WO2011095794A1

WO2011095794A1 - Gas storage tank

Info

Publication number: WO2011095794A1
Application number: PCT/GB2011/050140
Authority: WO
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ma (Innovation) 2T4 Limited
Priority date: 2010-02-04
Filing date: 2011-01-28
Publication date: 2011-08-11
Also published as: GB201011499D0; GB2477586A; GB201001776D0; GB201012528D0

Abstract

A gas storage tank is described comprising at least one inflatable bellows (20) confined within a casing (22) and preloaded to extend in length when the gas pressure within the bellows (20) exceeds a predetermined value above the ambient pressure as gases are blown into the bellows (20). The casing (22) has diverging sides (24) guiding the extending bellows (20) and is closed off by a moveable end wall (26) held against the extending bellows (20) by a spring (28), the end wall (26) having adjustable dimensions matching and closing off the widening opening of the diverging sides (24) as the bellows (20) extends against the spring (28).

Description

GAS STORAGE TANK

Field of the invention

The present invention relates to a gas storage tank suitable for installation on board a motor vehicle for storing pressurised gases that may later be used to support an air pressure or gas pressure utilisation on the vehicle.

Background of the invention

Gas storage tanks are commonly of fixed volume where pressurised gases stored within the tank are released for external consumption by expansion of the gases out of the tank. If a relatively small quantity of gases is released from the tank and the tank is topped up frequently, it can be maintained at full capacity and the pressure in it will not be significantly reduced by the small quantities released. However, if a substantial quantity of gases is taken from the tank, the pressure in the tank will drop and the utilisation of the gas pressure supplied from the tank will become ineffective. If a large tank is introduced, replenishing it sufficiently to raise the pressure to a useful level will take a considerable time during which the utilisation of the gas pressure will also be ineffective.

It is known to provide a spring-loaded variable volume gas storage tank which expands and contracts while the pressure within the tank is regulated within a predetermined range. The effect of this is that the available pressure in the tank is maintained within the pressure range regardless of the mass of gases contained within the tank. This allows substantially all the gases in the tank to be released at a useful pressure. As soon as the tank commences to replenish, effective utilisation of the gas pressure will also become available immediately.

Object of the invention

The present invention aims to improve the performance of a spring-loaded variable volume gas storage tank. Summary of the invention

According to the present invention, there is provided a gas storage tank comprising at least one inflatable bellows confined within a casing and preloaded to extend in length when the gas pressure within the bellows exceeds a predetermined value above the ambient pressure as gases are blown into the bellows, characterised in that the casing has diverging sides guiding the extending bellows and is closed off by a moveable end wall held against the inflated bellows by a spring, the end wall having adjustable dimensions matching and closing off the widening opening of the diverging sides as the bellows extends against the spring.

The bellows may be made of elastic material stretched by the gas pressure just sufficiently to firmly line the internal surfaces of the casing.

Alternatively, the bellows may be made of inelastic material inflated by the gas pressure to form pouches along the bellows constrained firmly by the walls of the casing, the pouches being separated by folds of any excess material of the bellows gathered into the interior of the bellows and pressed together by the gas pressure within the bellows.

In the invention, the divergence of the sides and the corresponding increased area of the end wall are such that the gas pressure within the inflated bellows is kept substantially constant at the predetermined value above the ambient pressure as the bellows extends against the spring, the resultant pressure force exerted by the bellows inflated laterally across the increased area of the end wall being such that it is sufficient to counteract the increased resisting force of the spring as the bellows extends against the spring.

The above condition is described by the equation:

Constant pressure x Increased area of the end wall

= Spring rate x Increased strain of the spring.

The end wall may comprise sliding elements arranged such that the effective area of the end wall is increased by extending the elements towards the diverging sides while following the contours of the diverging sides. The gas seal between the end wall and the diverging sides is provided by the inflated bellows serving as a flexible lining bridging the gap between the end wall and the diverging sides.

