WO2015114431A2

WO2015114431A2 - Lean-burn internal combustion engine

Info

Publication number: WO2015114431A2
Application number: PCT/IB2015/000028
Authority: WO
Inventors: Davinder KUMAR; Dharmapuri NAGENDRAKUMAR; Vemuri SATISH; Lakshminarasimhan Varadha IYENGAR; Maluvadu Sundaraman ANANDKUMAR
Original assignee: Tvs Motor Company Limited
Priority date: 2014-01-28
Filing date: 2015-01-15
Publication date: 2015-08-06
Also published as: WO2015114431A3; AP2016009409A0

Abstract

An adaptor (114) for mounting a cylinder head (116) of a lean-burn internal combustion (IC) engine (102) is described. In an embodiment, the adaptor (1 14) includes a body portion (118) having a hollow cylindrical shape for mounting the adaptor on an engine block (104), the body portion (118) being adapted for mounting the cylinder head (116). Further, the adaptor (114) includes a cylinder head partition (120) coupled to the body portion (118). When the cylinder head (1 16) is mounted on the body portion (118), the cylinder head partition (120) bifurcates an intake passage (122) formed by a central cavity of the cylinder head (116).

Description

LEAN-BURN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

[0001] The present subject matter, in general, relates to internal combustion engines and, in particular, relates to lean burn internal combustion engines.

BACKGROUND

[0002] One of the factors affecting performance of an internal combustion (IC) engine is air to fuel ratio (AFR). Based on various operating parameters, including varying load conditions on the engine and tolerances of engine parts, the engine may be run on rich AFR or lean AFR. For example, engines are run on a rich AFR during cold start and high load operations. Generally it has been observed that the engine operation is substantially efficient and releases low emissions when operated on lean AFR. An engine generally operated on lean AFR is referred to as a lean-burn engine. Usually, precise control of AFR can be achieved in engines operating with fuel injection systems for intake of charge.

[0003] Further, for facilitating the operation of the lean-burn engines, generally, turbulence is created in charge entering the lean-burn engine. For example, a swirling motion or a tumbling motion or both is created in the charge inducted into the engine. In order to generate the turbulent motion in the charge, structural features of the intake manifold can be modified. For instance, a bifurcation of an intake port may be done to form two ports and the induction of charge from each port can be controlled for achieving a turbulent motion of the incoming charge.

BRIEF DESCRIPTION OF DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout^" the drawings to reference like features and components. [0005] Fig. la illustrates an intake manifold of a lean-burn internal combustion (IC) engine, in accordance with an embodiment of the present subject matter.

[0006] Fig. lb and Fig. lc illustrate a cylinder head of the lean-burn IC engine, in accordance with an embodiment of the present subject matter.

[0007] Fig. 2a and Fig. 2b illustrate an exhaust gas recirculation device of the lean-burn engine, in accordance with an embodiment of the present subject matter.

[0008] Fig. 3 illustrates a schematic of a control executed by an engine control unit (ECU) on the lean-burn engine, in accordance with an embodiment of the present subject matter.

[0009] Fig. 4 illustrates a schematic of the ECU, in accordance with an embodiment of the present subject matter.

[0010] Fig. 5a and 5b illustrate maps for AFR control and ignition control executed by the ECU, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

[0011] Numerous research efforts have been directed in developing efficient lean-burn engines with low emissions. One general approach facilitating the operation of the lean-burn engines is includes assisting generation of turbulence in the charge entering the lean-burn engine, say to create swirl and tumble in the charge. In one case, to generate the turbulent motion in the charge, an intake port of the lean-engine is provided with a partition to form two intake ports and the induction of charge from each port is controlled for achieving a turbulent motion of the incoming charge. Such features are generally limited to multi-cylinder engines for four wheelers because the large size of the engine allows for such design variations. However, providing the partition in the intake port can decrease effective area of cross section of passage of the intake port, leading to low torque and loss in fuel economy of the lean-burn engine. In addition, in most cases, providing the partition at the intake port may not suffice and the partition has to be provided in other regions of the intake passage as well. For example, a partition may have to be provided in the passage formed in the cylinder head of the engine. [0012] Therefore, conventionally, efforts are made to design the intake passage with the partition and to also compensate for the reduction in the area of cross section because of the partition. In certain conventional engines, to compensate for the inclusion of the partition, the overall area of the part that is partitioned is increased. However, such modification in the design may lead to the part size being greater and may result in an increase in the weight of the part. For example, the area of cross section of the passage of intake port can be increased to compensate for the loss in area because of the partition. However, such design modification may not be possible throughout the intake passage. For instance, in cases where the design of the cylinder head has to be varied, the size and weight of the cylinder head may increase. This in turn may lead to difficulties in mounting of the cylinder head on the engine and packaging of the cylinder head or the engine in the engine bay.

[0013] In certain other cases, the thickness of the partition can be reduced to reduce the loss in area of cross-section in the intake passage. However, conventionally, the partition is integrally formed along with the part, say by die casting and the minimum thickness of the partition is limited by various parameters, For example, the minimum thickness of the partition can be limited by the tolerances and core angles that may have to be taken into consideration, and the manufacturing processes of casting used. Further, while die casting, the core has to be split into two cores for forming the partition in the hollow passage of the part. Therefore, usually, the thickness of the partition in the conventional intake passages, say in the passage in the cylinder head, is not below 3 to 5 millimeter (mm). In addition, the surface of the partition is internal to the cavity of the part and, therefore, cannot be machined. As a result, the surface of the partition is rough and may adversely affect the flow of incoming charge, thereby affecting the performance of the engine.

