Method of controlling a fuel supply system of an engine of a motor vehicle

A method of controlling a fuel supply system of an engine 10 of a motor vehicle 50 is disclosed in which an engine driven variable output high pressure fuel pump is operated at a high demand level to charge a high pressure fuel accumulator with fuel during a shutdown of the engine and, during a subsequent start-up of the engine, use fuel from the accumulator while operating the high pressure fuel pump at a low demand level. This reduces the fuel consumption of the engine by using kinetic energy from the slowing engine to drive the high pressure fuel pump and increases the deceleration of the engine.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Great Britain Patent Application No. 1222303.8, entitled “A Method of Controlling a Fuel Supply System of an Engine of a Motor Vehicle,” filed on Dec. 12, 2012, the entire contents of which are hereby incorporated by reference for all purposes.

FIELD

This invention relates to motor vehicles and in particular to the control of a fuel system of an engine of a motor vehicle during shutdown and start-up of the engine.

It is known to provide a motor vehicle with an engine stop-start system for automatically stopping and starting the engine whenever it is determined from driver actions that there is an opportunity to do so in order to reduce fuel consumption and reduce emissions from the engine.

However, the inventors herein have recognized potential issues with such engine stop-start systems. As one example, if the time taken to stop and then restart the engine is excessive, the delay may lead to dissatisfaction in a user of the motor vehicle. In addition, such an excessive delay, may also result in actual use problems if the driver wrongly concludes that the system has failed to restart the engine in response to their actions.

In one example, the issues described above may be addressed by a method for . . . controlling a fuel supply system of an engine of a motor vehicle wherein the method comprises, during a shutdown of the engine, operating an engine driven variable output high pressure fuel pump at a high demand level and storing fuel from the high pressure fuel pump in a fuel accumulator and, during a subsequent engine start-up, operating the high pressure fuel pump at a low demand level and supplying fuel from the accumulator to the engine.

In another example, a fuel supply system of an engine of a motor vehicle comprising an engine driven variable output high pressure fuel pump, a fuel accumulator to store fuel at high pressure, a valve means to control the flow of high pressure fuel within the system and an electronic controller to control the operation of the high pressure fuel pump and the valve means, wherein the controller is operable during a shutdown of the engine, to operate the high pressure fuel pump at a high demand level and control the valve means to store fuel from the high pressure fuel pump in the fuel accumulator and is operable, during a subsequent engine start-up, to operate the high pressure fuel pump at a low demand level and operate the valve means so that fuel from the fuel accumulator is supplied to the engine.

DETAILED DESCRIPTION

With reference toFIG. 1there is shown a high level flow chart of a method of controlling a fuel supply system of an engine of a motor vehicle according to the invention.

The method starts at box1which are manual key-on and engine start events. The method then advances to box2where the engine is running and then on to box3where it is checked whether the engine is to be stopped. This can be a manual stop by a driver of the motor vehicle or an automated stop initiated by a stop-start system in the case of a stop-start enabled motor vehicle.

If the engine is not to be stopped the method returns to box2and then cycles between boxes2and3until the engine is to be stopped. When it is determined in box3that the engine is to be stopped the method advances to box4where a variable output high pressure fuel pump for the engine is operated at a high demand level and fuel pumped by the high pressure pump is stored in a high pressure fuel accumulator until, as indicated in box5, the engine has stopped. Preferably, the high pressure fuel pump is operated at its maximum demand level because this will impose the greatest load on the engine. The pressure of the fuel stored in the accumulator is at a pressure suitable for injection into the engine as described with respect to a start-up of the engine hereinafter.

There are two primary advantages associated with the processes described in box4. Firstly, during the subsequent engine cranking and re-start no electricity from the battery and hence no fuel has to be used by the engine to charge the accumulator with high pressure fuel because kinetic energy from the slowing engine is recovered to drive the high pressure pump thereby improving the overall fuel consumption of the engine. Secondly, because operating the high pressure fuel pump at a high demand level requires a considerable driving force to be provided from the engine, the high pressure fuel pump acts as a brake increasing the rate at which the engine slows down. This braking effect will reduce the time taken for the engine to stop after the engine stop is initiated and will also reduce any tendency for the engine to run in reverse (overshoot zero) which is undesirable. In the case of a stop-start enabled motor vehicle the time taken for the engine to stop is important because it significantly affects the minimum cycle time possible for a stop-start event. Therefore, if the engine needs to be restarted as soon as it has stopped, a shorter shutdown period will allow the engine to be started sooner than would otherwise be the case.

After box5the method advances to box6with the engine stopped and, in box6, it is checked whether the engine is to be restarted. If the engine is not to be restarted, the method cycles back through box5to box6with the engine stopped. However, if in box6it is confirmed that the engine is to be started, the method advances from box6to box7. The restart can be a manual one by the driver of the motor vehicle or an automated start initiated by a stop-start system in the case of a stop-start enabled motor vehicle.

In either case, in box7the engine is cranked by a starter motor or any other suitable cranking device such as, for example and without limitation, an integrated starter generator (ISG), the high pressure fuel pump is operated at a low demand level and fuel is recuperated from the accumulator to fuel the engine by means of one or more fuel injectors. Because the fuel stored in the accumulator is at a pressure suitable for injection into the engine via the fuel injectors, there is no need for fuel to be supplied from the high pressure fuel pump during the engine start-up and so the low demand level set is advantageously the minimum demand level possible for the high pressure fuel pump and is preferably a demand level of zero.

One advantage of the use of a low demand level is that it reduces the load normally imposed by the high pressure fuel pump on the engine and therefore reduces the time taken for the engine to reach a self-sustaining rotational speed for the engine and, perhaps more importantly, the time taken to reach a speed Nt where useful torque can be produced by the engine. The speed Nt is an engine speed below which the application of a load to the engine will likely result in stalling of the engine whereas above this speed Nt useful torque can be produced.

