A controller

Abstract

A controller for a hydrogen fuel internal combustion engine, the engine comprising a cylinder, an intake system configured to supply hydrogen fuel and air to the cylinder for combustion, and an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder, wherein the controller is configured to: control one or more intake system parameters to set an air-fuel ratio in a standard operation mode; selectively enter a calibration mode to control one or more intake system parameters to set an air-fuel ratio closer to stoichiometric than the standard operation mode; and in the calibration mode, determine a difference between an expected air-fuel ratio based on the one or more intake system parameters and an actual air-fuel ratio based on a signal from the oxygen sensor arrangement.

Description

[0001] A CONTROLLER

[0002] FIELD

[0003] The present teachings relate to a controller for a hydrogen fuel internal combustion engine, a control system for a hydrogen fuel internal combustion engine, a hydrogen fuel internal combustion engine, a working machine, and a method for calibrating a hydrogen fuel internal combustion engine.

[0004] BACKGROUND

[0005] An internal combustion engine typically includes an intake system for supplying fuel and air to each cylinder of the engine for combustion. For example, the intake system may include one or more fuel injectors for supplying fuel to each cylinder. It is common for parts of such intake systems (e.g. the fuel injectors) to wear over the lifetime of the engine resulting in the air-fuel ratio for a given set of input parameters, to vary (e.g. the amount of fuel delivered by an injector for a given injection period). Such inadvertent changes to the air-fuel ratio of the engine may lead to reduced engine performance and / or increased harmful engine emissions.

[0006] To address this problem, engine control systems for gasoline and diesel fuelled internal combustion engines are known, which determine the actual air-fuel ratio of the engine using an air-fuel ratio sensor, such as a lambda sensor which measures the residual oxygen in the exhaust flow of combustion gas from the cylinders, and which then calibrate the engine to correct any error between the target and actual air-fuel ratios. This usually only occurs when one or more parameters of the engine, such as engine temperature and / or engine run time, are above predetermined minimum values that reflect the engine being at normal operating conditions. Such sensors have been found to be generally effective when the actual air-fuel ratio of the engine is close to stoichiometric.

[0007] The present applicant has however determined that this approach is not effective in internal combustion engines which utilise hydrogen as fuel.

[0008] SUMMARY

[0009] The present teachings seek to overcome or at least mitigate one or more problems associated with the prior art.

[0010] The present teachings provide a controller for a hydrogen fuel internal combustion engine, a control system for a hydrogen fuel internal combustion engine, a hydrogen fuel internal combustion engine, a working machine and a method according to the appended claims. A first aspect of the teachings provides a controller for a hydrogen fuel internal combustion engine. The engine may comprise a cylinder. The engine may comprise an intake system configured to supply hydrogen fuel and air to the cylinder for combustion. The engine may comprise an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder. The controller may be configured to control one or more intake system parameters to set an air-fuel ratio in a standard operation mode. The controller may be configured to selectively enter a calibration mode to control one or more intake system parameters to set an air-fuel ratio closer to stoichiometric than the standard operation mode. The controller may be configured to, in the calibration mode, determine a difference between an expected air-fuel ratio based on the one or more intake system parameters and an actual air-fuel ratio based on a signal from the oxygen sensor arrangement.

[0011] Advantageously, it has been found that in the calibration mode, a more accurate difference between the expected and actual air-fuel ratios may be determined since the air-fuel ratio is set to be closer to stoichiometric relative to the standard operation mode. This enables a more accurate air-fuel ratio during standard operation of the engine to be achieved via calibration of the intake system parameters, with resultant potential benefits in emissions and reduced risk of premature combustion ("knock").

[0012] The controller may be further configured to calculate a correction to the one or more intake system parameters based on the determined difference, so as to reduce the difference between the actual air-fuel ratio and expected air-fuel ratio.

[0013] Advantageously, calculating such a correction enables a more accurate air-fuel ratio during standard operation of the engine to be achieved, with resultant potential benefits in emissions and reduced risk of premature combustion ("knock").

[0014] The calculated correction may be such that the actual air-fuel ratio substantially corresponds to the expected air-fuel ratio.

[0015] Advantageously, calculating such a correction enables a more accurate air-fuel ratio during standard operation of the engine to be achieved, with resultant potential benefits in emissions and reduced risk of premature combustion ("knock").

[0016] The controller may be configured to apply the calculated correction to the one or more intake system parameters in the standard operation mode.

