Method for starting an internal combustion engine

Abstract

Method For Starting An Internal Combustion Engine A method of starting a gas fuelled internal combustion engine comprising opening a gas flow control valve to provide a supply of a gaseous fuel to a fuel supply rail when the engine is inoperative and then closing the gas flow control valve to shut-off the supply of gaseous fuel to the fuel supply rail while the engine remains inoperative An engine start is initiated while the gas flow control valve is shut. Before the gas flow control valve is re-opened, it is determined if the engine is in a stable running condition by determining that at least one predetermined stable engine running condition is satisfied. If it is determined that the engine is in a stable running condition, the gas flow control valve is re-opened.

Description

[0001] Method For Starting An Internal Combustion Engine

[0002] Field of the invention

[0003] The present invention relates to a method of starting an internal combustion engine. More particularly, the present invention relates to a method of starting a gas fuelled internal combustion engine. The present invention also relates to a vehicle comprising an engine management system and / or a non-transitory, computer-readable storage medium.

[0004] Background to the invention

[0005] Internal combustion engines which are fuelled by liquid fuels such as gasoline or diesel are well known. In recent years, internal combustion engines which are fuelled by gaseous fuels - such as compressed natural gas (CNG) or hydrogen - have become more popular as efforts are made to move to cleaner burning fuels.

[0006] Electromagnetically actuated spring controlled fuel injectors are used in both liquid and gas fuelled engines. For a typical inwardly opening fuel injector, a valve pin is maintained in the closed position by a spring and the pressure of the fuel in the fuel rail. At an appropriate moment (as determined by the engine timing) the electromagnetic coil of the injector is energised causing the pin to move outwardly, away from the cylinder, against the closing force of the spring and the pressure in the fuel rail. Fuel is then injected into the cylinder via the open injector valve. The injector valve is closed by the spring force and fuel pressure when the electromagnetic coil is de-energised.

[0007] Cold, inoperative, internal combustion engines can be difficult to start. One of the reasons for this is thought to be that the opening force generated by the electromagnets of the fuel injectors is insufficient to overcome the combined force of the spring, the fuel pressure and frictional forces between the injector valve and valve seat. When the engine is cold, dimensional tolerances between moving components such as the injector valves and valve seats may be reduced due to the contraction of materials at cooler temperatures. The additional friction that this creates may be sufficient to prevent the injector valve from opening.

[0008] Another contributing factor to the difficulty of starting cold internal combustion engines may be the phenomenon of regulator ‘lock-up’, a condition that can arise with mechanical gas regulators at no, or low, gas flow. A characterising feature of regulator ‘lock-up’ is the regulator regulating the gas pressure to a pressure slightly above the rated pressure of the regulator until the gas flow rate is above a certain minimum. Additional gas pressure in the fuel rail at engine start up when the gas flow rate is low may contribute to the forces acting to prevent injector valve opening.

[0009] It is against this background that the invention is devised.

[0010] Statements of the invention

[0011] According to an aspect of the present invention, a method is provided, comprising: opening a gas flow control valve to provide a supply of a gaseous fuel to a fuel supply rail when the engine is inoperative; closing the gas flow control valve to shut-off the supply of gaseous fuel to the fuel supply rail when the engine is inoperative; initiating an engine start while the gas flow control valve is shut; determining if the engine is in a stable running condition, wherein determining that the engine is in a stable running condition comprises determining that at least one predetermined stable engine running condition is satisfied, and if it is determined that the engine is in a stable running condition, opening the gas flow control valve.

[0012] The method of the present invention is advantageous as the pressure in the fuel rail drops as fuel is consumed thereby decreasing the forces that the fuel injectors must overcome to operate. Furthermore, following this, the engine can be run as normal if it is determined that the engine has started stably, i.e. is in a stable running condition. This extra check on the engine running condition prevents gaseous fuel being wasted when the engine does not start stably.

[0013] Optionally the method may comprise: after initiating the engine start and before it is determined that the engine is in a stable running condition, determining if the gas pressure in the fuel supply rail is at or below a first predetermined threshold; if it is determined that the gas pressure in the fuel supply rail is at or below the first predetermined threshold, opening the gas flow control valve; determining if the gas pressure in the fuel supply rail is at or above a second predetermined threshold; and if it is determined that the gas pressure in the fuel supply rail is at or above the second predetermined threshold, closing the gas flow control valve before it is determined that the engine is in a stable running condition. Beneficially, this allows the pressure in the fuel rail to be topped up if it drops below a set threshold.

