GB2477130A

GB2477130A - Controlling fuel injection of dual-fuel diesel engines

Info

Publication number: GB2477130A
Application number: GB1001049A
Authority: GB
Inventors: Gary Keep; Peter Harrison
Original assignee: MERCURY FUEL SYSTEMS Ltd
Current assignee: MERCURY FUEL SYSTEMS Ltd
Priority date: 2010-01-22
Filing date: 2010-01-22
Publication date: 2011-07-27
Also published as: GB201001049D0

Abstract

A method for controlling fuel injection of a diesel engine having a diesel injection controller to be fuelled by a secondary fuel, eg LPG, comprises producing a control signal corresponding to a desired injection timing for the secondary fuel and sending the control signal to the input of the unmodified diesel injection controller. An intake air temperature signal from a thermistor 1 which would have been sent from an output 3 to the diesel injection controller, fig.4, may be replaced by control signals 6 from an LPG electronic controller which simulates intake air temperature readings to enable optimal dual-fuel operation. Alternatively, the lines 16, 17 from crankshaft position sensor 11 and camshaft position sensor 12 to the diesel injection controller 20, fig.7, may be disconnected and redirected via an additional LPG controller 15. Injection timings for a diesel engine that has been converted to dual-fuel operation can thus be adjusted easily without making changes to the diesel controller.

Description

Diesel Iniection Timing Control This invention relates to an engine, a method for controlling diesel injection within an engine, and control equipment for an engine. In particular, the present invention is concerned with control of dual-fuel engines. In the context of the present invention, the term "diesel" encompasses not just petroleum-derived diesel, but also biodiesel, or other synthetic alternatives suitable for running a compression -ignition engine.

A conventional diesel engine typically includes at least one cylinder, each having a diesel injector for injecting diesel into the cylinder. The timing of this injection is controlled by diesel injection controller electronics (henceforth referred to as a "diesel controller"), which may act to vary the timing of the injection in relation to the stroke of a piston located within the cylinder. For successful operation, diesel must be injected into the cylinder at a precise point of the stroke, the timing of the injection being dependent on a range of variables.

Dual fuel engines are known which are based upon such conventional diesel engines. With such engines, a secondary system may be incorporated into the diesel engine to enable a secondary fuel, in particular liquid petroleum gas (LPG), to be used as fuel. Often, a conventional diesel engine may be converted for dual-fuel operation, for example by retro-fitting an LPG system to the engine. Such LPG systems will typically include a separate electronics control module for controlling the supply of LPG. This means that when adapted for dual-fuel operation, an engine will include two separate, dedicated fuel controllers, one for diesel, and one for LPG.

Such an arrangement can result in operational problems. In particular, the problem exists that in order to enable optimal dual-fuel operation, the timing of the diesel injection may need to be changed, i.e. so that the timing used is different to that used by the engine in a single-fuel configuration despite other operating conditions being similar. In order to effect an injection timing change to enable optimal dual-fuel operation, it is necessary to do so via the dedicated diesel controller.

However, changing the original diesel control settings is not normally possible -in effect the diesel controller is a "black-box" which cannot be easily adjusted.

Therefore, in conventional dual-fuel arrangements, the injection timing cannot easily be optimised for dual-fuel operation.

It is an aim of the present invention to overcome this problem, such that injection timings can be adjusted easily, without making any changes to the diesel controller. This aim is achieved by manipulating a sensor signal that is normally provided for input to the diesel controller.

As mentioned above, the optimal injection timing for a diesel engine (i.e. in single fuel mode) is dependent on a number of variables. Modern diesel engines include means for measuring, determining or otherwise accounting for these variables, such that the diesel controller may adjust the timing accordingly, such that is the engine's performance remains near constant over the required operating range.

One of these variables which affects the injection point is the temperature of the air entering the cylinder. As a general approximation, as the temperature of the intake air rises, the in-cylinder temperature for any given crankshaft angle during the compression stroke will also be proportionately higher. This means that any fuel present in the cylinder will reach its ignition temperature earlier, effectively advancing the point of fuel ignition. This effect may be countered however by measuring the air temperature using a sensor, passing this information to the diesel controller and adjusting the timing of the injection such that it occurs later in the cycle. This offsets the advance due to the higher intake air temperature. The reverse is true if the temperature of the air cools.

