Torque limiter

A torque limiter includes a first meshing portion provided at a surface of an input shaft which transmits a drive force of a drive motor, the surface intersecting with an axial direction of the input shaft, and a disc spring portion including a second meshing portion arranged facing the first meshing portion in the axial direction and which is configured to mesh with the first meshing portion. The disc spring portion is integrally rotatable with an output shaft which is provided coaxially with the input shaft and which is rotatable relative to the input shaft, and is deflected to displace the second meshing portion in a direction opposite to the first meshing portion in a case where a load equal to or greater than a set value is applied to the disc spring portion while the second meshing portion is being biased towards the first meshing portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2017-064629, filed on Mar. 29, 2017, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to a torque limiter.

BACKGROUND DISCUSSION

A known torque limiter which is incorporated in a differential gear is disclosed in JP2014-052048A (hereinafter referred to as Patent reference 1). The torque limiter disclosed in Patent reference 1 includes a first rotational member, a second rotational member, and a pressing mechanism which are arranged in a differential case rotatably provided about an axis of a drive shaft. The first rotational member integrally rotates with the differential case by an output of a transmission. The second rotational member faces and is coaxially arranged with the first rotational member so as to be engageable therewith. The pressing mechanism is disposed adjacent to the first rotational member and generates a pressing force in a circumferential direction of the pressing mechanism by a spring.

The first rotational member includes teeth extending in a radial direction of the first rotational member at a surface facing the second rotational member. The second rotational member includes teeth extending in a radial direction of the second rotational member at a surface facing the first rotational member. The first rotational member and the second rotational member engage with each other via the teeth thereof.

The first rotational member which is provided so as to be slidable in an axial direction of the first rotational member and the pressing mechanism which is provided so as to be slidable in the circumferential direction of the pressing mechanism are arranged such that inclination surfaces thereof engage with each other. Accordingly, the first rotational member is applied with the pressing force in the circumferential direction as a pressing force in the axial direction via the inclination surface, and thereby slides and is pressed towards the second rotational member.

In the aforementioned configuration, in a state where a torque which is equal to or lower than a maximum torque is inputted to the differential gear, the first rotational member and the second rotational member transmit such torque by maintaining the engagement therewith with the pressing force applied by the pressing mechanism. Meanwhile, in a case where the differential gear is inputted with a torque that is equal to or greater than a predetermined value, the first rotational member and the second rotational member disconnect the transmission of the torque by the disengagement of the first rotational member and the second rotational member by sliding of the first rotational member in a direction opposite to the second rotational member against the pressing force applied by the pressing mechanism.

However, because the torque limiter disclosed in Patent reference 1 uses a sliding member as a requisite component to establish an operation disconnecting the transmission of the torque (disconnecting operation), issues described below occur.

First, even though the torque limiter is designed to disconnect the transmission of the torque when the predetermined torque is inputted, in a case where the predetermined torque is actually inputted, the transmission of the torque may not be disconnected because the sliding member applied with a large amount of load slides against a frictional force. Specifically, when the aforementioned predetermined torque is inputted, it is intended that the first rotational member slides in a direction away from the second rotational member against the pressing force applied from the pressing mechanism. However, because the frictional force is generated at a part where the inclination surface of the first rotational member and the inclination surface of the pressing mechanism are in contact with each other, and at a part between the pressing mechanism and a guide wall surrounding the pressing mechanism, for example, the first rotational member may not slide as intended and the transmission of the torque may not be disconnected even though the aforementioned predetermined torque is inputted. Accordingly, in practice, the transmission of the torque may not be disconnected even when the torque which is larger than the aforementioned predetermined torque is inputted. Thus, a torque (a release torque) required by the torque limiter to establish the disconnecting operation may increase depending on the frictional force arising from the sliding member.

Moreover, in a case where a high-frequency impact load is inputted, the sliding member may move (slide) at a timing later than intended because of having a large inertia mass. Accordingly, in practice, the transmission of the torque may not be disconnected even when the torque larger than the predetermined torque is inputted. Thus, the release torque may increase depending on the inertia mass of the sliding member.

As above, when the torque limiter is designed, it is required to include a power transmission system, for example, the torque limiter, having a great torque strength by assuming that the release torque may increase. Thus, the power transmission system is required to be upsized.

