Patent Grant
8430775
The invention pertains to the field of pulleys and sprockets. More particularly, the invention pertains to a chain and multiple sprockets for reducing resonance tension.
Chain and sprocket systems are often used in automotive engine systems to transmit rotational forces between shafts. For example, a sprocket on a driven shaft may be connected via a chain to a sprocket on an idler shaft. In such a chain and sprocket system, rotation of the driven shaft and driven sprocket will cause the rotation of the idler shaft and idler sprocket via the chain. In an automotive engine system, sprockets on the crankshaft may be used to drive one or more cam shaft sprockets.
The chains used in chain and sprocket systems typically comprise a plurality of link plates connected with pins or rollers or chains with the plurality of link plates having engagement teeth connected with pins and/or links. The sprockets typically comprise a circular plate having a plurality of teeth disposed around the circumference thereof. Located between adjacent teeth are roots having generally arcuate or semi-circular profiles for receiving the pins, rollers, or teeth of the chain. Each root has a root radius which is the distance from the center of the sprocket to a point along the root closest to the center of the sprocket. The sprocket roots and/or teeth are also associated with a pitch radius, which is the distance from the center of the sprocket to a pin axis which is part of a chain joint when the chain is seated on the sprocket.
In a conventional (“straight”) sprocket, the root radii are all substantially equal, and the sprocket's pitch radii also are substantially equal. However, it has been found that as a chain rotates around a straight sprocket, audible sound frequencies creating undesirable noise are often generated as the chain teeth, pins or rollers connecting the links of the chain contact the sprocket teeth and impact sprocket engagement surfaces or the roots disposed between adjacent teeth of the sprockets.
Sound frequencies and volume of such noise created by the operation of chain and sprocket systems typically vary depending on the chain and sprocket designs, chain rotational speed, and other sound or noise sources in the operating environment. In the design of chain and sprocket systems, it can be desirable to reduce the noise levels generated as the rollers, pins or teeth of a chain engage a sprocket.
In chain tension measurements, certain chain tensions originating from occurrences outside the chain and/or sprocket in a particular system may vary on a periodic or repeating basis, which often can be correlated to tension inducing events. For example, in automotive timing chain systems, it has been observed from chain tension measurements that the engagement and disengagement of each sprocket tooth or root with the chain often results in repeating tension changes. These chain tension changes may be correlated with potentially tension-inducing events, such as the firing of piston cylinders. Reducing these tensions and forces on chains may be of particular importance if the chains include elements where they do not have the properties of steel, such as ceramic elements as described in U.S. application Ser. No. 10/379,669.
The number of tension events that occur relative to a reference time period, as well as the amount of the tension change for each event may be observed. For example, in an automotive timing chain system, one may observe the number or frequency of tension changes in the chain relative to rotations of a sprocket or a crankshaft, as well as the magnitude of the tension change in the chain. A tensioning event that occurs once per shaft or sprocket rotation is considered a “first” order event, and an event occurring four times for each shaft or sprocket rotation is considered a “fourth” order event. Depending on the system and the relative reference period, i.e., rotations of the crankshaft or the sprocket (or another reference), there may be multiple “orders” of events in a crankshaft or sprocket rotation in such a system that originate from one or more tension sources outside the chain and sprocket. Similarly, a particular order of the sprocket rotation may include or reflect the cumulative effect of more than one tensioning event. As used herein, such orders of tensioning events occurring during a sprocket (or crankshaft) rotation also may be referred to as the orders of the sprocket (or crankshaft) or the sprocket orders (or crankshaft orders).
In straight sprockets, measurable tensions typically are imparted to the chain at a sprocket order corresponding to the number of teeth on the sprocket, also known as the pitch order. Thus, in a sprocket with nineteen teeth, tensions would be imparted to the chain at the nineteenth order, i.e., nineteen times per revolution of the sprocket. This is engagement order. A tension event in a straight sprocket originating from outside the sprocket would typically occur at equal intervals relative to the sprocket rotation, with a generally equal tension change or amplitude.
A “random” sprocket typically has root and/or pitch radii that vary around the sprocket, i.e. it is not a straight sprocket. Random sprockets, in contrast, typically have different tensioning characteristics when compared to straight sprockets due to their differing root or pitch radii. As the chain rotates around the random sprocket, each of the different radii typically imparts a different tensioning event to the chain. For instance, as a roller of a roller chain engages a root having a first root radius, the chain may be imparted with a tension different from when a roller of the chain engages a root having a second root radius larger than the first root radius. Tension changes, in addition, may also be imparted to the chain by a random sprocket due to the relative positioning of the different root radii. A roller moving between adjacent roots having the same root radii may result in different chain tension changes than a roller moving between adjacent roots having different radii.
The change in chain tensions imparted by random sprockets due to the relative positioning of the root and/or pitch radii may be further accentuated when the sprocket has more than two different root or pitch radii. For example, in a random sprocket having first, second, and third successively larger root radii, the tension imparted to the chain may be greater when a chain roller moves from a root having a first root radii to a root having a third root radii than when a chain roller moves from a root having a first root radii to a root having a second root radii.
Random sprockets designed principally for noise reduction often cause increases in chain tensions and tension changes as compared to the maximum tensions imparted to the chain by straight sprockets. For example, a random sprocket design may reduce chain noise or chain whine by reducing the pitch order of the sprocket. However, reducing the pitch order of a sprocket may result in concentrating the tensional forces imparted to the chain by the sprocket over the lower orders of the sprocket. These lower orders can excite a chain drive resonance. This often results in increased chain tensions corresponding to the lower orders of the random sprocket.