A known system is schematically shown in Fig. 1. Typically, the air temperature is measured using a thermistor-type sensor 1 located in the air intake manifold (not shown). Usually, these sensors exhibit a negative temperature co-efficient, such that their resistance decreases with increasing physical temperature.

The sensor 1 may be arranged into a potential divider circuit as shown, and often a "pull-up" resistor 2 and I or constant current source (here +5V I OV rails are used) is used in conjunction with the sensor 1. The output signal voltage 3 present at the node between the two resistances is measured using suitable amplification (not shown) and analogue to digital conversion (not shown). A calculation or look-up table is then used to infer the physical temperature of the sensor 1. Knowing the air temperature allows a further calculation or look-up to obtain a value for the amount the diesel injection timing needs to be adjusted.

The air temperature signal received by the diesel controller from the air temperature sensor therefore has a direct influence on the diesel injection timing.

In certain embodiments the present invention makes use of this fact, and enables the diesel injection timing to be controlled by manipulation of this signal.

The present invention is not limited to use of the temperature signal however.

In alternative embodiments for example, a signal relating to the position of the is crankshaft may be used.

The desired injection point is stated relative to the angle of the engine's crankshaft. During a four-stroke cycle for example, the crankshaft rotates two complete revolutions per cycle. Therefore it is required that the position of the engine's camshaft is also known to correctly determine which cylinder to inject fuel into. The crankshaft position is found by processing a signal from a crankshaft position sensor.

Typically, engines use variable-reluctance sensors for the crankshaft and camshaft sensors, although hall-effect sensors with suitable amplification are also common. A variable-reluctance sensor comprises a permanent magnet, magnetically coupled to a magnetically hard-core, wound with at least one electrical windings. The completion of the magnetic circuit includes an air-gap between the end of the sensor and a toothed ring fitted to the engine. As the toothed ring rotates, the air-gap changes in length thereby changing the reluctance of the magnetic circuit. This in-turn directly varies the magnetic flux. By Faraday's law the changing flux excites a voltage in the or each winding. The crankshaft and camshaft position sensors typically therefore issue steams of electrical pulses. The toothed ring has typically about 30 to 120 equally-spaced teeth around its complete circumference.

The output waveform signal produced by the each sensor depends to some extent on the shape of the teeth used, however typical voltage signals from the crankshaft and camshaft can be seen in Figs. 2 and 3 respectively. The zero-cross is the most important part of the waveform as this designates the centre of the tooth passing across the front of the sensor. At one or more given key locations, extra teeth may be either added or removed at tooth spacings. This creates synchronisation pulses within the pulse stream and these, combined with the normal pulses, allow absolute position of the crankshaft to be calculated at any instant. In Fig. 2 for example, the synchronisation pulses are shown by the "gaps" at around 7.5 ms and 43 ms, which in this case are caused by the omission of a tooth at each of those respective locations on the circumference.

A camshaft sensor, working in similar manner but coupled directly with the engine's camshaft, provides a pulse stream giving camshaft position, as shown for example in Fig. 3. By combining the camshaft and crankshaft positions, the exact location of the engine in the combustion cycle is obtained.

In Figs. 2 and 3, the shape falling edge of the signal denotes the centre of a tooth aligned with the sensor. The crankshaft and camshaft signals shown in Figs. 2 and 3 are obtained using variable-reluctance sensors. Although these sensors are a very common choice, other sensor types such as Hall-Effect may alternatively be used.

The engine's location in the cycle is continuously compared with the desired diesel injection point by the engine's diesel controller electronics. When the two match, diesel injection commences. The signals received from the crankshaft and camshaft therefore directly influence the injection timing.

In certain embodiments, the present invention makes of this fact, and enables the diesel injection timing to be controlled by manipulation of the shaft signals.

In accordance with a first aspect of the present invention there is provided a method for controlling diesel injection within an engine, the engine comprising a cylinder, a diesel injector for injecting diesel into the cylinder, and a diesel injection controller, the diesel injection controller comprising a sensor input adapted for receiving a signal from a sensor and the controller being configured to control diesel injection in dependence of said received signal; the method comprising the steps of: producing a control signal corresponding to a desired injection timing, and sending the control signal to the input of the diesel injection controller.

