Delivery arrangement for gaseous fuel

Abstract

A gaseous fuel delivery arrangement for a vehicle. The fuel delivery arrangement comprises a compressor for compressing gaseous vehicle fuel (such as hydrogen) and a control arrangement configured to

Description

This invention relates a fuel delivery arrangement for gaseous vehicle fuel and to controlling operation of a compressor of such an arrangement. In particular, the invention relates to controlling the delivery of gaseous fuel, such as hydrogen, by the fuel delivery arrangement to an internal combustion engine of a vehicle. BACKGROUND As automotive vehicles transition away from reliance on fossil fuels, internal combustion engines that consume gaseous fuels such as hydrogen instead of liquid fuels are gaining interest. Such engines require fuel delivery arrangements configured to handle the gaseous fuel, which systems may have similar architectures to traditional systems for liquid fuels, but with modifications to account for the different challenges that the use of gaseous fuel presents. For example, it has been found that it is beneficial to engine performance to inject gaseous fuel at pressures greatly exceeding atmospheric pressure, for example at a pressure of approximately 300 bar (30 MPa). Although gaseous fuel may be held at high pressure in a vehicle fuel tank, for example at a pressure of around 700 bar (70 MPa) when the tank is full, this pressure reduces rapidly as the tank is depleted, potentially to as low as 30 bar (3 MPa) as the tank empties. Accordingly, a fuel compressor is used to pressurise the fuel supplied from the fuel tank when the fuel tank pressure drops below that required by the injectors. It follows that the fuel compressor and the associated fuel delivery arrangement may need to be capable of handling a wide variation in its compression ratio, namely the ratio of the output pressure to the input pressure, whilst delivering a demanded mass flow rate of fuel, since the input pressure varies widely while the output pressure may remain substantially constant. This is further complicated by the fact that a compressor would typically be driven by the engine and hence the compressor speed is directly related to the engine speed, whereas the required mass flow rate of fuel is dictated by the engine torque demand. It is against this background that the present invention has been devised. STATEMENTS OF INVENTION Against this background, the invention provides a fuel delivery arrangement for a vehicle, the fuel delivery arrangement comprising a compressor for compressing gaseous vehicle fuel and a control arrangement configured to operate the compressor. The compressor comprises a piston arrangement arranged for reciprocating movement along a piston axis, and at least one compression chamber, or volume, in which gaseous fuel is compressed by movement of the piston arrangement along the piston axis, in use. The control arrangement is configured to operate the compressor so that the piston arrangement performs a partial stroke during compression, so that an unswept portion of the compression chamber, that is not swept by the piston arrangement, is larger than if the piston arrangement performs a full stroke during compression. Advantageously, operating the piston arrangement to perform a partial stroke may enable the control arrangement to control and vary a throughput of the compressor to deliver an appropriate amount of gaseous fuel to an engine. The required throughput of the compressor may be based on a demand for gaseous fuel by the engine, when a fuel pressure in a fuel tank supplying the gaseous fuel drops below a required fuel supply pressure to the engine, for example. The fuel delivery arrangement may reduce wasted energy by avoiding pressurising fuel that is surplus to the demand of the engine. The control arrangement may be configured to operate the compressor to vary a stroke of the piston arrangement to control an output of the compressor. Varying the stroke of the piston arrangement may entail varying a length of strokes performed by the piston arrangement along the piston axis, for example. Beneficially, varying the stroke of the piston arrangement of the compressor in use allows controlled variability of the throughput of the compressor to meet a variable demand for pressurised gaseous fuel by an engine. This may improve the efficiency of the fuel delivery arrangement by aligning the extent to which the fuel is pressurised with the engine demand. The stroke may be varied dynamically to react to changes in a demand. The compressor may comprise a first compression chamber in which gaseous fuel could be compressed as the piston arrangement moves in a first direction along the piston axis, in use, and a second compression chamber in which gaseous fuel could be compressed as the piston arrangement moves in a second direction along the piston axis, in use. Providing two compression chambers halves the work done pressurising fuel in each chamber for a given throughput when compared to a compressor with just one chamber, thereby reducing the wear each piston and chamber combination exhibits and increasing the