[0014] In addition, another approach for achieving substantially efficient operation of the lean-burn engines is regulation of air-fuel ratio (AFR) of the charge inducted into the engine in a lean region. Generally, to control the AFR in conventional lean-burn engines, automated or electronic control is executed by way of, for example, electronic fuel injection (EFI) systems. However, such EFI systems are usually costly and the overall cost of the vehicle deploying the EFI system may be substantially high. On the other hand, vehicles using carburetor for fueling the engine do not execute AFR control besides the variation in AFR due to general operation of the carburetor. Therefore, stable lean-burn operation is usually unsustainable with carburetor-fuelled engines and may adversely affect cold starting and cold acceleration of the engines.

[0015] As mentioned previously, lean-burn engines are being prolifically used because of their low emissions along^" with the substantially high fuel efficiency. While the emissions from lean-burn engines are low in general, efforts are constantly directed towards further reducing emissions from lean-burn engines. In an example, techniques for reducing NOx emissions from the engines are developed. One such technique includes exhaust gas recirculation (EGR) in which exhaust gas from the engine is fed back into the engine for reducing NOx into less harmful products. However, in most lean-burn engines, stable operation is difficult to achieve along with EGR since the exhaust gas entering the engine as part of EGR further dilutes the charge. This may also cause variation in cycle-by-cycle indicated mean effective pressure (IMEP) in the engine, thereby causing variation in cycle-by-cycle torque which is perceived as a jerk during operation of the engine. Such operation of the engine may result in poor ride quality of the vehicle. While the regulation of lean- burn engines working with EFI systems is substantially precise and can be used along with EGR, carburetor-fuelled lean-burn engines are unable to operate along with EGR. In addition, as mentioned previously, carburetor-fuelled lean-burn engines are unstable in operation and complementing the operation of such engines with EGR degrades the stability of performance further.

[0016] The present subject matter describes a lean-burn internal combustion (IC) engine, an adaptor for mounting a cylinder head of the lean-burn IC engine, and a method for controlling the lean-burn IC engine, according to an embodiment of the present subject matter. The lean-burn IC engine, hereinafter referred to as engine, is fuelled by a carburetor and is capable of stable lean-burn operation.

[0017] According to said embodiment, the engine includes an engine block having an intake port formed therein. The intake port is connected to a combustion chamber of the engine for the intake of charge. According to an embodiment, the intake port is provided with a port partition to bifurcate an air passage in the intake port. In an example, the port partition has a cross-sectional thickness of less than about 3.5 millimeter (mm). The cross sectional thickness can be understood as the smaller of the two dimensions that can be measured in a cross-sectional view of the port partition. With such thickness of the port partition, the effect of the port partition on the effective area of cross section of the air passage in the intake port and, therefore, on the incoming charge is considerably low.

[0018] Further, according to an aspect, the adaptor for mounting the cylinder head is mounted on the engine block at the intake port. In an embodiment, the adaptor has a body portion having a hollow cylindrical shape for mounting the adaptor on an engine block and a cylinder head partition coupled to the body portion. When the cylinder head is mounted at the adaptor, the cylinder head partition is disposed inside an intake passage formed in the cylinder head, to bifurcate the intake passage in the cylinder head. In an example, the cylinder head partition is formed of metallic sheet and coupled to the body portion by welding or by soldering. Further, the adaptor can be formed of a non-metallic material for cost effectiveness. [0019] Since the cylinder head partition is formed as a separate component from the cylinder head, dimensions of the cylinder head partition can be controlled accurately. In an example, the cylinder head partition can have a cross-sectional thickness of about 1.5 mm. The cross sectional thickness can be understood as the smaller of the two dimensions that can be measured in a cross-sectional view of the cylinder head partition. With such small thickness, the effect of the cylinder head partition on the effective area of cross section of the air passage in the cylinder head is considerably low. As a result of the minimal effect on the air passage, the size of the cylinder head may not have to be changed. Further, since the cylinder head partition is not formed integral to the cylinder head, the partition can be machined so as to provide a substantially smooth surface. As a result, the incoming charge can flow unobstructed into the engine over the smooth surface with substantially high velocity.

[0020] The provision of the cylinder head partition and the port partition of such low thickness allows turbulence to be created in the incoming charge, in order to provide substantially high tumble and swirl characteristics. As a result, good lean- burn characteristics of the engine can be achieved and a stable lean-burn operation of the engine can be carried out. In addition, in lean-burn operation, the engine can provide consistent output torque and low coefficient of variance (COV) in low load conditions providing considerably high fuel economy.

[0021] In addition, according to an embodiment, the engine can include a carburetor coupled to the cylinder head. In said embodiment, the carburetor can include an intake passage in fluid coupling with the air passage in the cylinder head. According to an aspect, a carburetor partition can be provided in the intake passage to bifurcate the intake passage of the carburetor. In an example, the carburetor partition has a cross sectional thickness of less than about 3.5 mm. Further, the port partition, the cylinder head partition, and the carburetor partition can abut against each other and form a continuous partition in the intake manifold of the engine. As a result, the incoming charge can experience high velocity with high tumble and swirl, providing for substantially high combustion rate and good lean-burn performance of the engine.

