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(11) | EP 2 199 656 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Liquefied petroleum gas tank for a vehicle, and fuel supply system including said tank |
| (57) A tank (2) has a shell (3) defining an inner chamber (4), which contains liquefied
petroleum gas and houses a member (10) that is moveable in order to vary the volume
available for the liquefied petroleum gas; said member preferably being defined by
an inflatable bag (10).
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[0002] In vehicles provided with an internal combustion engine, liquefied petroleum gas, commonly known by the acronym LPG, is used as an alternative fuel to petrol or diesel to define what is known as a "multifuel" type of fuel supply system.
[0003] Said system has two tanks, one for the LPG and the other for the petrol (or other fuel), and comprises an electronic control unit which controls and regulates the supply of the two fuels to the engine. When the engine is started, especially when starting in cold climates, or in any case when the engine and supply system are "cold", the control unit sets the fuel supply system to use petrol, and switches to the gas supply system after a warming-up phase.
[0004] This setting is automatic and necessary in order to ensure correct engine operation. Such systems are not provided with a supply pump for the LPG, and it is merely the pressure of the tank that makes the LPG flow towards a pressure reducer upstream of the engine, so that in certain cold temperature conditions the pressure of the LPG might not be high enough to supply the injection system, especially in turbocharged engines. This phenomenon means the control unit must supply the engine with petrol (or other fuel) and delay switching to LPG until the temperature and, thus, the pressure, are high enough to ensure the continuous supply of LPG.
[0005] The amount of time that passes before automatically switching to supply of LPG depends greatly on the climatic conditions. In other words, in severe climatic conditions, there may be some delay before the ideal pressure and temperature conditions are established in the tank.
[0006] Since, in such conditions, the engine runs on petrol (or on another fuel), especially if the journey is particularly short, the LPG system cannot be exploited in the desired manner.
[0007] One solution could consist of installing a pump to suck the LPG and increase the supply pressure of the LPG towards the engine, but this would not be very reliable, in that said pump would be liable to faulty operation in the presence of "poor" quality fuel, which is fairly common in the case of LPG.
[0008] The object of the present invention is to provide a liquefied petroleum gas tank, which overcomes the drawbacks described above in a simple and cost-effective manner.
[0009] According to the present invention there is provided a liquefied petroleum gas tank comprising a shell defining an inner chamber suitable to contain the liquefied petroleum gas; the tank being characterized by also comprising a member housed in said chamber and moveable in order to vary the volume available for the liquefied petroleum gas.
[0010] Said member is preferably defined by a membrane that divides said fluid-tight chamber into two variable volume portions, one for the liquefied petroleum gas, and the other for an inert fluid.
[0011] In order to better understand the present invention a non-limiting preferred embodiment thereof will now be described by way of example with reference to the accompanying figure 1, which is a diagram of a preferred embodiment of the liquefied petroleum gas tank according to the present invention.
[0012] In the attached drawing, designated as a whole by number 1 is a fuel supply system (schematically and partially illustrated), which constitutes part of a motor vehicle and comprises a liquefied petroleum gas (LPG) tank 2.
[0013] The tank 2 comprises a shell 3, which is preferably toroidally shaped and defines an inner chamber 4, one portion 5 of which is occupied inferiorly by the liquid phase and superiorly by the gaseous phase of the LPG.
[0014] The tank 2 also comprises: an inlet device (not illustrated) to supply LPG into the chamber 4; and an outlet device 7 arranged on a lower portion of the shell 3 and connected to a supply circuit (not illustrated), which places the chamber 4 in communication with a pressure reducer (not illustrated) arranged in the engine of the vehicle, upstream of one or more fuel injectors.
[0015] An upper portion of the shell 3 carries a pressure sensor 8, which measures the pressure of the gaseous phase of the LPG in the portion 5 of the chamber 4.
[0016] The chamber 4 houses a member 10, which is carried by the shell 3 and is moveable to vary the volume available for the LPG and thus to vary the pressure of said LPG. In particular, the member 10 is defined by a bag, which is inflated with an inert fluid to reduce the volume available for the LPG, or deflated to achieve the opposite effect. In particular, the wall of the bag 10 is a membrane that comprises an inlet portion 11 fixed to the shell, separates the portion 5 of the fluid-tight chamber 4 from a portion 13 occupied by the inert fluid, and is extendable into the chamber 4 in response to the pressure of the inert fluid in the portion 13 to vary the volume of the portion 5.
[0017] The term "inert" is used to describe a non-oxidizing fluid. In particular, the fluid is defined by an inert gas, such as nitrogen.
[0018] Alternatively, instead of the bag, the member 10 could be defined by any other device or mechanism able to vary the volume and, thus, increase the pressure in the chamber, raising it to a suitable level to enable supply: for example it could be defined by a piston moveable in a relative seat housed in the chamber 4.
[0019] A regulating device 14 inflates/deflates the bag 10 to automatically vary the volume available in the chamber 4 for the LPG according to the pressure measured by the sensor 8 and, consequently, to vary the pressure in the portion 5 of the chamber 4. The device 14 comprises a control and regulating unit 15, which receives the signal from the sensor 8 and activates a compressor or a pump 17 arranged along a pipe 18 in response to the value of said signal. The pipe 18 joins, in a fluid-tight manner, the inlet portion 11 to a tank 20, containing the fluid with which the bag 11 is to be inflated.