service life of the compressor, for example. Arranging the compressor so that fuel is compressed when the piston moves in each direction along the piston axis may increase the compressor output for a given compressor speed. The first and second compression chambers may be mutually spaced along the piston axis and may be arranged at opposed ends of the piston arrangement. The piston arrangement may comprise a first piston configured to compress fuel in the first compression chamber, and a second piston configured to compress fuel in the second compression chamber. The control arrangement may be configured to operate the compressor so that the first and second compression chambers have respective unswept portions that are not swept by the piston arrangement. The control arrangement may be configured to operate the compressor to vary the volume of at least one of respective unswept portions of the first and second compression chambers, to control an output of the compressor. The respective unswept portions of the first and second compression chambers may be substantially equal in volume or, alternatively, different in volume. The control arrangement may be configured to control the respective volumes of the unswept portions so that one of the first and second compression chambers is inactive and delivers no pressurised fuel as the piston arrangement moves, while the other of the first and second compression chambers is active and delivers pressurised fuel as the piston arrangement moves. Optionally, the volume of only the unswept portion of the inactive compression chamber is varied to control an output of the compressor, while the volume of the unswept portion of the active chamber is kept substantially constant. In this scenario, the inactive compression chamber may have a larger unswept portion than the active compression chamber. Furthermore, the control arrangement may be configured to vary which of the first and second compression chambers is inactive during operation. The control arrangement may be configured to operate the compressor so that the piston arrangement moves symmetrically with respect to the first and second compression chambers. The control arrangement may be configured to operate the compressor so that the piston arrangement moves asymmetrically with respect to the first and second compression chambers. The control arrangement may implement symmetrical movement and asymmetrical movement at different times. The compressor may be hydraulically driven and, as such, the fuel delivery arrangement may comprise a pump for delivering hydraulic fluid to the compressor to drive movement of the piston arrangement. Additionally, the pump may have a variable output. The fuel delivery arrangement may comprise a spool valve, which may be operated by the control arrangement, through which the hydraulic fluid is delivered or diverted to operate the compressor. The invention also contemplates a vehicle comprising the above fuel delivery arrangement. Another aspect of the invention provides a method of operating a compressor of a vehicle fuel delivery arrangement. The compressor comprises a piston arrangement arranged for reciprocating movement along a piston axis, and at least one compression chamber in which gaseous fuel is compressed by movement of the piston arrangement along the piston axis, in use. The method comprises operating the compressor so that the piston arrangement performs a partial stroke during compression, so that an unswept portion of the compression chamber that is not swept by the piston arrangement is larger than if the piston arrangement performs a full stroke during compression. The method may comprise varying a volume of the unswept portion, and / or varying a stroke of the piston arrangement, to control an output of the compressor. The invention further provides a control arrangement for operating a compressor of a vehicle fuel delivery arrangement, the control arrangement being configured to perform the abovementioned method. BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an image of an example vehicle to which embodiments of the invention may apply; Figure 2 is a schematic diagram of a gaseous fuel delivery arrangement; Figure 3 is a schematic diagram of a compressor of the fuel delivery arrangement shown in Figure 2; Figure 4 is a schematic diagram of a control architecture of the gaseous fuel delivery arrangement of Figure 2; Figure 5 is a schematic diagram of the compressor of Figure 3 performing a short stroke version of a first piston motion type; Figure 6 corresponds to Figure 5 but shows a long stroke version of the first piston motion type; Figure 7 is a schematic diagram of the compressor of Figure 3 performing a short stroke version of a second piston motion type; Figure 8 corresponds to Figure 7 but shows a long stroke version of the second piston motion type; Figure 9 shows an example reference chart for the first piston motion type; and Figure 10 shows an example reference chart for the second piston motion type. SPECIFIC DESCRIPTION Figure 1 is an image of a vehicle V to which embodiments of the invention may apply. The vehicle V comprises an