GB2413850A

GB2413850A - Monitoring valve events in an internal combustion engine using a vibration sensor

Info

Publication number: GB2413850A
Application number: GB0509349A
Authority: GB
Inventors: David Richardson
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-05-08
Filing date: 2005-05-09
Publication date: 2005-11-09
Anticipated expiration: 2025-05-09
Also published as: GB0509349D0; GB0410324D0; GB2413850B

Abstract

A valve event (e.g. valve closing) monitoring system for an internal combustion engine 1 having a variable valve timing mechanism comprises at least one vibration sensor 12-19 (e.g. accelerometer, piezoelectric sensor) which produces an output signal dependent on vibrations in a portion of the engine (e.g. cylinder head, cylinder block). The sensor may also serve as a knock sensor. A signal processing means 21 determines the timing of valve events from the portion of output signal which falls within a time window defined around an expected time of the valve event. The start and end points of the time window are chosen such that the window will contain a valve event regardless of the amount of advance or retardation of the valve event produced by the variable valve timing mechanism. The system may form part of an emission control system which can indicate a fault in the valve timing of the engine and control the operation of the engine.

Description

24 1 3850 - 1 ImDrovements relating to Internal Combustion Enaines This

invention relates to engines, and in particular to a valve event monitoring system for an internal combustion engine having a variable valve timing mechanism. It also relates to an emission control system which incorporates such a valve event monitoring system.

In an internal combustion engine having a variable valve timing mechanism, the timing at which valves are opened and closed within the combustion cycle is varied according to the operational conditions, e.g. engine speed and load. Conveniently, this is achieved by advancing or retarding one or both inlet and exhaust camshafts.

According to a first aspect the invention provides a valve event monitoring system for an internal combustion engine having a variable valve timing mechanism, the system comprising at least one vibration sensor which is arranged to produce an output signal dependent upon vibrations in a portion of the engine and signal processing means arranged to determine the timing of a valve event from the information contained within the signal, the signal processing means being arranged to a receive an additional signal which is indicative of the approximate time that a valve event is expected to occur relative to the output signal and to apply a window around the expected time of the event such that the output signal within the window can be analysed to detect the valve event, the duration of the window being chosen such that the start of the windowed portion of the output signal and the end of the windowed portion define a windowed portion which will contain a valve event regardless of the amount of advance or retardation of the valve event produced by the variable valve timing mechanism.

Thus a valve event will always be detected within the window, or the window will track the expected position of the valve closing event.

The vibration sensor may comprise an accelerometer, such as a piezoelectric type sensor.

The sensor may comprise a knock sensor, meaning that it produces a signal which is analysed by a processing means to detect the onset of engine knocking. The same signal which is analysed to detect knocking may be analysed to detect the valve event.

The valve event may comprise the closing of the valve, which can be detected by the signal processing means identifying a characteristic in the output signal indicative of the vibrations produced by a valve colliding with a respective valve seat.

Typically, an engine will have more than one inlet valve and one exhaust valve for each cylinder. In this case the processing means may be adapted to analyse the output signal to identify a valve event corresponding to each valve.

The additional signal applied to the processing means may provide an indication of the mode of operation of the variable valve timing system such that in the event that the valve event is detected at a time which differs from that expected for a given mode of operation of the valve timing system the system may raise an error flag or generate a fault code.

The system may process anaiogue or digital signals from the vibration sensor. Where it processes analogue signals, the signals may be sampled within at least two detection windows, each window being temporally located such that the signal within the windows will differ dependent on which of two valve event timings the valve event has occurred at, the system being further adapted to determine which window an event has occurred in by comparing the signal sampled in each window.

The windowed signals may be compared by passing them both to a comparator.

Of course, if it is envisaged that valve events can occur at more than two temporal locations, then more than two windows can be provided. - 3

The signals may be sampled periodically when used on a running engine as the valves will be opening and closing periodically. The valve timing will depend on the speed of the engine, and so the time between windows will need to be varied as a function of engine speed. Nevertheless, this can be readily achieved provided that a signal indicative of crank position is known as the cam of an engine will ensure that the valve timings occur at the same points relative to crank angle.

In tests, a system in accordance with the first aspect has been shown to be operational on an engine having eight cylinders. The invention has application with engines of many different configurations and can be used in combination with engines having three, four, five, six, eight, ten, twelve or more cylinders in any one of a range of configuration (such as an in-line engine or a v-configuration).

The invention also provides, according to a second aspect thereof, an emissions control system for use in combination with an engine having a variable valve timing system which comprise a signal receiving means arranged to receive a signal from a valve event monitoring system according to the first aspect of the invention and a fault indicating means which is adapted to provide an emissions warning signal in the event that the signal from the valve event monitoring system indicates a fault in the valve timing system of the engine.

The system may be adapted to issue one or more signals to an engine management system which cause the system to modify the operation of the engine in response to the control signals.