One advantage of the use of fuel from the accumulator during the start-up is that, if an engine driven high pressure fuel pump is used to provide fuel for the engine, the engine cannot be started at the first available opportunity because it takes time for the high pressure fuel pump to build pressure after drive to the fuel pump commences. However, by using fuel stored in the accumulator at a pressure that it is suitable for efficient injection to the engine, then, as soon as the first opportunity for injection occurs, fuel can be injected into the engine thereby further reducing the time taken for the engine to reach the self-sustaining speed.

The method advances from box7to box8where it is checked whether the engine has started, that is to say reached a self-sustaining rotational speed where the starter motor can be switched off or disengaged. If the self-sustaining engine speed has not been reached, the method cycles back through box7to box8until the self-sustaining engine speed has been reached.

In the event that the engine has failed to start and the fuel in the accumulator has been exhausted to a level where there is no longer sufficient pressure to provide efficient fuel injection for the engine then, although not shown onFIG. 1, a fault routine is enabled in which fuel is provided from the high pressure fuel pump to the engine. If, after a predetermined period of time, the engine has still not started a warning can be given to the driver of the motor vehicle and starting of the engine can be temporarily inhibited to prevent damage occurring to the starter motor.

Referring back to box8, if the engine has started then the method returns to box2with the engine running.

After the engine has reached the required self-sustaining speed the fuel supply may be switched from the accumulator to the fuel pump or may remain from the accumulator until the pressure in the accumulator falls to a predefined level or a power demand for the engine is above a predefined level.

It will be appreciated that the above method can be ended at any time by a manual key-off event. In the event of a manual key-off event occurring it is preferable if the method steps of box4are used because then fuel is stored without incurring a fuel penalty that can be used in a subsequent key-on and start-up event such as that shown as box1inFIG. 1. That is to say, box1could include the steps shown in box7ofFIG. 1. This has the advantages of reduced fuel use and improved start-up performance. The reduced driving force required from the high pressure fuel pump during start-up would be particularly advantageous in the case of a cold start-up of a diesel engine where the combination of high friction and cranking loads place a considerable strain on the starter motor and associated electrical system.

The above method is particularly advantageous in the case of a stop-start enabled motor vehicle because it significantly reduces the time taken to stop and then restart the engine and so reduces the risk of driver dissatisfaction or erroneous conclusions regarding the operating state of the stop-start system.

With particular reference toFIG. 2there is shown a motor vehicle50having four road wheels ‘W’, a diesel engine10, a fuel supply system100for the engine10and a stop-start system20. Although the invention is described with reference to a diesel engine it will be appreciated that it could be applied to other engine types that utilise a high pressure fuel injection system such as, for example and without limitation, a direct injection gasoline engine.

The engine10is driveably connected in this case to two of the road wheels by a transmission (not shown) but it will be appreciated that the transmission could in other embodiments driveably connect the engine10to all four of the road wheels ‘W’. It will also be appreciated that the invention is not limited to use with a four wheeled road vehicle and could be applied to a vehicle having two wheels or more than four wheels.

A starter motor11is provided to the start when required the engine10. It will however be appreciated that any suitable cranking means could be used.

The fuel system100receives a number of vehicle information inputs25that are used by the fuel supply system100to control the fuelling of the engine10via one or more fuel injectors ‘I’. Such inputs25are well known in the art and may include, for example and without limitation, engine speed, driver demand, mass air flow, air temperature, coolant temperature, ambient temperature and ambient atmospheric pressure.

The fuel supply system includes an electronic controller160and an engine driven variable output high pressure fuel pump130that is driven, as is well known in the art, by a mechanical drive15from one end of a camshaft (not shown) of the engine10. It will however be appreciated by those skilled in the art that other mechanical drive means could be used and that the invention is not limited to the use of a camshaft driven high pressure fuel pump130.

Variable output high pressure fuel pumps are known from, for example and without limitation, US Patent Application 20120177505 and PCT patent publication WO2012113488.

The fuel supply system100is described in greater detail with reference to four embodiments shownFIGS. 3 to 6respectively hereinafter.

The motor vehicle is in this case a ‘stop-start enabled’ motor vehicle50because the engine10can be stopped and started automatically by the stop-start system20based upon driver and vehicle information inputs24,25. It will be appreciated that the invention could be applied to a motor vehicle that is not ‘stop-start enabled’ or to a hybrid motor vehicle whether or not the hybrid vehicle is ‘stop-start enabled’. However, the invention is particularly advantageous with respect to its use on any ‘stop-start enabled’ motor vehicle.

The driver inputs24are inputs that provide information to the stop-start system20regarding operation of vehicle controls such as, for example, the movement or position of an accelerator pedal, a brake pedal or a clutch pedal or the engagement state of the transmission.

The vehicle information inputs26are inputs that provide information to the stop-start system20regarding operation of the motor vehicle50such as, for example and without limitation, the speed of the motor vehicle, engine speed, the temperature of coolant for the engine, the operating state of an air-conditioning unit if fitted, the state of charge of a battery of the motor vehicle.

Such stop-start systems are well known in the art and the functionality and logic applied in such systems is not relevant to the enablement of this invention. It is merely necessary to know that the stop-start system20is operable to stop the engine10when a particular combination of driver input states and vehicle information input states is present and restart the engine10when a further set of driver input states and vehicle information input states is present.

Although the electronic controller160of the fuel supply system100and the stop-start controller20are shown inFIG. 2as separate units it will be appreciated that they could be embodied as a single electronic controller such as a powertrain controller.

