Note: Descriptions are shown in the official language in which they were submitted.
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1
TOOTHED BELT DRIVE OR CHAIN DRIVE
The present invention relates to a toothed belt drive or a chain drive with at
least one toothed gearwheel and at least one toothed belt or at least one
chain.
In order to improve the load characteristics of a toothed belt drive, EP-0 255
33 B1 describes a toothed belt of which the teeth have a tooth cross-section
with a
convex curve of cycloidal form. In particular, cyclically repeating peak
loads,
which arise, for example, in cam shaft drives at the moment of ignition in a
corresponding working cylinder) lead to premature wear, and damage to the
toothed
belt. When the toothed belt drive undergoes variable loading, in particular
rapidly
repeating load peaks, localized overloading occurs, which can only be allowed
for
by designing the entire toothed belt for the maximum peak loading, regardless
of
how often or in what time interval the peak loading occurs. For this reason,
toothed
belt drives are expensive and, commonly, for 95 % or more of the driving time
or of
the drive cycle, are oversized or must be prematurely replaced.
From DE-43 31 482 A1, DE-29 06 619 I31 and DE-31 09 172 C2, it is
known, in order to reduce or eliminate driving noise in a toothed belt or
chain, to
irregularly distribute the teeth of a toothed gearwheel, and correspondingly
the chain
links of a chain. However, this modality does not solve the problem of short-
term
peak loading, since the loading of the toothed belt is not changed merely by
variably
distributing the teeth.
From US-PS 3,377,875, it is known, in order to increase the life and reduce
the noise in a chain drive which includes a chain along with corresponding
toothed
wheels, to mill off certain of the teeth of one of the toothed wheels while
retaining
the flank geometry, in such away that these selected teeth have gradually
reducing
cross-section, i.e. one of the flanks undergoes essentially a parallel
displacement,
or, in addition to such parallel displacement some of the troughs between
respective
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teeth are more deeply milled while retaining the essential trough geometry. In
this
arrangement, either several of the teeth are simply smaller, or the teeth are
smaller
and the troughs are deeper.
Accordingly, the aim of one aspect of this invention is to provide a toothed
belt drive or chain drive of the kind identified above, in which the loading
capacity
and the working life are improved.
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In accordance with the invention, this object is attained in a toothed belt
drive or chain drive of the above kind, having the characteristics set forth
in claim
1.
In accordance with the invention, it is provided that at least one tooth of
the
belt drive wheel and/or at least one tooth of the toothed belt, or at least
one link of
the chain, has a flank geometry v~fhich differs from the flank geometry of
each of the
other teeth. This has the advantage that individual teeth of the toothed belt
drive are
so configured that load peaks do not place an additional burden on the toothed
belt.
Therefore, the toothed belt loading, particularly for high-load toothed belt
drives, is
decreased.
A particularly effective load relief in the case of peak loads is achieved by
providing an asymmetric flank geometry for the leading and trailing flanks of
at
least one tooth of the toothed belt and/or toothed gearwheel, or of the at
least one
chain link.
A particularly simple construction is possible if the at least one tooth of
the
toothed belt and/or toothed wheel, or the at least one chain link, exhibits a
steeper
or a flatter flank geometry, or a greater or smaller head radius, or if the at
least one
tooth has a greater or smaller foot radius.
It is advantageous if the at least one tooth of the toothed belt, or the at
least
one link of the chain, having a flank geometry differing from that of the
remaining
teeth or links, is arranged such that the said tooth or link, at the moment of
the load
peak, is in engagement with one of the toothed gearwheels; or if the at least
one
gearwheel tooth having a flank geometry differing from that of the remaining
teeth
is arranged such that said tooth, at the moment of peak load, is in engagement
with
the toothed belt or the chain. It is particularly advantageous if the latter
tooth or
chain link, at the moment of a load peak, is forming or releasing its
engagement
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with at least one of the toothed gears, or forming or releasing its engagement
with
the toothed belt or the chain. This achieves an optimal unloading effect
between the
tooth belt or chain and the toothed wheel.
S Advantageously, the load relief is improved even further if at least two
teeth
of the toothed belt or at least two links of the chain, these having a flank
geometry
differing from that of the remaining teeth or links, are arranged such that
these teeth
or these links, at the moment of a load peak, are entering or releasing their
engagement with at least one of the toothed wheels, or that at least two teeth
of the
toothed wheel having the flank geometry differing from that of the remaining
teeth
are arranged in such a way that these teeth, at the moment of a load peak, are
entering or releasing engagement with the toothed belt or chain.
