GB2224554A - A pair of silenced gears - Google Patents

Abstract

At least one of the gears of a pair of meshing gears with constant tooth spacing has irregularly distributed, variously-sized, limited deviations ( DELTA b, DELTA da DELTA s, ...) from the standard shape of the teeth (Z1, Z2 ...), so that single-frequency vibrations do not occur and the total gear noise is substantially reduced. The irregularities may take the form of variations in the tooth tip heights, as shown, and/or variations in the tooth tip relief (Figs. 5 & 6) and/or variations in the tooth flanks (Figs. 7 & 8). The gears may be straight or helical, spur gears, planet gears, or bevel gears. <IMAGE>

Description

INPROVED SILENCE GEARING This invention relates to a pair of silenced gears having varying contact geometry.

It is known to use non-uniformly spaced teeth for noise reduction or to prevent gears from "humming". It is also known to use irregularly varying spacings to avoid highly-disturbing single notes during the operation of a series of gears. It has been found that this method can almost completely eliminate resonance excitation at peak levels. However, it is difficult to adapt this technique to any pair of gears, mainly because when the spacing at the pinion and wheel is irregular, only whole-number gear ratios and certain assembly-angle positions are possible, if the spacing pattern on the teeth of the pinion is to be identically repeated on the larger gear. These methods are therefore not suitable for general application to vehicle and machine drives as the improved gear design would result in a considerable restriction in dimensional freedom.There would also be substantial difficulties in manufacture, more time would be needed owing to strict assembly regulations and there would be an increased risk of the gears breaking if they were incorrectly assembled.

It is an object of the invention therefore to obtain comparable silencing of pairs of gears by obliterating or suppressing prominent tooth frequencies, using a constant spacing and with a free choice of transmission ratio and with any desired number of paired gears.

In the preferred embodiment, constant spacings with teeth at equal intervals are provided, but owing to the irregular arrangement of differently sized deviations, from the most efficient tooth shapes, the conditions of contact action are varied from tooth to tooth in such a manner as to produce constantly-changing, partly self-compensating vibration pulses or sound pulses during operation.

The deviations from the respective standard tooth shape, which at least subjectively improve the overall noise level during operation, result in frequency interference or overlaps similar to those occuring with known differential spacings, but avoid the disadvantages thereof as regards manufacture and application. As a result, the noise-improvement effects are of general applicability to practically any pair of gears.

If the spacing is exactly regular and the gear ratios are arbitrary, prominent tooth frequencies are turned into partial overtones which are less acoustically noticeable, as a result e.g. of differences in the contact action path from tooth to tooth. When the two wheels mesh, there is no measurable decrease in power, although the silencing effect is clearly recognisable.

Experiments on a pair of gears containing 53/59 teeth in the last mentioned embodiment have already yielded values up to 6 dB lower at discrete frequencies.

To this end, in the preferred embodiment, variously-constructed, irregularly distributed contact-action shapes are provided on a maximum number of the teeth on the periphery of at least one wheel, so that the teeth engage and disengage in a differential manner instead of periodically.

The preferred gears of the invention have the following advantages: If even one wheel in a pair has irregularly changing tip contact-action paths, a marked reduction in noise can result. The effect is very considerable even if only the driven wheel is modified in accordance with the principles of the invention.

If the tip heights of the individual teeth are machined to varying depths, manufacture of the different contact action paths is very simple.

The noise-reducing effect of one-sided tip relief can be further improved by associated varying one-sided foot relief.

It has been found advantageous to choose at least three different tip heights following one another in irregular repetition.

In order not to eliminate certain frequencies in particular, the maximum number of similar teeth should have similar tip heights or tip relief but engage at varying times.

One simple mechanical method of obtaining different tip heights in spur or helical gearing is to coaxially machine the tips of the individual teeth.

In the particular case of helical gearing, a similar effect can be obtained by face edge chamfering at variable angles, because in that case the tip contact action paths also vary from tooth to tooth.

In the case of both spur and helical gearing, it is easy to vary the depth of face edge chamfers.

In the case of spur toothing, the desired effect may also be obtained by the conical machining of the tips or alternatively by varying the amounts of crown.

It is also mechanically very easy to manufacture varying contact action paths by means of linear chamfers, of varying length and offset at unequal angles, on the face edges, e.g. when forging gear blanks or during casting, because the irregular tooth tips or face edges remain when the teeth are manufactured, without additional special machining. One possibility of mechanically producing the shape deviations is to provide a programme-controlled deburring machine with irregular feed strokes on the spacing apparatus of the gear-cutting machine.

There are numerous possible variations from the quantities defining spur gear toothing, but the principle of the invention is concerned only with deviations in flanks, of limited size and deliberately irregular in spacing. No consideration is given to deviations from circular spacing or contact spacing or from truth of rotation or position, since these are not methods of obliterating frequencies so as to obtain a subjective improvement in noise while substantially maintaining high efficiency.

Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows the conditions for contact action between two meshing teeth and the dependence of the length of the contact action path on the tip circle diameters, Figure 2 shows a single gear in which the tip circles of individual teeth have various values which are variously associated with the teeth although the spacing remains the same, Figure 3 shows the irregular tip circle diameter, irregularly distributed among the teeth, Figures 4-12 show various other possible flank deviations for the purpose of silencing, by varying the contact-action conditions operative from tooth to tooth, Figure 13 shows a gear blank whose face edges are chamfered to an irregular width, resulting in varying tip heights or contact action paths when the teeth are machined, and Figure 14 is a partial section along the line XIV-XIV in Figure 13.

Referring to Figure 1 (which is based on DIN 3960, Fig.

33) there is shown an example of flank deviations with constant spacing and symmetrical axle position etc.

with variations in tip heights ha2 in-the driven wheel.

The irregularly distributed varying tooth tip heights ha2 on the driven wheel can be distributed as shown in the embodiment in Figure 2.

In Figure 1, the tip height ha2 is made different from tooth to tooth, by radially shortening the teeth to a varying extent, resulting in continuous differences in the tip circle diameter da2 . At the right hand edge of Figure 1, this is shown by short, closely adjacent arc portions notated da2min and da2max . With regard to their absolute size, the tooth tip heights vary, with arbitrary distribution among the various teeth, between the values of da2maX and da2min. In accordance with known tooth contact-action geometry laws, (e.g.

from DIN 3960), the rms values of the tip circle diameter da2 are factors in determining the length of the contact action path go between the initial point A and the end point E of contact action between two paired spur gears, and consequently variations in tip height ha produce corresponding variations in the respective contact action paths ga.

The effective length of the respective duration of contact action, together with the respective size and shape of the individual teeth, results in the individual vibration properties or tonalities at each new tooth contact action in accordance with the principle of the invention. Figure 1 shows a driving wheel 1 and a driven wheel 2.The tip circle diameter d or da2 and the base circle diameter d1and df2, as determined by calculation, are measured from the centre points 1 and 02. The foot base load diameters dNfl and dNf2 intersect the opposite tip circles da at the initial point A and the end point E of the contact action path ga . The point of intersection with the central axis Ol to O2 is the involute point C, which also determines the involute diameters dwl and dw2for wheels 1 and 2 respectively. These are not altered by the slight variations in the length of the contact action path ga in accordance with the invention.Correspondingly, the tip heights can be varied or other or additional variations can be made to the tooth flanks, and will similarly result in changes in sound frequency from one tooth contact action to another, resulting in a general silencing or subjective reduction of sound. For clarity, the drawings show the main variations in tooth shape greatly magnified and in Figures 4-12 separately from Figures 1-3. As will be clear to the skilled addressee, the procedure must follow the same laws of tooth contact action as explained with reference to Figure 1 in the case only of the example of tooth tip heights or variations in contact action paths.

In Figure 2, in the case of a spur gear 2 used as an example and having 11 teeth 2.1 to 2.11, separate dimensional arrows are used on each tooth to illustrate how each tip circle diameter da2 must be constructed within a range between a maximum and a minimum value, which in most teeth is greater or smaller than the absolute size da2 by a small amount (+/- 1 to 4 in the present case). Care must be taken that, if possible, each value is followed by a higher or lower value in a manner which results in deliberately irregular counter-pulses which are offset to the maximum extent, without any regular pulse sequences.

Figure 3 is a tabular diagram showing a similar irregular variation in tip circle diameter for 11 teeth. The tooth Z plotted along the abscissa have tip circle diameters idea2 plotted along the ordinate and varying between a maximum value da2max and the minimum value da2min with an irregularly offset arrangement of varying rms values. The increase and decrease of sound is also avoided by an angularly offset arrangement of the irregularities producing pulses of equal strength, so as substantially to avoid repetition of the time intervals between similar pulses. This avoids single-frequency sound vibrations, which often are very disturbing.

Figure 4 shows one of the simplest shapes for varying the contact action path by means of a number of different tip reliefs between da2maxand da2min In the tip region of the tooth marked iE da2 in the drawing, varying axially parallel top edges 3 are produced on each tooth.

In Figure 5, a further variation in tooth tip diameter Ada2 is obtained by the conical machining 4 of the tip surfaces particularly in the contact-action region, varying as before from tooth to tooth.

Figure 6 shows the longitudinal crowned machining 5, starting from one of the faces, marked da2 and of varying size, which is particularly advantageous for wheels rotating in alternating directions.

Figures 7 and 8 show the axially parallel machining and and G df2 of the tip 6 and foot 7, of varying size and on one flank only.

Figure 9 shows the continuously varying machining 8 at parallel angles with width # b and at an angle p , suitable for helical gears.

Figure 10 shows the angular machining 9 of the face edge starting from the foot circle df2 and capable, e.g. by variations between angles #&alpha;of o of 50 to 300 to the face, of producing a number of different contact action paths when the tip diameters da2 are constant. This likewise is suitable for helical gears.

