AU4262900A

AU4262900A - System for detecting fuel injection timing

Info

Publication number: AU4262900A
Application number: AU42629/00A
Authority: AU
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1999-07-07
Filing date: 2000-06-22
Publication date: 2001-01-11
Also published as: JP2001055954A; EP1067283A2; CA2298305A1; EP1067283A3; BR0002308A

Description

Our Ref:7489560 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Deere Company One John Deere Place Moline Illinois 61265 United States of America DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Address for Service: Invention Title: System for detecting fuel injection timing The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 SYSTEM FOR DETECTING FUEL INJECTION TIMING Background of the Invention The invention relates to a system and method for measuring the timing of a fuel injection pulse.

In a electronically controlled fuel injected Diesel engine, there is a need for an accurate measurement of the timing of a fuel injection pulse as feedback to the fuel injection control system so that the control system can adjust the fuel injection timing to match the desired timing. Desired timing of fuel injection can be determined as a function, at least partially, of the engine load (which can be represented by fuel quantity) or fueling rate. The quantity and timing of a fuel injection pulse can be determined from a fuel pressure signal supplied by a pressure sensor coupled to a fuel injection line. For example, it is known to determine the fuel quantity of a fuel injection pulse from the area, height and width of a fuel pressure signal. For example, US Patent 4,426,981 shows a system which determines fuel injection quantity via the integral of a pressure signal from a pressure sensor coupled to the 15 fuel pump. It is also known to determine the timing from a fuel pressure signal. For example, the system of US Patent 4,426,981 also determines the onset of a fuel injection pulse by comparing a differentiated pressure signal to a threshold. US patent No. 5,107,700 shows a system which detects the beginning of fuel injection by comparing a fuel pressure signal to a threshold which is derived from a peak value of the injection pressure signal of 20 the preceding injection period.

Summary of the Invention Accordingly, an object of this invention is to provide a system and method for determining the timing of a fuel injection pulse for use in an electronic fuel injection control system.

25 This and other objects are achieved by the present invention, wherein an engine has a source of pressurized fuel, a fuel line for delivering fuel to a combustion chamber of the engine supply. A control system includes a fuel pressure sensor for sensing fuel pressure and determines the timing of a fuel quantity delivered to the combustion chamber by a method including the following steps. The engine speed is sensed. The fuel injection quantity is sensed and an engine load signal derived therefrom. A variable threshold signal is generated as a function of the engine speed signal and the engine load signal. The fuel pressure signal is compared to the variable threshold signal, and a timing signal is generated when the fuel pressure signal crosses the variable threshold signal while the fuel pressure signal is increasing in magnitude.

I

Brief Description of the Drawings Fig. 1 is a simplified schematic diagram of a Diesel engine fuel injection control system according to the present invention; Fig. 2 is a circuit diagram of the timing circuit of FIG. 1; Fig. 3 is a circuit diagram of the pressure signal integration circuit of FIG. 1; and Fig. 4 is a logic flow diagram of an algorithm executed by the microprocessor of the control system of FIG. 1.

Description of the Preferred Embodiment This application includes a microfiche appendix including one microfiche and 21 frames.

Referring to Fig. 1, a Diesel engine 10 includes fuel injectors 11 supplied with fuel from a fuel pump 12 via fuel lines 14. The fuel pump is preferably a rotary type fuel injection pump with a stepper motor timing actuator 16. A control circuit 20 includes a microprocessor 22, an integration circuit 24 and a timing circuit 26, and provides a timing control signal to the 15 actuator 16 as a function of sensed inputs, including a temperature signal from temperature sensor 28, an engine speed signal from engine speed sensor 30, a crank angle signal from crank angle sensor 32 and a pressure signal from fuel pressure sensor 34.

i Fuel pressure sensor 34 is preferably a piezoelectric pressure sensor such as is available from Texas Instruments, (although many other sensor technologies would also 20 work) and is mounted on a fuel line 14 between the pump 12 and the corresponding injector o 11 or in the timing advance piston (not shown) of the pump 12. The sensor 34 preferably generates a voltage proportional to the strain of the sensing element. If the sensor element generates a charge proportional to the pressure in the injector line, the charge can be converted to a voltage.