internal combustion engine 12 for propelling the vehicle V, which is fuelled by a gaseous fuel, for example natural gas or hydrogen. The vehicle V further comprises a gaseous fuel delivery arrangement 10 or system for storing and supplying gaseous fuel to the engine 12. Although the vehicle V shown in Figure 1 resembles a passenger car, this is not intended to be limiting. The invention could relate to any vehicle with an internal combustion engine 12 fuelled by gaseous fuel. Figure 2 shows an example of the gaseous fuel delivery arrangement 10 in combination with the internal combustion engine 12 of the vehicle V, the delivery arrangement 10 being arranged to deliver gaseous fuel to the engine 12. In this example, the arrangement 10 comprises a fuel storage tank 14, a compressor 200, a heat exchanger 16, and a pressure control system, known henceforth as a regulator valve 18. The fuel storage tank 14 is a pressure vessel that is charged with and contains pressurised gaseous fuel for supply to the engine 12. The tank 14 may be a rigid structure or may be a flexible bag-like structure, for example. The tank 14 may be constructed using metallic, polymer or composite materials, for example. An operating fuel pressure, Prail, is defined as the substantially constant fuel pressure required to run the internal combustion engine 12. In this example, the operating fuel pressure, Prail, of the engine 12 may be, for example, 300 bar (30 MPa), although this may vary depending on the requirements of the engine 12. In contrast, a tank pressure Ptank, being the variable pressure of the fuel inside the tank 14, could be approximately 700 bar (70 MPa) at maximum capacity. When the tank pressure, Ptank, is above the operating fuel pressure, Prail, the fuel can be supplied to the engine directly from the tank 14, with the excess pressure being moderated by the regulator valve 18. As fuel is drawn from the fuel storage tank 14, the tank pressure Ptank reduces. A minimum operable pressure of the fuel storage tank may be, for example, 30 bar (3 MPa). A pressure Ptank below the minimum operable pressure is too low to ensure a correct mass flow rate, Mrail, is supplied to the engine 12 in all operating conditions. The compressor 200 is disposed between the fuel storage tank 14 and the engine 12, and is used to pressurise the fuel supplied from the fuel storage tank 14 when the tank pressure Ptank drops below the operating fuel pressure Prail required by the engine 12. The compressor 200 will be described in more detail below. The heat exchanger 16 manages a temperature Trail of the pressurised fuel flowing from the compressor 200, before the fuel enters the engine 12. If necessary, the fuel temperature, Trail, is altered by the heat exchanger 16, which can either cool or heat up the fuel to the desired temperature. As the operating fuel pressure, Prail, is held substantially constant, the mass flow rate, Mrail, flowing into the engine is dependent on the temperature, Trail, of the fuel. In the fuel delivery system 10 shown, the heat exchanger 16 can also perform the action of a buffer tank to minimise fluctuations in operating fuel pressure, Pra.il. Alternatively, or in addition, there may be a separate buffer tank included in the system 10 between the compressor 200 and the engine 12 for the same purpose, or in some arrangements no buffering is provided. The regulator valve 18 is operable to moderate the pressure of the fuel that is supplied to the engine 12, in particular to avoid overpressure when the tank pressure Ptank exceeds the operating fuel pressure Prail. In some arrangements, a compressor 200 is driven such that it operates at a speed that is proportional to the engine speed, so that the output mass flow rate from the compressor 200 varies in dependence on the engine speed. Not only could this deliver excessive amounts of fuel to the engine 12, which could cause over-pressurisation, but also this may entail pressurising fuel unnecessarily, for example when the vehicle is in a coast-down condition where engine speed, and therefore compressor speed, is relatively high and a demand for pressurised fuel is negligible or even non-existent. In contrast, and in this example, the compressor 200 is operated to deliver a variable output substantially independently of engine speed, and therefore to pressurise gaseous fuel selectively, when demanded. The compressor 200 shown in Figure 2 is a twin-chamber compressor. It should be noted that the configurations of the compressor are provided by way of example and are not intending to be limiting. Any compressor that is operable to produce a variable output is compatible with the inventive concept. The compressor 200 is hydraulically driven, and the system 10 includes a hydraulic circuit 28 including components for effecting hydraulic drive of the compressor 200. In this example, the hydraulic circuit 28 of the system 10 comprises a hydraulic fluid tank 20, a variable output hydraulic pump 22 and a spool valve 24. The system 10 may also comprise a hydraulic fluid filter, a cooler and a deaerator, although these components are not shown in Figure 2. Providing such elements