METHOD AND ARRANGEMENT FOR THE DETECTION OF MISFIRE OF INTERNAL COMBUSTION ENGINES

Abstract

A method and system are provided with which it is possible to detect non-firing and untimely firing events in internal combustion and, if necessary, the temperature of the gas in the exhaust gas pipe. This is performed in general by measuring the speed of sound and determining the phase angle between the sender and receiver either arranged on different sides of the exhaust gas pipe or on the same side of the exhaust gas pipe. The receiver, depending on the measurement principle, can include one, two, or in special applications three receivers. Additionally, if necessary, it is possible to suppress the structure-borne sound influence on a speed of sound measurement with low cost and high stability.

Claims

1. A method for detection of a misfire of an internal combustion engine, comprising measuring a speed of sound variations of an exhaust gas in an exhaust gas pipe of the engine as a function of time.

2. The method according to claim 1, wherein the sound used for measurement is an ultrasonic sound.

3. The method according to claim 1, comprising providing sound sending means and sound receiving means and either placing the sending means and the receiving means on one side of the pipe or placing the sending means and the receiving means on different sides of the pipe and determining the speed of sound either from the sound from the sending means traveling twice across the pipe before reaching the receiving means, or, respectively, the sound from the sending means traveling once across the pipe before reaching the receiving means on the other side of the pipe.

4. The method according to claim 3, comprising measuring the phase angle of the sound between the sending means and the receiving means.

5. The method according to claim 4, comprising providing a sound sender as the sending means and at least a first sound receiver and a second sound receiver as the receiving means, such that the travel distance of the sound provided by the sender to the first receiver is different from the travel distance of the sound provided by the sender to the second receiver.

6. The method according to claim 5, comprising arranging the second receiver near the first receiver in the same direction from the sender thereby providing in general only one measuring section of the sound excited by the sender.

7. The method according to claim 3, comprising providing a structure having a speed of sound which is higher than the speed of sound in the gas, arranging the sender and the receiver on the structure, operating the sender during a least one period of time in an “on”-status by sending an acoustical signal and during at least one period of time in an “off”-status without sending an acoustical signal, operating the receiver in an “off”-status during at least one period of time of the “on”-status of the sender and in an “on”-status during at least one period of time of the “off”-status of the sender.

8. The method according to claim 1, wherein a misfiring is determined as the speed of sound during the exhaust cycle being below a defined threshold value and/or having the correct timing.

9. The method according to claim 1, comprising determining misfiring as a change of the speed of sound in the exhaust gas in dependence of time and then determining the temperature of the exhaust gas using the same signals.

10. A sensor arrangement adapted to detect misfire of an internal combustion engine, comprising sound sending means and sound receiving means either arranged all on one side of an exhaust pipe of the combustion engine or the sound sending means and the sound receiving means arranged on different sides of the pipe, and a signal processing means adapted to determine the speed of sound either from the sound from the sending means traveling twice across the pipe before reaching the receiving means, or, respectively, the sound from the sending means traveling once across the pipe before reaching the receiving means on the other side of the pipe and to detect misfiring depending on whether the speed of sound during the exhaust cycle is below a defined threshold value and/or has the correct timing.

11. The sensor arrangement according to claim 10, wherein the sound sending means comprise one sound sender and the sound receiving means comprise at least a first sound receiver and a second sound receiver, are arranged such that the travel distance of the sound provided by the sender to the receivers is different to each of the at least first receiver and second receiver.

12. The sensor arrangement according to claim 11, wherein the at least second receiver is arranged near the first receiver in the same direction from the sender thereby providing in general only one measuring working section of the sound excited by the sender.

13. The sensor arrangement according to claim 10, wherein a sound sender and an acoustical receiver are both mounted on a common structure, wherein the signal processing means operates the sender during a least one period of time in an “on”-status by sending an acoustical signal and during at least one period of time in an “off”-status without sending an acoustical signal, operates the receiver in an “off”-status during at least one period of time of the “on”-status of the sender and in an “on”-status during at least one period of time of the “off”-status of the sender, and integrates the signal of the receiver, and calculates the speed of sound.

14. The sensor arrangement according to claim 10, wherein the signal processing means determine delay or premature of firing events in the internal combustion engine.

