An internal combustion engine having centred and offset cylinders

Abstract

An internal combustion engine 10 having a cylinder block 11 in which a plurality of cylinders 12 is arranged and a crankshaft (27, Fig. 2); At least one first cylinder 12a is centred relative to the crankshaft axis (ZZ, Fig. 2) such that its longitudinal axis (VV, Fig. 2) is perpendicular to the crankshaft axis and at least one second cylinder 12b is offset relative to the crankshaft axis (ZZ, Fig; 2) such that its longitudinal axis (WW, Fig. 3) is laterally offset from a plane defined by the crankshaft axis (ZZ, Fig. 2) and the longitudinal axis of the first cylinder (VV, Fig. 2). The invention aims to reduce friction in an engine that may deactivate cylinders in use.

Description

Technical Field The disclosure relates an internal combustion engine having at least one cylinder which is centred relative to the crankshaft axis and at least one cylinder which is offset relative to the crankshaft axis. Background Engines, such as internal combustion engines, often include one or more reciprocating pistons each mounted in a cylinder in a cylinder block. The combustion of a mixture of air and fuel causes the pistons to move in response to the resulting rapid pressure and temperature rise in the cylinder. The pistons are connected to a rotatable crankshaft to transform the reciprocating linear movement of the pistons into a rotational movement. Internal combustion engines commonly operate on a four-stroke cycle including an intake (or induction) stroke, a compression stroke, an expansion (or power) stroke, and an exhaust stroke. Other engine configurations may operate on a two-stroke pattern. Most traditional internal combustion engines have a centred crank arrangement in which the axes of the cylinders intersect with the longitudinal axis of the crankshaft. In such an arrangement, there may be friction losses due to the side force on the pistons, which can reduce the mechanical efficiency and fuel economy of the engine. During the expansion stroke, there is a diagonal component to the downward force (side force) which causes the piston to be pushed against the cylinder wall. To reduce the friction losses due to side force, it is known to use an offset crank arrangement in which the axis of rotation of the crankshaft is offset from the axes of the piston cylinders, such as is described in US-B-5816201. An offset crankshaft is located such that, during the expansion stroke, the crankshaft is perpendicular to the vertical axes of the piston cylinders and the connecting rod is collinear with the vertical axes of the piston cylinders. Offsetting the crankshaft may reduce the side force acting on the pistons, and therefore the friction, during the expansion stroke, which may be longer than in a centred crank arrangement. Whilst there is an increase in the piston side force, and therefore the friction, during the compression stroke, this increase is less than the reduction during the expansion stroke, leading to a net reduction in friction. Some internal combustion engines may include a system which may be configured to deactivate (or cut out) some of the cylinders within the engine while maintaining others as active in order to reduce the amount of fuel consumed by the engine, particularly when full power is not required. US-A2016 / 0252033 describes an example of a cylinder cutout strategy for an engine. However, there is a higher peak to peak friction force in a deactivated cylinder in an offset crankshaft arrangement compared to that in a deactivated cylinder in a centred crank arrangement. Therefore, the advantages of offsetting the crankshaft may be lost, and may even be reversed, if a cylinder in an offset crankshaft arrangement is deactivated. Summary According to the disclosure there is provided internal combustion engine comprising a cylinder block comprising a plurality of cylinders. A crankshaft having a crankshaft axis is rotatably mounted in the cylinder block. At least one first cylinder of the plurality of cylinders has a first cylinder longitudinal axis which is perpendicular to the crankshaft axis. At least one second cylinder of the plurality of cylinders has a second cylinder longitudinal axis which is laterally offset from a plane defined by the crankshaft axis and the longitudinal first cylinder axis. Brief Description of the Drawings Figurel is a perspective view of a cylinder block of an internal combustion engine according to the disclosure; Figure 2 is a cross-sectional side elevation of part of the cylinder block of Figure 1 showing a first cylinder which is centred relative to the crankshaft axis; Figure 3 is a cross-sectional side elevation of part of the cylinder block of Figure 1 showing a second cylinder which is offset relative to the crankshaft axis; Figures 4 and 5 are perspective views of opposing sides of a crankshaft for mounting in the cylinder block of Figure 1; Figure 6 is a graph comparing the piston side force in an active centred first cylinder with that in an active offset second cylinder; and Figure 7 is a graph comparing the