Engine balancer

A balancer mass is reciprocated linearly in the plane of the piston/cylinders of a four cylinder in-line engine by a pair of cams mounted on the crankshaft for rotation therewith. The second order vibrations can be substantially eliminated either by mounting a single balancer of the invention at the center of the crankshaft or by using a pair of balancers mounted one each at opposite ends of the crankshaft. The vibrations can also be substantially reduced by mounting a single balancer at the "free end" of the crankshaft opposite the clutch and flywheel.

BACKGROUND OF THE INVENTION 
The invention relates, generally, to a device for balancing second order 
vibrations of a rotating shaft and, more particularly, to an improved 
balancer for the crankshaft of a four cylinder in line engine for 
application in a motor vehicle. 
Four cylinder in-line engines have become very popular in recent years, 
due, in large part, to their fuel economy. In addition to the engines 
efficiency, the four cylinder in line engine is a simple, low weight, 
compact design that exhibits superior torque characteristics. 
While the engine's popularity has risen because of the aforementioned 
characteristics, the engine also exhibits undesirable second order 
vibrations. As is well known in the art, these second order vibrations are 
due to the fact that the piston rods are of finite length such that the 
motion of the pistons deviate from pure sinusoidal motion. The resulting 
imbalance cannot be compensated for by optimal dimensioning as is done 
with six cylinder engines. Moreover, because the vibration cannot be 
completely isolated from the body, the vibration results in unacceptably 
high levels of noise and vibration in the vehicle. 
Numerous attempts have been made to eliminate these vibrations. For 
example, a number of patents assigned to Mitsubishi (U.S. Pat. Nos. 
3,995,610, 4,000,666, 4,028,963, 4,074,589, 4,095,579, and 4,125,036) 
disclose a pair of counter rotating shafts set off from the axis of 
rotation of the crankshaft and operatively connected thereto by a rotary 
transmission means such as a chain. German Pat. Nos. 331,328 and 392,149 
also show counter rotating shafts having eccentric weights used to balance 
the Crankshaft A further method for eliminating the second order 
vibrations is disclosed in German Pat. No. 2,720,284 where the standard 
crankshaft is replaced by a cam arrangement. 
While these balancers are capable of reducing the second order vibrations, 
a complex and difficult installation procedure is required to arrange 
these large rotating shafts within the engine block. As a result, the 
practical applications of the prior art devices are severely limited. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention overcomes the above-noted shortcomings of the prior 
art by providing an engine balancer which reduces or eliminates the second 
order vibrations and yet is simple in construction and design so as to 
facilitate its installation either within the engine block or external 
thereto. 
Specifically, the invention includes a balancer mass reciprocated linearly 
in the plane of the piston/cylinders by a pair of cams mounted on the 
crankshaft for rotation therewith. The second order vibrations can be 
virtually eliminated either by mounting a single balancer of the invention 
at approximately the longitudinal center of the crankshaft or by using a 
pair of balancers which can be mounted one each at opposite ends of the 
crankshaft. Moreover, the vibrations can be substantially reduced by 
mounting a single balancer at the "free end" of the crankshaft, opposite 
the clutch and gearbox. Thus, the balancer or balancers can be placed on 
the crankshaft in a number of ways to accomplish the vibration reduction 
as will hereinafter be explained. 
OBJECTS OF THE INVENTION 
It is a general object of the invention to provide an improved balancer 
which eliminates or reduces the second order vibrations of a rotating 
shaft. 
It is a further object of the invention to provide an improved balancer 
designed specifically to reduce second order vibrations in a four cylinder 
in line engine. 
It is another object of the invention to provide an improved balancer that 
can simply and easily be used with existing engine designs without the 
need for extensive modifications. 
It is yet another object of the invention to provide an improved balancer 
in which the phase and direction of the balancing force can be optimized 
by proper angular positioning of the cams and orientation of the direction 
of motion of the mass. 
Other objects of the invention, in addition to those set forth above, will 
become apparent to one of ordinary skill in the art from the following 
detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
The balancer of the present invention, shown generally, at 1 in FIG. 1, is 
preferably disposed at the center of the crankshaft 3 of the standard four 
cylinder in-line engine 5. The balancer in FIG. 1 is optimally positioned 
at the approximate longitudinal center of the crankshaft 3 such that it is 
disposed between the first pair of piston/cylinders 7,9 and the second 
pair of piston/cylinders 11,13. An alternate positioning arrangement for 
the balancer 1 of the present invention is shown in FIG. 2, where a first 
balancer 1 is disposed at one end of the crankshaft 3 and a second 
balancer 1' is disposed at the opposite end of the crankshaft 3. It should 
be noted that instead of locating the balancers inside of the engine block 
4, they could be located outside of the engine block 4 as shown in phantom 
line position 1" in FIG. 2. 
