Method of injector control versus engine soak duration

Abstract

There is provided a method (300) for controlling an injector (1) for an engine, the injector comprising an actuator (6) and a valve (2) which is engageable with a valve seat (5) of the injector, the valve comprising an elastomer seal (4) disposed at an end of the valve proximal to the valve seat, the actuator being configured to receive a drive signal (11.2) to move the valve towards and away from the valve seat to control injection of gaseous fuel into an associated engine combustion chamber, the method comprising: determining (302) a soak time, wherein the soak time is a time interval between a most recent power-off time of the engine and a subsequent power-on time of the engine; determining (304) a peak current (A1) and / or a duration (T2-T1) for an initial portion of the drive signal for the actuator as a function of the determined soak time; and applying (306) the initial portion of the drive signal to the actuator, using the peak current and / or for the duration, to move the valve from a closed state to an open state.

Description

[0001] PH24075

[0002] METHOD OF INJECTOR CONTROL VERSUS ENGINE SOAK DURATION

[0003] Technical Field

[0004] The examples of the invention relate to improvements in control of fuel injectors, and particularly fuel injectors for internal combustion engines fuelled at least partially with hydrogen or another gaseous fuel delivered by port fuel injectors (PFIs).

[0005] Fuel injectors, for example gas specific PFIs, for internal combustion engines fuelled at least partially with hydrogen or another gaseous fuel, usually comprise an actuator (e.g. a solenoid actuator) and a valve, the actuator being configured to move the valve towards and away from the valve seat to control fuel injection into the engine combustion chamber. Valves such as this comprise an elastomer seal that engages a valve seat, i.e. an internal surface at the end of the injector from which the fuel is delivered, against which the valve sits when closed. The purpose of the elastomer seal is to prevent injector leakage, i.e. fuel leakage from the injector when the injector is closed.

[0006] To open such an injector, an electromagnetic force from the solenoid actuator must overcome an internal spring force of the injector (intended to keep the injector closed when not injecting) and friction forces as well as the force from the fuel pressure acting upon the valve. Valves actuated in other ways, for example by hydraulic actuators, would also have to overcome similar forces.

[0007] When the injector has been used at normal operating temperatures, the elastomer seal sometimes conforms to its valve seat, creating additional sticking between the valve and the valve seat, and therefore creating additional friction forces for the actuator to overcome.

[0008] Sometimes, there may not be enough injector force available to overcome the combined forces of this additional friction along with the spring and gas pressure force, preventing one or more of the injectors from opening. This leads to an engine that starts on a reduced number of cylinders or does not start at all. It is with these issues in mind that the embodiments of the invention have been devised.

[0009] Summary of the Invention

[0010] Against this background, according to an aspect of the invention, there is provided a method for controlling an injector for an engine, the injector comprising an actuator and a valve which is engageable with a valve seat of the injector, the valve comprising an elastomer seal disposed at an end of the valve proximal to the valve seat, the actuator being configured to receive a drive signal to move the valve towards and away from the valve seat to control injection of gaseous fuel into an associated engine combustion chamber, the method comprising: determining a soak time, wherein the soak time is a time interval between a most recent power-off time of the engine and a subsequent power-on time of the engine, determining a peak current and / or a duration for an initial portion of the drive signal for the actuator as a function of the determined soak time, and applying the initial portion of the drive signal to the actuator, using the peak current and / or for the duration, to move the valve from a closed state to an open state. Advantageously, by accounting for soak time, i.e. by determining a peak current and / or a duration for an initial portion of the drive signal for the actuator as a function of the determined soak time, the peak current and the duration of the drive signal required to overcome forces acting against the valve and preventing the valve from opening can be reduced.

[0011] The method may comprise applying the initial portion of the drive signal to the actuator at a current level that alternates between the peak current and a low or no current such that the actuator moves the valve repeatedly from the closed state to the open state for a majority of the duration. Advantageously, the duration of the drive signal required to open the valve using the “buzzing” or “unjam” strategy described herein can be reduced.

[0012] The method may comprise applying a secondary portion of the drive signal to the actuator, subsequent to the initial portion, to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection. Advantageously, the secondary portion of the drive signal may be part of an injector event, reducing wait time. The method may comprise determining a second peak current and / or a second duration for the secondary portion of the drive signal for the actuator as a function of the determined soak time wherein the second peak current comprises a boost peak current and / or the second duration comprises a boost duration. Advantageously, the peak current and the duration of the drive signal required to open the valve using the “boost” strategy described herein can be reduced.

[0013] The method may comprise applying the initial portion of the drive signal to the actuator while no fuel is present in the valve. Advantageously, fuel pressure forces acting against the valve and preventing the valve from opening are reduced.

[0014] The method may comprise applying the initial portion of the drive signal to the actuator at the peak current for a majority of the duration, wherein the peak current comprises a boost peak current and / or the duration comprises a boost duration. Advantageously, the peak current and the duration of the drive signal required to open the valve using the “boost” strategy described herein can be reduced.

[0015] The method may comprise applying the initial portion of the drive signal to the actuator to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection. Advantageously, the initial portion of the drive signal may be part of an injector event, reducing wait time.

[0016] Determining the peak current and / or the duration for the initial portion of the drive signal as a function of the determined soak time may comprise increasing one or more of the peak current and the duration from a respective one or more of a baseline current and a baseline duration as a function of increasing determined soak time. Advantageously, the peak current and / or the duration for the initial portion of the drive signal may be lower for lower soak times.