A consequence of the invention is that no gases can be blown into the bellows if the gas pressure does not exceed the said predetermined value above the ambient air pressure. Another consequence is that when the stored gases are later released from the bellows, these gases will be pushed out of the bellows by the compression spring at substantially constant pressure regardless of the mass of gases contained in the bellows.

Prior art spring-loaded variable volume gas storage tanks are commonly cylindrical in shape with parallel sides. A moveable end wall or piston of fixed area is used to contain the gas pressure within the tank against the compression force of a spring. The regulation of the gas pressure within the tank is determined by the length of the spring, the spring rate and the preload applied on the spring at the initial position of the piston. By choosing a long spring with low spring rate and high preload, the variation in gas pressure as the tank is being filled may be maintained within a narrow range determined by the low spring rate. However, this gas pressure will not be truly constant and will increase gradually as the spring is progressively compressed.

For example, in order to limit the variation in pressure to less than 10%, the free length of the spring must be greater than 10 times the storage length of the tank so that, after a preload compression of 90%, the change in the compressed length of the spring as the tank is filled is less than 10%, resulting in less than 10% increase in the spring force between the initial and final positions of the piston. This example serves to illustrate a serious problem experienced in the installation of such gas storage tank on board a vehicle because of the very long free length of the spring that has to be accommodated.

The present invention enables a stiffer and shorter spring to be used where the increased compression load of the spring as the tank is filled is counteracted by the increased area of the end wall without increasing the gas storage pressure. This not only provides a much shorter installation length, but also delivers pressurised gases from the tank at truly constant pressure regardless of the mass of gases contained within the tank so that the utilisation of the gas pressure supplied from the tank will be consistent and effective.

In contrast to the prior art example, the spring in the present invention may be preloaded with 50% compression and further compressed to 100%

compression as the bellows is filled, resulting in 2 times increase in the spring force between the initial and final positions of the moveable end wall and this is counteracted by 2 times increase in the effective area of the end wall while the gas pressure within the tank remains constant. In this case, the free length of the spring will be 2 times the storage length of the tank plus the compressed solid length, making it much shorter so that the design of the tank is significantly more compact.

The invention is suitable for storing pressurised air on board a road vehicle powered by an internal combustion engine. In this vehicle, air is blown into the bellows by an air charger or air compressor and is accumulated within the bellows at a substantially constant pressure regardless of the mass of air contained within the bellows. This air is later expelled from the bellows and supplied to boost the engine, to another air compressor, or to various pneumatic equipments on the board the vehicle.

In a first example, a small capacity air tank of for example five times the displacement of the engine will be sufficient to store pressurised air blown into the bellows by a turbocharger at times when there is excess boost air produced by the turbocharger. Subsequently, this stored air, pushed out of the bellows by the compression spring, will be available instantaneously to boost the engine for 10 engine revolutions or 0.3 seconds at 2000 rpm engine speed. This will be effective for eliminating turbo-lag during sudden accelerations by injecting a short burst of high boost to briefly supplement the turbocharger, thus improving vehicle performance and reducing fuel consumption.

In a second example, a larger capacity air tank may be used to store pressurised air blown into the tank by the engine itself working temporarily as an air charger (with fuel cut off) while being driven using energy derived from braking of the vehicle. The motored engine has a so-called exhaust brake in the form of an air throttle in the exhaust system for restricting the air flow leaving the engine creating a high back pressure in the exhaust system and producing compressed air which can be diverted from upstream of the air throttle to the bellows for storage in the bellows. Subsequently, this stored air, pushed out of the bellows by the compression spring, will be available to temporarily boost the fired engine (with fuel switched on) for a short period supplementing or replacing any existing turbocharger. This provides a vehicle with regenerative braking where some of the braking energy is converted and stored in the air tank partly as spring potential energy and partly as compressed air energy, and the stored air is later used for boosting the fired engine for free while any existing turbocharger may be temporarily turned down or switched off.

