WO2013144974A2

WO2013144974A2 - A method of predicting throttle position based on engine speed signal and a vehicle using the same

Info

Publication number: WO2013144974A2
Application number: PCT/IN2013/000114
Authority: WO
Inventors: Samraj JABEZ DHINAGAR; Himadri BHUSHAN DAS
Original assignee: Tvs Motor Company Limited
Priority date: 2012-03-29
Filing date: 2013-02-27
Publication date: 2013-10-03
Also published as: WO2013144974A3; PH12014502188A1

Abstract

The present invention describes a method for predicting a throttle position in a vehicle based on discrete values of engine speed and rate of change of discrete values of engine speed. A crank position sensor 60 generates a signal indicative of engine speed received by an Electronic Control Unit (ECU) which calculates the engine speed based on the signal. It also has a reluctor 20 fixed on an engine flywheel 10 such that when the reluctor 20 passes the crank position sensor 60, an electro-magnetic force is generated corresponding to the leading edge 22 of the reluctor 20 and also corresponding to the trailing edge 24 of the reluctor 20. This method can eliminate the need for throttle position sensor in a vehicle without constraining reluctor width or controller capability or other mechanical parameters of the engine.

Description

A METHOD OF PREDICTING THROTTLE POSITION BASED ON ENGINE SPEED SIGNAL AND A VEHICLE USING THE SAME

BACKGROUND

FIELD OF THE INVENTION

The present invention relates to a method of predicting throttle position based on engine speed signal and a vehicle using the same.

DISCUSSION OF PRIOR ART

Vehicles with an internal combustion engine allow the rider to control the engine output power by varying a throttle position. The throttle position, in turn, determines the rate of flow of air-fuel mixture allowed into the intake manifold of a petrol engine. In a diesel engine, the throttle position determines the quantity of fuel injected into the combustion chamber. 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 reaches 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 rate of flow of air-fuel mixture increases and the combustion flame propagation speed increases. 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 reluctor is fixed on the crankshaft 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 airflow rate and hence the rate of entry of air-fuel mixture into the intake manifold of the engine. In all the above cases, the throttle position sensor provides a signal indicative of the engine load.

JP2008-020244 titled "Operation Controlling System for Internal Combustion Engine" describes an operation controlling system for internal combustion engine in which ignition timing is determined based on an average engine speed and a partial crankshaft angular velocity. The partial crankshaft angular velocity is calculated based on the reluctor width sensed by the crank position sensor. The difference between the average engine speed and partial crankshaft angular velocity gives an indication of the engine load and hence throttle position sensor is not required. But such a system requires fast processing rates to calculate the partial crankshaft angular velocity based on reluctor width. It becomes further difficult when the reluctor width is small. This method also requires simultaneous calculation of average engine speed and partial crankshaft angular velocity which imposes further constraints on controller capability. US6553958 titled "Adaptive Torque Model for Internal Combustion Engine" describes an adaptive torque model for internal combustion engine in which engine torque and load torque is estimated based on an engine speed signal. The estimated engine torque and load torque are used to estimate an engine speed trajectory. The estimated engine speed trajectory and the actual engine speed are compared to adjust an operating parameter like ignition timing to meet the load torque requirements. But the adaptive torque model requires accurate measurement of engine parameters like engine inertia, viscous friction, driveline inertia and auxiliary load torque which varies from one engine to another.

A method to predict the throttle position based on the engine speed signal can eliminate the need for throttle position sensor in a vehicle without constraining reluctor width or controller capability or other mechanical parameters of the engine. SUMMARY OF THE INVENTION

The present invention describes a method of system identification based on least squares method. It is used to obtain a functional relationship to predict throttle position based on discrete values of engine speed and rate of change of the discrete values of engine speed. The predicted throttle position along with the engine speed signal is used to determine ignition timing for optimum control of a spark ignition engine. The method involves the generation of a signal indicating the engine speed received by the Electronic Control Unit (ECU) which comprises of a power supply circuit, signal conditioning circuit, a controller and a driver circuit. The ECU calculates engine speed based on the crank position signal where the engine speed signal calculated from the crank position signal is sampled at a fixed rate based on the operating speed range of the engine (20Hz in the preferred embodiment to use low cost microcontrollers). The filtered engine speed signal is finally generated by a 5^th order moving average digital filter. A rate of change of engine speed is calculated based on the difference between successive engine speed values. The throttle position is predicted based on a dynamic functional relationship between the throttle position, the filtered engine speed signal and rate of change of engine speed. The throttle prediction method can be used in vehicles with internal combustion engine to adjust operating parameters like ignition timing, fuel injection timing and valve timing. The need for throttle position sensor is eliminated and the method does not require high controller processing capability and can be implemented in mass production.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a flywheel connected with a crankshaft of the engine;

Figure 2 illustrates a block diagram of an Electronic Control Unit (ECU); and

Figure 3 illustrates a preferred embodiment of the invention. DETAILED DESCRIPTION OF THE ACCOMPANYING EMBODIMENTS

A preferred embodiment of the invention will be explained using Figures 1-3.