[0017] Determining the peak current and / or the duration of the initial portion of the drive signal as a function of the determined soak time may comprise increasing one or more of the peak current and the duration as a function of increasing determined soak time up to a respective one or more of a maximum peak current and a maximum duration. Advantageously, the peak current and / or the duration for the initial portion of the drive signal may be lower than a maximum peak current and / or maximum duration for lower soak times. The method may comprise determining the maximum peak current and / or the maximum duration as a function of a temperature of the gaseous fuel. Advantageously, the peak current and / or the duration for the initial portion of the drive signal may be lower than a maximum peak current and / or maximum duration at a certain temperature for lower soak times.

[0018] The method may comprise determining the maximum peak current and / or the maximum duration to be a respective one or more of a maximum peak current for the initial portion of the drive signal achievable by the actuator and a maximum duration for the initial portion of the drive signal achievable by the actuator. Advantageously, the peak current and / or the duration for the initial portion of the drive signal may be lower than a maximum achievable peak current and / or maximum achievable duration for lower soak times, thus preventing the injector from needing to work at full capacity.

[0019] The method may comprise determining the peak current and / or the duration for the initial portion of the drive signal as a function of the determined soak time and a temperature of the gaseous fuel.

[0020] Determining the soak time may comprise decrementing, by a lower power counter module of a control unit of the engine, a counter by 1 every second after the most recent power-off time until the subsequent power-on time, and determining the time interval between the power-off time and the power-on time based on the counter. Advantageously, the soak time may be determined even if the control unit is not switched on during the soak time.

[0021] Determining the soak time may comprise determining a time and date stamp at the most recent power-off time, storing the time and date stamp in a non-volatile memory of a control unit of the engine, retrieving, at the subsequent power-on time, the time and date stamp from the non-volatile memory, and determining the time interval between the power-off time and the power-on time based on the time and date stamp. Advantageously, the soak time may be determined even if the control unit is not switched on during the soak time.

[0022] The method may comprise applying a further portion of the drive signal to the actuator to hold the valve in the open state. The method may comprise applying one or more of the initial, secondary, and further portions of the drive signal to an electromagnetic actuator.

[0023] When fuel is supplied to the injector, the open state of the valve may be an injecting state of the injector, in which the injector is capable of delivering the fuel to the associated cylinder of an engine.

[0024] The open state may comprise a fully open state, wherein the actuator is opened to a full extent possible within the injector.

[0025] According to a further aspect of the invention, there is provided a control unit for an injector for an engine, the injector comprising an actuator and a valve which is engageable with a valve seat, the valve comprising an elastomer seal disposed at an end of the valve proximal to the valve seat, the actuator being configured to receive a drive signal to move the valve towards and away from the valve seat to control injection of gaseous fuel into an associated engine combustion chamber, the control unit configured to execute machine readable instructions to perform a method as described herein.

[0026] The control unit may take the form of an engine control unit of the engine.

[0027] It will be appreciated that any of the preferred or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the second aspect of the invention also.

[0028] Further optional and advantageous features are referenced in the detailed description and the appended claims.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Examples of the invention will now be described with reference to the following figures:

[0031] Figure 1 is a cutaway perspective view of an injector according to the present invention; Figure 2 is a schematic view of an engine system comprising an injector as in Figure 1 ;

[0032] Figure 3 is a flow chart illustrating an example method for controlling the injector of Figure 1 ;

[0033] Figures 4a and 4b are graphs illustrating example relationships between a soak time and a peak current and / or a duration of an initial portion of a drive signal for the injector of Figure 1 ; and

[0034] Figures 5a and 5b are graphs illustrating examples of an initial portion of the drive signal for the injector of Figure 1.

[0035] Detailed Description

[0036] In general, the examples of the invention provide a method for controlling an injector for an engine.

[0037] In overview, and referring to Figure 1 , there is shown an injector 1 for an engine. The injector 1 comprises an actuator 6, a valve 2, a valve seat 5, an end-stop 3. The valve 2 comprises an elastomer seal 4 disposed at an end of the valve 2 proximal to the valve seat 5. The valve 2 is engageable with the valve seat 5. Specifically, the elastomer seal 4 of the valve 2 is engageable with the valve seat 5.

[0038] The injector 1 is configured to deliver gaseous fuel to an associated combustion chamber of the engine. The injector 1 is supplied with fuel by a fuel supply system (not shown) including a pressurised fuel source or reservoir of gaseous fuel. The pressurised fuel source or ‘fuel tank’ may suitably be configured to store hydrogen gas at an appropriate pressure level, which may be between 350 and 700 bar. A pressure regulating device (not shown) is configured to reduce the gas pressure in the fuel tank to a pressure suitable for injection, which may be between 5 bar and 10 bar but could be higher for some systems. The engine typically comprises a number of combustion chambers, or cylinders, in an ‘in-line’ configuration and the injector 1 delivers fuel to an associated one of the cylinders. Herein, the term ‘combustion chamber’ will be considered synonymous with ‘engine cylinder’. Each combustion chamber has an inlet valve and an exhaust valve in a conventional manner to control, respectively, the airflow into and the exhaust flow out of the combustion chamber.

[0039] A network of air pipes feeds incoming fuel to an air inlet duct or ‘manifold’. As is known in the art, the air inlet manifold directs fresh air to each of the engine cylinders via separate air channels. The injector 1 is arranged to inject gaseous fuel, in this case hydrogen gas, into the fresh air flowing into the engine cylinders. The injector 1 therefore takes the form of a port fuel injector.

