Gear arrangement

Abstract

A gearbox includes an inner-outer gear pair having a small tooth difference, the inner-outer gear pair including: an inner gear disposed about an inner gear axis and having a first number of inner gear teeth; and an external gear having an external gear axis, the external gear arranged for orbital motion about the internal gear axis and having a second external gear tooth number, the external gear arranged for engagement with the internal gear teeth; the small tooth difference between the tooth number of the first outer gear and the tooth number of the second inner gear is smaller than one fifth of the tooth number of the inner gear. And wherein the internal gear teeth and the external gear teeth have an involute shape with no profile displacement or with a profile displacement below a value at which a working pressure angle of the internal-external gear pair will exceed a nominal pressure angle of the internal-external gear pair without application of a profile displacement by more than 20%, and wherein the internal gear teeth and the external gear teeth have an involute shape with no profile displacement or with a profile displacement below a value at which a working pressure angle of the internal-external gear pair will exceed a nominal pressure angle of the internal-external gear pair without application of a profile displacement. And wherein at least one of the internal gear teeth and the external gear teeth has an addendum coefficient of less than 0.8. Such a gearbox may provide improved efficiency.

Description

Technical Field

[0001] The invention relates to an internal-external gear pair with a small tooth difference and application thereof in a torque conversion gear box. Background Art

[0002] An internal-external gear pair may have a ring gear with gear teeth facing inwards and a relatively large pinion gear located inside the ring gear with gear teeth facing outwards. In the case of such a large pinion gear, standard gear tooth profiles and modules may result in interference between the gear tooth tops of the two gears, known as tooth interference. Known ways to address this interference include applying a profile shift to the gear tooth profiles, but shifting the gear tooth profiles may reduce the efficiency of these gears.

[0003] An improved arrangement of an internal-external gear pair with a small tooth difference is required. Summary of the invention

[0004] According to a first aspect of the invention, there is provided a gearbox comprising an inner-outer gear pair with a small tooth count difference, the inner-outer gear pair comprising any or all of the following features: an inner gear arranged about an inner gear axis and having a first inner gear tooth count; and an outer gear having an outer gear axis, the outer gear being arranged to orbit about the inner gear axis and having a second outer gear tooth count, the outer gear being arranged to engage with the inner gear teeth; wherein the small tooth difference between the first outer gear tooth count and the second inner gear tooth count is less than one-fifth of the inner gear tooth count; and wherein the inner gear teeth and the outer gear teeth have an involute shape, no tooth profile displacement or a tooth profile displacement below a value at which the pressure angles of the outer gear teeth and the inner gear teeth differ by more than 20% of the operating pressure angle of the outer gear teeth. The inner gear teeth and the outer gear teeth may have a tooth top height coefficient of less than 0.8. Such a gearbox may provide improved efficiency.

[0005] For any internal-external gear pair disclosed, the operating pressure angle of the gear pair formed by the internal gear and the external gear can exceed the nominal pressure angle of the same gear pair without the application of tooth profile displacement by less than 20%, optionally less than 15%, 10% or 5%.

[0006] For any disclosed internal-external gear pair, the pressure angles of the internal and external gear teeth measured at the midpoint of the working portion of the gear tooth flank can be the same. Alternatively, the pressure angles can differ by less than 20% of the pressure angle of the external gear teeth.

[0007] For any of the disclosed internal-external gear pairs, the internal and external gear teeth may have an involute shape, no profile modification, or a profile modification below a value at which the operating pressure angle of the internal-external gear pair will exceed the nominal pressure angle of the internal-external gear pair without the applied profile modification by more than 20%. The internal and external gear teeth may have a tooth addendum coefficient of less than 0.8. Such a gearbox may provide improved efficiency.

[0008] The sum of the addendum coefficients of the internal gear teeth and the external gear teeth of any gear pair disclosed herein may be less than 1.6.

[0009] The theoretical contact ratio of an external-internal gear pair calculated for a gearbox with the same geometry and no material deformation can be less than 1. Low contact ratios can be achieved due to the lack of profile displacement and having a tooth height coefficient below 0.8, and a contact ratio of 1 or greater after material deformation can allow the gearbox to transmit torque more consistently in practice.

[0010] The addendum coefficient may be less than 0.7, optionally less than 0.6. This may provide further clearance to avoid trochoidal interference if there may be play in the bearings, and may also be necessary if the tooth difference between the external and internal gears is very small.

[0011] The tooth tip height coefficient may be greater than 0.3, more preferably greater than 0.5. This may allow the surface stress on the side faces of the teeth to be reduced, thereby improving the life of the gear.

[0012] The theoretical contact ratio of the inner-outer gear pair calculated for a gearbox with the same geometry and without material deformation may be less than 0.8, optionally less than 0.6, and less than 0.4.

[0013] The tooth profile modification coefficient of the internal gear may be less than 0.05, optionally less than 0.04, further optionally less than 0.03, still further optionally less than 0.02, and further further optionally less than 0.01. There may be no tooth profile modification.

[0014] The pitch diameter of the outer gear may be at least half the pitch diameter of the inner gear.The inner gear may cover or overlap the axis of the outer gear while being in contact with the teeth of the outer gear.

[0015] The gearbox may produce a loaded contact ratio in use that is greater than 100% greater than a theoretical contact ratio calculated for a gearbox having the same geometry and without material deformation; optionally, the gearbox may produce a loaded contact ratio in use that is greater than 200% greater than the theoretical contact ratio; further optionally greater than 400%; still further optionally greater than 500%, and still further optionally greater than 1000%. This may allow the gearbox to not suffer interference due to the gears not contacting undesirably while maintaining an optimal pressure angle, and the gearbox may suffer reduced wear in use due to a high effective contact ratio that effectively spreads the load between the different teeth. The gearbox may also exhibit improved efficiency. The tooth profile displacement may be less than 0.1.

[0016] The internal-external gear pair can have an instantaneous rotation center ICR, which is defined as the point where the radius drawn through the internal gear axis and the external gear axis intersects the pitch circles of the internal gear and the external gear, and all tooth pairs that transmit load between the external gear and the internal gear can be contained within a 20 degree arc centered on the ICR.