[0022] Further, in an implementation, the carburetor has a sliding throttle valve and an edge of the sliding throttle valve is inclined to the carburetor partition. In conventional carburetors, the edge of the sliding throttle valve is usually parallel to the carburetor partition. As a result, when the sliding throttle valve is opened or closed, the movement of the throttle valve along the cross-sectional thickness of the carburetor partition does not bring about a change in the uncovered area of the air passage. In other words, even with the movement of the sliding throttle valve, there is no change in the amount of charge intake. As a result, the operation of the sliding throttle valve in the conventional carburetor can be redundant for a certain duration. According the present subject matter, with the carburetor partition inclined to the edge of the sliding throttle valve, upon movement of the sliding throttle valve, the effective area uncovered changes. In other words, with the movement of the throttle valve, covering or uncovering of the intake passage always takes place.

[0023] As mentioned above, the engine as described herein can be operated along with a carburetor and can provide for stable lean-burn operation, because of the features as explained above. In addition, the engine can be operated in order to effectively operate for stable lean-burn performance. Accordingly, an engine control unit (ECU) can be coupled to the engine for regulating the operation of the engine and to provide efficient lean-burn operation of the engine. In an embodiment, to control the operation of the engine, the ECU ascertains speed of the engine and throttle opening of the: carburetor at a given instant, and based on the speed and the throttle opening, determines a pulse width modulation (PWM) signal to be generated. Further, based on the PWM signal, the carburetor is operated for regulating air fuel ratio (AFR) of charge being supplied to the engine. In an implementation, an electromechanical actuator of a pilot circuit of the carburetor is operated to regulate the AFR. The electromechanical actuator can provide bleed air for mixing with the charge provided by a pilot fuel jet of the carburetor, to regulate the final AFR of the charge supplied to the engine.

[0024] In an example, the PWM signal to be generated is determined based on a mapping between the speed and throttle and the corresponding PWM signal. The mapping can be predefined based on the air-fuel ratio values, for different combinations of engine speed and throttle opening. Based on the PWM readings from the map, the bleed air to be mixed with the charge from the pilot fuel jet is controlled to regulate the AFR of mixture from the pilot circuit. Each combination of speed and throttle gives a specific engine condition, for which the AFR is predefined according to the map. In an example, the relation between the speed and throttle and the corresponding PWM signal is determined experimentally. In operation, according to an aspect, the ECU is configured as having the mapping between the engine speed, the throttle opening, and the PWM. Based on the engine speed and the throttle opening, the ECU determines the PWM signal from the map. In order to control the bleed air based on the PWM signal, the electromechanical actuator of the pilot circuit of the carburetor is designed, mounted, and tuned in such a way that the AFR corresponding to the PWM signal is achieved by the electromechanical actuator.

[0025] Further, the engine can include an exhaust gas recirculation (EGR) device for controlling emissions from the engine. In an implementation, the EGR device can include an EGR duct coupling an exhaust port of the engine with the intake passage of the carburetor for achieving exhaust gas recirculation. In such a case, the sliding throttle valve of the carburetor can also control the exhaust gas recirculation into the intake passage. Therefore, according to an aspect, the EGR device can operate with the sliding throttle valve, such as a piston valve, as the regulating device, and does not require an additional valve or other regulating device. Therefore, in an example, the EGR device can provide for a low cost exhaust gas recirculation technique using the existing carburetor valve of the lean-burn engine. [0026] Further, in an implementation, to control the EGR into the carburetor, the ECU can also obtain a feedback from an exhaust gas sensor, say deployed in an exhaust manifold, to determine at least one exhaust gas characteristic of the exhaust gas. In an implementation, based on the exhaust gas characteristic, the ECU can control an EGR solenoid valve in the EGR duct to regulate the EGR into the engine. In another implementation, the EGR into the engine can be controlled based on a throttle position of the sliding throttle valve of the carburettor, say based on the design of the sliding throttle valve. For example, the sliding throttle valve can be constructed in a way that at a certain throttle position, the exhaust gas from the EGR duct is allowed to enter the carburettor and, therefore, the engine. In addition, the electromechanical actuator of the pilot circuit can also be controlled based on the exhaust gas characteristic for regulating the AFR to control the air-fuel mixture strength or AFR in the engine for stable operation of the engine. The ECU can execute control based on the exhaust gas characteristics in a manner as it is done conventionally.

[0027] In addition, to further regulate the emissions, the engine is provided with a secondary air intake valve in the exhaust manifold. The secondary intake valve can regulate intake of secondary air into the exhaust manifold during exhaust cycle of the engine, for treating exhaust products from the engine before these products are expelled. In an example, the ECU regulates the intake of air from a secondary air intake valve into an exhaust manifold of the lean-burn IC engine, based on the exhaust gas characteristic determined above.

[0028] The engine as described in the present subject matter can achieve stable lean-burn operation, even when fuelled by a carburetor. In addition, the partition used in the intake manifold has substantially low thickness, as a result of which, the charge intake remains considerably unaffected. Accordingly, the engine has a good torque output and substantially high efficiency. In addition, the control executed by the ECU for regulating the AFR of the charge obtained from the carburetor further facilitates in the stable operation of the engine in the lean region of the AFR. The provision of the EGR device and the secondary air valve provide for low emission, without affecting stability of operation of the engine.

[0029] These and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.

[0030] Fig. la illustrates an intake manifold 100 of a lean-burn internal combustion (IC) engine 102, in accordance with an embodiment of the present subject matter. The lean-burn IC engine 102 of the present subject matter, hereinafter referred to as engine 102, is capable of stable operation with lean air fuel ration (AFR) and has provisions for regulating AFR. Further, an intake passage of the engine 102 is bifurcated substantially along a length of the intake manifold 100, for generating turbulence in the incoming charge.