Such increased chain tensions at the lower sprocket orders frequently cause the overall maximum chain tension force exerted on the chain and sprocket to increase. As a consequence, a chain and sprocket system subjected to such tensions typically will experience greater wear and increased opportunities for failure, as well as other adverse effects, due to the concentration of the tensional forces in the lower orders.
A recently issued U.S. Pat. No. 7,125,356 to Todd entitled “TENSION-REDUCING RANDOM SPROCKET” describes one approach for reducing chain tensions using repeating root and/or pitch radii patterns. The patent describes patterns or sequences effective to impart tensions to the chain to reduce maximum chain tensions during operation of the system relative to maximum chain tensions of a system. The disclosure of U.S. Pat. No. 7,125,356 to Todd is incorporated herein as if completely rewritten into this disclosure.
Generally speaking, when chain tensions reach a maximum or “spike” in a chain and sprocket system in an engine, a resonance condition has been reached and this resonance condition or mode typically corresponds to a given system oscillation frequency. As can be seen from U.S. Pat. No. 7,123,356, tension reducing sprockets providing tension reducing pitch radii or root radii patterns around the sprocket may be utilized to reduce such maximum tensions at resonance conditions.
In some systems, there may be more than one resonance mode, and a corresponding tension “spike”, though a range of system oscillation frequencies. Such multiple resonance conditions or modes may occur where there are multiple tensioning events from outside the chain and sprocket system interacting at one or more system frequencies; there are multiple chains and sprockets forming the system; or there are other excitations imposed on the system that results in multiple resonance modes. The presence of multiple resonance modes may complicate efforts to reduce overall chain tensions. For example, such a system having more than one driven sprocket may have a first resonance mode and a second resonance mode. A tension reducing sprocket designed and placed into the system, with a straight sprocket, to reduce tensions in the second resonance mode may increase chain tensions at the first resonance mode. Further, a similar result may occur if a second tension reducing sprocket is placed into the system to reduce the second (or other) resonance mode tensions.
While not intending to be bound by any theory, a chain and sprocket system may reach a resonance mode, with a tension spike, at relatively low frequency system oscillations. The chain and sprocket system may reach another (or more than one) resonance mode at higher system oscillation frequencies. The number of resonance modes and their corresponding system frequencies will depend on the nature and configuration of the systems, such as the chain stiffness, the number and types of sprockets used in the system, the sprocket and chain configuration, the nature and frequency of the external excitations imposed on the system, etc.
Again, without intending to be bound by theory, the system oscillations at the lower resonance modes tend to be in the same direction. At higher oscillation frequencies, part of the system will tend to oscillate in an opposite direction of another part of the system resulting in a second or other resonance mode. In some drive systems, the resonance mode at relatively high system oscillation frequencies does not contribute enough tension to the overall maximum chain tension to make it a concern for chain durability. In other drive systems, such as high inertia systems, the chain tensions at the resonance mode at such higher system oscillation frequencies can be significant. Further reducing tensions at the resonance mode at such higher oscillation frequency or higher resonance mode tensions can lead to improved drive efficiency, especially if a tension reducing sprocket has already been applied to reduce maximum tensions at first mode.
In the sprocket systems described herein, two or more tension reducing sprockets are oriented relative to each other and are provided with root or pitch radii patterns that cooperatively reduce, and in some instances cancel, maximum chain tensions in chain and sprocket systems having two or more resonance modes. In one aspect, the at least two tension reducing sprockets provide root or pitch sequences and are oriented to reduce maximum chain tensions in one resonance mode relative to the tensions at such mode using a straight sprocket in such system, without significantly increasing the effect of tension excitations from sources outside of the chain and sprocket system at other resonance modes. In another aspect, the tension reduction sprockets are oriented with each other so that tensions will be reduced at a second (or higher) resonance mode relative to the tensions at such mode using a straight sprocket(s), without significantly increasing the maximum chain tensions at a first resonance mode by more than 20%, preferably not more than 10% and most preferably not more than about 0%. Hence, two or more tension reducing sprockets may be used to reduce tensions at one resonance mode from sources outside the chain and sprocket system while minimizing tension increases at another (or multiple) resonance mode(s).
In yet another aspect, the tension reductions may be obtained with two tension reducing sprockets which are driven sprockets (as opposed to a driving sprocket), such as, one tension reducing sprocket on each of two separate cam shafts. Such dual tension reducing sprocket designs used in combination with a drive sprocket should be sized to generate similar levels of chain tension and should be oriented so that the tensions they generate substantially cancel each other at a first resonance mode of the drive. The tension contributions from the two tension reducing sprockets then add at a second resonance mode to generate tensions that offset, or substantially reduce, the second mode tensions, without increasing the first resonance mode tensions. In this aspect, the chain tensions do not increase at the first resonance mode by more than about 20%, preferably not more than about 10% and most preferably not more than about 0%. In still another aspect, certain relative orientations of the tension reducing sprockets provide tension reductions in the second mode without more than a 20% increase in tension in the first mode when compared to the tension at those modes where the sprockets are at other relative orientations. In yet another aspect, a third tension reducing sprocket can be inserted into the system to reduce tensions in the system to reduce tensions at the first resonance mode.
