Patent Abstract:
A three cylinder engine includes a vibration alleviation unit for alleviating vibrations in a vehicle. The vibration alleviation unit is disposed at least one of upon the crankshaft and upon a part that operates in unison with the crankshaft. The three cylinder is supported by engine mounts that are positioned upon at least both ends of the engine in the direction of the crankshaft axis. Given that K V  and K H  represent spring constants of one of the engine mounts in the pitch and yaw directions of the crankshaft, M V  and M H  represent components of a primary couple that occurs in the three cylinder engine in the pitch and yaw directions, and M V0  represents the sum of M V  and M H , then spring constants of the engine mounts are set such that K V &gt;K H  and the vibration alleviation unit is set so as to satisfy the condition  0 &lt;M V /M V0   &lt;0.5.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National stage application of International Application No. PCT/JP2010/071026, filed Dec. 14, 2010, which claims priority claims priority under to Japanese Patent Application No. 2009-268238, filed in Japan on Nov. 26, 2009, the entire contents of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to three cylinder engine. 
         [0004]    2. Background Information 
         [0005]    Japanese Laid-Open Patent Application (Tokkai) 2006-175894 discloses a three cylinder engine that is constructed to make a component of a primary couple in a crankshaft axis pitch direction substantially zero by using weights that reduce a couple produced upon reciprocating movement of moving parts including pistons. 
       SUMMARY 
       [0006]    However, in the technique of Patent document 1, in order to make the component of the primary couple in the crankshaft axis pitch direction substantially zero, the weights are relatively heavy, which tends to bring about an increased weight of the engine. 
         [0007]    Accordingly, in the present invention, given that K V  represents a spring constant of at least one of the engine mounts in a crankshaft axis pitch direction, K H  represents a spring constant of the engine mount in a crankshaft axis yaw direction, M V  represents a component (pitch moment) of a primary couple produced by the three cylinder engine in the crankshaft axis pitch direction , M H  represents a component (yaw moment) of the primary couple produced by the three cylinder engine in the crankshaft axis yaw direction , and M V0  represents a sum of M V  and M H , then the spring constants are set such that K V &gt;K E  and a vibration alleviating unit is set in a crankshaft system (the crankshaft and a part that operates in unison with the crankshaft) vibration alleviation unit such that 0&lt;M V /M V0 &lt;0.5. 
         [0008]    In the three cylinder engine, there is usually produced an unbalanced couple of forces between a force in a pitch direction and a force in a yaw direction, which tends to cause the engine to make a processional movement. Such unbalanced couple becomes a cause of vibration when the engine is mounted in a vehicle. In the present invention, K V &gt;K H  is established and the crankshaft system is provided with a vibration alleviation unit so as to satisfy the condition 0&lt;M V /M V0 &lt;0.5 and make a yaw vibration of the entire engine larger than a pitch vibration, thereby reducing the vehicle vibration as a whole while suppressing the weight of the vibration alleviation unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Referring now to the attached drawings which form a part of this original disclosure. 
           [0010]      FIG. 1  is a front view of a mounting structure a three cylinder engine according to the present invention in a vehicle. 
           [0011]      FIG. 2  is a perspective view schematically illustrating key portions of the three cylinder engine according to the present invention. 
           [0012]      FIG. 3  is a diagram schematically illustrating a conventional approach to balance mass adjustment. 
           [0013]      FIG. 4  is a perspective view more concretely illustrating the key portions of the three cylinder engine of the present invention while showing one example of a way to attach balance masses. 
           [0014]      FIG. 5A  is a front view of the three cylinder engine taken from in front of the vehicle, which schematically illustrates the state of a vibration occurring when the present invention is applied to a three cylinder engine mounted transversely in a vehicle. 
           [0015]      FIG. 5B  is a plan view of the three cylinder engine, which schematically illustrates the state of a vibration occurring when the present invention is applied to a three cylinder engine mounted transversely in a vehicle. 