Referring now toFIG. 3there is shown in greater detail a first embodiment of the fuel supply system shown inFIG. 2.

The fuel supply system100comprises of a fuel reservoir or fuel tank110used to store fuel for use by the engine10. Fuel is drawn from the fuel tank110by a low pressure fuel pump120and is supplied to an inlet of the variable output high pressure fuel pump130via a low pressure fuel supply line LPS. The high pressure fuel pump130is controlled by the electronic controller160between a minimum demand level and a maximum demand level. The minimum demand level will preferably result in a fuel flow rate from the high pressure fuel pump130of substantially zero and the maximum demand level will result in the maximum possible flow from the high pressure fuel pump130for the current engine speed. When operating at the minimum demand level, the high pressure fuel pump130requires a minimal driving force to be provided from the engine10and, when operating at the maximum demand level, the high pressure fuel pump130requires a high driving force to be supplied from the engine10. Excess or leaked fuel from the high pressure fuel pump130is returned to the fuel tank110via a low pressure return line HPR.

A valve means in the form of a single electronically controlled three way diverter valve190is connected to an output from the high pressure fuel pump130so as to receive a flow of fuel at high pressure therefrom.

The diverter valve190is best understood with reference toFIGS. 10ato 10cand has three selectable fuel flow paths. By way of example, a rotary diverter valve190is shown inFIGS. 10ato 10chaving a body191in which is rotatably mounted a valve member192defining a fuel flow passage193. The body191has first port P1connected to the high pressure fuel pump130, a second port P2connected to a common fuel rail150and a third port P3connected to a high pressure fuel accumulator140.

The diverter valve190is interposed between the high pressure fuel pump130and the common fuel rail150, between the high pressure fuel pump130and the accumulator140and between the accumulator140and the common fuel rail150.

InFIG. 10athe valve member192is shown in a position in which the fuel flow passage193defines a first flow path connecting the high pressure fuel pump130to the common fuel rail150.

InFIG. 10bthe valve member192is shown in a position in which the fuel flow passage193defines a second flow path connecting the high pressure fuel pump130to the accumulator140.

InFIG. 10cthe valve member192is shown in a position in which the fuel flow passage193defines a third flow path connecting the accumulator140to the common fuel rail150.

The valve member192is rotatable by an electric actuator (not shown) in response to a control input from the electronic controller160so that the selection of flow path is controlled by the electronic controller160.

It will be appreciated that alternative forms of three way diverter valve could be constructed and that the invention is not limited to the rotary diverter valve190shown inFIGS. 10ato10c.

Referring back now toFIG. 3, the common fuel rail150is arranged to supply fuel to four fuel injectors I1, I2, I3and I4, the operation of each of which is controlled by the electronic controller160.

Each of the fuel injectors I1, I2, I3and I4supply fuel to the engine10at the timing and volume required based upon a respective control input received from the electronic controller160. Excess fuel from the fuel injectors I1, I2, I3and I4is returned to the fuel tank110via respective low pressure return lines R1, R2, R3and R4.

It will be appreciated that the invention is not limited to use with four fuel injectors and that a fuel supply system have less or more fuel injectors could beneficially utilise the invention.

A fuel pressure sensor170is arranged to sense the pressure of fuel in the common fuel rail150and supply a signal indicative of the sensed pressure to the electronic controller160.

The high pressure accumulator140can be of any suitable construction. U.S. Pat. No. 7,717,077 discloses a free piston acted on by a spring for use as a fuel accumulator. Such an arrangement would be suitable for use but it is preferred if a sealed bellows type of accumulator such as that shown inFIGS. 11aand 11bis used because with such an accumulator no fuel can leak from the accumulator whereas with the free piston accumulator shown in U.S. Pat. No. 7,717,077 there is the potential for fuel to leak past the piston.

The accumulator140is shown inFIG. 11ain an empty state and inFIG. 11bin a full state. The accumulator comprises a body141defining a flow passage142by which fuel can enter or leave a storage volume145defined by a cup shaped piston, a metal bellows144and the body141. The piston143supports the bellows144and is slidingly supported by the body141. A spring146biases the piston143towards the end of the body141at which fuel enters or leaves the storage volume145via the flow passage142. The bellows144is sealed to both the body141and the piston143and so there is no possibility of leakage of fuel. It will be appreciated that in practice the body141will not be a single component but will be constructed to enable assembly of the various components143,144,146.

A fuel pressure sensor180is arranged to sense the pressure of fuel in the accumulator140and supply a signal indicative of the sensed pressure to the electronic controller160.

Operation of the fuel supply system100will now be described with reference toFIGS. 7, 8 and 9.

FIG. 7shows a relationship between engine speed and time during an engine shutdown for a prior art engine having a stop-start system and fuel supply system with no fuel accumulator and an engine10having a stop-start system20and a fuel supply system100constructed in accordance with this invention.

Referring firstly to the prior art situation, initially the engine is idling and then at time T0the stop-start system initiates an engine shutdown. In the case of the prior art engine the demand level for the high pressure fuel pump is then reduced to the minimum level because fuel is not required in a conventional fuel supply system having no accumulator. The engine begins to slow at time T0and will continue to slow, as shown by the line E2sd, until the engine finally stops after a period of engine reverse rotation when T2seconds have expired from the time T0.

Referring now to the situation when a fuel supply system100constructed in accordance with this invention is used, initially the engine10is, as before, idling and then, as before, at time T0the stop-start system20initiates an engine shutdown. However, in this case the demand level for the high pressure fuel pump130is then increased to or maintained at a high demand level and preferably the maximum possible demand level and fuel is supplied from the high pressure fuel pump130to the accumulator140. The engine10begins to slow at time T0and will continue to slow, as shown by the line E1sd, until the engine10finally stops after a period of engine reverse rotation when T1seconds have expired from the time T0.

