fuel supply unit

Abstract

A fuel supply system (16) for a gaseous vehicle fuel includes a fuel compressor (10), an inlet line (22) configured to deliver fuel from a reservoir (18) to the compressor (10), an outlet line (24) configured to receive fuel discharged from the compressor (10), a bypass line (32) extending between the inlet line (22) and the outlet line (24), a bypass valve (38) disposed on the bypass line (32) configured to open and close the bypass line (32) to fuel flow, and a buffer volume (20) connected to the outlet line (24), the buffer volume (20) configured to accommodate expansion and compression of the fuel to mitigate pressure fluctuations in the outlet line (24).

Description

[Technical Field]

[0001] FUEL SUPPLY SYSTEM FOR GAS VEHICLE FUEL FIELD OF THE INVENTION The present invention relates to a fuel supply system for gaseous vehicle fuels, and more particularly to a system for supplying gaseous fuels, such as hydrogen, to an internal combustion engine. [Background technology]

[0002] As automobiles move 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 supplies configured to accommodate gaseous fuels, and these systems can have similar architectures to conventional systems for liquid fuels, but with modifications to address the different challenges presented by the use of gaseous fuels.

[0003] For example, it has been found that injecting gaseous fuel at pressures significantly above atmospheric pressure, for example at a pressure of about 300 bar, is beneficial to engine performance. The gaseous fuel may be held at high pressure in a vehicle's fuel tank, for example at a pressure of around 700 bar when the tank is full, but as the tank becomes depleted this pressure drops rapidly and may be as low as 30 bar when the tank is empty.

[0004] Therefore, when the fuel tank pressure falls below the pressure required by the injectors, a fuel compressor is required to pressurize the fuel supplied from the fuel tank. Because the input pressure may vary widely while the output pressure remains substantially constant, it follows that the fuel compressor and associated fuel supply system may need to be able to accommodate large variations in its pressure ratio, i.e., the ratio of output pressure to input pressure, while still providing the required mass flow rate of fuel. This is further complicated by the fact that the compressor is typically driven by the engine, and therefore compressor speed is directly related to engine speed, while the required mass flow rate of fuel is determined by engine torque demand. Summary of the Invention [Problem to be solved by the invention]

[0005] It is against this background that the present invention was conceived. [Means for solving the problem]

[0006] According to one aspect of the present invention, a fuel supply system for a gaseous vehicle fuel, such as hydrogen, is provided, the system including a fuel compressor, an inlet line configured to deliver fuel from a reservoir to the compressor, an outlet line configured to receive fuel discharged from the compressor, a bypass line extending between the inlet and outlet lines, and a bypass valve disposed on the bypass line, the bypass valve configured to open and close the bypass line to fuel flow.

[0007] If the fuel supply device is used in the context of a vehicle, the reservoir may be, for example, a fuel tank of the vehicle, and the device may be configured to supply fuel to an engine of the vehicle.

[0008] The bypass line can provide a flow path around one or more compression chambers of the compressor. For example, the bypass line can extend around the compressor. The bypass line and bypass valve can enable various operating modes of the device. For example, the bypass line can be used to bypass the compressor when the fuel in the inlet line is at sufficient pressure for the final recipient of the fuel, such as a vehicle engine. The bypass line can also enable an idle operating mode of the compressor by creating a fluid short circuit connecting the compressor output to its input. This can be used to regulate the effective power output from the compressor to the outlet line, for example, by rapidly switching the state of the bypass valve to control the compressor output in a manner similar to pulse width modulation.

[0009] The fuel supply system can include a buffer volume connected to the outlet line, the buffer volume configured to accommodate expansion and compression of the fuel to mitigate pressure fluctuations in the outlet line. By absorbing pressure fluctuations in the outlet line, the buffer volume, which can be in the form of a tank, for example, can improve and / or compensate for discrepancies between compressor output and demand. The buffer volume can be configured to selectively hold and release compressed fuel. The buffer volume can be configured to hold fuel at a pressure above a threshold level and / or within a target pressure range. If the compressor is driven by the vehicle engine, the buffer volume can be configured to hold fuel under pressure when the vehicle engine is off.