[0017] The signal from the oxygen sensor arrangement may correspond to an oxygen concentration in the combustion gas. The controller may be configured to determine the actual air-fuel ratio based on a plurality of measurements taken by the oxygen sensor arrangement.

[0018] Advantageously, this may enable a more accurate actual air-fuel ratio to be determined.

[0019] The plurality of measurements may be taken over a measurement interval in the range of 5 to 20 seconds, for example 10 to 15 seconds.

[0020] Advantageously, this may enable a more accurate actual air-fuel ratio to be determined.

[0021] In the calibration mode, the controller may be configured to determine an air-fuel equivalence ratio of the actual air-fuel ratio to the stoichiometric ratio based on the signal from the oxygen sensor arrangement. The controller may be configured to determine the difference between the expected air-fuel ratio and the actual air-fuel ratio based on the determined air-fuel equivalence ratio.

[0022] Advantageously, such a configuration of the controller may enable the difference to be determined via present engine sensors, simplifying implementation of the controller.

[0023] The controller may be configured to only enter the calibration mode when a rotational speed of the engine is within a predetermined speed range.

[0024] Advantageously, this has been found to enable a more accurate difference between the expected and actual air-fuel ratios to be determined.

[0025] The predetermined speed range may be idle to 2000 RPM.

[0026] The predetermined speed range may be 830 to 1150 RPM.

[0027] The predetermined speed range may be 1450 to 1550 RPM.

[0028] The predetermined speed range may be 1750 to 1850 RPM.

[0029] The controller may be configured to only enter the calibration mode when a rotational speed of the engine is maintained substantially constant throughout a predetermined monitoring period.

[0030] Advantageously, this has been found to enable a more accurate difference between the expected and actual air-fuel ratios to be determined.

[0031] The controller may be configured to only enter the calibration mode when a torque of the engine is within a predetermined range, for example 0 to 45% of maximum torque output. Advantageously, this has been found to enable a more accurate difference between the expected and actual air-fuel ratios to be determined.

[0032] An air-fuel equivalence ratio of the air-fuel ratio in the standard operation mode to the stoichiometric ratio may be in the range of 2.5 to 3.0.

[0033] Advantageously, such an air-fuel equivalence ratio has been found to reduce NOx emissions of the engine.

[0034] An air-fuel equivalence ratio of the air-fuel ratio in the calibration mode to the stoichiometric ratio may be greater than or equal to 1.5.

[0035] It has been found that air-fuel equivalence ratio ratios below 1.5 results in increased engine knock. As such, implementing an air-fuel equivalence ratio greater than or equal to 1.5 enables a more accurate difference between the expected and actual air-fuel ratios may be determined whilst helping to reduce engine knock.

[0036] The air-fuel equivalence ratio in the calibration mode may be in the range of 1.5 to 2.0.

[0037] A second aspect of the teachings provides a control system for a hydrogen fuel internal combustion engine, comprising the controller of the first aspect.

[0038] The engine may comprise a cylinder. The engine may comprise an intake system configured to supply hydrogen fuel and air to the cylinder for combustion. The control system may comprise an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder. The determined difference may be based on a signal from the oxygen sensor arrangement.

[0039] The oxygen sensor arrangement may comprise a lambda sensor.

[0040] The lambda sensor may be a wide range air fuel (WRAF) sensor.

[0041] A third aspect of the teachings provides a hydrogen fuel internal combustion engine comprising the control system of the second aspect.

[0042] The engine may comprise a cylinder. The engine may comprise an intake system configured to supply hydrogen fuel and air to the cylinder for combustion.

[0043] The engine may further comprise an intake port configured to supply air to the cylinder for combustion. The intake system may be configured to supply hydrogen fuel to the cylinder via the intake port. The intake system may be configured to supply hydrogen fuel to the cylinder via direct fuel injection into the cylinder.

[0044] The intake system may be configured to supply hydrogen fuel to a plurality of cylinders of the engine. The oxygen sensor arrangement may be in the flow path of combustion gas exhausted from the plurality of cylinders.

[0045] A fourth aspect of the teachings provides a working machine or genset comprising the hydrogen fuel internal combustion engine of the third aspect.