[0017] Each of the inner gear and the outer gear may have 40 teeth or more.

[0018] The outer gear may be a first outer gear, the inner gear may be a first inner gear, and the gearbox may further include a second outer gear coupled to the first outer gear and a second inner gear movable relative to the first inner gear, the second outer gear being inside the second inner gear and arranged to engage with the second inner gear. In this way, a differential planetary gearbox may be formed, thereby providing a higher gear ratio.

[0019] The second external gear and the second internal gear can form a second small tooth number difference internal-external gear pair, which has a tooth difference less than one-fifth of the number of gear teeth of the second internal gear; and the second internal gear teeth and the second external gear teeth can have an involute shape, no tooth profile displacement or a tooth profile displacement below a certain value, at which the corresponding working pressure angles of the second external gear teeth and the second internal gear teeth differ by more than 20% of the working pressure angle of the second external gear teeth; and at least one of the second internal gear teeth and the second external gear teeth can have a tooth top height coefficient less than 0.8.

[0020] In general, the first internal-external gear pair and the second internal-external gear pair may be designed substantially similarly except for the tooth difference between the first external gear and the second external gear and / or between the first internal gear and the second internal gear.

[0021] The first external gear may be fixed to the second external gear, and the second internal gear may be arranged to rotate relative to the first internal gear about the internal gear axis.

[0022] Providing an input to drive the first external gear to orbit about the first internal gear axis can produce an output that is a relative rotation between the first internal gear and the second internal gear about the internal gear axis.

[0023] The engagement between the first internal gear and the first external gear may be axially aligned with the engagement between the second internal gear and the second external gear. In other words, the two gear pairs may have an engagement that is aligned in a plane perpendicular to the axes of rotation of the gears. This may reduce gear distortion due to engagement forces and may also provide a more compact gearbox.

[0024] One or both of the first external gear and the second external gear may include a stepped portion so that the teeth of the gear are located in a different plane than the central portion of the gear. This may allow compact packaging of the gears.

[0025] The engagement between the first internal gear and the first external gear and the engagement between the second internal gear and the second external gear may overlap and may further be coplanar with a common plane P1 , which is preferably orthogonal to one or both of the axes of rotation of these gears.

[0026] The gearbox may further include a third internal gear and a third external gear, the third external gear being inside the third internal gear and arranged to engage with the third internal gear, the third external gear may be coupled to the first external gear and the second external gear, such that the second external gear may be between the first external gear and the third external gear, and the third internal gear may be fixed relative to the first internal gear. This may provide a symmetrical gearbox having a greater torque capacity due to the axial balance of the external gears, which may reduce distortion of the external gears.

[0027] All gears may be spur gears, that is, non-helical gears. The teeth of the gears may be substantially parallel to the axis of rotation of the gears. It should be noted that the helix angle and contact ratio are related features considered together in gear design, and the contact ratios described herein may not be repeated for helical gears.

[0028] According to a second aspect of the present invention, a symmetrical gearbox is provided, which includes a first gearbox according to the first aspect and a second gearbox according to the first aspect, each of the gearboxes of the first aspect having multiple external gears and multiple internal gears, wherein the first internal gears are fixed together and the second internal gears are fixed together, and the first gearbox and the second gearbox are arranged symmetrically and coaxially.

[0029] The respective external gears of the first gearbox and the second gearbox may be arranged to orbit around the inner gear axis 180° out of phase with each other. In other words, the respective external gears may be diametrically opposed around the inner gear axis. This may provide a more balanced set of external gears and a more balanced gearbox overall.

[0030] According to a third aspect of the invention, there is provided an internal-external gear pair, the internal-external gear pair comprising any or all of the following features: an internal gear arranged about an internal gear axis and having a first number of internal gear teeth; and an external gear having an external gear axis, the external gear arranged to orbit about the internal gear axis and having a second number of external gear teeth, the external gear arranged to engage with the internal gear teeth; wherein the internal gear teeth and the external gear teeth have respective pressure angles measured at the midpoint of the working portion of the gear teeth, the pressure angles differing by less than 20% of the pressure angle of the external gear teeth; and wherein at least one of the internal gear teeth and the external gear teeth each has a tooth tip height coefficient of less than 0.8. The internal gear teeth and the external gear teeth may have the same pressure angle.

[0031] According to a fourth aspect of the present invention, there is provided an internal-external gear pair, which includes any one or all of the following features: an internal gear, which is arranged around an internal gear axis and has a first number of internal gear teeth; and an external gear having an external gear axis, which is arranged to perform orbital motion around the internal gear axis and has a second number of external gear teeth, and which is arranged to engage with these internal gear teeth; wherein the internal gear teeth and the external gear teeth have a standard module and no tooth profile displacement; and wherein at least one of the internal gear teeth and the external gear teeth each has a tooth top height coefficient less than 0.8.

[0032] According to a fifth aspect of the present invention, a gearbox is provided, which includes any one or all of the following features: a first inner-outer gear pair and a second inner-outer gear pair, the first inner-outer gear pair including a first inner gear and a first outer gear, the first outer gear being arranged inside the first inner gear and engaging with the first inner gear, and the second inner-outer gear pair including a second inner gear and a second outer gear, the second outer gear being arranged inside the second inner gear and engaging with the second inner gear, the first inner gear and the second inner gear being rotatable relative to each other, and the first outer gear and the second outer gear being fixed together, the first outer gear having a step portion so that the engagement of the first inner gear with the first outer gear and the engagement of the second inner gear with the second outer gear at least partially overlap in a common plane.

[0033] This may provide a more compact gearbox and may reduce distortion on the external gears as the deflection between the external gears may be reduced.

[0034] The first internal gear and the second internal gear may rotate about the first axis, the first external gear and the second external gear may orbit about the first axis, and / or the common plane may be perpendicular to the first axis.

[0035] The first external gear and the second external gear may form a compound pinion, and the compound pinion may have a recess for at least partially receiving the second internal gear. The second internal gear may be fully received in the recess.