As will be more fully described below, for the chain and sprocket systems described herein, two tension reducing sprockets, for example one on each cam shaft, may be used to cancel first mode tensions. A second mode root and/or pitch radii pattern may be combined with a first mode pattern on one sprocket, but tensions arising from first resonance mode tensions are not increased more than about 0% to about 20% as described above in both roller and silent chain systems. Further, more than one repeating root and/or pitch radii pattern for multiple orders for tension reduction can be included on one sprocket.
a is a plot for engine speed in rpm versus strand tension and is a baseline plot for the tension reducing sprockets in
b illustrates a chain wrapped around the maximum radii at center of the chain wrap.
c illustrates tension plots when the maximum radius of the tension reducing sprocket is advanced 16 degrees as shown in
d shows the maximum radius of the tension reducing sprocket advanced 16 degrees.
e illustrates tension plots when the maximum radius of the tension reducing sprocket is retarded 39 degrees as shown in
f illustrates the maximum radius of the tension reducing sprocket retarded 39 degrees.
g illustrates what happens to chain tensions when the maximum radius of the tension reducing sprocket is retarded 55 degrees as shown in
h illustrates the maximum radius of the tension reducing sprocket retarded 55 degrees.
a illustrates tensions in the four sprocket system of
b illustrates tensions in the four sprocket system of
c illustrates tensions in the four sprocket system of
a shows the variation of tensions on a tension reducing sprocket with a 1.0 mm radial amplitude and maximum radius at zero degrees on shaft 1 of
b shows the variation of tensions on a tension reducing sprocket with a 1.0 mm radial amplitude and maximum radius at zero degrees on shaft 3 of
a shows the variation in tensions on individual chain strands as a function of crank angle for a 1.0 mm tension reducing sprocket on shaft 1 of
b shows the variation in tensions on individual chain strands as a function of crank angle for a 1.0 mm tension reducing sprocket on shaft 1 of
a shows variations in tensions in a chain a sprocket system with externally generated tensions for a system as shown in
a, 13b, and 13c illustrate the tensions on chain strands 1, 2, and 3, respectively, of the seven sprocket system shown in
a, 14b, and 14c illustrate the tensions on chain strands 1, 2, and 3, respectively, of the seven sprocket system shown in
a and 15b show the tension plots for the system in
a and 18b show tension plots for the system shown in
a, 20b, 20c and 20d show tension plots for the system
A random sprocket may be used in an automotive chain and sprocket system, such as used in an engine timing system. The chain and random sprocket are coupled to an internal combustion engine which operates the chain and sprocket at variable speeds. In a simple chain and sprocket system with one resonance mode, the sprocket has a repeating pattern of root or pitch radii which are coupled to a chain at a wrap angle where the wrap angle of the chain with the sprocket and pattern are effective to reduce tensions imparted to the chain. The chain wrap angle, sprocket order and root or pitch radii pattern are selected to reduce tensions on the chain, especially at resonance, and to reduce noise generated as the chain contacts the sprocket.
In one aspect, the multiple sprocket systems described herein have at least one drive sprocket, at least two driven sprockets. At least two of the sprockets are tension reducing sprockets, which may be used in various combinations. For example, the drive sprocket may be a tension reducing sprocket used in combination with one or more of the driven sprockets. In other examples, the driven sprockets may be tension reducing sprockets and the drive and other sprockets may be straight sprockets.
In this aspect, the at least two tension reducing sprockets have a pattern of root radii or pitch radii, or sequence of pitch or root radii which emulates a repeating pattern of root or pitch radii, which reduces overall tensions in the chain when there is at least one recurring tensioning event originating outside the sprockets over a 360° revolution of the at least two tension reducing sprockets. The sprocket order, chain wrap angle and the pattern of pitch radii or root radii of the at least two tension reducing sprockets are coordinated to be effective to reduce maximum chain tensions during operation of the at least two tension reducing sprockets when operated with a chain system relative to where the sprockets are straight sprockets operated with the chain system. A Fourier series which creates a curve representative of pitch or root radii versus sprocket position of (1) the emulating sequence of the pitch or root radii or (2) the sequence of the variation from mean pitch radii or mean root radii, provides an amplitude of the order which is consistent with a sprocket of the same order that has a repeating pattern of pitch or root radii which is effective for overall tension reduction in the chain at resonance conditions. Further the wrap angle of the chain also has an effect as to whether the pattern or sequence will be effective in reducing tension.
In another aspect of the multiple sprocket systems described herein, the systems have at least one drive sprocket, at least two driven tension reducing sprockets and at least two resonance modes. The at least two tension reducing sprockets have a pattern of root radii or pitch radii, or sequence of pitch or root radii which emulates the repeating pattern of root or pitch radii, which reduces overall tensions in the chain when there is at least one recurring tensioning event originating outside the sprockets over a 360° revolution of the at least two tension reducing sprockets. The sprocket order, chain wrap angle and the pattern of pitch radii or root radii of the at least two tension reducing sprockets are coordinated to be effective to reduce maximum chain tensions during operation of the at least two tension reducing sprockets when operated with a chain system at second resonance mode conditions relative to where the sprockets are straight sprockets operated with a chain system operating at second mode resonance conditions. A Fourier series which creates a curve representative of pitch or root radii versus sprocket position of (1) the emulating sequence of the pitch or root radii or (2) the sequence of the variation from mean pitch radii or mean root radii, provides an amplitude of the order which is consistent with a sprocket of the same order that has a repeating pattern of pitch or root radii which is effective for overall tension reduction in the chain at resonance conditions. Further the wrap angle of the chain also has an effect as to whether the pattern or sequence will be effective in reducing tension.