           [0016]      FIG. 5C  is a side view of the three cylinder engine taken from a side of the vehicle, which schematically illustrates the state of a vibration occurring when the present invention is applied to a three cylinder engine mounted transversely in a vehicle. 
           [0017]      FIG. 6  is a diagram illustrating a setting range for a balance weight of a crankshaft system of the three cylinder engine of the present invention. 
           [0018]      FIG. 7  is a diagram illustrating the setting range for the balance weight of the crankshaft system of the three cylinder engine of the present invention. 
           [0019]      FIG. 8  is a diagram illustrating the setting range for the balance weight of the crankshaft system of the three cylinder engine of the present invention. 
           [0020]      FIG. 9  is a diagram schematically illustrating another to attach balance masses in the three cylinder engine of the present invention. 
           [0021]      FIG. 10  is an illustration schematically illustrating a second embodiment of a three cylinder engine according to the present invention. 
           [0022]      FIG. 11  is an illustration schematically illustrating a third embodiment of a three cylinder engine according to the present invention. 
           [0023]      FIG. 12  is an illustration schematically illustrating the third embodiment of the three cylinder engine according to the present invention. 
           [0024]      FIG. 13  is an illustration schematically illustrating a crank pulley employed in the other embodiment of the three cylinder engine according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    In the following, embodiments of the present invention will be described with reference to the drawings. 
         [0026]      FIG. 1  is a front view of a mounting structure of a three cylinder engine according to the present invention mounted in a vehicle, and  FIG. 2  is a perspective view schematically illustrating key portions of a main movement system of a three cylinder engine  1  to which the invention is applied. 
         [0027]    An engine unit  1  comprises a three cylinder in-line engine  1   a  and a transmission  1   b , and is supported on a vehicle body  12  through a plurality of supporting members such as engine mounts  10 A and  10 B and a torque rod  11 . 
         [0028]    In the embodiment, the engine unit  1  is transversely mounted on the vehicle body in such a manner that a crankshaft  2  of the engine  1   a  extends in the direction of the width of the vehicle. 
         [0029]    In this specification, a plurality of movement directions (viz., pitch direction, yaw direction, roll direction) of the engine unit  1  will be defined using a center axis (X-axis) of the crankshaft  2  as a reference. More specifically, the direction around a Y-axis (viz., an axis extending in a fore-and-aft direction of the vehicle) that is perpendicular to the crankshaft axis and extends horizontally will be defined as the pitch direction, the direction around Z-axis that is perpendicular to the crankshaft axis and extends in an up-and-down direction will be defined as the yaw direction and the direction around the crankshaft axis will be defined as the roll direction. 
         [0030]    Each of both ends of the engine unit  1  in the direction of the crankshaft axis is provided with a bracket  13 A or  13 B. Specifically, the bracket  13 A is positioned above the crankshaft  2  and provided on a lateral end face of a vehicle widthwise end portion of the engine  1   a , and the other bracket  13 B is provided on an upper end face of a vehicle widthwise end portion of the transmission  1   b . Each of the brackets  13 A or  13 B is connected to a corresponding one of the engine mounts  10 A and  10 B by means of a bolt or the like. That is, the engine unit  1  is supported on the vehicle body  12  through the engine mounts  10 A and  10 B that are arranged at both ends of the engine  1   a  along the direction of the crankshaft axis. The engine mounts  10 A and  10 B are respectively attached to front side members  14  that extend in a fore-and-aft direction of the vehicle along both sides of a front space (viz., engine room) of the vehicle body. 
         [0031]    In this embodiment, a spring constant K V  of each of the engine mount  10 A in an up-and-down direction (which corresponds to the crankshaft axis pitch direction) of the vehicle is set larger than a spring constant K H  of the same in a fore-and-aft direction (which corresponds to the crankshaft axis yaw direction). That is, by making the spring constant K V  in the up-and-down direction of the vehicle comparatively large, the engine unit  1 , which has a large mass, can be supported more stably and durability of the engine mount  10 A can be improved. Additionally, since a resonance frequency in an up-and-down direction of the vehicle due to provision of the engine unit  1  and the engine mounts  10 A and  10 B is increased, the riding comfort of the vehicle can be improved by decreasing the up-and-down shaking of the engine. Moreover, by decreasing the spring constant K H  in the fore-and-aft direction of the vehicle, attenuation of the vibration in such direction is increased. It is to be noted that the spring constant can be suitably adjusted by changing shape and material of a resilient member (not shown) that is used in the engine mount  10 A and made of a resilient body such as rubber material or the like. 
