ENGINE

FIELD OF THE INVENTION

[0001] This invention relates generally to Internal Combustion Engines and more particularly to a new and improved Constant frequency Variable displacement Engine.

BACKGROUND OF THE INVENTION

[0002] Different types of Internal Combustion Engines have been produced and are being used in automobiles, industries, power generation plants, ships and military equipment. These are further classified as Spark Ignition engines and Compression Ignition engines depending on the mode of igniting the fuel and generating the power stroke. A number of different fuels have also been used in these engines, from both natural and man-made origins.

[0003] Internal Combustion engines, as is well known in the field, rely on four operations, namely:

1. Suction

2. Compression

3. Power and

4. Exhaust.

[0004] These four operations can be completed in 2 rotations of the crankshaft i.e. 720 degrees for a four-stroke cycle engine. These operations can also be completed in one rotation of the crankshaft i.e. 360 degrees, for a two-stroke cycle engine or when each piston associated with its cylinder reciprocates inside the cylinder bore, completing all the required operations to complete a cycle.

[0005] ICEs can either be single cylinder engines or multi-cylinder engines. The arrangement of the cylinders is commonly an in-line arrangement, boxer arrangement or V-banked arrangement, knowledge of which is well known to one who is skilled in the art. [0006] It is also well known that these cylinders are so arranged in relation to the crankshaft, so that the power stroke is generated evenly throughout the engine's angular displacement in completing all the required operations in a cycle. For a four-stroke engine, the power impulse is at an angle equal to 720÷z, where z is the number of cylinders in the engine. For a two-stroke engine, the power impulse angle is equal to 360÷z. This is accomplished by building the crankshaft in such a way that the crank pin angles associated with the different cylinders are radially spaced, in an evenly distributed manner. The injection or ignition timing is also such that each cylinder develops its power stroke in a regular manner, evenly distributed over the engines operating cycle.

[0007] None of the engine cylinders are designed to "fire" i.e to generate a power stroke at the same instant and along with any other cylinder in the engine. This is primarily achieved by means of the crankshaft with its evenly distributed (radially as well as axially) crank pins. Hence the angular displacement between the "firing" of one cylinder to the "firing" of next cylinder will be several degrees apart, depending on the number of cylinders in a particular engine.

[0008] For e.g a four stroke 6-cylinder inline engine is so arranged that a power stroke is generated every 120 degrees (720÷6) of the crankshaft rotation. Thus, between one cylinder "firing" to the next cylinder "firing" there is a nominal angular displacement of 120 degrees. The actual real-time firing angle could be advanced or retarded, by means of the ignition control system, as the case may be, depending on the engine speed, load etc.

[0009] Refer figure 1.

[0010] In this schematic of a six-cylinder 4 stroke inline engine, the crank shaft is so designed that the crank pins are 120 degrees apart from each other. The cylinders are also designed to 'fire' in a predetermined manner, at equal intervals of 120 degrees and in a certain sequence termed as firing order. This is to ensure that the engine, during operation, is well balanced.

[0011] For clarity and simplicity, only those details which are pertinent are indicated. The engine gas exchange valves (inlet and exhaust valves) and the injection/ignition arrangement is not shown in the above figure. The gas exchange valves commonly are camshaft operated. These valves could also be servo/solenoid operated either electrically, hydraulically or pneumatically in the case of "cam-less" free-valve engines.

[0012] Some common examples of a firing order for a 4-stroke, six cylinder inline engine are:

[0013] 1-5-3-6-2-4

[0014] 1-4-2-6-3-5

[0015] Hence each cylinder completes its cycle of operation in a pre-arranged sequence, which is again repeated after all the other cylinders complete theirs'.

[0016] The firing of cylinder No. l is followed by cylinder No.5 after 120 degrees of crankshaft rotation, which in turn is followed by cylinder No. 3 and so on.

[0017] Now, in view of depleting resources and the rising cost of fuel thereby, it is the need of the hour to produce fuel efficient engines.

[0018] Another factor to consider is an engine's varying power output requirement in a real-life scenario. For e.g. a ship coming alongside the jetty to dock, requires minimal power output from her engine, for safe manoeuvring, whereas the same ship needs full power when cruising at maximum speed. A car driven uphill and while accelerating needs to develop more power than while it is being driven on the highway. A generating plant must develop more than its rated power during peak times and also has to develop minimal power during off-peak times when demand is slack from electricity consumers.

[0019] An Internal combustion engine running on low load condition will be operating at low Mean effective pressures. The efficiency of internal combustion engines is best at high mean effective pressures.

[0020] To operate during these varying engine power outputs and/or also to improve fuel economy, the Mean effective pressure has to be improved.