[0046] A fifth aspect of the teachings provides a method for calibrating a hydrogen fuel internal combustion engine. The engine may comprise a cylinder. The engine may comprise an intake system configured to supply hydrogen fuel and air to the cylinder for combustion. The engine may comprise an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder. The method may comprise controlling one or more intake system parameters to set an air-fuel ratio in a standard operation mode. The method may comprise selectively entering a calibration mode to control one or more intake system parameters to set an air-fuel ratio closer to stoichiometric than the standard operation mode. The method may comprise, in the calibration mode, determining a difference between an expected air-fuel ratio based on the one or more intake system parameters and an actual air-fuel ratio based on a signal from the oxygen sensor arrangement.

[0047] The method may comprise calculating a correction to the one or more intake system parameters based on the determined difference, so as to reduce the difference between the actual air-fuel ratio and expected air-fuel ratio.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments are now disclosed by way of example only with reference to the drawings, in which:

[0050] Figure 1 is a plan view of an internal combustion engine according to an embodiment;

[0051] Figure 2 is a cross-sectional view along section X-X shown in Figure 1;

[0052] Figure 3 is a side view of a working machine including the internal combustion engine of Figure 1 according to an embodiment;

[0053] Figure 4 is a block diagram of a control system of the internal combustion engine of Figure 1 according to an embodiment; and

[0054] Figure 5 is a flow chart of a method performed by the control system of Figure 4 according to an embodiment. DETAILED DESCRIPTION OF EMBODIMENT(S)

[0055] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments and the teachings. However, those skilled in the art will understand that: the present teachings may be practiced without these specific details or with known equivalents of these specific details; that the present teachings are not limited to the described embodiments; and, that the present teachings may be practiced in a variety of alternative embodiments. It will also be appreciated that well known methods, procedures, components, and systems may not have been described in detail.

[0056] Figures 1 and 2 show an internal combustion engine 1 according to an embodiment. Figure 1 shows a plan view of the engine 1, and Figure 2 shows a cross-sectional view of the engine 1 along section X-X shown in Figure 1.

[0057] The engine 1 is a gaseous fuel engine configured to be powered by hydrogen fuel.

[0058] The engine 1 may be suitable for use as the prime mover in a working machine 200 (see Figure 3 which depicts a backhoe loader, but may also be a telescopic handler, a forklift truck, a wheeled loading shovel, a dumper, an excavator or a tractor, for example). Such working machines are suitable for use in off-highway industries such as agriculture and construction. In these industries they are generally configured to perform tasks such as excavation, load handling, harvesting or planting crops. The engine may also be utilised in a genset - a self-contained unit to provide electrical power at off-grid locations. As such the engine 1 is typically required to have certain characteristics such as a high torque output over a wide engine speed band, with peak torque occurring at a relatively low engine speed, which differ from light passenger vehicles, for example. In off-highway applications, this provides "torque backup" that enables working machines to continue to carry out working operations when encountering increased loads, or resistance to a working operation - e.g. an excavator encountering a particularly solid piece of earth to be excavated.

[0059] In this embodiment, the engine 1 has four cylinder assemblies indicated generally at 19. As configured, the engine has a maximum power output of around 55kW, although it will be appreciated that the present teachings are applicable to engines with a wide range of power outputs.

[0060] Each cylinder assembly 19 includes a cylinder 15 including two inlets 6 (only one of which is shown in Figure 2) and two outlets 9 (only one of which is shown in Figure 2), a piston 20 translationally movable within the cylinder 15, an intake runner 16 leading to the two inlets 6, and an exhaust runner 33 leading away from the two outlets 9. Each inlet 6 is selectively opened and closed by an intake valve 7i, such that there are two intake valves 7i. Each outlet 9 is selectively opened and closed by an exhaust valve 7e such that there are two exhaust valves 7e.

[0061] Each cylinder assembly 19 includes an intake port 4. A downstream end of each intake port 4 leads to the corresponding inlets 6 of the cylinder assembly 19. Each intake runner 16 leads to the corresponding intake port 4 of the cylinder assembly 19.

[0062] Each cylinder assembly 19 includes an exhaust port 5. An upstream end of each exhaust port 5 leads away from the corresponding outlets 9 of the cylinder assembly 19. Each exhaust port 5 leads to the exhaust runner 33.

[0063] The engine 1 includes a cylinder block 2, a cylinder head 3, an intake system 10 and an exhaust system 40. The cylinder head 3 is mounted to the cylinder block 2. The intake system 10 is mounted to the cylinder head 3. The cylinder block 2 includes the cylinders 5. The cylinder head 3 includes the intake port 4 and at least a portion of the intake runner 16 of each cylinder assembly 19.