[0010] The fuel supply system may include a valve, such as a check valve, located on the outlet line downstream of the junction between the outlet line and the bypass line.

[0011] The fuel supply system may be configured to selectively activate and deactivate the compressor.

[0012] The fuel supply system may include a releasable coupling that transmits torque to drive the compressor, and that may be disengaged to stop the compressor. The releasable coupling may include, for example, a clutch.

[0013] The fuel supply system can be configured to switch the bypass valve between open and closed states while the compressor is operating to control the characteristics of the fuel flowing to a fuel receiver, such as a buffer volume, connected to the outlet line. The fuel supply system can be configured to control the characteristics of the fuel flowing to the fuel receiver by varying the ratio of compressor compression strokes during which the bypass valve is open to compression strokes during which the bypass valve is closed.

[0014] The fuel supply system can be configured to switch the bypass valve between open and closed states at a frequency proportional to the operating speed of the compressor. The fuel supply system can be configured to switch the bypass valve between open and closed states in synchronization with compression events in the compressor. In such an embodiment, the fuel supply system can be configured to switch the bypass valve state only when a compression event begins or completes.

[0015] The fuel supply system can be configured to vary the switching frequency of the bypass valve to control a characteristic, such as fuel pressure or flow rate, of the fuel flowing to a fuel receiver connected to the outlet line. The fuel receiver can be, for example, an engine or a fuel injection system associated with the engine. Alternatively, the fuel receiver can be a buffer volume.

[0016] The fuel supply system may include an electromechanical actuator for switching the bypass valve between open and closed states. The switching of the bypass valve may be controlled by a controller.

[0017] The present invention also extends to a vehicle device including the fuel supply device of the above aspect. The vehicle device may include a reservoir, such as a fuel tank, connected to an inlet line of the fuel supply device. The vehicle device may also include a fuel receptacle to which the fuel supply device supplies fuel. The fuel receptacle may be, for example, an engine or a fuel injection system associated with the engine. Alternatively, the fuel receptacle may be a buffer volume. The vehicle device may also include a controller for controlling operation of the fuel supply device, for example, controlling operation of a bypass valve.

[0018] The invention also extends to a vehicle including a fuel supply system or vehicle device of the above aspects.

[0019] Another aspect of the present invention provides a method for compressing a gaseous vehicle fuel, such as hydrogen, comprising the steps of delivering fuel to a compressor through an inlet line, discharging the fuel from the compressor to an outlet line connected to a fuel receiver, and operating a bypass valve to open and close a bypass line extending between the inlet and outlet lines to control the characteristics of the fuel flowing to the fuel receiver.

[0020] The fuel receiver may be, for example, an engine or a fuel injection system associated with the engine, or the fuel receiver may be a buffer volume.

[0021] The method can include switching the bypass valve between open and closed states at a frequency proportional to an operating speed of the compressor. The method can include switching the state of the bypass valve in synchronization with a compression event in the compressor. The method can include switching the state of the bypass valve only when a compression event begins or completes.

[0022] The method may include operating a bypass valve to open and close a bypass line while simultaneously operating a compressor to control the characteristics of the fuel flowing to the fuel receiver.

[0023] The method may include varying the ratio of compressor compression strokes during which the bypass valve is open to compression strokes during which the bypass valve is closed to control the characteristics of the fuel flowing to the fuel receiver.

[0024] The method may include varying the switching frequency of the bypass valve to control the characteristics of the fuel flowing to a fuel receiver connected to the outlet line.

[0025] Another aspect of the invention provides a controller configured to carry out the method of the above aspect to control the operation of a fuel supply system for a gaseous vehicle fuel, such as the fuel supply system of the above aspect.

[0026] Another aspect of the present invention provides a controller configured to control operation of a fuel supply system for a gaseous vehicle fuel, the controller being configured to operate a compressor to discharge fuel delivered to the compressor through an inlet line to an outlet line connected to a fuel receiver, and to operate a bypass valve to open and close a bypass line extending between the inlet and outlet lines to control the characteristics of the fuel flowing to the fuel receiver, the controller being capable of forming part of the vehicle system of the above aspect.