[0040] The actuator 6 is configured to move the valve 2 towards and away from the valve seat 5 along a movement axis aligned with the longitudinal axis of the valve, to control fuel injection into the associated engine combustion chamber. The actuator 6 is controlled by applying a drive signal to actuate the valve 2 in a first direction along the movement axis from a closed position, in which the valve 2 sits against (i.e., is engaged with) the valve seat 5, to an open position, in which the valve 2 is spaced apart from the valve seat 5. Thus, the actuator 6 is controlled to actuate the injector 1 to switch between a closed state, in which no injection occurs, and an injecting state, in which the injector 1 is capable of delivering fuel to the associated cylinder of the engine. That is to say, when there is fuel present in the injector, the open state of the valve 2 is equivalent to the injecting state of the injector 1 .

[0041] The actuator 6 may be an electromagnetic actuator 6, for example a solenoid actuator 6, and the drive signal may be applied in the form of a drive current or drive pulse.

[0042] The open state may comprise a fully open state, wherein the actuator 6 is opened to a full extent possible within the injector 1. In the fully open state, at least part of the valve 2 abuts the end-stop 3, and cannot be moved any further in the first direction. The end-stop 3 is arranged within the injector 1 for this purpose of defining the fully open state of the valve 2, as would be understood by a person skilled in the art.

[0043] The elastomer seal 4 is disposed at the end of the valve 2 proximal to the valve seat 5 to prevent injector 1 leakage, i.e. fuel leakage from the injector 1 , when the valve 2 is in the closed state, i.e. when the elastomer seal 4 of the valve 2 is engaged with the valve seat 5.

[0044] The injector 1 also comprises a spring for providing a force for returning the valve 2 to the closed state when the actuator 6 is not acting on the valve 2. The spring is configured to move the valve 2 in a second direction along the movement axis, the second direction being a closing direction of the valve 2, counter to the first direction.

[0045] Therefore, by not applying the drive signal, or by applying a zero or low current drive signal, the actuator 6 can be said to be configured to move the valve 2 in the second direction, i.e. towards the valve seat 5. While in Figure 1 this function is performed by the spring, it will be understood that the injector 1 may comprise any suitable means for providing a force for returning the valve 2 to a closed state, or allowing the valve 2 to return to a closed state, when the actuator 6 is not acting on the valve 2.

[0046] Referring to Figure 2, there is shown an engine system 10 comprising an injector 1 , one or more sensors 12, and a control unit 11. The injector 1 may be the injector 1 described with respect to Figure 1.

[0047] The one or more sensors 12 may comprise a temperature sensor 12. The temperature sensor 12 may also be provided on or associated with the injector 1 to provide the functionality of providing a measurement of the temperature of the fuel to be fed to the injector 1 as a data input 11.1 to the control unit 11. The temperature sensor 12 is shown schematically in Figure 2 as connected to the control unit 11 , but it will be understood that the actual position of the temperature sensor may be any suitable place suitable for measuring the fuel temperature, for example attached to a fuel supply line or a shut-off valve of the engine. Such temperature sensing functionality may also be determined by a suitable temperature sensing algorithm that predicts the fuel temperature based on ambient temperature, engine loading, tank temperature and any other appropriate factors, as is known in the art.

[0048] The control unit 11 , which may take the form of an engine control unit (ECU), which is adapted to receive data input to sense operational parameters of the engine to provide suitable control output signals to the injector 1 , for example providing a drive signal 11 .2 to the actuator 6, and other aspects of the engine system 10 to control its operation based on driver demands and sensor measurements, as is conventional. The control unit 11 may include a non-volatile memory component (NVM) 13. The NVM 13 stores data such as self-learnt control parameters and operating history data which can be retrieved by the control unit 11 even after a power down cycle. The control unit 11 may also include a low power counter 15 which is used to determine a time interval and which relies on a permanent power supply and is operable regardless of the key on / off state.

[0049] The control unit 11 is operable to perform various engine monitoring and control objectives to manage the performance of the vehicle or power plant system into which it is installed. It should be appreciated that the control unit may be any suitable control environment provided by the engine system 10. The control unit may be the “engine ECU” of the engine system 10 or it may be another control unit which is configured to carry out other performance and monitoring tasks within the engine system 10 of the broader vehicle or power plant system. In particular, the control unit 11 may be a control environment provided specifically for the purposes of performing the method. The control unit 11 is configured to control operation of the fuel injector 1 through the drive signal 11 .2, in accordance with engine demand and other sensor outputs. More specifically, the method is suitable to be performed on the port injection system in which the fuel injector 1s deliver fuel to the air inlet manifold before delivery to the engine cylinders.

[0050] Irrespective of the functionality of the control unit 11 , it will be appreciated that the control unit has the necessary memory (not shown), processing environment (not shown) and communications interface (not shown) to be integrated into the engine system 10 and the broader system of an associated vehicle or power plant system. These specific parts of the control unit 11 are not shown in the Figure, but their presence is implied.

[0051] It is important to have accurate control of opening and closing times of the valve 2 (and thus of the injector 1), as it allows precise control of the quantity of fuel which is delivered in an injection event. In practice, the demanded opening and closing time may not be fulfilled due to a variety of factors, including, for example, when the elastomer seal 4 conforms to its valve seat 5, creating additional forces for the actuator 6 to overcome to remove the elastomer seal 4 from the valve seat 5. Two example ways to either reduce friction or increase actuator 6 force in order to overcome these additional forces are as follows.