[0036] The engagement of the first internal gear with the first external gear and the engagement of the second internal gear with the second external gear may be coplanar.In general, the teeth of the first internal gear, the second internal gear, the first external gear and the second external gear may be coplanar.

[0037] The gearbox may further include a crank-shaped input shaft arranged to move the first external gear and the second external gear. The input shaft may be used to apply torque to the gearbox. One of the internal gears may be fixed and one of the internal gears may be movable so that torque can be output from the movable internal gear.

[0038] The gears of the gearbox of the fifth aspect of the invention may have teeth which may include any or all of the features of the teeth described with reference to any other aspect of the invention.

[0039] Any one or more features of the third and / or fourth aspects of the present invention may be combined with any of the above characteristics and features of the first and second aspects of the present invention. Any one or all features of the fifth aspect of the present invention may be combined with any of the above characteristics and features of the first to fourth aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A small-tooth-difference internal-external gear pair exhibiting trochoidal interference is shown;

[0041] Figure 2 A small tooth difference internal-external gear pair exhibiting profile displacement and no trochoidal interference is shown;

[0042] Figure 3 A small tooth difference internal-external gear pair with no profile displacement, low addendum coefficient and no trochoidal interference is shown;

[0043] Figure 4 shows the change of gear tooth profile with changing tooth addendum coefficient;

[0044] Figure 5a to Figure 5c A gear with profile modification is shown with certain geometrical features marked;

[0045] Figures 6a to 6c A gear without profile modification is shown with certain geometrical features marked;

[0046] Figure 7 The instantaneous center of rotation of an internal-external gear pair is shown, showing the teeth that are in contact at one time.

[0047] Figure 8a is a schematic diagram showing a first gear box according to an embodiment of the present invention;

[0048] Figure 8b is a cross-sectional view showing a first gear box according to an embodiment of the present invention;

[0049] Fig. 9 is a schematic diagram showing a second gear box according to an embodiment of the present invention;

[0050] Fig.10a is a schematic diagram showing a third gearbox according to an embodiment of the present invention;

[0051] Fig.10b is a sectional view showing a third gear box according to an embodiment of the present invention; and

[0052] Fig.11 is a schematic diagram showing a fourth gear box according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] When producing a high ratio gearbox or torque converter, an internal-external gear pair with a small tooth difference can be used. Such a gear pair can be used in a two-stage gear pair to produce a high transmission ratio gearbox that can convert a relatively high speed, low torque input into a low speed, high torque output. The efficiency of such a gearbox can vary depending on how the tooth profile is arranged. In addition, in some applications, the ability to drive a high transmission ratio gearbox in a reverse sense (i.e., applying a low speed, high torque input to the output end to produce a relatively high speed, low torque output at the input end) may be important. This can be referred to as the reverse drive capability of the gearbox. Minimizing losses in the gearbox is important for achieving the reverse drive capability and overall efficiency of the gearbox in either drive direction. The inventors have confirmed that the long-standing standard approach to gear design in a small tooth difference internal-external gear pair may give results that are not conducive to the overall performance of the gear pair.

[0054] When providing such a gearbox having an internal gear and an external gear with a relatively small difference between the number of teeth on each gear, the problem may arise that the teeth of the two gears may interfere, such as Figure 1 shown.

[0055] Figure 1 There is shown a gearing arrangement 10 having an internal gear 12 with 47 teeth 14 and a pitch circle C1 arranged to engage with external gear teeth 18 of an external gear 16 , and an external ring gear 16 with 50 external teeth 18 and a pitch circle C2 .

[0056] It will be appreciated that a variety of different terms may be used for these gears. The internal gear 12 may be referred to as a pinion, spur gear, or external gear because the gear teeth face outward. Similarly, the external gear 14 may be referred to as an annular gear, ring gear, or internal gear because the gear teeth face inward. Both the internal gear 12 and the external gear 14 may be straight-cut gears, i.e., non-helical gears.

[0057] The inner gear 16 is centered about the inner gear axis A2, and the outer gear 12 is centered about the outer gear axis A1. It should be understood that in suitable arrangements, the outer gear 12 can orbit about the inner gear axis A2 as the outer gear 12 rotates. In some arrangements, the outer gear axis A1 and the inner gear axis A2 can remain stationary, and the outer gear 12 and the inner gear 16 can each rotate about their respective axes A1, A2. The kinematic configuration of a gearbox using an inner-external gear pair is discussed in further detail with respect to subsequent figures.

[0058] In the engagement region 24, the teeth 14 of the outer gear 12 engage the inner gear teeth 18. In this region, the flanks of the respective teeth 14, 18 contact each other, thereby transmitting torque between the two gears 12, 16.

[0059] Figure 1 The teeth in are designed with a standard module and involute (the standard gear module is based on the well-known Japanese Industrial Standard JIS B 1701 (1973), the gear details of which are included below for reference). The standard gear teeth will also have a nominal pressure angle of 20°. JIS B 1701 specifies the tooth profile and dimensions of general involute spur gears and helical gears. The dimensions of the teeth are expressed in module m. The standard values ​​of module m are given in Table 1 below in mm. Preferably, the standard module is the module of any one of the series numbers 1, 2 and 3.

[0060]

[0061] Table 1. Standard values ​​of modulus

[0062] The tooth profile curve should be an involute curve with a standard pressure angle α0 of 20° and the dimensions should be as shown in Table 2. However, no tooth profile modification is specified in this standard. Other standard tooth profiles may have pressure angles including 25° and 14.5°, 20°, 22.5°, 25° and 30°.

[0063]

[0064] Table 2. Dimensions of involute spur and helical gears

[0065] Based on the working pressure angle α w, the nominal pressure angle α (nominal pressure angle according to recognized standards - usually 20°, and other examples provided above), the involute function inv about the relevant angle, and the number of teeth z1 of the internal gear and the number of teeth z2 of the external gear to calculate the tooth profile modification coefficient. For helical gears, the helix angle β can also be used. The following equation can be used to determine the tooth profile modification coefficient x1 of the first gear, and it should be understood that the rearrangement can be used to determine the tooth profile modification coefficient x2 of the second gear.

