Note: Descriptions are shown in the official language in which they were submitted.
CA 022~3047 1998-11-0~
BALANCING APPARATUS FOR A VEHICLE ENGINE
Field of the Invention
This invention relates to balancing apparatus for a vehicle engine and more particularly
5 to a twin counter-rotating balance shaft assembly for a four cylinder in-line internal combustion
engine, which reduces engine vibration.
Background of the Invention
Internal combustion engines of the reciprocating type have movable portions which
10 become off-balance during operation of the engine, causing vibration. The vibrations generate
noise and degrade or damage engine parts, such as individual bearings. In order to compensate
for these vibrations, balancing devices have been developed to cancel the inertia force or the
inertial couple of the piston, connecting rod and the like to reduce the vibration of the engine.
A conventional b~l~ncing device of this type typically includes a pair of cast or forged
15 steel balance shafts which incorporate un-machined, as-cast eccentric weights as well as
machined journal bearing surfaces or roller bearing surface seats. The bearings are held in split
housings, line-bored after pre-assembly. Since the balance shafts turn at over 12,000 rpm
(twice the engine speed), tolerances of the machined surfaces must be closely held. Thus, these
devices require costly m~çhining steps to achieve accuracy. Further, during operation of the
20 engine, the eccentric weights cause shaft deflection resulting in mi~lip;nment between the
shafts and bearing housings. This mi~lignment is greatest when the engine speed and bearing
loads are highest, which has necessitated the use of costly, extra-precision bearings or
pressure-fed lubrication of journals with engine oil.
Conventional balance shaft pairs typically incorporate sprockets and chains or steel
25 gears to drive one of the balance shafts via an engine crank shaft drive gear. The first balance
shaft drives the second balance shaft by the steel gears to produce counter-rotating motion.
During operation, gear noise and rattles occur which are caused by gear meshing and torsional
crank shaft vibrations. Counter-measures to avoid these problems have been proposed
including the use of anti-backlash gears and powder metal steel gears (with improved internal
30 damping), but have been only partially successful. Non-metallic gears have also been tried
unsuccessfully, due to high cyclic stresses caused by the torsional vibration of the crank shaft,
CA 022~3047 1998-11-0~
transmitted through the gears, resisted by the high inertia of the rotating balance shaft
components. Accordingly, a need exists to provide an improved balancing apparatus for an
internal combustion engine which overcomes the deficiencies of the conventional devices.
5 Summary of the Invention
The disadvantages of the prior art may be overcome by providing a b~l~ncing apparatus
for suppressing vibrations in an engine.
It is desirable to provide a balancing apparatus which reduces the size and mass of
rotating components, thereby reducing mi~lignment of shafts and bearings at high engine
10 speeds and reducing gear noise and to increase reliability.
It is desirable to provide a balancing apparatus which is simple in construction, effective
in operation and economical to m~mlf~cture and m~int~in
According to one aspect of the invention there is provided a balancing apparatus having
a housing assembly constructed and arranged to be mounted to the engine. First and second
15 support shafts are fixed in spaced relation within the housing assembly. First and second
rotatable shafts are associated with said first and second support shafts, respectively. Bearing
structure is disposed between each rotatable shaft and its associated support shaft such that
each rotatable shaft may rotate about its associated support shaft. A hydrodynamically
designed balance weight is coupled to each of the first and second rotatable shafts,
20 respectively, so as to rotate therewith. A pair of driven gears are provided, with a driven gear
of the pair of driven gears being coupled to each of the first and second rotatable shafts,
respectively. One of the driven gears is constructed and arranged to be driven by the drive
gear. The driven gears are in meshing relation such that rotation thereof causes rotation of the
balance weights.
According to another aspect of the invention, there is provided a b~l~ncin,~ apparatus
for a vehicle engine which has a housing assembly constructed and arranged to be mounted to
the vehicle engine. The housing has spaced apart endwalls and two parallel extending support
shafts connected to the endwalls. A first hollow shaft is rotatably mounted concentrically
about a first of the support shafts. A first gear is mounted for rotation with the first hollow
30 shaft. A first balance weight is mounted for rotation with the first hollow shaft and spaced
from the first gear. A second hollow shaft is rotatably mounted concentrically about a second
CA 022~3047 1998-11-0~
of the support shafts. A second gear is mounted for rotation with the second hollow shaft.