piston side force in a deactivated centred first cylinder with that of a deactivated offset second cylinder. Detailed Description Referring to Figure 1, there is shown a cylinder block 11 of an internal combustion engine 10, which may be configured to work on a compression ignition cycle. The engine 10 may be a diesel engine that may receive fuel, such as diesel fuel, for combustion and power generation. However, the engine 10 may use other fuels, such as gaseous fuels, including but not limited to propane gas, hydrogen gas, natural gas (methane), or other fuels, singularly or in combination with each other, or with the diesel fuel. The engine 10 may include at least one cylinder block 11 in which are formed a plurality of cylinders 12. The plurality of cylinders 12 may include at least one first cylinder 12a and at least one second cylinder 12b. The plurality of cylinders 12 may extend through the cylinder block 11, and they may extend between a top deck surface 13 and a bottom block surface 14 of the cylinder block 11. Depending on the configuration of the engine 10, the plurality of cylinders 12 may be arranged between a front block end 15 and a back block end 16. In the illustrated embodiment, in which the engine 10 is an in-line engine, there are three first cylinders 12a and three second cylinders 12b arranged between the front block end 15 and the back block end 16. In other embodiments there may be different combinations of numbers of first and second cylinders 12a, 12b (for example one first cylinder 12a and five second cylinders 12b). In other embodiments there may be any number of cylinders 12, of which there may be different combinations of first and second cylinders 12a, 12b. In another embodiment, the engine 10 have either one or two cylinder blocks 11. Alternatively, the engine 10 may be a V, boxer, radial or opposed engine. In an embodiment, in which the engine 10 is a V engine, the cylinders 12 may be arranged in two banks arranged in a V shape. One bank may include the at least one first cylinder 12a and at least one second cylinder 12b and the other bank may include no first cylinders 12a or no second cylinders 12b. Alternatively each bank may include at least one first cylinder 12a and at least one second cylinder 12b. In a further alternative, one bank may only include first cylinders 12a and the other bank may only include second cylinders 12b. In an embodiment, in which the engine 10 is an opposed or boxer engine, the cylinders 12 may be arranged in two opposing banks. One bank may include the at least one first cylinder 12a and at least one second cylinder 12b and the other bank may include no first cylinders 12a or no second cylinders 12b. Alternatively each bank may include at least one first cylinder 12a and at least one second cylinder 12b. Ina further alternative, one bank may only include first cylinders 12a and the other bank may only include second cylinders 12b. In an embodiment, in which the engine is a radial engine, the cylinders 12 may be arranged to radiate outwards. The at least one first cylinder 12a may have a longitudinal first cylinder axis VV. Depending on the configuration of the engine 10, the longitudinal first cylinder axis VV may be arranged such that the longitudinal first cylinder axis VV lies along a first cylinder block axis XX which extends between the front block end 15 and the back block end 16 of the cylinder block 11. In embodiments having more than one first cylinder 12a, all of the first cylinders 12a may be arranged such that the longitudinal first cylinder axis VV of each of the first cylinders 12a lies along the first cylinder block axis XX. The at least one second cylinder 12b may have a longitudinal second cylinder axis WW. Depending on the configuration of the engine 10, the longitudinal second cylinder axis WW may be arranged such that the longitudinal second cylinder axis WW lies along a second cylinder block axis YY which extends between the front block end 15 and the back block end 16 of the cylinder block 11. In embodiments having more than one second cylinder 12b, all of the second cylinders 12b may be arranged such that the longitudinal second cylinder axis WW of each of the second cylinders 12b lie along the second cylinder block axis YY. In a monobloc in line cylinder block 11, the second cylinder block axis YY may be offset from the first cylinder block axis XX by an offset distance D in a plane defined by the top deck surface 13. A cylinder head 17 (see Figures 2 and 3), which may have a fire deck 18, may be attached to the top deck surface 13 of the cylinder block 11. The cylinder head 17 may comprise a plurality of intake valves 19 for controlling the inlet of air into the cylinders 12 and a plurality of exhaust valves 20 controlling the discharge of exhaust from the cylinders 12. The cylinder head 17 may comprise a plurality of fuel injectors 21 positioned for injecting fuel into each of the cylinders 12 for mixing with the compressed air for combustion. A piston 22 may be slidably mounted within each of the cylinders 12 adapted to reciprocate between a top dead