As best seen in Fig. 2, the timing circuit 26 includes a comparator U3 (LM2901) with one input coupled to receive the pressure signal from pressure sensor 34 and a second input coupled to receive a trigger threshold signal from the microprocessor 22. Preferably, the trigger threshold signal from the microprocessor 22 is a pulse width modulated square wave signal which has duty cycle proportional to the trigger threshold which is converted to a proportional d.c. voltage by a resister/capacitor filter consisting of resistor R8 (40K Ohm) and capacitor C3 (0.1 pF). The output of the comparator U3 is connected to an integrator trigger signal input of the microprocessor 22.

The integration circuit 24 includes the following components connected as shown in Fig. 3: resistor R1 (40K Ohm), resistors R2, R6 and R7 (100K Ohm), resistor R3 (10K Ohm), resistor R4 (50K Ohm), resistor R5 (1K Ohm), capacitor Cl (0.1 AiF) capacitor C2 (0.02 F), transistors Q1 and Q2 (2N7002), comparators U1 and U2 (LM2901). Thus, integration circuit 24 is a standard hardware based integrator with reset and windowing logic. The trigger thresholds to begin and end the integration are determined by the measurement of background signal levels and generated by the microprocessor 22. The windowing of the integration is controlled by the microprocessor 22 as a function of the engine position signal from the crank angle sensor 32, and allows better noise rejection in the system. The triggers at the beginning and end of integration are used by the microprocessor 22 to correct the integrated value for the background levels and to determine the beginning of injection. With respect to Figs. 2 and 3, the components values set forth herein are merely exemplary and other components could be utilized without departing from scope of the present invention.

The micro 22 executes an algorithm represented by Fig. 4. For further details regarding this algorithm, reference may be made to the computer program listing included in S the microfiche appendix. The timing calculation algorithm is entered at step 200. Step 202 15 directs the algorithm to step 204 if the signal from crank angle sensor 32 indicates that the engine 10 is at the start of a fuel injection window period, otherwise the algorithm is directed to step 214. Step 204 obtains an initial pressure threshold or trigger threshold value from a stored look-up table, based on the engine speed from sensor 30 and based on the fuel quantity value which results from the integration of the pressure signal from sensor 34. This 20 fuel quantity value is representative of the load on the engine 10. Thus, if the engine speed varies, and/or if the engine load varies, the initial trigger threshold will also vary.

If the pressure signal is noisy, then step 206 can be used to filter and smooth the pressure signal. Step 206 can be dispensed with if the pressure signal is sufficiently free of noise, or alternatively, this function can be performed by a hardware circuit.

25 Step 208 then calculates a new trigger threshold value by adding an offset to the value from step 204. The offset may be derived from the filtered background fuel injection pressure level from step 206. Preferably, the threshold is set relative to the background level, but this is done with a table rather than calculated directly by the microprocessor. The background pressure is determined for all engine speed and fuel flow rates. The background pressure level changes with changes in speed and fuel, but the level can be predicted based on engine speed and fuel flow. Therefore, the trigger level offset can be mapped into a stored data table of speed vs. fuel flow. The values in such a table represent the sum of the background level and a percentage of the peak pressure pulse. Using a single table to represent 2 physical values reduces the microprocessor requirements for memory, speed and overall cost. Piezoelectric pressure sensors typically have an output which responds to changes in pressure. While such an output will increase or decrease when the pressure changes, the output level may not correspond to an absolute pressure, and the output of such a sensor can drift several volts even while the pressure remains constant. When the pressure changes, the sensor accurately measures the change relative to the sensors output voltage before the pressure change. The algorithm described here is designed to function with. such a pressure sensor.

Step 210 outputs the calculated trigger threshold value to an input of the timing circuit 26 so that the timing circuit 26 will generate a start of injection timing signal when the signal from pressure sensor 34 exceeds the trigger threshold value. Step 212 enables an interrupt so that the start of injection timing signal can be received by the microprocessor 22, after which step 230 returns control to a main fuel injection control algorithm (not shown).

If, in step 202, if the signal from crank angle sensor 32 indicates that the engine 10 is not at the start of a fuel injection window period, step 202 directs the algorithm to step 214.