Figure 1 shows a conventional crank position sensor 60 which generates a signal 50 indicative of engine speed based on variable reluctance principle. The conventional crank position sensor 60 comprises a coil 30 wound around a soft magnetic core and a permanent magnet 40. Whenever the reluctor 20 fixed on an engine flywheel 10 passes the crank position sensor 60, an Electro Motive Force (EMF) is generated corresponding to the leading edge 22 of the reluctor 20 and also corresponding to the trailing edge 24 of the reluctor 20 due to electromagnetic induction principle. Figure 2 shows an Electronic Control Unit (ECU) in the vehicle which receives the crank position signal 50 from the crank position sensor 60. The ECU comprises a power supply circuit 85, signal conditioning circuit 90, a microcontroller 95 and a driver circuit 100. The power supply circuit 85 receives electrical supply from vehicle power supply 75, converts the power supply voltage to levels suitable for functioning of other circuits within ECU 70. Signal conditioning circuit 90 converts the engine speed sensor signal 80 to voltage levels that can be processed by microcontroller 95. The driver circuit 100 receives signals from microcontroller 95 and supplies the required current to drive ignition circuit to produce the ignition signal 105.

Figure 3 shows the software blocks which can be used to explain the method implemented by the ECU 70. The microcontroller 95 receives the engine speed signal 80 which is then processed to predict throttle position using the TPS (Throttle Position Sensor) prediction software block 200. The predicted throttle position 210 and the engine speed signal are then used by the microcontroller 95 to calculate ignition timing 230 based on the 3-dimensional ignition timing map 220.

The ECU 70 calculates engine speed based on the crank position signal 50. The engine speed signal 80 calculated from the crank position signal 50 is sampled at a fixed rate based on the operating speed range of the engine (20Hz in the preferred embodiment to use low cost microcontrollers). A moving average digital filter calculates an average speed of the engine. A 5^th order moving average digital filter is used in the preferred embodiment to provide the filtered engine speed signal as given in equation [1].

EngineSpeedfi„_erd(k) = .EngineSpeed (k+5) +...+EngineSpeed (k) +...+EngineSpeed (k- 5)

[1] n

Where EngineSpeedfii_terct(k)is the filtered variable and EngineSpeed(k) is raw signal data.

The difference between successive samples of engine speed that is used to calculate the rate of change of engine speed is given in equation [2].

.EngineSped(k + 1) - EngineSpeed(k)

dEngineSped (k)= - -— [2]

0.05

By the least squares method for system identification, a dynamic functional relationship between throttle position, engine speed and rate of change of engine speed can be obtained. An experiment is performed to capture engine speed signal 80, throttle position signal and ignition timing 230 at different operating conditions of the vehicle. A model is created based on the experimental data to relate throttle position to engine speed and rate of change of engine speed such that the error in predicted throttle position signal 210 is minimized when compared to actual throttle position signal. The predicted throttle position signal 210 for a sample vehicle is given in equation [3]. y(k)= -13.7498+0.1124*x(k)-0.1276*x(k-l)+0.0473*x(k-2)-0.0245*x(k-3) +0.0071 k-4)-0.0023 k-5)+0.0179 k-6)-0.0179 k-7)+0.0043*x(k-8)- 0.0027*x(k-9)+0.0057*x(k-10)-0.0078*x(k-ll)+0.0023 *x(k-12)+0.0009*x(k- 13)+0.0060*x(k-14)-0.0078*x(k-15) +0.0012*x(k-16) +0.0098*x(k-17)-0.0078*x(k- 18)+0.0020*x(k-19)-0.00001 *dx(k)-0.0001 *dx(k-l)-0.0001 ^

