Patent Application
20200318720
The invention relates to an actuator for a link mechanism for an internal combustion engine and a wave gear speed reducer.
A well-known actuator for a link mechanism for an internal combustion engine is, for example, the actuator disclosed in a Patent Literature 1. This actuator for a link mechanism for an internal combustion engine includes a control shaft of a variable compression ratio mechanism and an actuator which changes a rotational position of the control shaft. The actuator is equipped with a wave gear speed reducer which reduces and transmits the rotation speed (revolution speed) of an electric motor to the control shaft. The technology disclosed in a Patent Literature 2 is related to a well-known wave gear speed reducer. This wave gear speed reducer, invented by C. W. Musser, is so configured that a planetary gear which is one of KHV planetary gears is bent into an elliptical shape and comes into engagement at a major axis end, and that a major axis rotation is one system of the apparatus.
The wave gear speed reducer comprises a thin-walled cylinder-like flexible external gear and a rigid internal gear whose number of teeth is an even multiple of the number of teeth of the flexible external gear. The flexible external gear and the rigid internal gear are coaxially arranged. The wave gear speed reducer is bent into an elliptical shape by a wave generating device fitted in an inside of the flexible external gear. Although the ellipse's major axis rotates in synchronization with a rotating motion inputted into the wave generating device, the flexible external gear remains deformed while being provided with degrees of rotational freedom in the circumferential direction and therefore makes a deforming motion while changing the position of engagement with the rigid internal gear on the ellipse's major axis. During the deforming motion, due to the tooth number difference between the flexible external gear and the rigid internal gear, a circumferential relative position between the rigid internal gear and the flexible external gear changes by the difference. The difference is outputted as speed reduction rotation.
PTL 1: Japanese Unexamined Patent Application Publication (Kokai) No. 2012-251446
PTL 2: U.S. Pat. No. 2,906,143
In the wave gear speed reducer, gear teeth keep changing the engagement position by making a relative motion in a radial direction of the gears while being in contact with one another. It is therefore important to consider the tooth profile of the flexible external gear and that of the rigid internal gear with a view to the relative motion of the teeth. The wave gear speed reducer disclosed in the Patent Literature 2 is capable of constantly maintaining teeth engagement at the major axis end and transmitting the rotation at the same time. In view of this, tooth profiles have been considered in pursuit of high positioning accuracy while increasing engagement area to improve high load torque performance. To that end, tooth contact area has been increased to enlarge the engagement area by designing tooth profiles so that the flexible external gear and the rigid internal gear are equal in tooth sectional curvature at their contact point, regardless of changes in position of a tooth contact point due to the relative motion, or by another way. On the other hand, in spite of the fact that the increase of the tooth contact area makes input efficiency relatively low when the gears rotate under a loaded condition, there has been no consideration of tooth profiles designed for driving efficiency.
One embodiment of the invention has been made in view of the foregoing issue. It is an object of the invention to provide an actuator for a link mechanism for an internal combustion engine and a wave gear speed reducer, which improve both input efficiency and driving efficiency.
To achieve the object, the one embodiment of the invention includes a wave gear speed reducer in which external teeth of the flexible external gear are partially engaged with internal teeth of an internal gear portion while the flexible external gear is bent into an elliptical shape by a wave generating device which is rotated by an input shaft, and an engaging part between the flexible external gear and the internal gear portion is rotated. According to the wave gear speed reducer, the external teeth are larger in curvature than the internal teeth in a contact portion between the internal and external teeth.
The one embodiment of the invention thus can reduce contact area of the internal and external teeth and improve input efficiency, driving efficiency, and torque resistivity of the wave gear speed reducer.
The first control shaft 10 extends in parallel with the crankshaft 4 extending in a direction of a cylinder row located inside the internal combustion engine. The first control shaft 10 includes a first journal portion 10a rotatably supported by an internal combustion engine body, a control eccentric shat portion 10b to which the lower end portion of the first control link 7 is rotatably coupled, and an eccentric shaft portion 10c to which one side portion 12a of the second control link 12 is rotatably coupled. A first arm portion 10d has one end coupled to the first journal portion 10a and the other end coupled to the lower end portion of the first control link 7. The control eccentric shaft portion 10b is disposed in a position which is eccentric to the first journal portion 10a by predetermined amount. A second arm portion 10e has one end coupled to the first journal portion 10a and the other end coupled to the one side portion 12a of the second control link 12. The eccentric shaft portion 10c is disposed in a position eccentric to the first journal portion 10a by predetermined amount. The second control link 12 has the other side portion 12b to which one end of an arm link 13 is rotatably coupled. The second control shaft 11 is coupled to the other end of the arm link 13. The arm link 13 and the second control shaft 11 do not make relative displacement. The second control 11 is rotatably supported within a later-described housing 20 through a plurality of journal portions.