In both of the above described arrangements, the balancers of the invention 
are optimally positioned such that the second order vibrations are 
virtually eliminated. The compact nature and simple construction of the 
balancer of the present invention facilitate the installation of the 
balancers at either the internal or external positions. However, in 
certain circumstances, it may not be feasible to install the balancer 1 at 
these optimum positions. Therefore, it is further contemplated that the 
balancer 1 be located only at the "free end" of the crankshaft opposite 
the clutch 17 and flywheel 15, as shown in FIG. 3. This arrangement will 
reduce second order vibrations because the elements mounted on the 
opposite side of the engine block (i.e. the clutch and gearbox) reduce the 
vibration of that side of the engine block by virtue of their additional 
mass. While this placement does not completely eliminate the vibrations, 
as is the case with the placements shown in FIGS. 1 and 2, it does 
substantially reduce the vibrations. Moreover, installation of the 
balancer 1 at the "free end" of the crankshaft, particularly external to 
the engine block as shown in phantom at 1", is a very simple operation 
because of the relatively unrestricted access to this end of the 
crankshaft and the minimal modification required to the engine. As a 
result, the second order vibrations can be substantially reduced with a 
very simple modification of the engine using the balancer of the present 
invention. 
Description of the preferred embodiment of the balancer 1 will be made with 
specific reference to FIGS. 4, 5, and 6. FIG. 4 shows the balancer 1 
arranged on the crankshaft 3. It should be noted that the construction of 
the balancer itself is identical regardless of which of the positioning 
arrangements (previously discussed with reference to FIGS. 1-3) is used. 
The balancer 3 consists of a first cam 21 of approximately elliptical shape 
and a second identical cam 23 secured to the crankshaft 3 for rotation 
therewith. The cams 21 and 23 are positioned on the crankshaft 3 so as to 
be ninety degrees out of phase with one another. A mass 25 is supported by 
any suitable arrangement of guides, a preferred arrangement of guides will 
be hereinafter described, such that it linearly reciprocates under the 
forces generated by the rotation of the cams 21 and 23. The exact shape of 
the cams 21 and 23 must be determined in connnection with the shape of the 
surface on the mass 25 with which they contact. The shape of the cams 21 
and 23 is chosen so as to ensure a sinusoidal motion of the mass 25 or 
slight derivations from such motion as desired for optimization purposes. 
The mass 25 consists of a pair of plates 27 and 29 of identical 
configuration. The plates include circular apertures 31 and 33 as shown in 
FIGS. 4-6. The circular shape of the apertures 31 and 33 in the preferred 
embodiment is chosen to facilitate the incorporation of bearing structures 
therein. However, the functional principle of the invention allows the use 
of apertures of many different shapes. If circular apertures are used, 
their radius is approximately equal to the arithmetic average of the long 
and short axes of the cams 21 and 23. In order to arrive at the most 
compact construction of the illustrated balancer, it is necessary to 
optimize the major construction parameters such that the larger radius of 
curvature of the cam is equal to or smaller than the inside radius of the 
circular apertures 31 and 33. This requirement ensures that a single 
contact line exists between the cams 21 and 23 and the apertures 31 and 
33, respectively. The optimization process will depend on the specific 
shapes of the cams and apertures selected as will be apparent to one of 
ordinary skill in the art. 
In the assembled balancer the plates 27 and 29 are offset 180 degrees from 
on another such that the crankshaft 3 passes through the two apertures, as 
shown in FIGS. 4 and 5. The cams 21 and 23 contact the inner periphery of 
the the apertures 31 and 33, respectively, to linearly reciprocate the 
mass 25 in the plane defined by the piston/cylinders 7, 9, 11 and 13. In 
the preferred embodiment a guide consisting of a pair of leaf springs 41 
and 42, fixed at opposite ends to the engine block 4 and mass 25, ensures 
that the mass reciprocates linearly. Cam 21 contacts the lower edge of 
aperture 31 to move the mass 25 in the direction of arrow D and cam 23 
contacts the upper edge of aperture 33 to move the the mass in the 
direction of arrow E. A slotted center plate 35 can be disposed between 
the plates 27 and 29 to further define their location with respect to one 
another and to define the relative positions of the cams 21 and 23 and 
mass 25 in the axial direction, if so desired. The center plate 35 has a 
centrally located aperture 37. See FIG. 7, that is shaped and dimensioned 
to receive the bearing ring 39, as will hereinafter be described. 
