Patent Description:
When closing exhaust valves of a combustion engine, a certain amount of exhaust gas remains in the cylinders, especially in combustion engines comprising a turbocharger, because the counter-pressure of the turbocharger raises the pressure of the combustion gases in the cylinder during the exhaust stroke compared to engines that are not equipped with turbochargers. The high pressure in the cylinder of the engine can interfere with the injection of fuel into the cylinder, for example, using a nozzle that forms a thin, conical, short penetration jet into the cylinder.

It is well known in the field that injection of fuel at a cylinder pressure of more than <NUM> bar using the aforementioned nozzle significantly hinders the vaporization of the fuel, for example, when seeking to create a homogeneous (gas-)fuel mixture for so-called homogeneous combustion in the engine. In certain conditions, homogeneous combustion permits the free combustion of particles and nitrogen oxide (NOx) in engines, making it possible to avoid almost entirely the expensive further processing of exhaust gases.

Document <CIT> discloses that in an internal combustion engine with valve timing gear with two exhaust ports per cylinder, which are each controlled by one exhaust valve respectively, and with an exhaust turbocharger, the turbine of which can be bypassed by a bypass line, controlled by a blow-off valve, for the purpose of limiting the charge pressure, the first exhaust port of each cylinder is connected by way of an exhaust line to the turbine inlet and the second exhaust port of each cylinder to the bypass line. The cross-section of the exhaust line is designed solely for the exhaust gas mass flow needed for the maximum admissible charge pressure. As a result, a high rate of flow for the exhaust gases entering the turbine and a rapid response of the exhaust turbocharger are achieved.

Further, document <CIT> describes an exhaust flow system for a split exhaust flow in a multi-cylinder internal combustion engine fitted with an exhaust-driven supercharger of the turbocompressor type, whose exhaust system incorporates a catalytic exhaust cleaner, where each cylinder of the engine has both a first exhaust valve, from which released exhaust gas is fed to a first exhaust collector common to the cylinders, which collector is connected directly to the exhaust turbine inlet by a first exhaust branch pipe, and a second exhaust valve, from which released exhaust gas is fed to an exhaust pipe, which incorporates a silencer. At least one valve adjustable according to the operating conditions of the engine, is arranged downstream from the second exhaust valves of the cylinders, in their connection to the exhaust pipe between the exhaust turbine outlet and the silencer. The aim of this construction is to prevent the negative influence of the other cylinders with regards to emptying exhaust gases from the cylinder.

Furthermore, document <CIT> teaches an engine having exhaust gas turbochargers comprising two outlet valves arranged at each of multiple cylinders. The outlet valves of each cylinder are integrated to two groups. Exhaust gas is guided from the outlet valves to the exhaust gas turbochargers over exhaust gas channels that are attached to the group. A variable valve controller controls opening times of the exhaust gas valves depending on operating conditions of the engine. The exhaust gas turbochargers are equally dimensioned.

Additionally, document <CIT> discloses an internal combustion engine with valve timing gear with two exhaust ports per cylinder and with an exhaust turbocharger, the first exhaust ports of all cylinders are connected to the turbine inlet and the second exhaust ports of all cylinders to a bypass line bypassing the turbine. The second exhaust valves are opened later than the first exhaust valves, so that the greater portion of the exhaust gas energy can be used to drive the exhaust gas turbine. On opening of the second exhaust valves, a portion of the exhaust gas mass flow is led past the exhaust gas turbine, thereby limiting the charge pressure. The second exhaust valves are preferably provided with a variable valve timing gear, which on attainment of a certain charge pressure shifts the opening point towards earlier opening and/or increases the valve lift.

The publication "<NPL> describes a Z engine.

In view of the foregoing, it would be beneficial to provide a combustion engine and a method of operating a combustion engine, wherein the amount of exhaust gas remaining in the cylinders of the combustion engine can be controlled and/or reduced. The system should be capable of being manufactured in industrial scale.