[0052] Firstly, the actuator 6 may be turned rapidly on and off for a period of time. This may be referred to as “buzzing” to “unjam” the valve 2 of the injector 1 (and thus the elastomer seal 4 of the valve 2) from the valve seat 5. This strategy will herein be referred to as the buzzing or unjam strategy.

[0053] This may be achieved by applying the drive signal 11 .2 to the actuator 6 at a current level that alternates, thereby controlling the actuator 6 to alternate between moving the valve 2 in the first direction and allowing the spring to move the valve 2 in the second direction counter to the first direction. The actuator 6 therefore will repeatedly move the valve 2 from the closed state to the open state for the period of time. The actuator 6 therefore will repeatedly remove the elastomer seal 4 from contact with the valve seat 5, with the spring bringing the valve 2 and the elastomer seal 4 back into contact with the valve seat 5, thereby increasing the temperature of the elastomer seal 4. This will reduce the additional friction forces experienced at the elastomer seal 4 to ensure control of valve movement is improved.

[0054] During this period of buzzing, the injector 1 may be kept substantially empty of fuel in order to reduce the fuel pressure forces acting on the valve 2 in the second direction (i.e. fuel pressure forces holding the valve 2 in the closed state), and to prevent accidental injection of fuel into the associated combustion chamber. This may be referred to as the injector 1 being at zero pressure.

[0055] This buzzing strategy may advantageously be applied in cold conditions, e.g. at low fuel temperatures, during which the additional friction forces from the elastomer seal 4 are increased.

[0056] However, because the actuator 6 is turned on and off rapidly, and further because the injector 1 may be at zero pressure for this period, an injection event cannot occur during this buzzing period. This buzzing strategy therefore increases the amount of waiting time needed for the engine to start.

[0057] Secondly, a current and / or pulse duration may be applied to the actuator 6 at a level larger than required to move the valve 2 from a closed state to an open state under normal operating conditions of the injector 1 . This may be referred to as a “boost”, or applying the initial portion of the drive signal 11 .2 to the actuator 6 at a “boost current” and / or for a “boost duration”. Normal operating conditions refer to conditions present once the injector 1 is properly operating, e.g. once the sticking and the additional friction forces from the elastomer seal 4 have been overcome, or once the injector has been operating for a period of time.

[0058] The boost strategy may be applied as part of an injection event, i.e. while fuel is being supplied to the injector. Thus, the boost strategy may be applied to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection.

[0059] This boost strategy provides additional forces to the actuator 6 to help overcome a force of the spring, fuel pressure, and additional friction forces. This boost strategy may also advantageously be applied in cold conditions, e.g. at low fuel temperatures, during which the additional friction forces from the elastomer seal 4 are increased.

[0060] However, this boost strategy increases a speed of movement of the valve 2 of the injector 1 and consequently increases an impact force of the valve 2 against the endstop 3. This increased impact force has adverse durability effects, and can increase a risk of injector 1 damage and / or failure over time.

[0061] The increased speed may also affect the control timings of the injector 1 and can result in erroneously releasing too much fuel in a single injection event.

[0062] The “buzzing” strategy and the “boost” strategy may both be applied in sequence.

[0063] Through testing, the inventors have found that there is a strong positive correlation between an amount of time that the engine has spent turned off before turning on again and the above described additional sticking and associated additional friction forces.

[0064] The amount of time that the engine has spent turned off before turning on again, or more specifically, a time interval between a most recent power-off time of the engine and a subsequent power-on time of the engine, may be referred to as the “soak time”. Both of the above discussed strategies are independent of the soak time, and can only provide one peak current and / or duration per fuel temperature value. The current and duration of the drive signal 11 .2 required for the above strategies result in the above discussed adverse effects. However, by taking soak time into account, a peak current and a duration of the drive signal 11.2 required for the above strategies can be reduced at all-but the highest soak times, as will be described with reference to Figures 3-5.

[0065] Figure 3 illustrates the steps of the method 300 which may be implemented to control the injector 1 for the engine as described herein. The method may be performed by the control unit 11 described with respect to Figure 2.

[0066] The method 300 comprises, at step 302, determining the soak time, wherein the soak time is a time interval between a most recent power-off time of the engine and a subsequent power-on time of the engine.

[0067] The power-on time and the power-off time for the engine are the times at which a power-on or a power-off request for the engine are generated, i.e. a request for the engine to start or stop delivering power and / or utilizing the injector 1 . A power-on time of the engine is therefore a time at which the engine starts utilizing the injector 1 , i.e. a time at which the engine starts delivering power. A power-off time of the engine is therefore a time at which the engine stops utilizing the injector 1 , i.e. a time at which the engine stops delivering power.

[0068] The power-on or power-off request may be generated by an engine system 10 in response to a user of the engine system 10 turning the ignition key to the ‘engine’ on or off position, respectively, or by pressing an ‘engine stop / start’ button on a screen interface or physical button, for example. This is often referred to as ‘key on / off’. The engine control unit 11 receives the key on / off signal in the data input 11.1 , at the power-on / off time. The power-on may be initiated by a user demand, for example key on, or may be initiated by the low power counter 15 ‘waking up’ the control unit 11 after a pre-determined time period following power off.

[0069] Therefore, it is not required that other features of the engine have stopped / started for this to be considered a power-off / on time, for example the control unit 11 may remain running for a period after the engine has stopped delivering power, or for example the control unit 11 may be run for a period during the soak time, without the engine delivering power, and therefore without affecting the most recent power-off time or the subsequent power-on time of the engine.

