GB2478718A

GB2478718A - An internal combustion engine with different cylinder displacements

Info

Publication number: GB2478718A
Application number: GB1004256A
Authority: GB
Inventors: Giovanni Cipolla
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-03-15
Filing date: 2010-03-15
Publication date: 2011-09-21
Also published as: GB201004256D0

Abstract

An internal combustion engine 2 has a plurality of cylinders 4, 6, 8, 10 with a predetermined overall displacement D and an electronic control unit 12 controlling the operation thereof. At least one first cylinder has a respective displacement greater than a reference value obtained by dividing said overall displacement D by the number of cylinders, and at least one second cylinder has a respective displacement smaller than said reference value; and in that said electronic control unit 12 is predisposed for selectively turning off at least one of the engine cylinders 4, 6, 8, 10 in predetermined operating conditions. The cylinders may be of different bore volumes or may have different stroke lengths.

Description

An internal combustion engine with different cylinder displacements

Technical field

The present invention relates to an internal combustion engine having different cylinder displacements.

More specifically, the invention relates to an internal combustion engine having a plurality of cylinders with a predetermined overall displacement, and an electronic control unit controlling the operation thereof.

Background

The engine displacement is related to the brake mean effective pressure (BMEP) which is a quantity indicative of the operation of an internal combustion engine, in particular it is a measure of the engine capacity to do work. The mean effective pressure is proportional to the ratio of the engine torque to the engine displacement.

Figure 1 shows an example of a graph wherein curves indicative of engine specific fuel consumption are depicted in a plane identified by the brake mean effective pressure vs. the engine speed (revolutions per minute) . Each curve joints points corresponding to a same specific fuel consumption whose value (measured in g/kWh) is quoted on the graph.

As can be noted from the curves of figure 1, for a predefined value of engine speed, internal combustion engines having a lower displacement (and therefore a higher brake mean effective pressure) have a lower specific fuel consumption with respect to engines having a bigger displacement.

In order to reduce the fuel consumption, it is known to perform a down-sizing of the displacement of internal combustion engines when the latter are operating at partial load (i.e. when a reduced power is requested, for example during city driving) . These systems are known as Displacement on Demand (DoD) systems.

A rnulticylinder engine is conventionally designed with all cylinders having a same displacement in order to have an uniform behaviour in terms of performance and NVH (Noise, Vibration and Harshness) . In addition, such an approach has also manufacturing and assembly advantages.

Due to this fact, in order to downsize the displacement of a four-cylinder engine, two cylinders are turned off, for example by discontinuing the supply of fuel to said cylinders and, in gasoline engines, also by not turning on the respective plugs or by not allowing air to enter said cylinders.

These known systems suffer from the disadvantage that they allow only a 2-step operation, i.e. the engine can operate only in two conditions, a first condition wherein all four cylinders are active and a second condition wherein two cylinders are active and two cylinders are inactive. In the first condition the engine displacement has a first value while in the second condition the engine displacement has a second value which is half the first value.

This leads to a bad driving comfort because of the big displacement difference between the first and the second condition.

Furthermore, it is known that the combustion process in an internal combustion engine produces NOR, CO, C02, HC (unburned Hydrocarbons) and soot (in diesel engines) : in low fuel consumption conditions, the HC and CO, due to an incomplete and inefficient combustion, vary in opposite way with respect to NO and C02, which are subjected, on the contrary, to a complete and high temperature/high efficient combustion. As a consequence, the known two-step "Displacement On Demand" technique doesn't allow to get a fine optimization of all engine parameters (i.e. consumption and emissions) Figure 2 and figure 3 show graphs wherein curves indicative of the hydrocarbon and NO emissions, respectively, of an engine are depicted in a plane identified by the brake mean effective pressure vs. the engine speed (revolutions per minute) . Each curve joints points having the same hydrocarbons and NO emission, respectively, whose value (measured in ppm) is quoted on the graph.

As can be noted, considering a predefined value of engine speed, the hydrocarbon emissions are higher for low BMEP values than for high BMEP values, while the NOx emissions are higher for high BMEP values than for low BI"IEP values.