         [0032]    The torque rod  11  is positioned below the crankshaft  2  and arranged to support the engine unit  1  on a front cross member  15  that extends in a widthwise direction of the vehicle in a lower portion of a front space of the vehicle body, and thus the torque rod  11  functions to mainly restrain the movement of the engine unit  1  in the roll direction. 
         [0033]    If, among transfer sensitivities of vibration from the engine mount  10 A to a floor of the vehicle, a transfer sensitivity in the crankshaft axis pitch direction (viz., the up-and-down direction of the vehicle) is represented by H V  and a transfer sensitivity in the crankshaft axis yaw direction (viz., the fore-and-aft direction of the vehicle) is represented by H H , the relation “H V &gt;H H ” is usually established because the vehicle body is longer in a fore-and-aft direction and moves more readily in response to input oriented in an up-and-down direction than input oriented in a fore-and-aft direction at the position of the engine mount  10 A. Denoted by references Wb 1  to Wb 3  in  FIG. 2  are a plurality of counterweights  3  (see  FIG. 4  which will be explained hereinafter) schematically depicted as point masses, which constitute a part of a balance weight (viz., vibration alleviation unit) that cancels a force produced due to reciprocating movement of moving portions including pistons. 
         [0034]    If, in case of a three cylinder engine, an unbalanced pitch moment is produced due to a primary couple of forces produced under reciprocating movement of moving portions including pistons, a pitch vibration of the engine can be reduced by adding a counterweight to a balance mass, for example, so as to produce a pitch moment that has a phase reversed to that of the unbalanced pitch moment. However, although the pitch vibration is suppressed, a yaw vibration is produced and the engine  1  undergoes a so-called processional movement. 
         [0035]    If now the balance weight is so adjusted (see solid line of  FIG. 5  that will be described hereinafter) as to equalize a pitch moment produced by the engine  1   a , i.e., a component M V  of a primary couple produced by the engine  1   a  oriented in the crankshaft axis pitch direction, with a yaw moment produced by the engine, i.e., a component M H  of the primary couple produced by the engine  1   a  oriented in the crankshaft axis yaw direction, then the equation M V /M V0 =0.5 is established as is shown in  FIG. 3 , which improves the vibration displacement of the engine  1   a . M V0  is the sum of the pitch moment M V  and the yaw moment M H  (viz., M V0 =M V +M H ). 
         [0036]    While, in the embodiment, considering that the condition K V &gt;K H  is set and H V &gt;H H  is generally satisfied, further reduction of the vehicle vibration is realized by setting a balance weight of a crankshaft system (viz., the crankshaft and portions that rotate as an integral unit with the crankshaft) in such a manner that the yaw vibration of the engine  1   a  is larger than the pitch vibration. 
         [0037]    More specifically, as shown in  FIG. 4 , among the counterweights  3 , additional weights  31  and  33  are added to the counterweights  3  corresponding to the #1 and #3 cylinders of the engine, and a pair of balance masses  6  and  7  each constituting part of a balance weight are respectively provided on a crank pulley  4  and a drive plate  5  which rotate as an integral unit with the crankshaft  2 , so that 0&lt;M V /M V0 &lt;0.5 is established. It is to be noted that in the embodiment, the additional weights  31  and  33  and the balance masses  6  and  7  are arranged at positions displaced by 90 degrees with respect to a rotation phase of the #2 cylinder under rotation of the crankshaft  2 , and the additional weights  31  and  33  and the balance masses  6  and  7  are arranged in positions spaced from each other by 180 degrees in terms of crank angle. 
