GB2577904A

GB2577904A - A method of controlling exhaust gas recirculation for an engine

Info

Publication number: GB2577904A
Application number: GB1816493.9A
Authority: GB
Inventors: Jenkinson Samuel
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-10-10
Filing date: 2018-10-10
Publication date: 2020-04-15
Anticipated expiration: 2038-10-10
Also published as: GB2577904B; GB201816493D0

Abstract

Disclosed is a method of controlling exhaust gas recirculation for an engine 20 having individually controllable valve actuation means 27. The method comprises controlling valve actuation means 27 to, during a period of time associated with at least part of the duration for a combustion cycle, cause at least one exhaust valve 24 for a combustion chamber 21 to be open during an increase in volume of the combustion chamber and cause at least one intake valve 23 for the combustion chamber to be open during a subsequent reduction in volume of the combustion chamber. The exhaust valve may be closed before the volume of the combustion chamber stops increasing and the intake vale may be open during the reduction in volume whilst the exhaust valve is closed. The method allows exhaust gas to be pulled from the exhaust passage and pumped back to the inlet passage to provide a means of internal exhaust gas recirculation.

Description

A METHOD OF CONTROLLING EXHAUST GAS RECIRCULATION FOR AN ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of controlling exhaust gas recirculation for an engine. In particular, but not exclusively it relates to a method of controlling exhaust gas recirculation for an engine having individually controllable valve actuation means.

Aspects of the invention relate to a method, a controller, a system, a vehicle, a computer program and a non-transitory computer-readable storage medium.

BACKGROUND

It is known for some vehicles equipped with internal combustion engines to be able to reduce nitrogen oxide emissions by recirculating a portion of exhaust gas from the exhaust manifold to the intake manifold. This dilutes the oxygen with inert exhaust gases, resulting in lower in-cylinder temperatures. The lower temperature results in lower nitrogen oxide emissions, because nitrogen oxides are produced in a narrow band of high cylinder temperatures and pressures. The recirculation can also be an effective form of engine knock control.

A known 'exhaust gas recirculation (EGR) system comprises one or more control valves, piping, and an optional cooler. The system is arranged to capture a portion of exhaust gases from the exhaust manifold when the control valve is open, and transport the exhaust gases to the intake manifold. In the intake manifold, the exhaust gases mix with fresh charge air before the mixture is aspirated into the engine. Recirculated exhaust gases may constitute, for example, 5-15% of the total aspirated mixture. The cooler, if provided, cools the exhaust gases via heat exchange with engine coolant.

An EGR system adds cost and weight. Further, there are complexities particularly with boosted powertrains in ensuring that the pressure gradient draws gases in the correct direction through the EGR system, from the exhaust side towards the intake side of the engine.

It is an aim of the present invention to address disadvantages of the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a method, a controller, a system, a vehicle, a computer program and a non-transitory computer-readable storage medium as claimed in the appended claims.

According to an aspect of the invention there is provided a method of controlling exhaust gas recirculation for an engine having individually controllable valve actuation means, the method comprising controlling valve actuation means to, during a period of time associated with at least part of the duration for a combustion cycle: cause at least one exhaust valve for a combustion chamber to be open during an increase in volume of the combustion chamber; and cause at least one intake valve for the combustion chamber to be open during a subsequent reduction in volume of the combustion chamber.

This provides the advantage that the engine functions as a pump for drawing exhaust gases from the exhaust manifold into the combustion chamber on one stroke and then expelling them into the intake manifold on a subsequent stroke. This technique for recirculating exhaust gases is less sensitive than existing techniques to high pressures in the intake manifold compared to the exhaust manifold, and may be capable of very high levels of recirculation to create mixtures constituting over 30% recirculated exhaust gases. A dedicated EGR system is not required, saving cost and weight. The temporary repurposing of a combustion chamber for EGR rather than for producing torque causes no inconvenience at least while the other combustion chambers are generating sufficient torque to meet torque demand.

In some examples, the valve actuation means may be referred to as a 'variable valve actuation arrangement'.

In some examples, the method comprises controlling the valve actuation means to close the exhaust valve before the volume of the combustion chamber stops increasing.

This provides the advantage that no dedicated cooling hardware is required because the engine itself can cool the exhaust gas by adiabatic expansion while the volume is increasing and valves to the combustion chamber are closed, so that the exhaust gases are at a suitable temperature before being provided to the intake manifold.

In some examples, the exhaust valve is open during the increase in volume while the intake valve is closed and/or the intake valve is open during the reduction in volume while the exhaust valve is closed. In some examples, the increase in volume starts at a first time and ends at a second time, the reduction in volume starts at the second time and ends at a third time, the exhaust valve is open for at least 5% of the time between the first time and the second time, and/or the intake valve is open for at least 80% of the time between the second time and the third time. In some examples, the intake valve is closed between the first time and the second time for at least as long as the exhaust valve is open for, and/or wherein the exhaust valve is open between the second time and the third time for at least as long as the intake valve is open for.

These timings provide the advantage of increasing pumping and/or cooling efficiency.