Due to these facts, it is not always possible to make the engine operate in the best conditions as far as the fuel consumption and/or the emissions are concerned.

Summary of the invention

In view of the above, it is an object of the present invention to provide an improved engine, allowing to overcome the above outlined inconveniences of the prior art systems.

This and other objects are achieved according to the present invention by an internal combustion engine whose main features are defined in annexed claim 1.

Particular embodiments are the subject of the dependent claims, whose content is to be understood as an integral and

integrating part of the present description.

Another object of the invention is to provide a computer program as claimed.

Briefly summarised, an engine of the present invention has a plurality of cylinders with a predetermined overall displacement and an electronic control unit controlling the operation thereof, and is characterized in that at least one first cylinder has a respective displacement greater than a reference value obtained by dividing the overall displacement by the number of cylinders, and at least one second cylinder has a respective displacement smaller than said reference value. The electronic control unit is predisposed for selectively turning off at least one of the engine cylinders in predetermined operating conditions.

Preferably, all the cylinders have a same piston stroke and at least one first cylinder has a respective bore greater than a reference bore value correlated with the reference value of the overall displacement, and at least one second cylinder has a respective bore smaller than said reference bore value. The above indicated choice provides enhanced efficiency of operation of the engine.

Preferably, two cylinders have a respective bore greater than said reference bore value and the other two cylinders have a respective bore smaller than the reference bore value, thus allowing to obtain better engine performances.

Preferably, the engine has four in-line cylinders, the first and the fourth cylinders having a respective bore cross-sectional area reduced by 20% with respect to 1/4 of the overall engine displacement, the second and third cylinders having a respective bore cross-sectional area increased by 20% with respect to 1/4 of the overall engine displacement.

This allows to obtain three engine displacement conditions reduced in proportional way with respect to the overall engine displacement by selectively turning off one, two or three cylinders.

Preferably, all the cylinders have a same bore and at least one first cylinder has a respective piston stroke greater than a reference piston stroke value correlated with the reference value of the overall engine displacement, and at least one second cylinder has a respective piston stroke smaller than said reference piston stroke value. The above indicated choice provides an equally efficient alternative for the operation of the engine.

Preferably, two cylinders have a respective piston stroke greater than the reference piston stroke value and the other two cylinders have a respective piston stroke smaller than the reference piston stroke value, thus simplifying the manufacturing process of the engine.

Preferably, at least one first cylinder has a respective bore greater or smaller than a reference bore value correlated with the reference value of the overall displacement, and at least one second cylinder has a respective piston stroke greater or smaller than a reference piston stroke value correlated with the reference value of the overall displacement. The above indicated choice allows to fine tune the engine.

From another point of view, the invention provides a computer program executable by an electronic control unit of said engine for selectively turning off at least one of the engine cylinders in predetermined operating conditions.

Further characteristics and advantages of the invention will become apparent from the following description, provided merely by way of a non-limiting example, with reference to the accompanying drawings, in which: -Figure 1, already disclosed, is a graph of curves of fuel specific consumption; -Figure 2, already disclosed, is a graph of curves of hydrocarbon emissions; -Figure 3, already disclosed, is a graph of curves of NO emissions; and -Figure 4 is a schematic representation of an internal combustion engine according to the present invention.

Detailed description

Figure 4 shows a four-cylinder engine 2 having an overall displacement D, wherein two cylinders 4 and 6 have respective displacements increased with respect to D/4, and the other two cylinders 8 and 10 have respective displacements correspondingly reduced with respect to D/4.

The cylinders 4,6 have each a respective bore Dl and the cylinders 8,10 have each a respective bore D2. The cylinders 4 and 6 with the increased bore Dl have a correspondingly bigger displacement than the cylinders 8 and 10 with the reduced bore D2, but the piston stroke is the same for all four cylinders 4-10.

Alternatively, the cylinders 4-10 can have correspondingly increased or reduced piston strokes and a same bore for all four cylinders 4-10.

Alternatively, the cylinders 4-10 can have correspondingly increased or reduced bore and increased or reduced piston stokes. In particular, a same cylinder 4-10 may have both an increased or reduced bore and an increased or reduced piston stokes.