[0064] The intake system 10 is configured to supply hydrogen fuel and air to the cylinders 15 for combustion.

[0065] The intake system 10 includes a fuel supply system 21 configured to supply hydrogen fuel to each cylinder 15 for combustion. In the illustrated embodiment, the fuel supply system

[0066] 21 includes a plurality of fuel injectors 22, and a common fuel rail 52 in fluid communication with each fuel injector 22 for supplying hydrogen fuel to the fuel injectors

[0067] 22 from a pressurised fuel tank 202 (Figure 3). The rated pressure of the fuel tank 202 is typically in excess of 35MPa and the hydrogen pressure may be stepped down before being introduced into the cylinders 15.

[0068] In the illustrated embodiment, each fuel injector 22 is configured to selectively inject hydrogen fuel into the intake runner 16 of one of the cylinder assemblies 19. The intake system 10 supplies a mixture of air and fuel to the intake ports 4 of the cylinder head 3 via the intake runners 16. The air-fuel mixture is then supplied from the intake ports 4 to the corresponding cylinders 15 of the cylinder block 2 via the inlets 6. As such, the engine 1 is a port fuel injection engine (i.e. fuel is provided to the cylinders 15 via port fuel injection).

[0069] Additionally or alternatively, the fuel supply system 21 may be configured to supply hydrogen fuel to each cylinder 15 via direct fuel injection into the cylinder 15 (e.g. via a fuel injector 25 in or adjacent to the cylinder 15, illustrated schematically in broken lines in Figure 2).

[0070] The intake system 10 includes an intake manifold 11. The intake manifold 11 includes a first plenum 12, and a second plenum 14. An air supply inlet 13 is provided upstream of the intake manifold. The intake runners 16 are fluidly connected to, and extend from, the second plenum 14. In use, air supplied via the air supply inlet travels sequentially along the first plenum 12, the second plenum 14, and the intake runners 16 towards the inlets 6.

[0071] In alternative embodiments (not shown), air may be supplied to the intake runners 16 via any suitable arrangement.

[0072] The exhaust system 40 includes a downstream portion of the exhaust runner 33.

[0073] The exhaust system 40 includes an exhaust manifold 42 (represented schematically in Figure 1). The exhaust manifold 42 connects the exhaust runners 33 to an exhaust outlet 46 leading to an exhaust pipe (not shown). In use, combustion gas exhausted from the cylinders 15 travel sequentially from the outlets 9, and along the exhaust runners 33 to the exhaust manifold 42 where the gas converges and flows to the exhaust outlet 46.

[0074] As the engine 1 utilises hydrogen as a fuel, a spark is required to initiate combustion. Thus, each cylinder assembly 19 includes a spark plug 23 (illustrated schematically) mounted intermediate the intake and outlet ports 6, 9 in the cylinder head 3.

[0075] With reference to Figures 1 and 4, the engine 1 includes a control system 100 configured to control the intake system 10, and may control other parts of the engine 1. The control system 100 includes a controller 102 (e.g. a ECU), an intake mass air flow sensor arrangement 104, an oxygen sensor arrangement 108, and an engine rotational speed sensor arrangement 110. In addition, the controller 102 models a torque output of the engine 1 based on parameters such as air flow, air fuel ratio and ignition timing. The controller 102 receives input signals from these sensors 104, 108, 110 and the torque model and provides control output signals to the intake system 10 based thereon.

[0076] The controller 102 may include: control circuitry; and / or processor circuitry; and / or at least one application specific integrated circuit (ASIC); and / or at least one field programmable gate array (FPGA); and / or single or multi-processor architectures; and / or sequential / parallel architectures; and / or at least one programmable logic controllers (PLCs); and / or at least one microprocessor; and / or at least one microcontroller; and / or a central processing unit (CPU), to perform the described methods. The controller may include an associated memory or the memory may be located locally to the controller or remotely. The memory may be a non-volatile flash memory.

[0077] In the illustrated embodiment, the controller 102 is configured to determine the mass flow rate of the air supplied to the cylinders 15 for combustion (i.e. the intake mass flow rate) based on an input signal from the intake mass air flow sensor arrangement 104. The intake air flow sensor arrangement 104 may include one or more mass flow rate sensors arranged in the intake system 10 in an intake air flow path upstream of the cylinders 15, depicted in Figure 1 in mounted to the air supply inlet 13. Additionally or alternatively, the intake air flow sensor arrangement 104 may include one or more air pressure sensors in said intake air flow path (e.g. within the intake manifold 11). In such embodiments, the intake mass flow rate may be determined based on the air pressure within the intake manifold 11 and a suitable model of the intake mass flow rate. For example, such a model may be physics-based or derived via a system identification approach.