To provide a tension reducing sprocket which is used in the multiple sprocket systems described herein, the order of the sprocket and the wrap angle of the chain are selected such that the resonance tension of the chain and sprocket assembly is minimized at resonance conditions. It has been found, however, that certain average chain wrap angles should not be used with a sprocket and chain that is designed to provide a least one pattern of varying root or pitch radii which repeat at least twice. At the wrap angles described herein, the repeating patterns of root or pitch radii and timing of the tensions provided by the root or pitch radii are particularly effective to reduce maximum chain tensions during operation of the tension reducing sprocket when operated with a chain system at resonance conditions relative to where the sprocket is a straight sprocket operated with a chain system at resonance conditions. Average wrap angles outside the average wrap angles defined by the equation set forth below should be avoided to best reduce maximum chain tensions:
average wrap=360N/Order±120/Order
where: N=1, 2, . . . , ORDER−1
and ORDER=sprocket order as a result of tensioning events which originate outside the chain and/or sprocket.
Average wrap angle is the average of angles about the sprocket center from where the chain first contacts the sprocket to where the chain last contacts the sprocket. It is the average difference of the angular distance between the chain engagement angle and disengagement angle. Wrap angles change each time a sprocket is engaged or disengaged; hence, average angle is used herein.
As mentioned above, in one aspect, the multiple sprocket systems described herein have at least one drive sprocket, and at least two driven sprockets, where at least two of the sprockets are tension reducing sprockets. In this aspect of the multiple tension reducing sprocket systems described herein, the at least two tension reducing sprockets are oriented relative to each other in a way which is effective for reducing tensions from the tension sources outside the chain and sprocket system relative to the maximum chain tensions for the system using straight sprockets.
In another aspect, the multiple tension reducing sprocket systems described herein, there are at least three sprockets, two are driven tension reducing sprockets and one is drive sprocket. In the multiple tension reducing sprocket systems described herein, the at least two driven tension reducing sprockets are oriented relative to each other in a way which is effective for reducing tensions from the tension sources outside the chain and sprocket system at the second resonance mode associated with the tension reducing sprockets while not increasing chain tensions more than about 0 to about 20% at the first resonance mode associated with the system.
The orientation between the sprockets may be readily maintained with a mounting coupling (or orientation structure) disposed to maintain the sprocket in a predetermined orientation with respect to the other sprocket(s) being made a part of the sprocket. This mounting coupling (or orientation structure) can be a key and slot, a known hole pattern for mounting each sprocket, a set screw or bolt system, a permanent fixation approach (e.g. welding or casting) to a shaft or other sprocket or other sprocket orientation approaches as are known.
While not bound by theory and not a limitation on the invention, it is believed that for an engine to have a second resonance mode for an engine chain drive, there must be at least two driven sprockets and one drive sprocket. As noted above, and again while not intending to by bound by theory or as a limitation on the invention, it is believed that at the first resonance mode, the two driven sprockets oscillate in unison. They will oscillate in the same direction at the same time resulting in fluctuations in angular speed. When a tension reduction sprocket is applied to address and reduce first resonance mode tensions, the tension reduction sprocket can be the driven or drive sprocket or it could be a combination of two tension reduction sprockets. These sprockets are oriented so that the tensions add with the maximum radius at the center of the chain wrap (at the center of the chain as measured from where the chain first engages the sprocket and where the chain leaves the sprocket). To cancel tensions generated from outside the chain and sprocket system at first resonance mode, the sprockets have to be oriented, but they must be rotated together when they are re-oriented so that the relative angle between them will remain the same.
For tension reduction at second mode in the multiple tension reducing sprocket system, the maximum of the sprocket radius is at the center of the chain wrap in a first sprocket and the minimum of the sprocket radius for one tension reducing sprocket is at the center of the chain wrap for the second tension reducing sprocket. Thereafter, the tension reducing sprockets are reoriented to reduce the tensions generated from outside of the chain and sprocket system at the second resonance mode, but still keeping tensions at the first resonance mode from increasing not more than 0 to 20%. The tension reducing sprockets used in the multiple tension reducing chain and sprocket systems using silent and or roller chains, now will be described in more detail and compared to known random and straight sprockets. Generally, a first resonance mode occurs at the above mentioned lower system oscillation frequencies, and a second, third, etc. resonance mode occurs at the above mentioned higher system oscillation frequencies. However, such references to “first” and “second” resonance modes are not intended as a limitation on the relevant resonance modes, and, where appropriate, refer to resonance conditions occurring at different system oscillation frequencies.
When reference herein is made to resonance and overall reduction of tension on a chain at resonance, torsional resonance is generally being referred to. In torsional resonance, the chain strands act as springs and the sprockets and shafts act as interias or masses. A simple chain drive with one driven sprocket and two chain strands has one torsional mode and acts like a rotational version of a simple spring mass system. It has a resonance frequency that amplifies the response (including shaft angular velocity and tension variation) to forces external to the sprocket. This torsional resonance can be excited by periodic torque fluctuations (such as cam torques) applied to the driven shaft at the same frequency as the resonance frequency. Resonance also can be excited by angular velocity variation at a driving (such as a crank) shaft or by internal tension fluctuations caused by engagement of the chain with the sprocket or variation in chain and sprocket shape.
