GB2585911A

GB2585911A - A liquid injection system for a vehicle

Info

Publication number: GB2585911A
Application number: GB1910522.0A
Authority: GB
Inventors: Scott Baylis Warren; Bevan Neil; Andrew Pike Danyal; Weng Kou Chen Victor
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-07-23
Filing date: 2019-07-23
Publication date: 2021-01-27
Anticipated expiration: 2039-07-23
Also published as: GB201910522D0; DE102020119265A1; GB2585911B

Abstract

A liquid injection system 26 comprises at least one injector 2a, 2b, a pump apparatus 3 for conveying liquid in a forward direction to pressurise the system for performing liquid injection and for conveying liquid in a backward direction to depressurise the system, a pipe 4, 10a, 10b between the pump apparatus and the injector, and a pressure sensor 5 to measure pressure of liquid within the system. A method comprises instructing the injector to close, controlling the pump apparatus to run in the backward direction to depressurise the system, and determining a rate of pressure reduction during depressurisation. The method is carried out by a controller. A measurement of the amount of gas entrained within the liquid may by determined from the rate of pressure reduction. The system is a urea injection system for an exhaust gas treatment system of an internal combustion engine, or a water injection system for an internal combustion engine. A vehicle comprises the system. A non-transitory computer readable medium comprises computer readable instructions that cause performance of the method.

Description

A LIQUID INJECTION SYSTEM FOR A VEHICLE

TECHNICAL FIELD

The present disclosure relates to a liquid injection system particularly, but not exclusively, to a urea injection system for the treatment of nitrogen oxides in vehicle exhaust gas, and a method for measuring gas entrainment in a liquid injection system. Aspects of the invention relate to a controller, to a system, to a vehicle and to a method.

BACKGROUND

Vehicle exhaust aftertreatment systems for diesel engines typically deploy a selective catalytic reduction (SCR) process, where nitrogen oxides (NOx) react with ammonia to produce less toxic compounds of nitrogen and water in order to meet legislated limits to NOx emissions.

Ammonia is typically delivered in the form of a measured dose of urea, commonly called Diesel Exhaust Fluid (DEF, tradename AdBlue) which is injected into the flue gas stream before the catalyst. The same technology may be used on ultra-lean gasoline engines.

It is known that in such systems urea is injected through an injector into the flue gas upstream of one or more catalysts. The injector is a valve which receives pressurised urea conveyed from a reservoir and pump through a pipe. More stringent legislation necessitates more complex exhaust treatment systems with multiple injectors and junctions in the pipe to convey urea to the different injectors.

Following assembly or servicing operations and before such an injection system may be used the system would normally need to undergo a priming operation, which typically consists of opening injectors and using the pump to pump urea into the pipework and injectors, and so expel gas to achieve a liquid-filled state of the entire system, ready for injecting measured doses of urea. In cold weather an injector may be damaged if the liquid is allowed to freeze inside it, so current systems typically perform a purge operation when the vehicle is switched off. A purge operation typically comprises running the pump backwards to suck gas back through an open injector, so evacuating urea from some or all of the system. It is not desirable to purge the entire system including the pump because this would require the full system to be re-primed again before liquid injection recommences, so increasing pump wear, using excessive energy and generating noise which may be undesirable. Thus the desired normal state of the system following a purge operation is that the system is gas-filled in the region of the injectors, and urea-filled in the region of the pump, and with a clear boundary between the two regions which is retained by the surface tension of the urea.

However, the inventors have identified that this desired state does not always occur in practice, since the introduction of gas into the system can lead to bubbles being entrained within the urea itself and this gas may become distributed throughout the system in ways which are difficult to predict and control.

When the system is pressurised for performing liquid injection the presence of gas entrainment within the urea reduces the pressurisation of the system, and this loss of pressure, and the presence of a fraction of gas, significantly reduces the injection dosage. Therefore unaccounted variability in gas entrainment is a problem for ensuring that urea dosing is optimal and that emissions are adequately controlled.

It is an aim of the present invention to address the disadvantages associated with known systems.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a controller, a system, a method and a vehicle as claimed in the appended claims.

According to an aspect of the present invention there is provided a controller for operating a liquid injection system. The liquid injection system comprises at least one injector for injecting a dose of pressurised liquid, a pump apparatus for conveying liquid in a forward direction to pressurise the liquid injection system for performing liquid injection, and for conveying liquid in a backward direction to depressurise the liquid injection system, a pipe for conveying liquid between the pump apparatus and the at least one injector, a pressure sensor to measure pressure of liquid within the liquid injection system.

