GB2114709A

GB2114709A - Flywheel for internal combustion engine

Info

Publication number: GB2114709A
Application number: GB08300338A
Authority: GB
Inventors: Kazuaki Kobayashi
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1982-01-26
Filing date: 1983-01-07
Publication date: 1983-08-24
Also published as: DE3302364C2; GB8300338D0; GB2114709B; DE3302364A1; JPS58128546A

Abstract

In a flywheel (1) for a straight type four-cylinder engine wherein each pair of the four cylinders reach their upper dead points each time the crank angle reaches 0 DEG and 180 DEG , a main weight portion (5a and 5b) is provided which is made to be heavier in the portions corresponding to the 90 DEG and 270 DEG crank angles than in the remainder. With this flywheel, it is possible to increase the natural frequency of bending vibration of the crank shaft system of the engine, while at the same time achieving a moment of inertia required to decrease engine torque variations. <IMAGE>

Description

SPECIFICATION Flywheel for straight-type four-cylinder engine This invention relates to a flywheel for a straight type four-cylinder engine.

With conventional flywheels, there has been no special distinction between one for a four-cylinder engine and one for a six-cyiinder engine, for example. In other words, flywheels of a substantially identical configuration have heretofore been employed with all sorts of engines. In order to have a better understanding of the present invention, reference will first be made to Figures 1 A and 1 B of the accompanying drawings, where is shown an example of the conventional flywheel for an automotive engine, wherein the flywheel 1 comprises bolt inserting apertures 2 adapted for coupling the flywheel 1 to the crank shaft of the engine by means of bolts; a contact surface 3 adapted to be disposed in contact with a clutch disc; a ring gear 4 adapted to be brought into intermeshing relationship with the pinion gear of a starter when the engine is started, the ring gear 4 being usually press-fitted on the body of the flywheel; and a main weight portion 5 with a high moment of inertia, which serves to reduce engine torque variations as well as variations in the rotational speed of the engine.

Generally, the moment of inertia of a rotating body, when the weight of the body is constant, is proportional to the radius of rotation of the body.

Thus, it has been the usual practice that the main weight portion 5 is provided, in a ring-like form in a portion of the flywheel in the vicinity of the outer periphery thereof.

The aforementioned conventional arrangement in which the main weight portion is provided, in a ring-like form, in a portion of the flywheel in the neighbourhood of the outer periphery thereof as mentioned above is advantageous in that a high moment of inertia can be achieved for its weight, and thus can be said to constitute an extremely suitable configuration for the flywheel to minimize engine torque variations.

In an ordinary four-stroke straight type fourcylinder engine, the pistons in each two of the four cylinders reach their upper dead points each time the crank angle reaches 0 and 1800 so that for each 180" rotation of the crank, explosion takes place in the four cylinders in succession. In the case where such a straight type four-cylinder engine, combined with a direct coupling type transmission, is installed in a motor vehicle, the natural frequency of bending vibration which occurs in such a combination will become very close to the natural frequency of bending variation of the crank shaft system associated with the straight type four-cylinder engine so that resonance will tend to occur between the two natural frequencies.Thus, due to such a resonance phenomenon, there is the tendency that the vibration of the engine including the transmission is increased so that in some types of motor vehicle, such vibration may be transmitted to the vehicle body so as to be felt as "beat sound" by the driver and/or passenger. To avoid occurrence of the aforementioned resonance phenomenon, it is only required that the two natural frequencies mentioned above be made to be different from each other. In the case where a transmission is combined with a four-stroke straight type four-cylinder engine, however, it has empirically been shown that from the standpoint of basic construction it is technically almost impossible to achieve a sufficiently high rigidity to make the natural frequency of bending vibration of the resultant construction higher than that of the conventional one.In the crank shaft system of a four-stroke straight type four-cylinder engine, bending vibration is produced by the fact that the crank shaft is bent upwardly and downwardly at the 0 and 1800 crank angles, so that the flywheel is subjected to oscillation; if it is attempted to make the frequency of such bending vibration deviate away from the resonance frequency by decreasing the rigidity of the crank shaft so as to decrease the natural vibration frequency thereof, then an increased vibration tends to occur when the engine operates in its normal speed range below 6,000 rpm, thus giving rise to the problem of rumbling sound. In this connection, it might be considered that the natural vibration frequency of the crank shaft could be deviated to be higher either by increasing the rigidity of the crank shaft or reducing the weight of the flywheel.Obviously, however, the former approach is disadvantageous in terms of weight, and the latter approach is also disadvantageous in that the flywheel will fail to attain the necessary moment of inertia to restrain engine torque variations in the necessary range.

Accordingly, it is an object of the present invention to provide a novel and improved flywheel which is so designed as to solve the aforementioned problems with four-stroke straight type four-cylinder engines.

Briefly, according to the present invention, there is provided a flywheel for a four-stroke straight type four-cylinder engine in which the pistons in each pair of the four cylinders reach their upper dead points each time the crank angles reaches 0 and 1800 so that for each 1 800 rotation of the crank, explosion takes place in the four cylinder engine in succession, the flywheel comprising a main weight portion which is comprised of a sub portion provided in annular form in the flywheel in the vicinity of the outer periphery thereof and two heavier sub portions provided in the flywheel in positions corresponding to the 900 and 2700 crank angles and in the neighbourhood thereof.