In most chain drives this first torsional resonance occurs between 100 and 400 Hz. This is too low to be excited by engagement, but can easily be excited by the lower orders introduced by a random sprocket. Chain drives also can have transverse and longitudinal resonances. In a transverse resonance a chain strand vibrates like a guitar string. These can be excited by tension variations or movement at the end of the strands. While reducing chain tension variation can reduce transverse resonance activity, pitch radius variation can excite transverse resonance activity. In longitudinal resonance, the chain strands act as springs and the sprocket acts as a translating (as opposed to a rotating) mass. Typical chain drives do not have significant longitudinal resonance activity which will deleteriously affect the chain and sprocket. Most important in engine chain and sprocket drives is torsional resonance in the drive.
Sprocket root radii 14 are defined between adjacent teeth 12 for receiving pins or rollers 84 that connect the links 82 of the chain 80. The roots 14 have a generally arcuate profile to facilitate engagement with the pins 84 of the chain. Each root 14 has a root radius R (see
Different tensioning events on a chain (not shown for sprocket 10) may be repeated on a periodic basis during each rotation of the sprocket. As mentioned above, the number of times a given tensioning event resulting from forces external to the sprocket is repeated in one rotation of the sprocket may be referred to as an “order” relative to the sprocket rotation. For example, a tensioning event of the chain that occurs once during each rotation of the sprocket may be termed a first order event, events occurring twice during one sprocket revolution may be termed second order events, etc.
When the tension in the chain 80 is observed during operation of the system, increases in the tension of the chain 80 may occur at certain orders of the sprocket 10 revolution. In a straight sprocket, such as the sprocket 10 of
Thus, a chain rotating about the sprocket 10, having nineteen teeth 12, will have a peak in the tension imparted to the chain by the sprocket at the nineteenth order of the sprocket revolution, or nineteen times for every revolution of the sprocket 10. Peaks in the tension imparted to a chain by a sprocket 10 may also be due to other factors besides the number of sprocket teeth 12. For example, a sprocket 10 that is not rotating about its exact center may impart a tension to the chain at the first sprocket order, or once for every rotation of the sprocket, due to the eccentric rotation of the sprocket.
As mentioned above, in order to reduce noise generated by contact between the chain, and roots 14 and teeth 12 of a sprocket 10, “random” sprockets have been developed with plurality of different root radii. For example, a random sprocket may have two different root radii arranged in a predetermined pattern selected to decrease noise. A random sprocket may also be designed to incorporate three different root radii arranged in a predetermined pattern to further reduce noise generated by engagement of the chain 80 with the sprocket. The root radii may vary based on the particular system and sprocket design.
The random sprocket 20 illustrated in
The root depths 1-3 are arranged in a pattern selected to modulate the engagement frequency between pins of a chain and roots 24 between adjacent teeth 22 of the sprocket 20 in order to reduce noise generation. As the pins of the chain move between adjacent roots 24 of the sprocket 22, the radial position at which the pins seat varies between a maximum radius, a nominal radius, and a minimum radius. In the noise reducing sprocket 20 of
In the random sprocket 20 of
Coordinating chain wrap angles, sprocket order and root radii or pitch radii patterns or sequences as described herein, provide reduced chain tensions with random sprockets. A plurality of different root or pitch radii are used with the wrap angles described herein. The radii are arranged in one or more patterns that are effective to permit reduction of chain tensions occurring at one or more selected sprocket orders by virtue of the external forces on the sprocket which are translated to the chain. The root or pitch radii patterns or sequences also may be selected to reduce chain noise or whine without the disadvantages of prior art random sprockets.
The sprocket pitch radii or root radii to be used as described herein are selected relative to a maximum radius and a minimum root radius as determined from the chain link size and configuration; the chain connecting pin size and spacing; and/or the number of sprocket teeth, tooth configuration and sprockets size. The root radii also may be selected relative to a nominal root or pitch radius which typically is the mid-point between the maximum and minimum radii.
The selection of varying root radii or varying pitch radii allows for the overall reduction of the pitch tensions generated by the chain to sprocket tooth/root contact. It is believed that this is due to the contact of the chain pins (or equivalent chain elements) with the sprocket teeth/roots at different times and at different tension levels as a result of the varying depths of the sprocket roots.
In one aspect, the root radii or pitch radii are arranged in a pattern that repeats at least twice, but the repetition may be multiple times around the outer sprocket circumference. This circumference has a generally round circumferential profile defined by the outer edges of the sprocket teeth. The pattern of root or pitch radii typically includes one or more sets or multiple, non-uniform or random root or pitch radii. Each set of radii typically includes the same number of root or pitch radii having the same length and arranged in the same order. In one aspect, the pattern may repeat where the pitch radii or root radii are arranged in ascending and descending order, e.g. 1, 2, 3, 4, 4, 3, 2, 1, 1, 2, 3, 4, 4, 3, 2, 1. Hence, in this aspect the pattern may ascend from a minimum pitch radius and then descend from the maximum pitch radius to a minimum pitch radius. Further, beneficial results may be obtained where one pitch or root radius in one pattern is missing. When the phrase “substantially repeats” is used, this means one root or pitch radius may be missing from a repeating pattern of root or pitch radii. In other aspects, when there is a number of repeating patterns, and more than one pattern may be missing, a radius coordinating the chain wrap angle, order and pattern can provide chain tension reduction over a straight sprocket, especially at resonance. Further, different sets of root radii may have radii of different lengths, number and arrangement.