In some examples, the increase in volume and reduction in volume are associated with stages of the combustion cycle based on their timing with respect to a firing order. In some examples, the increase in volume is associated with an intake stage of the combustion cycle and the reduction in volume is associated with a compression stage of the combustion cycle, and/or the increase in volume is associated with an expansion stage of the combustion cycle and the reduction in volume is associated with an exhaust stage of the combustion cycle.

This provides the advantage that even while the combustion chamber is operating as an EGR pump, its timing with respect to a normal combustion firing order is maintained. This improves engine balance, smoothness and reliability.

In some examples, at least one other combustion cycle is ongoing in one or more other combustion chambers of the engine during the increase in volume and the reduction in volume, for contributing to positive engine output torque as well as for driving the EGR pumping of the combustion chamber operating as the EGR pump.

This provides the advantage that the vehicle can be driven using the engine during EGR pumping.

In some examples, the method comprises inhibiting at least one of: fuel injection into the combustion chamber; aspiration of fresh air into the combustion chamber; or ignition within the combustion chamber, so that the combustion chamber does not contribute to positive engine output torque over a time duration corresponding to a complete combustion cycle that includes the period of time.

This provides the advantages of improved fuel efficiency, improved pumping efficiency, and fewer unnecessary load cycles on an ignition system.

In some examples, the valve actuation means is capable of controlling valve timing independently of crank timing of the engine. In some examples, the valve actuation means comprises at least one of: an electromagnetic actuator; a pneumatic actuator; or a hydraulic actuator.

This provides the advantage that the combustion chamber can operate in a plurality of different modes depending on how the valves are controlled.

In some examples, the at least one intake valve is for controlling gas exchange between an intake manifold and the combustion chamber, and wherein the intake manifold is shared with a plurality of other combustion chambers of the engine.

This provides the advantage that only one combustion chamber is needed to recirculate exhaust gas to other combustion chambers.

In some examples, the valve actuation means opens the at least one intake valve(s) after the at least one exhaust valve(s) have been closed and at or around a time when the volume of the combustion chamber stops increasing.

In some examples, either or both of the intake valves and exhaust valves are dedicated exhaust gas recirculation valves separate from intake and/or exhaust valves used in the combustion cycle.

According to another aspect of the invention there is provided an exhaust gas recirculation method comprising controlling valve actuation means to: aspirate exhaust gases into a combustion chamber of the engine; cool the exhaust gases in the combustion chamber; and exhaust the exhaust gases to an intake side of the engine to enable mixing of the cooled exhaust gases with fresh intake air.

According to a further aspect of the invention there is provided a controller comprising means to cause one or more of the methods described herein to be performed.

According to a further aspect of the invention there is provided a controller for an engine having individually controllable valve actuation means, the controller comprising means to control exhaust gas recirculation for the engine by controlling valve actuation means to, during a period of time associated with at least part of the duration for a combustion cycle: cause at least one exhaust valve for a combustion chamber to be open during an increase in volume of the combustion chamber; and cause at least one intake valve for the combustion chamber to be open during a subsequent reduction in volume of the combustion chamber.

In some examples, the controller comprises means to control the valve actuation means to close the exhaust valve before the volume of the combustion chamber stops increasing.

In some examples, the controller comprises means to control the valve actuation means such that the exhaust valve is open during the increase in volume while the intake valve is closed and/or such that the intake valve is open during the reduction in volume while the exhaust valve is closed.

In some examples, the increase in volume starts at a first time and ends at a second time, wherein the reduction in volume starts at the second time and ends at a third time, the controller comprising means to control the valve actuation means such that the exhaust valve is open for at least 5% of the time between the first time and the second time, and/or such that the intake valve is open for at least 80% of the time between the second time and the third time.

In some examples, the controller comprises means to control the valve actuation means such that the intake valve is closed between the first time and the second time for at least as long as the exhaust valve is open for, and/or such that the exhaust valve is open between the second time and the third time for at least as long as the intake valve is open for.

In some examples, the increase in volume and reduction in volume are associated with stages of the combustion cycle based on their timing with respect to a firing order.

In some examples, the increase in volume is associated with an intake stage of the combustion cycle and the reduction in volume is associated with a compression stage of the combustion cycle, and/or wherein the increase in volume is associated with an expansion stage of the combustion cycle and the reduction in volume is associated with an exhaust stage of the combustion cycle.

In some examples, the controller comprises means to control the valve actuation means such that at least one other combustion cycle is ongoing in one or more other combustion chambers of the engine during the increase in volume and the reduction in volume, for contributing to positive engine output torque.

In some examples, the controller comprises means to cause inhibition of at least one of: fuel injection into the combustion chamber; aspiration of fresh air into the combustion chamber; or ignition within the combustion chamber, so that the combustion chamber does not contribute to positive engine output torque over a time period corresponding to a complete combustion cycle that includes the period of time.

In some examples, the valve actuation means is capable of controlling valve timing independently of crank timing of the engine.

In some examples, the valve actuation means comprises at least one of: an electromagnetic actuator; a pneumatic actuator; or a hydraulic actuator.

According to a further aspect of the invention there is provided a system comprising the controller and the valve actuation means as described herein, wherein the controller comprises means to control the valve actuation means to cause one or more of the methods described herein to be performed.