in a hydraulic system such as the system shown is known in the art. Figure 3 shows the compressor 200 in more detail, revealing that the compressor 200 includes two coaxially aligned cylindrical piston chambers, defining first and second piston chambers. More specifically, in this example, the compressor 200 has an upper piston chamber 208 and a lower piston chamber 210, in the orientation shown in Figure 3, although it is noted that the compressor 200 may have any orientation in practice. Each piston chamber 208, 210 houses a respective disc-shaped piston 202 that is arranged for reciprocating motion within its piston chamber 208, 210, along a piston axis that is colinear with the central axes of the piston chambers 208, 210. The pistons 202 are interconnected by a rod 212 to form a piston arrangement 206, or piston assembly, such that the two pistons 202 move in unison. The piston chambers 208, 210 are mutually spaced and oppositely oriented, in that a compressive movement for one piston 202 corresponds to a decompressive movement for the other piston 202, and vice versa. Each piston 202 divides its respective piston chamber 208, 210 into two mutually isolated and sealed sub-volumes, one on each side of the piston 202, namely a driving volume 214 and a compression volume 216. The compressor 200 therefore has first and second compression volumes 216 which may alternatively be known as compression chambers. The size of each of the driving and compression volumes varies with movement of the pistons 202. The driving volumes 214 are located on inward sides of their respective pistons 202 and thus between the two pistons 202, while the compression volumes 216 are on the outboard sides of the pistons 202 and so at opposed ends of the compressor 200. The driving volumes 214 are configured to receive pressurised hydraulic fluid to drive movement of the pistons 202. The compression volumes 216 are configured to receive and compress the gaseous fuel for supply to the engine 12. Hydraulic fluid is supplied to the compressor 200 via the spool valve 24. The state of the spool valve 24 determines which driving volume 214 the hydraulic fluid is delivered to and which driving volume 214 fluid is released from. In this respect, piston movement is achieved by pressurising one driving volume 214 with pressurised hydraulic fluid and releasing hydraulic fluid from the other driving volume 214. In the context of the orientation shown in Figure 3, upward movement of the piston arrangement 206 may be effected by delivering hydraulic fluid to the upper driving volume 214A while releasing hydraulic fluid from the lower driving volume 214B. This piston movement results in a compression stroke of the upper piston 202, in which the volume of the upper compression volume 216A reduces causing compression of the gaseous fuel in the upper compression volume 216A, and an expansion stroke of the lower piston 202 in which the volume of the lower compression volume 216B increases, allowing decompression of fuel in the lower compression volume 216B. The spool valve 24 can be actuated to switch to a different state and so reverse the flow of the pressurised hydraulic fluid to and from the driving volumes 214 to effect the opposite movement of the piston arrangement 206, or to deactivate the compressor 200 by bypassing the hydraulic fluid from the compressor 200 completely. The method of driving the compressor 200 is not intended to be limiting. For example, the compressor 200 may be driven pneumatically instead of hydraulically. Alternatively, the compressor 200 may be driven electro-mechanically by a servo, solenoid, linear actuator or any other type of electro-mechanical device. Each piston chamber 208, 210 comprises an inlet and an outlet to allow the gaseous fuel to enter and exit the respective compression volume 216. An input valve 26A is provided on the inlet, and correspondingly an output valve 26B is provided on the outlet. The input valve 26A is a one-way valve that is operable to allow passage of gaseous fuel from the tank 14 into the compression volume 216 as the piston 202 undergoes an expansion stroke, which imparts a pressure in the compression volume 216 that is less than the stored fuel pressure Ptank, allowing gaseous fuel to flow into the compression volume 216. Correspondingly, the input valve 26A prevents the supplied gaseous fuel from escaping the compression volume 216 as the piston 202 performs a compression stroke, thereby pressurising the gaseous fuel in the compression volume. Correspondingly, the output valve 26B is a one-way valve that is operable to allow passage of pressurised gaseous fuel out of the compression volume 216 when the gaseous fuel within the compression volume 216 is pressurised by the piston 202 for supply to the engine 12. Likewise, the output valve 26B prevents the pressurised gaseous fuel from reentering the compression volume 216 when the piston 202 subsequently performs an expansion stroke. The output valve 26B is configured to open only when the gaseous fuel within the compression volume 216 is equal to or greater than the required supply pressure Prail for the engine 12. Figure 