[0066]

[0067] The center distance a of an internal-external gear pair can be determined using the following equation, where m is the gear module and y is the center distance increment factor.

[0068]

[0069] The center distance increment factor can then be determined by the following equation.

[0070]

[0071] Using the standard gears described may result in trochoidal interference because the tips of the outer gear teeth 14 may contact the tips of the inner gear teeth 18 outside the area 24 where contact is desired. This can be Figure 1 The trochoidal interference can be fatal to the gearbox and is Figure 1 In the case shown, it may be prevented at all that a gearbox can be constructed.

[0072] In order to avoid trochoidal interference, a common solution is to modify the gear tooth profile. Figure 2 An example of a profile-shifted gear tooth profile for avoiding trochoidal interference is shown in . The gear transmission arrangement 30 shows an external gear 32 having 47 outwardly facing gear teeth 34 arranged about an external gear axis A3.

[0073] On the outside of the outer gear 32 (which may also be referred to as a pinion gear) there is an inner gear 36 . The inner gear 36 has inwardly facing gear teeth 38 that are arranged to contact the outwardly facing gear teeth 34 in a contact area 44 .

[0074] Conventional gear design may involve selecting the center distance between the two gears (i.e., the distance between their axes) and the number of teeth on each gear, which is determined by the desired gear ratio. In the case of two spur gears, the pitch diameters of the respective gears will conventionally be selected so that the sum of the pitch diameters is twice the center distance, and the ratio of the two pitch diameters will be the same as the ratio of the number of teeth (i.e., the gear ratio). In the case of an internal-external gear pair, the difference in the pitch diameters may be twice the center distance of the gears. The pitch diameters determined in this way may be described as nominal pitch diameters.

[0075] Profile modification of a gear involves moving the cutting tool closer to or further away from the gear during cutting to adjust the working pitch diameter of the gear. Thus, a profile modified gear may have a working pitch diameter that is different from its nominal pitch diameter.

[0076] Since the same cutting tool can be used, the base circle of the involute describing the tooth flank remains the same during the profile modification process. However, the profile modification effectively changes the portion of the involute describing the tooth flank, thereby moving this portion of the involute closer to or further away from the base circle.

[0077] It can be seen that there is no trochoidal interference between the outer gear teeth 34 and the inner gear teeth 38. This is due to the profile shift that has been applied to the gear teeth. Profile shifting involves changing the standard gear cutter so that the involute shape of the gear teeth remains the same and the base circle of the involute remains in the same position. Profile shifting will therefore change the pitch circle of the gear: from the nominal pitch circle with the standard profile to the shifted profile. However, profile shifting of the gear increases the operating pressure angle of the gear and one of the effects is a reduction in gear efficiency.

[0078] therefore, Figure 2 The profile-modified gear has an operating pressure angle that is 20° different from the nominal pressure angle of the standard involute profile (in Figure 2 In this case, the working pressure angle is 37.42°). Figure 2 The profile-modified teeth also have a standard addendum factor of 1. Higher operating pressure angles may result in reduced bearing life and lower gearbox efficiency due to the higher sliding speeds between teeth 34 and 38 when loaded in meshing area 44.

[0079] Figure 3A gear transmission arrangement 100 is shown which is intended to avoid the problem of trochoidal interference while maintaining high efficiency. The gear transmission arrangement 100 has an internal gear or ring gear 106. The example shown has 50 inwardly facing gear teeth 108, but other tooth counts are contemplated. The example also has an external gear or pinion 102 having 47 outwardly facing gear teeth 104, but other external gears having a small difference in tooth count from the internal gear 106 are contemplated. In general, the above reference Figure 1 The interference problem occurs when the inner-outer gear pair is constructed with a small difference in the number of teeth between the inner gear and the outer gear, for example, less than 5 teeth, or about one fifth of the number of teeth of the inner gear.

[0080] The inner gear 106 is arranged about the inner gear axis A6, and the outer gear 102 is arranged about the outer gear axis A5. It should be understood that the outer gear 102 can rotate and orbit about the outer gear axis A6 while the inner gear 106 can remain stationary.

[0081] Although Figure 3 The gears shown in FIG. 1 have a specific number of teeth, with the inner gear 106 having 50 teeth 108 and the outer gear 102 having 47 teeth 104, but it should be understood that the outer and inner gears may have any number of teeth with a relatively small difference between the number of teeth. For example, the difference in the number of teeth may be less than 5, such that the inner gear 106 has less than 5 more teeth than the outer gear 102. Alternatively, the difference may be considered as a percentage, and the difference in the number of teeth may be less than 20% or one-fifth of the number of teeth of the inner gear, optionally less than 10% or one-tenth of the number of teeth of the inner gear.

[0082] In the gear transmission arrangement 100, trochoidal interference is avoided by modifying the tooth addendum coefficient. The gears do not exhibit a profile shift, which can be determined by the fact that the pressure angle at a point M located in the middle of the effective tooth profile (measured as the angle between the normal to the tooth flank and the tangent to a circle centered at the center of the gear and passing through this same point M) is the same for both gears. The pressure angle of the two gears at point M can vary by up to 20% without significantly affecting the operating principle that does not provide a profile shift. In some cases, the lack of profile shift can also be determined due to the use of a standard module and the pressure angle of the gear teeth being the standard pressure angle. The standard module can be as referenced above Figure 1and as defined in Japanese Industrial Standard JIS B1701 (1973). Specifically, the tooth top height coefficients of both the outer gear tooth 104 and the inner gear tooth 108 are less than 0.8. However, the tooth top height coefficients may be different on the outer gear tooth 104 and the inner gear tooth 108. This may be referred to as an asymmetric tooth top height coefficient. Typically, the sum of the tooth top height coefficients may be less than 1.6 to avoid trochoidal interference. Further, the sum of the tooth top height coefficients may be greater than 0.6, because a smaller tooth top height coefficient may result in excessive surface pressure under load, which is undesirable. Therefore, the sum of the tooth top height coefficients of the outer gear tooth and the inner gear tooth may be between 0.6 and 1.6. More preferably, the sum of the tooth top height coefficients is between 1 and 1.6.