The controller is configured to: instruct the at least one injector to close, control the pump apparatus to run in the backward direction to depressurise the system, and determine a rate of pressure reduction during depressurisation.

The present invention is advantageous in that it allows a measurement to be made of the hydraulic stiffness of the contents of the liquid injection system. It is understood from physical principles that a nominally closed system containing a mixture of gas and liquid will have a stiffness which is substantially dependent on the average compressibility of the contents of the closed system. The pump apparatus running in a backward direction thus develops a pressure change within the system such that the pressure reduces as the pump apparatus operates. Providing other factors remain substantially constant the rate of pressure reduction is indicative of the compressibility of the total system contents. The other factors referred to include the duty cycle or speed of the pump apparatus, the compliance of the system boundaries such as pipes and valves and also the leakage of the system being nominally zero.

The present invention may advantageously be used with various types of liquid injection systems.

The controller may comprise one or more controllers. The one or more controllers collectively comprise: at least one electronic processor having an electrical input for receiving information associated with the pressure of liquid within the liquid injection system; and at least one electronic memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to cause the control system to control the liquid injection system in dependence on the information.

The controller may be configured to derive a measurement of an amount of gas entrained within the liquid from the rate of pressure reduction and output a signal indicative of the amount of gas entrained within the liquid.

The advantageous effect of this feature of the invention is to enable monitoring and then controlling the levels of gas within a liquid injection system.

The controller may be configured to control the pump apparatus to run in a forward direction to perform liquid injection by controlling an opening duration of the at least one injector and/or a conveying power of the pump apparatus and/or an operating duration of the pump apparatus in dependence on the measurement of the amount of gas entrained in the system.

The advantageous effect of this feature of the invention is to modify the liquid injection process to take account of the amount of gas entrained in the liquid, thus enabling more precise control of the dosage of liquid to be applied by the system.

The controller may be configured to control the duration of a subsequent purge operation in dependence on the measurement of the amount of gas entrained in the system.

The advantageous effect of this feature of the invention is to run purge operations which can remove gas, or control the gas content to within expected boundary limits.

The controller may be configured to control a system comprising at least two injectors, the controller being configured to run in the backward direction to depressurize the system with only a first injector being open to evacuate liquid from a length of pipe feeding the first injector, and then run the pump in a backward direction to depressurize the system with only a second injector being open to evacuate liquid from the length of pipe for feeding the second injector.

The advantageous effect of this feature of the invention is to allow multi-injector systems to be partially purged of liquid whilst also enabling the controller to derive measurements for the amount of gas in the various parts of the system.

In an aspect, there is provided a system comprising a controller as described above and a liquid injection system, wherein the liquid injection system is a urea injection system for an exhaust gas treatment system of an internal combustion engine.

In a further aspect, there is provided a system comprising a controller as described above and a liquid injection system, wherein the liquid injection system is a water injection system for an internal combustion engine.

In yet another aspect, a vehicle comprising an internal combustion engine and a urea injection system or a water injection system is provided.

According to another aspect of the invention there is provided a method for operating a liquid injection system, the system comprising at least one injector for injecting a dose of pressurised liquid, a pump apparatus for conveying liquid in a forward direction to pressurise the liquid injection system for performing liquid injection, and for conveying liquid in a backward direction to depressurise the liquid injection system, a pipe for conveying liquid between the pump apparatus and the at least one injector, a pressure sensor to measure pressure of liquid within the liquid injection system, wherein the method comprises closing the at least one injector, controlling the pump apparatus to run in the backward direction to depressurise the system, and determining a rate of pressure reduction during depressurisation.

The method may comprise deriving a measurement of an amount of gas entrained within the liquid from the rate of pressure reduction, and outputting a signal indicative of the amount of gas entrained within the liquid.

The method may comprise controlling the pump apparatus to run in a forward direction to perform liquid injection by controlling an opening duration of the one or more injectors and/or a conveying power of the pump apparatus and/or an operating duration of the pump apparatus in dependence on the measurement of the amount of gas entrained in the system.

The method may comprise adjusting the duration of a subsequent purge operation in dependence on the measurement of the amount of gas entrained in the system.

The method for operating a liquid injection system may be applied to a system comprising at least two injectors, and may comprise controlling the pump apparatus to run in the backward direction to depressurize the system with only a first injector being open to evacuate liquid from a length of pipe feeding the first injector, and then controlling the pump apparatus to run in a backward direction to depressurize the system with only a second injector being open to evacuate liquid from a length of pipe feeding the second injector.