4 shows in schematic form a control architecture, or control arrangement 108, for the fuel delivery arrangement 10, which includes an example Electronic Control Unit (ECU) 100 configured to control the fuel delivery arrangement 10. The ECU 100 comprises a processing module 102, a memory module 104 and a communication bus 106. The communication bus 106 is operable to send and receive signals to and from sensors and components of the fuel delivery arrangement 10 and other systems of the vehicle V. The memory module 104 is configured to store data, in this example including numerical map data and mathematical functions that are used to correlate output to input variables, shown in the form of maps or plots in Figures 9 and 10. This data enables a required fuel mass flow rate delivery to be determined for given inputs. The processor 102 is configured to process input data received by the communication bus 106 from the sensors and components of the fuel delivery arrangement 10, based on the data stored in the memory module 104. A control output to deliver the required mass flow rate of pressurised fuel, Mrah, to the engine 12 is then outputted by the ECU 100. The control output may comprise a control signal that is issued to a component of the arrangement 10 to cause that component to implement the required action. Figure 4 also shows examples of the components of the fuel delivery arrangement 10 that are in communication with the communication bus 106 of the ECU 100. The components include: the fuel storage tank 14, where stored fuel temperature, Ttank, and pressure, Ptank, are measured; the compressor 200, where the position of the piston arrangement 206 is captured; the spool valve 24, which is configured to receive control signals from the ECU 100 to actuate into an appropriate state, the states of the spool valve 24 corresponding to a first flow direction, a second flow direction or a bypass state; the variable output hydraulic pump 22, which is configured to receive control signals from the ECU 100 to moderate the flow of hydraulic fluid; the engine 12, where supplied fuel pressure, Prail, is measured; and the heat exchanger 16, where supplied fuel temperature, Trail, is measured. Moving on, Figures 5 to 8 show the compressor 200 in different operating modes. Figures 5 and 6 show the compressor 200 operating using a first piston motion type corresponding to a first operating mode. Correspondingly, Figures 7 and 8 show the same compressor 200 operating using a second piston motion type corresponding to a second operating mode. The first and second piston motion types represent different ways of operating the compressor 200 to produce a variable output. Both piston motion types involve controlling the compressor 200 to perform partial strokes of the pistons 202, such that a portion of at least one of the compression volumes 216 is unswept, i.e., that portion is not swept by the piston 202, as the compressor 200 operates, when that portion would be swept if the piston 202 were to perform a full stroke. The unswept portion of the compression volume 216 defines a ‘dead volume’ DV of the piston chamber 208, 210. In examples to be described, the stroke S of the piston arrangement 206 is varied in relation to fixed references to control an output of the compressor 200. For the first piston motion type, the fixed reference is a central plane that is equidistant between the outboard ends of each piston chamber 208, 210. For the second piston motion type, a dead volume DV of an active piston chamber is held constant and so this volume represents a fixed reference. The details of the first and second piston motion types will be discussed in more detail below. As shown in Figures 5 and 6, in the first operating mode the piston arrangement 206 moves symmetrically with respect to a central plane 204. This movement represents the first piston motion type, in which the piston arrangement 206 reciprocates symmetrically about the central position 204, while the pistons 202 undergo mirrored strokes. This is to allow both chambers 208, 210 to work in substantially the same manner, thereby providing an even distribution of wear between the chambers 208, 210, should wear occur. As such, the dead volumes DV or unswept portions of each respective piston chamber 208, 210 are equal in volume. In varying the length of a stroke S that each piston 202 performs, the size of the dead volumes DV is varied. Figure 6 shows the compressor 200 operating with a minimum dead volume, DVmin, in each piston chamber 208,210, which occurs when the piston 202 moves with a maximum stroke Smax. The minimum dead volume DVmin is non-zero in this example, which is typical for a compressor 200 of this type. In this situation, a compression ratio, which is the pressure of the gas supplied to the compressor 200 as a ratio against the pressure of the gas discharged from the compressor 200, is at a maximum. The compression ratio can be reduced by decreasing the stroke S of the piston 202, thereby increasing the dead volume DV, as shown in Figure 5. If the dead volume DV is too large, then the gaseous fuel will not be sufficiently compressed to reach