[0031] In an embodiment, the engine 102 includes an engine block 104 having an intake port 106 formed therein. The intake port 106 is connected to a combustion chamber (not shown) of the engine 102 for induction of charge into the combustion chamber. The intake of charge is regulated by an intake valve assembly 108. According to an embodiment, for providing turbulent motion in the incoming charge, the intake port 106 is provided with a port partition 1 10 to bifurcate an intake passage 1 12 formed by a central cavity of the intake port 106. In an example, the port partition 1 10 can have a cross-sectional thickness of less than about 3.5 millimeter (mm). Further, in order to compensate for a decrease in area for intake of charge in the intake port 106, the dimensions of the intake port 106 can be selected accordingly. For example, if the area of the intake port 106 for intake of charge before providing the port partition 1 10 is x, then even after providing the port partition 1 10, the overall area of the intake port 106 is provided to be as x. [0032] Further, according to an aspect, the engine 102 includes an adaptor 114 capable of being mounted on the engine block 104. In said embodiment, the adaptor 1 14 is mounted on the engine block 104 for further mounting a cylinder head 1 16 of the engine 102 at the intake port 106. In an embodiment, the adaptor 1 14 has a body portion 118 having a hollow cylindrical shape and can provide for mounting of the adaptor 1 14 on the engine block 104. The adaptor 1 14 can be formed of a non- metallic material for cost effectiveness. Further, according to an aspect, a cylinder head partition 120 is coupled to the body portion 1 18 of the adaptor 1 14. When the cylinder head 1 16 is mounted at the engine block 104 on the adaptor 1 14, the cylinder head partition 120 is disposed inside an intake passage 122 formed by a central cavity in the cylinder head 1 16, to bifurcate the intake passage 122 in the cylinder head 116.

[0033] In an example, the cylinder head partition 120 is formed as an insert, manufactured from a metallic sheet and coupled to the body portion 1 18. In an example, the cylinder head partition 120 can be coupled to the body portion 1 18 by welding or soldering. In another example, the cylinder head partition 120 can be formed integral to the adaptor 1 14. In such a case, the adaptor 1 14 can be cast or in- situ moulded along with the adaptor 1 14. The adaptor 1 14 can be formed of a non- metallic material for cost effectiveness. [0034] Accordingly, as would be understood, the cylinder head partition 120 is formed as a separate component from the cylinder head 1 16 and therefore, dimensions of the cylinder head partition 120 can be precisely controlled, say the cross-sectional thickness can be reduced in comparison to the conventional cylinder head partitions. For example, the cross sectional thickness of the cylinder head partition 120 can be less than about 3.5 millimeter. For instance, the cylinder head partition 120 can have a cross-sectional thickness of about 1.5 mm. In addition, since the cylinder head partition 120 is not formed integral to the cylinder head 120, the cylinder head partition 120 can be machined so as to provide a substantially smooth surface thereof. As a result, the incoming charge can flow unobstructed into the engine 102.

[0035] In another embodiment, the port partition 1 10 can also be formed as being separate from the engine block 104. In such a case, the port partition 110 can also be formed in the similar manner as the cylinder head partition 120 and coupled to the adaptor 1 14. Therefore, in the manner as explained above, the dimensions of the port partition 1 10 can also be controlled precisely. In such a case, the port partition 1 10 can have a cross-sectional thickness of about 1.5 mm and can be provided as having a machined, smooth surface. [0036] The provision of the cylinder head partition 120 and the port partition 1 10 of such low thickness allows turbulence to be effectively created in the incoming charge along the intake manifold 100, in order to provide substantially high tumble and swirl characteristics. As a result, good lean-burn characteristics of the engine 102 can be achieved and a stable lean-burn operation of the engine 102 can be carried out. In addition, in lean-burn operation, the engine 102 can provide consistent output torque and low coefficient of variance (COV) in low load conditions providing considerably high fuel economy.

[0037] Further, with such a low thickness of the cylinder head partition 120 and cantilever-type mounting of the cylinder head partition 120 on the adaptor 1 14 as mentioned above, the cylinder head partition 120 may vibrate, leading to unwanted noise and possible damage or wearing of the cylinder head partition 120. Accordingly, according to an implementation, a groove 123 can be provided in an inner wall of the cylinder head 1 16. Fig. l b illustrates the cylinder head 1 16 showing the groove 123 formed in the inner wall. Fig. l c illustrates the cylinder head partition 120 disposed in the groove 123. With the provision of the groove 123, the vibrational motion of the cylinder head partition 120 is substantially alleviated. As a result, the operation of the engine 102 is considerably silent and service life of the cylinder head partition 120 can be prolonged.

[0038] In addition, according to an embodiment, the engine 102 can be carburetor-fuelled. Accordingly, in said embodiment, the engine 102 can be coupled to a carburetor 124 at the cylinder head 1 16 and an intake passage 126 of the carburetor 124 can be in fluidic connection with the intake passage 122 of the cylinder head 1 16. For example, the carburetor 124 can be mounted on the cylinder head 1 16 through an insulating member 128. In one implementation, the cylinder head partition 120 can be formed as being coupled to the adaptor 114 on one side and the insulating member 128 on the other.

[0039] According to an aspect, a carburetor partition 130 can be provided in the intake passage 126 to bifurcate the intake passage 126 of the carburetor 124. In an implementation, the carburetor partition 130 can be formed as integrated to an inner wall of the intake passage 126. In one example of said implementation, the carburetor partition has a cross sectional thickness of less than about 3.5 mm. In another implementation, the carburetor partition 130 can be formed as a separate component, similar to the implementations described above with reference to the port partition 1 10 and the cylinder head partition 120. In said implementation, the carburetor partition 130 can be formed as a sheet-like component coupled to the insulating member 128. In said implementation, the cross-sectional thickness of the carburetor partition 130 can be about 1.5 mm.