Other objects, features and advantages of the present invention will become apparent from the ensuing description taken in conjunction with the accompanying drawings.

Figure 1 A is a front view of a conventional flywheel.

Figure 1 B is a sectional view of Figure 1 A.

Figure 2A is a front view showing the flywheel for a straight type four-cylinder engine according to an embodiment of the present invention.

Figure 2B is a sectional view taken along tne line A-A of Figure 2A.

Figure 2C is a sectional view taken along the line B-B of Figure 2A.

Figure 3 is a view useful for explaining the operation of the present flywheel.

Referring to Figures 2A to 3, detailed description will now be made of the flywheel for a four-stroke straight type four-cylinder engine according to an embodiment of the present invention.

Figures 2A to 2C illustrate the construction of the flywheel 1 embodying the present invention, wherein parts corresponding to those of Figures 1A and 1 B are indicated by like reference numerals just for the sake of simplicity. The flywheel 1 is formed with bolt inserting apertures 2, a contact surface 3, and a ring gear 4, the elements which may be similar in construction to those of the conventional flywheel mentioned above. The present flywheel 1 is provided with a main weight portion which comprises a sub portion 5a provided in annular form along the outer periphery of the flywheel and two sub portions 5b provided in positions corresponding to the 900 and 2700 crank angles and in the neighbourhood thereof in such a manner as to be concentrated in two portions adjacent to the outer periphery of the flywheel.In this connection, it may be regarded that the fact that the main weight portion 5 is comprised of the aforementioned sub portions 5a and 5b corresponds to the case where the main weight portion 5 shown in Figures 1A and 18 is divided into two types of portions so that the total moment of inertia of those sub portions 5a and 5t becomes substantially equal to the moment of inertia of the main weight portion 5 shown in Figures 1 A and 1 B.Thus with the flywheel embodying the present invention, it is possible to reduce engine torque variations to substantially the same extent as with the conventional one shown in Figures 1 A dnd 1 B, and yet, by virtue of the fact that the sub portions 5a and 5b of the main weight portion are provided symmetrically with respect to the crank shaft, it is also possible to avoid occurrence of unbalance in weight therebetween so that balancing procedures can be carried out in the same manner as in the prior art.

Description will next be made of the operation of the flywheel having the aforementioned construction according to the present invention.

Figure 3 is a view useful for explaining the bending vibration of a crank shaft system. In a four-stroke straight type four-cylinder engine, explosion load is imparted onto the crank shaft 6 in such a direction as shown by an arrow mark C in Figure 3 each time the crank angle reaches 0 and 1800; consequently, the crank shaft 6 is vibrated upwardly and downwardly so that the flywheel is oscillated in such directions as shown by arrow marks D in Figure 3. In other words, the crank shaft 6 is subjected to bending vibration, thus causing the flywheel 1 to be oscillated.In a four-stroke straight type four-cylinder engine, due to the fact that explosion load is applied each time the crank assumes the angular positions of 0 and 1 800 as mentioned above, the oscillation of the flywheel is effected in the directions corresponding to the 0 and 1 800 crank angles.

Thus, by decreasing the moment of inertia of those portions of the flywheel which correspond to such crank angles, it is possible to increase the natural frequency of bending vibration of the crank shaft system. In this way, the natural frequency of bending vibration of the crank shaft system can be deviated away from the natural frequency of bending vibration in the engine per se, so that resonance phenomenon which tends to occur, can be mitigated.

As will be appreciated from the above discussion, in accordance with the present invention, in order to decrease the moment of inertia of the flywheel in the directions corresponding to the 0 and 1800 crank angles or the directions of oscillation of the flywheel, the weight of the main weight portion of the flywheel as viewed in the directions corresponding to the 0 and 1800 angles is made to be smaller than that of the conventional one, while the weight of the main weight portion of the flywheel as viewed in the directions corresponding to the 900 and 270 crank angles, which has no effect on the oscillatory movement of the flywheel, is made to be greater than that of the conventional one, whereby the moment of inertia of the entire flywheel is made to be substantially equivalent to that of the conventional flywheel. In this way, according to the present invention, a necessary moment of inertia can be achieved to reduce engine torque variations, while at the same time the natural frequency of bending vibration of the crank shaft system can be increased to be deviated away from that of the entire engine and the extent of resonance phenomenon tends to occur, can be lessened. As will be appreciated, despite its simplified construction, the present flywheel for a four-stroke straight type fourcylinder engine works out to make the natural frequency of bending vibration of the crank shaft system different from that of the entire engine, thus lessening the extent of resonance phenomenon which tends to occur therebetween.

Claims

1. A flywheel for a straight type four-cylinder engine wherein each pair of the four cylinders reach their upper dead points each time the crank angle reaches 0 and 1 800, comprising a main weight portion made to be heavier in positions corresponding to the 900 and 2700 crank angles than in the remainder.

2. A flywheel according to claim 1, wherein said main weight portion comprises: a first sub portion extending, in a ring-like form, along and adjacent to the outer periphery of the flywheel: and second sub portions provided at positions corresponding to the 90 and 270 crank angles adjacent to the outer periphery of the flywh9el.

3. A flywheel substantially as described with reference to, and as illustrated in, Figs. 2A to 2C, of the accompanying drawings.