[0014] Determining that at least one predetermined stable engine running condition is satisfied may optionally comprise at least one of: determining that the engine speed is at or above a predetermined engine speed threshold; determining that the rate of change of the gas pressure in the fuel supply rail is within a predetermined range; and / or determining that a first predetermined period of time has passed since initiating the engine start. Multiple conditions may be required to be satisfied, or only one.

[0015] Determining that at least one predetermined stable engine running condition is satisfied may comprise: determining that the engine speed is at or above the predetermined engine speed threshold; and determining that a second predetermined period of time has passed since the engine speed was last at or above the predetermined engine speed threshold.

[0016] In one example, determining that at least one predetermined stable engine running condition is satisfied may comprise: determining that the rate of change of the gas pressure in the fuel supply rail is within the predetermined range; and determining that a third predetermined period of time has passed since the rate of change of the gas pressure in the fuel supply rail was last within the predetermined range.

[0017] Optionally the method may comprise: after initiating the engine start and before it is determined that the engine is in a stable running condition, determining if: the rate of change of the gas pressure in the fuel supply rail is at or below a predetermined threshold; and if it is determined that the rate of change of the gas pressure in the fuel supply rail is at or below the predetermined threshold, maintaining the gas flow valve closed. Advantageously, this allows the pressure in the fuel rail to drop lower than the first predetermined threshold if the fuel is not being consumed by the engine at the expected rate (indicating that one or more fuel injectors remain inoperative).

[0018] The method may optionally comprise: determining if the gas pressure in the fuel supply rail is at or below a minimum predetermined threshold; if it is determined that the gas pressure in the fuel supply rail is at or below the minimum predetermined threshold, opening the gas flow control valve. Beneficially this ensures that the pressure in the fuel rail cannot drop below a minimum pressure.

[0019] The method may comprise performing a leak test before initiating the engine start.

[0020] According to another aspect of the present invention, computer software is provided that, when executed, is arranged to perform the method described above.

[0021] According to a further aspect of the present invention, non-transitory, computer-readable storage medium is provided storing instructions thereon that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out the method described above.

[0022] According to a still further aspect of the present invention, an engine management system is provided comprising the non-transitory, computer-readable storage medium of claim 10.

[0023] According to a yet further aspect of the present invention, a vehicle is provided comprising the engine management system described above, or the non-transitory, computer-readable storage medium described above.

[0024] Brief description of the drawings

[0025] A non-limiting example of the present invention will now be described with reference to the following drawings in which:

[0026] Figure 1 shows a schematic view of a gas fuelled internal combustion engine system;

[0027] Figure 2 shows a chart of engine speed, fuel rail pressure, and injection valve opening for a prior art method of starting an internal combustion engine;

[0028] Figure 3 shows a chart of engine speed, fuel rail pressure, and injection valve opening for a method of starting an internal combustion engine according to the present invention;

[0029] Figure 4 shows a flowchart of the method of starting an internal combustion according to the present invention;

[0030] Figure 5 shows an expanded flowchart of the method of Figure 4;

[0031] Figure 6 shows an expanded flowchart of the method of Figures 4 and 5; and

[0032] Figure 7 shows a schematic illustration of a vehicle comprising an engine management system for implementing the method of the present invention.

[0033] Detailed description

[0034] Figure 1 is a schematic view of a gas fuelled internal combustion engine system 1 . The internal combustion engine system 1 comprises a gas tank 2 for storing fuel gas at a storage pressure (which is higher than the pressure used in the fuel rail 5). A mechanical pressure regulator 3 is located downstream of the gas tank 2 and upstream of a gas flow control (or shut off) valve 4. In use, when the gas flow control valve 4 is opened, gas flows from the gas tank 2 through the pressure regulator 3 and into the fuel rail 5. The pressure regulator 3 reduces the gas pressure for the storage pressure to the pressure seen in the fuel rail 5. Fuel injectors 6 control delivery of the gas into the cylinders 7. In another example (not shown) the positions of the pressure regulator 3 and gas flow control valve 4 may be reversed such that the pressure regulator 3 is downstream of the gas flow control valve 4.