centre position and a bottom dead centre position within the cylinder 12. The cylinders 12 may each have a radial cylinder sidewall 24 and a combustion chamber 23 may be defined by the cylinder sidewall 24 , a crown 25 of the piston 22 and the fire deck 18. The combustion chamber 23 may be configured to have a variable volume between a maximum volume and a minimum volume as the piston 22 reciprocates within the cylinder 12. A crankshaft 27 may be rotatably mounted in the cylinder block 11 extending between the front block end 15 and the back block end 16. The cylinder block 11 may include a crankcase 26 (see Figure 1) in which the crankshaft 27 (see Figures 4 and 5) may be rotatably mounted by means of a plurality of main bearings (not shown). Each piston 22 may be coupled to the crankshaft 27 by a connecting rod 28. Each piston 22 may be coupled to a connecting rod 28 by suitable means, such as a wrist pin 32. The crankshaft 27 may include a plurality of main journals 29 axially aligned along a longitudinal crankshaft axis ZZ and rotatably mounted in the main bearings. The crankshaft 27 may also include a plurality of rod journals 30 radially offset from the crankshaft axis ZZ. Each of the rod journals 30 may be configured to couple to a connecting rod 28. Various coupling mechanisms may be used to couple the connecting rods 28 to the rod journals 30. The crankshaft 27 may also include a plurality of webs 31. One or more of the webs 31 may be coupled between at least one of the main journals 29 and one of the rod journals 30. Other components such as flywheels, dampers, counterweights etc. may be coupled to the crankshaft 27. The rod journals 30 may be configured to enable the mounting and operation of the pistons 22 in the configuration described below. The longitudinal first cylinder axis VV of the at least one first cylinder 12a may be perpendicular to the crankshaft axis ZZZ such that the at least one first cylinder 12a may be “centred” relative to the crankshaft axis ZZ (as shown in Figure 2). Thus, when a piston 22 mounted in the at least one first cylinder 12a is at top dead centre, the centre of the rod journal 30 and a centre of the wrist pin 32 (or other coupling mechanism) are aligned along the longitudinal first cylinder axis VV of the at least one first cylinder 12a with the crankshaft axis ZZ. The longitudinal second cylinder axis WW of the at least one second cylinder 12a may be laterally offset from a plane defined by the crankshaft axis ZZ and the longitudinal first cylinder axis VV of the at least one first cylinder 12a) by an offset distance D such that the at least one second cylinder 12b may be “offset” relative to the crankshaft axis ZZ (as shown in Figure 3). Thus, when a piston 22 mounted in the at least one second cylinder 12b is at top dead centre, the centre of the rod journal 30 and a centre of the wrist pin 32 (or other coupling mechanism) are aligned on the longitudinal second cylinder axis WW of the at least one second cylinder 12b and are offset from the plane defined by the crankshaft axis ZZ and t the longitudinal first cylinder axis VV by offset distance D. In the illustrated example, the three first cylinders 12a may alternate with the three second cylinders 12b. However, other arrangements may be used, for example in an inline six cylinder engine, the sixth cylinder may be a first cylinder 12a and the first to fifth cylinders may be second cylinders 12b. The offset distance D may range from 5 to 50mm, from 15 to 30mm or be 10mm. However, the optimal offset distance D to minimize the friction losses may vary according to the design and geometry of the engine 10 and the geometry of the crank train (typically comprising the pistons 22, the connecting rods 28, the crankshaft 27 and a flywheel or other power take-off device) and may be confirmed for each engine design based on simulation. The connecting rod 28 attached to the piston 22 mounted in the at least one second cylinder 12b may be longer than that attached to the piston 22 mounted in the at least one first cylinder 12a. This may be to accommodate the offset and to ensure a consistent cylinder volume in the at least one first and second cylinders 12a, 12b. Rocker arms (not shown), operated by a rocker shaft (not shown), may be used to operate the inlet and exhaust valves 19, 20. The length of the rocker arms may be different for those used to operate the inlet and exhaust valves 19, 20 on the at least one first cylinder 12a compared to those used to operate the inlet and exhaust valves 19, 20 on the at least one second cylinders 12 as a result of the offset. The engine 10 may further comprise a controller (not shown) configured to control operation of the engine 10 and, in particular, to control the operation of the engine 10 in response to an increase or decrease in the load on the engine 10. The controller may be configured to deactivate one or more of the at least one first cylinders 12a under predetermined conditions, such as a decrease in the load on the engine 10, and to reactivate one or more of the deactivated at least one first cylinder(s)12a