[0027] It will be understood that the various features of each aspect of the invention are equally applicable to the other aspects of the invention, either alone or in any appropriate combination.

[0028] These and other aspects of the present invention will now be described, by way of example only, with reference to FIG. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a vehicle system including a fuel supply system for a gaseous fuel; DETAILED DESCRIPTION OF THE INVENTION

[0030] 1 illustrates a gaseous fuel compressor 10 in the context of a vehicle system 12 that also includes an internal combustion engine 14. Compressor 10 forms part of a fuel supply system 16 according to one embodiment of the present invention, which is configured to supply gaseous fuel, specifically hydrogen fuel in this embodiment, to engine 14 from a fuel tank 18.

[0031] However, it is noted that a fuel supply system according to the present invention can be used in a wide range of applications, and therefore the system shown in Figure 1 is purely exemplary. Indeed, in some embodiments, the fuel supply system can be applied outside the context of a vehicle, for example at a gas station.

[0032] In addition to the compressor 10 , the fuel supply system 16 of FIG. 1 also includes a controller configured to regulate the operation of the compressor 10 , and a buffer volume or tank 20 .

[0033] Engine 14 includes a fuel injection system that includes a plurality of fuel injectors that each supply fuel to a respective cylinder of engine 14 in use. Although not shown, the fuel injection system may also include an accumulator, or "common rail," as is known, that holds a reserve of pressurized fuel to be drawn by the injectors.

[0034] The fuel tank 18 holds fuel and thus acts as a fuel reservoir within the vehicle system 12. In this example, when the fuel tank 18 is filled to its maximum capacity, hydrogen is held in the fuel tank 18 at 700 bar, but this pressure decreases as the fuel tank 18 becomes depleted during use. The fuel tank 18 is equipped with a pressure regulator, or "tank valve," that reduces the pressure of the fuel output by the fuel tank 18 to a level slightly above the pressure required by the fuel injection system, for example, approximately 320 bar in this embodiment. When the pressure inside the fuel tank 18 falls below this level, the tank valve shuts off and fuel is output at a pressure corresponding to the pressure inside the fuel tank.

[0035] It is noted that in other embodiments multiple fuel tanks may be used.

[0036] In this example, the fuel compressor 10 is generally configured as a positive displacement compressor 10 having a piston performing a compression stroke to compress the fuel. The compressor 10 is configured to accommodate a pressure ratio which in this example may be 10 or greater. It is noted that other types of compressors may be used in alternative embodiments.

[0037] The fuel compressor 10 includes one or more inlets that receive gaseous fuel from an inlet line 22 extending from a fuel tank 18. Fuel is delivered to the inlet of the compressor through the inlet line 22 at a pressure that substantially corresponds to the pressure at which fuel is output from the fuel tank 18, which in this example is 320 bar or less due to the tank valve.

[0038] The fuel compressor 10 also includes one or more outlets that discharge fuel into an outlet line 24 at a pressure required by the engine 14, in this example at a pressure of about 300 bar or greater. A first portion of the outlet line 24 extends to a buffer tank 20 that is configured to hold the pressurized fuel received from the compressor 10 until fuel is required by the engine 14. At this point, the buffer tank 20 is connected to the fuel injection system by a second portion of the outlet line 24.

[0039] The buffer tank 20 is therefore disposed in the outlet line 24 between the compressor outlet and the fuel injection system. Broadly speaking, the buffer tank 20 is an additional fuel storage tank, which may be generally similar in construction to the fuel tank 18, and which provides additional fuel storage capacity within the fuel supply 16. As will become more apparent from the description that follows, in use, the buffer tank 20 receives pressurized fuel from the compressor 10 or directly from the fuel tank 18, thereby pressurizing the buffer tank 20 so that it always holds a reservoir of fuel at the pressure required by the fuel injection system. Fuel is then selectively released from the buffer tank 20 to the fuel injection system when required.

[0040] The buffer tank 20 also acts to smooth out fluctuations in the pressure output by the compressor 10, thereby making the fuel delivery characteristics more closely match the demands from the engine 14, which are normally relatively stable.