The second control link 12 has a lever-like shape. The one side portion 12a coupled to the eccentric shaft portion 10c is formed in a substantially rectilinear manner, whereas the other side portion 12b to which the arm link 13 is coupled is formed in a curved manner. The one side portion 12a includes an end portion in which an insertion hole is formed to extend through the end portion. The eccentric shaft portion 10c turnably extends through the insertion hole. The arm link 13 is formed as a separate body from the second control shaft 11. A rotational position of the second control shaft 11 is shifted by torque transmitted from a drive motor 22 through a wave gear speed reducer 21 which is a part of the actuator for a link mechanism for an internal combustion engine. After the rotational position of the second control shaft 11 is shifted, the first control shaft 10 rotates through the second control link 12 to shift a position of the lower end portion of the first control link 7. The lower link 5 is thus changed in its position, which changes stroke position and amount of the piston 1 within the cylinder. An engine's compression ratio is then accordingly shifted.
(Configuration of the Actuator for a Link Mechanism for an Internal Combustion Engine)
The drive motor 22 is a brushless motor. The drive motor 22 includes a bottomed cylinder-like motor casing 45, a tubular coil 46 fixed to an inner peripheral surface of the motor casing 45, a rotor 47 rotatably disposed in an inside of the coil 46, and a motor drive shaft 48 with one end portion 48a fixed at a center of the rotor 47. The motor drive shaft 48 is rotatably supported by a ball bearing 52 disposed in a bottom portion of the motor casing 45.
The second control shaft 11 includes a shaft portion body 23 extending in an axial direction, and a fixing flange 24 having a larger diameter than the shaft portion body 23. The second control shaft 11 comprises the shaft portion body 23 and the fixing flange 24 integrally made of a ferrous metal material. The fixing flange 24 is provided with a plurality of bolt insertion holes at an outer peripheral portion. The plurality of bolt insertion holes are arranged at regular intervals in a circumferential direction of the fixing flange 24. The fixing flange 24 is coupled to a flange portion 36b of a flexible external gear 36 of the wave gear speed reducer 21 with bolts inserted in the bolt insertion holes.
(Configuration of the Wave Gear Speed Reducer)
The wave gear speed reducer 21 is accommodated in an opening groove portion 20a of the housing 20. A feeding hole 20b opens in the opening groove portion 20a to be located gravitationally above the wave gear speed reducer 21. The feeding hole 20b supplies lubricant oil from a hydraulic power source, not shown, or the like. When the lubricant oil is supplied from the feeding hole 20b, the lubricant oil is dripped to the wave gear speed reducer 21 located beneath the feeding hole 20b, to thereby lubricate rotational elements. The wave gear speed reducer 21 includes an annular rigid internal gear 27 bolted within the opening groove portion 20a of the housing 20 and provided with a plurality of internal teeth 27a in an inner periphery, the flexible external gear 36 disposed on the inner periphery side of the rigid inner gear 27, deformable in a bent manner, and including an outer peripheral surface provided with external teeth 36a engaged with the internal teeth 27a, and a wave generating device 37 formed into an elliptical shape and having an outer peripheral surface which slides along an inner peripheral surface of the flexible external gear 36.
The flexible external gear 36 is made of a metal material. The flexible external gear 36 is a thin-walled cylinder-like member including a bottom portion and being deformable in the bent manner. The external teeth 36a of the flexible external gear 36 are fewer in number by two than the internal teeth 27a of the rigid internal gear 27. The flange portion 36b formed in the bottom portion of the flexible external gear 36 has an inner periphery formed with an insertion hole 36c through which the second control shaft 11 extends. The second control shaft 11 is inserted into the insertion hole 36c from the thin-walled cylinder-like member side of the flexible external gear 36, and the fixing flange 24 of the second control shaft 11 and the flange portion 36b are bolted together, which enables an inner periphery of the insertion hole 36c to be supported by the second control shaft 1, and also ensures rigidity of the bottom portion of the flexible external gear 36.
The wave generating device 37 includes a wave generator plug 371 having an elliptical shape, and a deep groove ball bearing 372 including flexible thin-walled inner and outer races which allow relative rotation between an outer periphery of the wave generator plug 371 and the inner periphery of the flexible external gear 36. The motor drive shaft 48 is press-fitted in a center of the wave generator plug 371 to be coupled to the wave generator plug 371.