In accordance with a second aspect of the present invention there is provided control equipment for an engine, the engine comprising a cylinder, a diesel injector for injecting diesel into the cylinder, and a diesel injection controller, the diesel injection controller comprising a sensor input adapted for receiving a signal from a sensor and being configured to control diesel injection in dependence of said received sensor signal; the control equipment comprising: control means for producing a control signal corresponding to a desired injection timing, and connection means connected to the output of the control means, adapted for connection to the sensor input, to enable the produced control signal to be sent to the sensor input.

In accordance with a third aspect of the present invention there is provided an engine comprising control equipment in accordance with the second aspect.

The invention will now be described with reference to the accompanying drawings, in which: Fig. I schematically shows a section of a known diesel engine; Fig. 2 shows an exemplary signal output from a crankshaft position sensor; Fig. 3 shows an exemplary signal output from a camshaft position sensor; Fig. 4 schematically shows a first embodiment of the present invention; Fig. 5 schematically shows a second embodiment of the present invention; Fig. 6 schematically shows a third embodiment of the present invention; and Fig. 7 schematically shows a fourth embodiment of the present invention.

As far as possible, similar numbering is used for generally similar components throughout the figures.

A first embodiment of the invention, in which a diesel engine is converted for use as a dual-fuel engine, is schematically shown in Fig. 4. In Fig. 4, and indeed Figs. 5 and 6 also, a broken line 4 is shown, to schematically divide the equipment illustrated into that which is normally present in a conventional diesel engine (shown to the right of line 4), and that control equipment which is added to the conventional equipment in accordance with the present invention, shown to the left of line 4. In the case of a dual-fuel engine as illustrated, the equipment to the right of line 4 can be thought of a "diesel-specific", while that to the left is introduced to enable LPG to be used as fuel.

In Fig. 4, as in the known system of Fig. 1, it can be seen that the diesel engine includes a potential divider circuit which in normal use, i.e. before fitting of the LPG system, would enable the temperature of intake air to be determined. Similarly to the known system of Fig. 1, the air temperature is sensed by a temperature sensor, in this case a thermistor 1. Typically (e.g. as shown in Fig. 1), this thermistor 1 would be connected in series with a resistance 2 ("R11") and connected between -i-5V and OV rails. The signal output 3, connected between thermistor 1 and resistance 2, would then be indicative of the temperature at thermistor 1. The signal output 3 is connected to a temperature input (not shown) of a diesel injection controller (not shown).

As described previously, in conventional diesel engines, the signal received at the temperature input is used to adjust the diesel injection timing.

In the embodiment shown however, the connection between thermistor I and resistance 2 is broken, so that thermistor 2 is removed from the circuit. The new control equipment, shown to the left of line 4, includes a variable voltage source (Vs) 5, connected to signal output 3 via an operational amplifier 7. The amplifier 7 is set with unity gain and must be rated to sink the maximum current passed by resistance 2. The voltage source 5 is controlled by input control signals 6 from an LPG electronic controller (not shown), to regulate its output voltage level. With this embodiment, a desired diesel injection timing may be determined, for example by calculation or by reference to a look-up table populated with values determined as optimum when setting up the system. In order to effect this timing, suitable control input signals 6 are sent to the voltage source 5, such that the output voltage from voltage source 5, amplified by amplifier 7, acts as a control signal corresponding to the desired timing.

s With this embodiment, the control equipment acts to simulate an air temperature reading to suit the timing adjustment required, for example to enable optimal dual-fuel operation. This is a relatively simple method of influencing the diesel injection timing. As such there are some limitations. In particular, since thermistor 1 is removed from the circuit, there is no longer any automatic temperature-based regulation of the injection timing, such regulation being desirable.

Fig. 5 shows a second embodiment of the present invention, in which some degree of automatic temperature-based regulation of the injection timing is retained.

This embodiment has many similarities to that of Fig. 4. However, here thermistor 1 is remains connected in series with resistance 2. In addition, a resistance 8 ("R0") is provided between amplifier 7 and signal output 3. Since thermistor 1 remains connected, the signal output 3 will still depend, at least partially, on the air temperature. The value of R0 of resistance 8 may be calculated and selected such that extremes in physical air temperature still provide some diesel injection timing adjustment.