15. The sensor arrangement according to claim 10, wherein the signal processing means additionally average the phase angle of the signals of the receivers and calculate the exhaust gas temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The figures show:

[0037] FIG. 1 a sensor arrangement in an exhaust gas pipe having sender and receiver on the same side of the gas pipe together with a block diagram of a signal processing unit comprising a signal processing means,

[0038] FIG. 2 another sensor arrangement with one sender and one receiver on different sides of the gas pipe,

[0039] FIG. 3 a sensor arrangement in an exhaust gas pipe having a sender and two receivers on the same side of the gas pipe together with a block diagram of a signal processing unit comprising the signal processing means,

[0040] FIG. 4 another sensor arrangement in an exhaust gas pipe according to the principle of FIG. 3 having sender and receivers on the opposite sides of the gas pipe.

[0041] FIG. 5 a principle depiction of a sensor arrangement comprising a sender and a receiver on a common structure and reflection means arranged apart from the sender and the receiver such that the sound excited by the sender travels via the reflection means to the receiver through the gas for providing a gas-borne signal, together with a block diagram of a signal processing unit comprising signal processing means, and

[0042] FIG. 6 a diagram of the cycle times of the sender and the receiver with different receiver cycle times.

DETAILED DESCRIPTION

[0043] In the following description of the figures the reference numerals of the same parts in the different figures have the same numerals. The embodiments of the different arrangements all can be used for detecting misfire and, if required, additionally the temperature of the gas in an exhaust gas pipe of an internal combustion machine.

[0044] FIG. 1 shows a misfire detection arrangement comprising a sound sender 1, which is in this example an ultrasonic sound sender, and a respective sound receiver 2 both arranged in a recess 3a of an exhaust gas pipe 3. The propagation 4 of the sound from the sender 1 to the receiver 2 is via the wall 3b of the exhaust gas pipe 3 as a reflector of sound. The propagation of the exhaust gas is depicted with numeral 5.

[0045] Sender 1 and receiver 2 are connected to a signal processing unit 7 which comprises a sound function generator 8, which in this case is capable to provide ultrasound and is connected with the sender 1. The signal processing unit 7 further comprises a pre-amplifier/AD converter 10 connected with the receiver 2. The sound function generator 8 and the pre-amplifier/AD converter 10 are all connected with a lock-in amplifier 11 which is connected with a microprocessor 13, which controls the function of the total sensor arrangement. The lock-in amplifier 11 provides a signal indicating the phase angle between the signal provided by the receiver 2 and a reference signal provided by the sound function generator 8 to the lock-in amplifier 11. Number 14 indicates the output of the result for further processing the detection of misfire. In another advantageous embodiment, the lock-in amplifier 11 can be integrated digitally within the microprocessor 13.

[0046] FIG. 2 shows only another arrangement of the sender 1 and the receiver 2 which are arranged on opposite sides of exhaust the gas pipe 3. The sender 1 as well as the receiver 2 are arranged in different recesses 3a. The sender 1 and the receiver 2 are connected to the signal processing unit 7 in the same way as shown in FIG. 1.

[0047] FIG. 3 shows a similar arrangement as in FIG. 1, however with a first receiver 2 and a second receiver 2a. As shown in the figure, the receivers 2, 2a are arranged close together but offset to each other. In view of that, the propagation of sound depicted with numeral 4 excited by the sender 1 and reflected at the wall 3b of the exhaust gas pipe 3 reaches the receivers 2, 2a along nearly the same measuring working section but with different path lengths. The two receivers 2, 2a thus have different distances for the propagation of sound 4.

[0048] Sender 1 and the two receivers 2, 2a are connected to a signal processing unit 7 which comprises a sound function generator 8, which in this case is capable to provide ultrasound and is connected with the sender 1. The signal processing unit 7 further comprises a first pre-amplifier/AD converter 10 connected with the first receiver 2 and a second pre-amplifier/AD converter 10a connected with the second receiver 2a. The sound function generator 8 and the two pre-amplifier/AD converters 10, 10a are all connected with a lock-in amplifier 11 which is connected with a microprocessor 13, which controls the function of the total sensor arrangement. The lock-in amplifier 11 provides a signal indicating the phase angle between the signals provided by the first receiver 2 and the second receiver 2a, which has to be compared with a given threshold phase value indicating whether the ignition is correct or presents a misfire. Number 14 indicates the output of the result for further processing the detection of misfire. In another advantageous embodiment, the lock-in amplifier 11 can be integrated digitally within the microprocessor 13.

[0049] FIG. 4 shows another arrangement of the sender 1 and the first receiver 2 and the second receiver 2a, which are both arranged opposite to the sender 1 on the other side of exhaust the gas pipe 3. The sender 1 as well as the receivers 2, 2a are arranged in different recesses 3a. The receivers 2, 2a here also are arranged such that the distance between the sender 1 and the two receivers 2, 2a is different. The sender 1 and the receivers 2, 2a are connected to the signal processing unit 7 in the same way as shown in FIG. 3.