[0041] It is noted that in other embodiments, the buffer tank 20 may be omitted, allowing fuel to be supplied to the fuel injection system directly from the fuel compressor 10 or the fuel tank 18. Conversely, in other embodiments, multiple buffer tanks may be included and arranged in series or parallel.

[0042] It is also noted that the buffer tank 20, if present, is separate from the fuel injection system accumulator. In practical terms, the accumulator typically holds fuel under pressure only while the engine 14 is running, whereas the buffer tank 20 stores fuel under pressure even when the engine 14 is off. Also, the volume of the buffer tank 20 is typically many times larger than the volume of the accumulator.

[0043] A pressure regulator may be placed at the outlet of the buffer tank 20 or in the outlet line 24 downstream of the buffer tank 20 to reduce the fuel pressure in the outlet line 24 to a level slightly above the pressure required by the fuel injection system, e.g., about 320 bar in this embodiment. Such a pressure regulator may be included in addition to or instead of a tank valve.

[0044] Thus, from the above, the buffer tank 20 and the engine 14 can each be considered to define a fuel receptacle, in that each receives compressed fuel from the fuel supply 16. Similarly, the buffer tank 20 forms part of the fuel supply 16 that supplies compressed fuel to the engine 14.

[0045] The outlet line 24 also includes a check valve defining an outlet valve 26 which forms part of a control device, as will be further explained below. The outlet valve 26 is located upstream of the buffer tank 20.

[0046] In this example, the fuel compressor 10 includes a drive arrangement including a drive shaft driven by the engine 14. More specifically, as shown generally in Figure 1, a coupling 28 is provided by which the fuel compressor drive shaft is operably connected to the crankshaft of the engine 14 such that rotation of the crankshaft when the engine 14 is operating drives corresponding rotation of the drive shaft. The coupling 28 thus transfers torque from the crankshaft to the compressor drive arrangement to power the compressor 10. The fuel compressor 10 in this example is sized to couple directly to the engine crankshaft without a gearbox so that the drive shaft rotates at the same rotational speed as the crankshaft.

[0047] The drive shaft-to-crankshaft coupling 28 includes a multi-plate clutch 30 disposed between the engine 14 and the compressor 10, such that the engine 14 drives the fuel compressor 10 through the clutch 30. The multi-plate clutch 30 maintains low actuation forces while providing high transmission forces without significantly increasing the overall size of the clutch 30. The clutch 30 may be similar to those known in the motorcycle industry, for example. The mechanical connection between the clutch 30 and the compressor drive shaft, and between the crankshaft and the clutch 30, may be any suitable method for transmitting torque from the crankshaft to the drive shaft.

[0048] Clutch 30 includes a servo mechanism operable to selectively engage and disengage under the control of, for example, an engine control unit (ECU) (not shown in FIG. 1 ), i.e., an electronic control unit responsible for managing the operation of engine 14. The ECU can be considered part of vehicle equipment 12 in this example. In this manner, the fuel compressor drive shaft can be coupled to and decoupled from engine 14 at any time during operation, allowing fuel compressor 10 to be activated and deactivated while engine 14 is running. For example, when fuel pressure in inlet line 22 is already high enough for engine 14, fuel compressor 10 can be disengaged to stop compressing fuel, allowing fuel to be routed directly from fuel tank 18 to engine 14 without requiring mechanical work from fuel compressor 10.

[0049] In this regard, fuel supply system 16 also includes a bypass line 32 extending between a first end 34 that connects to inlet line 22 and a second end 36 that connects to outlet line 24 at a point between the compressor outlet and outlet valve 26. Bypass line 32 thus creates a path that allows fuel to bypass compressor 10, allowing fuel to be routed directly from fuel tank 18 to engine 14 when, for example, the fuel exiting fuel tank 18 and its tank valve is at sufficient pressure for engine 14, in this example 320 bar.

[0050] The bypass line 32 includes a bypass valve 38 that is operable, under control of the ECU, to switch between open and closed positions to allow or block flow through the bypass line 32. The change of state of the bypass valve 38 between the open and closed positions is actuated in this embodiment by a solenoid actuator 40. The bypass valve 38 is thus capable of rapid, frequent state changes. It is noted that other actuation methods for changing the state of the bypass valve 38 are possible.