According to a further aspect of the invention there is provided a powertrain system comprising a boosted powertrain, and the controller as described herein, wherein the controller comprises means to control valve actuation means to cause one or more of the methods described herein to be performed. The boosted powertrain may be turbocharged and/or supercharged.

According to a further aspect of the invention there is provided a controller comprising: at least one electronic processor; and at least one electronic memory device electrically coupled to the electronic processor and having instructions stored therein, the at least one electronic memory device and the instructions configured to, with the at least one electronic processor, cause one or more of the methods as described herein to be performed.

According to a further aspect of the invention there is provided a vehicle comprising the controller(s) described herein or the system described herein.

According to a further aspect of the invention there is provided a computer program that, when run on at least one electronic processor, causes one or more of the methods described herein to be performed.

According to a further aspect of the invention there is provided a non-transitory computer-readable storage medium embodying a computer program comprising computer program instructions that, when executed by at least one electronic processor, causes one or more of the methods described herein to be performed.

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 illustrates an example of the vehicle; Fig 2 illustrates an example of a cross-section through a combustion chamber of an engine; Fig 3 illustrates an example of how valve timing can be controlled for a combustion chamber; and Fig 4 illustrates an example electronic controller and an example non-transitory computer-readable storage medium.

DETAILED DESCRIPTION

Fig 1 illustrates an example of a vehicle 10 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 10 is a passenger vehicle, also referred to as a passenger car or as an automobile. Passenger vehicles generally have kerb weights of less than 5000 kg. In other examples, embodiments of the invention can be implemented for other applications, such as industrial vehicles, air or marine vehicles.

Fig 2 illustrates an example of an engine 20 in transverse cross-section. The engine 20 is illustrated schematically with a dashed line. The engine 20 may be configured to be provided to a vehicle such as the vehicle 10 of Fig 1. The cross-section represents a cut through a combustion chamber 21 of the engine 20.

The engine 20 is configured to perform combustion cycles for providing an output torque. Each combustion cycle has a number of stages. In some, but not necessarily all examples the combustion cycle is a four-stage combustion cycle. If the engine 20 is a reciprocating piston engine, the term 'stage' may be referred to as 'stroke'. Each cycle may have a duration of two crankshaft rotations, or in some implementations one or another number of crankshaft rotations.

In some examples, the engine 20 can be configured in the vehicle 10 to provide its output torque to a drivetrain. In other examples, the engine 20 can be configured to provide its output torque to a generator for charging a traction battery, if the vehicle 10 is for example a hybrid vehicle.

In some, but not necessarily all examples the engine 20 is a reciprocating piston engine.

The engine 20 of Fig 2 comprises one or a plurality of combustion chambers. Each combustion chamber may comprise at least all of the elements shown in Fig 2.

The engine 20 comprises, or is configured to be coupled to, one or more intake manifolds 25.

The engine 20 comprises, or is configured to be coupled to, one or more exhaust manifolds 26.

The intake manifold 25 is arranged to receive fresh oxygen-containing intake air, which may in some implementations be compressed by at least one upstream turbomachine compressor.

The intake manifold 25 has an intake opening and comprises branches defining a plurality of outlet openings each opening into a combustion chamber 21.

In some, but not necessarily all examples, the intake manifold 25 is shared by a plurality of combustion chambers of the engine 20. An opening in one combustion chamber and an opening in another combustion chamber each open into respective branches of the same intake manifold 25. In some examples, a combustion chamber may have multiple openings to the same intake manifold 25.

The exhaust manifold 26 is arranged to receive exhaust gases from the engine 20. The exhaust manifold 26 comprises branches defining a plurality of intake openings each opening into a combustion chamber, and at least one outlet opening. In some implementations, the at least one outlet opening of the exhaust manifold 26 is arranged to provide exhaust gases to at least one turbomachine turbine.

In some, but not necessarily all examples, the exhaust manifold 26 is shared by a plurality of combustion chambers of the engine 20. An opening in one combustion chamber and an opening in another combustion chamber each open into respective branches of the same exhaust manifold 26. In some examples, a combustion chamber may have multiple openings to a same or different (parallel) exhaust manifold(s).

Gas exchange between the illustrated intake manifold 25 and combustion chamber 21 is controlled by an intake valve 23. In some, but not necessarily all examples the intake valve 23 is a poppet valve. If the combustion chamber 21 has multiple openings to the intake manifold(s) 25, an intake valve may be provided for each opening.

When the intake valve 23 is 'open', the intake valve 23 allows gas exchange between the intake manifold 25 and the combustion chamber 21. While open, the intake valve 23 could be described as 'lifted' from its seat/'unseated', at least in the case of poppet valves. While closed (e.g. 'seated'), the intake valve 23 blocks gas exchange between the intake manifold 25 and the combustion chamber 21.

Gas exchange between the illustrated exhaust manifold 26 and combustion chamber 21 is controlled by an exhaust valve 24. In some, but not necessarily all examples the exhaust valve 24 is a poppet valve. If the combustion chamber 21 has multiple openings to the exhaust manifold(s) 26, an exhaust valve may be provided for each opening. An open exhaust valve may be described as 'lifted' from its seat/unseated'.