[0035] Figure 2 is a schematic chart 10 showing the change of engine speed 20, fuel rail gas pressure 30, and injection valve opening 40 with time T for a prior art method of starting an internal combustion engine system such as system 1 described above. At time To the engine crank is turned over by an electric motor so that engine speed 20 increases from zero. A short time later (approximately 0.1 to 3 seconds), at time Ti, the gas flow control valve 4 is opened. The gas flow control valve 4 is closed again at time T2. In the time interval between Ti and T2(approximately 0.1 to 3 seconds) the engine speed rises to Si , and the pressure in the fuel rail 5 rises. The pressure in the fuel rail 5 reaches its first peak Pi. This may be, for example, approximately 10 percent or more above the rated pressure of the gas regulator 3, and is reached shortly after the gas flow control valve 4 is closed at T2.

[0036] In time period TA (between time T2and T3> a leak test is performed. T can be flexibly set based upon system requirements. During the leak test, the pressure in the fuel rail 5 may decrease to pressure P2. The pressure P2is not critical but may be higher than the rated pressure of the gas regulator 3. Provided that the pressure decrease from Pi to P2is within an acceptable threshold, the leak test is passed and the gas flow control valve 4 is reopened at time T3when an engine start is initiated. Provided that the engine starts, at time T4 the engine speed has reached speed S2, which indicates that the engine is in a stable running condition.

[0037] As indicated by the fuel rail gas pressure trace 30 in Figure 2, in the time period between T2and T3 the gas pressure in the fuel rail 5 increases to pressure P3. This increase is due to regulator ‘lock-up’ as discussed above. Once the fuel flow rate is sufficient, the gas regulator 3 is able to regulate the gas to the rated pressure P4.

[0038] As mentioned above, cold, inoperative, internal combustion engines can be difficult to start. One of the reasons for this is thought to be that the opening force generated by the electromagnets of the fuel injectors 6 is insufficient to overcome the combined force of the spring, the fuel pressure and frictional forces between the injector valve and valve seat when the engine is cold.

[0039] Figure 3 is a schematic chart 100 showing the change of engine speed 120, fuel rail gas pressure 130, and injection valve opening 140 with time T for an alternative method of starting an internal combustion engine system such as system 1 described above. The initial phase of the engine start up illustrated in chart 100 is the same as that discussed above for chart 10 of Figure 2 from time To to time T2 so will not be described again here.

[0040] For the engine start method illustrated by chart 100 of Figure 3, at the end of the leak test at time Ta the gas flow control valve 4 remains closed as illustrated by trace 140. Provided that the leak test is passed, an engine start is nonetheless initiated at time T3. The fuel rail gas pressure trace 130 of Figure 2 differs from the fuel rail gas pressure trace 30 of Figure 1 because the pressure in the fuel rail 5 drops as fuel is used within the engine during the engine start but is not replaced. The gas flow control valve 4 is not opened for normal engine running until after it has been determined that the engine is in a stable running condition as discussed further below.

[0041] After the engine start up is initiated at T3, the pressure in the fuel rail 5 decreases. At time T5 the pressure in the fuel rail 5 reaches pressure P5 which, in this example, is a first predetermined pressure threshold which, when reached before it is determined that the engine is in a stable running condition, triggers a re-opening of the gas flow control valve 4. The gas flow control valve 4 is re-opened at time T5 for a short time until pressure in the fuel rail 5 reaches pressure Pe. In this example pressure Pe is a second predetermined pressure threshold which when reached triggers the gas flow control valve 4 to close once again at time Te. Since it has not yet been determined that the engine is in a stable running condition, the pressure in the fuel rail 5 again begins to decrease while the gas flow control valve 4 remains closed during the engine start.

[0042] At time T7the engine speed is at speed S3 which, in this example, is a predetermined engine speed threshold which, when reached, satisfies a stable running condition of the engine. It is therefore determined that the engine is in a stable running condition and the gas flow control valve 4 is opened for normal engine running as illustrated by trace 140. As shown, in the time following time T7the fuel rail gas pressure increases to pressure P4and the engine speed increases to speed S2. It will be appreciated that the times (T), fuel rail pressures (P) and engine speeds (S) of the start up method illustrated by chart 100 in Figure 3 need not be the same as the times (T), fuel rail pressures (P) and engine speeds (S) as described with reference to the prior art start up method as illustrated by chart 10 in Figure 2, and that the same references have been used for ease of explanation. An example of this is included in the above description where, in the prior art method, the predetermined engine speed threshold which, when reached, satisfies a stable running condition of the engine is S2, whereas in the method of chart 100 it is S3 (where S3<S2).