The system may display the warning signal audibly or visibly or both to an operator, e.g. the driver of a vehicle in which the engine is fitted. Alternatively, it may generate a fault code to indicate that a fault has occurred. The warning may simply indicate that a valve is closing or opening at the wrong time, and may perhaps indicate which valve from a set of valves is incorrect. - 4

Moreover, the invention also provides, according to a third aspect thereof, a method of controlling an internal combustion engine having a variable valve timing mechanism in which signals from an emission control system according to the second aspect of the invention are used to control the operation of the engine.

The method may comprise modifying the timing of valve events in response to receiving control signals. The modification of timing of the valve events in the engine may be such as to reduce levels of unwanted emissions.

It will, of course, be understood that the third aspect of the invention is not to be limited to emission control systems that provide a warning signal to an operator. It may control the operation of the engine without alerting the operator that it is doing so.

In the event of a failure of the valve timing for one or more cylinders of an engine, the method may comprise shutting off the supply if fuel, or reducing the supply of fuel to the or each failed cylinder to control the emissions.

Alternatively, the method may comprise, or the apparatus of the second aspect may be adapted to, hold one or more valves which are functioning incorrectly in a fully closed or a fully open position whilst the fault persists to control the emissions of the engine.

The emission effect will depend on the valve movement strategy in the engine, and the method may modify the behaviour of individual valves when a fault has been detected according to the strategy used. For example, the valve movement strategy may provide for two cam profiles: a high lift and a low lift. If the engine is calibrated to always start in low lift profile then the combustion system will be developed to make use of high air velocities over the valves to vaporise fuel. If the valves are incorrectly in high lift on start up then the fuel preparation will not be so good leading to increased emissions. The change in emissions from just one or two cylinders may be enough for the engine to fail an emissions test - 5 standard. Such a fault can be detected by the apparatus of the present invention and a fault may be issued.

There now follows, by way of example only, a description of one embodiment of the invention, described with reference to the accompanying drawings, of which: Fig.1 is a diagrammatic representation of an internal combustion engine having a variable valve timing mechanism engine fitted with the valve event monitoring system of the present invention; Fig.2 is a plot of the average amplitude of signals taken from vibration sensors shown in Fig.1 over the range 12-24 kHz plotted against crank angle position through a four-stroke cycle with the engine running at 3500rpm; Fig.3 shows the valve event of two cams fitted to the engine shown in Fig. 1 with a detection window for the closing event of each cam; and Figs. 4 and 5 show the output signals from two integrators which take signals from vibration sensors shown in Fig.1 as passed through band pass filters to isolate the relevant frequencies and rectified.

The valve event monitoring system comprises one or more vibration sensors 12, 13, 15, 16, 17, 18, 19 fitted to an internal combustion engine, in this particular example a V6 engine 1 which is fitted with mechanical bucket valve gear and has cylinders 1, 2, 3, 4, 5, 6.

Sensors can be fitted on the cylinder heads as typified by sensors 12, 13, 15, 16, fitted to the cylinder heads of cylinders 2, 3, 5 and 6 respectively, fitted to the engine block as shown as positions 17 or 18 or the usual knock sensor 19 can be used. It has been found that, generally, head-mounted sensors give the best results, although block- mounted sensors and the knock sensor both give useable results. Typically one vibration sensor would be used - in this example sensor 13. However, more than one sensor may be used and the results combined. - 6

As the engine 1 runs, the valves associated with each cylinder 1-6 open and close as appropriate. As discussed above, it is advantageous to determine when the valves are opening and closing in order to monitor the emissions of the engine. This is particularly advantageous in an engine with switchable valve cams, as a check can be made that the correct set of cams are operating. If the incorrect cams are in use, the valve or valves may not open far enough, may open too far, or may open too late or too early. In all of these cases, increased emission of such substances as higher hydrocarbons and carbon monoxide can occur such that the engine would begin to pollute in an undesirable manner.

Furthermore, the engine may misfire, decreasing performance and efficiency.

In order to monitor the valve opening and closing times (hereinafter "events"), the vibrations from the vibration sensor 13 are recorded by a capture device 20 as the engine runs. One sensing option is to continually convert the analogue signal from the vibration sensors into digital form such that further processing may be performed.

The digitised signal is then passed to analysis unit 21 where it may, optionally, be squared and rooted to make all values positive. As the action of the engine is cyclic, equivalent points from several fourstroke cycles (720 degrees crank angle) can be averaged together to improve measurement accuracy. The averaged signal at each point in the cycle is then subjected to a Fast Fourier Transform (FFT) to determine its frequency components.

Unfortunately, artefacts which do not correspond to valve events can typically be seen in the frequency spectrum. However, these are present at a restricted range of frequencies compared to the valve events and so a frequency domain filter is applied to remove these.

The passband of the filter will vary depending on the position of the sensor, but will be typically in the region of 12 to 24 kHz. The average amplitude in the passband is then calculated for each point in the cycle. Peaks over a predetermined threshold in the filtered average amplitude are determined to be valve events.