While a tooth portion of the flexible external gear 36 has flexibility, the flange portion 36b cannot be deformed from its circular shape for the purpose of retrieving output and is fastened directly to the second control shaft 11. The flexible external gear 36 therefore has a shape spreading out from the flange portion 36b toward a thin-walled cylinder-like opening end portion into an elliptical shape. This shape makes it possible to transmit a rotating motion of the flexible external gear 36, which is retrieved from a deforming motion in the vicinity of the opening end portion, from the flange portion 36b to the second control shaft 11.
Input of the rotation into the wave gear device is converted by the wave generating device 37 into a reciprocating displacement motion in a direction perpendicular to a rotation input shaft. The wave generator plug 371 including a rotation transmission mechanism is driven by an input shaft connected to the wave generator plug 371, and the inner race of the deep groove ball bearing 372 that is a fitting counterpart of the wave generator plug 371 is also accordingly driven. A shape of the inner race of the deep groove ball bearing 372 is transmitted to the outer race of the deep groove ball bearing 372 by balls held between the inner and outer races. The balls have six translational and rotational degrees of freedom, so that the inner and outer races have respective degrees of freedom in the circumferential direction. Since the wave generator plug 371 driven by the rotation input is an elliptic body, the wave generator plug 371 has a radius which varies depending on positions on a circumference of the ellipse. Due to such an elliptical characteristic, radius increase and decrease due to the rotation of the wave generator plug 371 are transmitted to the outer race of the wave generator plug 371 through the balls. Since the inner and outer races have a flexible thin-walled structure, the outer race of the deep groove ball bearing 372 makes a deforming motion synchronized with the radius increase and decrease in a case where the outer race is regulated in its degrees of freedom in the circumferential direction.
Since the outer race of the deep groove ball bearing 372 is fitted to the flexible external gear 36, the flexible external gear 36 also makes a deforming motion along with the deforming motion of the outer race. The deforming motion changes an engagement position on the major axis between the rigid internal gear 27 and the flexible external gear 36.
Since the flexible external gear 36 is fastened to the second control shaft 11, when the second control shaft 11 receives torque from an external system, the torque is transmitted through the flange portion 36b to the flexible external gear 36 to cause the teeth of the flexible external gear 36 to push the respective teeth of the rigid internal gear 27. In this manner, the torque is received by the rigid internal gear 27. Hereinafter, a curvature of the internal teeth 27a is γs, and a curvature of the external teeth 36a is γe. On this condition, when a tooth sectional curvature of the flexible external gear 36 and that of the rigid internal gear 27 at a tooth contact point are γs≈γe as in a tooth profile of conventional wave gear devices, a contact surface is expanded according to an elastic contact theory to increase a tooth surface sliding resistance. This degrades input efficiency when load is applied to the wave gear speed reducer 21.
To solve the foregoing problem, the tooth sectional curvature of the flexible external gear 36 and that of the rigid internal gear 27 at the tooth contact point are determined as γs<<γe, and at the same time, the tooth profile is so designed that the engagement position can be shifted by the deforming motion of the flexible external gear 36. By so doing, contact area at the tooth contact point is reduced, decreasing the tooth surface sliding resistance and thus improving the input efficiency.
The wave gear speed reducer 21 of the Embodiment 1 is characterized in that the tooth profile is designed in the following manner. An engagement state between the rigid internal gear 27 and the flexible external gear 36, which have a straight tooth profile with stub teeth, is obtained on the basis of basic data including a standard pitch circle DS and a speed reduction ratio ID of the rigid internal gear 27, and a standard pressure angle α. Subsequently, a straight tooth surface of the flexible external gear 36 is corrected to a single arc with the curvature γe, which contacts a tooth root R and a tooth top R in order to avoid an engagement interference at each engagement position.
HA=0.8×M [Equation (1)]
HF=1.0×M [Equation (2)]
From the addendum HA obtained by the Equation (1), a radial displacement amount of the wave gear speed reducer 21 can be obtained. This makes it possible to engage the flexible external gear 36 with the rigid internal gear 27 at a position where the flexible external gear 36 does not interfere with the rigid internal gear 27 on the minor axis, and where the standard pitch circles DS and DE contact each other on the major axis. This radial displacement amount is overall amplitude S shown in
Subsequently, the flexible external gear 36 in the neutral circle state is deformed into an elliptical shape with the teeth arranged thereon to obtain the engagement state with the rigid internal gear 27. Regular pitch points on the circumference are changed by the elliptical deformation. The following description is focused on deformation in a state where planes, namely horizontal and vertical planes, are represented by an X-axis and a Y-axis, respectively, when the axis is an origin on a cross-sectional surface perpendicular to the axis of the wave gear speed reducer 21 shown in
P=(A2 sin2 θ+B2 cos2 θ)1/2−RDn
A sectional shape perpendicular to the axis of the flexible external gear and a sectional shape perpendicular to the axis of the rigid internal gear, which are obtained by the Equation (5), are superposed on each other to set tooth thickness and a tooth groove without interference. In this way, the wave gear speed reducer 21 using the stub-tooth straight tooth profile can be obtained. The invention is characterized in that the tooth surface sliding resistance is reduced by forming the tooth surface of the straight tooth profile into the single are having the curvature γe. As shown in
As discussed above, the Embodiment 1 provides advantageous effects listed below.
