CLIAMS:We claim:
1. A method of determining pressure of a gaseous fuel in a fuel rail (16) of a vehicle, said method comprising:
determining at least one of real time fuel injection duration based on driver demand;
computing mass flow rate of said gaseous fuel based on said real time fuel injection duration and a fuel-cylinder pressure; and
retrieving said pressure of said gaseous fuel in said fuel rail (16) from at least one pre-stored rail pressure map based on said computed mass flow rate of said gaseous fuel and said real time fuel-cylinder pressure.

2. The method as claimed in claim 1, wherein said pre-stored rail pressure map comprises rail pressure values measured beforehand corresponding to each mass flow rate of gaseous fuel at a plurality of fuel-cylinder pressures.

3. A method of determining abnormal-pressure condition of a gaseous fuel in a fuel rail (16) of a vehicle, said method comprising:
monitoring fuel injection duration over a time period at a real time fuel-cylinder pressure; and
judging abnormal-pressure condition of the gaseous fuel in the fuel rail based on the monitoring result.

4. The method of claim 3 further comprises detecting said under-pressure of condition said gaseous fuel in said fuel rail (16), if said fuel injection duration increases over said time period.

5. The method of claim 3 further comprises detecting said over-pressure condition of said gaseous fuel in said fuel rail (16), if said fuel injection duration decreases over said time period.
6. An electronic controller (22) for determining pressure of a gaseous fuel in a fuel rail (16) of a vehicle, said electronic controller (22) adapted to:
determine at least one of real time fuel injection duration based on driver demand;
compute a mass flow rate of gaseous fuel based on said real time fuel injection duration and a fuel-cylinder pressure; and
retrieve pressure of said gaseous fuel in said fuel rail (16) that correspond to said computed mass flow rate of gaseous fuel and said real time fuel-cylinder pressure from a pre-stored rail pressure map.

7. The electronic controller (22) as claimed in claim 6, wherein said pre-stored rail pressure map is present in a memory of said electronic controller (22).

8. The electronic controller (22) of claim 6 further determines at least one of an under-pressure condition and an over-pressure condition of a gaseous fuel in a fuel rail (16) of a vehicle, by monitoring fuel injection duration over a time period at a real time fuel-cylinder pressure.

9. The electronic controller (22) of claim 8 detects said under-pressure condition of said gaseous fuel in said fuel rail (16), if said fuel injection duration increases over said time period.