When the exhaust valve 24 is 'open', the exhaust valve 24 allows gas exchange between the combustion chamber 21 and the exhaust manifold 26. While open, the exhaust valve 24 could be described as 'lifted' from its seat/'unseated', at least in the case of poppet valves. While closed (e.g. 'seated'), the exhaust valve 24 blocks gas exchange between the combustion chamber 21 and the exhaust manifold 26.

Fig 2 also shows variable valve actuation means 27 (also referred to herein as a variable valve actuation arrangement). According to Fig 2, the variable valve actuation means 27 comprises intake-side variable valve actuation means a for controlling the intake valve(s) 23, and exhaust-side variable valve actuation means b for controlling the exhaust valve(s) 24.

The variable valve actuation means 27 comprises one or more actuators. Each actuator is configured to actuate one or more intake valves or one or more exhaust valves. Each actuator is configured to receive input energy in the form of mechanical, electrical, pneumatic or hydraulic energy, or a combination thereof, and to convert the input energy into motion of the respective valve.

In a conventional engine 20, the timing of input energy to an actuator may be constrained based on a crank angle domain (angular position). The synchronisation is commonly achieved by using a camshaft lobe to provide the required input energy and by providing a crank-cam coupling mechanism to couple the camshaft to the crankshaft with a 2:1 (crank:cam) ratio. Some engines employ simple variable valve timing mechanisms, enabling switching between two or more discrete (yet still constrained to crank angle domain) timing strategies by changing the angular relationship between the camshaft and the crankshaft.

In some, but not necessarily all examples, the variable valve actuation means 27 is configured so that timing of input energy to each actuator is unconstrained by crank angle domain. This enables the variable valve actuation means 27 to control valve timing independently of crankshaft timing of the engine 20. For example, a valve could be opened at any crank angle, and closed at any later crank angle.

The variable valve actuation means 27 may even be configurable to change a combustion cycle of the engine 20, for example between four-stroke and two-stroke operation.

Electromagnetic, pneumatic and hydraulic actuators are capable of this independent behaviour. Such actuators may have the benefit of changing from one state to another quickly, for example with a delay of only one or two top dead centres. In an example implementation, an electromagnetic actuator, rather than a crank-cam coupling mechanism, is configured to rotate a camshaft.

Even if not independent of crank angle domain, the variable valve actuation means 27 may at least be configured for sufficient discrete or continuous timing variability to enable examples of the present disclosure to be implemented. For example, the input energy may be provided by one or more camshafts, and the camshaft angle may be varied with respect to the crank angle domain via a known form of timing adjustment mechanism. Such an adjustment mechanism may include any independent valve actuation means on each valve, for example an electromagnetic actuation means on each valve cam.

In some, but not necessarily all examples the variable valve actuation means 27 is configured to enable continuously variable valve lift, by which the peak lift distance of the valve from its seated (closed) position is variable by hundreds or more increments. One hydraulic implementation could involve controlling a filling of hydraulic fluid into a hydraulic tappet of known type. One electrical implementation could involve controlling when to reverse a direction of rotation of a cam-driving electric motor.

In some, but not necessarily all examples, desmodromic means are provided in conjunction with the variable valve actuation means 27 to enable desmodromic valve actuation.

The variable valve actuation means 27 may be operably coupled to one or more electronic controllers 30 ('controller' for short) as shown in Fig 2. Electronic controllers will be described in more detail later.

It would be understood that it is possible for at least part of the engine 20, and the intake valve(s) 23, the exhaust valve(s) 24, the intake manifold(s) 25, the exhaust manifold(s) 26, the variable valve actuation means 27, and the electronic controller(s) 30 to each be supplied by a different supplier and fitted at different stages of manufacture of a vehicle 10 or a system.

Certain aspects of the present invention relate to a system comprising at least the electronic controller(s) 30 and the variable valve actuation means 27. The system could optionally comprise one or more pieces of the additional above-listed hardware depending on the state of assembly of the vehicle 10.

Fig 3 illustrates an example of how valve timing can be controlled for a combustion chamber 21, for realizing one or more advantageous aspects of the present invention. The illustrated combustion chamber 21 is the type shown in Fig 2, for example. The combustion chamber 21 is illustrated in cross-section in Fig 3 at six different times labelled A-F.

If the variable valve actuation means 27 were operated in a normal 'combustion cycle mode' (not shown in Fig 3), a four-stroke combustion cycle would occur in the combustion chamber 21, in which: a first stroke of the cycle would be an the intake stroke during which at least one intake valve 23 would open during a downstroke; the next stroke would be a compression stroke throughout which all valves would be closed; the next stroke would be an expansion/power stroke during which all valves would be closed and the fuel-air mixture would be ignited to contribute positive engine output torque; and the next, final stroke would be an exhaust stroke during which at least one exhaust valve 24 would be open.

The variable valve actuation means 27 for at least one combustion chamber 21 can be controlled to switch from 'combustion cycle mode' to 'deactivated mode'. The deactivated mode may be any mode which does not have combustion (that is, no fuel is being injected). When in deactivated mode, at least the intake valve 23 may not open during the intake stroke.