3)-0.0003*dx(k-4)-0.0003*dx(k-5) +0.000 l *dx(k-6) -0.00001 * dx(k-7) +0.0001 *dx(k-8) [3] Where y(k) is the predicted TPS variable, [x(k),..x(k-19)] is the set of Filtered Engine speed variable for different sample instants and [dx(k),..dx(k-8)] is the differential of engine speed variable. The coefficients in equation [3] are particular to the sample vehicle and if all operating conditions have been captured in the experiment then equation [3] can be used in mass production of vehicles with same engine characteristics. The predicted throttle position signal 210 along with engine speed signal 80 is used in the preferred embodiment to determine optimum ignition timing 230. The ECU 70 provides an ignition signal 105 at time instants calculated based on the predicted throttle position signal 210 and engine speed signal 80. The above disclosed method of throttle position prediction can also be used to determine other engine operating parameters like fuel injection timing, fuel injection duration and valve timing. In essence the method predicts the engine load based on engine speed signal 80 received from a conventional crank position sensor 60. The above disclosed method can be used in vehicles with an internal combustion engine irrespective of the fuel type, number of cylinders and vehicle construction.

Claims

A system to predict the throttle position in vehicles with an internal combustion engine, said prediction based on an engine speed signal 80 comprising (a) a crank position sensor 60, (b) an Electronic Control Unit (ECU) 70 and (c) a microcontroller with stored machine-readable instructions 95 wherein:

a. A conventional crank position sensor 60 comprises a coil 30 wound around a soft magnetic core and a permanent magnet 40 such that when the reluctor 20 fixed on an engine flywheel 10 passes the crank position sensor 60, an EMF is generated corresponding to the leading edge 22 of the reluctor 20 and also corresponding to the trailing edge 24 of the reluctor 20 due to electromagnetic induction principle;

b. The ECU 70 comprises of a power supply circuit 85, signal conditioning circuit 90, a microcontroller 95 and a driver circuit 100; and

c. The ECU 70 calculates a filtered average engine speed value and a rate of change of engine speed and predicts a throttle position based on a dynamic functional relationship between the filtered average engine speed, rate of change of engine speed and throttle position.

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein:

a. The power supply circuit 85 receives electrical supply from vehicle power supply 75, converts the power supply voltage to levels suitable for functioning of other circuits within ECU 70;

b. The Electronic Control Unit (ECU) 70 receives a crank position signal

50 from the crank position sensor 60;

c. The Signal conditioning circuit 90 converts the engine speed sensor signal 80 to voltage levels that can be processed by microcontroller 95; and d. The driver circuit 100 receives signals from microcontroller 95 and supplies the required current to drive ignition circuit.

a. The microcontroller 95 receives the engine speed signal 80 which is then processed to predict throttle position using a block of instructions referred to as the Throttle Position Sensor Prediction block 200 such that the predicted throttle position 210 and the engine speed signal 80 are then Used by the microcontroller 's to calculate ignition timing . 230 based on the 3 -dimensional ignition timing map 220.

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein the ECU 70 calculates engine speed based on the crank position signal 50 such that the engine speed signal 80 calculated from the crank position signal 50 is sampled at a fixed rate based on the operating speed range of the engine.

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein the engine speed signal 80 calculated from the crank position signal 50 is sampled at a fixed rate such that 20Hz is used in the preferred embodiment to enable the use of low cost microcontrollers.

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein a moving average digital filter calculates an average speed of the engine.

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein a 5^th order moving average digital filter is used in the preferred embodiment to provide the filtered engine speed signal as given by a pre-determined equation [1].

The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein by using the least squares method for system identification, a dynamic functional relationship between throttle position, engine speed and rate of change of engine speed is obtained where an experiment is performed to capture engine speed signal 80, throttle position signal and ignition timing 230 at different operating conditions of the vehicle and a model is created based on the experimental data to relate throttle position to engine speed and rate of change of engine speed such that the error in predicted throttle position signal 210 is minimized when compared to actual throttle position signal where the predicted throttle position signal 210 for a sample vehicle is given by a pre-determined equation [3] wherein:

a. y(k) is the predicted TPS variable;

b. [x(k),..x(k-19)] is the set of Filtered Engine speed variable for different sample instants ;and

c. [dx(k),..dx(k-8)] is the differential of engine speed variable.

9. The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein the coefficients in equation [3] are particular to the sample vehicle and if all operating conditions have been captured in the experiment then equation [3] can be used in mass production of vehicles with same engine characteristics.

10. The system to predict the throttle position in vehicles with an internal combustion engine as claimed in Claim 1 wherein the predicted throttle position signal 210 along with engine speed signal 80 is used to determine optimum ignition timing 230 wherein the ECU 70 provides an ignition signal 105 at time instants calculated based on the predicted throttle position signal 210 and engine speed signal 80.