[0070] In addition, although at power-off of the engine the control unit 11 is placed into a sleep mode, the low power counter module 15 is able to work through a permanent power supply line from a vehicle battery or an electricity source within the vehicle to determine the time interval until the subsequent power-on time.

[0071] The low power counter module 15 decrements a counter by 1 every second after power off until the engine is powered on by the subsequent power-on event, for example by the key-on, at the subsequent power-on time. In this way the low power counter 15 determines the time interval between the power-off time and the subsequent power-on time. The power-off time may be a most recent power-off time.

[0072] Determining the soak time may therefore comprise the exemplary sub-steps of decrementing, by the lower power counter module 15 of the control unit 11 of the engine, the counter by 1 every second after the most recent power-off time until the subsequent power-on time, and determining the time interval between the power-off time and the power-on time based on the counter.

[0073] At power-off, a time and date stamp, representing the power-off time, may be received by any suitable means, for example from a Real Time Clock module of the vehicle or power plant system. The time and date stamp may be stored in the NVM 13 of the control unit 11 of the engine, such that it will be retained while the engine is powered off.

[0074] At the subsequent power-on time, the time and date stamp may be retrieved from the NVM 13 and compared to a second time and date stamp, representing the subsequent power-on time. Thus, the time interval between the power-off time and the power-on time may be determined based on the time and date stamp.

[0075] Determining the soak time may therefore comprise the exemplary sub-steps of determining the time and date stamp at the most recent power-off time, storing the time and date stamp in the NVM 13 of the control unit 11 of the engine, retrieving, at the subsequent power-on time, the time and date stamp from the NVM 13, and determining the time interval between the power-off time and the power-on time based on the time and date stamp.

[0076] In either case, at the subsequent power-on time, a valid check may be made of the count on the low power counter 15 and / or a valid check may be made on the NVM 13. The valid checks determine, for example, whether there has been a power cut to the low power counter 15 as a result of a battery disconnection, and / or whether there is a data corruption in the NVM 13 caused by an interrupted data saving process.

[0077] At step 304, the method 300 comprises determining a peak current and / or a duration for the initial portion of the drive signal 11.2 for the actuator 6 as a function of the determined soak time.

[0078] Graphs 400, 450 that illustrate example relationships between the soak time and the peak current and / or duration of the initial portion of the drive signal 11.2 are shown in Figures 4a and 4b.

[0079] Figure 4a is a graph 400 illustrating an example relationship between the soak time and the duration of the initial portion of the drive signal 11.2 according to the “buzzing” strategy to “unjam” the valve 2 of the injector 1 (i.e. applying the drive signal 11.2 to the actuator 6 at a current level that alternates between the peak current and low or no current such that the actuator 6 moves the valve repeatedly from the closed state to the open state for a majority of the duration).

[0080] The graph 400 has three axes - soak time in hours, fuel temperature in degrees Celsius, and “unjam” duration (i.e. the duration for the initial portion of the drive signal 11.2) in seconds. The soak time is determined as described in the previous method step. The fuel temperature may be determined as discussed above with reference to the control unit 11 discussed with reference to Figure 2.

[0081] Therefore, in this example, the duration for the initial portion of the drive signal 11 .2 is determined as a function of the determined soak time by taking the value of the unjam duration at the determined soak time and at the determined fuel temperature as illustrated in the graph 400. In this example, the duration for the initial portion of the drive signal 11.2 may positively correlate with a number of times that the actuator 6 moves the valve from the closed state to the open state. It will also be appreciated that the duration for the initial portion of the drive signal 11 .2 may be determined as a function of the determined soak time by taking the value of the unjam duration at the determined soak time at the lowest fuel temperature as illustrated in the graph 400 to ensure that the relevant forces are overcome, but without needing to know the fuel temperature.

[0082] It can be seen from the graph 400 that the unjam duration generally increases, from a baseline duration, with decreasing fuel temperature, and generally increases, from the baseline duration, with increasing soak time. That is, the soak time and the duration have a positive correlation, and the temperature and the duration have a negative correlation. In this graph, the baseline duration is 0.5 seconds, however it will be understood that other baseline durations will be envisaged.

[0083] It can also be seen from the graph 400 that a maximum duration is shown, as a function of fuel temperature, at the highest soak time. In this case, the maximum duration is 5 seconds and the highest soak time is 20 hours, however it will be understood that other maximum durations will be envisaged, and higher soak times may be recorded.

[0084] Using the “buzzing” strategy without accounting for soak time would require always using this maximum duration as a function of fuel temperature to ensure that the fuel injector 1 operates correctly. Advantageously, by taking soak time into account, the duration can be reduced at shorter soak times. This mitigates the problems of the known “buzzing” strategy described above.

[0085] Figure 4b is a graph 450 illustrating another example relationship between the soak time and the duration of the initial portion of the drive signal 11.2 according to the “boost” strategy to overcome forces acting against the valve 2 of the injector 1 (i.e. applying the initial portion of the drive signal 11 .2 to the actuator 6 at the peak current for a majority of the duration, wherein the peak current and / or the duration are larger than those required to move the valve 2 from a closed state to an open state under normal operating conditions of the injector 1).

[0086] The graph 450 has two axes - soak time in hours and fuel temperature in degrees Celsius. The soak time is determined as described in the previous method step. The fuel temperature may be determined as discussed above with reference to the control unit 11 discussed with reference to Figure 2.