[0043] Any suitable condition may be used to determine a stable running condition of the engine. For example: determining that the engine speed is at or above a predetermined engine speed threshold, determining that the rate of change of the gas pressure in the fuel supply rail is within a predetermined range, and / or determining that a predetermined period of time has passed since initiating the engine start. In another example, determining that the engine is in a stable running condition may comprise satisfying two conditions such as determining that the engine speed is at or above the predetermined engine speed threshold, and determining that a predetermined period of time has passed since the engine speed was last at or above the predetermined engine speed threshold. Alternatively, in another example, determining that the engine is in a stable running condition may comprise satisfying two conditions such as determining that the rate of change of the gas pressure in the fuel supply rail is within the predetermined range or is above a predetermined threshold, and determining that a predetermined period of time as passed since the rate of change of the gas pressure in the fuel supply rail was last within the predetermined range or was above the predetermined threshold. It will be appreciated that these are a non-exhaustive example and that any combination of the above conditions, or other suitable engine running conditions or condition indicators, may be used in any suitable decision logic.

[0044] It is thought that the method described above with reference to Figure 3 facilitates engine starting by reducing the pressure in the fuel rail 5 thereby reducing the closing forces acting on the fuel injector valve during engine start up. For the pressure to begin to drop in the fuel rail 5 at least one on the fuel injectors must operate when the engine start up is initiated. Furthermore, following this, the engine can be run as normal if it is determined that the engine has started stably, i.e. is in a stable running condition. This extra check on the engine running condition prevents gaseous fuel being wasted when the engine does not start stably.

[0045] In the example described above with reference to Figure 3 a leak test is performed between times T2and T3. It is currently standard practice to complete a leak test before start up of gas fuelled engines for safety and regulatory reasons. It will be understood that the performance of a leak test is not essential to the engine start up method described above with reference to Figure 3. The method may be completed without the leak test by opening and then closing the gas flow valve to pressurise the fuel rail, and then initiating an engine start which the gas flow control valve is closed without conducting a leak test.

[0046] Figure 4 shows a flowchart 150 of the method of starting an internal combustion as illustrated in chart 100 of Figure 2. In a first step 151 the gas flow control valve 4 is opened to provide a supply of a gaseous fuel to the fuel supply rail 5 when the engine is inoperative. In a second step 152 the gas flow control valve 4 is closed shut-off the supply of the gaseous fuel to the fuel supply rail 5 while the engine remains inoperative. In a third step 153 an engine start is initiated while the gas flow control valve 5 is shut. In a fourth step 161 it is determined if the engine is in a stable running condition, and in a fifth step 162, if it is determined that the engine is in a stable running condition, the gas flow control valve 4 is re-opened. If at step 161 it is determined that the engine is not in a stable start condition, the method may return to the beginning of step 161 as illustrated.

[0047] Figure 5 shows an expanded flowchart of the method 150 described above. After the third step 153 in which the engine start is initiated, and before it is determined that the engine is in a stable running condition at step 161 , in step 154 it is determined if the gas pressure in the fuel supply rail 5 is at or below a first predetermined threshold. If it is determined that the gas pressure in the fuel supply rail 5 is at or below the first predetermined threshold the gas flow control valve 4 is opened at step 155. It is then determined if the gas pressure in the fuel supply rail 5 is at or above a second predetermined threshold in step 156, and if it is determined that the gas pressure in the fuel supply rail is at or above the second predetermined threshold, the gas flow control valve is closed again in step 157. The method then moves onto step 161 as described above. If at step 161 it is determined that the engine is not in a stable start condition, the method may return to step 154 as illustrated. If it is determined that the gas pressure in the fuel supply rail 5 is not at or below the first predetermined threshold in step 154, the method moves onto step 161 as described above. If it is determined that the gas pressure in the fuel supply rail 5 is not at or above the second predetermined threshold in step 156, the method returns to the beginning of step 156 as illustrated.

[0048] Figure 6 shows an expanded flowchart of the method 150 described above. After the third step 153 in which the engine start is initiated, and before it is determined that the engine is in a stable running condition at step 161 , in step 158 it is determined if the rate of change of the gas pressure in the fuel supply rail 5 is at or below a predetermined threshold. If it is determined that the rate of change of the gas pressure in the fuel supply rail 5 is at or below the predetermined threshold in step 158, the gas flow valve 4 is kept closed in step 159. This may be done by sending an instruction to actively keep the gas flow control valve 4 closed, or it may be done by failing to send an instruction to open the gas flow control valve 4. At step 160 a check is done to see if the gas pressure in the fuel supply rail 5 is at or below a minimum predetermined threshold beyond which the pressure in the fuel rail 5 may not fall. If it is determined that the gas pressure in the fuel supply rail 5 is at or below the minimum predetermined threshold, the gas flow control valve 4 is opened at step 155. If it is determined that the gas pressure in the fuel supply rail 5 is not at or below the minimum predetermined threshold, the method moves onto step 161 as described above. If it is determined that the rate of change of the gas pressure in the fuel supply rail 5 is not at or below the predetermined threshold in step 158, the method moves onto step 154 as described above.