However it would be useful if when deactivated the variable valve actuation means 27 could control the valves to perform a useful function.

In some, but not necessarily all examples the variable valve actuation means 27 can be controlled to switch from 'combustion cycle mode' or 'deactivated mode' to perform a useful 'EGR mode' function. Fig 3 illustrates the valve timing for an EGR cycle in EGR mode. To complete an EGR cycle, the valve timing is controlled so that the combustion chamber 21 back-pumps exhaust gas from the exhaust side to the intake side of the engine 20.

In some, but not necessarily all examples, an EGR cycle is made possible by controlling the variable valve actuation means 27 to: cause at least one exhaust valve 24 for a combustion chamber 21 to be open during an increase in volume of the combustion chamber 21 (e.g. downstroke); and cause at least one intake valve 23 for the combustion chamber 21 to be open during a subsequent reduction in volume of the combustion chamber 21 (e.g. upstroke). Fig 3 shows several additional features which further improve EGR mode.

An EGR cycle is performed during a period of time associated with at least part of the duration for a combustion cycle of the combustion chamber 21 (wherein the combustion cycle is not actually performed in the combustion chamber at the same time as the EGR cycle). For example, the period of time is two strokes in the example of Fig 3, which is associated with half of the duration of a four-stroke combustion cycle.

While an EGR cycle is performed in the combustion chamber 21, at least one other combustion cycle is ongoing in one or more other combustion chambers of the engine 20 concurrently, for contributing to positive engine output torque.

Fig 3 will now be explained in order from times A-F.

Times A and B represent the final two strokes in 'combustion cycle mode' operation of the combustion chamber 21.

At time A, a piston 22 in the combustion chamber 21 is at the end of an expansion stroke. The piston 22 is at bottom dead centre (BDC). All valves are closed.

At time B, the piston 22 is at the end of the next stroke which is an exhaust stroke. The piston 22 is at top dead centre (TDC). The (or a plurality of or all) exhaust valve(s) 24 are open and all intake valve(s) 23 are closed.

From times C-F, the variable valve actuation means 27 is controlled to switch from combustion cycle mode to EGR mode. Times C-F show one EGR cycle (two strokes).

Instead of performing an intake stroke on the downstroke (combustion cycle mode) the variable valve actuation means 27 is controlled to cause the (or a plurality of or all) exhaust valve(s) 24 for the combustion chamber 21 to be open during the increase in volume of the combustion chamber 21/downstroke (EGR mode stage 1), as shown in Fig 2 at time C. Causing 'to be open' means either actively re-opening the exhaust valve(s) 24 if they are closed, or not closing the exhaust valve(s) 24 if they are open. 'During' means for at least part of the downstroke. The duration of exhaust valve opening defines how much exhaust gas will be aspirated into the combustion chamber 21.

In the downstroke, the volume in the combustion chamber 21 increases due to the piston's travel from TDC to BDC. Therefore, the volume increase is increasing suction pressure in the combustion chamber 21 which draws exhaust gas back into the combustion chamber 21 past the open exhaust valve(s) 24.

In some, but not necessarily all examples, the exhaust valve(s) 24 are open during the increase in volume while the (or a plurality of or all) intake valve(s) 23 for the combustion chamber 21 are closed.

Time D is later than time C but shows the same downstroke as time C. At time D, an optional step is performed of controlling the variable valve actuation means 27 to close the open exhaust valve(s) 24 before the volume of the combustion chamber 21 stops increasing.

The reason for closing the valves before BDC (bBDC) is to allow the subsequent volume increase bBDC to adiabatically expand and therefore cool the aspirated exhaust gas. The cooling provides additional EGR benefits for reducing nitrogen oxide emissions and engine knock control.

The proportion of time allocated to exhaust gas aspiration (c.f. time C) relative to adiabatic cooling (c.f. time D) can be controlled, even variable from cycle to cycle. This control will now be discussed in more detail.

The increase in volume starts at a first time (TDC) and ends at a second time (BDC), wherein the exhaust valve(s) 24 are open for at least X1% of the time between the first time and the second time.

A good lower limit for X1 is X15%. Alternative lower limits for X1 are X1-1 0%, X133% and X1a.50% if cooling is less important.

An upper limit for X1 may be X1 00%, wherein X1=100% provides maximum exhaust gas aspiration.

Of course, the exhaust valve(s) 24 do not need to be open exactly at TDC. If the opening time of the exhaust valve(s) 24 occurs within x% of the time between TDC and BDC starting from TDC, a suitable value for x could be ±33%.

The closing time of the exhaust valve(s) 24 occurs within y% of the time between TDC and BDC starting from TDC. If y=100%, the exhaust valve(s) 24 close at BDC so no adiabatic cooling is performed. If y>100%, the exhaust valve(s) 24 close after the beginning of the next upstroke. If adiabatic cooling is desired, y can be in the range 066% or ys50°/0.

In an example, if x=0% (TDC) and y=10% (10% after TDC [aTDC]), X1 will be 10% and exhaust gases will be expanded to a volume of 10:1 for a good amount of cooling.