The use of such patterns or otherwise random root radii repeated as sequences which emulate patterns as described above along the circumference of the sprocket permits the cancellation or reduction of tensions to specific sprocket orders (or other orders based on the applicable reference). In doing so, the cumulative effect of canceling the tension forces permits the planned overall reduction of chain tension incorporated to the system by the sprocket at specific sprocket orders (or other reference orders).
The selection of the patterns of non-uniform or random root or pitch radii, and the lengths of the root radii further permit the use of major and minor patterns or sub-patterns of radii. Such major and minor patterns are effective to reduce the overall tensions imparted to the chain (and overall system) to multiple sprocket orders (or other applicable orders) and at different magnitudes. This along with the selection of chain wrap angles at given orders provides the additional flexibility in the selection of the sprocket root radii and patterns to offset multiple tension sources in the system and/or to balance the overall tensions on the chain and sprocket regardless of other sources of the tensional forces.
As seen in
Using chain wrap angles at the orders as described herein and the use of a random pattern of root or pitch radii grouped in sets of patterns of root or pitch radii such as seen herein in the discussion of tension reducing sprockets, provide a repeating pattern which may be used to effectively concentrate and cancel the lower order tensions of the chain 80 at the fourth order of the sprocket 30. In a simple system with one resonance mode, this reduces the overall maximum tensions imparted to the chain 80 by the sprocket 30 and external forces imposed on the sprocket which create the chain tension. These chain tensions may be imparted to the chain 80 by various parts of the automotive engine system external to the sprockets, such as the shaft and/or the pistons.
These external sources may impart tension events to the chain 80 in addition to those imparted to the chain 80 by the sprockets 20 and 30 of the above examples. These external tensioning events may occur at intervals that correspond to orders of the sprocket revolution. Use of a combination of specific orders with chain wrap angles, random root radii and repeating root radii patterns all go to cancel tensions imparted to the chain 80 by the sprocket 30 and reduce the overall maximum chain tensions relative to a straight sprocket and also reduces chain noise or whine, especially at resonance conditions with engines (such as internal combustion engines) which operate at variable speeds.
The arrangement of the root radii or pitch radii for tension reducing sprockets may be selected by substantially repeating the radii pattern a number of times equal to the sprocket order at which it is desired to concentrate the chain tensions to reduce overall tension. To reduce maximum tensions due to a second order tensioning event, generally one would expect a pattern will be a second order pattern which will repeat twice to reduce overall tensions. In another example, to concentrate the tensions imparted to the chain 80 by the sprocket 30 of the invention at the fourth or more sprocket order, the arrangement of the root radii may comprise a pattern that substantially repeats four or more times around the sprocket 30.
As mentioned above, the repeating radii pattern and chain wrap angles can provide the benefit of reducing the overall maximum tensions imparted to the chain 80 by the sprocket 30, while also reducing noise generated by contact between the sprocket 30 and the chain 80. In connection with an internal combustion piston engine, the expected overall maximum tension reducing effects of the random sprocket 30 of the invention are illustrated in
As illustrated in
The maximum tensions imparted to the chain 80 by the random sprocket 30 designed for both noise reduction and reduced maximum chain tensions are expected to be significantly lower than for the random sprocket 20 designed principally to reduce noise. In fact, the tension reducing sprocket 30 may impart comparable, and in some instances, lower maximum tensions to the chain 80 than the straight sprocket 10 at engine speeds reflected in
Although the fourth order was selected for illustration in
The tensions imparted to the chain 80 by the sprocket also may be concentrated at more than one sprocket order. For example, a root or pitch radii pattern may be selected that has a major root radii pattern repeating twice for each revolution of the sprocket and a minor pattern that repeats twice within each major pattern. Thus in this aspect, the major and minor radii are provided by having the minor pattern repeating within the major repeating pattern. A benefit of having both major and minor repeating patterns at a selected order and with an appropriate chain wrap angle is the ability to further redistribute the sprocket orders and reduce tensions imparted to the chain 80 by the sprocket. Thus, for every revolution of a sprocket having such a pattern, the major radii pattern is effective to impart two tensioning events, while the minor radii pattern is effective to impart four tensioning events. The tensioning events imparted by the minor radii pattern may be of a lesser magnitude than the tensioning events imparted by the major radii pattern.
In order to reduce overall chain tensions in a simple chain and sprocket system where one resonance mode is of concern, the tensions imparted to the chain 80 by the wrap angles and random and repeating root or pitch radii patterns, such as those of sprocket 30, are selected to at least partially offset tensions imposed on the chain 80 by such sources external to the sprocket 30 and chain 80. In one aspect, the orders of the sprocket revolution corresponding to peaks in the chain tension due to external sources, as well as those due to the sprocket 30, are determined. The sprocket 30 is then configured to cancel chain tensions at a sprocket order at which the chain tensions due to external sources are at a maximum. This provides the potential to reduce the overall tensions in the chain 80, such as may occur if both the chain tension due to the sprocket 30 and the chain tension due to external sources are at their maximums due to resonance. For example, when the external tensions occur four times for every rotation of the sprocket 30, the root radii of the sprocket 30 may be arranged using the wrap angles described herein to concentrate the maximum tensions imparted to the chain 80 by the sprocket 30 at sprocket orders phased to at least partially cancel the external tensions imparted to the chain at resonance. In this manner, the external tensions in the chain 80 may be at least partially offset by the sprocket tensions in the chain 80 to reduce the overall tension in the chain 80 and increase the life cycle of both the chain 80 and the sprocket 30.