[0078] The controller 102 is configured to determine the oxygen concentration in the combustion gas exhausted from the cylinders 15 based on an input signal from the oxygen sensor arrangement 108. The oxygen sensor arrangement 108 is located in the exhaust system 40, in a flow path of combustion gas exhausted from (i.e. downstream of) the cylinders 15. In this embodiment the oxygen sensor arrangement is located on the exhaust outlet 46

[0079] In the illustrated embodiment, the oxygen sensor arrangement 108 includes a lambda sensor configured to determine the air-fuel equivalence ratio of the engine 1 based on the oxygen concentration in the exhausted combustion gas. The air-fuel equivalence ratio (A) is defined as the ratio of the engine's air-fuel ratio to the stoichiometric air-fuel ratio. In other words, the presence of oxygen in the exhausted combustion gas is indicative of a A greater than 1, with there being more oxygen the greater the A. The lambda sensor may be a wide range air fuel ratio (WRAF) sensor, or similar. The lambda sensor may be configured to output a signal, such as a voltage, which is indicative of (e.g. proportional to) the engine's air-fuel equivalence ratio. The lambda sensor may be located in the exhaust manifold 42 or the exhaust outlet 46.

[0080] In alternative embodiments (not shown), the oxygen sensor arrangement 108 may additionally or alternatively include any suitable sensor configured to send a signal to the controller 102, from which the controller 102 can determine the oxygen concentration in the exhausted combusted gas.

[0081] The controller 102 is configured to determine a rotational speed of the engine 1 (e.g. of the engine's crankshaft) based on an input signal from the engine rotational speed sensor arrangement 110.

[0082] The controller 102 is configured to determine an output torque of the engine 1 (e.g. of the engine's crankshaft) based on the model described above.

[0083] The controller 102 is configured to control one or more intake system parameters (i.e. parameters of the intake system 10) to set an air-fuel ratio of the engine 1. Such intake parameters may correspond to the quantity of fuel and / or air supplied to each cylinder 15 within each engine cycle.

[0084] One way of adjusting the fuel air ratio is to adjust the amount of fuel supplied to each cylinder 15 for a given quantity of air supplied to each cylinder 15. In the illustrated embodiment, the controller 102 is configured to control one intake system parameter corresponding to the amount of fuel supplied to each cylinder 15 within each engine cycle to set the air-fuel ratio of the engine 1.

[0085] In the illustrated embodiment, the controller 102 controls the intake system parameter based on the intake mass flow rate and a functional relationship between the intake mass flow rate and the intake system parameter, so as to set the air-fuel ratio of the engine 1. The functional relationship may take the expected air-fuel ratio (i.e. the air-fuel ratio to be set) and the intake mass flow rate as inputs, and provide a value for the intake system parameter as an output to be sent to the intake system 10 via an output control signal. The functional relationship is stored in a memory of the controller 102, and may correspond to a look-up table or map for example.

[0086] Over the lifetime of the engine 1, wear of the fuel injectors 22 leads to the injection mass flow rate of each fuel injector 22 changing from its initially determined value. It has been found that fuel injection mass flow rates of fuel injectors tend to inadvertently increase over time, leading to richer air-fuel ratios, which may result in reduced engine performance and / or increased harmful engine emissions. As such, it is desirable to calibrate the air-fuel ratio of the engine 1 to account for this.

[0087] It is impractical in production engines to directly monitor the fuel injection mass flow rates of the fuel injectors 22 via a sensor arrangement so as to ensure that the correct amount of fuel is injected within each engine cycle. Instead, for gasoline engines, it is known to use the oxygen sensor arrangement 108 (lambda sensor) to calibrate the air-fuel ratio. Typical modern port injected gasoline engines operate at or close to stoichiometric (i.e. A=l). For these air-fuel ratios, lambda sensors are highly accurate (<1% error), enabling effective air-fuel ratio calibration of the engine.