         [0038]    Thus, even though the yaw vibration becomes higher than the pitch vibration as shown in  FIGS. 5A to 5C  (see the broken line in  FIGS. 5  A to  5 C), a vehicle floor vibration acceleration caused by the vibration through the engine mount  10 A is reduced on the whole as is seen from  FIG. 6 . In other words, by adjusting the additional weights  31  and  33  and the balance masses  6  and  7  connected to the crank pulley  4  and the drive plate  5  in such a manner as to make the yaw moment larger than the pitch moment produced by the engine  1   a , the vehicle vibration can be reduced as a whole while restraining an increase of weight of the balance weight. With this, particularly, a vehicle vibration level during idling of the engine can be reduced. Since the primary couple produced by the engine is a force that is produced by an inertial force of moving portions including pistons, the vehicle body vibration during idling is not changed largely by the engine speed. However, the sensitivity of a human being to a vibration becomes high as the vibration frequency becomes low (that is, the engine speed becomes low). Accordingly, by reducing the vehicle body vibration level under idling of the vehicle, it becomes possible to reduce the engine speed during idling and thus, it becomes possible to improve the fuel consumption during the idling. The line V V  of  FIG. 6  depicts an acceleration of a vehicle floor vibration resulting from a vibration that is caused by the pitch moment produced by the engine  1   a  and transferred through the engine mount  10 A, and the line V H  of the drawing depicts an acceleration of a vehicle floor vibration resulting from a vibration that is caused by the yaw moment produced by the engine  1   a  and transferred through the engine mount  10 A. 
         [0039]    Assuming now that a displacement in an up-and-down direction of engine mount  10 A caused by the pitch moment produced by the engine  1   a  is represented by X V  and a displacement in a fore-and-aft direction of the engine mount  10 A caused by the yaw moment produced by the engine  1   a  is represented by X H , the values V V  and V H  are expressed by V V =X V ×K V ×H V  and V H =X H ×K H ×H H . Since K V &gt;K H  and H V &gt;H H  are satisfied, the sensitivity to the vehicle floor vibration acceleration is higher with respect to the displacement X V  in the up-and-down direction of the engine mount  10 A than with respect to the displacement X H  in the fore-and-aft direction of the engine mount. 
         [0040]    Accordingly, as is seen from  FIG. 6 , the value V V  occurring when M V /M V0 =1 (that is, M H =0) is greater than the value of V H  occurring when M V /M V0 =0 (that is, M V =0). Accordingly, as is seen from  FIG. 6 , the vehicle floor vibration acceleration V V +V H , which results from a vibration that is caused by the pitch moment and yaw moment produced by the engine  1   a  and transferred through engine mount  10 A, exhibits a minimum value in the range 0&lt;M V /M V0 &lt;0.5 and is smaller in that range than in the range 0.5≦M V /M V0 ≦1. 
         [0041]    Regarding a vehicle floor vibration acceleration resulting from a vibration that is caused by the pitch moment and yaw moment produced by the engine  1   a  and transferred through the engine mount  10 B, the exact same thing can be said as has been explained regarding the vehicle floor vibration acceleration caused by the vibration transferred through the engine mount  10 A, and the vehicle floor vibration acceleration V V +V H  caused by the vibration transferred through the engine mount  10 B exhibits a minimum value in the range 0&lt;M V /M V0 &lt;0.5 and is smaller in that range than in the range 0.5≦M V /M V0 &lt;1. Accordingly, when the balance masses of the crank pulley  4  and the drive plate  5  are so adjusted as to make the yaw moment larger than the pitch moment produced by the engine  1   a  (viz., 0&lt;M V /M V0 &lt;0.5), the vehicle floor vibration can be reduced by only setting the spring constant of at least one of the engine mounts  10 A and  10 B such that K V &gt;K H . When both the spring constants are set such that K V &gt;K H , the effect of reducing the vehicle floor vibration can be enhanced even further. Next, the value of M V /M V0  at the minimum value (or smallest value) of V V +V H  will be derived. If a vibration angular acceleration in a pitch direction of the crankshaft caused by the vibration of the engine, a vibration angle amplitude, and a crankshaft rotation angular speed are represented by A V , Y V  and ω), respectively, and a moment of inertia in a crankshaft axis pitch direction and a moment of inertia in a crankshaft yaw direction are represented by I V  and I H , respectively, then the value Av is represented by the following equation (1). 