FIGS. 5a and 5b show the position of the balancer 1 when cam 21 has moved 
the mass 25 in the direction of arrow D to the first extreme position 
through its engagement with aperture 31. FIGS. 6a and 6b show the position 
of the balancer 1 after the crankshaft has rotated ninety degrees such 
that cam 23 has moved the mass 25 in the direction of arrow E to its other 
extreme position through its engagement with aperture 33. The dimensions a 
and b illustrate the extreme positions of the mass 25 relative to the 
crankshaft 3, where a&lt;b. Continued rotation of the crankshaft 3 will 
alternately move the balancer between the first extreme position shown in 
FIGS. 5a and 5b, and the second extreme position shown in FIGS. 6a and 6b. 
As is evident from this description the mass 25 reciprocates at two times 
the frequency of the rotation of the crankshaft 3. A permanent mechanical 
connection, such as bolts (not shown), connects the plates 27, 29, and 35, 
together such that the plates 27 and 29 and the center plate 35 move as a 
unit. When the center plate 35 and bearing ring 39 are used to guide the 
mass, it is necessary for the aperture 37 to be able to accommodate the 
bearing ring 39. Thus, the aperture 37 is defined by semi circular arcs 43 
and 45 that have the same radius as the bearing 39 and are spaced from one 
another a distance equal to or greater than the distance traveled by the 
mass 25, shown in FIG. 7. 
A second more rudimentary embodiment of the invention, illustrating its 
functional principle more clearly, is shown in FIGS. 8, 9, and 10, and 
includes a pair of cams 51 and 53 mounted on the crankshaft 3 in the same 
manner as in the first embodiment. A mass 55 is supported by guides (not 
shown) for linear reciprocating movement in the plane of the 
piston/cylinders 7', 9', 11', and 13'. Specifically, the mass 55 includes 
a pair of contact surfaces 57 and 59 having stepped portions 57a, 57b and 
59a, 59b, respectively. In the illustrated embodiment, the mass 55 is 
composed of two pieces 61 and 63 as a manufacturing expedient; however, it 
is also possible to construct the mass 55 of a single piece without 
departing from the scope of the invention. Cam 51 contacts surface 59a to 
move the mass 55 in the direction of arrow A and cam 53 contacts surface 
57a to move the mass 55 in the direction of arrow B. 
The rotation of the cams 51 and 53 and the corresponding movement of the 
mass 55 is shown in FIGS. 9 and 10. FIGS. 9a and 10a show the mass 55 in 
its first extreme position with the cam 51 contacting the surface 59a and 
FIGS. 9b and 10b show the position of the mass 55 in the other extreme 
position (after the crankshaft 3 and the cams 51 and 53 have rotated 
ninety degrees from the positions shown in FIGS. 9a and 10a) with the cam 
53 contacting the surface 57a. Continued rotation of the crankshaft 3 will 
alternately move the balancer 1 between these extreme positions. As is 
evident from this description, the mass 55 moves in the plane of the 
piston/cylinders at twice the frequency of rotation of the crankshaft 3. 
Moreover, surfaces 57a and 59a are contacted by cams 51 and 53, 
respectively, such that the mass 55 is moved in both linear directions by 
the positive force of the cams. However, the two cam system could be 
replaced by a single cam for driving the mass 55 in one of the two linear 
directions and a spring for moving the cam in the opposite linear 
direction, if so desired. 
In either of the disclosed embodiments the direction of motion of the mass 
can be adjusted to optimize the direction of the balancing force. For 
example, the guides 41 and 42, illustrated in FIG. 4, could be made 
movable so as to optimally position the mass. The orientation of the cams 
on the crankshaft, while always maintaining a 90.degree. difference 
therebetween, could also be adjusted in order to optimize the phase of the 
balancing force. 
Although the invention has been described in a preferred and an 
illustrative form with a certain degree of particularity, it is to be 
understood that the present disclosure has been made by way of example 
only. Numerous changes in the details and construction of the combination 
and arrangement of parts will be apparent without departing from the 
spirit and scope of the invention. The breadth of the invention should be 
measured by reference to the appended claims.