the operating fuel pressure Prail, and no gaseous fuel will leave the compressor 200 and the compression ratio in this condition is zero. Therefore, the maximum effective dead volume, DVcomp, is the dead volume DV at and below which the compression ratio becomes non-zero. Alternatively, as dead volume DV and stroke S are inversely proportional, the minimum effective stroke length, Scomp, is the minimum stroke length at which the compression ratio is non-zero. The ECU 100 acts to vary the stroke S and dead volume DV to control the output of the compressor 200 by issuing a suitable input signal to the spool valve 24. Changing operation from a shorter stroke S to a longer stroke S increases the swept volume for each piston 202 and thereby provides a potential increase of volumetric efficiency. The result of a larger swept volume is increased delivery of gaseous fuel for the same compressor speed, provided that the dead volume DV is smaller than the maximum effective dead volume DVcomp. If the dead volume DV is greater than the maximum effective dead volume DVcomp, the fuel delivery is zero despite each piston 202 moving with a non-zero stroke S. In this situation, the gas is compressed but it remains trapped inside the compressor as it is not compressed sufficiently to open the output valve 26B. Moving on to Figures 7 and 8, which show the second operating mode, here the piston arrangement 206 moves asymmetrically relative to the central plane 204, demonstrating a second piston motion type of the piston arrangement 206. Instead, relative to the first operating mode, the movement of the piston assembly 206 is offset upwardly in the orientation shown in Figures 7 and 8. A consequence of this asymmetrical movement is that the unswept or dead volumes DV1, DV2 of the compression chambers 208, 10 are unequal. Beneficially, this allows one of the compression chambers, in this case the lower chamber 210, to be effectively deactivated, as the combination of the relatively large dead volume DV2 (compared to DV1) and the relatively short stroke S (compared to the maximum stroke Smax) are insufficient to compress the gaseous fuel to the operating fuel pressure Prail and therefore open the output valve 26B. As such, in the examples shown in Figures 7 and 8 only the upper chamber 208 is active and delivers some gaseous fuel output while the lower chamber 210 is inactive, i.e., it does not deliver any gaseous fuel output. It is worth noting that the piston of the inactive lower chamber does move and compress the gas in the compression volume of the lower chamber, however, the pressure of the gas in the compression volume of the lower chamber is kept below the operating fuel pressure Prail- The roles of the upper and lower chambers 208, 210 can be periodically switched, so that the upper chamber 208 becomes inactive and the lower chamber 210 is active. For example, 20 compression events may be performed in one chamber 208, followed by 20 compression events in the other chamber 210 and continuing to alternate between the chambers 208, 210. This may distribute mechanical wear substantially evenly between both the pistons 202 and the compression chambers 208, 210, for example. With the arrangement shown in Figures 7 and 8, the dead volume DV1 of the upper chamber 208 is fixed and therefore independent of the stroke S, preferably at a maximum dead volume DVmin, and the size of the dead volume DV2 of the lower chamber 210 is dependent on the stroke S of the piston arrangement 206. This arrangement causes an offset movement of the piston assembly 206 relative to the central plane 204. in this example, dead volume DV1 of the active upper chamber 208 and stroke S are not proportional. A change in compression ratio is achieved by modifying stroke S, which varies the swept volume, and thus a ratio of the swept volume and DV1, in the active upper chamber 208. The maximum effective stroke length, Scomp, is the stroke length at which the compression ratio becomes non-zero. Although DV1 is fixed in the shortterm, DV1 can be changed in the longer term according to the working conditions. For example, a small DV1 could be used when the pressure ratio (PraiuPtank) is close to its maximum, while a larger DV1 could be used when the pressure ratio (Prail: Ptank) is close to unity. Deactivation of the inactive chamber, which is the lower chamber 210 in the examples shown in Figures 7 and 8, entails zero flow from the lower chamber 210. Therefore, there is a maximum allowable stroke S of the piston arrangement 206, and a corresponding maximum dead volume DV2, to prevent the gas in the inactive lower chamber 210 from being pressurised to be equal to or above the operating fuel pressure Prail. . The first and second piston motion types may be implemented in any piston type compressor with either a singular piston or multi-piston arrangement, where it is possible to vary the stroke S and dead volume DV of the piston(s) in the compression chamber(s). The ECU 100 controls the output of gaseous fuel from the compressor 200 by managing the position of the piston arrangement 206 in the compressor 200 and thereby the stroke S and the dead