According to another aspect, there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of the method described above.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 shows a vehicle with a urea injection system fitted to the exhaust of an internal combustion engine; Fig 2 shows a urea injection system and a controller for a urea injection system; Fig 3 shows the sequence of events for performing a measurement of the gas entrainment; Fig 4 is a graph showing the operation of the pump and associated system pressure for two different gas fractions of gas-entrained liquid during the process shown in Fig 3.

Fig 5 shows the sequence of events for injecting a dose of liquid.

Fig 6 shows the sequence of events for performing selective purging of the pressure pipes feeding each injector.

Fig 7 shows a vehicle with a water injection system fitted to the internal combustion engine; Fig 8 shows a controller for a liquid injection system.

Fig 9a, 9b, 9c and 9d shows a variety of possible gas-entrainment scenarios in a liquid injection system

DETAILED DESCRIPTION

A liquid injection system, a vehicle and a method in accordance with embodiments of the present invention is described herein with reference to the accompanying Figs 1 to 9.

In the below discussion the term duty cycle (sometimes called duty factor) is used to refer to the control of the pump or an injector wherein the operation may be intermittent rather than continuous, and the duty cycle then refers to the operating time as a percentage of available time. A common method for implementing a variable duty cycle is the use of Pulse Width Modulation (PWM) to intermittently turn the device on and off. For example, a square-wave pulse train used in PWM, having equal on (high) and off (low) durations, would provide a 50% duty cycle since the device is on (operating) for half of the available time. Other duty cycles may then be obtained through similarly periodic but asymmetrical waves. For example, a 10Hz pulse train where the on (high) duration is 0.09 seconds in a 0.1 second cycle would provide a 90% duty cycle. Continuous operation (always on/operating) therefore equates to 100% duty cycle. In this way PWM control of duty cycle may be used to continuously modify dosage between 0 and 100% while the system is functioning, for example for gradually increasing the duty cycle as the exhaust gas flow rate increases at higher engine speeds and loads. The duty cycle of injector and pump is thereby used to control the dose of urea liquid applied to the exhaust gas.

In the below discussion the term prime is used to mean filling a system or part of a system with liquid so that it is ready for injecting liquid, and would normally be achieved by operating the pump in a forward direction. Thus priming the system avoids an operational delay in applying a dose due to liquid flowing through the pipes for the first time. Similarly the term purge is used to refer to removing liquid from a system or part of a system, and would normally be achieved by operating the pump in a backward direction.

Fig 1 shows a vehicle 20 with a urea injection system 26 for injecting urea into an exhaust system 24 for the treatment of exhaust gases emitted by an engine 22 in the vehicle.

Fig 2 shows a urea injection system 26 comprising a urea storage tank 6 containing stored urea 7 which is fed through an inlet pipe 8 to a pump apparatus 3 whose outlet 1 conveys pressurised urea in a forward direction through pipes 4, 10a, 10b and their interconnector 9 towards urea injectors 2a, 2b. The urea injectors 2a, 2b inject urea into an exhaust system not shown in Fig 2. It will be appreciated by those skilled in the art that the length of the common feed pipe 4 is likely to be of the order of 1 to 3 metres, and so is very long (12) relative to the length of individual feed pipes 10a, 10b although this will depend on the location of the pump apparatus in the vehicle. A pressure sensor 5 is located so as to measure the pressure in the feed pipe 4. Dashed lines in Fig 2 indicate signals passing to or from a controller 11 which comprise at least a sensor input from the pressure sensor 5 and controlling outputs to the pump apparatus 3 and injectors 2a, 2b. The controlling outputs may take the form of a PWM signal which thereby controls the duty cycle of the injector 2a, 2b or the pump apparatus 3.

It will be appreciated that inlet pipe 8 and the pump apparatus outlet 1 are so named according to the forward direction of urea, and that in some circumstances the urea may otherwise be conveyed in a backward direction in which case the functions of inlet pipe 8 and pump apparatus outlet 1 are reversed whilst the names of the physical parts remain unchanged for ease of referral.

It will be appreciated that the controller 11 may receive additional input signals and send additional output signals, none of which are shown in the Figures. For example the controller may additionally receive a signal from a sensor in the urea storage tank 6 indicating the level of urea remaining in the tank, and so output a warning signal to other systems in the vehicle or to the vehicle operator display if the level of urea is below a defined threshold value. The controller will also receive signals indicating the required urea dosage, or signals that enable the controller to calculate the required urea dosage, such as engine operating conditions, exhaust gas temperature and exhaust gas constituents.