[0021] This can be achieved by varying the "active displacement" of the engine through deactivating some of the cylinders when power requirements are minimal, and again reactivating the cylinders when boost in power is sought. In these methods, some cylinders will not "fire" i.e. these cylinders will not generate a power stroke at the instant that it would have, had the cylinder been "active". The gas exchange valves will also be inoperative during this low output period, thus reducing pumping losses.

[0022] Although there can be significant gains in efficiency by means of cylinder deactivation, there are some limitations as well. When an engine is running on low load conditions and some cylinders are deactivated, the engines excitation order will change. The frequency of the combustion torque pulses onto the crankshaft is lowered, and the balance cylinders that are active will be operating under a higher load to maintain the output torque.

[0023] Thus as shown in the figure 2.0 the amplitude of the combustion torque pulse is larger

[0024] These conditions are detrimental for systems excited by the engine and with an eigen frequency below the engine idling frequency.

[0025] Hence, cylinder deactivation is preferably resorted at a higher engine rpm.

[0026] Also the overall power strokes in variable displacement" engine, are generated in an irregular manner whenever the cylinder(s) is/are deactivated in this manner. This is because the crankshaft's crank pin angles are designed and manufactured for maximum active displacement i.e when all cylinders are "active".

[0027] For illustration purpose, for e.g in a 4 stroke 6- cylinder in-line engine the crankshaft is manufactured with the crank pins 120 degrees apart. The angular displacement between the "firing" of any two cylinders is also nominal 120 degrees when all of its cylinders are active. Hence, engines whose cylinders are all active and are firing at this angle is well balanced with low Noise Vibration and Harshness (NVH)

[0028] Due to reduced Power requirement, if say two cylinders in this engine are deactivated, and the engine is running on only 4 cylinders, the crank pin angle should ideally change to 720÷4= 180 degrees, in order to have an even pulse, throughout the operating cycle of the engine, without any increase in NVH. But due to the inherent mechanical limitations of the crankshaft this is impossible. [0029] If any cylinder(s) is/are deactivated, the nominal firing angular displacement between two successively fired cylinders will change to 240 degrees, or even 360 degrees, depending on the number of cylinders deactivated. This gives rise to large magnitudes of Noise, Vibration and Harshness (NVH), since the engine which is designed to be balanced at a power impulse angle of 120 degrees, with all six cylinders active cannot be easily and economically balanced at other firing pulse angles.

[0030] NVH has detrimental effect on both comfort and reliability. Resonances excited by this engine can cause structural failure under stress.

[0031] An internal combustion engine is a source of several periodic excitations, depending on the engine configuration and number of cylinders. These excitations are caused by the reciprocating engine inertias and by the combustion torque pulses.

[0032] The main order of excitation caused by the combustion torque pulses

[0033] Nmain = Number of cylinders ÷ z, where ζ =1 for a 2- stroke engine and z =2 for a 4-stroke engine

[0034] Now assume that the cylinders are deactivated, the engine order Nmain, changes. This affects the excitation frequency, which is dependant of the engine order:

[0035] f _a = (n Nmain) ÷60,

[0036] where f _ex is the excitation frequency (Hz) and n is the engine speed in rpm

[0037] Although we have illustrated a 4-stroke, 6-cylinder engine, the same applies to all other multi cylinder engines as well, whether they have 2 cylinders or more. It also applies to engines having in-line arrangement or V banked, whether the engines are based on the four- stroke cycle or the two stroke cycle or which might operate on any other cycle.

[0038] Problems faced due to these deactivation methods, are an increase in Noise, Vibration and Harshness (NVH), decreased engine life due to crankshaft fatigue, and general discomfort. SUMMARY OF THE INVENTION

[0039] To overcome problems as set forth above, the purpose of this invention is to generate a power impulse in the engine, evenly during the cylinder(s)' deactivated condition

[0040] In other words, the nominal power impulse angle between two sequentially fired cylinders in this engine will be regular and balanced, irrespective of whether any of the cylinders in the said engine are deactivated or not.

[0041] In one aspect of the invention, where the engines' gas exchange valves are camshaft operated, the engine cylinders are so arranged so as to have a set (of at least two) on the same crank pin angle. These cylinders belonging to one set are also designed to be in phase, i.e to have the same cycle of operation like suction, compression, power and exhaust simultaneously. Thus, all the cylinders in a given set will "fire" and generate a power stroke at the same nominal angle in the engines' operating cycle (which is 720 degrees for 4-stroke or 360 degrees for a 2-stroke engine)

[0042] Thus, we can have a 4-cylinder engine in two sets of 2 cylinders, a six- cylinder engine in three sets of 2 cylinders, an eight-cylinder engine in four sets of 2-cylinders, a 10 cylinder engine in 5 sets of 2 cylinders and so on.