The engine10will slow more rapidly in this case because it is required to drive the high pressure fuel pump130to charge the accumulator140. In addition, because of the braking effect of the high pressure fuel pump130on the engine10, the magnitude and duration of any reverse engine rotation is reduced.

Therefore the time taken for the engine to stop has been reduced from T2seconds, in the case of a prior art engine, to T1seconds, in the case of the engine10having a fuel supply system according to the invention, by using the high pressure fuel pump130to slow the engine10.

Operation of the fuel supply system100shown inFIG. 3during the shutdown period is as follows.

Prior to time T0the electronic controller160controls the fuel injectors I1, I2, I3and I4so as to provide fuel at the correct timing and volume to the engine10, sets the demand level for the high pressure fuel pump130to a level required to satisfy the fuel usage needs of the engine10and controls the three way diverter valve190so that it adopts the position shown inFIG. 10awith the valve member192in a position in which the fuel flow passage193provides a flow path connecting the high pressure fuel pump130to the common fuel rail150.

While in this operating state the fuel supply system100operates as a conventional fuel supply system with fuel being drawn from the fuel tank110by the low pressure fuel pump120, supplied to the high pressure fuel pump130from the low pressure fuel pump120, pressurized by the high pressure fuel pump130under the control of the electronic controller160, supplied to the common fuel rail150from the high pressure fuel pump130and drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4for injection into the engine10to meet the current operating demands of the engine10.

At time T0the electronic controller160receives an indication from the stop-start system20that the engine10is to be stopped. In response to this indication from the stop-start system20, the electronic controller160, switches off the fuel injectors I1, I2, I3, I4, sets the demand level for the high pressure fuel pump130to a high level, preferably a maximum demand level, and controls the three way diverter valve190so that the valve member192adopts the position shown inFIG. 10bin which the fuel flow passage193defines a flow path connecting the high pressure fuel pump130to the accumulator140. Fuel is then pumped into the accumulator140by the high pressure fuel pump130until the engine10has stopped rotating.

In a case where a signal from the fuel pressure sensor180associated with the accumulator140indicates that a maximum safe operating pressure for the accumulator140has been reached before the engine10stops rotating fuel is vented back to the fuel tank110. This has the advantage that the high pressure fuel pump130is still operating at high demand increasing the deceleration of the engine10.

When the time T1has elapsed, the engine10has stopped rotating and the electronic controller160is then preferably operable to control the three way diverter valve190so that the valve member192adopts the position shown inFIG. 10ain which the fuel flow passage193provides a flow path connecting the high pressure fuel pump130to the common fuel rail150. The common fuel rail150is therefore isolated from the pressurised fuel within the accumulator140while the engine10is stationary thereby reducing the risk of leakage from the fuel injectors I1, I2, I3and I4while the engine10is stationary.

FIG. 8shows a relationship between engine speed and time during an engine start-up for a prior art engine having a stop-start system and fuel supply system with no fuel accumulator and an engine10having a stop-start system20and a fuel supply system100constructed in accordance with this invention.

Referring firstly to the prior art situation, initially the engine is stationary and then at time T0′ the stop-start system initiates an engine start-up. In the case of the prior art engine the demand level for the high pressure fuel pump is at a high level in order to provide fuel for the engine and the fuel injectors are controlled to supply the required quantity of fuel to the engine. The engine begins to rotate at time T0′ due to the action of a starter motor and will continue to speed up, as shown by the line E2su, and, at time t2, the engine has reached a speed Nt where it can generate useful power.

Referring now to the situation where a fuel supply system100constructed in accordance with this invention is used. As before, initially the engine10is stationary and then, as before, at time T0′ the stop-start system20initiates an engine start-up. However, in this case, the demand level for the high pressure fuel pump130is set to a low demand level and is preferably set to a zero demand level. This is made possible because fuel is supplied not by the high pressure fuel pump130but from the accumulator140. The engine10begins to rotate at time T0′ due to the action of the starter motor11and will continue to accelerate, as shown by the line E1sd, and, at time t1, the engine10has reached the speed Nt where it can generate useful power.

The engine10will accelerate more rapidly in this case because it is not required to drive the high pressure fuel pump130to provide fuel to the engine10. In addition, because the fuel is supplied from the accumulator140, there is no time delay waiting for the high pressure fuel pump130to speed up and generate fuel pressure, the required fuel pressure is immediately available from the accumulator140and the first opportunity to inject fuel can be utilised.

Therefore the time taken for the engine to reach the speed Nt from stationary (T0′) is reduced from t2seconds, in the case of a prior art engine, to t1seconds, in the case of an engine having a fuel supply system according to the invention.

At some point in time after reaching the engine speed Nt, fuelling of the engine10is switched back to the high pressure fuel pump130.

Operation of the fuel supply system100shown inFIG. 3during engine start-up is as follows.

At time T0′ or at a point in time after the engine10has sensed to have stopped but before the time T0′ the electronic controller160is also operable to set the demand level for the high pressure fuel pump130to a low level and preferably to the lowest possible level which in some cases is a zero flow demand level.

At time T0′, the diverter valve190is switched from the position shown inFIG. 10ato the position shown inFIG. 10cto supply fuel from the accumulator140to the engine10. This switching occurs very rapidly and will have no significant adverse effect on starting of the engine10because the time taken to switch the valve190is considerably less than the time taken for the first available cylinder of the engine10to reach a potential ignition position.