[0083] In existing gear design technology and related literature, it has long been generally believed that reducing the tooth height coefficient in a gear pair to below 0.8 will undesirably reduce the contact ratio. The contact ratio is the average number of gear teeth in which one gear is in contact with the teeth of another gear at any one time. Therefore, with a contact ratio below 1, the gear transmission arrangement has a period of time when no gears are in contact, which means that the gears cannot actually mesh properly, that is, in a smooth and efficient manner. This can lead to inconsistent torque transfer between gears, jitter, and damage to the gear teeth. For these reasons, contact ratios below 1 are generally considered undesirable, and common practice and gear design literature does not teach contact ratios below 1.

[0084] exist Figure 3 In an arrangement of, the theoretical contact ratio (i.e. the contact ratio calculated based on the undeformed teeth in their idle state) will be less than 1. However, due to the deformation of the teeth under load, i.e. when the gears are transmitting torque, the contact ratio can increase to 1 or can increase to more than 1. This contact ratio can be referred to as the loaded contact ratio. Therefore, although the gearbox may initially appear to be non-operable, it may be operational in actual circumstances. The skilled person will readily understand deformation under load, at least in the limiting case, which is a case where the strain is below the limiting tensile strain. For most gearboxes with a contact ratio below 1, the contact ratio will not increase to 1, even when the material is deformed to the maximum possible length without causing plastic deformation or failure. However, in the present case, due to the elastic deformation of the gear teeth, the contact ratio can change from below 1 to above 1.

[0085] Figure 4a and 4b The shape of the gear teeth is shown with varying tooth height coefficient a for both the internal gear teeth 108 and the external gear teeth 104. c Changes from Figure 4a and 4bIt can be seen that the base and pitch circles of the involute remain constant, as does the module of the gear tooth. In this way, the pressure angle is also maintained at a constant nominal pressure angle. Effectively, the reduction in the addendum factor truncates the tooth by removing the top portion of the tooth. Figure 4b As shown, contact with the tooth tops can thus be avoided without changing the desired pressure angle provided by the tooth shape.

[0086] The addendum height of a gear tooth is the distance the gear tooth protrudes beyond the pitch circle, which can be found in a c = 0. Addendum coefficient a c is a dimensionless number obtained by dividing the tooth addendum by the module of the tooth. Although the conventional tooth addendum coefficient is 1, it can be seen that a reduction in the tooth addendum coefficient can reduce the likelihood of interference between the tooth tips of the gear teeth. Therefore, it may be advantageous to design a gear with a tooth addendum coefficient below 0.8 or optionally even lower.

[0087] supply Figures 5a to 6c This is to more clearly illustrate how the tooth profile displacement can be determined.

[0088] Figure 5a Shows Figure 2 The gear with the tooth profile modified is in the meshing area 44. The working part of the inner gear tooth 38 is from point V I and U I Define. I is a point on the inner gear tooth 38 that is on the outer radius of the outer gear 32 and therefore contacts the tooth tip of the outer gear tooth 34. I is the tooth tip of the inner gear tooth 38. Similarly, for the outer gear tooth 34, a point U is defined. E and V E .U E is the tooth top of the external gear tooth 34, and V E V is the position on the outer gear tooth 34 where the tooth top contacts the inner gear tooth 38. E Also when the gear teeth 34 and 38 are in the meshing region, U I Therefore, it should be understood that the only part of the tooth flanks that touch each other is the working part of the tooth, as indicated by point U I 、V I , U E and U E Limited.

[0089] Go to Figure 5b , another point M is defined on the internal gear 36 I . M I It's U I With V I The midpoint between. Pressure angle α I The midpoint is defined as a circle C centered on the gear axis.M Tangent T M With M I Normal line N of tooth flank M For completeness, circle C is also shown. M The radius R M Angle α I Can be described as the working pressure angle as it is measured in the middle of the working part of the tooth.

[0090] Figure 5c The equivalent point on the outer gear 32 is shown. Another point M is defined E . M E It's U E With V E The midpoint between. Pressure angle α E The midpoint is defined as a circle C centered on the gear axis. M Tangent T M With M E Normal line N of tooth flank M For completeness, circle C is also shown. M The radius R M Angle α E Can be described as the working pressure angle as it is measured in the middle of the working part of the tooth.

[0091] As described above, by comparing the corresponding midpoints M of the corresponding working parts of the corresponding internal gear and the external gear I and M E The pressure angles of the two gears measured at , show that the pressure angles differ by more than 20% of the pressure angle of the outer gear. Therefore, these gears exhibit profile displacement.

[0092] Figure 6a Shows Figure 3 The gears are in meshing area 110, where there is no profile displacement of the gears. The working part of the inner gear teeth 108 is defined by point V. I and U I Define. I is a point on the inner gear tooth 108 that is on the outer radius of the outer gear 102, so this point contacts the tooth top of the outer gear tooth 104. I is the tooth tip of the inner gear tooth 108. Similarly, for the outer gear tooth 104, a point U is defined. E and V E .U E is the tooth top of the external gear tooth 104, and V E is the location on the outer gear tooth 104 that contacts the tooth top of the inner gear tooth 108. Therefore, it should be understood that the only portion of the tooth flanks that contact each other is the working portion of the tooth, as indicated by point U I 、VI , U E and U E The area between is limited.

[0093] Go to Figure 6b , another point M is defined on the internal gear 106 I . M I It's U I With V I The midpoint between. Pressure angle α I The midpoint is defined as a circle C centered on the gear axis. M Tangent T M With M I Normal line N of tooth flank M For completeness, circle C is also shown. M The radius R M Angle α I Can be described as the working pressure angle as it is measured in the middle of the working part of the tooth.

[0094] Figure 6c An equivalent point on the outer gear 102 is shown. Another point M is defined E . M E It's U E The midpoint between VE and pressure angle α E The midpoint is defined as a circle C centered on the gear axis. M Tangent T M With M E Normal line N of tooth flank M For completeness, circle C is also shown. M The radius R M Angle α E Can be described as the working pressure angle as it is measured in the middle of the working part of the tooth.