[0040] In addition, in an implementation, the carburetor 124 can include a main circuit (not shown) and a pilot circuit (not shown). Generally, in an example, the main circuit operates in general conditions when the throttle operation is beyond 40%. On the other hand, when the throttle opening is low, say below 40%, the pilot circuit comes into the play to provide the charge to the engine 102. The pilot circuit can facilitate the lean-burn operation of the engine 102 by supplying air to the charge from a pilot fuel jet for diluting the charge. The operation of the main circuit and the pilot circuit of the carburetor 124 are explained later in detail, with reference to fig. 3

[0041] Further, the port partition 1 10, the cylinder head partition 120, and the carburetor partition 130 can form a continuous partition in the intake manifold 100 of the engine. As a result, the incoming charge in the intake manifold 100 can experience high velocity and high tumble and swirl, providing for substantially high performance, say lean-burn performance, of the engine 102. In addition, the partitions 110, 120, 130 can be positioned in the respective intake passages 1 12, 122, 126 so as to divide the intake manifold 100 proportionately into two passages. In an example, the proportions for dividing the intake manifold 100 can be determined based on relevant flow characteristics in the intake manifold 100. For example, the intake manifold 100 can be divided into two passages in a proportion of 1 : 1 of an area of cross section, i.e., the two passages can have equal area of cross section. In other examples, instance, the intake manifold 100 can be designed to have the area of cross section in a proportion of 50:50, 40:60, 30:70, or 20:80. The proportions can be selected in such a way so as to provide good lean burn performance of the engine.

[0042] Further, in an implementation, the carburetor 124 has a throttle valve assembly 132 for regulating the charge intake into the intake manifold 100, and therefore, into the engine 102. In an implementation, the throttle valve assembly 132 can include a throttle valve (not shown) and a valve actuator (not shown). In an example, the throttle valve of the carburetor 124 can be a sliding throttle valve, say a piston valve. In conventional carburetors, the edge of the sliding throttle valve is usually parallel to the carburetor partition. Consequently, in conventional carburetors with partition, upon the movement of the sliding throttle valve along the cross- sectional thickness of the carburetor partition, there is no change in the uncovered area of the intake manifold. In addition, since the cross-sectional thickness of the carburetor partition in the conventional carburetors is large, the throttle valve movement for which there is no change in the uncovered area is substantially large. In other words, conventionally, even with a substantial opening of the throttle, there is no change in the amount of charge intake by the carburetor. As a result, the operation of the throttle valve in the conventional carburetor can be redundant for a certain duration.

[0043] In an embodiment of the present subject matter, an edge of the throttle valve of the carburetor 124 can be inclined to the carburetor partition 130. For example, referring to fig. lc, the carburettor partition 130 is shown as being inclined with respect to the horizontal direction. In said example, the edge of the throttle valve can be parallel to the horizontal direction. According the present subject matter, with the carburetor partition 130 inclined to the edge of the sliding throttle valve, when the sliding throttle valve is actuated, the effective area uncovered changes in accordance with the change in throttle opening. Consequently, there is not an instant where the charge intake does not change with the movement of the throttle valve, providing for effective operation of the engine 102.

[0044] In addition, to regulate the emissions in the engine 102, the engine 102 can be provided with a secondary air intake valve (not shown) in an exhaust manifold (not shown). The secondary intake valve can regulate intake of secondary air into the exhaust manifold during exhaust cycle of the engine 102, for treating exhaust products from the engine 102 before these products are expelled. The operation and control of the secondary intake valve is explained later in detail. In addition, to further regulate emissions from the engine 102, the engine 102 can include an exhaust gas recirculation (EGR) device (not shown).

[0045] Further, in accordance with an embodiment, the engine 102 and the peripheral components of the engine 102 can be coupled to an engine control unit (ECU) (not shown) for controlling operation of the engine 102. In an implementation, the ECU can be coupled to the carburetor and regulate the AFR of the charge supplied from the carburetor 124. Similarly, the ECU can be coupled to the EGR device and the secondary air intake valve for regulating the operation. In addition, peripheral components of the engine 102 can include various sensors, such as exhaust gas sensors, temperature sensors, and throttle position sensors, for providing inputs and diagnostic information to the ECU. The operation of the ECU is explained later in detail with reference to fig. 3 and fig. 4.

[0046] Fig. 2a and fig. 2b illustrates the EGR device 200 of the engine 102, in accordance with an embodiment of the present subject matter. While fig. 2a shows the EGR device 200 in a front view, fig. 2b illustrates the EGR device 200 in a top view. For the sake of brevity, fig. 2a and 2b are described in conjunction henceforth. , In an implementation, the EGR device 200 can include an EGR duct 202 for coupling an exhaust port 204 of the engine 102 with the intake passage 126 of the carburetor 124 for achieving exhaust gas recirculation. In an example, while passing through the EGR duct 202, the exhaust gases can lose energy and can be allowed to cool down to a predetermined temperature. Accordingly, in one example, a length of the EGR duct 202 can be selected based on various factors, including size of the engine 102, maximum speed of the engine 102, state of tuning of the engine 102, and general operational parameters associated with the engine 102, say average temperature of exhaust gases exiting the engine 102. [0047] Further, in one example, the throttle valve of the carburetor 124 can control the exhaust gas recirculation from the exhaust port 204 into the intake passage 126. In said example, the throttle valve of the carburetor 124 provides an auxiliary control in addition to the basic control of AFR during induction of charge by the engine 102. For instance, the sliding throttle valve can be constructed in a way that at a certain throttle position, the exhaust gas from the EGR duct 202 is allowed to enter the carburettor 124 and, therefore, the engine 102. Accordingly, the exhaust gas to be circulated into the engine 102 can be controlled based on a throttle position of the sliding throttle valve of the carburettor 124, based on the design of the sliding throttle valve. In another implementation, the ECU can obtain a feedback from an exhaust gas sensor, say deployed in an exhaust manifold (not shown), to determine one or more exhaust gas characteristic of the exhaust gas. Based on the exhaust gas characteristic, the ECU can control an EGR solenoid valve (not shown) in the EGR duct 202 to regulate the EGR into the intake passage 126 and, therefore, into the engine 102.