[0050] FIG. 5 shows a mounting structure 3′ (which can be included in the wall 3 of an exhaust pipe) with a sender 1 and a receiver 2 mounted on that structure 3′. Sender 1 and receiver 2 are mounted such that the sound propagation 4 from the sender 1 to the sender 2 travels via an acoustic reflector 6, which corresponds with the wall 3b of the FIGS. 1 to 4, before reaching the sender 2. That sound provides a gas-borne signal. The sound propagation 5 of the sound provided by the sender 1 also travels via the structure 3′ to the receiver 2 thereby providing a structure-borne signal. The difference between the sender 1 and receiver 2 in the arrangement according to FIG. 1 is in their distance being less than 10 mm, preferably on the order of 4 mm. It is important that the time which the sound needs from the sender 1 to the receiver 2 via the different media (gas or solid material) is significant different in order to determine the speed of sound after processing the received signals with a sufficient accuracy.

[0051] A signal processing unit 7 which comprises a sound function generator 8, which in this embodiment provides an ultrasound, is connected with the sender 1. The receiver 2 is connected with a receiver pre-amplifier/AD-converter 10 of the signal processing unit 7. The signal processing unit 7 also comprises a switching function generator 9 which controls the sound function generator 8 or the receiver pre-amplifier/AD-converter 10 in view of their duty cycle. The sound function generator 8 is connected with a lock-in amplifier 11 as well as the receiver pre-amplifier/AD-converter 10. The sound function generator 8 provides the lock-in amplifier 11 with a respective reference signal. The lock-in amplifier 11 determines the phase angle between the reference signal delivered from the sound function generator 8 and the receiver signal from the receiver pre-amplifier/AD-converter 10. A microprocessor 13 receives the output signal from the lock-in amplifier 11 and provides a value output 14 in form of a respective signal for further processing as already explained in connection with the signal processing unit 7 in the other figures. In another advantageous embodiment, the lock-in amplifier 11 can be integrated digitally within the microprocessor 13.

[0052] In an exemplary embodiment, the sender 1 and the receiver 2 as shown in FIG. 1 are mounted very closely (distance of 4 mm) in parallel on the structure 3′ made of steel. The sound of speed in steel is approximately 4′000 m/s, which means that any structure-borne sound takes 1 μs to travel from the sender to the receiver.

[0053] Through the gas, the sound will travel via the acoustical reflector 6 and a total distance of 40 mm. With a sound of speed in the gas on the order of 400 m/s, the gas-borne sound takes 100 μs to travel from the sender 1 to the receiver 2.

[0054] Both contributions can therefore be separated in time as shown in FIG. 6. In that figure the first diagram shows the duty times of the sender 1 over time. The second and middle diagram shows the duty time of the receiver 2 without delay in in respect to the “on”-status of the sender 1, whereas in the third and lowest diagram the duty time of the receiver 2 is delayed in respect to the shut-off of the sender 1. In the above example with the mentioned dimensions and material, the sender 1 is operated during 100 μs, while the input from the receiver 2 to the amplifier 10 is switched off. During the next 100 μs, the sender 1 is switched off while the signal of the receiver 2 is measured by the amplifier 10. As the last structure-borne sound will reach the receiver 2 1 μs after the sender 1 has been switched off, the structure-borne contribution to the receiver signal has been reduced to 1%, if both contributions have the same amplitude. The structure-borne contribution can be reduced further by introducing a delay of some few microseconds between switching off the sender 1, and switching on the receiver 2 as shown in the lowest diagram of FIG. 6. Such a delay might be necessary, if internal reflections of the sound within the structure 3′ delay the transition time of the structure-borne sound.

[0055] As the overall noise level of the measurement strongly depends on over how many signal oscillations the amplifier can integrate, the on time of the receiver 2 should correspond to the time of travel of the gas-borne sound. For the same reason, the on time of the sender 1 should span the same amount of time, so that the duty cycles of sender 1 and receiver 2 are both 50% with a phase shift of π.

[0056] At an operational frequency of 50 kHz, the amplifier 11 will therefore integrate the receiver's signal over 5 periods. However, with a lock-in amplifier 11 as used it is possible to integrate the receiver signal continuously over extended periods of time. The amplitude measured by the lock-in amplifier 11 will be half of a continuous signal, whereas the phase angle information is entirely maintained. In this case, the function generator 8 driving the sender 1 must supply a reference signal to the lock-in amplifier 11 all the time.