The radii patterns or sequences which emulate the repeating patterns should be coordinated with chain wrap angles. By way of example for sprockets which have 2, 3 or up to 8 orders, wrap angles are determined by applying equation (1) set forth above. In this illustration, Table I below sets forth wrap angles which should be used for each of 2 up to 8 orders.
These wrap angles set forth above in the table are used so that the sprocket or pulley radial variation generates sufficient tension variation at the drive resonance to cancel the tensions generated by external sources. Wrap angles outside these values result in insufficient tension generation due to radial variation. Set forth below in Table II are wrap angles which should be avoided where N and Order are set forth in the equation 1 above.
A sprocket pattern order in a tension reducing sprocket may be selected based on measured or predicted chain tensions. In one procedure, pin locations may be generated for a seated chain around the sprocket with the correct number of teeth, pitch length, and radial amplitude. The pin locations are positioned to achieve the correct pitch radius variation amplitude while maintaining a constant pitch length and a chain wrap angle as defined by equation (1) above. Then dynamic system simulations are run with the sprocket without external excitations. Strand tensions from the tension reducing sprocket are compared to strand tensions from a simulation of straight sprocket and external excitations. The tension reduction sprocket orientation is adjusted so that the sprocket's tensions will be out of phase with external tensions. A dynamic system simulation with the tension reduction sprocket and external excitations is run. Adjustments to the tension reduction sprocket orientation and amplitude are made if necessary. Simulations at a range of conditions are run to make sure the sprocket is always effective. A CAD based program, or similar software, is used to convert pin locations to the actual sprocket profile. Then prototype sprockets are made and tested on engines to confirm performance. After the tension reducing sprockets have been designed as described herein, they are made a part of a multiple tension reducing sprocket systems as described below.
The initial orientation shown in
a shows a plot for engine speed in rpm versus strand tension in Newtons.
As generally seen by trends illustrated in
It also can be seen that the tensions generated on shaft 3 (sprocket 304) are larger than the tensions by the shaft 1 (sprocket 302) by about 15% at the first mode resonance. It is desired to have these two amplitudes close. To do this, the radial variation amplitude on shaft 1 (sprocket 302) needs to be 15% larger than on shaft 3 (sprocket 304) radial variation amplitude.
At first mode resonance, it is desired that strand 312 (strand 4) tension peaks with the right bank (RB) tension reducing sprocket (sprocket 302) to occur half way between the 312 strand peaks (strand 4) with the left bank (LB) tension reducing sprocket (304). To achieve this, the orientation of the right bank tension reducing sprocket 302 is advanced about 40 crank degrees (20 cam degrees). This advancement is shown in
Generating the data shown in
It is desired that the strand 4 (312) tension peaks with both tension reducing sprockets to occur half way between the strand 4 (312) tension peaks from the baseline system. The initial estimate was close. Both tension reducing sprockets should be advance about 20 crank degrees (10 cam degrees). Normally it is desired that the strand 4 maximum tensions with both tension reducing sprockets match the maximum stand 4 tension from the baseline. In this case, the tension reducing sprocket radial amplitudes are already quite large and may cause unwanted strand vibrations. To limit the excitation to strand vibration, radial variation will be kept as it is and only partially cancel the second mode tensions. Then it should be confirmed that the two tension reducing sprockets partially cancel the second mode tensions.
The base line for externally generated tensions only for a system as shown in
When sprockets 406 and 412 are converted to third order tension reducing sprockets, significant tension reduction of tensions at the second resonance mode can be achieved without increasing tension at the first resonance mode. When the sprocket 406 on shaft 2 has 0.5 mm radial amplitude maximum at 18 degrees and when sprocket 412 on shaft 5 has a 1.3 mm radial amplitude maximum at −112 degrees the tensions on chain strands 1, 2, and 3 are illustrated in
a and 15b show the tension plots for the system 200 shown in
b is a chain tension plot for the system shown in
Each of the tension reducing sprockets are provided with pattern of pitch radii that repeats with each rotation of the sprocket. The angular variation of the pitch radii, in addition, is adjusted to ensure that the chain pitch length (distance between link pin axes) is maintained at approximately a constant length where the chain engages the sprockets.
The tension reducing sprocket 504 (intake) is provided with a maximum of approximately 1 mm radial amplitude relative to a straight sprocket of the same size and number of teeth, which has a constant pitch radius. In this example, the radial amplitude of the tension reducing sprocket is provided by varying the pitch radii of the tension reducing sprocket from that the equivalent straight sprocket pitch radius by the amounts shown the Table 1 below. The pitch radii pattern also is indicated below in Table 1. The pitch radii pattern is directed at tension reductions at a 3rd sprocket order and a 3rd engine cycle order. The tension reducing sprocket 504 (intake) is oriented at a root 1 angle of approximately 5 degrees.
The tension reducing sprocket 508 (driving, crank sprocket) is provided with a maximum of approximately 0.2 mm radial amplitude relative to the pitch radius radius of a straight sprocket of the same size and number of teeth. The radial amplitude of the tension reducing sprocket is provided by varying the pitch radii of the tension reducing sprocket from that the equivalent straight sprocket pitch radius by the amounts shown the Table 2 below. The pitch radii pattern also is indicated below in Table 2. The pitch radii pattern is directed at tension reductions at a 3rd sprocket order and a 6th engine cycle order. The tension reducing sprocket 508 (driving, crank sprocket) is oriented at a root 1 angle of approximately 40 degrees.
a and 18b show the tension plots for the system 500 shown in
As indicated in
Each of the tension reducing sprockets is provided with sequence of pitch radii that provides a pattern that repeats with each rotation of the sprocket. The angular variations of the pitch radii, in addition, are adjusted to ensure that the chain pitch length (distance between link pin axes) is maintained at approximately a constant length where the chain engages the sprocket.