(1) The invention comprising:
the first and second control links 7 and 12 (control links) each having one side portion coupled to the link mechanism for an internal combustion engine;
the second control shaft 11 (control shaft) configured to rotate to change the position of the first and second control links 7 and 12;
the housing 20 configured to rotatably support the second control shaft 11; and
the wave gear speed reducer 21 configured to reduce and transmit the rotation speed (revolution speed) of the motor drive shaft 48 (output shaft) of the drive motor 22 to the second control shaft 11, wherein
the wave gear speed reducer 21 includes:
the rigid internal gear 27 (internal gear portion) disposed in the housing 20 and including internal teeth 27a;
the flexible external gear 36 located in an inside of the rigid internal gear 21, provided with the external teeth 36a at the outer periphery, and configured to transmit rotation to the second control shaft 11; and
the wave generating device 37 rotated by the motor drive shaft 48 of the drive motor 22, configured to bend the flexible external gear 36 into the elliptical shape to partially engage the external teeth 36a of the flexible external gear 36 with the internal teeth 27a of the rigid internal gear 27, and configured to rotate the engaging part between the flexible external gear 36 and the rigid internal gear 27; and
the external teeth 36a are larger in curvature than the internal teeth 27a in the contact portion between the internal and external teeth 27a and 36a.
It is therefore possible to reduce the contact area between the internal and external teeth 27a and 36a, and improve the driving efficiency and the torque resistivity of the actuator for a link mechanism for an internal combustion engine.
(2) The actuator for a link mechanism for an internal combustion engine according to the (1), wherein a basic profile of each of the external teeth 36a of the flexible external gear 36 is such a straight tooth profile that each of the external teeth 36a does not contact each of the internal teeth 27a in a state where the flexible external gear 36 is bent by the wave generating device 37 at a maximum in a radial direction, and the external teeth 36a with the straight tooth profile are subjected to overlay with respect to tooth thickness so that the external teeth 36a contact in the state where the flexible external gear 36 is bent by the wave generating device 37 at the maximum in the radial direction. The tooth thickness here particularly means tooth thickness along the standard pitch circle radius RD of the flexible external gear 36 in the elliptically deformed state.
It is therefore possible to ensure the rigidity of the external teeth 36a.
(3) The actuator for a link mechanism for an internal combustion engine according to the (1), wherein each of the internal teeth 27a is formed to have a straight tooth profile.
It is therefore possible to reduce contact resistance generated when the external tooth 36a moves inwardly in the radial direction along the internal tooth 27a.
(4) The actuator for a link mechanism for an internal combustion engine according to the (3), wherein each of the external teeth 36a is formed to have a curved tooth profile. It is therefore possible to reduce contact area between the internal and external teeth 27a and 36a.
(5) The actuator for a link mechanism for an internal combustion engine according to the (1), wherein the housing 20 includes the feeding hole 20b for supplying the lubricant oil to the wave gear speed reducer 21.
It is therefore possible to lubricate the wave gear speed reducer 21.
(6) The actuator for a link mechanism for an internal combustion engine according to the (5), wherein the feeding hole 20b is disposed gravitationally above a shaft center of the second control shaft 11. It is therefore possible to feed the lubricant oil supplied through the feeding hole 20b in a dripping manner without separately providing a mechanism or the like for supplying the lubricant oil.
(7) The actuator for a link mechanism for an internal combustion engine according to the (1), wherein the rigid internal gear 27 is an annular member fixed to the housing 20; and the flexible external gear 36 is formed into a bottomed cylinder-like shape and provided with the external teeth 36a at an outer periphery of a cylinder portion, the flexible external gear 36 including the flange portion 36b which is a bottom portion, to which the second control shaft 11 is fixed.
It is therefore possible to ensure the rigidity of the flexible external gear 36.