         [0000]        A   V   =M   V   /I   V   (1)
 
         [0042]    Since the value A V  is a value provided by differentiating Y V  twice by time, the value Y V  is expressed by the following equation (2). 
         [0000]        Y   V   =−A   V /ω  (2)
 
         [0043]    From Equations (1) and (2), the value Y V  is expressed by the following equation (3). 
         [0000]        Y   V   =−M   V /(ω 2   ×I   V )  (3)
 
         [0044]    When now the distance from the center of gravity of the engine unit  1  to the engine mount  10 A as viewed from the front of vehicle is represented by L, the value X V  is expressed by the following equation (4). 
         [0000]        X   V   =L×Y   V   (4)
 
         [0045]    From Equations (3) and (4), the value X V  is expressed by the following equation (5). 
         [0000]      X V =α×( M   V   /I   V )
 
         [0000]      (α=−L/ω 2 )  (5)
 
         [0046]    Since V V =X V ×K V ×H V  as has been mentioned hereinabove, the following equations are derived based on this and Equation (5), namely V V =α×M V ×K V ×H V /I V  and M V =(V V ×I V )/(α×K V ×H V ). Similarly to this, M H =(V H ×I H )/(α×K H ×H H ) is derived. 
         [0047]    Accordingly, the value M V /M V0  is represented by the following equation (6). 
         [0000]        M   V   /M   V0   =M   V /( M   V   +M   H )=(( V   V   ×I   V )/( K   V   ×H   V )/((V V   ×I   V )/( K   V   ×H   V )+(V H   ×I   H )/( K   H   ×H   H ))  (6)
 
         [0048]    Since an equation V V =V H  is established when the value V V +V H  shows the smallest value (or minimum value), the value M V /M V0  at this time is represented by the following equation (7). 
         [0000]        M   V   /M   V0 =( I   V   ×K   H   ×H   H )/( I   H   ×K   V   ×H   V   +I   V   ×K   H   ×H   H )  (7)
 
         [0049]    Although the above derives the value M V /M V0  that causes the minimum value of the vehicle floor vibration acceleration V V +V H  resulting from a vibration that is caused by the pitch moment and yaw moment produced by the engine  1   a  and transferred through the engine mount  10 A, exactly the same derivation can be made regarding the vehicle floor vibration acceleration resulting from a vibration transferred through the engine mount  10 B. 
         [0050]    In the above-mentioned embodiment, the weights of the additional weights  31  and  33  and the weights of the balance masses  6  and  7  respectively provided on the crank pulley  4  and the drive plate  5  are so set as to establish the inequality 0&lt;M V /M V0 &lt;0.5. Thus, as the weights of such weight members increase, the value M V /M V0  reduces, and, thus, as is seen from  FIG. 7 , if, in engine mount  10 A or engine mount  10 B, the weights of the additional weights  31  and  33  and the weights of the balance masses  6  and  7  provided on the crank pulley  4  and the drive plate  5  are so set as to establish the inequality (I V K H H H )/(I H K V H V +I V K H H H )≦M V /M V0 &lt;0.5, then it is possible to reduce the vehicle floor vibration with a relatively small amount of balance masses. 
         [0051]    As is seen from  FIG. 8 , if the value M V /M V0  is set to the value (I V K H H H )/(I H K V H V +I V K H H H ) at the engine mount  10 A, then the vibration transferred to the vehicle floor through the engine mount  10 A is minimized, and if the value M V /M V0  is set to the value (I V K H H H )/(I H K V H V +I V K H H H ) at the engine mount  10 B, then the vibration transferred to the vehicle floor through the engine mount  10 B is minimized. Accordingly, if the weights of the balance masses  6  and  7  respectively connected to the crank pulley  4  and the drive plate  5  are so set as to cause the value M V /M V0  to take a value between the value (I V K H H H )/(I H K V H V +I V K H H H ) corresponding to the engine mount  10 A and the value (I V K H H H )/(I H K V H V +I V K H H H ) corresponding to the engine mount  10 B, then the vehicle floor vibration can be reduced even further. 