If there are several exhaust valves that open and close at different times, take X1, x and y and any other relevant metrics to be the arithmetic average across all exhaust valves.

In some, but not necessarily all examples, the above exhaust valve timing is capable of providing a volume expansion of the exhaust gases of up to 15:1 (or more in some examples).

Control of X1 and/or x and/or y can be continuously variable in some examples, or at least variable by a plurality of increments, depending on the implementation of the variable valve actuation means 27.

During the downstroke (c.f. times C and D), the intake valve(s) 23 may be closed as mentioned above. The intake valve(s) 23 may be closed at TDC. The intake valve(s) 23 may still be closed at BDC. The intake valve(s) 23 may be closed for 100% of the downstroke. Alternatively, the intake valve(s) 23 may be closed for at least 98% or at least 90% of the stroke, provided that the EGR cycle does not become overly inefficient.

In some, but not necessarily all examples, the intake valve(s) 23 are closed between TDC and BDC for at least as long as the exhaust valve(s) 24 are open for. There may be no period of overlapping opening throughout the downstroke defined by any one of the intake valve(s) 23 and any one of the exhaust valve(s) 24 being open at the same time.

Moving on, time E shows the piston 22 at BDC (the second time), and time F shows the piston 22 at TDC following an upstroke between times E and F that occurs after the downstroke of times C and D. Instead of performing a compression stroke on the upstroke between times E and F (combustion cycle mode), the variable valve actuation means 27 is controlled to cause the (or a plurality of or all) intake valve(s) 23 for the combustion chamber 21 to be open during this subsequent reduction in volume of the combustion chamber 21/upstroke (EGR mode stage 2).

Causing 'to be open' means either actively opening the intake valve(s) 23 if they are closed, or not closing the intake valve(s) 23 if they are open. 'During' means for at least part of the upstroke. The duration of intake valve opening defines how much exhaust gas will be exhausted from the combustion chamber 21.

In the upstroke, the volume in the combustion chamber 21 decreases due to the piston's travel from BDC to TDC. Therefore, the volume is increasing pressure in the combustion chamber 21 which pushes the exhaust gases out into the intake manifold 25 past the open intake valve(s) 23.

In some, but not necessarily all examples, the intake valve(s) 23 are open during the reduction in volume while the or a plurality of or all exhaust valve(s) 24 for the combustion chamber 21 are closed.

The upstroke between times E and F may be the upstroke that immediately follows the downstroke of times C and D. However, in other examples a plurality of intervening strokes (not shown) between times D and E may occur during which the gases are compressed and expanded one or more times for engine braking (by pumping losses) or for other reasons.

In Fig 3 at time E, but not necessarily in all examples, the variable valve actuation means 27 is controlled to cause the or a plurality of or all intake valve(s) 23 to be open at BDC. This equalizes the pressure between the combustion chamber 21 and intake manifold 25 and helps to lower the overall in-cylinder temperature (since the gases in the intake manifold can be expected to be cooler than the exhaust gases, even after adiabatic cooling). In other examples, the intake valve(s) 23 may be opened within ±2% or ±5% or ±10% of TDC (100% representing full travel between TDC and BDC). This process is facilitated if the pressure in the combustion chamber 21 is substantially lower than the pressure in the intake manifold, which will be the case if both the intake and exhaust valves were closed between D and E. In Fig 3 at time F, but not necessarily in all examples, the intake valve(s) 23 are still open at TDC at the end of the upstroke. In other examples, the intake valve(s) 23 may be in their closed positions within ±2% or ±5% or ±10% of TDC (100% representing full travel between 20 TDC and BDC).

Regarding the timing of opening of the intake valve(s) 23, the reduction in volume starts at the second time (BDC, time E) and ends at a third time (TDC, time F), wherein the intake valve(s) 23 are open for at least X2% of the time between the second time and the third time.

In some examples X2=100% to minimise pumping losses due to compression, and maximise the exhaust gases that are exhausted into the intake manifold 25. In other examples, X2 may be at least 98% or at least 90% of the stroke, provided that efficiency is not significantly harmed. Other values may be possible in other examples if engine braking by pumping losses is desired.

If there are several intake valves that open and close at different times, take X2 and any other relevant metrics to be the arithmetic average across all exhaust valves.

During the upstroke from times E to F, the exhaust valve(s) 24 may be closed as mentioned above. The exhaust valve(s) 24 may be closed at BDC. The exhaust valve(s) 24 may be still closed at TDC. The exhaust valve(s) 24 may be closed for 100% of the upstroke. Alternatively, the exhaust valve(s) 24 may be closed for at least 98% or at least 90% of the stroke, provided the EGR cycle does not become overly inefficient.

In some, but not necessarily all examples, the exhaust valve(s) 24 are closed between BDC and TDC for at least as long as the intake valve(s) 23 are open for. There may be no period of overlapping opening throughout the upstroke defined by any one of the intake valve(s) 23 and any one of the exhaust valve(s) 24 being open at the same time.

After time F, the process may loop back to time C for another EGR cycle, or switch to a combustion cycle mode.