Therefore, at time T0′ when the stop-start system20indicates that the engine10is to be started and cranking of the engine commences, the electronic controller160can control whichever of the fuel injectors I1, I2, I3and I4has the first opportunity to inject fuel to the engine10to commence injection of fuel into the engine10without delay. As fuel is drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4it is replaced by fuel supplied to the common fuel rail150from the accumulator140thereby maintaining the fuel pressure in the fuel rail150at an appropriate pressure for efficient injection into the engine10.

Because the volume of the accumulator140is finite, at some point in time after time T0′ the electronic controller160must control the diverter valve190to switch the flow path from the accumulator140to the high pressure fuel pump130. This can occur when the pressure sensor170associated with the common fuel rail150indicates that the fuel pressure is beginning to drop, when a predefined volume of fuel that is less than the known volume of the accumulator140has been injected into the engine or when a power demand on the engine10exceeds a predefined level. When this point in time is reached, the electronic controller160is operable to control the three way diverter valve190so that the valve member192moves from the position shown inFIG. 10cto the position shown inFIG. 10ain which the fuel flow passage193defines a flow path connecting the high pressure fuel pump130to the common fuel rail150. Fuel is then pumped directly into the common fuel rail by the high pressure fuel pump130for use by the engine10.

With reference toFIG. 9the combined effect of the improvements in engine shutdown and engine start-up is shown.

The lines E2sdand E2suare those representing respectively engine speed during shutdown and start-up for a prior art engine and fuel supply system and the lines E1sdand E1suare those representing respectively engine speed during shutdown and start-up for an engine having a fuel supply system constructed in accordance with this invention utilising a control method according to this invention.

The time period “x” is a time delay between the time when the respective engine reaches zero and the time when the subsequent start commences and is identical in both cases. T0is the point in time when shutdown of the respective engine commences and the time periods T2and T1are the periods of time required for the engine to reach zero in the case of a prior art and engine using a fuel supply system and method in accordance with this invention.

In the case of a prior art engine, the time taken from the point in time T0when the shutdown commences to the point in time where the engine speed reaches a speed Nt where useful power can be produced is Tt2seconds.

In the case of an engine using a fuel supply system and method in accordance with this invention, the time taken from the point in time T0when the shutdown commences to the point in time where the engine speed reaches a speed Nt where useful power can be produced is Tt1seconds.

Therefore a reduction in cycle time of Td seconds is produced by using a fuel supply system and method in accordance with this invention.

Referring now toFIGS. 4, 7, 8 and 9a second embodiment of fuel supply system is shown that is in many respects the same as that previously described and for which the same components have the same reference numerals.

The only significant difference between the second embodiment shown inFIG. 4and the first embodiment shown inFIG. 3is that the valve means which is a single three way diverter valve190inFIG. 3is replaced by first and second valves190A,190B inFIG. 4. The operation of the fuel supply system has the same advantageous effects as previously described and the shutdown and start-up of the engine10is as previously described with reference toFIGS. 7, 8 and 9.

Operation of the fuel supply system100shown inFIG. 4during an engine shutdown is as follows.

Prior to time T0(FIGS. 7 and 9) the electronic controller160controls the fuel injectors I1, I2, I3and I4so as to provide fuel at the correct timing and volume to the engine10, sets the demand level for the high pressure fuel pump130to a level required to satisfy the fuel usage needs of the engine10and controls the two valves190A,190B so that fuel flows via first valve190A to the common fuel rail150but cannot flow to the accumulator140via the second valve190B.

A flow path is thereby provided connecting the high pressure fuel pump130to the common fuel rail150.

While in this operating state the fuel supply system100operates as a conventional fuel supply system with fuel being drawn from the fuel tank110by the low pressure fuel pump120, is supplied to the high pressure fuel pump130from the low pressure fuel pump120, is pressurised by the high pressure fuel pump130under the control of the electronic controller160, is supplied to the common fuel rail150from the high pressure fuel pump130and is drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4for injection into the engine10to meet the current operating demands of the engine10.

At time T0the electronic controller160receives an indication from the stop-start system20that the engine10is to be stopped. In response to this indication from the stop-start system20, the electronic controller160, switches off the fuel injectors I1, I2, I3, I4, sets the demand level for the high pressure fuel pump130to a high level, preferably a maximum demand level, and controls the two valves190A,190B so that a flow path connecting the high pressure fuel pump130to the accumulator140is produced. To do this the first valve190A is closed and the second valve190B is opened by the electronic controller160.

Fuel is then pumped into the accumulator140by the high pressure fuel pump130until the engine10has stopped rotating.

As before, in a case where a signal from the fuel pressure sensor180associated with the accumulator140indicates that a maximum safe operating pressure for the accumulator140has been reached before the engine10stops rotating, it will be necessary to vent fuel back to the fuel tank110.

When the time T1has elapsed, the engine10has stopped rotating and the electronic controller160is then preferably operable to control the valve190A so that there is no flow path connecting the accumulator140to the common fuel rail150. The common fuel rail150is therefore isolated from the pressurised fuel in the accumulator140while the engine10is stationary to prevent leakage from the fuel injectors I1, I2, I3and I4. Preferably, the valve190B is also closed to prevent leakage back through the high pressure fuel pump130.

Operation of the fuel supply system100shown inFIG. 4during a subsequent engine start-up is as follows.

At time T0′, the two valves190A,190B are moved to the positions required to supply fuel from the accumulator140to the engine10. Also, at time T0′, when the stop-start system20indicates that the engine10is to be started and cranking of the engine commences, the electronic controller160controls whichever of the fuel injectors I1, I2, I3and I4has the first opportunity to inject fuel to the engine10to commence injection of fuel into the engine10without delay. As fuel is drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4it is replaced by fuel supplied to the common fuel rail150from the accumulator140thereby maintaining the fuel pressure in the fuel rail150at an appropriate pressure for efficient injection into the engine10.