Turning down or switching off the turbocharger by diverting the engine exhaust gases bypassing the turbine of the turbocharger has the effect of reducing the fired engine exhaust back pressure and removing the auxiliary load on the engine driving the turbine so that the nett output power available at the drive shaft of the engine will jump up immediately by an equivalent amount while the gross output power remains the same, hence the effective driving torque from the engine is increased for a short period at the same time the specific fuel consumption is reduced resulting in substantial fuel saving in urban driving conditions with frequent braking followed by frequent accelerations.

On average, every three revolutions of the motored engine working as an air charger with naturally aspirated intake will produce sufficient compressed air stored and later used for approximately one revolution of the fired engine supplied with denser air for free at boost pressure without incurring the

turbocharger auxiliary load. This translates to 12 seconds of engine braking that would support 4 to 6 seconds of the fired engine with free boost at the same engine speed and producing higher than the rated output torque gained from removing the auxiliary load, followed by smooth transition back to normal boost by turning up or switching on the turbocharger before the tank is emptied.

The above motored engine working as an air charger may alternatively be supplied with pressurised air produced by a supercharger connected to and driven by the motored engine. This increases the air mass flow through the engine while maintaining a similar back pressure in the exhaust system and diverting more compressed air per engine revolution to the air tank. Thus every one revolution of the motored engine could produce sufficient compressed air to later support at least one revolution of the fired engine with free boost without incurring auxiliary loads from either the turbocharger or the supercharger each being turned down or temporarily switched off. This translates to 12 seconds of engine braking that would support up to 12 seconds of the fired engine with free boost at the same engine speed and producing higher than the rated output torque gained from removing the auxiliary loads.

In a third example, a high pressure air tank may be used to stored compressed air at for example 10 to 20 bar air pressure supplied by an air compressor driven using energy produced by the engine or derived from braking of the vehicle. This compressed air may later be used to boost the engine or drive various pneumatic equipments on board the vehicle.

The above air compressor may draw intake air from the ambient

atmosphere. Alternatively it may be supplied with pressurised air from the air tank described in the earlier second example filled by the engine itself working temporarily as an air charger while being motored using energy derived from braking of the vehicle. In this case, high pressure compressed air is produced in two stages: a first stage by the engine working as an air charger and a second stage by the said air compressor. The final compressed air may then be stored for use on board the vehicle. Because the engine working as air charger has significantly larger displacement than the said air compressor, the pressurised air it produces during braking can be stored and supplied to the compressor for a prolonged period during and after braking so that less energy is consumed by the air compressor at any time during its duty cycle resulting in substantial fuel saving.

Brief description of the drawings

The invention will now be described further by way of example with reference to the accompanying drawings in which

Figure 1 a is a schematic sectional drawing of a gas storage tank according to the present invention,

Figure 1 b is a schematic sectional drawing of an alternative design of the gas storage tank,

Figure 2 is a schematic drawing of a vehicle powered by an

internal combustion engine and having on board a gas storage tank of the present invention, and Figure 3 is a schematic drawing of a vehicle powered by an

internal combustion engine with regenerative braking and having on

board a gas storage tank of the present invention.

Detailed description of the preferred embodiment

In Figure 1 a, an inflatable bellows or air bag 20 is shown confined within a casing 22. The bellows 20 is preloaded by a compression spring 28 calibrated so that the bellows 20 extends in length within the casing 22 when the gas pressure within the bellows 20 exceeds a predetermined value above the ambient pressure as gases are blown into the bellows 20. The casing 22 has diverging sides 24 guiding the extending bellows 20 and is closed off by a moveable end wall 26 held against the inflated bellows 20 by the spring 28. The end wall 26 has adjustable dimensions matching and closing off the widening opening of the diverging sides 24 as the bellows extends against the spring 28.

The bellows 20 may be made of elastic material stretched by the gas pressure just sufficiently to firmly line the internal surfaces of the casing 22.