Fig 3 and the above description should only be taken as representative of one of several possible implementations of the examples disclosed herein. Fig 3 is representative of a particular scenario of switching from four-stroke combustion cycle mode to EGR mode. However, alternative scenarios and timings are possible which will now be discussed.

It would be appreciated from the above that the above-described increase in volume/downstroke and reduction in volume/upstroke of the EGR cycle are associated with stages of the combustion cycle based (solely) on their timing with respect to a firing order, wherein no combustion cycle actually occurs during the EGR cycle.

Fig 3 illustrates the scenario in which the increase in volume/downstroke is associated with an intake stage of the combustion cycle (with respect to the firing order) and the reduction in volume is associated with a compression stage of the combustion cycle (with respect to the firing order).

However, since the above EGR cycle requires only two strokes, another implementation would involve the increase in volume/downstroke being associated with an expansion stage of the combustion cycle (with respect to the firing order) and the reduction in volume being associated with an exhaust stage of the combustion cycle (with respect to the firing order).

Further regarding timing, in some, but not necessarily all examples the EGR mode is controlled so that a place of the combustion chamber 21 within the firing order is retained despite switching into and out of EGR mode. The electronic controller(s) 30 may be configured to prohibit the situation where a single two-stroke EGR cycle occurs and the next cycle is a four-stroke combustion cycle. This could imbalance the engine 20 by phasing the combustion chamber 21 two strokes out of its firing order. It would be preferable to perform consecutive EGR cycles if necessary, and to switch modes at certain times so that a firing order is preserved. In some examples, if the hardware is flexible, one two-stroke EGR cycle could be followed by one two-stroke combustion cycle, before switching back to a normal four-stroke combustion cycle having a same place in the engine firing order.

A further optional feature for EGR mode is that fuel, air and/or ignition strategies for the combustion chamber 21 may differ from normal. In the normal combustion cycle mode, fuel would be injected into the air charge in the intake manifold 25 or into the combustion chamber 21, during or just before an intake stroke. Fresh air/the air-fuel mixture would be aspirated into the combustion chamber 21 during the intake stroke. The compressed mixture would be ignited just before or after the start of the expansion stroke.

Although not shown in Fig 3, the electronic controller(s) 30 may in some examples be configured to cause appropriate hardware (e.g. variable valve actuation means 27, fuel injection system, ignition system) to cause inhibition of at least one of: fuel injection into the combustion chamber 21; aspiration of fresh air into the combustion chamber 21; or ignition within the combustion chamber 21. As a result the combustion chamber 21 does not contribute to positive engine output torque over (throughout) a time duration corresponding to a complete combustion cycle that includes the EGR cycle period of time. This may improve engine efficiency and at least reduce unnecessary load cycles on the fuel injection and ignition systems.

In a further optional feature of the present disclosure, the EGR mode could be assigned, not to one combustion chamber 21, but could be a rolling deactivation. For example, in a two combustion chamber engine 20: - one or more EGR cycles occurs in a first combustion chamber while a combustion cycle occurs in a second combustion chamber; then - one or more EGR cycles occurs in the second combustion chamber while a combustion cycle occurs in the first combustion chamber.

The rolling deactivation could be applied to all combustion chambers in a sequence following the engine firing order. The result is reduced noise, vibration and harshness from the engine 20.

The hardware and functionality disclosed above may be controlled by one or more electronic controllers, including for example the electronic controller 30 of Fig 2. The electronic controller(s) may include an engine control unit (ECU), and/or may include a dedicated variable valvetrain controller. The electronic controller can communicate with each other (if several) and control hardware/actuators such as the variable valve actuation means 27 to enable examples of the present disclosure to be implemented. One or more communication buses may be provided to enable communication.

Fig 4 illustrates an example architecture for an electronic controller 30 capable of performing a method of controlling exhaust gas recirculation for an engine 20. The electronic controller comprises at least one electronic processor 42; and at least one electronic memory device 44 electrically coupled to the electronic processor 42 and having instructions 48 stored therein, the at least one electronic memory device 44 and the instructions 48 configured to, with the at least one electronic processor, cause any one or more of the methods described herein to be performed. The instructions 48 may be stored in a computer program 46 stored in the electronic memory device 44.

Alternatively, the instructions 48 may be stored in a non-transitory computer-readable storage medium 49 as shown in Fig 4 prior to loading into the electronic memory device 44, for example in situations where the instructions 48 are to be loaded as a software update.

For purposes of this disclosure, it is to be understood that the controller(s) described herein can each comprise a control unit or computational device having one or more electronic processors. A vehicle 10 and/or a system thereof may comprise a single control unit or electronic controller 30 or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions 48 could be provided which, when executed, cause said controller(s) 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 42, or alternatively, the set of instructions 48 could be provided as software 46 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 48 described above may be embedded in a computer-readable storage medium 49 (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 ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Various inputs may be received by the electronic controller(s) 30 enabling decisions to be made regarding whether to switch to EGR mode, and whether to perform other functions disclosed herein.

For example, the electronic controller(s) 30 could control the variable valve actuation means 27 to switch from combustion cycle mode to deactivated mode and/or EGR mode in dependence on one or more monitored factors such as engine speed, engine load (e.g. torque demand), hybrid vehicle battery parameters (state of charge etc).