Although not shown in the Figures, for reasons of manufacturability and cost the pump apparatus 3 and pressure sensor 5 may be incorporated within the same assembly as each other and/or incorporated into the same assembly as the storage tank 6. The pump apparatus 3 may be situated within the tank so eliminating the need for an inlet pipe 8 altogether, the inlet to the pump apparatus 3 thus being directly located within the body of the stored urea 7.

The storage tank 6 will normally be provided with an access port for replenishing urea during service operations. In other embodiments the pump apparatus 3 may comprise multiple outputs connected to feed pipes 10a and 10b so obviating the need for the common feed pipe 4. In such a configuration the pressure sensor may connect directly to the pump apparatus 3 in order to measure feed pipe pressure. The pressure sensor 5 may also comprise a plurality of pressure sensors which may have differing pressure sensing capabilities or be distributed at more locations within the system, nevertheless such distributed pressure sensing systems would be understood to provide the same pressure signal to the controller 11 indicative of the pressure of the contents of the system.

It will be appreciated that in other variants the pump apparatus 3 may alternatively comprise different configurations that enable the functionality of a reversible pump capable of pumping liquid in either the forward or backward direction. The pump apparatus 3 may comprise a unidirectional pump coupled with a reversing valve for providing forward and backward direction of liquid flow. The pump apparatus 3 may further comprise two pumps wherein one pump is configured to pump liquid in the forward direction and the other pump is configured to pump liquid in the backward direction. Such pumps may comprise positive displacement pumps or centrifugal pumps.

Fig 2 illustrates two injectors 2a, 2b but other variants are possible with only a single injector or with more than two injectors. Multiple injectors are becoming more common in order to provide greater control of the dosage of urea as exhaust gas emission legislation becomes more stringent. For example two injectors may be required for the application of urea to two separate SCR devices within an exhaust system. For any system with more than one injector it is necessary for the common feed pipe 4 to be divided at one or more junctions 9 into at least two individual feed pipes 10a, 10b...10n which each provide flow to an injector 2a, 2b 2n. The individual feed pipes may be of equal or different lengths and are typically shorter than the common feed pipe 4.

The injectors 2a, 2b of Fig 2 may be valves which control the flow of urea by their degree of opening or by control of their duty cycle. Such valves may be opened and closed by means of a solenoid. Liquid injectors may otherwise be called dosing modules by those working in the field. The dose of urea applied by an injector depends on the valve flow characteristics, the total duration of operation, the duty cycle, and also on the pressurisation and flow capabilities of the pump apparatus 3. Any gas entrained in the liquid will also impact the dose of active liquid ingredient applied.

If the pressure of urea in the system is lower than the gas pressure within the exhaust system then gas will flow backwards through an open injector into the urea injection system pipes 10a, 10b and 4, and pump apparatus 3. This situation may arise if a nominally closed injector leaks gas, or if the pump apparatus 3 is run in a backward direction to purge an injector of urea while the injector is open. In a purge operation an injector may be open to the lumen of the exhaust system as described above, or some injectors possess a separate valve which opens to atmospheric air. Purging of the individual feed pipe 10a feeding injector 2a may be accomplished by closing injector 2b and opening only injector 2a whilst the pump apparatus 3 is running backward. By this means different sections of the feed pipe 4, 10a, 10b, and inlet pipe 8 may be purged of urea and filled with gas.

Purge operations are required in order to avoid problems caused by urea freezing within the urea injectors 2a, 2b. However there are other reasons why gas may be present within the injection system, such as leakage. The injectors themselves are prone to gas leakage, so typically the purge operation withdraws urea back to any junction 9 in the pipe of multi-injector systems, since this minimises the hydrostatic pressures acting at injectors and reduces consequent gas leakage at injectors. Gas is also present within injection systems during manufacturing assembly, or during service operations and some gas may be retained during inadequate priming of the system. In all these cases the feed pipes 4, 10a, 10b and junctions 9 may contain gas. Junctions 9 and other discontinuities or surface irregularities within the feed pipes 4, 10a, 10b, injectors 2a, 2b, pressure sensor 5 or pump apparatus 3 can disturb the flow of urea and allow air to form discrete bubbles entrained within the urea even once the system is fully primed. For these reasons gas entrainment is difficult to predict and control.

Various scenarios for gas-entrainment are depicted in Figs 9a to 9d.