to an active state under other predetermined conditions, such as an increase in the load on the engine 10. The controller may be configured to always maintain the at least one second cylinder 12b in an active state during operation of the engine 10. The term ‘deactivate’, as used herein, means to stop a supply of fuel to a cylinder 12, while the term ‘active state’ means that fuel is being supplied to the cylinder 12 to enable it to work normally in the compression ignition cycle. In effect, therefore, a deactivation / activation of one or more cylinders 12 of the engine 10 may correspond to a deactivation / activation of fuel injectors 21 associated with the cylinder 12. The number of the at least one first cylinders 12a that may be deactivated, a sequence of cylinder deactivation and a duration of cylinder deactivation may all be pre-determined and be stored within a memory of the controller for various predetermined conditions. For example, a processing unit within the controller may refer to charts and models stored within the memory that may help establish the number of the at least one first cylinders 12a that may be deactivated, the sequence of cylinder deactivation, and / or the duration of cylinder deactivation. In one example, the number of at least one first cylinders 12a that may be deactivated may depend upon a measure of a decreased load. For example, the higher measure of decrease of the load, the higher may be number of at least one first cylinders 12a that may be deactivated. The controller may determine the number of the at least one first cylinders 12a to be deactivated based on, for example, one or more of engine speed, engine fuelling, engine altitude, engine temperature and / or additional or different engine operating parameters. In another embodiment (not illustrated), the crankshaft 29 may be offset relative to the cylinder block 11, which means that the positions of the at least one first and second cylinders 12a, 12b are reversed from that shown in the Figures. In other words, the at least one first cylinder 12a (which is centred with respect to the crankshaft axis ZZ) may be offset relative to the centre line of the cylinder block 11 and the at least one second cylinder 12b (which is offset relative to the crankshaft axis ZZ) may be centred relative to the centre line of the cylinder block. Industrial Applicability During normal operation of the engine 10 the pistons 22 may reciprocate within the cylinders 12 causing a rotation of the crankshaft 27. The pistons 22, when in an active state, may follow a four-stroke sequence, moving up and down between a bottom dead centre position and a top dead centre position. The first stroke of a piston 22 may be an intake stroke, during which the piston 22 moves downward toward bottom dead centre. During this stroke, the intake valve 19 may be opened to allow air into combustion chamber 23. The second stroke of the four-stroke sequence may be a compression stroke, during which the piston 22 moves upward toward top dead centre. During this stroke, the intake valve 19 and the exhaust valve 20 may normally be closed, such that the air drawn into the cylinders 12 may be compressed by the movement of piston 22. The third stroke of the engine 10 may be an expansion stroke, during which the piston 22 is moved downward toward bottom dead centre by combusting gases. During this stroke, both the intake valve 19 and the exhaust valve 20 may be closed to allow the expanding gases to work against the piston 22. The fourth stroke may be an exhaust stroke during which the piston 22 moves upward toward top dead centre. During this stroke, the exhaust valve 20 may open to allow the piston 22 to force exhaust out of the combustion chamber 23. The four-stroke operation of the engine 10 may be continuously repeated. The firing order, i.e. the sequence of ignition for the cylinders 12, may correspond to the order in which fuel is injected into each cylinder 12 and may be determined by the controller. During operation of the engine 10, the controller may detect one or more engine parameters, such as a change in engine speed, as an indicator of a decrease or increase in the load. Additionally, or optionally, the controller may use other parameters of the engine 10 to detect a decrease or increase in the load. Based on a decreased load condition, the fuel injectors 21 associated with one or more of the at least one first cylinders 12a may be fed with a modified fuelling command (i.e. according to the fuelling timing pattern) to deactivate one or more of the at least one first cylinders 12a. In one example, the number of the at least one first cylinders 12a that need to be deactivated may depend upon a measure of a decreased load. For example, the higher measure of decrease of the load, the higher may be number of the at least one first cylinders 12a that may be deactivated. The controller may determine the number of the at least one first cylinders 12a to be deactivated based on, for example, one or more of engine speed, engine fuelling, engine altitude, engine temperature and / or additional or