Figures 11 and 12 show a possibility of influencing the tip contact action paths gal t ga2 simply by varying the size of the machined corners in the face-edge region, the tooth widths b and the tooth thicknesses 22 S being machined to varying widths at constant angles 7.

This principle is applicable to all conventional gears and applications, whether straight or helical, spur gears, planet gears or bevel gears and is compatible with conventional manufacture with uniform spacing and arbitrary gear ratios.

Figures 13 and 14 show a possible method of using a casting or forging mould to prepare the irregularity of face edge chamfers, e.g. as shown in Figure 9, so that the irregular distribution automatically results when the teeth are machined and no additional work is necessary apart from deburring.

Figure 13 is a plan view of a gear blank prepared in this manner, with a maximum tip circle diameter da2max At its outer periphery, a number of uniformly peripherally distributed linear edge chamfers 11.111.8 are made with varying lengths, resulting in variations in the depthAy of machining or of the edge recess of individual teeth. The depth y varies along the arc with the position of the tooth, as shown by the various Y values of the embodiment shown in section in Figure 14. A corresponding effect can also be obtained if the edge chamfers are at different angles.

Even without the aforementioned linear face edge chamfers 11, a variable feed deburring machine can be used for efficient manufacture, -if for example a programme control is used to vary the - feed stroke from tooth to tooth.

Reference Numerals 1 driving gear 2 driven gear 2.1 - 2.11 teeth of gear 2 3 coaxial tooth tip machining 4 conical tooth tip machining 5 crowned tooth tip machining 6 tip relief tooth tip machining 7 foot relief tooth tip machining 8 variable length face edge chamfer 9 variable angle face edge chamfer 10 face edge chamfer with variable depths and thicknesses 11 face edge chamfers 11.1 - 11.8 offset chamfers A initial point of contact action C involute point E final point of contact action 01, 02 neutral axles in wheel centres Tw1g , TW2 contact points of line-of-action and base circle zl, Z2 numbers of teeth a wt action angle in operation b b face width dimension from working depth dal, da2 tip circle diameter of driving and driven wheel respectively dbl, db2 base circle diameter of driving and driven wheel respectively.

d1, d2 pitch circle diameter of driving and driven wheel respectively.

#df1, # df2 axially parallel machining on tooth base df1, df2 tooth base circles diameter of driving and driven wheel respectively.

A dk1, Ad axially parallel machining on tooth tip dnf1, dnf2 foot base load diameter dw1' dw2 operating involute-diameter of driving and driven wheel respectively.

tooth ga1, ga2 tooth tips contact action path of driving and driven wheel respectively ga total contact action path hall ha2 tooth tip height of driving and driven wheel respectively Pt pitch circle spacing # S1, # S2 machining of tooth thickness of driving 2 and driven wheel respectively Y depth of edge recess linear chamfers.

Claims (15)

CLAINS

1. A silenced pair of gears provided with varying contact-action geometries characterised in that the spacing between the teeth is constant and assembly is possible at any angle with either whole-number or arbitrary gear ratios, and deviations or removed areas from the mass defining the intrinsically most efficient tooth shape are provided on a number of individual teeth on at least one of the gears, the deviations varying in amount from tooth to tooth.

2. A pair of gears according to claim 1, characterised in that the deviations result, in use, in contact action paths of continuously irregular length with irregularly varying distribution during rotation.

3. A pair of gears acording to claim 1, characterised in that only the driven wheel is equipped with the deviations.

4. A pair of gears according to claim 1, characterised in that the number of teeth with equally sized deviations is substantially the same on the same respective gear.

5. A pair of gears according to claim 1, characterised in that at least three irregularlydistributed and irregularly-sized deviations are provided on the periphery of at least one wheel and go beyond conventional manufacturing tolerances and result in at least one beginning of contact action which is offset in time.

6. A pair of gears according to claim 5, characterised in that the deviations comprise variations in the tooth tip heights resulting at least in varying beginnings of contact action.

7. A pair of gears according to claim 6, characterised in that the varying tip heights are obtained by the coaxial machining of the tips of the individual teeth.

8. A pair of gears according to claim 6, characterised in that the varying tip heights are determined by the conical machining of the tips of the teeth.

9. A pair of gears according to claim 6, characterised in that the varying tip heights in the case of straight-toothed gears are determined by the crowned machining of the face edges of the teeth.

10. A pair of gears according to claim 6, characterised in that the deviations obtained by varying tip relief and/or foot relief.

11. A pair of gears according to claim 6, characterised in that the varying tip heights are determined at least by variations in the depth of face edge chamfers.

12. A pair of gears according to claim 6, characterised in that the varying tip heights are determined by varying the angle of the face edge chamfers.

13. A pair of gears according to claim 1, characterised in that the deviations are obtained by chamfering the tooth blanks with varying width at the face edge before manufacture of the teeth.

14. A pair of gears according to claim 1, characterised in that the deviations are produced by a deburring machine with programme-controllable feed drive adapted to be actuated with varying strength in variously-spaced steps in the spacing, which is constant per se.

15. A pair of silenced gears substantially as herein described with reference to the accompanying drawings.