignition timing as the three axes. Ignition timing is determined by an electronic controller which has the three-dimensional map of engine speed, throttle position and ignition timing in its memory. Based on the engine speed signal and throttle position signal, an ignition control unit comprising the electronic controller provides appropriate output signal to generate an electric arc discharge in a spark-plug electrode gap. Similarly, in a diesel engine with compressed ignition the fuel injection timing and duration is based on engine speed and engine load.

Engine speed signal is conventionally obtained from a variable reluctance based crank position sensor in most low cost applications. At least one reluctor is fixed on a crankshaft flywheel and the crank position sensor is fixed to the crankcase close to the flywheel such that a signal is generated whenever the reluctor passes along the crank position sensor. The position of the reluctor on the crankshaft flywheel is such that a signal will be generated by the crank position sensor when the piston is close to the TDC. Thus crank position signal is obtained during the end of compression stroke or exhaust stroke.

Throttle position signal is obtained from a throttle position sensor which is either connected with a throttle grip of a handle bar in a two-wheeled or three-wheeled vehicle or accelerator pedal in a four-wheeled vehicle. Alternatively the throttle position sensor is connected with a carburettor or throttle body which controls the quantity of air-fuel mixture or air flow. In all the above cases, the throttle position sensor provides a signal indicative of the engine load.

Manifold air pressure sensor (MAP sensor) is also used instead of throttle position sensor to determine engine load. In this case a MAP sensor is mounted on the intake manifold or throttle body of the engine. The MAP sensor provides a signal indicative of the intake manifold air pressure which in turn is indicative of the engine load.

US Patent Publication US2002/0043245 discloses an improved method for the control of engine ignition timing. Speed variations either during a portion of the complete cycle and/or from cycle to cycle are sensed to determine the engine load from predetermined maps. The engine speed and the determined engine load are used to control the engine operation. Thus the requirement of additional sensors, like throttle position sensor and manifold air pressure sensor, to determine engine load is eliminated. A crank position sensor is formed by a reluctor on the outer periphery of the crankshaft flywheel and a pulser coil fitted on the engine crankcase. The time taken for the reluctor to pass the puiser coil is measured from the puiser coil signal and a partial crankshaft angular velocity is calculated by an electronic control unit. A complete rotation crankshaft angular velocity is also calculated based on the puiser coil signal. The ratio between the partial crankshaft angular velocity and the complete rotation crankshaft angular velocity is proportional to the engine load for a two-stroke engine. The difference between the ratio for the intake-compression cycle and power-exhaust cycle is proportional to the engine load for four-stroke engine.

JP2008-020244 describes a control section which calculates a partial crankshaft angular velocity simultaneously in a period wherein an average crankshaft angular velocity is calculated in a stroke prior to the compression stroke where ignition is provided.

For such systems to determine the engine load accurately, the difference in variations between the partial crankshaft angular velocity calculated and the average crankshaft angular velocity at different engine loads should be high. Nowadays 3-dimensional ignition timing maps with 16 curves based on different engine load conditions are common in order to optimize performance, exhaust emissions, fuel efficiency and driving comfort at all environmental conditions. It is difficult to implement these multi-curve ignition timing maps without using additional throttle position sensor or MAP sensor.

The sensitivity of engine load detection possible using the methods disclosed in prior art is limited. Particularly at high engine speeds, the variation between the average engine speed and a partial crankshaft angular velocity is small. These methods are also less effective for controlling engines having low inertia crank train assembly. The speed variation at low loads for such engines will be low. Moreover the use of sensor to detect engine load is more costly and also the reliability of the sensor is major concern.
Therefore the present invention tries to overcome the problem of the prior art and provides an improved method to control an internal combustion engine.