10. The electronic controller (22) of claim 8 detects said over- pressure condition of said gaseous fuel in said fuel rail (16), if said fuel injection duration decreases over said time period.
,TagSPECI:Field of the invention
[0001] This invention relates to a method of determining pressure of a gaseous fuel in a fuel rail of a vehicle. More particularly, it relates to determining pressure of the gaseous fuel in the fuel rail of a gaseous fuel vehicle, or a bi-fuel vehicle without using a fuel pressure sensor.
[0002] Background of the invention
[0003] In a gaseous fuel system, natural gas may be compressed and stored in a cylinder at high pressure. A pressure regulator is used to supply the natural gas to a fuel rail. The fuel rail is defined as a container or an accumulator where fuel is stored before it is injected into the engine. The pressure regulator reduces the high pressure natural gas into lower pressures as required for particular application. The low pressure natural gas is thus supplied to the fuel rail.
[0004] A pressure sensor is mounted on the fuel rail for monitoring the pressure of the natural gas in the fuel rail. Pressure monitoring is critical as it is required to regulate fuel metering into the engine. However, sometimes it is unable to mount the pressure sensor on the fuel rail because of size of the pressure sensor, pressure range that can be detected by the pressure sensor, or it becomes unable to mount the pressure sensor on certain specific material of the fuel rail such as plastic. Hence a technique for determining the pressure of the fuel rail without using a pressure sensor is required. Also, elimination of pressure sensor reduces system cost.
[0005] Brief description of the accompanying drawings
[0006] Figure 1 is a block diagram of a gaseous fuel supply system of a vehicle, in accordance with an embodiment of the present disclosure; and
[0007] Figure 2 is a flowchart that illustrates a method of determining pressure of a gaseous fuel in a fuel rail of a vehicle, in accordance with an embodiment of the present disclosure.
[0008] Detailed description
[0009] Figure 1 is a block diagram of a gaseous fuel supply system, in accordance with an embodiment of the present disclosure.
[00010] The gaseous fuel supply system comprises cylinder 12 that stores the gaseous fuel at high pressures. Usually, the gaseous fuel is stored at pressure between 200bar and 300bar. Examples of the gaseous fuel, can include but not limited to, Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG), hydrogen, etc. The cylinder 12 comprises a valve for opening and closing the cylinder 12. The valve may be manually controlled or electronically controlled. When the valve is opened, the high pressure gaseous fuel travels through the high pressure line 18 to a pressure regulator 14.
[00011] The pressure regulator 14 is adapted to reduce the high pressure of the gaseous fuel into a low pressure that is required to be maintained in the fuel rail 16. The fuel rail 16 is defined as a container or an accumulator where fuel is stored before it is injected into the engine. Suitable pressure is required to be maintained in the fuel rail 16 to control the metering based on the engine operating condition. The pressure regulator 14 may be a diaphragm type regulator. However it should be noted that the pressure regulator 14 is not limited to the diaphragm type regulator and various other pressure regulators may also be used. The low pressure gaseous fuel entering the fuel rail is injected into the engine using one or more injectors such as injectors 20a, 20b and 20c.
[00012] In prior arts, a pressure sensor is mounted on the fuel rail for determining the pressure of the fuel in the fuel rail. In the present disclosure, the pressure sensor is not used for determining the pressure of the fuel in the fuel rail 16. An electronic controller 22 present in the vehicle is adapted to determine or estimate the pressure of the fuel in the fuel rail 16 without the pressure sensor. Further, the electronic controller 22 is also adapted to detect an over-pressure condition or an under-pressure condition in the fuel rail 16. The method of determining the pressure of a fuel rail 16 in a gaseous fuel system is explained in detail in the below paragraphs.