In a further advantageous arrangement, the individually adapted tooth flank
geometry can be utilized both for a driving wheel and for a driven wheel, or
at the
corresponding position on the belt or the chain. For example, in a belt drive
between a crankshaft and a cam shaft in an automobile, three teeth on the
driving
wheel, or on the driven wheel, can exhibit an individual flank geometry which
is
configured in such away that the stretching of the toothed belt caused by the
non-
uniform excitation, and the pitch defect arising therewith, can be
compensated. The
latter pitch defect compensation can be reduced over the several tooth flank
geometries to a zero value as a function of the stretching.
The toothed belt drive or chain drive in accordance with the invention is
particularly advantageous for the drive of a pump-nozzle-direct spray system
or a
high pressure pump for a common-rail-high pressure spray of a driving
assembly, in
particular for an automobile.
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Further characteristics, advantages and configurations of the invention are
set forth in the appended claims, as well as in the accompanying description
of the
invention utilizing the attached drawings. The latter show,
in Figure 1 a schematic sectional view of a conventional toothed belt
assembly,
in Figure 2 a preferred embodiment of the toothed wheel in accordance with
the present invention,
in Figures 3a and 3b an enlarged view of a tooth of the toothed wheel in the
region A and B of Figure 2, and
in Figures 4a and 4b a schematic illustration of the loading pattern on the
1 S teeth of the toothed wheel of Figure 1 or Figure 2.
Figure 1 shows a schematic section through a conventional toothed belt drive
with a toothed belt 14 which engages a toothed wheel 10 with teeth 1001 to
1015.
In the illustrated embodiment, the toothed wheel 10 is driven by a crankshaft
12 of
an internal combustion engine, and in turn activates ) by way of the toothed
belt 14,
a cam shaft which is not illustrated. Arrow 16 shows the rotational direction
of the
toothed wheel 10.
The tooth 1001 is at the beginning of engagement while the tooth 1015 is at
the release position of the engagement between the toothed wheel and the
toothed
belt 14.
Figure 2 shows an advantageous embodiment of the toothed wheel 10, while
Figures 3a and 3b show enlarged views, respectively, of the regions A and B of
Figure 2, as well as the flank geometry of the respective teeth 24 and 26. The
4
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broken line shows the flank geometry of the teeth 24 and 26, whereas the solid
line
shows the flank geometry of the remaining teeth. The flanks 18 and 20 of the
teeth
24 and 26 have differing geometries, such that during the beginning and during
the
end of the engagement between the tooth wheel 10 and the tooth belt (not
illustrated)
5 there is a reduced loading. In other words, the teeth 24 and 26 have an
asymmetrical flank geometry.
The teeth 24 and 26 are so selected that they are found exactly in the
position
shown in Figure 2 when a load peak occurs during ignition in a corresponding
working cylinder of the internal combustion engine.
Figures 4a and 4b illustrate the curve of a flank-force on the tooth from the
teeth 1001 to 1015 of the toothed wheel 10. Marked on the x-axis are the
corresponding numbers of the teeth 1001 to 1015, while the y-axis shows the
flank
force on the tooth. The solid line represents the curve of the flank force
under
normal load, and the broken line shows the same under a load peak.
Figure 4a shows the flank force curve of a conventional toothed wheel,
whereas Figure 4b shows the curve for a toothed wheel 10 in accordance with
the
invention. It is immediately evident that, in the region of flank power peaks
for
teeth 1001 and 1015, the loading of the toothed wheel 10 in accordance with
the
invention is less than with a conventional toothed wheel. This reduced loading
brings about a reduction in wear for the toothed belt 14 and the toothed wheel
10,
and leads to longer life for the toothed belt drive.
It is clear that the question of which teeth or chain links are to be provided
with an altered flank geometry depends upon the particulars of the toothed
belt or
chain drive, and also how the altered geometry is arranged. As an example,
differing teeth for a 4- or a 5-cylinder internal combustion engine would be
correspondingly altered.
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F
The choice of whether the altered teeth are located on the toothed wheel 10
and/or the toothed belt 14 determines whether the toothed wheel 10 or the
toothed
belt 14, or the chain, is to be mounted in a precisely predetermined position,
such
that, during the running of the internal combustion engine, the altered flank
geometry interacts with the crankshaft wheel 10 in the correct time-wise
sequence,
i.e. under load peaks due to ignition in the respective cylinder.
Individual teeth or a11 of the teeth of the tooth wheel 10 can be provided
with
an optimal geometry. According to a known loading curve around the periphery
of
the toothed belt 14 or toothed wheel 10, it is also possible for the flank
geometries
over the running of the toothed belt 14 or toothed wheel 10 to vary
accordingly. In
the extreme case, each tooth has a different flank geometry.
The invention is not limited to drive systems of the kind shown in Figure 1.
Rather
it is generally useful in transmission systems with loading peaks which can be
balanced using the arrangement in accordance with the invention, including,
for
example, bicycle drives.
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