[0088] However, it has been found beneficial to operate the hydrogen fuel engine 1 at a much leaner A in the range of A=2.5 to 3.0. Such a lean air-fuel ratio is chosen to reduce NOx emissions and reduce premature combustion ("knock"). It has been found that for engines running at such lean air-fuel ratios, current lambda sensors have low accuracy (e.g. >5% error) relative to engines running at air-fuel ratios closer to stoichiometric such as gasoline engines, which prevents effective air-fuel ratio calibration of the engine 1. Such a reduction in accuracy of current lambda sensors may be due to an inherent difficulty in distinguishing between changes in oxygen concentration when the overall concentration of oxygen is higher.

[0089] To address this problem, the controller 102 is configured to perform the engine calibration method illustrated in the flowchart shown in Figure 5, which is outlined in more detail below.

[0090] In step SI of the method, in a standard operation mode, the controller 102 is configured to control the one or more intake system parameters to set a first expected air-fuel ratio (corresponding to an air-fuel equivalence ratio of Al). By "expected air-fuel ratio", it is intended to mean the air-fuel ratio the controller 102 expects to instigate via control of the one or more intake system parameters.

[0091] In the illustrated embodiment, as outlined above, the controller 102 controls the amount of fuel supplied by the intake system 10 to the cylinders 15 based on the intake mass flow rate and corresponding stored functional relationship so as to set the first expected airfuel ratio Al.

[0092] In the illustrated embodiment, the first expected air-fuel ratio is greater than stoichiometric (i.e. A1>1). Since the engine 1 will be operated mainly in the standard operation mode, the first expected air-fuel ratio may be chosen to maximise engine performance and / or reduce harmful engine emissions such as NOx. For example, the first expected air-fuel ratio may correspond to an air-fuel equivalence ratio of Al in the range of 2.5 to 3.0.

[0093] In step S2, the controller 102 determines the rotational speed of the engine 1 based on an input from the engine speed sensor arrangement 110, and compares the determined rotational speed to a predetermined speed band or range. The predetermined speed range may be idle to 2000 RPM. However, a range may be chosen where the engine may commonly operate at a constant speed. For example, for engines intended for use in construction or agricultural working machines, the range may be around idle (e.g. 830- 1150rpm), whereas in an engine for use in a genset the range may be 1450-1550rpm (e.g. approximately 1500rpm) where the electricity is to be supplied at 50Hz AC, or may be in the range of 1750-1850 rpm (e.g. approximately 1800 RPM) where the electricity is supplied at 60Hz AC, since the engine tends to operate for long periods at those speeds. If the rotational speed is outside of the predetermined range, the method returns to step SI, otherwise, the method proceeds to step S3.

[0094] In step S3, the controller 102 determines the output torque of the engine 1 based on an input from the output torque model, and compares the determined output torque to a predetermined torque band or range. The predetermined torque range may be 0 to 45 % of maximum torque output. For example, for engines intended for use in construction or agricultural working machines the torque range may be 0 to 40% (e.g. 0 to 35%) of maximum torque output, and the torque range may be 0 to 45% (e.g. 0 to 40%) of maximum torque output for engines for use in a genset. If the output torque is outside of the predetermined torque range, the method returns to step SI, otherwise, the method proceeds to step S4.

[0095] The controller 102 may determine the output torque of the engine 1 based on an indicated mean effective pressure (IMEP) of the engine 1. For example, the input from the output torque model may correspond to the IMEP of the engine 1.

[0096] The output torque of the engine 1 may be controlled according to a torque demand, determined on the basis of a speed governor position and other parameters. In some conditions, the engine 1 is not capable of supplying enough fuel and / or air to the cylinders to achieve the torque demand, or there is a delay whilst output torque adjusts to match the torque demand, in which case torque demand and torque output will differ. Otherwise, they will be substantially equal.

[0097] In some embodiments, the controller 102 may additionally or alternatively compare the torque demand to the predetermined torque range, and proceed to step S4 only if the torque demand is within the torque range.

[0098] In step S4, the controller 102 monitors the rotational speed of the engine 1 during a predetermined monitoring period (e.g. of 1 to 10 seconds). If the rotational speed of the engine 1 is maintained substantially constant throughout the monitoring period, the method proceeds to step S5, otherwise the method returns to step SI.

[0099] In step S5, the controller 102 enters a calibration mode to control one or more intake system parameters to set a second expected air-fuel ratio of the engine 1 (corresponding to an air-fuel equivalence ratio A2) that is closer to stoichiometric than Al in the standard operation mode.