15 Step 214 directs the algorithm to step 216 if the signal from crank angle sensor 32 indicates that the engine 10 is at the end of a fuel injection window period, otherwise the algorithm returns via step 230. Step 216 disables the threshold interrupt. Step 218 determines whether or not a single interrupt occurred. If more than a single interrupt occurred, it means that a failure has occurred and step 218 directs the algorithm to step 220. If the number of errors detected by step 220 is high, step 220 directs the algorithm to step 222 which sets a 0 0 timing value to a default value, such as 10 degrees from top-dead-center, and then step 222 directs the algorithm to a fault management step 224, and then returns via step 230. If the number of errors detected by step 220 is not high, step 220 directs the algorithm to step 221 which sets the corrected angle value to the previous corrected angle.

25 If, in step 218 only a single interrupt occurred, then step 218 directs the algorithm to step 226 which calculates the crank angle value (relative to top-dead-center) at which the timing circuit 26 generated the timing signal. Then, step 228 generates a corrected angle value from a stored look-up table and as a function of engine speed from sensor 30 and the fuel quantity derived from the integration of the fuel pressure signal. This corrected angle value represents the crank angle at which a fuel injection pulse begins, and this value can be used to control fuel injection timing in a closed-loop control system.

A portion of the disclosure of this patent document contains material which is subject to a claim of copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all other rights whatsoever.

While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Throughout this specification and the claims which follow, lo unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the I exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

1. In an engine control system having a source of pressurized fuel, a fuel line for delivering fuel to a combustion chamber of the engine supply and a fuel pressure sensor for generating a fuel pressure signal, a method for determining the timing of a fuel quantity delivered to the combustion chamber, the method comprising: sensing a speed of the engine and generating an engine speed signal; sensing a fuel injection quantity of the engine and generating an engine load signal therefrom; generating a variable threshold signal which varies as a function of the engine speed signal and the engine load signal; comparing the fuel pressure signal to the variable threshold signal; and generating a timing signal when the fuel pressure signal crosses said variable threshold signal while the fuel pressure signal is increasing in magnitude.

2. The method of claim 1, further comprising: obtaining a variable threshold value from a look-up table stored in a memory of a computer; and converting the variable threshold value to the variable threshold signal.

3. The method of claim 2, further comprising: deriving a new threshold value by adding an offset value to the variable threshold value obtained from the look-up table.

4. The method of claim 3, wherein: *.0-the offset value is derived from a filtered background fuel injection pressure level.

The method of claim 1, further comprising: 0: defining a timing window; and o. .25 if only a single timing signal is generated during said timing window, calculating a crank angle value (relative to top-dead-center) at which the timing signal was generated.

6. The method of claim 5, further comprising: generating a corrected crank angle value from a stored look-up table and as a function of engine speed and fuel quantity, said corrected angle value representing a crank angle at which a fuel injection pulse begins.

7. The method of claim 1, further comprising: defining a timing window; and if more than a single timing signal is generated during said timing window, generating a default crank angle value (relative to top-dead-center) representing a timing of the timing signal.

8. The method of claim 1, wherein the control system comprises: a microprocessor which generates the variable threshold signal; and a timing circuit having a comparator having a first input coupled to receive the fuel pressure signal and a second input coupled to receive the variable threshold signal, the comparator having an output coupled to an input of the microprocessor for providing a timing signal to the microprocessor.

9. The method of claim 8, further comprising: obtaining a variable threshold value from a look-up table stored in a memory of a computer; and converting the variable threshold value to the variable threshold signal.

The method of claim 8, further comprising: deriving a new threshold value by adding an offset value to the variable threshold value obtained from the look-up table. 15

11. The method of claim 10, wherein: the offset value is derived from a filtered background fuel injection pressure level.

12. The method of claim 8, further comprising: defining a timing window; and if only a single timing signal is generated during said timing window, calculating a crank angle value (relative to top-dead-center) at which the timing signal was generated.

13. The method of claim 12, further comprising: generating a corrected crank angle value from a stored look-up table and as a function of engine speed and fuel quantity, said corrected angle value representing a crank angle at which a fuel injection pulse begins. S: 25

14. The method of claim 8, further comprising: defining a timing window; and if more than a single timing signal is generated during said timing window, generating a default crank angle value (relative to top-dead-center) representing a timing of the timing signal. -86- A method for determining the timing of a fuel injection pulse substantially as hereindescribed with reference to the drawings. DATED this NINETEENTH day of JUNE 2000 Deere Company By its Patent Attorneys DAVIES COLLISON CAVE 0O t 0@Sa a *fl. a 9* 9 9**e a .9 0 0@ 09 9* 9 9* a.