different engine operating parameters. At the same time, the controller may control the at least one second cylinder 12b by keeping it in an active state. Whilst one or more of the at least one first cylinders 12a are deactivated, if the controller determines an increased load condition, the fuel injectors 21 associated with one or more of the at least one first cylinders 12a may be fed with a modified fuelling command (i.e. according to the fuelling timing pattern) to reactivate one or more of the at least one first cylinders 12a. However, as explained previously, it is known that a deactivated offset cylinder may exhibit a higher friction force compared to a deactivated centred cylinder. The following worked examples demonstrate this. The graph of Figure 6 illustrates the piston side forces in a prior art 7.1L six cylinder in line engine during rotation of the crankshaft. In a first configuration, the engine has a centred crank arrangement, so the cylinders are centred relative to the crankshaft axis. The side forces in one of these cylinders (when active) is represented by the dashed line and the peak to peak piston side force during a four stroke cycle is approximately 18.992kN per cylinder. Across all six cylinders, this would represent a total peak force of:- 6 x 18.992 = 113.952kN In a second configuration, the engine has an offset crankshaft, and the cylinders are offset relative to the crankshaft axis by 10mm. The side forces in one of these cylinders (when active) is represented by the solid line and the peak to peak piston side force during a four stroke cycle is approximately 18.705kN per cylinder. This represents a reduction of approximately 0.287kN in peak to peak side force per cylinder compared with the first configuration. Across all six cylinders in the second configuration, this would represent a total peak to peak side force of:- 6 x 18.705= 112.23kN Thus, the second configuration provides a 1.722kN reduction in the total peak side force across all six cylinders, compared to that in the first configuration. The graph of Figure 7 compares the piston side forces in a deactivated cylinder in the first and second configurations described above. In the first configuration (again shown by the dashed line), the peak to peak piston side force in the deactivated cylinder is approximately 3.167kN. If the engine of the first configuration is operating with five active cylinders and one deactivated cylinder, the total peak to peak side forces across all six cylinders would be:- (5 x 18.992) + (1 x 3.167) = 98.127kN In the second configuration, the peak to peak piston side force in the deactivated cylinder is approximately 3.813kN, which represents an increase in peak to peak side compared to that in the deactivated cylinder of the first configuration of approximately 0.646kN. If the engine of the second configuration is operating with five active cylinders and one deactivated cylinder, the total peak to peak side forces would be:- (5 x 18.705) + (1 x 3.813) = 97.338kN Thus, the second configuration provides only a 0.789kN reduction in the total peak side force across all six cylinders compared with that of the first configuration. Furthermore, this reduction is significantly less than the reduction of 1.722kN in second configuration when all of the cylinders are active. The engine 10 of the present disclosure may make it possible to combine the known benefits of an offset crankshaft arrangement and a cylinder deactivation routine to reduce the total peak forces across the engine 10 by providing a combination of cylinders 12 which are offset and centred relative to the crankshaft axis ZZZ. As explained above, the at least one first cylinder 12a which may be deactivated may be centred relative to the crankshaft axis ZZ, whilst the at least one second cylinder 12b may be offset relative to the crankshaft axis ZZ. In such an arrangement, the disadvantages described previously with respect to deactivating a cylinder in an offset crankshaft arrangement may be overcome. In one example according to the disclosure, the engine 10 may be a six cylinder in line engine which has a 7.1L capacity and may have one first cylinder 12a (centred relative to the crankshaft axis ZZ) and five second cylinders 12b (offset relative to the crankshaft axis ZZ). During full power, with all of the first and second cylinders 12a, 12b active, the total peak to peak side forces would be:- (5 x 18.705) + (1 x 18.992) = 112.571 kN This represents a reduction in total peak force compared to that of the first configuration (in which all six cylinders are centred) of 1.381 kN, although there is a very small increase of 0.341 kN compared to that of the second configuration (in which all six cylinders are offset). However, when the first cylinder 12a is deactivated, the total peak to peak side forces would be:- (5 x 18.705) + (1 x 3.167) = 96.692kN This therefore provides a reduction in the total peak side to side forces compared with that in both the first and second configurations of prior art engines with all six cylinders active and with one cylinder deactivated.