volume DV of the respective chambers 208, 210. The ECU 100 produces an output to control the compressor 200 based on inputs received from other components of the gaseous fuel delivery arrangement 10. In the above example, this is implemented through appropriate control of the hydraulic pump 22 and the spool valve 24 in particular. Figure 9 shows a first set of charts, plots or maps which represent reference data for the first piston motion type. Specifically, the reference data allow the ECU 100 to process the input signals to produce suitable control signals to control operation of the compressor 200 using the first piston motion type. These maps are stored in the memory module 104 of the ECU 100. The maps show the mass flow rate Mrail demand of the engine 12 on the vertical axis, throughout the working range between idle engine speed and maximum engine speed. Correspondingly, a required compressor displacement range, or stroke range, is shown on the horizontal axis. The relationship between mass flow rate Mrail requirement and compressor displacement to deliver that mass flow rate is provided by a series of curves on the map, each representing a respective value of pressure ratio (PrailPtank). When Ptank is greater than or equal to Prail (ratio<=1.0 on the map), the map indicates that the compressor 200 always delivers a higher mass flow rate Mrail than required. In this condition, the compressor 200 may work intermittently. Alternatively, the compressor 200 may be deactivated and configured to either allow gaseous fuel to flow through the inactive compressor 200 or bypassed externally around the compressor 200. For example, although not shown in Figure 2, the fuel delivery system may include a bypass line through which fuel may flow to bypass the compressor 200. Figure 10 shows a second set of maps which represent reference data for the second piston motion type. As above, the reference data allows the ECU 100 to process input signals into suitable control signals, in this example for controlling operation of the compressor 200 using the second piston motion type. Similarly, these maps will be stored in the memory module 104 of the ECU 100. The second set of maps show the relationship between mass flow rate and required compressor displacement or stroke S for both the active chamber, in an upper portion of each map, and the inactive chamber, in a lower portion of the maps. As the lower map of the second set visible in Figure 10 shows, the maximum displacement of the inactive chamber 210 has an effect on the allowable stroke S of the piston arrangement, as the stroke S must be limited to maintain inactivity, i.e., compressing the gas within the chamber but keeping the pressure below the supply pressure Prail. In both of the abovementioned sets of maps, each map of the set relates to a different temperature of the gaseous fuel stored in the gaseous fuel storage tank. This is because, in general, mass flow rate is affected by temperature of the gas in question. it should be noted that the ECU 100 of the fuel delivery arrangement 10 may switch between the first and second piston motion types for the compressor 200, for example depending on the required demand for gaseous fuel by the engine 12 or according to operating conditions. In an alternative arrangement, the variable output hydraulic pump 22 could be replaced with a fixed displacement hydraulic pump and the ECU 100 would include a new strategy. This may entail that the flow delivered by the pump is proportional to the engine speed and so cannot be altered, in which case the ECU may be configured to change the compressor displacement to deliver the correct mass flow rate Mrail- For example, if there is a large hydraulic fluid flow, the ECU 100 may operate the compressor with a small displacement and so a short piston stroke. Conversely, if there is a limited oil flow the ECU may operate the compressor with a larger displacement and so a longer piston stroke, in this case, the ECU may contain stored maps to take account of both the temperature of the stored gaseous fuel in the fuel storage tank Ttank and the flow rate of hydraulic fluid being supplied to the compressor. The ECU identifies the correct map, identifies the correct delivery curve based on the pressure ratio (Prail: Ptank), and calculates the corresponding output to the compressor in accordance with the required mass flow rate. It will be appreciated that various other embodiments of the invention are also envisaged without departing from the scope of the appended claims. LIST OF PARTS V - vehicle 10 - gaseous fuel delivery arrangement 12 - internal combustion engine 14 - fuel storage tank 16 - heat exchanger 18 - regulator valve 20 - hydraulic fluid tank 22 - hydraulic pump 24 - spool valve 26 - one-way valve 26A - input valve 26B - output valve 28 - hydraulic circuit 100 - electronic control unit (ECU) 102 - processing module 104 - memory module 106 - communication bus 108 - control arrangement 200 - compressor 202 - piston 204 - central plane 206 - piston arrangement 208 - upper piston chamber 210 - Sower piston chamber 212 - rod 214 - driving volume 216 - compression volume