According to a first aspect of the present invention, there is provided a combustion engine according to independent claim <NUM>. Said engine comprises a first exhaust gas channel and a separate second exhaust gas channel each connected to at least one cylinder, wherein the first exhaust gas channel is further connected to a turbocharger and the second exhaust gas channel is configured to bypass the turbocharger, and a throttling valve in the second exhaust gas channel configured to control an exhaust gas pressure in the cylinder.

According to a second aspect of the present invention, there is provided a method of operating an internal combustion engine according to independent claim <NUM>, the method comprising opening a first exhaust gas valve which is connected to a first exhaust gas channel, wherein the first exhaust gas channel is connected to a turbocharger, opening a second exhaust gas valve which is connected to a separate second exhaust gas channel, wherein the second exhaust gas channel is configured to bypass the turbocharger, and controlling an exhaust gas pressure in at least one cylinder by a throttling valve.

Various embodiments of the second aspect may comprise at least one feature from the following bulleted list:.

Considerable advantages are obtained by means of certain embodiments of the present invention. An internal combustion engine and a method of operating an internal combustion engine are provided. According to certain embodiments, the present invention is directed to a so called Z-motor. In particular, a two-stroke engine comprising a first exhaust gas channel connecting at least one cylinder and a turbocharger as well as a second exhaust gas channel connected to the cylinder and bypassing the turbocharger, wherein a throttling valve is arranged in the second exhaust gas channel by means of which the pressure in the cylinder can be controlled. Therefore, free burning of particles and NOx can take place according to certain embodiments of the present invention. Consequently, aftertreatment of exhaust gas can be completely or nearly completely avoided.

Additionally, the future temperature of the mixture in the cylinder can be controlled by the throttling valve. Further, also the ignition sensitivity of the mixture in the cylinder can be controlled by the throttling valve.

In <FIG> a schematic view of a combustion engine <NUM> in accordance with at least some embodiments of the present invention is illustrated. The internal combustion engine <NUM> is a two-stroke engine, for example a Z-motor, and comprises a turbocharger <NUM> configured to force air into a compressor <NUM> of the engine <NUM>. The turbocharger <NUM> is connected to a controllable compressor <NUM> via a first intercooler <NUM>. A mass flow of induction air can be adjusted by the compressor <NUM>. Pressure, temperature, and density of the air can be increased by the compressor <NUM>. The first intercooler <NUM> is configured to reduce induction air heat created by the turbocharger <NUM>. The compressor <NUM> is further connected to at least one cylinder <NUM> of the combustion engine <NUM> via a second intercooler <NUM>. The second intercooler <NUM> is configured to reduce induction air heat created by the compressor <NUM>. Additionally, a controllable intercooler bypass <NUM> is provided. The second intercooler <NUM> can be bypassed partially or completely by the intercooler bypass <NUM> in order to allow induction air to directly flow from the compressor <NUM> to the combustion chamber <NUM> provided in the at least one cylinder <NUM> of the combustion engine <NUM>, if required. The induction air is guided into the cylinders <NUM> of the combustion engine <NUM> via inlet valves <NUM>. At least one inlet valve <NUM> is provided for each cylinder <NUM> in the shown embodiment.

Further, each cylinder <NUM> comprises a first exhaust valve <NUM> and a second exhaust valve <NUM>. When the piston (not shown) is moving upwards in the cylinder <NUM>, the combustion gases are pushed out of the cylinder <NUM> to the turbocharger <NUM> through the engine's exhaust valves <NUM> against the turbocharger's counter pressure until the exhaust valves <NUM> close, i.e. typically earlier than <NUM> degrees before the piston's top dead centre. The majority of exhaust gases is guided from each cylinder <NUM> to a single main exhaust channel or exhaust duct <NUM> which is connected to the turbocharger <NUM> and further provides an exit for the exhaust gases from the combustion engine <NUM>.