Fig. 6 shows a further embodiment, again which enables the diesel injection timing to be adjusted in dependence of the air temperature. For clarity, thermistor 2 has been removed from the circuit completely, although it may simply be disconnected as in Fig. 4. A separate temperature sensor, in this case thermistor 9, is provided, in series with a resistance 10 between the +5V and OV rails. An output is taken between the thermistor 9 and resistance 10, forming a potential divider circuit. The output is converted to a digital signal (conversion means not shown), and sent via a microprocessor (not shown) to voltage source 5, such that it forms one of the voltage source's input control signals 6. In this way, the output voltage of voltage source 5 is adjusted at least partially (or as desired) by the microprocessor in dependence of the air temperature measured by thermistor 9. This adjustment may for example comprise changing the phase of the signal received from thermistor 9.

A further embodiment is shown in Fig. 7, in which the diesel injection timing may be adjusted by way of the crankshaft position input signal. As shown, a diesel injection controller 20 has two inputs 18 and 19, adapted for receiving position signals from a crankshaft position sensor 11 and camshaft position sensor 12 respectively. In standard systems, these signals would be sent from sensors 11 and 12 via lines 16 and 17 respectively, however in the present embodiment these lines are disconnected as shown, and instead, the output signals from sensors 11 and 12 respectively are fed to LPG controller 15 via lines 13, 14 respectively. The crankshaft and camshaft position signals are manipulated as required, and then control signals relating to a desired injection timing are sent by LPG controller 15 to the inputs 18, 19 of diesel controller 20.

As discussed above, in this embodiment, position signals from the crankshaft and camshaft position sensors are used as the reference for the diesel injection is timing. In order to adjust the timing, the original crankshaft and camshaft signals are re-directed via the LPG controller 15. The LPG controller 15 may then adjust the original signals, for example such that their phase is altered as required to facilitate dual-fuel operation. The altered signals are then re-directed to the standard diesel controller 20. It is necessary that the LPG controller 15 is able to condition the signals from the sensors 11, 12 to obtain positions of the crankshaft and camshaft.

A suitable way to achieve this is for the LPG controller 15 to include an input processing circuit to detect the zero-crossings of the input signals' waveforms, and there are various integrated circuits available for performing this task, such as the 1V1AX9924 (from Maxim Integrated Products), LM1815 (from National Semiconductor) and NCV1 124 (from ON Semiconductor).

As can be seen, the control signals sent by LPG controller 15 may still depend on the input shaft position signals, and so the shaft positions will still have an effect on the diesel injection timing. As with previous embodiments, the controller 15 may use a variety of techniques to determine the desired diesel injection timing, including for example by calculation or by reference to a look-up table populated with values determined as optimum when setting up the system.

The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art.

For example, although the above description refers to intake air temperature, the temperature input of the diesel injection controller may be adapted for a different temperature measurement point, e.g. for connection to a fuel temperature sensor.

With regard to the embodiment using crankshaft position sensor signals, according to the type of sensors used, the diesel injection timing could be controlled using a combination of crankshaft and camshaft position signals, or alternatively one or other of the position signals may be used alone, i.e. not in conjunction with the position signals in respect of the other shaft.

i5 Although the above description is primarily concerned with dual-fuel diesel engines where LPG is the secondary fuel, the invention is not so limited. Other fuels which could be used as the secondary fuel include for example methanol, hydrogen, methane etc. Furthermore, while the above description is particularly concerned with enabling dual-fuel operation, the present invention does not have to be used with such a system, since it in general provides an alternative procedure for controlling diesel injection timing without resorting to changing the diesel injection controller's electronics I programming, regardless of whether dual-fuel operation is required or not.