[0049] The method illustrated in Figure 6 and described above is an example only. It will be appreciated that the gas flow rate check of step 158 could be undertaken at another position in the flow logic and that placing this flow immediately after step 153 is not essential.

[0050] Figure 7 shows a schematic illustration of a vehicle 200 comprising an engine management system 210 for implementing the method described herein. The engine management system 210 comprises a non-transitory, computer-readable storage medium 211 which stores instructions thereon that, when executed by one or more electronic processors 212, causes the one or more electronic processors 212 to carry out the method described herein. The instructions may be in the form of software to be run on a computer. It will be appreciated that the non-transitory, computer-readable storage medium 211 and the one or more electronic processors 212 need not be part of the engine management system 210 and may be part of another system of the vehicle 200 or a system of their own.

[0051] It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

Claims1 . A method of starting an internal combustion engine, the method comprising: opening a gas flow control valve to provide a supply of a gaseous fuel to a fuel supply rail when the engine is inoperative; closing the gas flow control valve to shut-off the supply of gaseous fuel to the fuel supply rail when the engine is inoperative; initiating an engine start while the gas flow control valve is shut; determining if the engine is in a stable running condition, wherein determining that the engine is in a stable running condition comprises determining that at least one predetermined stable engine running condition is satisfied, and if it is determined that the engine is in a stable running condition, opening the gas flow control valve.

2. The method of claim 1 , comprising: after initiating the engine start and before it is determined that the engine is in a stable running condition, determining if the gas pressure in the fuel supply rail is at or below a first predetermined threshold; if it is determined that the gas pressure in the fuel supply rail is at or below the first predetermined threshold, opening the gas flow control valve; determining if the gas pressure in the fuel supply rail is at or above a second predetermined threshold; and if it is determined that the gas pressure in the fuel supply rail is at or above the second predetermined threshold, closing the gas flow control valve before it is determined that the engine is in a stable running condition.

3. The method of claim 1 or 2, wherein determining that at least one predetermined stable engine running condition is satisfied comprises at least one of: determining that the engine speed is at or above a predetermined engine speed threshold; determining that the rate of change of the gas pressure in the fuel supply rail is within a predetermined range; and / or determining that a first predetermined period of time has passed since initiating the engine start.

4. The method of claim 3, wherein determining that at least one predetermined stable engine running condition is satisfied comprises:determining that the engine speed is at or above the predetermined engine speed threshold; and determining that a second predetermined period of time has passed since the engine speed was last at or above the predetermined engine speed threshold.

5. The method of claim 3 or 4, wherein determining that at least one predetermined stable engine running condition is satisfied comprises: determining that the rate of change of the gas pressure in the fuel supply rail is within the predetermined range; and determining that a third predetermined period of time has passed since the rate of change of the gas pressure in the fuel supply rail was last within the predetermined range.

6. The method of any preceding claim, comprising: after initiating the engine start and before it is determined that the engine is in a stable running condition, determining if: the rate of change of the gas pressure in the fuel supply rail is at or below a predetermined threshold; and if it is determined that the rate of change of the gas pressure in the fuel supply rail is at or below the predetermined threshold, maintaining the gas flow valve closed.

7. The method of claim 6, comprising: determining if the gas pressure in the fuel supply rail is at or below a minimum predetermined threshold; if it is determined that the gas pressure in the fuel supply rail is at or below the minimum predetermined threshold, opening the gas flow control valve.

8. The method of any preceding claim, comprising performing a leak test before initiating the engine start.

9. Computer software that, when executed, is arranged to perform a method according to any one of claims 1 to 8.

10. A non-transitory, computer-readable storage medium storing instructions thereon that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out the method of any one of claims 1 to 8.

11. An engine management system comprising the non-transitory, computer-readable storage medium of claim 10.

12. A vehicle comprising the engine management system of claim 11 or the non-transitory, computer-readable storage medium of claim 10.

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