[00013] The electronic controller 22 is adapted to store a map comprising rail pressures measured for a plurality of mass flow rate of gaseous fuel at a plurality of fuel-cylinder pressures and a plurality of temperature values of the gaseous fuel in a memory. This map is referred as a rail-pressure map. The mass flow rate of gaseous fuel is referred to as quantity of gaseous fuel required for the engine at a particular engine operating condition. The mass flow rate of gaseous fuel is, in one example, measured in kg/hour. The fuel-cylinder pressure is the high pressure at which the gaseous fuel is stored in the cylinder 12. For a particular fuel-cylinder pressure, the rail pressure is measured for various mass flow rate of gaseous fuel and temperature. The rail pressure that is measured using a pressure sensor during a pre-calibration stage for each mass flow rate of the gaseous fuel are stored in a rail pressure map. Similarly, at different fuel-cylinder pressures, the rail pressure is measured for each mass flow rate of the gaseous fuel. Such measured rail pressures at various fuel-cylinder pressures and temperatures are stored in the rail pressure map that is stored in a memory which is accessible by the electronic controller 22.
[00014] In one embodiment, the rail pressure map comprises same rail pressure for wide range of fuel-cylinder pressures and temperatures. If the pressure regulator 14 is such that for a wide range of fuel-cylinder pressures and temperatures, the rail pressure for each mass flow rate is not changing then the pre-stored rail pressure map will contain same rail pressure corresponding to each mass flow rate of gaseous fuel for wide range of fuel-cylinder pressures and temperatures. For example, if the rail pressure is 3 bar for a mass flow rate of 20kg/hour CNG then the rail pressure would remain 3 bar for a wide range of fuel-cylinder pressures such as at 200bar cylinder pressure, 300 bar cylinder pressure, 500 bar cylinder pressure and so on. In another example, if the rail pressure is 7 bar for a mass flow rate of 30kg/hour gaseous fuel then the rail pressure would remain 7 bar for a wide range of fuel-cylinder pressures such as at 200bar cylinder pressure, 300 bar cylinder pressure, 500 bar cylinder pressure and so on.
[00015] In one embodiment, there may be one or more pre-stored rail pressure maps stored in the memory. The pressure of the fuel rail is measured for different mass flow rates. When driver demand increases, the mass flow rate also increases. Subsequently, when the driver demand and the mass flow rate decreases, the measured rail pressure may not be exactly same as the pressure values measured during increasing trend of mass flow rate and the driver demand. That is, the rail pressure measured may be P2 for a driver demand D2 (and mass flow rate MF2), when the driver demand increases from D1 to D2. However, the rail pressure measured may be P2’ for the driver demand D2, when the driver demand reduces from D3 to D2. Therefore there may be another rail pressure map that includes rail pressures measured when the mass flow rate of gaseous fuel is decreasing at each fuel-cylinder pressure and temperature. These two different rail pressure maps are pre-stored because the rail pressures are different when the mass flow rate of gaseous fuel is increasing and when the mass flow rate of gaseous fuel is decreasing. Therefore the rail pressures when the mass flow rate of gaseous fuel is increasing and decreasing are recorded separately and stored in memory. Such difference in the rail pressures when the mass flow rate of gaseous fuel is increasing and when the mass flow rate of gaseous fuel is decreasing is due to the working and construction of the pressure regulator 14.
[00016] For the purpose of clear understanding, exemplary rail pressure map when mass flow rate is increasing is shown in table. 1 and exemplary rail pressure map when mass flow rate is decreasing is shown in table. 2.
[00017] Table. 1 [00018] 20kg/hr [00019] 40kg/hr [00020] 60kg/hr [00021] 80kg/hr
[00022] 200/T1 [00023] P11 [00024] P12 [00025] P13 [00026] P14
[00027] 300/T2 [00028] P21 [00029] P22 [00030] P23 [00031] P24