[0087] In the graph 450, a contour is given with values between 0 and 100 (with 10 to 90 labelled and 0 and 100 implicit). The contour represents a percentage value, wherein 100% represents a maximum combination of the peak current and duration of the initial portion of the drive signal 11.2 achievable by the actuator 6. However, it will be appreciated that the percentage value may relate to a peak current or a duration individually, such that 100% may represent a maximum peak current for the initial portion of the drive signal 11.2 achievable by the actuator 6 or a maximum duration of the initial portion of the drive signal 11.2 achievable by the actuator 6.

[0088] The maximum combination may be determined as an area under a current vs time graph of the initial portion of the drive signal 11 .2 when applied at the maximum peak current achievable by the actuator 6 for the maximum duration achievable by the actuator 6. These percentage values may therefore be referred to respectively as either a combined “boost demand”, a “boost peak current” or a “boost duration”. A drive signal that would be applied under normal operating conditions may be thought of as having a percentage value of 0.

[0089] It is noted that the maximum duration for the initial portion of the drive signal 11.2 is a maximum duration for which the initial portion of the drive signal 11.2 can be applied to the actuator 6 without encountering problems. The initial portion of the drive signal 11.2 is applied at a peak current larger than required to move the valve 2 from the closed state to the open state under normal operating conditions of the injector 1 . It is not a maximum duration for which any drive signal 11.2 can be applied to the actuator 6. For example, under normal operating conditions of the injector 1 , a portion of the drive signal 11.2, for example a further portion of the drive signal 11.2, with a lower peak current may be applied to the actuator 6 for a duration longer than the maximum duration for the initial portion of the drive signal 11 .2.

[0090] Therefore, in this example, the peak current and / or the duration for the initial portion of the drive signal 11.2 is determined as a function of the determined soak time by taking the value of the boost demand at the determined soak time and at the determined fuel temperature as illustrated in the graph 450. It will also be appreciated that the peak current and / or the duration for the initial portion of the drive signal 11.2 may be determined as a function of the determined soak time by taking the value of the boost demand at the determined soak time at the lowest fuel temperature as illustrated in the graph 450 (or the highest required boost demand for any given soak time as illustrated in the graph 450, regardless of temperature) to ensure that the relevant forces are overcome by the valve 2, but without needing to know the fuel temperature.

[0091] It can be seen from the graph 450 that the boost demand generally increases with decreasing fuel temperature, and generally increases with increasing soak time. That is, the soak time and the peak current and / or duration have a positive correlation, and the fuel temperature and the peak current and / or duration have a negative correlation.

[0092] It can also be seen from the graph 450 that a highest required boost demand is shown, as a function of fuel temperature, at the highest soak time. In this case, the highest soak time is 100 hours, however it will be understood that higher soak times may be recorded.

[0093] Using the “boost” strategy without accounting for soak time would require always using this highest required boost demand as a function of fuel temperature to ensure that the fuel injector 1 operates correctly. Advantageously, by taking soak time into account, the boost demand, and thus the peak current and / or the duration of the initial portion of the drive signal 11 .2 can be reduced at shorter soak times. This mitigates the problems of the “boost” strategy described above.

[0094] Returning to the method 300, at step 304, determining the peak current and / or the duration for the initial portion of the drive signal 11.2 as a function of the determined soak time may therefore comprise the exemplary sub-step of increasing one or more of the peak current and the duration from a respective one or more of a baseline current and a baseline duration as a function of increasing soak time.

[0095] Furthermore, at step 304, determining the peak current and / or the duration for the initial portion of the drive signal 11.2 as a function of the determined soak time may therefore comprise the exemplary sub-step of increasing one or more of the peak current and the duration as a function of increasing soak time up to a respective one or more of a maximum peak current and a maximum duration.

[0096] It will be appreciated that the step 304 may comprise determining the maximum peak current and / or the maximum duration to be a respective one or more of a maximum peak current achievable by the actuator 6 and a maximum duration achievable by the actuator 6.

[0097] It will also be appreciated that the step 304 may comprise may comprise the exemplary sub-step of determining the maximum peak current and / or the maximum duration as a function of only a temperature of the gaseous fuel.

[0098] As discussed with reference to Figures 4a and 4b, but generally applicable to the method 300, the method 300 may comprise determining the peak current and / or the duration for the initial portion of the drive signal 11.2 as a function of the determined soak time and a temperature of the gaseous fuel.

[0099] At step 306, the method 300 comprises applying the initial portion of the drive signal 11.2 to the actuator 6, using the peak current and / or for the duration, to move the valve 2 from a closed state to an open state.

[0100] Figures 5a and 5b are graphs 500, 550 illustrating examples of portions of the drive signal 11.2 which is applied to the actuator 6 to move the valve 2 from the closed state to the open state. In both Figure 5a and Figure 5b, the drive signal 11.2 is denoted as Line A, and shows changes to a current (in Amps) over time (in milliseconds in Figure 5a, and in micro seconds in Figure 5b). Firstly, an initial portion of the drive signal 11.2 is applied to the actuator 6 at time T 1 and the valve 2 of the injector 1 starts to lift away from the valve seat 5. A peak current A1 can be seen in each of the graphs 500, 550. The valve 2 reaches the fully open state and hits the end-stop 3 of the injector 1. This equates to the furthest extent of the movement of the valve 2 in the first direction. The initial portion of the drive signal 11.2 ends at time T2. The initial portion of the drive signal 11.2 is defined between times T1 and T2. Thus the duration of the initial portion of the drive signal is T2-T 1.

