GB2524111A

GB2524111A - Method of operating an exhaust valve of an internal combustion engine

Info

Publication number: GB2524111A
Application number: GB1404690.8A
Authority: GB
Inventors: Davide Di Nunno
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2014-03-14
Filing date: 2014-03-14
Publication date: 2015-09-16
Also published as: GB201404690D0

Abstract

Disclosed is a method of operating an exhaust valve 215 of an internal combustion engine 110, the method comprising the step of re-opening the exhaust valve during an engine compression stroke, to actuate a variable engine compression ratio. The method may also provide a step of opening the exhaust valve during an engine intake stroke to provide internal exhaust gas recirculation. Also disclosed is a camshaft comprising a multi lobed cam. In addition to a lobe for the main exhaust valve actuation the cam also has a lobes for opening the exhaust valve during the compression stroke and may have a further lobe for opening the exhaust valve during the intake stroke to provide the EGR function.

Description

METHOD OF OPERATING AN EXHAUST VALVE

OF AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of operating an exhaust valve of an internal combustion engine, to combine the effects of the compression ratio reduction and the internal exhaust gas recirculation (EGR).

BACKGROUND

In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. By using the variable valve timing, both a variable compression ratio and an internal exhaust gas recirculation can be performed.

As known, the compression ratio of an internal-combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. In particular, in a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.

Because cylinder-bore diameter, piston-stroke length and combustion-chamber volume are almost always constant, the compression ratio for a given engine is almost always constant. On the other hand, in order to improve the fuel consumption of the engines, one possible strategy is to have a variable compression ratio. This can be realized by having an expansion stroke bigger than the compression stroke. This cycle is known as "Miller cycle" and is realized keeping open the intake valve, after the end of the intake stroke, to let a certain amount of air be pumped back in the intake manifold and start the physical compression when the intake valve is closed. Delaying the intake valve closing in this way reduces the trapped air and consequently decreases the compression ratio.

As also known, to reduce the emissions content, in particular NOx emissions, normally Diesel engines include an exhaust gas recirculation (EGR) system coupled between the exhaust manifold and the intake manifold. As known, the EGR works by recirculating a portion of an enghe's exhaust gas back to the engine cylinders. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture. Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates.

Exhaust gas recirculation can also be actuated in a different way, the so called internal EGR. Internal EGR makes use of the valve overlap period, thus regulating how much exhaust gas still remains in the cylinder during the combustion process. Intemal EGR can also be actuated by re-opening the exhaust valve during the intake phase. For turbocharged engines, internal EGR is a benefit due to the increase of amount of air crossing the turbine and increase the efficiency of the turbo-compressor. The typical warm up requirement is also to have it as fast as possible and with the variable valve actuation this is done re-opening the exhaust valve during the intake stroke and have some exhaust gas re-breath in the combustion chamber to decrease the NOx emission and keep the overall temperature higher compared to the standard pipe gas recirculation.

At the time being a combined effect of variable compression ratio and internal EGR has never been realized in an efficient and cheap way.

Therefore a need exists for a method of operating ICE valves which can realize the above combined effect..

An object of an embodiment of the invention is to provide a method of operating an exhaust valve of an internal combustion engine, in particular, the method realizing the combined effect of a compression ratio reduction and an internal EGR.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, oy an apparatus, by a camshaft, by an engine, by a computer program and computer program product having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of operating an exhaust valve of an internal combustion engine, the method comprising the step of re-opening the exhaust valve during an engine compression stroke, to actuate a variable engine compression ratio.

Consequently, an apparatus is disclosed for performing the method of operating an exhaust valve of an internal combustion engine, the apparatus comprising means for re-opening the exhaust valve during an engine compression stroke, to actuate a variable engine compression ratio.

An advantage of this embodiment is that the method allows to obtain a variable compression ratio of the engine, in particular a reduction of the compression ratio, by only acting on the exhaust valve of the engine. Re-opening the exhaust valve during the compression stroke means that part of the trapped air flows through the exhaust valve, thus reducing the engine compression ratio.

According to another embodiment, the method further comprises the step of re-opening the exhaust valve during an engine intake stroke, to actuate an internal exhaust gas recirculation.

Consequently, the apparatus further comprises means for re-opening the exhaust valve during an engine intake stroke, to actuate an internal exhaust gas recirculation.

An advantage of this embodiment is that the method allows to actuate the variable compression ratio strategy and the internal EGR, by acting on the exhaust system only.

Another embodiment of the disclosures provides a camshaft of an intemal combustion engine, wherein the camshaft comprises at least a multi-lobed exhaust cam, configured for performing the method according to the previous embodiments.

An advantage of this embodiment is that the method for actuating a variable compression ratio of the internal combustion engine can be actuated with a simple mechanical system adopting multi-lobed exhaust cams.

According to an aspect of this embodiment, the multi-lobed exhaust cam is a bi-lobed cam.

The bi-lobed cam can be used to actuate the re-opening of the exhaust valve during the compression stroke.

According to another aspect of this embodiment, the multi-lobed exhaust cam is a tn-lobed cam.