[00032] Table. 2 [00033] 80kg/hr [00034] 60kg/hr [00035] 40kg/hr [00036] 20kg/hr
[00037] 200/T1 [00038] P11 [00039] P12 [00040] P13 [00041] P14
[00042] 300/T2 [00043] P21 [00044] P22 [00045] P23 [00046] P24

[00047] Where, P11, P12, P13, P14, P21, P22, P23, and P24 are rail pressure values when mass flow rate is increasing and;
[00048] P11, P12, P13, P14, P21, P22, P23 and P24 are rail pressure values when mass flow rate is decreasing.
[00049] In another embodiment, only one rail pressure map is maintained when the mass flow rate is increasing and decreasing because the rail pressure is same when the mass flow rate is increasing and decreasing. In such cases, there is no need to record rail pressures separately when the mass flow rate of gaseous fuel is increasing and when the mass flow rate of gaseous fuel is decreasing.
[00050] Also, the electronic controller 22 is adapted to compute mass flow rate of the gaseous fuel at particular fuel-cylinder pressure based on real time fuel injection duration. The fuel injection duration is defined as an injector opening time for a particular mass flow rate of gaseous fuel and is determined based on driver demand.
[00051] For determining the pressure of the fuel rail 16 in the gaseous fuel system, the real time fuel injection duration is determined based on the driver demand. Upon determining the real time fuel injection duration, the mass flow rate of gaseous fuel is computed based on the real time fuel injection duration and the fuel-cylinder pressure by the electronic controller 22. Based on the real time fuel injection duration, the intake air is known. Based on the intake air and the fuel-cylinder pressure which is obtained using a high pressure sensor located in the cylinder or in a high pressure line, the mass flow rate of gaseous fuel is computed.
[00052] Once the mass flow rate of gaseous fuel is computed, the rail pressure that corresponds to the computed mass flow rate of gaseous fuel at that particular fuel-cylinder pressure value is retrieved from the pre-stored rail pressure map. Hence the rail pressure is determined/ estimated without any pressure sensor being mounted on the fuel rail 16.
[00053] In the present disclosure, the electronic controller 22 is further adapted to determine an abnormal pressure condition of a gaseous fuel in a fuel rail (16) of a vehicle. The method of determining abnormal pressure condition includes monitoring fuel injection duration over a time period at a real time fuel-cylinder pressure and judging abnormal-pressure condition of the gaseous fuel in the fuel rail based on the monitoring result. The abnormal pressure condition can include either under-pressure condition in the fuel rail 16 or an over-pressure condition in the fuel rail 16. For determining this, the fuel injection duration is monitored over a time period that is pre-specified. The fuel injection duration refers to duration of time the fuel injector is opened for injecting fuel into the engine cylinder. If the fuel injection duration reduces over that time period then an over pressure condition in the fuel rail 16 is determined. Over pressure in the rail leads to more fuel injection and thereby creating a rich mixture. Since, it is rich mixture the lambda controller/sensor at the exhaust pipe will trigger a control signal to the electronic controller 22 so that the required air to fuel ratio is maintained. The control signal triggered by the lambda controller is such that it causes reduction of fuel in order to compliment the rich mixture. For reduction of fuel, the fuel injection duration is reduced. Hence, when the fuel injection duration is monitored over a time period and upon monitoring if it is determined that the fuel injection duration is continuously reduced beyond a threshold value during this time period then it is considered as an over pressure condition in the fuel rail 16.
[00054] Similarly if the fuel injection duration increases over the time period then an under pressure condition in the fuel rail 16 is detected. Under pressure of the fuel in the fuel rail 16 leads to reduced fuel injection into the engine thereby leading to lean mixture. When lean mixture is detected, the lambda controller triggers a control signal to the electronic controller 22 so that the lean mixture tends to get rich for maintaining balanced air to fuel ratio. The control signal is such that it causes increase in the fuel injection. For increasing the fuel injection, the fuel injection duration should be increased. Hence, when the fuel injection duration is continuously increasing beyond a threshold value during this time period then it is considered as an under pressure in the fuel rail 16. Therefore by monitoring the fuel injection duration over a time period, an under pressure or an over pressure is detected in the fuel rail 16.
[00055] Figure 2 is a flowchart that illustrates a method of determining pressure of a gaseous fuel in a fuel rail of a vehicle, in accordance with an embodiment of the present disclosure.
[00056] At step 105, at least one of real time fuel injection duration is determined based on a driver demand.
[00057] At step 110, mass flow rate of gaseous fuel is computed based on the real time fuel injection duration and a fuel-cylinder pressure.
[00058] At step 115, the rail pressure that corresponds to the computed mass flow rate of gaseous fuel and the real time fuel-cylinder pressure is retrieved from a pre-stored rail pressure map.
[00059] The rail pressure map is pre-stored in a memory of an electronic controller 22 and comprises rail pressures corresponding to each mass flow rate of gaseous fuel at a plurality of fuel-cylinder pressures. Further, separate rail pressure maps can be maintained when the mass flow rate of gaseous fuel is increasing and when the mass flow rate of the gaseous fuel is decreasing. When the driver demand is increasing, the mass flow rate also increases. This trend is identified by the controller and the rail pressure map which stores rail pressure values when the mass flow rate of gaseous fuel is increasing is referred to obtain the pressure in the fuel rail for a particular fuel-cylinder pressure and a particular mass flow rate of the gaseous fuel.
[00060] Similarly, when the driver demand is decreasing then the mass flow rate of the gaseous fuel also decreases. In such cases, this trend of decreasing mass flow rate is determined by the electronic controller 22 and the rail pressure map that includes rail pressure values when the mass flow rate of the gaseous fuel is decreasing is referred to determine the pressure in the fuel rail.
[00061] This invention helps to estimate the pressure of the gaseous fuel at the fuel rail precisely without the need for a pressure sensor. Hence cost reduction is achieved. Further, abnormal pressure condition of the fuel rail can be detected easily without using the pressure sensor.
[00062] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to the type of fuel like any gaseous fuel for example, CNG LPG or hydrogen, the type of pressure regulator, technique for determining the fuel injection duration, type of lambda sensor, for example, 2 point lambda sensor or wide lambda sensor are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.