[0100] As outlined above, the accuracy of oxygen sensors, such as lambda sensors, increases when the air-fuel ratio of the engine is closer to stoichiometric. As such, operating the intake system 10 at the second expected air-fuel ratio A2 enables a more accurate engine air-fuel ratio to be determined for the prevailing operating parameters.

[0101] It has been found that As below 1.5 result in increased engine knock in hydrogen fuelled engine. As such, the second expected air-fuel ratio may correspond to a A2 of greater than or equal to 1.5 (e.g. in the range of 1.5 to 2.0). In step S6, whilst in the calibration mode, the controller 102 determines the actual airfuel ratio of the engine 1 (corresponding to an air-fuel equivalence ratio A2a) based on a signal from the oxygen sensor arrangement 108.

[0102] In the illustrated embodiment, the controller 102 is configured calculate the air-fuel equivalence ratio A2a based on a signal from the lambda sensor of the oxygen sensor arrangement 108. The signal may be a voltage indicative of the actual air-fuel equivalence ratio A2a. Since in the calibration mode, the engine 1 operates at an air-fuel ratio which is closer to stoichiometric relative to the normal operation mode, the accuracy of the lambda sensor has been found to be higher.

[0103] The controller 102 may be configured to determine the actual air-fuel ratio A2a based on a plurality of measurements by the oxygen sensor arrangement 108. For example, the actual air-fuel ratio A2a may be based on an average of the measurements. The plurality of measurements may be taken by the oxygen sensor arrangement 108 over a measurement interval in the range of 5 to 20 seconds, for example 10 to 15 seconds.

[0104] In step S7, in the calibration mode, the controller 102 is configured to determine a difference between the second expected air-fuel ratio A2 (i.e. determined based on the one or more intake system parameters) and the actual air-fuel ratio A2a (i.e. determined based on the signal from the oxygen sensor arrangement 108).

[0105] Advantageously, it has been found that in the calibration mode, a more accurate difference between the expected and actual air-fuel ratios can be determined since the second expected air-fuel ratio is closer to stoichiometric relative to the first expected air-fuel ratio set in the standard operation mode.

[0106] In step S8, the controller 102 is configured to calculate a correction to the one or more intake system parameters based on the difference determined in step S7, so as to reduce the difference between the second expected air-fuel ratio A2 and the actual air-fuel ratio A2a. For example, if the actual air-fuel ratio A2a is greater than or less than the second expected air-fuel ratio A2, this offset is used by the controller 102 to apply a global correction factor to the intake system operating parameters. In some embodiments, the calculated correction may be such that the actual air-fuel ratio A2a substantially corresponds to the expected air-fuel ratio A2.

[0107] Subsequent to step S8, the method returns to step SI, in which the controller 102 is configured to apply the calculated correction to the one or more intake system parameters in the standard operation mode, when A is higher. As such, the difference between the first expected air-fuel ratio Al and the actual air-fuel ratio of the engine 1 in the standard operation mode is reduced. Regarding steps S2, S3 and S4, it has been found that performing the calibration only when the engine speed and / or output torque are below respective thresholds, and / or when the engine speed has been kept substantially constant for the preceding monitoring period, helps to ensure a more effective calibration of the air-fuel ratio of the engine 1 is achieved. The method shown in Figure 5 may be performed continuously, or periodically (e.g. every X hours) to find suitable opportunities for calibration to occur. One or more of the steps S1-S8 may be removed where appropriate. The order of the steps S1-S8 may be altered where appropriate.

[0108] The one or more embodiments are described above by way of example only and it will be appreciated that the variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

CLAIMS1. A controller for a hydrogen fuel internal combustion engine, the engine comprising a cylinder, an intake system configured to supply hydrogen fuel and air to the cylinder for combustion, and an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder, wherein the controller is configured to: control one or more intake system parameters to set an air-fuel ratio in a standard operation mode; selectively enter a calibration mode to control one or more intake system parameters to set an air-fuel ratio closer to stoichiometric than the standard operation mode; and in the calibration mode, determine a difference between an expected air-fuel ratio based on the one or more intake system parameters and an actual air-fuel ratio based on a signal from the oxygen sensor arrangement.

2. The controller of claim 1 further configured to calculate a correction to the one or more intake system parameters based on the determined difference, so as to reduce the difference between the actual air-fuel ratio and expected air-fuel ratio.