SUMMARY OF THE INVENTION

The present invention describes an improved method and apparatus for controlling an internal combustion engine, wherein the engine load is determined by calculating the passage time of the pips. The crankshaft flywheel is provided with four pips on its outer periphery, particularly three pips uniformly spaced from each other at or near the TDC, during a compression stroke and a fourth pip located with a different spacing away from the first three pips. A pulser coil mounted on the crankcase for sensing the crankshaft flywheel position provides a signal indicating the passage of the four pips. An Electronic Control Unit (ECU) calculates the time taken for each pip to pass based on which an engine load is determined. The accuracy of engine load determination' is improved because variation in crankshaft angular velocity between two successive strokes is measured in one rotation of crankshaft. Unlike the methods disclosed in the prior art, the crankshaft angular velocity is calculated during an accelerating stroke (power stroke) of the engine also. The difference between the crankshaft angular velocity during an accelerating stroke and a decelerating stroke (compression stroke) is a clear indication of the engine load and improves the sensitivity of engine load detection. The existence of three pips close to each other increases the crankshaft angular velocity information during the compression stroke. Since variation in crankshaft angular velocity is maximum during the compression stroke, accurate information of crankshaft angular velocity during this stroke further improves sensitivity of engine load detection. Also the arc-length of the fourth pip located away from the first three pips is adjusted to minimize rotor imbalance.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a motorcycle, on which the invention is applicable.

Figure 2 illustrates an engine, for which the control method is proposed.

Figure 3 is a pictorial representation of a crankshaft flywheel and pulser coil assembly with piston at Top Dead Centre (TDC).

Figure 4 is a block diagram representation of an Electronic Control Unit (ECU).

DETAILED DESCRIPTION OF THE DRAWINGS

A detailed description of the preferred embodiment is provided using Figure 1,2, 3 and 4.
Figure 1 illustrates a motorcycle 100, wherein the motorcycle 100 includes an engine 9 a front wheel 25, a rear wheel 27, a body frame 19, a fuel tank 56. An Upper bracket 42 and a lower bracket 43 retain a front suspension 16 that supports front wheel 25. The front wheel 25 is connected at the lower end of the front fork 16. A head light 36 is arranged on an upper portion of the front fork 16. A side stand 58 is arranged on lower portion of engine unit the 9 of motorcycle 100. Left and right rear arm bracket portions support a rear arm 26 to swing vertically, and a rear wheel 27 is connected to rear end of the rear arm 26. The rear wheel 27 is arranged below seat and rotates by the driving force of engine transmitted by chains, belts and so on. A rear wheel suspension 34 is arranged
between the rear arms 26. A tail light unit 64 is disposed on a rear cover 61.

Figure 2 illustrates the engine 9 on which the present invention is applicable, wherein the engine body includes a crankcase 2, a cylinder block 1 coupled to the crankcase 2, a cylinder head 3 coupled to the upper part of the cylinder block 1. The crankcase 2 is constructed by connecting a left crankcase 2(a) and a right crankcase 2(b). A crankcase flywheel 10 (rotor) is fixed to the left crankcase 2(a), wherein pips 50, 60, 70 and 80 are provided on the outer periphery of the crankcase flywheel 10. A gear shift pedal 8 is attached to the left side of the engine 9.

Figure 3 is an exemplary description of the present invention, illustrating the crankshaft flywheel 10 and a pulser coil 40, wherein crankshaft flywheel 10 has three uniformly spaced pips 50, 60 and 70 on its outer periphery. A fourth pip 80 is present on the outer periphery of the crankshaft flywheel 10 with a different spacing. The periphery of the crankshaft flywheel 10 and the four pips 50, 60, 70 and 80 are made of ferromagnetic materials. A pulser coil 40 is wound around a soft magnetic core 20 for linking flux generated by a permanent magnet 30. The pulser coil 40 along with the magnetic core 20 and permanent magnet 30 is fixed to an engine crankcase and separated from the crankshaft flywheel 10 by a small air-gap. Whenever the crankshaft flywheel 10 rotates, an electromotive force (emf) is generated across the pulser coil 40 due to change in reluctance. There is a change in reluctance whenever the edges of the pips 50, 60, 70 and 80 pass along the pulser coil 40. The width of the ferromagnetic pips 50, 60, 70 and 80 are chosen based on the type of engine and capability of an ECU 90.

Figure 4 illustrates a block diagram of an Electronic Control Unit (ECU) 90 which comprises a power supply circuit 110, a signal conditioning circuit 120, a microcontroller 140 and a driver circuit 150. The ECU 90 receives electrical power from a power supply 130 and an engine speed signal 100 from the pulser coil 40. The emf generated by the pulser coil 40 is converted into suitable voltage for processing by the microcontroller 140. The Power supply circuit 110 distributes electrical power into forms suitable for different circuits in the ECU 90. The microcontroller 140 calculates engine speed from the pulser coil 40 signal. In addition the microcontroller can also calculate the time taken for the passage of each pip 50, 60, 70 and 80.