[0051] Typically, the bypass valve 38 is opened to reduce stress on the clutch 30 while the clutch 30 is transitioning between engaged and disengaged states.

[0052] When the bypass valve 38 is closed and the clutch 30 is engaged, the fuel discharged by the fuel compressor 10 exerts pressure on the outlet valve 26, creating enough force to open the outlet valve 26. Once the outlet valve 26 is open, fuel flows through the outlet valve 26 and into the buffer tank 20.

[0053] When the bypass valve 38 is open, fuel can flow in either direction through the bypass line 32. The direction of fuel flow depends in part on whether the clutch 30 is engaged.

[0054] If the clutch 30 is disengaged so that the fuel compressor 10 is off, fuel flows directly from the fuel tank 18 through the bypass line 32 to the outlet valve 26. The control system is normally only configured in this manner when the fuel output from the fuel tank 18 is already at the pressure required by the fuel injection system, so that the outlet valve 26 opens and fuel continues to flow to the buffer tank 20. Thus, in this scenario, fuel is routed directly from the fuel tank 18 to the buffer tank 20, bypassing the fuel compressor 10.

[0055] When the clutch 30 is engaged so that the fuel compressor 10 operates while the bypass valve 38 is open, fuel output by the fuel compressor 10 takes the path of least resistance and therefore passes through the bypass line 32 back to the inlet of the fuel compressor, and the outlet valve 26 therefore remains closed. With the outlet valve 26 closed, backflow from the buffer tank 20 into the bypass line 32 or towards the compressor 10 is prevented. The fuel then circulates around the bypass line 32 and the fuel compressor 10, and thus between the inlet and outlet of the compressor 10, remaining at a substantially constant pressure corresponding to the inlet pressure, provided that pressure losses are sufficiently small.

[0056] Thus, in this situation, the bypass line 32 acts as a hydraulic short circuit, effectively causing the fuel compressor 10 to idle and defining an idle mode for the fuel compressor 10 in which the fuel is held at inlet pressure without performing significant compression work. Because no mechanical work is performed other than to overcome friction, power consumption by the fuel compressor 10 in idle mode is therefore minimal. Conversely, when the bypass valve 38 is closed and the clutch 30 is engaged, a compression mode for the compressor 10 is defined in which the compressor 10 performs mechanical work on the fuel.

[0057] The idle mode of the fuel compressor 10 can be used to regulate the pressure and flow rate of fuel output by the compressor 10 and delivered to the buffer tank 20. In this regard, the state of the bypass valve 38 can be changed frequently to operate intermittently at a desired duty cycle, with the actual delivered output pressure and flow rate being proportional to the relative percentage of time the compressor 10 is operating to compress fuel. For example, the bypass valve 38 can change state at a frequency up to the same as the engine speed, which in a typical application can be up to 3000 revolutions per minute, corresponding to a valve switching frequency of up to 50 Hz. The bypass valve 38 can even change state at a frequency higher than the engine speed, e.g., twice the frequency corresponding to the engine speed. More generally, the bypass valve 38 can be operated at a frequency that may involve a change of state for every compression stroke of the compressor 10, depending on the applied duty cycle. In this regard, in this example, rotation of the compressor drive shaft drives the compression stroke of the piston of the compressor 10 at a frequency proportional to the engine speed.

[0058] The bypass valve 38, outlet valve 26 and clutch 30 thus define a control device that is configured to modulate the output of the fuel compressor 10 in a manner similar to a pulse width modulation (PWM) control, thereby enabling the output pressure and flow rate delivered by the compressor 10 to be adjusted to required levels in response to input pressure variations, independent of engine speed.

[0059] To maintain efficient idling of the fuel compressor 10, the opening and closing of the bypass valve 38 is synchronized with the compression strokes taking place within the compressor 10, with the valve either open or closed throughout each compression stroke, not changing state mid-stroke. The frequency of the bypass valve 38 changing state is therefore proportional to the compressor speed. The ratio of compression strokes during which the bypass valve 38 is open to compression strokes during which the bypass valve 38 is closed can be considered the duty cycle applied to the bypass valve 38, which determines the rate at which fuel is delivered to the buffer tank 20, thereby helping to maintain the pressure in the buffer tank 20 within a desired range.