[0048] In addition, in an example, to regulate the flow of exhaust gases for EGR and to control the temperature to which the exhaust gases are cooled before being provided to the carburetor as part of EGR, the EGR duct 202 can be provided with a reservoir or a valve.

[0049] Fig. 3 illustrates a schematic of a control executed by the engine control unit (ECU) 300 on the engine 102, in accordance with an embodiment of the present subject matter. As described previously, the ECU 300 can control the lean-burn operation of the engine 102 to facilitate stable operation, with substantially high efficiency and low emissions, even while the engine is fuelled by the carburetor 124. In said embodiment, the two circuits of the carburetor 124, namely, the main circuit and the pilot circuit 301 operate in a coordinated manner to facilitate the functioning of the engine 102.

[0050] In an embodiment, the main circuit can be understood as the main fuelling component of the carburetor 124. The AFR in the main circuit is regulated purely on the basis of the opening of the throttle valve by an operator of the engine 102, say a driver of a vehicle in which the engine 102 is deployed. Therefore, the main circuit provides a rich mixture as compared to the lean AFR at which the engine 102 is configured to operate. The pilot circuit 301 provides a lean mixture air for mixing with the rich mixture from the main circuit before entering the engine 102 to bring the AFR in the lean range. [0051] In an implementation, the pilot circuit 301 can include a pilot fuel jet 302, a mixer branch 304, and an electromechanical actuator 306. The pilot fuel jet 302 provides rich fuel mixture which mainly comprises fuel to the mixer branch 304. The electromechanical actuator 306 can be operable by the ECU 300 for regulating the amount of air to be mixed with the rich mixture in the mixer branch 304. In one example, the electromechanical actuator 306 can be a solenoid valve.

[0052] In an embodiment, to control the electromechanical actuator 306, the ECU 300 can ascertain speed of the engine 102 and throttle opening of the carburetor 124 at a given instant. In an example, the ECU 300 can determine the speed of the engine 102 from an engine speed sensor and the throttle opening from the throttle position sensor. Further, based on the speed and the throttle opening, the ECU 300 can determine a pulse width modulation (PWM) signal, and in turn, based on the PWM signal, the ECU 300 can regulate the extent of opening of the electromechanical actuator for allowing air to bleed in and mix with the mixture in the mixer branch 304.

[0053] Further, in an implementation, the ECU 300 can control the EGR into the carburetor 124. For instance, the ECU 300 can obtain a feedback from the exhaust gas sensor 308, say positioned in an exhaust manifold, to determine one or more exhaust gas characteristics of the exhaust gas. In said implementation, based on the exhaust gas characteristics, the ECU 300 can control the exhaust gas recirculation into the carburetor 124.

[0054] Fig. 4 illustrates the engine control unit (ECU) 300 of the engine 102, in accordance with an implementation of the present subject matter. As mentioned above, the ECU 300 can execute a control of the engine 102 to regulate lean-burn operation and also regulate EGR to control the emissions from the engine 102.

[0055] In an embodiment, the ECU 300 can be implemented as a microcontroller, a microcomputer, and/or any device that manipulates signals based on operational instructions. According to said embodiment, the ECU 300 can include a processor 400 and a device memory 402. The processor 400 can be a single processing unit or a number of units, all of which could include multiple computing units. The processor 400 may be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals, based on operational instructions. Among other capabilities, the processor(s) is provided to fetch and execute computer-readable instructions stored in the device memory 402. The device memory 402 may be coupled to the processor 400 and can include any computer-readable medium known in the art including, for example, volatile memory, such as Static Random Access Memory (SRAM) and Dynamic Random Access Memory (DRAM), and/or non- volatile memory, such as Read Only Memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes. [0056] Further, the ECU 300 may include module(s) 404 and data 406. The modules 404 and the data 406 may be coupled to the processor 400. The modules 404, amongst other things, include routines, programs, objects, components, data structures, etc., which perform particular tasks or implement particular abstract data types. The modules 404 may also, be implemented as, signal processor(s), state machine(s), logic circuitries, and/or any other device or component that manipulate signals based on operational instructions.

[0057] In an implementation, the module(s) 404 include a measurement module 408, an analysis module 410, an air- fuel ratio (AFR) control module 412, a feedback module 414, an exhaust gas recirculation (EGR) control module 416, a secondary intake control module 418, and other module(s) 420. The other module(s) 420 may include programs or coded instructions that supplement applications or functions performed by the ECU 300. Additionally, in said implementation, the data 406 can include a mapping data 422 and other data 424. The other data 424 amongst other things, may serve as a repository for storing data that is processed, received, or generated, as a result of the execution of one or more modules in the module(s). Although the data 406 is shown internal to the ECU 300, it may be understood that the data 406 can reside in an external repository (not shown in the figure), which may be operably coupled to the ECU 300. Accordingly, the ECU 300 may be provided with I/O interface(s) (not shown) to communicate with the external repository to obtain information from the data 406. The I/O interfaces may include a variety of software and hardware interfaces, which may enable the ECU 300 to . communicate with the external repository and peripheral components of the engine 102, such as the various sensors and valves.