At time T0′ (FIG. 8) or preferably at a point in time after the engine10has sensed to have stopped but before the time T0′, the electronic controller160is also operable to set the demand level for the high pressure fuel pump130to a low level and preferably to the lowest possible level which in some cases is a zero flow demand level.

Because the volume of the accumulator140is finite, at some point in time after time T0′, the electronic controller160must control the two valves190A,190B to switch the flow path from the accumulator140to the high pressure fuel pump130. This switching can occur when the pressure sensor170associated with the common fuel rail150indicates that the fuel pressure is beginning to drop, when a predefined volume of fuel that is less than the known volume of the accumulator140has been injected into the engine or when a power demand on the engine10exceeds a predefined level. To switch the flow path, the electronic controller160is operable to control the two valves190A,190B so that the second valve190B is closed and the first valve190A is opened thereby providing a fuel flow path connecting the high pressure fuel pump130to the common fuel rail150. Fuel is then pumped once again directly into the common fuel rail150by the high pressure fuel pump130for use by the engine10.

Referring now toFIGS. 5, 7, 8 and 9a third embodiment of fuel supply system is shown that is in some respects the same as that previously described and for which the same components have the same reference numerals.

The third embodiment shown inFIG. 5differs from the second embodiment shown inFIG. 4in that the valve means in the form of the first and second valves190A,190B are connected to the common fuel rail150in a different manner inFIG. 5.

InFIG. 4the two valves190A,190B are both connected to the common fuel rail150by a common supply line whereas inFIG. 5separate supply lines are used. The flow of fuel does not therefore have to pass from the accumulator140through the first valve190A to reach the common fuel rail150in the case of the third embodiment shown inFIG. 5but does have to in the second embodiment shown inFIG. 4. That is to say, the high pressure fuel pump130and the accumulator140are independently connectable to the common fuel rail150in the case of the third embodiment shown inFIG. 5. In the third embodiment the fuel from the high pressure fuel pump130to the accumulator140is controlled by the first valve190A.

Therefore in both embodiments the first valve190A provides two flow paths whereas the second valve190B provides only one flow path. The first valve190A is therefore a two way diverter valve whereas the second valve190B is a simple flow control valve having at least open and closed positions.

The operation of the fuel supply system shown inFIG. 5has the same advantageous effects as previously described and the shutdown and start-up of the engine10is as previously described with reference toFIGS. 7, 8 and 9.

Operation of the fuel supply system100shown inFIG. 5during an engine shutdown is as follows.

Prior to time T0(FIGS. 7 and 9) the electronic controller160controls the fuel injectors I1, I2, I3and I4so as to provide fuel at the correct timing and volume to the engine10, sets the demand level for the high pressure fuel pump130to a level required to satisfy the fuel usage needs of the engine10and controls the two valves190A,190B so that fuel flows via first valve190A to the common fuel rail150but cannot flow from the accumulator140to the common fuel rail150via the second valve190B. To do this the second valve190B is closed and the first valve190A is placed in a position in which a flow path between the high pressure fuel pump130and the common fuel rail150is provided but no flow path is provided between the high pressure fuel pump130and the accumulator140.

While in this operating state the fuel supply system100operates as a conventional fuel supply system as previously described with reference toFIGS. 3 and 4.

At time T0the electronic controller160receives an indication from the stop-start system20that the engine10is to be stopped. In response to this indication from the stop-start system20, the electronic controller160, switches off the fuel injectors I1, I2, I3, I4, sets the demand level for the high pressure fuel pump130to a high level, preferably a maximum demand level, and controls the two valves190A,190B so that a flow path connecting the high pressure fuel pump130to the accumulator140is produced. To do this, the first valve190A is moved to a position connecting the high pressure fuel pump130to the accumulator140and the second valve190B is kept closed by the electronic controller160.

Fuel is then pumped into the accumulator140by the high pressure fuel pump130until the engine10has stopped rotating.

As before, in a case where a signal from the fuel pressure sensor180associated with the accumulator140indicates that a maximum safe operating pressure for the accumulator140has been reached before the engine10stops rotating, it will be necessary to vent fuel back to the fuel tank110.

When the time T1has elapsed, the engine10has stopped rotating and the electronic controller160is then preferably operable to control the two valves190A,190B so that the two valves190A and190B provide no flow path connecting the accumulator140to the common fuel rail150. To do this the second valve190B is closed and the first control valve190A is preferably left in the current closed position or be repositioned so as to connect the common fuel rail150to the high pressure fuel pump130.

It will be appreciated that if the first valve190A is not in a flow blocking position then the high pressure fuel pump130must either be of a construction where back flow from the high pressure fuel pump130to the low pressure fuel pump120or fuel tank is not possible or must include a non-return valve to prevent such flow. Such a fuel pump will be referred to hereinafter as being a ‘non-return flow’ high pressure fuel pump. A non-return fuel pump could be used in other embodiments of fuel supply system shown and described herein.

Operation of the fuel supply system100shown inFIG. 5during a subsequent engine start-up is as follows.

At time T0′ (FIG. 8) or at a point in time after the engine10has sensed to have stopped but before the time T0′ the electronic controller160is operable to set the demand level for the high pressure fuel pump130to a low level and preferably to the lowest possible level which in some cases is a zero flow demand level.

At time T0′, the second valve190B is opened to a position required to supply fuel from the accumulator140to the engine10and the common fuel rail150is pressurised with fuel. Therefore, at time T0′ when the stop-start system20indicates that the engine10is to be started and cranking of the engine commences, the electronic controller160can control whichever of the fuel injectors I1, I2, I3and I4has the first opportunity to inject fuel to the engine10to commence injection of fuel into the engine10without delay. As fuel is drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4it is replaced by fuel supplied to the common fuel rail150from the accumulator140thereby maintaining the fuel pressure in the fuel rail150at an appropriate pressure for efficient injection into the engine10.