[0101] In the graph 500 shown in Figure 5a, the initial portion of the drive signal 11.2 is shown according to the “buzzing” or “unjam” strategy described herein. It can be seen from the graph 500 that the initial portion of the drive signal 11.2 is applied at a current level that alternates between the peak current and a low or no current. The graph 500 also shows a valve lift, denoted as Line B, where 1 is the fully open state, and 0 is the closed state.

[0102] Therefore, as can seen by the changes in the valve lift in the graph 500, the initial portion of the drive signal 11 .2 is applied at a current level that alternates between the peak current and a low or no current such that the actuator 6 moves the valve 2 repeatedly from the closed state to the open state for a majority of the duration T2- T1. That is to say, the initial portion of the drive signal 11.2 is applied such that the actuator 6 moves the valve 2 from the closed state to the open state, then (while the drive signal is at low or no current) the spring moves the valve 2 in the second direction, from the open state to the closed state. Then, this process repeats for the duration T2-T1 of the initial portion of the drive signal 11.2.

[0103] In the graph 550 shown in Figure 5b, the initial portion of the drive signal 11.2 is shown according to the “boost” strategy described herein. It can be seen from the graph 550 that the drive signal 11.2 is applied at the peak current A1 for a majority of the duration T2-T1 .

[0104] Furthermore, graph 550 also shows an example drive signal that would be applied under normal operating conditions, denoted as Line B. Line B is labelled as 0% boost in the graph 550. It can therefore also be seen from Figure 5b that the peak current comprises a boost peak current and the duration comprises a boost duration, i.e. the peak current and the duration of the initial portion of the drive signal 11.2 are at a level larger than required to move the valve 2 from the closed state to the open state under normal operating conditions of the injector 1. In fact, as labelled in the graph 550, the drive signal 11.2 in this example is at 100% boost, i.e. at the maximum combination of the peak current and duration of the initial portion of the drive signal 11 .2 achievable by the actuator 6 as described with respect to Figure 4b.

[0105] In the graph 550 of Figure 5b, following the initial portion of the drive signal 11.2, a further portion of the drive signal 11.2 may be applied to the actuator 6. The further portion of the drive signal 11 .2 is applied at a reduced current as compared to the peak current, the reduced current being configured to hold the valve 2 against the end-stop 3, during which time the injector 1 may inject fuel into the associated engine combustion chamber. After a predefined injection period, during which a required quantity of fuel may be injected, the drive signal 11.2 is removed at time T3 (referred to as the closing drive signal 11 .2), to end injection. At this point, the valve 2 is moved back to the closed position. The further portion of the drive signal 11.2 is defined between times T2 and T3. It will therefore be appreciated that the method 300 may comprise an exemplary sub-step of applying a further portion of the drive signal 11.2 to the actuator 6 to hold the injector 1 in the open state.

[0106] It will be appreciated that the buzzing strategy may be used as described herein and then the boost strategy also used as described herein. In these circumstances, the boost portion of the drive signal 11 .2 may be denoted as a secondary portion of the drive signal 11.2, applied subsequently to the initial portion of the drive signal 11 .2. In these circumstances, the method may comprise determining a second peak current and / or a second duration for the secondary portion of the drive signal 11.2 for the actuator 6 as a function of the determined soak time, wherein the second peak current comprises a boost peak current and / or the second duration comprises a boost duration. Advantageously, both strategies may be applied together in cold conditions, when there is an increased likelihood of increased forces acting against the valve 2.

[0107] Other events may happen between the initial portion of the drive signal 11.2 being applied and the secondary portion of the drive signal 11.2 being applied, for example, the engine may start cranking, and / or may enable gas pressure to the injector 1. There may be a time delay between the initial portion of the drive signal 11.2 being applied and the secondary portion of the drive signal 11.2 being applied.

[0108] As discussed previously with reference to the “buzzing” strategy and with reference to Figures 4a and 5a, but generally applicable to the method 300, it will be appreciated that the step 306 may comprise the exemplary sub-step of applying the initial portion of the drive signal 11 .2 to the actuator 6 at a current level that alternates between the peak current and a low or no current such that the actuator 6 moves the valve repeatedly from the closed state to the open state for a majority of the duration.

[0109] As discussed with reference to Figures 4a and 5a, but generally applicable to the method 300, it will be further appreciated that the step 306 may comprise the exemplary sub-step of applying a secondary portion of the drive signal 11.2 to the actuator 6, subsequent to the initial portion, to move the valve 2 from the closed state to the open state in accordance with a predetermined injector 1 opening time for injection (of fuel).

[0110] As discussed with reference to Figures 4a and 5a, but generally applicable to the method 300, it will be further appreciated that the step 306 may comprise the exemplary sub-step of determining a second peak current and / or a second duration for the secondary portion of the drive signal for the actuator 6 as a function of the determined soak time wherein the second peak current comprises a boost peak current and / or the second duration comprises a boost duration.

[0111] As discussed with reference to Figures 4a and 5a, but generally applicable to the method 300, it will be further appreciated that the step 306 may comprise the exemplary sub-step of applying the initial portion of the drive signal to the actuator 6 while no fuel is present in the valve.