[0095] As from Figure 6b and 6c As can be seen in the figure, the pressure angles at the midpoints of the working parts of the internal and external gear teeth are the same.

[0096] As can be seen from the above explanation, the following becomes clear. The presence of tooth profile displacement can be detected by detecting the difference between the pressure angles of the internal gear teeth and the external gear teeth. The pressure angle of the internal gear teeth at the midpoint of the working part of the internal gear teeth can be determined. The pressure angle of the external gear teeth at the midpoint of the working part of the external gear teeth can be determined. The difference between the determined pressure angles can be determined. The difference between the working pressure angles of the internal gear and the external gear can be determined. The difference in pressure angles can be determined at the corresponding midpoints of the working parts of the corresponding internal gear teeth and external gear teeth.

[0097] With the present disclosure, the difference in the measured pressure angle between the internal gear teeth and the external gear teeth is advantageously less than 20% of the pressure angle of the pressure angle of the internal gear teeth or the external gear teeth. This indicates the degree of tooth profile displacement that has the least effect on the efficiency of the gear pair. It is further advantageous to limit the difference in pressure angle to lower values, such as 15%, 10%, or 5% or less. These lower values ​​further limit the impact on the efficiency of the gear pair due to tooth profile displacement and / or pressure angle differences.

[0098] Figure 7 The diagram with the label l is shown. α Line of action of the gearbox 100. α Describes the gear teeth that are in contact and transferring load at any time. Assuming that the internal gear 108 is fixed, the line of action l α The instantaneous center of rotation ICR of the gearbox is the point on the pitch circle about which the external gear 104 can be said to rotate. The ICR is the point at the intersection of the line described by the two gear axes and one or the other of the pitch circles. It is also the location where these pitch circles intersect. Describes the line of action l α The angle defined by the axis of the outer gear is preferably less than 20°, as indicated by the maximum action angle. It is preferred that the load on the gearbox be within this range to avoid efficiency losses due to friction.

[0099] Figures 8a to 11 A gearbox is shown that can implement various forms of gear teeth. In particular, one or more features of the internal-external gear pair described in the present disclosure can be advantageously implemented in the gearbox shown.

[0100] Figure 8a and Figure 8b Schematic and cross-sectional views of a first gearbox 200 are shown, respectively, in which the inner-outer gear pairs described in this specification can be advantageously implemented. The illustrated example includes two inner-outer gear pairs: a first gear pair 204 and a second gear pair 210. These gear pairs can be the same as those described above with reference to Figure 3 Gear pairs of the type described, and in particular, the teeth of the gears of these gear pairs can have no profile modification or a small profile modification, and a tooth top height coefficient below 0.8, so that the operating pressure angle of the gear teeth does not exceed more than 20% of the nominal pressure angle of these gear teeth without applying the profile modification.

[0101] The gearbox has a first inner-external gear pair 204 having an outer pinion 206 and an inner ring gear 208. The gearbox 200 also has a second inner-external gear pair 210, which in turn includes an outer pinion 214 and an inner ring gear 216. The outer pinion 214 of the second inner-external gear pair 210 is rigidly fixed to the outer pinion 206 of the first inner-external gear pair 204. Therefore, the two outer pinions 214, 206 will orbit around the inner gear axis A7 at the same speed, and will also have the same angular velocity around their own axis A8. The two pinions 206, 214 are combined to form a combined pinion 212.

[0102] The gearbox 200 has an input shaft 202 arranged to receive torque from a drive source such as a motor. The input shaft 202 is shaped as a crank so that the crank receives torque about the gearbox axis A7 (i.e., the axis of the inner gears 208, 216) and provides a force deviating from the gearbox axis to the outer pinion gear, which is a linear force passing through the outer gear axis A8. The input shaft 202 is supported by a first bearing arrangement 222 for rotation about the gearbox axis and is coupled to the outer pinion gear via a bearing 224 so that the outer pinion gear can rotate about the portion of the input shaft passing through the outer gear. These outer gears are also engaged with an inner ring gear so that the outer pinion gears 206, 214 (i.e., the combined pinion gear 212) and the deviated portion of the input shaft 202 can orbit together around the inner gear axis A7. The input shaft also has a counterweight 203 to balance the off-axis load of the deviated portion.

[0103] The respective gear ratios of the first inner-outer gear pair 204 and the second inner-outer gear pair 210 may have a small difference. Such a small difference may be achieved in a variety of ways, such as by having the same tooth difference between the inner gear and the outer gear, but having a different total number of teeth in the inner gear and / or the outer gear of the respective gear pair. In other examples, the amount of tooth difference in each gear pair may be varied to achieve a different gear ratio. In one example, the inner gear 208 and the outer gear 206 of the first inner-outer gear pair 204 may have 60 teeth and 57 teeth, respectively, and the inner gear 216 and the outer gear 214 of the second inner-outer gear pair 210 may have 90 teeth and 87 teeth, respectively.

[0104] The total output of the gearbox 200 can be realized as the relative difference in rotation between the two internal gears 208 and 216 about a common axis. One of the internal gears 208, 216 can be fixed, i.e., remain stationary, and the other of the internal gears 208, 216 can be rotatable and used as an output gear. The two gears can be coupled via a bearing 226. The fixation of the internal gear 208 is demonstrated in FIG5 by the internal gear 208 of the first inner-external gear pair 204 being connected to ground, thereby indicating that the internal gear is the reference gear. Since one of the internal gears remains stationary and the two inner-external gear pairs have similar gear ratios, a high gear ratio can be achieved on the gearbox. Although the internal gear 216 of the second inner-external gear pair 210 is shown as being coupled to a bearing close to the input shaft, it should be understood that the output can be taken at the opposite axial end of the gearbox and any suitable bearing arrangement can be used.

[0105] In general, the gearbox portions described as "fixed," "input," and "output" are described as such only to reflect the conventional use of gearboxes, and it should be understood that considerations regarding input, output, and fixed portions may be a matter of reference frame, and any portion labeled, for example, "fixed" may alternatively be used as "input" or "output." In the context of the illustrated example, the drive input provided as the difference in rotation between the input shaft 202 and the internal gear 208 produces an output that is the relative difference in rotation between the internal gear 216 and the internal gear 208.