In the invention, the divergence of the sides 24 and the corresponding increased area of the end wall 26 are such that the gas pressure within the inflated bellows 20 is kept substantially constant at the predetermined value above the ambient pressure as the bellows 20 extends against the spring 28, the resultant pressure force exerted by the bellows 20 inflated laterally across the increased area of the end wall 26 being such that it is sufficient to counteract the increased resisting force of the spring 28 as the bellows 20 extends against the spring 28. This condition is described by the equation:

Constant pressure x Increased area of the end wall 26

= Spring rate x Increased strain of the spring 28.

The end wall 26 comprises sliding elements 26a, 26b arranged such that the effective area of the end wall 26 is increased by extending the elements 26a, 26b across a base plate 26c towards the diverging sides 24 while following the contours of the diverging sides 24. A flat spring 26d acts to keep the elements 26a, 26b in contact with the diverging sides 24 and rollers 30 are provided for reducing friction between the sliding element 26a, 26b and the diverging sides 24. The gas seal between the end wall 26 and the diverging sides 24 is provided by the inflated bellows 20 serving as a flexible lining bridging the gap between the end wall 26 and the diverging sides 24.

Figure 1 b shows an alternative design of the end wall 26 where the flat spring 24d in Figure 1 a is replaced by hinged plates 27a, 27b connected to the sliding elements 26a, 26b such that the gas pressure exerted on plates 27a, 27b by the inflated bellows 20 would push the elements 26a, 26b against the diverging sides 24 and maintain rolling contact with the diverging sides 24 as the end wall 26 moves with the extending bellows 20.

Figure 1 b also shows an alternative design of the bellows 20 inflated by the gas pressure to form pouches 21 along the bellows 20 constrained firmly by the walls of the casing 22, the pouches 21 being separated by folds 23 of any excess material of the bellows 20 gathered into the interior of the bellows 20 and pressed together by the gas pressure within the bellows 20. In this case, the bellows 20 may be made of slippery inelastic material inflated to fit firmly within the casing 22, easily conforming in shape and without sticking or stretching of the material. Additionally elastic collars or pull cords may be provided to gather any excess material into the bellows.

In Figures 1 a and 1 b, when the gases stored within the bellows 20 are later released from the bellows 20, the gases will be pushed out of the bellows 20 by the spring 28 at substantially constant pressure regardless of the mass of gases contained within the bellows 20.

The present invention enables a stiff and short spring 28 to be used. This not only provides a much shorter installation length, but also delivers pressurised gases from the bellows 20 at truly constant pressure regardless of the mass of gases contained within the bellows 20 so that the utilisation of the gas pressure supplied from the bellows 20 will be consistent and effective. For example, the spring 28 may be preloaded with 50% compression and further compressed to 100% compression as the bellows 20 is filled, resulting in 2 times increase in the spring force between the initial and final positions of the moveable end wall 26 and this is counteracted by 2 times increase in the effective area of the end wall 26 while the gas pressure within the bellows 20 remains constant. In this case, the free length of the spring 28 will be 2 times the storage length of the tank 22 plus the compressed solid length, making the design of the tank very compact.

Figure 2 shows a gas storage tank of the present invention installed on board a road vehicle powered by a boosted internal combustion engine 16. In this vehicle, pressurised air is blown into the bellows 20 by an air charger 10 and is accumulated within the bellows 20 at a substantially constant pressure regardless of the mass of air contained within the bellows 20. This air is later expelled from the bellows 20 and supplied to the engine 16 for boosting the engine 16 while supplementing or replacing the existing turbocharger/supercharger of the engine 16, or to various pneumatic equipments on board the vehicle, thus saving fuel.