Fig 3 shows the inventive method implemented by the controller for measurement of gas entrainment within the liquid of the system. In the first step, S1, all injectors are closed in order to isolate a single contiguous test volume comprising the internal volumes of the feed pipes 4, 10a, 10b, junctions 9, pump apparatus 3, pressure sensor 5 and any other ancillary elements that may provide a volume in continuity with the volume being tested. At this juncture the pressure within the system may have previously been raised above atmospheric pressure due to pumping of the pump apparatus 3 in a forward direction. The second step, S2, is to operate the pump apparatus 3 in a backward direction in order to withdraw fluid comprising either liquid, gas or a combination of both liquid and gas. Whilst step S2 is carried out the output data of the pressure sensor 5 is recorded by the controller 11 in order to derive the rate of pressure reduction, shown as step S3.

The next step S4 of the method is to derive a measurement of the amount of gas entrained from the rate of pressure reduction. In an ideal system the rate of pressure reduction will depend on the pump flow rate, the total test volume and the gas fraction of the contents within the test volume. In reality the system is non-ideal and other factors such as the elasticity of the pipes, leakage of valves and pump, the composition and compressibility of the contents will have an influence on the rate of pressure reduction. Providing these other factors which make the system non-ideal are sufficiently controlled then the rate of pressure reduction will be substantially dependent on the gas fraction within the test volume.

Since the test volume and pump flow rate are known in advance then the controller is able to calculate the gas fraction using the foregoing theoretical basis. Alternatively it is also possible to configure the controller to calculate the gas fraction by comparison with test data, in which case a lookup table is provided in the controller with test data which associates a given rate of pressure reduction, or range of rates of pressure reduction, with a given gas fraction, or range of gas fractions. Alternatively an empirical equation relating gas fraction to rate of pressure reduction may be derived from test data. By whatever practical means is desirable or most suitable in any given application, the calculation of gas fraction from rate of pressure reduction makes use of this relationship, and is illustrated in step S4 of Fig 3.

Once a value for the amount of gas entrainment has been calculated the final step S5 is for the value to be output as a data value within the memory of the controller 11, or as a signal to another part of the controller, or to another controller within the vehicle, for example over a data bus known in the automotive industry such as a LIN (Local Interconnect Network), CAN bus (Controller Area Network), Ethernet or similar. This step is illustrated as step S5 in Fig 3.

Fig 4 depicts the condition of various elements of the system along a time axis 33 during the method of Fig 3, in which the injectors are closed throughout and the initial condition of the system pressure is stable 37. The pump apparatus is run in a backward direction between times t34 and t35. In Fig 4 the top graph illustrates the condition of the pump apparatus 30 as either running backwards 31 or stopped 32. The lower graph illustrates the output 36 of the pressure sensor 5 for two different examples -one being a relatively high level of gas 3o entrainment in which the pressure drops slowly 38, and the other being a relatively low level of gas entrainment in which the pressure drops more quickly 39. The rate of pressure reduction 38, 39 is then recorded by the controller 11.

Comparing Figs 3 and 4, the closing of the injectors S1 of Fig 3 is completed prior to starting of the pump apparatus in the backward direction at time t34 of Fig 4. Once the pump apparatus is started at t34 of Fig 4 then the pump apparatus runs as described in step S2 of Fig 3 and pressure is monitored as described in step S3 of Fig 3 until the pump apparatus is switched off at time t35 of Fig 4. The rate of pressure reduction is determined as described at step S4 of Fig 3 after time t35 of Fig 4 then the signal indicative of the amount of gas entrainment is output at step S5 of Fig 3.

Although not shown, a variation of the method may also be applied by first starting the operation of the pump apparatus running in a backwards direction before closing the injectors. Therefore, although it has been achieved in a different order of steps, the system is then at the same state as S2 of Fig 3 with pump running and injectors closed. The rate of pressure drop S3 may then be measured as before. In this case the pressure is unlikely to be stable before the injectors are closed at t34. But during the time period t34 to t35 the pressure is still decreasing at a rate dependent on the amount of gas entrained within the system.

In another alternative, rather than waiting until t35 of Fig 4, the rate of pressure reduction may be used to perform the calculation at step S4 of Fig 3 intermittently or continually during the period t34 to t35 of Fig 4. In this case steps S2, S3 and S4 may be occurring at the same time. In this case step S4 may occur multiple times between t34 and t35 of Fig 4, so generating multiple interim values of gas entrainment before a final value is generated.