[0106] Fig. 9 Another gearbox 300 is shown, which has a symmetrical arrangement. The symmetrical gearbox 300 has a first inner-outer gear pair 304 and a second inner-outer gear pair 310, each gear pair having a corresponding inner gear 308, 316 and outer gear 306, 314, which gears can be substantially similar to those described above with reference to FIG. 5. The outer gears can orbit around the inner gear axis A9 and can rotate around their own outer gear axis A10, about which the inner gears are arranged. The gearbox 300 further includes a third inner-outer gear pair 320, which includes an outer gear 324 and an inner gear 326. The inner-outer gear pair 320 can be substantially similar to the first inner-outer gear pair 304, having the same gear ratio. The outer gear 324 of the third inner-outer gear pair 320 can be rigidly fixed to the other outer gears 306, 314, so that the three gears orbit and rotate together and form a combined pinion 312.

[0107] A symmetrical arrangement may be preferred because it may prevent or reduce twisting of the central outer gear due to the axially opposed inner gears providing balancing forces to the outer gear about an axis perpendicular to the gearbox axis.

[0108] Further, the input shaft 302 may have bearings at both axial ends, thereby avoiding a cantilever arrangement due to reaction forces from the planetary gears 306 , 314 , 324 . This may strengthen the input shaft 302 .

[0109] Fig.10a and Fig.10b A third gearbox arrangement 400 is shown which is substantially similar to two diametrically opposed and axially mirrored copies of the gearbox 200 of FIG. 5 .

[0110] The gearbox 400 has two separate planetary gears 412, 422, each having two external gears rigidly fixed together. The first planetary member 412 has external gears 406, 414 arranged about a first external gear axis A12, which are arranged to engage with corresponding internal gears 408, 416 so that the external gears 406, 414 orbit about the internal gear axis A11. The gears 406, 408, 414, 416 form first and second inner-external gear pairs 404, 410. The second planetary member 422 has a third external gear 424 and a fourth external gear 434 arranged about a second external gear axis A13. The third external gear 424 and the fourth external gear 434 are arranged to engage with corresponding internal gears 426, 436 and orbit about the internal gear axis A12. The gears 424, 426, 434, 436 form third and fourth inner-external gear pairs 420, 430.

[0111] It should be understood that the first external gear 406 and the fourth external gear 434 can be identical, and the second external gear 414 and the third external gear 424 can be identical. In some cases, the first external gear 406, the second external gear 414, the third external gear 424, and the fourth external gear 434 can all be identical. The first external gear 408 and the fourth external gear 436 can also be identical, and the second internal gear 416 and the third internal gear 426 can be identical. In some cases, the second internal gear 416 and the third internal gear 426 can be integrally formed with common gear teeth and can be mounted on bearings 452 to rotate relative to the first internal gear 408 and the fourth internal gear 436. Overall, the first inner-external gear pair 404 and the fourth inner-external gear pair 430 can each have a small gear ratio difference with the second inner-external gear pair 410 and the third inner-external gear pair 420, so that a differential planetary gearbox 400 can be provided overall.

[0112] The gearbox 400 has an input shaft 402 that is crank-shaped so that it has two diametrically opposed portions, each portion being offset from the inner gear axis A11 by the same distance so that each offset portion is located along the axis of the corresponding outer gear A12, A13. Each of these offset portions is coupled to a corresponding one of the first planetary member 412 and the second planetary member 422 via a bearing so that the input shaft 402 applies a linear force offset from the inner gear axis A11 to these planetary members.

[0113] In this way, a symmetrical gearbox 400 with a centered output and improved balance may be provided.

[0114] Fig.11 A gearbox 201 is shown having a substantially similar Figure 8a and Figure 8b Features of the gearbox 200. For the sake of brevity, similar features are numbered similarly and are not described again here.

[0115] In the gearbox 201, the outer pinion 214 of the second inner-outer gear pair 210 has a stepped portion 214a that allows the outer pinion 214 to be located in two separate axial planes perpendicular to one or more rotational axes of the combined gear pair 212. In particular, the engagement of the second inner-outer gear pair 210 and the engagement of the first inner-outer gear pair 204 overlap or are coplanar with at least a common plane P1, which is perpendicular to the rotational axes of the gears A7, A8. The inner gear 208 is at least partially located in a recess or cavity of the combined pinion 212. This can allow the gear pair 204 to be at least partially arranged in the outer gear 214. This can further allow the gear pair 204 to be partially or completely positioned in the gear pair 210.

[0116] By engaging the first inner-external gear pair 204 and the second inner-external gear pair 210 in a common plane, distortion of the combined pinion 212 may be reduced. Further, a more compact gearbox 201 may be provided because the axial extent of the gearbox 201 may be reduced.

[0117] Fig.11 The gearbox 201 shown can have any type of gear teeth. In some examples, Fig.11 The gearbox 201 may have a Figures 1 to 7 And special reference Figure 3 One or more features of the gear teeth described. These gear teeth may have reference Figure 3 Any characteristic of a gear tooth described, such as a tooth addendum coefficient within a defined range and / or a tooth profile variation within a defined range.

[0118] In any or all of the above gearbox arrangements, the gears may have the above reference Figures 1 to 7 Any of the Figure 3 Specifically, these gears can exhibit small profile variations and low addendum coefficients, as described above.

Claims

1. A gearbox comprising an inner-outer gear pair with a small tooth number difference, the inner-outer gear pair comprising: an internal gear disposed about an internal gear axis and having a first number of internal gear teeth; as well as an external gear having an external gear axis, the external gear being arranged to orbit about the internal gear axis and having a second number of external gear teeth, the external gear being arranged to engage with the internal gear teeth; wherein the difference in the number of small teeth between the number of teeth of the first external gear and the number of teeth of the second internal gear is less than one fifth of the number of teeth of the internal gear; and wherein the internal gear teeth and the external gear teeth have an involute shape, have no profile displacement or have a profile displacement below a value at which the respective operating pressure angles of the external gear teeth and the internal gear teeth differ by more than 20% of the operating pressure angle of the external gear teeth; and Wherein, at least one of the internal gear teeth and the external gear teeth has a tooth height coefficient less than 0.