The pips 50, 60, 70 and 80 are located on the outer periphery of the crankshaft flywheel 10 such that when the piston reaches a Top Dead Centre (TDC) with crankshaft rotation as indicated in Figure 1, the trailing edge of the first pip 50 is at an angle 'g' from the pulser coil 40 axis. The pips 50, 60 and 70 are equally spaced while pip 80 is located at an angle 'a' from the pulser coil 40 axis. During a compression stroke of the engine, the instantaneous crankshaft angular velocity drops and the time taken for passage of pips 50, 60 and 70 will be greater than the time taken for passage of pip 80. As the engine load increases, the difference in the time taken for passage of equally spaced pips 50, 60 and 70 and the farther spaced pip 80 will increase. The microcontroller 140 can recognize the location of the pip independent of the direction of rotation due to the unequal spacing of pip 80 and equal spacing of pips 50, 60 and 70.

Depending on the engine and vehicle used, experiments are conducted to map engine load against the variation in time of passage of equally spaced pips 50, 60 and 70 and the farther spaced pip 80. The method is more effective if the time of passage of pip 50, located closer to the pulser axis at TDC, and time of passage of pip 80 are measured and the difference calculated. The sensitivity of load detection which can be expressed as the ratio between variation in passage time between chosen pips and the engine load will be greater using this embodiment. Another map is derived by experiments on the vehicle to provide optimum ignition timing based on engine speed and engine load. Both the maps are stored in the memory of microcontroller 140. The microcontroller 140 identifies the location of pips 50, 60, 70, 80, measures the passage time and then predicts the engine load. The predicted engine load and measured engine speed are used by the microcontroller 140 to determine optimum ignition timing. Appropriate signal is provided by the microcontroller 140 to driver circuit 150 in order to generate spark discharge in the internal combustion engine at optimum timing.

Instead of calculating a difference of passage times of pips, the microcontroller could also perform other arithmetic calculations like division. Based on the variation in passage times, the microcontroller can also distinguish the compression stroke from the exhaust stroke and thereby inhibit spark discharge during exhaust stroke. In addition to passage time, the microcontroller could also measure the time interval between passages of edges of successive pips and thereby improve the sensitivity of load detection method. Also, the arc-length of the farther spaced pip 80 is adjusted to minimize rotor imbalance. This would simplify the rotor balancing process performed after manufacturing the part.

Since engine load is predicted based on pulser coil 40 signal, a separate throttle position sensor or Manifold Air Pressure (MAP) sensor is not required. The predicted engine load can be used to perform other engine control functions like fuel injection control, valve timing control and gear position determination.

We Claim:

1. An improved method and apparatus for controlling an internal combustion engine comprising:

a crankshaft flywheel removably connected with an engine crankshaft;

at least three uniformly spaced ferromagnetic pips located on the outer periphery of the crankshaft flywheel;

at least one additional ferromagnetic pip located on the outer periphery of the flywheel spaced farther away from the said equally spaced ferromagnetic pips;

a pulser coil for generating a signal indicative of the position of the said crankshaft flywheel based on the pips;

an Electronic Control Unit (ECU) for measuring an engine speed based on the said pulser coil signal, and also measures passage time of the ferromagnetic pips and further determines an engine load based on the variation in passage times;

wherein, the said ECU controls the engine based on measured engine speed and predicted load.

2. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein ignition timing is controlled by the ECU based on measured engine speed and predicted engine load.

3. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein the uniformly spaced ferromagnetic pips are located close to the pulser coil axis when the engine piston is at top Dead Centre (TDC).

4. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein the engine load is calculated based on time interval between passages of edges of the ferromagnetic pips.

5. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein the time taken for passage of equally spaced pips and the farther spaced pip along the pulser coil is different, based on which the engine load is determined.

6. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein spark can be inhabited during exhaust stroke of the engine.

7. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein reverse rotation of crankshaft flywheel can be identified and suitable engine control is performed.

8. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein the method and apparatus are applicable for internal combustion engine independent of the number of cylinders, type of fuel used and vehicle structure.

9. The improved method and apparatus for controlling an internal combustion engine as claimed in claim 1, wherein the arc-length of the farther spaced pip is adjusted to minimize rotor imbalance.

10. The improved method- and apparatus for controlling an internal combustion engine, substantially as herein described in the specification and as illustrated in the accompanying drawings.