[0058] In an example, the mapping data 422 can include a predefined mapping which is formed as a matrix between engine speed, throttle opening or throttle position, and PWM signal. The mapping can include the PWM signals for different combinations of engine speed and throttle opening. In an example, the relation between the speed of the engine 102 and throttle position and the corresponding PWM signal is determined experimentally, say by mounting the engine 102 on a test rig. The ECU 300 can access the mapping to determine the PWM signal on the basis of which the electromechanical actuator 306 is controlled. An example of the mapping for AFR control is shown in fig. 5a. [0059] In an implementation, the measurement module 408 can ascertain the speed of the engine 102 and the throttle opening of the carburetor 124 coupled to the engine 102 as described above. Further, based on the speed of the engine 102 and the throttle opening, the analysis module 410 can determine the pulse width modulation (PWM) signal from the mapping or the matrix. For example, the analysis module 410 can obtain as inputs the speed of the engine 102 and the throttle position and can provide the PWM signal corresponding to the combination of the engine speed and the throttle opening, based on the map. Subsequently, the AFR control module 412 can operate the electromechanical actuator 306, say the solenoid, of the pilot circuit 301 of the carburetor 124 based on the PWM signal, for regulating air fuel ratio of charge being supplied to the engine 102.

[0060] In an example, the PWM signal determined from the mapping is directly related to the AFR values, for different combinations of engine speed and throttle opening. In addition, in one case, the AFR control as executed above can be an open loop control and accordingly, the control of the bleed air to be mixed with the mixture from the pilot fuel jet 302 can be achieved based on the design, mounting, and tuning of the pilot circuit 301, say the electromechanical actuator 306 of the pilot circuit 301. In an example, based on the design, mounting, and tuning of the electromechanical actuator 306, the AFR can be controlled corresponding to the PWM signal.

[0061] In addition, the ECU 300 can exercise ignition control based on speed of the engine 102 and throttle position. Such ignition control can be based on a mapping between the speed of the engine 102, the throttle opening, and ignition timing, and can be determined experimentally in the same manner as described above. The ignition control so executed by the ECU 300 along with the AFR control gives synergistic effect in regulating performance of the engine 102. An example of the mapping for ignition control is shown in fig, 5b.

[0062] In an example, the enhancement in the performance of the engine 102 with the control executed as described above with reference to the ECU 300 is more defined in the lean-burn region of operation of the engine 102, when the throttle opening is below about 40%. Also, the control in AFR and ignition timing can be executed in certain cases and not executed in few other cases.

[0063] In addition, the ECU 300 can execute control of AFR or ignition timing or both based on a temperature of the engine 102. In one example, the ECU 300 can obtain temperature readings for the engine 102 from the temperature sensor and regulate the operation accordingly. For example, when the temperature is high, i.e., above a predetermined threshold, the AFR control module 412 can regulate the AFR in the charge to be lean and when the temperature is low, i.e., below the threshold, the AFR control module 412 can regulate the AFR in the charge to be in the rich region. [0064] Further, as explained previously, the ECU 300 regulates the emissions from the engine 102, by controlling the EGR. In an implementation, the feedback module 414 is coupled to the exhaust gas sensor to determine the one or more exhaust gas characteristics, say amount of oxygen in the exhaust gas and temperature of the exhaust gas. Based on the determined exhaust gas characteristics, the EGR control module 416 can regulate the exhaust gas to be recalculated into the intake manifold 100 to mix with the charge. For example, the EGR control module 416 can operate the electromechanical actuator 306 based on the exhaust gas characteristics to regulate the exhaust gas recirculation. In another example, the EGR control module 416 can control the EGR solenoid valve in the EGR duct 202 to regulate the recirculation of exhaust gases into the engine 102.

[0065] In addition, to further regulate the emissions, the ECU 300 can regulate the secondary air intake valve in the exhaust manifold. In an implementation, the secondary intake control module 418 can obtain the exhaust gas characteristics from the feedback module 414, and regulate the intake of air from the secondary air intake valve into the exhaust manifold during an exhaust cycle of the engine 102. Accordingly, the secondary intake control module 418 can facilitate in the treatment of exhaust products exiting the engine 102, before these products are expelled into the environment. In an example, the secondary intake control module 418 can allow for the conversion of NOx into less harmful products before the NOx are released from the exhaust manifold.

[0066] Although the subject matter has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. It is to be understood that the appended claims are not necessarily limited to the features described herein. Rather, the features are disclosed as embodiments of the lean burn IC engine 102.

Claims

I/We claim:

1. An adaptor (114) for mounting a cylinder head (116) of a lean-burn internal combustion (IC) engine (102), the adaptor (114) comprising:

a body portion (1 18) having a hollow cylindrical shape for mounting the adaptor on an engine block (104), wherein the body portion (1 18) is adapted for mounting the cylinder head (1 16); and

a cylinder head partition (120) coupled to the body portion (1 18), wherein the cylinder head partition (120) bifurcates an intake passage (122) formed by a central cavity of the cylinder head (1 16) when the cylinder head (1 16) is mounted on the body portion (1 18).