In order to discriminate further against noise, the monitoring system only checks for valve events around an expected time for the valve events. Typically this system would only determine a peak in the filtered amplitude to be a valve event if it was within X crank angle of the expected position.

In practice there is an offset between the measured crank angle at the time the vibration is detected and the actual crank angle at which the relevant valve event occurred.

This depends on the position of the vibrations sensor relative to the valve and the speed at which the engine is running. The offset is effectively constant for a given set of conditions, and so a look-up table of offsets calculated during any of manufacture, fitting and testing of the system is kept in the analysis unit 21 and applied as necessary.

The amount of noise present in the detected signal is dependent upon the speed at which the engine is running. Using this system, it has been found that valve events can be detected up to around 6000rpm. Above this speed, noise obliterates the signals due to the valve events such that they cannot be discriminated. Accordingly, the analysis unit may take account of the engine speed and only make determinations of valve event timing if the engine speed is below a given threshold. An engine speed monitor 22 is provided for this purpose.

Once the analysis unit 21 has determined the timing of the valve events, it can determine the effect this has on the emissions of the engine 1. If a serious mistiming is detected, the driver of the vehicle which the engine powers can be alerted by means of a Malfunction Indicator Light (MIL) which, in the case of a vehicle engine, can conveniently be provided on the vehicle dashboard. This indicates that the engine should be checked and repaired as necessary to remove the cause of the mistiming.

In an alternative embodiment, wavelet analysis could be used in place of the FFT.

A system can also be provided which is analogue. A signal is obtained as before but instead of digitising the signal it is passed through band pass filters to isolate the frequencies of most interest. The signal may then be rectified and passed through two integrators which are windowed over different, set, crank angles. Fig.3 shows the valve event of two cams (A and B) shown by curves 53 and 54 (valve lift versus cam angle). A detection window 51 for one integrator is centred on the expected crank angle of one valve event, i.e. the closing of cam B whilst the detection window 52 for the other integrator is centred on the expected crank angle for an alternative event, i.e. the closing of cam A. A comparison of the outputs from the two integrators can then made to determine which window the event has occurred in. Figs 4 and 5 show the output signals from the two integrators and how they vary over time within each window 51,52 for the two different valve events. Only one integrator has a high output, this being the integrator which is measuring across the window in which the valve event has occurred.

Of course, as with the digital system, three or more events could be detected in this way by providing three or more windows. - 9 -

Claims

1. A valve event monitoring system for an internal combustion engine having a variable valve timing mechanism, the system comprising at least one vibration sensor which is arranged to produce an output signal dependent upon vibrations in a portion of the engine and signal processing means arranged to determine the timing of a valve event from the information contained within the signal, the signal processing means being arranged to a receive an additional signal which is indicative of the approximate time that a valve event is expected to occur relative to the output signal and to apply a window around the expected time of the event such that the output signal within the window can be analysed to detect the valve event, the duration of the window being chosen such that the start of the windowed portion of the output signal and the end of the windowed portion define a windowed portion which will contain a valve event regardless of the amount of advance or retardation of the valve event produced by the variable valve timing mechanism.

2. A system according to claim 1 in which the vibration sensor comprises an accelerometer, such as a piezoelectric type sensor.

3. A system according to claim 2 in which the sensor comprises a knock sensor and in which the same signal which is analysed to detect knocking may be analysed to detect the valve event.

4. A system according to any preceding claim in which the valve event comprises the closing of the valve.

5. A system according to any preceding claim in which the additional signal applied to the processing means provides an indication of the mode of operation of the variable valve timing system and in which in the event that the valve event is detected at a time - 1 0 which differs from that expected for a given mode of operation of the valve timing system the system may raise an error flag or generate a fault code.

6. An emissions control system for use in combination with an engine having a variable valve timing system which comprise a signal receiving means arranged to receive a signal from a valve event monitoring system according to any one of claims 1 to 5 and a fault indicating means which is adapted to provide an emissions warning signal in the event that the signal from the valve event monitoring system indicates a fault in the valve timing system of the engine.

7. An emissions control system according to claim 6 which is adapted to issue one or more signals to an engine management system which cause the system to modify the operation of the engine in response to the control signals.

8. An emissions control system according to claim 6 or claim 7 which is adapted to display the warning signal audibly or visibly or both to an operator.

9. An emission control system according to any of claims 6 to 8 which is adapted to generate a fault code to indicate that a fault has occurred.

10. A method of controlling an internal combustion engine having a variable valve timing mechanism in which signals from an emission control system according to any one of claims 6 to 9 are used to control the operation of the engine.

11. A method according to claim 10 and further comprising modifying the timing of valve events in response to receiving control signals.

12. A method according to claim 11 in which the step of modification of timing of the valve events in the engine is such as to reduce levels of unwanted emissions.