[0112] As discussed previously with reference to the “boost” strategy and with reference to Figures 4b and 5b, but generally applicable to the method 300, it will be appreciated that the step 306 may comprise the exemplary sub-step of applying the initial portion of the drive signal 11.2 to the actuator 6 at the peak current A1 for a majority of the duration, wherein the peak current A1 comprises a boost peak current and / or the duration comprises a boost duration.

[0113] As discussed previously with reference to Figures 4b and 5b, but generally applicable to the method 300, it will be appreciated that the step 306 may comprise the exemplary sub-step of applying the initial portion of the drive signal to the actuator 6 to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection.

[0114] It will be appreciated that the step 306 may comprise the exemplary sub-step of applying one or more of the initial, secondary, and further portions of the drive signal to an electromagnetic actuator 6.

[0115] It will be appreciated that other variants of the invention are envisaged without departing from the scope of the invention as set out in the accompanying claims.

Claims

Claims1. A method (300) for controlling an injector (1) for an engine, the injector comprising an actuator (6) and a valve (2) which is engageable with a valve seat (5) of the injector, the valve comprising an elastomer seal (4) disposed at an end of the valve proximal to the valve seat, the actuator being configured to receive a drive signal (11.2) to move the valve towards and away from the valve seat to control injection of gaseous fuel into an associated engine combustion chamber, the method comprising: determining (302) a soak time, wherein the soak time is a time interval between a most recent power-off time of the engine and a subsequent power-on time of the engine; determining (304) a peak current (A1) and / or a duration (T2-T1) for an initial portion of the drive signal for the actuator as a function of the determined soak time; and applying (306) the initial portion of the drive signal to the actuator, using the peak current and / or for the duration, to move the valve from a closed state to an open state.

2. A method according to claim 1 , comprising applying the initial portion of the drive signal to the actuator at a current level that alternates between the peak current and a low or no current such that the actuator moves the valve repeatedly from the closed state to the open state for a majority of the duration.

3. A method according to claim 2, comprising applying a secondary portion of the drive signal to the actuator, subsequent to the initial portion, to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection.

4. A method according to claim 3, comprising determining a second peak current and / or a second duration for the secondary portion of the drive signal for the actuator as a function of the determined soak time wherein the second peak current comprises a boost peak current and / or the second duration comprises a boost duration.

5. A method according to any preceding claim, comprising applying the initial portion of the drive signal to the actuator while no fuel is present in the valve.

6. A method according to claim 1 , comprising applying the initial portion of the drive signal to the actuator at the peak current for a majority of the duration, wherein the peak current comprises a boost peak current and / or the duration comprises a boost duration.

7. A method according to claim 6, comprising applying the initial portion of the drive signal to the actuator to move the valve from the closed state to the open state in accordance with a predetermined injector opening time for injection.

8. A method according to any preceding claim, wherein determining the peak current and / or the duration for the initial portion of the drive signal as a function of the determined soak time comprises increasing one or more of the peak current and the duration from a respective one or more of a baseline current and a baseline duration as a function of increasing determined soak time.

9. A method according to any preceding claim, wherein determining the peak current and / or the duration of the initial portion of the drive signal as a function of the determined soak time comprises increasing one or more of the peak current and the duration as a function of increasing determined soak time up to a respective one or more of a maximum peak current and a maximum duration.

10. A method according to claim 9, comprising determining the maximum peak current and / or the maximum duration as a function of a temperature of the gaseous fuel.

11. A method according to claim 9, comprising determining the maximum peak current and / or the maximum duration to be a respective one or more of a maximum peak current for the initial portion of the drive signal achievable by the actuator and a maximum duration for the initial portion of the drive signal achievable by the actuator.

12. A method according to any preceding claim, comprising determining the peak current and / or the duration for the initial portion of the drive signal as a function of the determined soak time and a temperature of the gaseous fuel.

13. A method according to any preceding claim, wherein determining the soak time comprises: decrementing, by a lower power counter module (15) of a control unit (11) of the engine, a counter by 1 every second after the most recent power-off time until the subsequent power-on time; and determining the time interval between the power-off time and the power-on time based on the counter.

14. A method according to any of claims 1 to 12, wherein determining the soak time comprises: determining a time and date stamp at the most recent power-off time; storing the time and date stamp in a non-volatile memory (13) of a control unit (11) of the engine; retrieving, at the subsequent power-on time, the time and date stamp from the non-volatile memory; and determining the time interval between the power-off time and the power-on time based on the time and date stamp.

15. A method according to any preceding claim, comprising applying a further portion of the drive signal to the actuator to hold the valve in the open state.

16. A method according to any preceding claim, comprising applying one or more of the initial, secondary, and further portions of the drive signal to an electromagnetic actuator.

17. A method according to any preceding claim, wherein when fuel is supplied to the injector, the open state of the valve is an injecting state of the injector, in which the injector is capable of delivering the fuel to the associated cylinder of an engine.

18. A method according to any preceding claim, wherein the open state comprises a fully open state, wherein the actuator is opened to a full extent possible within the injector.

19. A control unit (11) for an injector (1) for an engine, the injector comprising an actuator (6) and a valve (2) which is engageable with a valve seat (5), the valve comprising an elastomer seal (4) disposed at an end of the valve proximal to the valve seat, the actuator being configured to receive a drive signal (11.2) to move the valve towards and away from the valve seat to control injection of gaseous fuel into an associated engine combustion chamber, the control unit configured to execute machine readable instructions to perform a method (300) according to any preceding claim.

20. A control unit according to claim 19, the control unit taking the form of an engine control unit of the engine.

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