The second gear is in driven engagement with the first gear for counter rotation therewith. The
first of the support shafts is positioned relative to the engine cr~nk.qh~ PL for drivingly eng~ging
the first gear with the crankshaft. A second balance weight is mounted for rotation with the
5 second hollow shaft and spaced from the second gear for rotation in a plane common with the
first balance weight. The second balance weight is positioned diametrically opposite to the first
balance weight for counter rotation therewith.
Description of the Drawings
The invention may best be understood with reference to the accompanying drawingswherein an illustrative embodiment is shown.
Figure 1 is a perspective view of a balancing apparatus provided in accordance
with the principles of the present invention;
Figure 2 is an elevational view, partially in section, of a balancing apparatus of
Figure 1;
Figure 3 is a plan view, in section, of the apparatus of Figure 1, taken through the
center of the support shafts;
Figure 4 is an exploded perspective view of the rotating shafts of the apparatus of
Figure 1.
Description of the Invention
Referring now more particularly to the drawings, there is shown therein a balancing
apparatus, generally indicated at 10, which embodies the principles of the present invention.
The balancing apparatus 10 is constructed and arranged to suppress second order vibrations in
25 a conventional four cylinder in-line internal combustion engine, as disclosed, for example, in
U.S. Patent No. 5,305,656, the disclosure of which is hereby incorporated into the present
specification by this reference. The conventional engine includes a rotatable crank shaft and a
plurality of piston and cylinders for causing rotation of the crank shaft. As is typical, the crank
shaft includes a helical drive gear mounted for rotation therewith, of the type disclosed in U. S .
30 Patent No. 5,305,656.
CA 022=,3047 1998-11-0=,
As shown in Figure 1, the apparatus 10 incllldes a housing assembly, generally
indicated at 12, preferably of alllminllm or other light-weight material. The housing assembly
12 includes pairs of opposing sidewalls 13 and 14, respectively, connected together by support
shafts 20 and 22. The housing assembly 12 includes mounting bosses, 18, for mounting the
5 housing assembly 12 to the engine cylinder block 19 by bolts (not shown). Thus, the apparatus
10 is constructed and arranged to be mounted to the engine block 19 under the crankshaft and
within the oil pan.
First and second solid, hardened and ground support shafts, 20 and 22, respectively, are
spaced in generally parallel relation and are fixed within the housing assembly 12 against
10 rotation and axial displacement. Both ends 21 and 25 of each shaft 20 and 22 are fitted in bores
23 in the walls 14 of the housing assembly 12. They are coupled to the housing assembly via
associated cross-pins 24.
First and second cylindrical, hollow rotatable shafts 26 and 28, respectively, are
mounted for rotation about the first and second support shafts 20 and 22, respectively, by
15 means of bearing structure, including pairs of associated needle rolling bearings 30.
Cast or powder metal balance weights 32 and 34 are fixed to one end of each of the
rotatable shafts 26 and 28, respectively. As shown in Figures 1 and 2, the balance weights 32
and 34 are hydrodynamically shaped having mass distribution designed in such manner that it
gives required eccentricity inertia in respect to the axes of rotation of each shaft 20 and 22
20 respectively. Balance weights 32 and 34 space envelope conforms to the maximum radius B
and minimllm radius C. Balance weights generally have a semi-circular, semi-spherical or
semi-toroidal shaped portion with leading and trailing edges smoothly contoured or tapered to
the minimllm radius C opposite the shaped portion.
In the illustrated embodiment, a driven helical gear is coupled to an end of each hollow,
25 rotatable shaft 26 and 28 opposite a respective balance weight. Thus, each driven gear is
disposed in spaced relation with respect to a balance weight on an associated rotatable shaft.
Driven gear 36 is coupled to a periphery ofthe rotatable shaft 26. Gear 36 is preferably
phenolic or non-ferrous material or ferrous material with high damping quality or powder metal
and is constructed and arranged to be driven by the crank shaft drive gear (not shown), in the
30 known manner, as disclosed, for example, on U.S. Patent No. 5,305,656.
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Gear 38 iS coupled to the periphery of the rotatably shaft 28 and is preferably of
phenolic or non-ferrous material or ferrous material with high damping quality or powder metal
selected to match gear 36 in such manner to obtain the best noise and wear characteristics. The
two gears 36 and 38 are in meshing relation with each other at teeth 37 and 39, respectively.