Claims

1. A fuel delivery arrangement (10) for a vehicle (V), comprising:a compressor (200) for compressing gaseous vehicle fuel, the compressor (200) comprising a piston arrangement (206) arranged for reciprocating movement along a piston axis, and at least one compression chamber (216) in which gaseous fuel is compressed by movement of the piston arrangement (206) along the piston axis, in use; anda control arrangement (108) configured to operate the compressor (200) so that the piston arrangement (206) performs a partial stroke during compression, so that an unswept portion (DV) of the compression chamber (216), that is not swept by the piston arrangement (206), is larger than if the piston arrangement (206) performs a full stroke during compression.

2. The fuel delivery arrangement (10) of claim 1, wherein the control arrangement (108) is configured to operate the compressor (200) to vary a stroke of the piston arrangement (206) to control an output of the compressor (200).

3. The fuel delivery arrangement (10) of any preceding claim, wherein the compressor (200) comprises a first compression chamber (216) in which gaseous fuel is compressed as the piston arrangement (206) moves in a first direction along the piston axis, in use, and a second compression chamber (216) in which gaseous fuel is compressed as the piston arrangement (206) moves in a second direction along the piston axis, in use.

4. The fuel delivery arrangement (10) of claim 3, wherein the first and second compression chambers (216) are mutually spaced along the piston axis and are arranged at opposed ends of the piston arrangement (206).

5. The fuel delivery arrangement (10) of claim 3 or claim 4, wherein the piston arrangement (206) comprises a first piston (202) configured to compress fuel in the first compression chamber (216), and a second piston (202) configured to compress fuel in the second compression chamber (216).

6. The fuel delivery arrangement (10) of any of claims 3 to 5, wherein the control arrangement (108) is configured to operate the compressor (200) to vary the volume of at least one of respective unswept portions of the first and second compression chambers (216), to control an output of the compressor (200).

7. The fuel delivery arrangement (10) of any of claims 3 to 6, wherein the control arrangement (108) is configured to operate the compressor (200) so that respective unswept portions of the first and second compression chambers (216) are substantially equal in volume.

8. The fuel delivery arrangement (10) of any of claims 3 to 7, wherein the control arrangement (108) is configured to operate the compressor (200) so that respective unswept portions of the first and second compression chambers (216) are different in volume.

9. The fuel delivery arrangement (10) of claim 8, wherein the control arrangement (108) is configured to control the respective volumes of the unswept portions of the first and second compression chambers (216) so that one of the first and second compression chambers (216) is inactive and delivers no pressurised fuel as the piston arrangement (206) moves, while the other of the firstand second compression chambers (216) is active and delivers pressurised fuel as the piston arrangement (206) moves.

10. The fuel delivery arrangement (10) of claim 9, wherein the control arrangement (108) is configured to vary a volume of only the unswept portion of the inactive compression chamber (216) to control an output of the compressor (200).

11. The fuel delivery arrangement (10) of claim 9 or claim 10, wherein the inactive compression chamber (216) has a larger unswept portion than the active compression chamber (216).

12. The fuel delivery arrangement (10) of any of claims 9 to 11, wherein the control arrangement (108) is configured to vary which of the first and second compression chambers (216) is inactive during operation.

13. The fuel delivery arrangement (10) of any of claims 3 to 12, wherein the control arrangement (108) is configured to operate the compressor (200) so that the piston arrangement (206) moves symmetrically with respect to the first and second compression chambers (216).

14. The fuel delivery arrangement (10) of any of claims 3 to 13, wherein the control arrangement (108) is configured to operate the compressor (200) so that the piston arrangement (206) moves asymmetrically with respect to the first and second compression chambers (216).

15. The fuel delivery arrangement (10) of any preceding claim, wherein the compressor (200) is hydraulically driven.

16. The fuel delivery arrangement (10) of claim 15, comprising a pump (22) for delivering hydraulic fluid to the compressor (200) to drive movement of the piston arrangement (206).

17. The fuel delivery arrangement (10) of claim 16, wherein the pump (22) has a variable output.

18. The fuel delivery arrangement (10) of any of claims 15 to 17, comprising a spool valve (24) through which hydraulic fluid is delivered to the compressor (200).

19. A vehicle (V) comprising the fuel delivery arrangement (10) of any preceding claim.

20. A method of operating a compressor (200) of a vehicle fuel delivery arrangement (10), the compressor (200) comprising a piston arrangement (206) arranged for reciprocating movement along a piston axis, and at least one compression chamber (216) in which gaseous fuel is compressed by movement of the piston arrangement (206) along the piston axis, in use, the method comprising operating the compressor (200) so that the piston arrangement (206) performs a partial stroke during compression, so that an unswept portion of the compression chamber (216), that is not swept by the piston arrangement (206), is larger than if the piston arrangement (206) performs a full stroke during compression.

21. The method of claim 20, comprising varying a volume of the unswept portion tocontrol an output of the compressor.

22. A control arrangement (108) for operating a compressor (200) of a vehicle fuel 5 delivery arrangement (10), the control arrangement (108) being configured to perform the method of claim 21 or claim 22.

Images