[0043] Also, at least one of the cylinders from any given set will be active during the period the engine is operating, no crank angle will be without a power stroke in the 720 degree (or 360 degrees) displacement.

[0044] At no time during the operation of the engine will all the cylinders in the set on one crank pin angle be de-active at the same instant.

[0045] In another aspect of invention, during the periods when the power requirement from this engine is low, a cylinder associated with each of the crankpins will be successively deactivated.

[0046] Thus there will be a gradual reduction in the number of active cylinders - in this particular example of a six cylinder engine - from 6 cylinders to 5 cylinders to 4 cylinders and finally to 3 cylinders, without a change in the power impulse angle or frequency BRIEF DESCRIPTION OF THE ACCOMPANYING SCHEMATIC

DIAGRAMS

[0047] Only the Pertinent details as necessary to understand the present invention are shown. The valve gear train, gas exchange valves, the camshaft, free valve solenoids et are not shown.

[0048] Fig-1 depicts a conventional Internal Combustion Engine, in particular a 4-stroke, 6-cylinder inline engine.

[0049] Fig 2.0 indicates the comparative curves for an engine operating on full power mode and the same engine when half the cylinders are "deactive", i.e. when a 4-stroke, 4-cylinder inline engine is operating in four-cylinder baseline mode and when the engine is operating in a 2-cylinder mode.

[0050] Fig 3 depicts the schematic layout of the cylinder and the crankshaft in the present invention. In particular a 4-stroke, six cylinder in line engine having three power impulse crankpin angles

[0051] Fig. 4 depicts the schematic layout of an alternate arrangement of same 4-stroke, 6 cylinder in- line engine in the present invention.

[0052] Fig.5 depicts an e.g. of an engine with an odd number of cylinder arranged for the present inventions' constant frequency variable displacement engine.

DETAILED DESCRIPTION OF THE INVENTION

[0053] The preferred highlight of the present invention will now be described in greater detail herein below, with particular reference to the accompanying diagrams.

[0054] Figure 3 shows a schematic layout of the 4-stroke, 6-cylinder in-line engine as is in the present invention.

[0055] For clarity and simplicity, only those details which are pertinent are indicated. The engine gas exchange valves and the injection /ignition arrangement is not shown in the above figure. The gas exchange valves could either be camshaft operated or as in the case of "camless" free-valve engines be servo operated either electrically, hydraulically or pneumatically.

[0056] As shown in fig. 3, pistons PI &P2 in cylinders CI &C2 are connected to crankpin-Al by means of connecting rod E, forming one set. Pistons P3&P4 in cylinders C3&C4 are connected to crankpin A2, forming the second set. Pistons of cylinders P5 &P6 in cylinders C5&C6 are connected to crankpin A3, forming a third set.

[0057] Hence, this can be considered a three-crank engine, with the crank angles at 240 degrees between each other.

[0058] The cycles of operation i.e suction, compression, power and exhaust of the cylinders CI & C2 are in unison, and take place at the same nominal angles. Similarly, the cycles of operation of cylinders C3&C4 and C5&C6 are also in unison as depicted in fig.3.

[0059] In this example of a six-cylinder 4 stroke in-line engine there will be three power impulses in a cycle during the period when all the 6 cylinders are active.

The angle between the power impulses will be (720÷3) = 240 degrees.

[0060] Thus, power impulse angle between the cylinders connected on

Crankpin Al and the power impulse angle of the next sequentially fired set of cylinders on Crankpin A3, is 240 degrees.

[0061] The firing sequence of the crank pins could be:

[0062] A1-A3-A2, or also denoted by identifying the pistons,

[0063] (P1&P2) - (P5&P6) - (P3&P4)

[0064] Here Pistons PI &P2 will be operating in unison and having the same nominal power pulse angle. Similarly, Pistons P5 &P6 will also be in unison as will be Pistons P3&P4. [0065] The below table will illustrate the firing or the power stroke sequence.

0066] Now, if there is a condition of reduced power requirement, any one of the cylinders (say for e.g cylinder C6) will become deactive. Thus, the engine will effectively become a 5-cylinder engine.

[0067] Now the firing will be shown below

480 STRO 3

POWER

720 TROK STROK

!3

[0068] Even though a cylinder is deactive, the crank pin, with which it is a set of, will still be experiencing a power pulse at its pre-determined instant i.e 240 degrees, hence there will be no NVH because the pulse frequency will not be altered.