The tension reducing sprocket 604 (intake) is provided with a maximum of approximately 1 mm radial amplitude relative to the radial amplitude of a straight sprocket of the same size and number of teeth. In this example also, the radial amplitude of the tension reducing sprocket is provided by varying the pitch radii of the tension reducing sprocket from that the equivalent straight sprocket pitch radius by the amounts shown the Table 3 below. The pitch radii pattern also is indicated below in Table 3. The pitch radii pattern is directed at tension reductions at a 3rd sprocket order and a 3rd engine cycle order. The tension reducing sprocket 604 (intake) is oriented at a root 1 angle of approximately 5 degrees.
The tension reducing sprocket 608 (driving, crank sprocket) is provided with dual order pitch pattern with the rotation of the sprocket. The dual order pattern is provided by determining a first pitch radii sequence with a preselected order pattern and a root 1 angle, and a second pitch radii sequence with another preselected order pattern and a second root 1 angle (which may be the same as or different from the root 1 angle of the first pitch sequence). The pitch radii sequences are then effectively overlaid or combined to provide a pitch pattern with the cumulative variation in radial amplitude of each pitch radii sequence relative to the radial amplitude of a straight sprocket of the same size and number of teeth. When the patterns are effectively overlaid, they are angularly displaced to account for the differences in the root one angles of the pitch sequences.
In this example, the first pitch radii sequence has a maximum of approximately 0.2 mm radial amplitude relative to the radial amplitude of a straight sprocket of the same size and number of teeth. In this example, the radial amplitude of the first pitch sequence is provided by varying the pitch radii of the tension reducing sprocket from that the equivalent straight sprocket pitch radius by the amounts shown the Table 4 below. The pattern of the pitch radii sequence also is indicated below in Table 4. The pitch radii sequence is directed at tension reductions at a 3rd sprocket order and a 6th engine cycle order. This pitch radii sequence is oriented at a root 1 angle of approximately 30 degrees.
The second pitch radii sequence has a maximum of approximately 0.05 mm radial amplitude relative to the radial amplitude of a straight sprocket of the same size and number of teeth. The radial amplitude of the second pitch radii sequence is provided by varying the pitch radii of the tension reducing sprocket from that the equivalent straight sprocket pitch radius by the amounts shown the Table 5 below. The pattern of the pitch radii sequence also is indicated below in Table 5. The pitch radii sequence is directed at tension reductions at a 2nd sprocket order and a 4th engine cycle order. This pitch radii sequence is oriented at a root 1 angle of approximately −12.14 degrees.
The combined pitch radii sequence providing the final dual order pitch pattern for the driving sprocket 608 (crank) is shown below in Table 6. As can be seen, the dual order pattern repeats with the rotation of the sprocket. A Fourier series of the dual order pattern also may be used which creates a curve representative of pitch or root radii versus sprocket position of (1) the emulating sequence of the combined two pitch radii patterns or (2) the sequence of the variation from mean pitch radii or mean root radii of the combined patterns, to provide amplitudes of the order which is consistent with a sprocket of the same orders as the above referenced combined repeating pattern of pitch or root radii which is effective for overall tension reduction in the chain.
a and 20b show the tension plots for the system 600 shown in
As indicated in
c and 20d show tension plots for the system 600 with the above mentioned straight sprockets compared with the system using the above mentioned single order tension reducing driven sprocket 606 (intake) and above mentioned dual order driving sprocket 608 (crank sprocket). In this example, the external excitations are modified. As indicated in
As indicated in
The graph of
The valve timing refers to a base setting with the exhaust valve timing advanced to the earliest point in the engine cycle and the intake valve timing is set at the latest point in the engine cycle. The full valve timing is where the intake valve timing advanced to the earliest point in the engine cycle and the exhaust valve timing set at the latest point in the engine cycle. The mid timing is at the approximate mid-point between the full and base timing settings. The chain elongation refers to chain wear conditions where the chain is elongated approximately 0%, 0.35% and 0.70%. The approximately 0.35% condition represents a chain with moderate to heavy wear, and the approximately 0.70% condition represents a chair near or past the end of its useful life. The throttle condition is where the throttle is set at 20% of the maximum and the WOT (wide open throttle) setting is the maximum throttle setting.
As shown in
Furthermore, the tension reducing sprockets and did not increase chain tensions relative to the straight sprocket system at operating conditions where the straight sprocket tensions were in or below the acceptable range. As shown in
This application claims the benefit under 35 USC 119 (e) of U.S. provisional patent application Nos. 60/976,399 filed Sep. 28, 2007, and 60/976,977 filed Oct. 2, 2007, which are hereby incorporated herein by reference in their entirety.
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|---|---|---|---|---|
| PCT/US2007/088828 | 12/26/2007 | WO | 00 | 6/11/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/041986 | 4/2/2009 | WO | A |
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| Number | Date | Country | |
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| 20100292038 A1 | Nov 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60976399 | Sep 2007 | US | |
| 60976977 | Oct 2007 | US |