Claims

1. An internal combustion engine (10) comprising:a cylinder block (11) comprising a plurality of cylinders (12); anda crankshaft (27) having a crankshaft axis (ZZ) rotatably mounted in the cylinder block (11);wherein at least one first cylinder (12a) of the plurality of cylinders (12) has a first cylinder longitudinal axis (VV) which is perpendicular to the crankshaft axis (ZZ); and at least one second cylinder (12b) of the plurality of cylinders (12) has a second cylinder longitudinal axis (WW) which is laterally offset from a plane defined by the crankshaft axis (ZZ) and the longitudinal first cylinder axis (W).

2. The internal combustion engine (10) according to claim 1, further comprising a piston (22) reciprocally mounted in each of the plurality of cylinders (12), each piston (22) being coupled to the crankshaft (27) by a connecting rod (28).

3. The internal combustion engine (10) according to claim 2, wherein the connecting rod (28) coupled to a piston (22) mounted in the at least one second cylinder (12b) is longer than the connecting rod (28) coupled to a piston (22) mounted in the at least one first cylinder (12a).

4. The internal combustion engine (10) according to any one of the preceding claims, comprising a plurality of first cylinders (12a).

5. The internal combustion engine (10) according to any one of the preceding claims, further comprising a controller configured to deactivate one or more of the first cylinders (12a) under predetermined conditions whilst maintaining the at least one second cylinder (12b) in an active state.

6. The internal combustion engine (10) according to claim 5, wherein the controller is configured to reactivate one or more of the first cylinders (12a) which have been deactivated under other predetermined conditions.

7. The internal combustion engine (10) according to any one of the preceding claims in which the cylinder block (11) comprises:a top deck surface (13);a bottom block surface (14);a front block end (15);a back block end (16); anda plurality of cylinders (12) arranged between the front block end (15) and the back block end (16) and extending through the cylinder block (11) between the top deck surface (13) and the bottom block surface (14).

8. The internal combustion engine (10) according to claim 7, in which the first cylinder longitudinal axis (VV) lies on a first cylinder block axis (XX) which extends between the front block end (15) and the back block end (16) and which is parallel to the crankshaft axis (ZZ).

9. The internal combustion engine (10) according to claim 7, in which second cylinder longitudinal axis (WW) which lies on a second cylinder block axis (YY) which extends between the front block end (15) and the back block end (16), the second cylinder block axis (YY) is offset relative to the first cylinder block axis (XX) and the crankshaft axis (ZZ).

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