2. The adaptor (1 14) as claimed in claim 1, wherein the adaptor (1 14) is formed of a non-metallic material.

3. The adaptor (1 14) as claimed in claim 1, wherein the cylinder head partition (120) is formed of metallic sheet.

4. The adaptor (1 14) as claimed in claim 1 , wherein the cylinder head partition (120) has a cross-sectional thickness of less than about 3.5 millimeter (mm).

5. The adaptor (1 14) as claimed in claim 1, wherein the cylinder head partition (120) has a cross-sectional thickness of about 1.5 mm.

6. A lean-burn internal combustion (IC) engine (102) comprising:

an engine block (104) having an intake port (106) formed therein, wherein the intake port (106) comprises a port partition (110) to bifurcate an intake passage (1 12) formed by the intake port (106);

an adaptor (1 14) mounted on the engine block (104) at the intake port (106), wherein the adaptor (1 14) comprises a body portion (1 18) and a cylinder head partition (120) coupled to the body portion (1 18); and

a cylinder head (1 16) mounted on the adaptor (1 14), wherein the cylinder head partition (120) is disposed inside an intake passage (122) formed by a central cavity of the cylinder head (1 16) to bifurcate a central cavity of the cylinder head (1 16), in mounted position of the cylinder head (1 16).

7. The lean-burn IC engine (102) as claimed in claim 6, wherein the port partition (1 10) has a cross sectional thickness of less than about 3.5 mm.

8. The lean-burn IC engine (102) as claimed in claim 6, wherein the cylinder head partition (120) has a thickness of about 1.5 mm.

9. The lean-burn IC engine (102) as claimed in claim 6, wherein the lean-burn IC engine (102) is coupled to a carburetor (124) at the cylinder head (1 16), the carburetor (124) comprising an intake passage (126) in fluid coupling with the intake passage (122) in the cylinder head (1 16), wherein the intake passage

(126) of the carburetor (124) is provided with a carburetor partition (130) to bifurcate the intake passage (126) of the carburetor (124).

10. The lean-burn IC engine (102) as claimed in claim 9, comprising an exhaust gas recirculation (EGR) duct (202) for coupling the intake passage (126) of the carburetor (124) to an exhaust port (204) of the lean-burn engine (102) for achieving exhaust gas recirculation in the lean-burn IC engine (102), the EGR duct (202) comprising an EGR solenoid valve controllable to regulate exhaust gas recirculation into the intake passage (126).

1 1. The lean-burn IC engine (102) as claimed in claim 6, comprising a secondary air intake valve in an exhaust manifold to regulate intake of secondary air into the exhaust manifold during exhaust cycle of the lean-burn IC engine (102).

12. A carburetor (124) for a lean burn internal combustion (IC) engine ( 102), the carburetor (124) comprising an intake passage (126) in fluid coupling with an intake passage (122) in a cylinder head (1 16) of the lean-burn IC engine (102), wherein the intake passage (126) of the carburetor (124) is provided with a carburetor partition (130) to bifurcate the intake passage (126) of the carburetor (124).

13. The carburetor (124) as claimed in claim 12, wherein the carburetor partition (130) has a cross sectional thickness of less than about 3.5 mm.

14. The carburetor (124) as claimed in claim 12, wherein the carburetor (124) comprises a sliding throttle valve, an edge of the sliding throttle valve being inclined to the carburetor partition (130).

15. An engine control unit (ECU) (300) for a lean-burn internal combustion (IC) engine (102), the ECU (300) comprising:

a measurement module (408) to ascertain speed of the lean-burn IC engine (102) and throttle opening of a carburetor (124) coupled to the lean-burn IC engine (102);

an analysis module (410) to determine a pulse width modulation (PWM) signal, based on the speed and the throttle opening; and

an air-fuel ratio (AFR) control module (412) to operate an electromechanical actuator (306) of a pilot circuit (301) of the carburetor (124) based on the PWM signal for regulating air fuel ratio of charge being supplied to the lean-burn IC engine (102).

16. The ECU (300) as claimed in claim 15, wherein the AFR control module (412) operates the electromechanical actuator (306) to regulate amount of bleed air to be mixed with the charge for regulating the air fuel ratio.

17. The ECU (300) as claimed in claim 15, wherein the electromechanical actuator (306) is a solenoid valve.

18. The ECU (300) as claimed in claim 15, comprising:

a feedback module (414) coupled to an exhaust gas sensor to determine at least one exhaust gas characteristic; and

an exhaust gas recirculation (EGR) control module (416) to regulate exhaust gas recirculation into the carburetor (124), based on the at least one exhaust gas characteristic. The ECU (300) as claimed in claim 18, wherein the EGR control module (416) operates an EGR solenoid valve in an EGR duct (202), based on the at least one exhaust gas characteristic to regulate the exhaust gas recirculation.

The ECU (300) as claimed in claim 18, comprising a secondary intake control module (418) to regulate intake of air from a secondary air intake valve into an exhaust manifold of the lean-burn IC engine (102), based on the at least one exhaust gas characteristic.

A method for controlling a lean-burn internal combustion (IC) engine (102), the method comprising:

ascertaining speed of the lean-burn IC engine (102) and throttle opening of a carburetor (124) coupled to the lean-burn IC engine (102);

determining a pulse width modulation (PWM) signal, based on the speed and the throttle opening; and

operating an electromechanical actuator (306) of a pilot circuit (301) of the carburetor (124) based on the PWM signal for regulating air fuel ratio of charge being supplied to the lean-burn IC engine (102).