8.

2. The gearbox according to claim 1, wherein: The theoretical contact ratio of this inner-outer gear pair calculated for a gearbox with the same geometry and without material deformation is less than 1.

3. The gearbox according to claim 1 or 2, wherein: At least one of the internal gear teeth and the external gear teeth has a tooth height coefficient less than 0.7, optionally less than 0.

6.

4. A gearbox as claimed in any preceding claim, wherein: At least one of the internal gear teeth and the external gear teeth has a tooth height coefficient greater than 0.3, optionally greater than 0.

5.

5. A gearbox as claimed in any preceding claim, wherein: The tooth profile modification coefficient of the internal gear is less than 0.1, optionally less than 0.05, optionally less than 0.04, further optionally less than 0.03, still further optionally less than 0.02, further further optionally less than 0.01, and still further optionally 0.

00.

6. A gearbox as claimed in any preceding claim, wherein: The theoretical contact ratio of the external-internal gear pair calculated for a gearbox with the same geometry and without material deformation is less than 0.8, optionally less than 0.6, and further optionally less than 0.

4.

7. A gearbox as claimed in any preceding claim, wherein: The pitch diameter of the outer gear is at least half the pitch diameter of the inner gear.

8. A gearbox as claimed in any preceding claim, wherein: The loaded contact ratio generated by the gearbox during use is greater than 100% greater than the theoretical contact ratio calculated for a gearbox having the same geometry and no material deformation; optionally, the loaded contact ratio generated by the gearbox during use is greater than 200% greater than the theoretical contact ratio; further optionally greater than 400% greater, still further optionally greater than 500% greater, and still further optionally greater than 1000% greater.

9. A gearbox as claimed in any preceding claim, wherein: The sum of the addendum coefficients of the internal gear teeth and the external gear teeth is less than 1.

6.

10. A gearbox as claimed in any preceding claim, wherein: The external-internal gear pair has an instantaneous center of rotation ICR, which is defined as the point where a radius drawn through the internal gear axis and the external gear axis intersects the pitch circles of the external gear and the internal gear, and wherein all tooth pairs that transfer load between the external gear and the internal gear are contained within a twenty degree arc centered on the ICR.

11. A gearbox as claimed in any preceding claim, wherein: Each of the internal gear and the external gear has 40 teeth or more.

12. A gearbox as claimed in any preceding claim, wherein: The inner gear and the outer gear have a helix angle of 0°.

13. A gearbox as claimed in any preceding claim, wherein: The external gear is a first external gear, the internal gear is a first internal gear, and wherein the gearbox further includes a second external gear connected to the first external gear and a second internal gear movable relative to the first internal gear, the second external gear being inside the second internal gear and being arranged to engage with the second internal gear.

14. The gearbox of claim 13, wherein: The second external gear and the second internal gear form a second small tooth difference internal-external gear pair, the gear pair having a tooth number difference that is less than one fifth of the fifth gear tooth number of the second internal gear; and wherein the second internal gear teeth and the second external gear teeth have an involute shape, have no profile displacement or have a profile displacement below a value at which the respective operating pressure angles of the second external gear teeth and the second internal gear teeth differ by more than 20% of the operating pressure angle of the second external gear teeth; and Wherein, at least one of the second internal gear teeth and the second external gear teeth has a tooth height coefficient less than 0.

8.

15. A gearbox according to claim 13 or 14, wherein: The first external gear is fixed to the second external gear, and the second internal gear is arranged to rotate relative to the first internal gear about the internal gear axis.

16. A gearbox according to any one of claims 13 to 15, wherein: Providing an input to drive the first external gear to orbit about the first internal gear axis will produce an output that is a relative rotation between the first internal gear and the second internal gear about the internal gear axis.

17. A gearbox according to any one of claims 13 to 16, wherein: The engagement between the first internal gear and the first external gear and the engagement between the second internal gear and the second external gear overlap with a common plane perpendicular to their rotational axes.

18. The gearbox according to any one of claims 13 to 16, further comprising a third internal gear and a third external gear, the third external gear being inside the third internal gear and being arranged to engage with the third internal gear, in, The third external gear is coupled to the first external gear and the second external gear so that the second external gear is between the first external gear and the third external gear, and Wherein, the third internal gear is fixed relative to the first internal gear.

19. A symmetrical gearbox comprising a first gearbox according to any one of claims 13 to 17 and a second gearbox according to any one of claims 13 to 17, in, The first internal gears are fixed together and the second internal gears are fixed together, and The first gear box and the second gear box are arranged symmetrically and coaxially.

20. The symmetrical gearbox of claim 19, wherein: The respective external gears of the first and second gearboxes are arranged to orbit around the internal gear axis 180° out of phase with each other.

21. An internal-external gear pair, comprising: an internal gear disposed about an internal gear axis and having a first number of internal gear teeth; as well as an external gear having an external gear axis, the external gear being arranged to orbit about the internal gear axis and having a second number of external gear teeth, the external gear being arranged to engage with the internal gear teeth; wherein the internal gear teeth and the external gear teeth have respective pressure angles measured at the midpoint of the working portions of the gear teeth that differ by less than 20% of the pressure angle of the external gear teeth; and Wherein, at least one of the internal gear teeth and the external gear teeth has a tooth height coefficient less than 0.

8.

22. The gear pair of claim 21, wherein: The internal gear teeth and the external gear teeth have the same respective pressure angles measured at respective midpoints of respective working portions of the gear teeth.

23. An internal-external gear pair, comprising: an internal gear disposed about an internal gear axis and having a first number of internal gear teeth; as well as an external gear having an external gear axis, the external gear being arranged to orbit about the internal gear axis and having a second number of external gear teeth, the external gear being arranged to engage with the internal gear teeth; wherein the internal gear teeth and the external gear teeth have a standard module and no profile variation; and Therein, at least one of the internal gear teeth and the external gear teeth each has a tooth addendum coefficient less than 0.8.

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