As before, because the volume of the accumulator140is finite, at some point in time after time T0′, the electronic controller160must control the two valves190A,190B to switch the flow path to the engine10from the accumulator140to the high pressure fuel pump130. As previously discussed, this can occur when the pressure sensor170associated with the common fuel rail150indicates that the fuel pressure is beginning to drop, when a predefined volume of fuel that is less than the known volume of the accumulator140has been injected into the engine or when a power demand on the engine10exceeds a predefined level.

To achieve this flow switching, the electronic controller160is operable to control the two valves190A,190B so that the second valve190B is closed and the first valve190A is either repositioned or maintained in the position required to provide a fuel flow path connecting the high pressure fuel pump130to the common fuel rail150. Fuel is then pumped once again directly into the common fuel rail150by the high pressure fuel pump130for use by the engine10.

Referring now toFIGS. 6, 7, 8 and 9, a preferred or fourth embodiment of fuel supply system is shown that is in some respects the same as that previously described and for which the same components have the same reference numerals.

The fourth embodiment shown inFIG. 6differs from the third embodiment shown inFIG. 5in that the valve means in the form of the first and second valves190A,190B used in the third embodiment are replaced by a single valve290located in the same position as the second valve190B and being of the same construction as the simple control valve190B in that is has at least open and closed positions.

In the fourth embodiment shown inFIG. 6there is no valve controlling the flow of fuel from the high pressure fuel pump130to the common fuel rail150and so the high pressure fuel pump130is permanently connected to the common fuel rail150.

The flow of fuel from the accumulator140to the common fuel rail150is controlled by the electronically controlled valve290. However, in this case, the flow of fuel can be in either direction through the valve290because not only is fuel supplied to the common fuel rail150from the accumulator140through the valve290it is received by the accumulator140from the high pressure fuel pump130via the common fuel rail150and valve290. Such an arrangement requires the use of a ‘non-return’ high pressure fuel pump130previously referred to with respect toFIG. 5.

The operation of the fuel supply system shown inFIG. 6has the same advantageous effects as previously described and the shutdown and start-up of the engine10is as previously described with reference toFIGS. 7, 8 and 9.

Operation of the fuel supply system100shown inFIG. 6during an engine shutdown is as follows.

Prior to time T0(FIGS. 7 and 9) the electronic controller160controls the fuel injectors I1, I2, I3and I4so as to provide fuel at the correct timing and volume to the engine10, sets the demand level for the high pressure fuel pump130to a level required to satisfy the fuel usage needs of the engine10and controls the valve290so that fuel cannot flow from the common fuel rail150to the accumulator140. To do this the valve290is closed.

While in this operating state the fuel supply system100operates as a conventional fuel supply system as previously described with reference toFIGS. 3 and 4.

At time T0the electronic controller160receives an indication from the stop-start system20that the engine10is to be stopped. In response to this indication from the stop-start system20, the electronic controller160, switches off the fuel injectors I1, I2, I3, I4, sets the demand level for the high pressure fuel pump130to a high level, preferably a maximum demand level, and controls the valve290so that a flow path connecting the high pressure fuel pump130to the accumulator140via the common fuel rail150is produced. To do this the valve290is moved to an open position.

Fuel is then pumped into the accumulator140by the high pressure fuel pump130until the engine10has stopped rotating.

As before, in a case where a signal from the fuel pressure sensor180associated with the accumulator140indicates that a maximum safe operating pressure for the accumulator140has been reached before the engine10stops rotating, it will be necessary to either reduce the demand level to the high pressure fuel pump130to a minimum level and/or vent fuel back to the fuel tank110.

When the time T1(FIG. 7) has elapsed, the engine10has stopped rotating and the electronic controller160is then operable to control the valve290so as to provide no flow path connecting the accumulator140to the common fuel rail150to prevent fuel leakage as previously referred to.

It will be appreciated that with such an arrangement the high pressure fuel pump130should be of a ‘non-return flow’ high pressure fuel pump or fuel could leak back to the fuel tank110when the accumulator140is connected to the common fuel rail150and the high pressure fuel pump130is operating a low demand.

Operation of the fuel supply system100shown inFIG. 6during a subsequent engine start-up is as follows.

At time T0′ (FIG. 8) or at a point in time after the engine10has sensed to have stopped but before the time T0′ the electronic controller160is operable to set the demand level for the high pressure fuel pump130to a low level and preferably to the lowest possible level which in some cases is a zero flow demand level.

At time T0′, the valve290is opened to a position required to supply fuel from the accumulator140to the engine10and the common fuel rail150is pressurised with fuel. Therefore, at time T0′ when the stop-start system20indicates that the engine10is to be started and cranking of the engine commences, the electronic controller160can control whichever of the fuel injectors I1, I2, I3and I4has the first opportunity to inject fuel to the engine10to commence injection of fuel into the engine10without delay. As fuel is drawn from the common fuel rail150by the fuel injectors I1, I2, I3and I4it is replaced by fuel supplied to the common fuel rail150from the accumulator140thereby maintaining the fuel pressure in the fuel rail150at an appropriate pressure for efficient injection into the engine10.

Because the volume of the accumulator140is finite, at some point in time after time T0′, the electronic controller160is operable to close the valve290after which time the flow path to the engine10is solely from the high pressure fuel pump130and the demand for the high pressure fuel pump130is increased to the level required to supply fuel to the engine10.

Because the high pressure fuel pump130is permanently connected to the common fuel rail150, the supply of fuel is continuous and there is no actual flow switchover required. As the high pressure fuel pump130accelerates with the engine10it will reach a speed where it will be able to provide the required fuel pressure and this will normally occur before the valve290is closed.