[0069] If the load further reduces, another cylinder, but not from the same set as the one from which a cylinder is already deactive (say for e.g cylinder-Cl) will become deactive. Thus, the engine will effectively become a 4-cylinder engine.

[0070] Now the firing will be as shown below

CRANKSHAFT CYLINDERS / CRANKPINS

DEGREES A ₂ A ₃

P ₂ P ₃ P ₄ Ps P ₆

240

STROKE

480

TROKE

POWER POWER

720

STROKE TROKE

[0071] If the load reduces still further, another cylinder, but not from the same sets as the ones from which cylinders are already deactive (say for e.g cylinder-C3) will become deactive. Thus the engine will effectively become a 3 -cylinder engine.

[0072] Now the firing will be as shown below

[0073] To keep the wear and tear equal in all the cylinders, the engine's cylinder firing can be managed, such that alternately or at a predetermined intervals, cylinders that were active will become deactive and vice versa

[0074] During the transition from a full power condition to a reduced power condition, the power impulse angle will be unchanged, i.e in this e.g of a 4-stroke, 6 cylinder in-line engine the angle remains constant at a nominal 240 degrees. This can take place without stopping the engine irrespective of whether the engine is camshaft operated or free valve camless engine.

[0075] Another arrangement, where only two steps of change in power output are adequate, the full power operation will have all six cylinders active and firing at an equal angle of 120 degrees, and the reduced power operation will have three cylinders firing at an equal angle of 240 degrees. For a free valve, camless engine, this operation can take place without stopping the engine, whereas for a camshaft operated engine, the engine has to be stopped and a cam shaft suitable for only the three cylinders activation will be put in operation, to facilitate the optimum gas exchange through the cylinders.

[0076] The invention will now be described in detail in connection with the design of the crankshaft and in particular to the firing impulse angles so as to have minimum magnitudes of Noise, Vibration and Harshness (NVH) [0077] For illustration purpose, we shall take an example of a six-cylinder inline engine, although the principle of this present invention is applicable to any and all engines, whether inline or V banked.

[0078] Divide the number of cylinders in the in-line engine (or number of cylinders on a given bank in a V-type engine) by the number of cylinders to be associated in a crank angle set.

[0079] Thus, if we want this 6-cylinder engine to have a set of two cylinders to have the same power impulse angle, we shall arrive at (6÷2) = 3 crank angles.

[0080] Now, for a four-stroke cycle engine, the crank angle :720÷3 = 240 degrees.

[0081] Hence the power impulse angle between two sets of cylinders (between two crank pins) will be 240 degrees.

[0082] Fig, 4 depicts an alternate arrangement of the cylinders is shown. This is in addition to the crankshaft depicted in fig 3. In fig 3 the cylinder sets on crankpin angle are adjacent to each other.

[0083] In Fig.5 the pistons PI &P2 are one set connected on crankpin Al, but are not adjacent to each other, Similarly the other two Pistons P3 and P4 are a second set and Pitons P5 &P6 are the third set are not adjacent to each other.

[0084] In some instances where the engine design entails having an odd number of cylinders, this engine too could be configured to have a constant pulse frequency and a reduced NVH as has been depicted in fig. 5.

[0085] As shown in fig.5, four of the cylinders are arranged in sets of two, and the fifth cylinder is a lone cylinder associated with the third crank pin angle.

[0086] The cylinder diameters Dl, D2, D3, D4, D5 and D6 could either be identical to each other or different.

[0087] Similarly the crank throws Rl, R2, R3,R4,R5 and R6 could either be identical to each or different.

[0088] Similarly, this arrangement can be designed for any other combination of odd cylinder engines. [0089] The arrangement of the engine cylinders in the present invention can have any combination of cylinders, firing order, cylinder crankpin connections etc. so as to have a constant pulse frequency during the deactivated cylinder mode.

ADVANTAGES

[0090] The main advantage of this invention is the smoothly variable power under economical and efficient operation, without the associated NVH as experienced in current variable displacement engines, thus improving comfort and structural integrity.

[0091] The cylinders can be deactivated one by one without any change in the power impulse angle up to until there is only a single cylinder on the crankpin which is active.

[0092] This purpose of the invention is to have a simple reliable multi- displacement engine operation without the complexity and expense of the currently available engine systems .

[0093] Another advantage is that the engine shall have a wide range of displacements for different operating conditions, keeping the engine efficiency at the maximum.

[0094] This invention allows deactivation even at low engine rpm, which is not possible in currently available variable displacement engines, thus increasing the time period of high efficiency operation.

[0095] This invention is applicable for even as well as odd number of cylinders in an engine.

[0096] This type of improved arrangement can have deactivation of cylinders for even two-cylinder engines, which currently is not possible for the existing engines