         [0052]    In the above-mentioned embodiment, the counterweights  3  and the two balance masses  6  and  7  provided on the crank pulley  4  and the drive plate  5 , respectively, serve to adjust the balance weight of the engine  1   a . However, if desired, as seen from  FIG. 9 , a balance weight of the engine  1   a  like the balance weight explained above can be achieved by arranging the balance masses  8  and  9  on the crankshaft at the positions of the #1 cylinder and the #3 cylinder, respectively. In this case, too, the two balance masses  8  and  9  are arranged at angular positions displaced by 90 degrees relative to a rotation phase of the #2 cylinder in rotation of the crankshaft  2  and the balance masses  8  and  9  are spaced from each other by 180 degrees in terms of the crank angle. Instead of arranging the balance masses  8  and  9 , the additional weights  31  and  33  may be enlarged in size, which brings about the same effects. It is to be noted that  FIG. 9  shows a three cylinder engine of which the firing order is #1 cylinder-#2 cylinder-#3 cylinder. 
         [0053]    In the above-mentioned embodiment, further reduction of the vehicle vibration is achieved by providing the balance masses and the additional weights so as to adjust the balance weight that constitutes the vibration alleviation unit. However, the balance weight can also be adjusted in the manner of other embodiments that will now be explained. In the other embodiments that will now be explained, elements that are the same as those described in the above-mentioned embodiment are denoted by the same reference numerals and duplicated explanation on the elements will be omitted. 
         [0054]    In a three cylinder internal combustion engine equipped with a manual transmission (not shown) according to a second embodiment of the present invention that is shown in  FIG. 10 , a flywheel  20  provided on one end portion of the crankshaft  2  has two through bores  21  and  21  that are formed adjacent to each other in a side face of a peripheral portion of the flywheel, are spaced from each other in a circumferential direction of the flywheel  20 , and have equal diameters. Thus, the portion of the flywheel  20  where the bores  21  and  21  are provided is reduced in weight thereby inducing the same effects as those that would be obtained if balance masses were provided at positions spaced 180 degrees in crank angle away from the bores  21  and  21 . That is, in the second embodiment, adjustment of the vibration alleviation unit is achieved by providing bores in the crankshaft system (viz., the crankshaft and the portions that rotate as integral unit with the crankshaft). 
         [0055]    In the second embodiment, the crank pulley  4  provided on the other end portion of the crankshaft  2  is a cast part, and an inwardly projected plate-like balance mass  41  is formed integrally on an inner surface of the crank pulley  4  when the crank pulley  4  is cast. 
         [0056]    A middle position between the balance mass  41  provided in the crank pulley  4  and the bores  21  and  21  provided in the flywheel  20  is arranged in a position offset by 90 degrees relative to a rotation phase of the #2 cylinder under rotation of the crankshaft  2 , and the middle position between the balance mass  41  and the bores  21  and  21  is the same position in terms of crank angle as the position where the additional weights  31  are provided. 
         [0057]    Although, in the above-mentioned second embodiment, the bores  21  are through bores that pierce through the flywheel  20 , the bores  21  do not necessarily need to pierce through the flywheel  20 . That is, a notch or other structure may be used so long as it reduces the weight. Furthermore, instead of providing bores  21  in the flywheel  20 , a bolt or other member serving as a balance mass can be connected to the flywheel at a position separated by  180  degrees in terms of crank angle from the position where the bores  21  would be formed. 