One of the advantages of the third and fourth embodiments shown inFIGS. 5 and 6respectively is that, if required, the accumulator140could be topped up with fuel by the high pressure fuel pump130at the same time fuel is being supplied to the common fuel rail150by the high pressure fuel pump130.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

In this way, a method of controlling a fuel supply system of an engine of a motor vehicle wherein the method comprises, during a shutdown of the engine, operating an engine driven variable output high pressure fuel pump at a high demand level and storing fuel from the high pressure fuel pump in a fuel accumulator and, during a subsequent engine start-up, operating the high pressure fuel pump at a low demand level and supplying fuel from the accumulator to the engine. The high demand level may be the maximum demand level of the high pressure fuel pump.

The low demand level may be the minimum demand level of the high pressure fuel pump. The motor vehicle may be a stop-start enabled motor vehicle having a stop-start controller to control stopping and starting of the engine and the shutdown and subsequent start-up of the engine are initiated by the stop-start controller.

As such, a fuel supply system of an engine of a motor vehicle comprising an engine driven variable output high pressure fuel pump, a fuel accumulator to store fuel at high pressure, a valve means to control the flow of high pressure fuel within the system and an electronic controller to control the operation of the high pressure fuel pump and the valve means, wherein the controller is operable during a shutdown of the engine, to operate the high pressure fuel pump at a high demand level and control the valve means to store fuel from the high pressure fuel pump in the fuel accumulator and is operable, during a subsequent engine start-up, to operate the high pressure fuel pump at a low demand level and operate the valve means so that fuel from the fuel accumulator is supplied to the engine. The valve means may include at least one valve to selectively isolate the accumulator from the engine and the high pressure fuel pump. This has the advantage that fuel can be supplied to the accumulator only when the high pressure pump can recover energy from the engine thereby reducing the fuel consumption of the engine.

The system may further comprise a fuel reservoir, a low pressure fuel pump to supply fuel from the reservoir to the high pressure fuel pump and at least one fuel injector to supply fuel at high pressure to the engine wherein the controller is operable during a shutdown of the engine, to operate the high pressure fuel pump at a high demand level and to control the valve means to store fuel from the high pressure fuel pump in the fuel accumulator and, during a subsequent engine start-up, is operable to operate the high pressure fuel pump at a low demand level, to operate the valve means so that fuel from the fuel accumulator is supplied to the at least one fuel injector and to control the at least one fuel injector to supply fuel to the engine. There may be at least two fuel injectors, fuel may be supplied to the fuel injectors via a common fuel rail and the valve means may include at least one valve controlled by the electronic controller to control the flow of fuel between the accumulator and the common fuel rail.

This has the advantage that, if the engine is stationary for a long period of time the fuel remains stored in the accumulator with reduced risk of leakage via the at least two fuel injectors. The valve means may comprise a single diverter valve interposed between the high pressure fuel pump and the common fuel rail, between the high pressure fuel pump and the accumulator and between the accumulator and the common fuel rail. The diverter valve may have three selectable fuel flow paths, a first flow path connecting, when selected, the high pressure fuel pump to the common fuel rail, a second flow path connecting, when selected, the high pressure fuel pump to the accumulator and a third flow path connecting, when selected, the accumulator to the common fuel rail and the selection of each respective flow path is controlled by the electronic controller.

Alternatively, the valve means may comprise a first electronically controlled valve to control the flow of fuel from the high pressure fuel pump to the common fuel rail and a second electronically controlled valve to control the flow of fuel from the high pressure fuel pump to the accumulator wherein a flow path from the accumulator to the common fuel rail passes through both the first and the second electronically controlled valves.

As yet a further alternative, the valve means may comprise a first electronically controlled valve to control the flow of fuel from the high pressure fuel pump to the common fuel rail, a second electronically controlled valve to control the flow of fuel between the accumulator and the common fuel rail wherein a flow path from the high pressure fuel pump to the accumulator is also controlled by the first electronically controlled valve.

During shutdown of the engine, the first electronically controlled valve may be controlled by the electronic controller to permit fuel to flow from the high pressure fuel pump to the accumulator and the second electronically controlled valve is closed so as to prevent the flow of fuel from the accumulator to the common fuel rail. During start-up of the engine, the fuel injectors may be controlled by the electronic controller to supply fuel to the engine and the second electronically controlled valve may be controlled by the electronic controller to permit fuel to flow from the accumulator to the common fuel rail.

As yet a further alternative there may be no control valve between the high pressure fuel pump and the common fuel rail, the valve means may comprise an electronically controlled valve to control the flow of fuel between the accumulator and the common fuel rail and a flow path from the high pressure fuel pump to the accumulator may pass through the common fuel rail and the electronically controlled valve. During shutdown of the engine, all fuel injectors may be switched off by the electronic controller and the electronically controlled valve may be controlled by the electronic controller to permit fuel to flow from the high pressure fuel pump via the common fuel rail to the accumulator. During start-up of the engine, the fuel injectors may be controlled by the electronic controller to supply fuel to the engine and the electronically controlled valve may be controlled by the electronic controller to permit fuel to flow from the accumulator to the common fuel rail. The high pressure fuel pump may be a non-return high pressure fuel pump. The high demand level may be the maximum demand level of the high pressure fuel pump.

The low demand level may be the minimum demand level of the high pressure fuel pump. The motor vehicle may be a stop-start enabled motor vehicle having a stop-start controller to control stopping and starting of the engine and the shutdown and subsequent start-up of the engine may be initiated by the stop-start controller.

According to a third aspect of the invention there is provided a motor vehicle having a fuel supply system constructed in accordance with said second aspect of the invention.