3. The controller of claim 2, wherein the calculated correction is such that the actual air-fuel ratio substantially corresponds to the expected air-fuel ratio.

4. The controller of claims 2 or 3, wherein the controller is configured to apply the calculated correction to the one or more intake system parameters in the standard operation mode.

5. The controller of any preceding claim, wherein the signal from the oxygen sensor arrangement corresponds to an oxygen concentration in the combustion gas.

6. The controller of any preceding claim, wherein the controller is configured to determine the actual air-fuel ratio based on a plurality of measurements taken by the oxygen sensor arrangement.

7. The controller of claim 6, wherein the plurality of measurements are taken over a measurement interval in the range of 5 to 20 seconds, for example 10 to 15 seconds.

8. The controller of any preceding claim, wherein, in the calibration mode, the controller is configured to:determine an air-fuel equivalence ratio of the actual air-fuel ratio to the stoichiometric ratio based on the signal from the oxygen sensor arrangement; and determine the difference between the expected air-fuel ratio and the actual air-fuel ratio based on the determined air-fuel equivalence ratio.

9. The controller of any preceding claim, configured to only enter the calibration mode when a rotational speed of the engine is within a predetermined speed range.

10. The controller of claim 9, wherein the predetermined speed range is idle to 2000 RPM, for example, 830 to 1150 RPM, or 1450 to 1550 RPM, or 1750 to 1850 RPM.

11. The controller of any preceding claim, configured to only enter the calibration mode when a rotational speed of the engine is maintained substantially constant throughout a predetermined monitoring period.

12. The controller of any preceding claim, configured to only enter the calibration mode when a torque of the engine is within a predetermined range, for example 0 to 45% of maximum torque output.

13. The controller of any preceding claim, wherein an air-fuel equivalence ratio of the air-fuel ratio in the standard operation mode to the stoichiometric ratio is in the range of 2.5 to 3.0.

14. The controller of any preceding claim, wherein an air-fuel equivalence ratio of the air-fuel ratio in the calibration mode to the stoichiometric ratio is greater than or equal to 1.5.

15. The controller of claim 14, wherein the air-fuel equivalence ratio in the calibration mode is in the range of 1.5 to 2.0.

16. A control system for a hydrogen fuel internal combustion engine, the engine comprising a cylinder, and an intake system configured to supply hydrogen fuel and air to the cylinder for combustion, wherein the control system comprises: the controller of any preceding claim; and an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder, wherein the determined difference is based on a signal from the oxygen sensor arrangement.

17. The control system of claim 16, wherein the oxygen sensor arrangement comprises a lambda sensor.

18. The control system of claim 17, wherein the lambda sensor is a wide range air fuel sensor.

19. A hydrogen fuel internal combustion engine comprising: a cylinder; an intake system configured to supply hydrogen fuel and air to the cylinder for combustion; and the control system of any one of claims 16 to 18.

20. The engine of claim 19, further comprising an intake port configured to supply air to the cylinder for combustion, and wherein the intake system is configured to supply hydrogen fuel to the cylinder via the intake port.

21. The engine of claims 19 or 20, wherein the intake system is configured to supply hydrogen fuel to the cylinder via direct fuel injection into the cylinder.

22. The engine of any one of claims 19 to 21, wherein the intake system is configured to supply hydrogen fuel to a plurality of cylinders of the engine, and wherein the oxygen sensor arrangement is in the flow path of combustion gas exhausted from the plurality of cylinders.

23. A working machine or genset comprising the hydrogen fuel internal combustion engine of any one of claims 19 to 22.

24. A method for calibrating a hydrogen fuel internal combustion engine, the engine comprising a cylinder, an intake system configured to supply hydrogen fuel and air to the cylinder for combustion, and an oxygen sensor arrangement in a flow path of combustion gas exhausted from the cylinder, the method comprising: a) controlling one or more intake system parameters to set an air-fuel ratio in a standard operation mode; b) selectively entering a calibration mode to control one or more intake system parameters to set an air-fuel ratio closer to stoichiometric than the standard operation mode; andc) in the calibration mode, determining a difference between an expected air-fuel ratio based on the one or more intake system parameters and an actual air-fuel ratio based on a signal from the oxygen sensor arrangement.

25. The method of claim 24 further comprising: d) calculating a correction to the one or more intake system parameters based on the determined difference, so as to reduce the difference between the actual air-fuel ratio and expected air-fuel ratio.

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