         [0058]    A third embodiment of the present invention will now be described with reference to  FIGS. 11 and 12 . In a three cylinder internal combustion engine equipped with an automatic transmission (not shown) according to this third embodiment, attachments fixed to the drive plate  5  are configured to have asymmetrical shapes such that the same effects are obtained as those obtained when balance masses are provided on the drive plate 
         [0059]    In this third embodiment, a signal plate  51  for detecting a rotation angle of the crankshaft  2  is attached to the drive plate  5 , which is provided on one end portion of the crankshaft  2 . The signal plate  51  comprises an annular main body portion  52  on which a plurality of teeth  52   a  are formed at intervals and a plurality (even number) of flange portions  53  that are formed to extend perpendicular to the main body portion  52  for fixing the signal plate  51  to the drive plate  5 . The flange portions  53  are arranged in pairs spaced apart from each other by 180 degrees in terms of crank angle, and the shapes of the flange portions  53  making up each pair are the same except for one pair. Of this one pair, a flange portion  53   a  is configured to be larger than a flange portion  53   b  positioned 180 degrees away in terms of crank angle such that the flange portion  53   a  and the flange portion  53   b  are shaped differently from each other. That is, in this third embodiment, by making the shapes of one pair of the flange portions  53   a  and  53   b,  which are spaced apart from each other by 180 degrees in terms of crank angle, asymmetrical, the same effects are obtained as those that would be obtained if a balance mass were provided at the position of the flange portion  53   a.    
         [0060]    Like the above-mentioned second embodiment, the crank pulley  4  in the third embodiment is a cast part and a plate-like balance mass  41  is integrally cast to an inner surface of the crank pulley  4 . 
         [0061]    The balance mass  41  and each of the flange portions  53   a  and  53   b  are displaced by 90 degrees with respect to a rotation phase of the #2 cylinder under rotation of the crankshaft  2 , and the balance mass  41  and the flange portion  53   a  are spaced from each other by 180 degrees in terms of crank angle. 
         [0062]    In this third embodiment, by making the shapes of the paired flange portions  53   a  and  53   b,  which are two of the plurality of flanges  53  provided by the signal plate  51  and spaced from each other by 180 degrees in terms of crank angle, asymmetrical, there are obtained the same effects as those that would be obtained if a balance mass were provided on the drive plate  5 . However, in case wherein the shape of the signal plate  51 , which is an attachment fixed to the drive plate  5 , is symmetrical (that is, in a case wherein all of the flange portions  53  of the signal plate  51  are configured such that flange portions  53  spaced apart from each other by 180 degrees in terms of crank angle are symmetrical), providing a through bore at a position corresponding to the aforementioned flange portion  53   b  of the drive plate  5  (that is, at a position that is displaced by 90 degrees with respect to the rotation phase of the #2 cylinder under rotation of the crank shaft  2  and is the same as the position of the balance mass  41  in terms of crank angle) brings about a reduction in weight of the portion where the bore is provided and induces the same effects as those that would be obtained if a balance mass were provided at a position that is spaced from the through bore by 180 degrees in terms of crank angle. 
         [0063]    In the above-mentioned embodiments, there is employed an arrangement in which the crank pulley  4  is provided with balance masses. However, as is seen from  FIG. 13 , if a plurality of bores  42  are provided in an outer circumferential portion of the crank pulley  4 , then the weights of the portions where the bores  42  are provided will be reduced, and thus, without providing balance masses on the crank pulley  4 , the same effects can be obtained as those which would be obtained if balance masses were provided at portions that are spaced from the bores  42  by 180 degrees in terms of crank angle. 
         [0064]    Although, in the above, preferred embodiments of the invention have been described, the present invention is not limited to such embodiments and various modifications are possible. For example, the balance masses and the bores may take other positions and the number of the balance masses may change so long as they generate the same inertial force. Furthermore, the balance masses, the additional weights and bores may take any combination so long as they generate the same inertial force. Furthermore, it is acceptable to use another engine mounting configuration, e.g., engine mounts can be provided at front and rear portions of an associated vehicle in addition to the above-mentioned engine mounts. Furthermore, the present invention can be applied in the same manner to a three cylinder engine in which the firing order is #1 cylinder-#3 cylinder-#2 cylinder.

Technology Classification (CPC): 5