The tn-lobed cam can be used to actuate the re-opening of the exhaust valve also during the intake stroke.

Another embodiment of the disclosure provides an internal combustion engine comprising an exhaust valve and a camshaft having a multi-lobed exhaust cam, wherein the exhaust valve is operated by a method according to any of the previous embodiments.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above1 and in the form of computer program product comprising the computer program.

The computer program product can be embedded in a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a schematic overview of an engine valve timing according to an embodiment of the present invention.

Figure 4 is a flowchart of the method according to an embodiment of the present invention.

Figure 5 schematically shows a bi-lobed cam of an engine camshaft.

Figure 6 is a flowchart of the method according to another embodiment of the present invention.

Figure 7 schematically shows a tn-lobed cam of an engine camshaft.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140.

The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) 250 with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine. In other embodiments, the turbocharger 230 may be a fixed geometry turbine including a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in

B

communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow, pressure, temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the waste gate actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulated technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

Instead of an ECU 450, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

According to an embodiment of the present invention, the function of the variable compression ratio is performed by only using the exhaust valve 215, better adopting a variable valve timing only for the exhaust valve.

According to a different embodiment, both the two functions (variable compression ratio and internal EGR) are realized by adopting a variable valve timing only for the exhaust valve.

Figure 3 is a schematic overview of an engine valve timing according to an embodiment of the present invention. In detail, curve 510 shows the intake valve opening, during the intake stroke, curve 520 is the exhaust valve opening during the exhaust stroke, curve 530 represents the exhaust valve first re-opening, during the intake stroke, operating the engine re-breathing i.e. the internal EGR. Finally, curve 540 is an exhaust valve second re-opening, during the compression stroke, realizing the variable compression ratio of the engine.

Goal of this invention is to improve fuel consumption and emissions of the internal combustion engines using only a variable valve actuation in the exhaust valve train. The benefit of a reduced compression ratio and internal EGR is achieved only using the exhaust valves re-opening instead of the intake and exhaust valve re-opening.

The exhaust valve will be open more thai one time during an engine cycle. For example, according to Fig. 4, the exhaust valves can be open two times in one cycle, with two different opening functions per cycle: a) opening during the normal exhaust stroke 5410; b) re-opening during the compression stroke 8420 to reduce the trapped air. i.e. the compression ratio. In this way near the bottom dead center (BOC) the intake valve is closed and the exhaust is open till to have the desired compression ratio. As an example, the variable valve timing can be a very simple mechanical system with a camshaft 135 having a bi-lobed exhaust cam 550, as shown in Fig. 5.

According to another embodiment, as shown in Fig. 6, the exhaust valves can be open three times in one cycle, with three different opening functions per cycle: a) opening during the normal exhaust stroke 8610; b) re-opening during the intake stroke 5620 to re-breath exhaust gas and reduce NOx emissions (i.e. performing internal EGR); c) re-opening during the compression stroke 8630 to reduce the trapped air, i.e. the compression ratio.

As an example, the variable valve timing can be a very simple mechanical system with a camshaft 135 having a tn-lobed exhaust cam 560 as shown in Fig. 7.

Summarizing, the present method allows to actuate the variable compression ratio strategy and the internal EGR system, by applying the technology to the exhaust system only, that is to say, only one variable valve timing system for the exhaust valves. In this way, the cost of a double system mechanization (variable valve timing applied to both intake and exhaust valves) is reduced by 50%.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 165 fuel injection system fuel rail fuel pump fuel source intake manifold 205 air intake duct 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGRcooler 320 EGR valve 330 throttle body 340 mass airflow, pressure, temperature and humidity sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail digital pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 510 intake valve opening 520 exhaust valve opening 530 exhaust valve first re-opening 540 exhaust valve second re-opening 550 bi-lobed cam 560 tn-lobed cam 8410 step 8420 step 8610 step 8620 step 8630 step

Claims

CLAIMS1. Method of operating an exhaust valve (215) of an internal combustion engine (110), the method comprising the step of re-opening the exhaust valve during an engine compression stroke, to actuate a variable engine compression ratio.
2. Method according to claim 1, wherein the method further comprises the step of re-opening the exhaust valve (215) during an engine intake stroke, to actuate an internal exhaust gas recirculation.
3. Camshaft (135) of an internal combustion engine (110), wherein the camshaft comprises at least a multi-lobed exhaust cam (550. 560), configured for performing the method according to claim 1 or 2.
4. Camshaft (135) according to claim 3, wherein the multi-lobed exhaust cam is a bi-lobed cam (550).
5. Camshaft (135) according to claim 3, wherein the multi-lobed exhaust cam is a tn-lobed cam (560).
6. Internal combustion engine (110) comprising an exhaust valve (215) and a camshaft 135) having a multi-Lobed exhaust cam (550, 560), wherein the exhaust valve is operated by a method according to claim 1 or 2.
7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-2.
8. Computer program product on which the computer program according to claim 7 is stored.
9. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 7 stored in the data carrier.