The output of step S5 may be generated at any point once step S4 has occurred. Indeed, steps S2, S3, S4 and S5 may be occurring at the same time, so generating a time-varying output signal indicating gas entrainment. At any point when a determination as to the rate of pressure reduction has been completed then the signal indicative of the amount of gas entrainment may be output at step S5.

As mentioned above, when urea contains entrained gas bubbles this will affect the urea dose applied during the subsequent dosing procedure. This effect will occur directly as a consequence of the fraction of gas within the liquid; for example, a nominal gas fraction of 10% will mean only a nominal 90% of the injected fluid is urea, though this relationship would also depend on pressure. The effect of the fraction of gas may also occur indirectly by interfering with the flow and pressurisation characteristics of the injection system. Consequently, the measurement of gas entrainment may be taken into account during a subsequent injection of a dose of urea in order to ensure that the applied dose is corrected for gas entrainment. This may involve correcting for the gas fraction in the injected liquid and/or correcting for changes in flow characteristics of gas-entrained liquid.

Fig 5 illustrates one example of how the gas entrainment is taken into account in subsequent dosing operations, for example by changing the duty cycle of the injector(s) and pump apparatus. In step S6 the controller 11 receives a demand for urea dosage of the exhaust gas, where this demand will be dependent on the temperature, flow and composition of the exhaust gas or anticipated exhaust gas. At step S7 the controller 11 calculates the required pump apparatus and injector duty cycles using the value of gas fraction previously calculated from an earlier measurement, for example during the method of Fig 3. In step S8 the pump apparatus is operated in a forward direction to pressurize the urea injection system according to the calculated duty cycle, and in step S9 one or more urea injectors are operated according to the calculated duty cycle in order to deliver the correct dosage of urea as demanded in step S6.

During the injection of urea the degree of gas entrainment is likely to change as gas-entrained urea is injected into the exhaust system. Therefore the initial duty cycle of pump apparatus and injectors may be adjusted in response to this change of gas entrainment. Steps S8 and S9 may be reversed, or may occur simultaneously.

In an alternative example only one of the pump and injector duty cycles are altered. In which case only the duty cycle being altered is calculated at step S7.

If partial purge operations are carried out as detailed below then the injection process may also take account of any sections of purged (evacuated) pipe as well as gas entrainment in a pipe which still contains urea. This may involve adjustment to the duty cycle of the pump apparatus or injector, or an extension of the operation period.

Fig 6 illustrates one method of purging the system of urea. At step S10 one of the injectors 2a is opened and all others are closed, then at step S11 the pump apparatus is operated in a backward direction to purge urea from feed pipe 10a. If the control system is pre-configured with information relating to the volume of feed pipe and the flow rate of the pump apparatus then step 611 may be used to purge only the feed pipe 10a, and so purging may be stopped when the urea is retracted to the junction 9. At this point the pump apparatus may be stopped, as indicated in step S12, while the open injector 2a is closed and another 2b is opened, as shown in step S13. The pump apparatus is then operated in a reverse direction to purge urea from the feed pipe 10b in step S14. If more than two injectors are present then steps S12 to S14 may be repeated to purge their feed pipes. As with the first purge operation of feed pipe 10a, the controller 11 may be operated to purge urea back to the junction 9 but no further.

Alternatively the controller 11 may be operated to purge urea back up the common feed pipe 4 towards the pump apparatus 3 and beyond into the inlet pipe 8.

The measurement of pressure reduction and derivation of gas fraction as shown in steps S3 and S4 of Fig 3 may be performed at the beginning of, end of, or during a purge operation shown in Fig 6. For example it may be desirable to purge the urea from only one individual feed pipe 10a by performing only steps S10, S11 and S12 of Fig 6, and then perform the measurement of gas fraction according to steps S3 and S4 to determine the gas fraction in individual feed pipe 10b and common feed pipe 4. Or it may be desirable to purge the urea from both individual feed pipes 10a and 10b as illustrated in steps S10 to S14 of Fig 6, and then perform the measurement to confirm the gas fraction within the common feed pipe 4 according to steps S3 and S4. By such means it is possible to manipulate the state of the system to have separate regions of gas and urea, albeit with the urea region to potentially contain entrained gas bubbles. By providing the controller 11 with such data as the volume of pipes and the flow rate of the pump apparatus while operating at different duty cycles it is possible for the controller 11 to calculate the gas fraction within a region of urea for a system which contains separate regions of both gas and urea. These calculations require the controller 11 to have access to additional data which correlates the rate of pressure reduction to a given gas fraction for each of the conditions to be tested. This correlation may take the form of look-up tables or an empirical equation based on test data, or on a theoretical calculation based on system volumes such as the volumes of pipes 10a, 10b and 4 depending on the condition to be tested. Using these various methods the system may achieve various states as indicated in Figs 9a, 9b, 9c or 9d.