[0060] It is noted that the state of the bypass valve 38 does not necessarily change at regular intervals. Instead, the switching of the bypass valve 38 is controlled according to a desired duty cycle, which in this example is implemented by the ECU. For example, the bypass valve 38 may open for three compression strokes and then close for the fourth compression stroke, in a repeating pattern, providing a 25% duty cycle, with compression occurring when the bypass valve 38 is closed. In other words, the compressor 10 operates in compression mode 25% of the time in this scenario. While the bypass valve 38 is controlled in this manner, the state of the bypass valve 38 changes twice every four cycles of the compressor 10, so that the switching frequency of the bypass valve 38 is proportional to the compressor speed. In practice, the duty cycle can be dynamically varied to adjust the compressor output as appropriate.

[0061] During operation, the engine 14 draws fuel from the buffer tank 20 at a continuous rate that is typically relatively stable in the short term. Meanwhile, when the bypass valve 38 is closed, fuel is output from the compressor 10 intermittently, in pulses corresponding to the compression stroke, which may not exactly match engine demand. If the compressor 10 were directly connected to the engine 14, this could lead to pressure fluctuations in the outlet line 24. The buffer tank 20 is sized sufficiently so that the expansion and compression of the fuel inside the buffer tank 20 in response to the pulses and intermittent gaps in the compressor output absorbs these pressure fluctuations, thus providing a smoothing effect that improves fuel delivery. If a pressure regulator is added at or downstream of the outlet of the buffer tank 20, this may allow the size of the buffer tank 20 to be reduced. Meanwhile, the bypass valve 38 operates to match the average output of the compressor 10 to engine demand.

[0062] As noted above, buffer tank 20 may be omitted in other embodiments, for example, if compressor output can be controlled with sufficient precision. Eliminating buffer tank 20 may, for example, save space within fuel supply system 16 and improve storage efficiency.

[0063] In summary, the fuel supply system 16 compensates for pressure fluctuations in the source of gaseous fuel, i.e., the fuel tank in the above example, thereby making it possible to supply fuel to the internal combustion engine at the required pressure. This is achieved using a control device that makes it possible to adjust the output of the system's compressor or to bypass the compressor entirely, depending on the system's current operating state. To improve and reduce the demands placed on the compressor and control device regarding the accuracy with which the output is regulated, a buffer tank can be included.

[0064] It will be understood that various other embodiments of the invention are contemplated without departing from the scope of the appended claims.

[0065] For example, instead of a check valve as in the example above, an actuated valve could be used as the outlet valve located upstream of the buffer tank on the outlet line. In this case, the actuated valve could be controlled in a manner similar to the check valve in the example above, e.g., to act to open at the appropriate time to allow flow from the compressor to the outlet line and close to prevent backflow from the outlet line to the bypass line. This could involve, for example, closing the outlet valve whenever the bypass valve is open and the compressor is running, and opening the outlet valve whenever the bypass valve is closed and the compressor is running or when the compressor is being bypassed. [Explanation of symbols]

[0066] 10 Fuel Compressor 12 Vehicle equipment 14 Engine 16 Fuel supply system 18 Fuel Tank 20 Buffer Tank 22 Entrance Line 24 Exit Line 26 Outlet valve 28 Coupling 30 Clutch 32 Bypass Line 34 First end of bypass line 36 Second end of bypass line 38 Bypass valve 40 Solenoid actuator for bypass valve

Claims

1. A fuel supply system (16) for a gaseous vehicle fuel, comprising: a fuel compressor (10); an inlet line (22) configured to deliver fuel from a reservoir (18) to the compressor (10); an outlet line (24) configured to receive fuel discharged from the compressor (10); a bypass line (32) extending between the inlet line (22) and the outlet line (24); a bypass valve (38) disposed on the bypass line (32), the bypass valve (38) being configured to open and close the bypass line (32) to fuel flow; a buffer volume (20) connected to the outlet line (24), the buffer volume (20) configured to accommodate fuel expansion and compression to mitigate pressure fluctuations in the outlet line (24); A fuel supply system (16) comprising:

2. The fuel supply system (16) of claim 1, wherein the buffer volume (20) is configured to hold fuel at a pressure above a threshold level.