In order to reduce the pressure of the combustion gases in the cylinder <NUM>, an additional second exhaust valve <NUM> is installed in the cylinder <NUM>. From each cylinder <NUM> exhaust gases can be guided to a single turbine bypass channel or bypass duct <NUM> which leads past the turbocharger's turbine <NUM> and then connects to the exhaust duct <NUM> coming from the turbocharger's turbine <NUM>. In the part of the exhaust duct <NUM> subsequent to the turbocharger's turbine <NUM> a low counter pressure prevails of nearly ambient atmospheric pressure. The turbine bypass duct <NUM> further comprises an adjustable throttle valve <NUM>.

The second exhaust valve <NUM>, by means of which combustion gases are capable of bypassing the turbocharger's turbine <NUM>, is configured to start to open when the piston is close to the bottom dead center, typically when the piston begins to move upwards during the exhaust of combustion gases from the cylinder <NUM>, and typically closes at the same time as the first exhaust valves <NUM>, which take exhaust gases to the turbocharger's turbine <NUM>, i.e. typically earlier than <NUM> degrees before the piston's top dead centre. The pressure in the cylinder <NUM> may be, for example, in the range between <NUM> bar and <NUM> bar, when the second exhaust valve <NUM> starts to open.

By controlling the aforementioned throttle valve <NUM> in the exhaust duct <NUM>, which is connected to the combustion engine's <NUM> second exhaust valves <NUM>, the pressure and amount of exhaust gas remaining in the cylinders <NUM> can be controlled or adjusted. Additionally, the future temperature and ignition sensitivity of the mixture <NUM> in the cylinder <NUM>, when the piston has compressed the mixture at the piston's <NUM> top dead centre, can be controlled or adjusted.

A new gas charge is then brought to the cylinder <NUM> under high pressure, about <NUM>-<NUM> crank degrees or about <NUM>-<NUM> crank degrees before the piston's top dead centre. The first and second exhaust valves <NUM>, <NUM> have been already closed before that.

Computer simulations and a test engine have shown that operation of an internal combustion engine <NUM> as described in this document works. For example, the combustion engine's <NUM> maximum rotation speed may be about <NUM> rpm so that it needs only one exhaust valve <NUM>. There is therefore space, e.g., in the cylinder head of the engine <NUM>, for the turbocharger's turbine's bypass exhaust valve <NUM> and its turbine bypass duct <NUM>.

In <FIG> a schematic cross sectional view of a cylinder <NUM> of a combustion engine in accordance with at least some embodiments of the present invention during ignition fuel injection, combustion and work stroke is illustrated. The moment of ignition of the mixture can then be controlled by various external methods, e.g., using a spark plug, or an injection of an ignition fuel <NUM> as shown in <FIG>.

In <FIG> a schematic cross sectional view of a cylinder <NUM> of a combustion engine in accordance with at least some embodiments of the present invention during the exhaust stroke is illustrated. When the engine's exhaust valve <NUM> opens, typically about <NUM>-<NUM> crank-angle degrees before the piston's <NUM> bottom dead centre, a rapid reduction in cylinder pressure, a so-called blowdown, occurs. This pressure pulse, which lasts for about <NUM>-<NUM> crankshaft degrees, contains as much as <NUM> % of the turbocharger's potential energy, when using a so-called pulse-turbocharger. After this, the upwards moving piston <NUM> pushes the combustion gases out of the cylinder <NUM> to the turbocharger <NUM> through the engine's exhaust valves <NUM> against the turbocharger's counter pressure, which is typically <NUM>-<NUM> bar, until the exhaust valves <NUM> close. Typically, the exhaust valves <NUM> close earlier than <NUM> degrees before the piston's top dead centre. In such a case, a significant amount of combustion gas remains in the cylinder <NUM>, the pressure of which is about the same as the turbocharger's counter pressure.