Based on measurements of gas entrainment the controller 11 may carry out extended purge operations in order to evacuate urea from one or more of the feed pipes 4, 10a, 10b, pump apparatus 3 and inlet pipe 8.

Following purging of part or all of the urea injection system 26 the controller 11 may carry out a priming procedure to refill one or more of the feed pipes 4, 10a, 10b, pump apparatus 3 and inlet pipe 8 with urea.

Figs 9a to 9d show a variety of possible gas-entrainment scenarios in a liquid injection system. In Fig 9a a liquid injection system is shown comprising a reservoir 6 containing liquid 7 and a pump 3 with integrated pressure sensor 5 supplying liquid to a common feed pipe 4 which then divides at a connector 9 into two individual feed pipes 10a, 10b which connect to two injectors 2a, 2b. The contents of the individual feed pipes 10a, 10b contain small bubbles 32 of gas with areas 31 of liquid in between the bubbles 32 of gas. Common feed pipe 4 contains liquid which does not contain gas 30. Fig 9c has the same identifying features as Fig 9a but the bubbles 32 of gas are so large as to be better described as remnants of liquid 31 in a gas-filled region of the individual feed pipes 10a and 10b. These alternatives are then seen as being essentially the same scenario but differing by matters of degree. These types of situation may arise due to leakage of air through injectors into the system, perhaps due to a differential pressure acting at the injector. Alternatively these situations may arise due to a partially effective purge operation, perhaps because some liquid becomes trapped within convolutions of the system. Or these situations may arise due to a partially effective priming operation, perhaps because some gas becomes trapped in the minor discontinuities of the system inner surfaces. These are only sample illustrations and those skilled in the art will appreciate that a wide range of scenarios are possible.

Fig 9b shows the system of Fig 9a once a successful purge operation of Fig 6 has been carried out. In this case the individual feed pipes 10a and 10b have been evacuated of all liquid, so containing only the gas 33 drawn into the system through the injectors 2a and 2b during the purge operation. The common feed pipe 4 contains the liquid 31 with bubbles of gas 32 which had been present in the individual feed pipes 10a and 10b prior to the purge operation of Fig 6. The pressure reduction measured during the purge operation provides an indication of the amount of gas in the common feed pipe 4 which is taken into account in subsequent injection or purge operations as previously described. Similarly Fig 9d shows the system of Fig 9c once a successful purge operation of Fig 6 has been carried out.

Fig 7 shows an alternative embodiment of a liquid injection system used for injecting water into an internal combustion engine 22 of a vehicle 20 for controlling engine temperatures and combustion. Similar issues occur in water injection systems as urea injection systems, e.g. damage to injectors when water freezes and expands inside the injector, and hence water injectors are purged to address this issue. Likewise this may cause gas entrainment which may affect the dose of water provided to the engine. Thus the above described method is useful for water injection systems as well. In this case the liquid injection system of Fig 7 would be described as a water injection system 28 having the same layout and identifying features as shown in Fig 2 except that water is used as the injected medium instead of urea 7. The injector is then arranged to inject water into an engine rather than urea into an exhaust. The skilled user would appreciate the need for system specifications such as pressure, flow rates and material specifications to be different between a urea injection system 26 in Fig 1 and 2 and a water injection system 28 in Fig 7.

The methods described above for application to a urea injection system 26 may usefully be applied to such a water injection system 28. Most particularly the measurement of pressure reduction and derivation of gas fraction as shown in Fig 3 may be performed in a water injection system shown in Fig 7. In such a water injection system 28 the injectors 2a, 2b are water injectors and the storage tank 6 is a water storage tank, and the principles of operation and control methods as described herein and illustrated in Figs 4, 5 and 6 remain the same.

The controller 11 will also receive signals not shown in the Figures, indicating the required water dosage, or signals that enable the controller 11 to calculate the required water dosage, such as engine operating conditions and engine speed and torque demands.

Fig 8 shows a schematic diagram of the controller 11 of Fig 2. In Fig 8 the controller 11 comprises a single processor 100 but, in other embodiments of the invention the controller 11 may comprise more than one processor 100. The controller 11 comprises at least one electronic memory device 101, having instructions 102 stored therein, and the electronic processor 100 is electrically coupled to the at least one electronic memory device 101, so that it can access the instructions 102.