3. The fuel supply system (16) of claim 1 or 2, wherein the buffer volume (20) is configured to maintain fuel within a target pressure range.

4. 4. The fuel supply system (16) of claim 1, further comprising a valve (26) disposed on the outlet line (24) downstream of a junction between the outlet line (24) and the bypass line (32).

5. 5. The fuel supply system (16) of claim 4, wherein the valve (26) disposed on the outlet line (24) is a check valve.

6. The fuel supply system (16) of any one of claims 1 to 5, wherein the compressor (10) can be selectively activated and deactivated.

7. The fuel supply system (16) of any one of claims 1 to 6, including a releasable coupling (28) that transmits torque to the compressor (10) to drive the compressor (10).

8. The fuel delivery system (16) of claim 7, wherein the releasable coupling (28) includes a clutch (30).

9. 9. The fuel supply system (16) of claim 1, configured to switch the bypass valve (38) between open and closed states while the compressor (10) is operating to control the characteristics of the fuel flowing to a fuel receiver (14, 20) connected to the outlet line (24).

10. 10. The fuel supply system (16) of claim 9, wherein the bypass valve (38) is configured to vary the percentage of the compression stroke of the compressor (10) that is open to control the characteristics of the fuel flowing to the fuel receiver (14, 20).

11. 11. The fuel supply system (16) of claim 1, configured to switch the bypass valve (38) between open and closed states at a frequency proportional to an operating speed of the compressor (10).

12. 12. The fuel supply system (16) of any one of claims 1 to 11, configured to switch the bypass valve (38) between open and closed states in synchronization with compression events in the compressor (10).

13. The fuel supply system (16) of claim 12, configured to switch the state of the bypass valve (38) only when a compression event begins or completes.

14. 14. The fuel supply system (16) of claim 11, configured to vary the switching frequency of the bypass valve (38) to control the characteristics of the fuel flowing to a fuel receiver (14, 20) connected to the outlet line (24).

15. A vehicle system (12) including a fuel supply system (16) according to any one of claims 1 to 14.

16. 16. The vehicle system of claim 15, further comprising a reservoir (18), the inlet line (22) configured to deliver fuel from the reservoir (18) to the compressor (10).

17. 17. A vehicle system according to claim 15 or 16, including a controller for controlling the operation of the fuel supply system (16).

18. A vehicle comprising a fuel supply device (16) according to any one of claims 1 to 14 or a vehicle device according to any one of claims 15 to 17.

19. 1. A method for compressing gaseous vehicle fuel, comprising: delivering fuel to a compressor (10) through an inlet line (22); Discharging fuel from the compressor (10) into an outlet line (24) connected to a fuel receiver (14, 20); operating a bypass valve (38) to open or close a bypass line (32) extending between the inlet line (22) and the outlet line (24) to control the characteristics of the fuel flowing to the fuel receiver (14, 20); A method comprising:

20. 20. The method of claim 19, including switching the bypass valve (38) between open and closed states at a frequency proportional to the operating speed of the compressor (10).

21. 21. The method of claim 19 or 20, comprising switching the bypass valve (38) between open and closed states in synchronization with compression events in the compressor (10).

22. 22. The method of claim 21, including switching the state of the bypass valve (38) only when a compression event begins or completes.

23. 23. The method of any one of claims 19 to 22, comprising operating the compressor (10) simultaneously with operating the bypass valve (38) to open and close the bypass line (32).

24. 24. The method of any one of claims 19 to 23, comprising varying the percentage of the compression stroke of the compressor (10) during which the bypass valve (38) is open to control the characteristics of the fuel flowing to the fuel receiver (14, 20).

25. A controller configured to carry out a method according to any one of claims 19 to 24 to control the operation of a fuel supply system (16) for a gaseous vehicle fuel.

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