A decision to enter EGR mode could be made in dependence on one or more monitored factors such as: entering a certain region of an engine map based on engine speed, engine load or other conditions; monitored nitrogen oxide; monitored carbon dioxide; monitored temperature; monitored engine knock from a knock sensor. An optional gas model for mass flow could be implemented, taking as inputs the pressure or another airflow parameter from at least one of a combustion chamber, the exhaust manifold 26, the intake manifold 25, and calculating the mass flow through the engine 20. The inputs could feed in to an open loop, feed forward or closed loop process for providing a desired level of EGR.

A decision to enter or return to normal combustion cycle mode could occur if an overriding engine load occurs indicated for example by accelerator pedal position.

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.

Further, although example implementations have been discussed in relation to the 'intake' valves and 'exhaust' valves, it would be appreciated that another implementation could involve fitting one or more dedicated valves for EGR purposes, separate from the intake and exhaust valves. The dedicated valves may be for controlling gas flow into or out of one or more dedicated EGR plenums able to exchange gases with the relevant manifolds.

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 method of controlling exhaust gas recirculation for an engine, the method comprising controlling valve actuation means to, during a period of time associated with at least part of the duration for a combustion cycle: cause at least one exhaust valve for a combustion chamber to be open during an increase in volume of the combustion chamber; and cause at least one intake valve for the combustion chamber to be open during a subsequent reduction in volume of the combustion chamber.
2. The method as claimed in claim 1, comprising controlling the valve actuation means to close the exhaust valve before the volume of the combustion chamber stops increasing.
3. The method as claimed in claim 1 or 2, wherein the exhaust valve is open during the increase in volume while the intake valve is closed and/or wherein the intake valve is open during the reduction in volume while the exhaust valve is closed.
4. The method as claimed in claim 1, 2 or 3, wherein the increase in volume starts at a first time and ends at a second time, wherein the reduction in volume starts at the second time and ends at a third time, wherein the exhaust valve is open for at least 5% of the time between the first time and the second time, and/or wherein the intake valve is open for at least 80% of the time between the second time and the third time.
5. The method as claimed in claim 4, wherein the intake valve is closed between the first time and the second time for at least as long as the exhaust valve is open for, and/or wherein the exhaust valve is open between the second time and the third time for at least as long as the intake valve is open for.
6. The method as claimed in any preceding claim, wherein the increase in volume and reduction in volume are associated with stages of the combustion cycle based on their timing with respect to a firing order.
7. The method as claimed in claim 6, wherein the increase in volume is associated with an intake stage of the combustion cycle and the reduction in volume is associated with a compression stage of the combustion cycle, and/or wherein the increase in volume is associated with an expansion stage of the combustion cycle and the reduction in volume is associated with an exhaust stage of the combustion cycle.
8. The method as claimed in claim 6 or 7, wherein at least one other combustion cycle is ongoing in one or more other combustion chambers of the engine during the increase in volume and the reduction in volume, for contributing to positive engine output torque.
9. The method as claimed in claim 8, comprising inhibiting at least one of: fuel injection into the combustion chamber; aspiration of fresh air into the combustion chamber; or ignition within the combustion chamber, so that the combustion chamber does not contribute to positive engine output torque over a time duration corresponding to a complete combustion cycle that includes the period of time.
10. The method as claimed in any preceding claim, wherein the valve actuation means is capable of controlling valve timing independently of crank timing of the engine.
11. The method as claimed in any preceding claim, wherein the valve actuation means comprises at least one of: an electromagnetic actuator; a pneumatic actuator; or a hydraulic actuator.
12. The method as claimed in any preceding claim, wherein the at least one intake valve is for controlling gas exchange between an intake manifold and the combustion chamber, and wherein the intake manifold is shared with a plurality of other combustion chambers of the engine.
13. The method as claimed in any preceding claim, wherein the valve actuation means opens the at least one intake valve after the at least one exhaust valve have been closed and at or around a time when the volume of the combustion chamber stops increasing.
14. The method as claimed in any preceding claim, wherein either or both of the intake valves and exhaust valves are dedicated exhaust gas recirculation valves separate from intake and/or exhaust valves used in the combustion cycle.
15. A controller comprising means to cause the method as claimed in any one or more of claims 1 to 14 to be performed.
16. A system comprising the controller of claim 15 and valve actuation means, wherein the controller comprises means to control the valve actuation means for causing the method as claimed in any one or more of claims 1 to 14 to be performed.
17. A controller comprising: at least one electronic processor; and at least one electronic memory device electrically coupled to the electronic processor and having instructions stored therein, the at least one electronic memory device and the instructions configured to, with the at least one electronic processor, cause the method as claimed in any one or more of claims 1 to 14 to be performed.
18. A vehicle comprising the controller of claim 15, the system of claim 16 or the controller of claim 17.
19. A computer program that, when run on at least one electronic processor, causes the method as claimed in any one or more of claims 1 to 14 to be performed.
20. A non-transitory computer-readable storage medium embodying a computer program comprising computer program instructions that, when executed by at least one electronic processor, causes the method as claimed in any one or more of claims 1 to 14 to be performed.