The controller 11 comprises an electrical input 103 for receiving signals from the sensors (not shown) configured to at least detect the pressure in the system. The controller 11 also comprises an electrical output 104 for providing output signals to at least the injectors 2a, 2b and pump apparatus 5 in the embodiment of Fig 1.

The processor 100 is configured to access the instructions 102 stored in the memory device 101 and execute the instructions so that it is operable to perform the functions as described previously and as summarised in the flowcharts of Figs 3, 5 and 6 for measuring gas entrainment, performing liquid injection and performing purge operations.

For the purpose of this disclosure, it is to be understood that the controller 11 described herein can comprise a control unit or computational device having one or more electronic processors. A vehicle and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller 11 may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller or control unit(s) to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

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.

The blocks illustrated in Figs 3, 5 and 6 may represent steps in a method and/or sections of code in the computer program 102. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A controller for operating a liquid injection system, the liquid injection system comprising: at least one injector for injecting a dose of pressurised liquid, a pump apparatus for conveying liquid in a forward direction to pressurise the liquid injection system for performing liquid injection, and for conveying liquid in a backward direction to depressurise the liquid injection system, a pipe for conveying liquid between the pump apparatus and the at least one injector, a pressure sensor to measure pressure of liquid within the liquid injection system, wherein the controller is configured to: instruct the at least one injector to close, control the pump apparatus to run in the backward direction to depressurise the system, and determine a rate of pressure reduction during depressurisation.
2. The controller of claim 1 wherein the controller is configured to derive a measurement of an amount of gas entrained within the liquid from the rate of pressure reduction and output a signal indicative of the amount of gas entrained within the liquid.
3. The controller of any preceding claim wherein the controller is configured to control the pump apparatus to run in a forward direction to perform liquid injection by controlling an opening duration(s) of the at least one injector and/or a conveying power of the pump apparatus and/or an operating duration of the pump apparatus, in dependence on the measurement of the amount of gas entrained in the system.
4. The controller of claim 2 wherein the controller is configured to control the duration of a subsequent purge operation in dependence on the measurement of the amount of gas entrained in the system.
5. The controller of claim 4 for a system comprising at least two injectors, the controller being configured to control the pump apparatus to run in the backward direction to depressurise the system with only a first injector being open to evacuate liquid from a length of pipe feeding the first injector, and then controlling the pump apparatus to run in the backward direction to depressurise the system with only a second injector being open to evacuate liquid from a length of pipe feeding the second injector.
6. A system comprising the controller of any preceding claim and a liquid injection system, wherein the liquid injection system is a urea injection system for an exhaust gas treatment system of an internal combustion engine.
7. A system comprising the controller of any of claims 1 to 5 and a liquid injection system, wherein the liquid injection system is a water injection system for an internal combustion engine.
8. A vehicle comprising an internal combustion engine and a system according to claim 6 or claim 7.
9. A method for operating a liquid injection system, the system comprising at least one injector for injecting a dose of pressurised liquid, a pump apparatus for conveying liquid in a forward direction to pressurise the liquid injection system for performing liquid injection, and for conveying liquid in a backward direction to depressurise the liquid injection system, a pipe for conveying liquid between the pump apparatus and the at least one injector, a pressure sensor to measure pressure of liquid within the liquid injection system, wherein the method comprises: closing the at least one injector, controlling the pump apparatus to run in the backward direction to depressurise the system, and determining a rate of pressure reduction during depressurisation.
10. The method of claim 9 comprising deriving a measurement of an amount of gas entrained within the liquid from the rate of pressure reduction, and outputting a signal indicative of the amount of gas entrained within the liquid.
11. The method of any preceding claim comprising controlling the pump apparatus to run in a forward direction to perform liquid injection by controlling an opening durations of the at least one injector and/or a conveying power of the pump apparatus and/or an operating duration of the pump apparatus in dependence on the measurement of the amount of gas entrained in the system.
12. The method of claims 9 or 10 comprising adjusting the duration of a subsequent purge operation in dependence on the measurement of the amount of gas entrained in the system.
13. The method of claim 12 for a system comprising at least two injectors, comprising controlling the pump apparatus to run in the backward direction to depressurise the system with only a first injector being open to evacuate liquid from a length of pipe feeding the first injector, and then controlling the pump apparatus to run in the backward direction to depressurise the system with only a second injector being open to evacuate liquid from a length of pipe feeding the second injector.
14. A non-transitory computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of the method of claims 9 to 13.