Claims

Claims 1. A method for controlling diesel injection within an engine, the engine comprising a cylinder, a diesel injector for injecting diesel into the cylinder, and a diesel injection controller, the diesel injection controller comprising a sensor input adapted for receiving a signal from a sensor and the controller being configured to control diesel injection in dependence of said received signal; the method comprising the steps of: producing a control signal corresponding to a desired injection timing, and sending the control signal to the input of the diesel injection controller.
2. A method according to claim 1, wherein the step of producing a control signal comprises receiving a signal from the sensor and adjusting it to produce said control signal.
3. A method according to claim 3, wherein the signal from the sensor is adjusted by changing the phase of the signal.
4. A method according to any preceding claim, wherein the sensor input is a temperature sensor input adapted for receiving a temperature signal from a temperature sensor.
5. A method according to claim 4, wherein the temperature sensor input is adapted for receiving a temperature signal from an air temperature sensor.
6. A method according to either of claims 4 and 5, comprising the initial step of disconnecting a temperature sensor connected to the temperature sensor input.
7. A method according to any preceding claim, comprising the step of providing a variable voltage source, wherein the control signal is dependent on the voltage output of the voltage source.
8. A method according to claim 7, further comprising the step of providing an amplifier for amplifying the output of the voltage source.
9. A method according to claim 8, further comprising the step of providing a resistance in series with the output of the amplifier.
10. A method according to any preceding claim, further comprising providing a temperature sensor.
11. A method according to any of claims 4 to 10, wherein the temperature sensor is adapted for measuring the temperature of intake air for the engine.
12. A method according to either of claims 10 and 11 when dependent on any of claims 7 to 9, wherein the output of the temperature sensor is connected to the voltage source, such that the output of the voltage source is dependent on the temperature sensor output.
13. A method according to any of claims 1 to 3, wherein the sensor input is a shaft position sensor input adapted for receiving a position signal from a shaft position sensor.
14. A method according to claim 13, wherein the sensor input is a crankshaft position sensor input.
15. A method according to claim 13, wherein the sensor input is a camshaft position sensor input.
16. A method according to any preceding claim, further comprising an initial step of determining the desired injection timing, the control signal produced being dependent on this timing.
17. A method according to claim 16, wherein the control signal is produced by an LPG controller.
18. Control equipment for an engine, the engine comprising a cylinder, a diesel injector for injecting diesel into the cylinder, and a diesel injection controller, the diesel injection controller comprising a sensor input adapted for receiving a signal from a sensor and being configured to control diesel injection in dependence of said received sensor signal; the control equipment comprising: control means for producing a control signal corresponding to a desired injection timing, and connection means connected to the output of the control means, adapted for connection to the sensor input, to enable the produced control signal to be sent to the sensor input.
19. Control equipment according to claim 18, the engine further comprising a sensor, wherein the control means comprises an input for connection to the sensor and receiving a sensor signal therefrom, the control means further comprising adjustment means for adjusting the received sensor signal to produce said control signal.
20. Control equipment according to claim 19, wherein the adjustment means adjusts the sensor signal by changing the phase of the signal.
21. Control equipment according to any of claims 18 to 20, wherein the sensor input is a temperature sensor input adapted for receiving a temperature signal from a temperature sensor.
22. Control equipment according to any of claims 18 to 21, wherein the control means comprises a variable voltage source, and wherein the control signal is dependent on the voltage output of the voltage source.
23. Control equipment according to claim 22, wherein the control means further comprises an amplifier for amplifying the output of the voltage source.
24. Control equipment according to claim 23, wherein the control means further comprises a resistance in series with the output of the amplifier.
25. Control equipment according to any of claims 18 to 24, further comprising a temperature sensor.
26. Control equipment according to claim 25, wherein the temperature sensor is adapted for measuring the temperature of intake air for the engine.
27. Control equipment according to either of claims 25 and 26 when dependent on any of claims 22 to 24, wherein the output of the temperature sensor is connected to the voltage source, such that the output of the voltage source is dependent on the temperature sensor output.
28. Control equipment according to any of claims 18 to 20, wherein the sensor input is a shaft position sensor input adapted for receiving a shaft position signal from a shaft position sensor.
29. Control equipment according to claim 28, wherein the sensor input is a crankshaft position sensor input.
30. Control equipment according to claim 28, wherein the sensor input is a camshaft position sensor input.
31. An engine comprising the control equipment of any of claims 18 to 30.
32. An engine according to claim 31, adapted for dual-fuel operation.
33. An engine according to claim 32, wherein the fuels comprise diesel and one selected from the group consisting of liquid petroleum gas, methanol, methane and hydrogen.
34. A method substantially as herein described with reference to the accompanying figures.
35. Control equipment substantially as herein described with reference to the accompanying figures.
36. An engine substantially as herein described with reference to the accompanying figures.