Shaft 22 iS radially offset relative to shaft 20. The offset spaces gear 38 to engage the
crank shaft gear without eng~ging gear 36
The needle rolling bearings 30 are disposed in pairs about each support shaft, between
an outer peripheral surface of support shaft and an inner peripheral surface of a rotatable shaft.
In the illustrated embodiment, one needle bearing 30 iS located generally under a balance
10 weight and one needle bearing 30 iS located under a driven gear 36,38. Thus, one needle
bearing is disposed on a common axis D with a driven gear and another needle bearing is
disposed on a common axis E with a balance weight.
Pairs of thrust washers 40 are disposed about each of the support shafts 20 and 22 with
one thrust washer being disposed between an inner surface 43 of side wall 14 and each end
15 surface 45 of an associated rotatable shaft 26,28. The thrust washers 40 are constructed and
arranged to absorb axial loads caused by the helical gear forces.
Each of the support shafts 20 and 22 includes lubrication or oil passage structure
therein. In the illustrated embodiment, the oil passage structure includes an axial passage 42
and a cross passage 44 in communication therewith for directing a lubricant or oil in the
20 direction of arrows A, so as to lubricate the moving parts of the apparatus 10 such as the
bearings 30. Lubrication is assisted by the pumping action of the needle rolling bearings 30.
The widths and masses of the balance weights 32 and 34 are minimi7ed by ma~imi7.ing
their large radii B and minimi7.in3~ their small radii C. Further, the rotatable shafts 26 and 28
are made as light as possible, while the driven gears 36 and 38 are weight reduced by material
25 selection or provision of hydrodynamically shaped webs and holes, as is well know in the art.
These features greatly reduce the length, weight, and complexity of the apparatus 10.
The balancing apparatus 10 operates as follows. The app~s 10 is mounted to an
engine within the oil pan such that the crank shaft helical gear is in meshing relation with teeth
39 of the driven gear 38. Rotation ofthe crank shaft gear is transmitted to the driven gear 38
30 to rotate the first balance weight 34 via shaft 28. Since gears 36 and 38 are in meshing
relation, rotation ofthe second gear 38 iS transmitted to the first gear 36 to rotate the second
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balance weight 32 via shaft 26. Rotation of the balance weights 32 and 34 generates a load
which cancels the inertial forces caused by the pistons and connecting rods of the engine, which
in turn reduces vibration of the crank shaft.
Applicant has found that the mass moment of inertia of the rotating components of the
5 balancing apparatus 10 of the invention is the same as conventional designs, but utilizing only
half of the mass. This permits the potential use of a phenolic gear or a non-ferrous gear for
one of the driven gears, so as to reduce noise of the driven gears. It also allows for use of a
high damping ferrous material or powder metal provided that it reduces the noise of the driven
gears as opposed to steel gears. In the illustrated embodiment, the phenolic gear is preferably
10 driven gear 38 which is driven by the crank shaft gear. Other plastic or non-ferrous materials or
high damping ferrous materials or powder metal may be used instead of the phenolic material,
as long as noise and reliability criteria are met. The crank shaft gear can be of any material
mentioned above provided that noise and reliability criteria are met.
It can be appreciated that the length of the support shafts 20 and 22, the rotating shafts
15 26 and 28 the housing assembly 12 can be changed to accommodate any designed spacing from
the crank shaft gear to the center of gravity of the engine.
The housing assembly 12 can be made of ~ mimlm or other lightweight material having
sufficient strength. Since the thermal coefficient of expansion of phenolic lies between that of
steel and alllminllm, with the structure of the invention, gear tooth clearances have been found
20 to be acceptable in an operating range of-40~C to 150~C.
The installation of the needle bearings 30 in the appal~ s 10 is similar to the proven
design of the planetary gears in automotive tr~n.cmi~ions. The needle bearings 30 may be
cage-guided shell bearings, press-fitted into the rotating shaft 26 or 28, or unit cages with
hardened or ground raceways in the rotating shafts 26 and 28, or unit cages with hardened or
25 ground raceways in the rotating shafts 26 and 28. The low deflection of the fixed support
shafts 20 and 22 under the bearings 30 assures minim~l shaft and bearing mi~lignment and
maximizes bearing life.
It thus will be seen that the objects of this invention have been fully and effectively
accomplished. It will be realized, however, that the foregoing plerelled embodiment of the
30 present invention has been shown and described for the purposes of illustrating the structural
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and functional principles of the present invention and is subject to change without departure
from such principles.