The air charger 10 may be a turbocharger 10 driven by exhaust gases from the engine 16. Alternatively, it may be a supercharger driven mechanically in various ways such as by the engine 16, by a jackshaft taken from the

transmission drivetrain of the vehicle, or by an electric motor. As a further alternative, the air charger may be a high pressure air compressor. The energy used for driving the supercharger or air compressor may be derived from the power output of the engine 16 or from the road wheels 18 while braking the vehicle. Valve 14 controls the charging and discharging of the bellows 20.

In Figure 2, a small capacity air tank of for example 5 times the

displacement of the engine 16 will be sufficient to store pressurised air blown into the bellows 20 by the turbocharger 10 at times when there is excess boost air produced by the turbocharger 10. Subsequently, this stored air, pushed out of the bellows by the compression spring, will be available instantaneously to boost the engine 16 for 10 revolutions or 0.3 seconds at 2000 rpm engine speed. This will be effective for eliminating turbo-lag during sudden accelerations by injecting a short burst of high boost into the engine 16 to briefly supplement the turbocharger 10.

In Figure 3, a larger capacity air tank of for example 100 times the displacement of the engine 16 may be used to store pressurised air blown into the bellows 20 by the engine 16 itself working temporarily as an air charger (with fuel cut off) while being driven using energy derived from braking of the vehicle through the road wheels 18. The motored engine 16 has a so-called exhaust brake in the form of an air throttle 40 for restricting the air flow leaving the engine 16 creating a high back pressure in the exhaust system of the engine 16 and producing compressed air which can be diverted from an upstream section of the air throttle 40 by way of an orifice and check valve 36 and line 42 to the bellows 20 for storage in the bellows 20. Subsequently, this stored air, pushed out of the bellows by the compression spring via control valve 44 and line 46, will be available to temporarily boost the fired engine 16 (with fuel switched on) for a short period supplementing or replacing any existing turbocharger. This provides a vehicle with regenerative braking where some of the braking energy is converted and stored in the air tank partly as spring potential energy and partly as compressed air energy, and the stored air is later used for boosting the fired engine 16 for free while any existing turbocharger, such as the one annotated 32, may be temporarily turned down or switched off.

Turning down or switching off the turbocharger 32 by diverting the engine exhaust gases via valve 38 bypassing the turbine 34 has the effect of reducing the fired engine exhaust back pressure and removing the auxiliary load on the engine 16 driving the turbine 34 so that the nett output power available at the drive shaft of the engine 16 will jump up immediately by an equivalent amount while the gross output power remains the same, hence the effective driving torque from the engine is increased for a short period at the same time the specific fuel consumption is reduced resulting in substantial fuel saving in urban driving conditions with frequent braking followed by frequent accelerations.

On average, every three revolutions of the motored engine 16 working as an air charger with naturally aspirated intake 50 will produce sufficient

compressed air stored and later used for approximately one revolution of the fired engine 16 supplied with denser air for free at boost pressure without incurring the turbocharger auxiliary load. This translates to 12 seconds of engine braking that would support 4 to 6 seconds of the fired engine 16 with free boost at the same engine speed and producing higher than the rated output torque gained from removing the auxiliary load, followed by smooth transition back to normal boost of the engine 16 by turning up or switching on the turbine 34 before the tank is emptied.

In Figure 3, the motored engine 16 working as an air charger may alternatively be supplied with pressurised intake air produced by a supercharger 52 connected to and driven by the motored engine. This increases the air mass flow through the engine 16 while maintaining a similar back pressure in the exhaust system and diverting more compressed air per engine revolution to the bellows 20. Thus every one revolution of the motored engine 16 could produce sufficient compressed air to later support at least one revolution of the fired engine with free boost without incurring auxiliary loads from either the

turbocharger 32 or the supercharger 52 each being turned down or temporarily switched off. This translates to 12 seconds of engine braking that would support up to 12 seconds of the fired engine with free boost at the same engine speed and producing higher than the rated output torque gained from removing the auxiliary loads.