[0020] The compressor or pump 17 is associated with a two-way valve 22, which is arranged along the pipe 18 and is controlled by the unit 15 with the compressor or pump 17 to select the direction of the flow of the inert fluid between the tank 20 and the bag 10.
[0021] The unit 15 regulates the passage of fluid from and towards the bag 10 so as to maintain the pressure in the chamber 4 at around a desired value (for example approximately 15 bar), in order to ensure sufficient pressure upstream of said pressure reducer.
[0022] Alternatively or in combination with the pressure in the portion 5 of the chamber 4, the control performed by the unit 15 could be based on other parameters measured by suitable sensors, for example it could be based on the temperature measured in an area of the system 1 where it is bi-univocally related to the pressure of the LPG, and/or be based on the pressure of the LPG in another part of the system 1. For instance, the unit 15 could control the passage of fluid from and towards the bag 10 directly as a function of the pressure upstream of said pressure reducer, for example to maintain said pressure at values of around 3-4 bar.
[0023] When the vehicle is started and when the temperature of the tank 2 is relatively low, the pressure in the portion 5 of the chamber 4 is also relatively low; if the pressure of the LPG is lower than the self-supply threshold the unit 15 automatically activates the inflation of the bag 10: the increase in the volume of the bag 10 causes an increase in the pressure in the portion 5 up to the desired value and, thus, causes an increase in the pressure of the LPG in the supply circuit upstream of the pressure reducer, thus fostering the establishment of ideal conditions for supplying LPG to the injectors.
[0024] The device 14 is deactivated gradually, that is to say the bag 10 is gradually deflated so that the fluid returns to the tank 20, as the heat from, for instance, the vehicle exhaust system tends to increase the temperature and, thus, the pressure in the portion 5 of the chamber 4.
[0025] From the above description it is apparent that the device 14 enables the engine to run on LPG immediately even at start-up, that is to say without the need to supply another fuel while waiting for the system 1 to warm up before supplying LPG: this satisfies the increasing demand for systems based on the exclusive use of a gaseous fuel to power the engine of the vehicle, instead of petrol or diesel.
[0026] Moreover, the bag 10 is relatively light, it is relatively simple to connect to the shell 3 and to the pipe 18 in order to guarantee fluid-tightness, and has no moving parts or parts that slide against one another and on which tightness must also be guaranteed.
[0027] Lastly, it is clear that modifications and variations may be made to the tank 2 described and illustrated herein without departing from the scope of the present invention, as set forth in the appended claims.
[0028] In particular, to introduce the fluid into the bag 10 there could be provided a system different from the pump or compressor 17, and/or the pump or compressor 17 could be integrated into the tank 20. Instead of gas, the fluid for the bag 10 could also be defined by a liquid; and/or the bag 10 could be replaced with a flat membrane, joined along its entire edge to the shall 3 so as to divide the portions 5 and 13, and deformable or extendible in order to move in the chamber 4 and vary the volumes of the portions 5 and 13.
1. Liquefied petroleum gas tank (2) comprising a shell (3) defining an inner chamber
(4) suitable to contain the liquefied petroleum gas; the tank being characterized by also comprising a member (10) housed in said chamber (4) and moveable in order to
vary the volume available for the liquefied petroleum gas.
2. Tank according to claim 1, characterized in that said organ (10) is defined by a membrane that divides said fluid-tight chamber (4)
into two variable volume portions (5, 13), one for the liquefied petroleum gas, and
the other for an inert fluid.
3. Tank according to claim 2, characterized in that said membrane is joined in a fixed position to said shell (3), and is deformable
or extendible in response to the pressure of said inert fluid.
4. Tank according to claim 3, characterized in that said membrane is the wall of an inflatable bag (10).
5. Tank according to claim 4, characterized in that said inflatable bag (10) has an inlet portion (11) joined in a fixed position to
said shell (3).
6. Tank according to any one of the previous claims, characterized by comprising a pressure sensor (6) carried by said shell (3) in a position such as
to measure the pressure of the liquefied petroleum gas in said chamber (4).
7. Fuel supply system (1) comprising:
- a tank (2) made according to any one of the previous claims, and
- a control device (14) comprising:
a) at least one sensor (6) to measure a value indicating the pressure of the liquefied petroleum gas;
b) activating means (17) to move said member (10) and, consequently, vary the volume available for the liquefied petroleum gas in said tank (2);
c) control means (15) to control said activating means (17) in response to the measured value.
8. System according to claim 7, characterized in that said activating means comprise a compressor or a pump (17).
9. System according to claim 8, characterized by comprising a pipe (18) that connects said pump or compressor (17) to an isolated
variable volume portion (13) constituting part of said chamber (4).
10. System according to claim 9, characterized by comprising a container (20) for an inert fluid, and in that said pump or compressor
(17) is controlled in both directions to move said inert fluid between said isolated
portion (13) and said container (20).