The combustion engine further comprises a second exhaust valve <NUM> which is connected to a second exhaust gas channel. The second exhaust gas channel bypasses the turbocharger <NUM>. A throttling valve <NUM> is arranged in the second exhaust gas channel <NUM>. The throttling valve <NUM> is configured to control a pressure in the cylinder <NUM>. As the pressure at the exit of the exhaust gas channel <NUM> is the pressure of ambient air, the amount of combustion gas remaining in the cylinder <NUM> can be consequently reduced by the combination of a second exhaust valve, a second exhaust gas channel, and the throttling valve.

In <FIG> a schematic cross sectional view of a cylinder <NUM> of a combustion engine in accordance with at least some embodiments of the present invention during fuel injection is illustrated. In terms of the fault-free operation of the engine <NUM>, it is necessary to control the pressure of the combustion gases in the cylinder <NUM>. Also the amount of the combustion-gas residue in the cylinder <NUM> of the engine is controlled so that the injection of fuel into the gas contained in the cylinder <NUM> will function well before the introduction of a new gas-charge into the cylinder <NUM> as shown in <FIG>. The fuel may be, for example, injected into the cylinder <NUM> in the form of a conical jet <NUM>. The pressure of the gas contained in the cylinder <NUM> may be less than <NUM> bar, for instance.

In <FIG> a schematic cross sectional view of a cylinder <NUM> of a combustion engine <NUM> in accordance with at least some embodiments of the present invention during air intake is illustrated. The inlet valves <NUM> have been opened in order to allow a new gas charge to flow into the cylinder <NUM>. The temperature of the mixture <NUM> of combustion gases, the scavenging gas, and fuel vapour in the cylinder <NUM> will drop sufficiently, so that the temperature of the aforementioned mixture in the cylinder <NUM>, when the piston <NUM> has compressed it to its top dead centre as shown in <FIG>, will be sufficiently low to prevent self-ignition of the mixture.

In <FIG> a schematic cross sectional view of a cylinder <NUM> of a combustion engine <NUM> in accordance with at least some embodiments of the present invention during final compression is illustrated.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the scope of the invention as defined by the claims.

Claim 1:
A combustion engine (<NUM>) comprising:
- a controllable compressor (<NUM>) connected to a turbocharger (<NUM>), wherein the compressor (<NUM>) is configured to adjust a mass flow of induction air,
- a first intercooler (<NUM>) arranged between the turbocharger (<NUM>) and the compressor (<NUM>) and configured to reduce induction air heat created by the turbocharger (<NUM>),
- a second intercooler (<NUM>) arranged between the compressor (<NUM>) and at least one cylinder (<NUM>) and configured to reduce induction air heat created by the compressor (<NUM>),
- a first exhaust gas channel (<NUM>) connected to the at least one cylinder (<NUM>), wherein the first exhaust gas channel (<NUM>) is further connected to the turbocharger (<NUM>),
- a first exhaust gas valve (<NUM>) configured to control an exhaust gas flow from the cylinder (<NUM>) to the first exhaust gas channel (<NUM>), and
- wherein the combustion engine (<NUM>) is a two-stroke engine,
characterized in that
- the combustion engine further comprises a separate second exhaust gas channel (<NUM>) connected to the at least one cylinder (<NUM>), wherein the second exhaust gas channel (<NUM>) is configured to bypass the turbocharger (<NUM>), and a throttling valve (<NUM>) in the second exhaust gas channel (<NUM>) configured to control an exhaust gas pressure in the cylinder (<NUM>),
- wherein the combustion engine (<NUM>) even further comprises a second exhaust gas valve (<NUM>) configured to control an exhaust gas flow from the cylinder (<NUM>) to the second exhaust gas channel (<NUM>), and
- wherein the second exhaust gas valve (<NUM>) is configured to be opened as a piston (<NUM>) begins to move upwards in the at least one cylinder (<NUM>) and to be closed earlier than <NUM> crank degrees before a piston's top dead center and as the first exhaust valve (<NUM>) is closed, and wherein the combustion engine (<NUM>) is configured to subsequently provide the at least one cylinder (<NUM>) with a gas charge in the range between about <NUM>-<NUM> crank degrees before the piston's top dead center.