Preferably, with an engine 2 having four in-line cylinders, the first and the fourth cylinders 8 and 10 have a respective bore cross-sectional area reduced for instance by 20%, whereas the second and third cylinders 4 and 6 have a respective bore cross-sectional area increased for instance by 20%.

Thanks to the different bores of the cylinders 4-10, the engine 2 can operate in a plurality of different conditions, i.e. a first condition wherein all four cylinders 4-10 are active, a number of conditions wherein three cylinders are active and one cylinder is inactive, and a number of conditions wherein two cylinders are active and two cylinders are inactive, in each condition the engine 2 having a corresponding displacement An electronic control unit 12 is associated with the engine 2 and is arranged to control the engine 2 by activating or de-activating the cylinders 4-10 so as to make the engine 2 operate in the plurality of different conditions above disclosed.

In a possible embodiment, the displacements of the cylinders 4-10 are such that in a first condition (four cylinders active) the engine displacement has a first predefined overall value, in a second condition the engine displacement has a second value which is about two-thirds of the first value while in a third condition the engine displacement has a third value which is about one-third of the first value.

The manufacturing of the crankshaft and the mechanical balancing of the engine (same piston masses) are performed in a per se known manner.

The electronic control unit 12 is further arranged to selectively turn off, in a per se known manner, only one or two of the cylinders in order to obtain the best engine displacement according to the instantaneous operating conditions, thus achieving a better balance between the reduction of fuel consumption and the increase of fuel emissions and a better driving comfort because of smaller displacement variation steps.

The invention is applicable in both Diesel and gasoline engines.

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 illustrative 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.

Claims

CLAIMS1. An internal combustion engine (2) having a plurality of cylinders (4, 6, 8, 10) with a predetermined overall displacement (D) and an electronic control unit (12) controlling the operation thereof, characterized in that at least one first cylinder has a respective displacement greater than a reference value obtained by dividing said overall displacement (D) by the number of cylinders, and at least one second cylinder has a respective displacement smaller than said reference value; and in that said electronic control unit (12) is predisposed for selectively turning off at least one of the engine cylinders (4, 6, 8, 10) in predetermined operating conditions.
2. The engine according to claim 1, wherein all the cylinders (4, 6, 8, 10) have a same piston stroke and at least one first cylinder has a respective bore (Dl) greater than a reference bore value correlated with the reference value of the overall displacement (D), and at least one second cylinder has a respective bore (D2) smaller than said reference bore value.
3. The engine according to claim 2, wherein two cylinders (4, 6) have a respective bore (Dl) greater than said reference bore value and the other two cylinders (8, 10) have a respective bore (D2) smaller than the reference bore value.
4. The engine according to claim 3, wherein the engine (2) has four in-line cylinders (4, 6, 8, 10), the first and the fourth cylinders (8, 10) having respective bore cross-sectional area reduced by 20% with respect to 1/4 of the overall displacement (D), the second and third cylinders (4, 6) having a respective bore cross-sectional area increased by 20% with respect to 1/4 of the overall displacement (D)
5. The engine according to claim 1, wherein all the cylinders (4, 6, 8, 10) have a same bore and at least one first cylinder has a respective piston stroke greater than a reference piston stroke value correlated with the reference value of the overall displacement (D), and at least one second cylinder has a respective piston stroke smaller than said reference piston stroke value.
6. The engine according to claim 5, wherein two cylinders have a respective piston stroke greater than the reference piston stroke value and the other two cylinders have a respective piston stroke smaller than the reference piston stroke value.
7. The engine according to claim 1, wherein at least one first cylinder has a respective bore greater (Dl) or smaller (D2) than a reference bore value correlated with the reference value of the overall displacement (D), and at least one second cylinder has a respective piston stroke greater or smaller than a reference piston stroke value correlated with the reference value of the overall displacement CD)
8. A computer program or group of programs executable by an electronic control unit (12) of an internal combustion engine (2), comprising one or more code modules for selectively turning off at least one of the engine cylinders (4, 6, 8, 10) in predetermined operating conditions.