(8) The actuator for a link mechanism for an internal combustion engine according to the (7), wherein the flange portion 36b which is the bottom portion of the flexible external gear 36 includes the insertion hole 36c through which the second control shaft 11 extends. It is therefore possible to support the flange portion 36b which is the bottom portion by the second control shaft 11 and ensure the rigidity of the flexible external gear 36.
(9) The invention comprising:
the rigid internal gear 27 (internal gear portion) disposed in the housing 20 and including the internal teeth 27a;
the flexible external gear 36 located in the inside of the rigid internal gear 27, provided with the external teeth 36a at the outer periphery, and configured to transmit rotation to the second control shaft 11 (output shaft); and
the wave generating device 37 rotated by the motor drive shaft 48 (input shaft), configured to bend the flexible external gear 36 into an elliptical shape to partially engage the external teeth 36a of the flexible external gear 36 with the internal teeth 27a of the rigid internal gear 27, and configured to rotate the engaging part between the flexible external gear 36 and the rigid internal gear 27, wherein
the external teeth 36a are larger in curvature than the internal teeth 27a in the contact portion between the internal and external teeth 27a and 36a.
It is therefore possible to improve the driving efficiency and the torque resistivity of the wave gear speed reducer 21.
(10) The wave gear speed reducer 21 according to the (9), wherein a basic profile of each of the external teeth 36a of the flexible external gear 36 is such a straight tooth profile that each of the external teeth 36a does not contact each of the internal teeth 27a in a state where the flexible external gear 36 is bent by the wave generating device 37 at a maximum in a radial direction, and the external teeth 36a are subjected to overlay to obtain the straight tooth profile with overlaid tooth thickness so that each of the external teeth 36a contacts each of the internal teeth 27a in the state where the flexible external gear 36 is bent by the wave generating device 37 at the maximum in the radial direction.
It is therefore possible to ensure the rigidity of the external teeth 36a.
(11) The wave gear speed reducer 21 according to the (9), wherein each of the internal teeth 27a is formed to have a straight tooth profile.
It is therefore possible to reduce contact resistance generated when the external tooth 36a moves inwardly in the radial direction along the internal tooth 27a.
(12) The wave gear speed reducer 21 according to the (11), wherein each of the external teeth 36a is formed to have a curved tooth profile.
It is therefore possible to reduce contact area between the internal and external teeth 27a and 36a.
(13) The wave gear speed reducer 21 according to the (9), wherein a plane formed of the X- and Y-axes orthogonal to each other with the rotational axis served as the origin is defined on a cross-sectional surface perpendicular to the rotational axis of the flexible external gear 36, and when the angle formed by the line segment connecting the pitch point on the circumference of the flexible external gear 36 in the neutral circle state and the origin to each other and the X-axis is θ; the angle formed by the line segment connecting the pitch point on the elliptical circumference of the flexible external gear 36 deformed into an elliptical shape and the origin to each other and the X-axis is ϕ; the basic standard pitch circle radius RDn of the external teeth 36a and the internal teeth 27a; and the overall amplitude that is a radial motion amount which allows teeth engagement at the position where the flexible external gear 36 does not interfere with the rigid internal gear 27 on the minor axis, and where the standard pitch circle Dn contacts on the major axis, is S, a relationship described by arg ϕ=arcsin[{(RDn−(S×cos3 θ))/((A2 sin2 θ+B2 cos2 θ)1/2−RDn)}×cos θ] is satisfied.
It is therefore possible to obtain the tooth profile of the wave gear device, in which the tooth surface sliding resistance is reduced, and yet, the engagement is ensured.
The invention has been described on the basis of the embodiments. Instead of the foregoing embodiments, other configurations may be adopted. According to the Embodiment 1, for example, the invention is applied to the variable compression ratio mechanism capable of varying the compression ratio for an internal combustion engine. Instead, the invention may also be applied to a valve timing control system for an internal combustion engine, which is described in the Japanese Unexamined Patent Application Publication Nos. 2015-1190, 2011-231700, and other like documents, and a variable steering angle mechanism capable of varying a turning angle relative to a steering angle.
Although the embodiments of the invention have been described, one skilled in the art should easily understand that the exemplary embodiments may be modified or improved in various ways without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications and improvement are intended to be included within the technical scope of the invention. The embodiments may be combined in any manner.
The present application claims priority under Japanese Patent Application No. 2016-054589 filed on Mar. 18, 2016. The entire disclosure of Japanese Patent Application No. 2016-054589 filed on Mar. 18, 2016, including the description, claims, drawings and abstract, is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-054589 | Mar 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/007667 | 2/28/2017 | WO | 00 |