In Figure 3, in addition to supplying boost air to the engine 16, the bellows 20 may also be connected via valve 44 and line 48 to supply pressurised air to another air compressor (not shown) driven using energy produced by the engine or derived from braking of the vehicle through the road wheels. In this case, high pressure compressed air at for example 10 to 20 bar air pressure may be produced in two stages: a first stage by the engine 16 working as an air charger filling the bellows 20 at an intermediate pressure; and a second stage by the said air compressor taking the pressurised air from the bellows 20 and further compressing it to 10 or 20 bar. The final compressed air may then be stored in another high pressure air tank (not shown) and used to drive pneumatic equipments on the vehicle. Because the engine working as air charger has significantly larger displacement than the air compressor in line 48, the pressurised air it produces during braking can be stored and supplied to the compressor for a prolonged period during and after braking so that less energy is consumed by the air compressor at any time during its duty cycle resulting in substantial fuel saving.

Claims

1 . A gas storage tank comprising at least one inflatable bellows (20) confined within a casing (22) and preloaded to extend in length when the gas pressure within the bellows (20) exceeds a predetermined value above the ambient pressure as gases are blown into the bellows (20), characterised in that the casing (22) has diverging sides (24) guiding the extending bellows (20) and is closed off by a moveable end wall (26) held against the inflated bellows (20) by a spring (28), the end wall (26) having adjustable dimensions matching and closing off the widening opening of the diverging sides (24) as the bellows (20) extends against the spring (28).

2. A gas storage tank as claimed in claim 1 , wherein the divergence of the sides (24) and the corresponding increased area of the end wall (26) are such that the gas pressure within the inflated bellows (20) is kept substantially constant at the predetermined value above the ambient pressure as the bellows (20) extends against the spring (28), the resultant pressure force exerted by the bellows (20) inflated laterally across the increased area of the end wall (26) being such that it is sufficient to counteract the increased resisting force of the spring (28) as the bellows (20) extends against the spring (28).

3. A gas storage tank as claimed in claim 1 or 2, therein the end wall (26) comprises sliding elements (26a, 26b) arranged such that the effective area of the end wall (26) is increased by extending the elements (26a, 26b) towards the diverging sides (24).

4. A gas storage tank as claimed in any preceding claim, wherein the bellows (20) is made of elastic material stretched by the gas pressure just sufficiently to firmly line the internal surfaces of the casing (22).

5. A gas storage tank as claimed in any preceding claim, wherein the bellows (20) is inflated by the gas pressure to form pouches (21 ) along the bellows (20) constrained firmly by the walls of the casing (22), the pouches (21 ) being separated by folds (23) of any excess material of the bellows (20) gathered into the interior of the bellows (20) and pressed together by the gas pressure within the bellows (20).

6. A vehicle powered by an internal combustion engine and fitted with a gas storage tank as claimed in any preceding claim, the vehicle further comprising an air charger or air compressor (10) connected to blow pressurised air into the bellows (20) for storage in the bellows (20) at substantially constant pressure, the engine having an intake system connected to receive boost air from the tank.

7. A vehicle as claimed in claim 6, wherein, in use, pressurised air is blown into the bellows (20) by a turbocharger (10) at times when there is excess boost air produced by the turbocharger (10).

8. A vehicle as claimed in claim 6, wherein, in use, pressurised air is blown into the bellows (20) by the engine (16) itself working temporarily as an air charger driven using energy derived from braking of the vehicle, the engine (16) under such conditions being operated with fuel cut off and with an air throttle (40) restricting the air flow leaving the engine (16) creating a high back pressure in the exhaust system of the engine (16) and producing compressed air which is diverted from upstream of the air throttle (40) to the bellows (20) for storage in the bellows (20).

9. A vehicle as claimed in claim 6, 7 or 8, comprising a further air compressor connected to receive pressurised air from the gas storage tank and to serve as a source of compressed air at a higher pressure than the storage tank pressure for powering pneumatic equipment on the vehicle.