A need thus exists for a torque limiter which is not susceptible to the drawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a torque limiter includes a first meshing portion provided at a surface of an input shaft which transmits a drive force of a drive motor, the surface intersecting with an axial direction of the input shaft, and a disc spring portion including a second meshing portion which is arranged facing the first meshing portion in the axial direction and which is configured to mesh with the first meshing portion, the disc spring portion being integrally rotatable with an output shaft which is provided coaxially with the input shaft and which is rotatable relative to the input shaft, the disc spring portion being deflected to displace the second meshing portion in a direction opposite to the first meshing portion in a case where a load equal to or greater than a set value is applied to the disc spring portion while the second meshing portion is being biased towards the first meshing portion.

DETAILED DESCRIPTION

Embodiments in this disclosure are explained with reference to the attached drawings. In the drawings, the same or similar components bear the same reference numerals. In addition, some of the components illustrated in one or more of the drawings may be omitted in the other of the drawings, for example, for the purpose of explanation. Further, a reduction scale may not be accurate in the drawings.

A torque limiter in this disclosure is mounted, for example, at a vehicle which employs a part-time four-wheel-drive system where the vehicle is driven in a front-wheel-drive mode under a usual condition and is driven in a four-wheel-drive mode under an optional condition. The torque limiter in this disclosure is also applicable to a vehicle which employs any drive system including a front-wheel-drive system (i.e., a front-engine, front-wheel-drive layout (FF) vehicle), a rear-wheel-drive system (i.e., a front-engine, rear-wheel-drive layout (FR) vehicle, a mid-engine, rear-wheel-drive layout (MR) vehicle, and a rear-engine, rear-wheel-drive layout (RR) vehicle), and a full-time/part-time four-wheel-drive system, for example.

A construction of a powertrain where the torque limiter is mounted is explained with reference toFIG. 1.

As illustrated inFIG. 1, a vehicle1mainly includes, as a front-wheel powertrain, an engine (ENG)2generating a drive force, a transmission (T/M)3transmitting the drive force of the engine2, and a front-wheel differential gear (Fr differential)4configured to transmit the drive force that is transmitted from the transmission3to a left-front wheel5aand a right-front wheel5b. The front-wheel differential gear4operates to equalize a rotation speed (the number of rotations) of the left-front wheel5aand a rotation speed (the number of rotations) of the right-front wheel5bin a case where the vehicle1is driven forward and to adjust the rotation speed of the left-front wheel5aand the rotation speed of the right-front wheel5bto appropriate numbers respectively in a case where the vehicle1turns right or left.

In addition, the vehicle1mainly includes, as a rear-wheel powertrain, a battery6supplying an electric power, a control apparatus7controlling a motor unit8with the electric power supplied from the battery6, and the motor unit8controlled by the control apparatus7to rotate a left-rear wheel9aand a right-rear wheel9b. The motor unit8includes a motor (drive motor) generating a drive force, a decelerator transmitting the drive force of the motor and a rear-wheel differential gear (Rr differential) configured to transmit the drive force that is transmitted from the decelerator to the left-rear wheel9aand the right-rear wheel9b. The rear-wheel differential gear operates to equalize a rotation speed (the number of rotations) of the left-rear wheel9aand a rotation speed (the number of rotations) of the right-rear wheel9bin a case where the vehicle1is driven forward and to adjust the rotation speed of the left-rear wheel9aand the rotation speed of the right-rear wheel9bto appropriate numbers respectively in a case where the vehicle turns right or left.

The vehicle1including the aforementioned powertrain is operated in the front-wheel-drive mode under the usual condition so that the drive force is transmitted to the left-front wheel5aand the right-front wheel5bsimply by the front-wheel powertrain. In addition, the vehicle1is operated in the four-wheel-drive mode under the optional condition, i.e., when the vehicle is driven on a snowy road, for example, so that the drive force is transmitted not only to the left-front wheel5aand the right-front wheel5bbut also to the left-rear wheel9aand the right-rear wheel9bby an operation of a driver of the vehicle or the control of the control apparatus7.

The motor unit8incorporates therein the torque limiter according to one embodiment as explained below.

A basic construction of the motor unit8where the torque limiter is mounted is explained with reference toFIG. 2.

The motor unit8includes, as main shafts, a motor drive shaft10in a hollow form, a counter shaft20, a left-rear wheel drive shaft30aand a right-rear wheel drive shaft30b. The motor drive shaft10is rotatably supported by a bearing12. A rotor16provided facing a stator14is mounted at an outer circumference of the motor drive shaft10. The counter shaft20is arranged in parallel to the motor drive shaft10and is rotatably supported by a bearing22. The left-rear wheel drive shaft30apenetrates through the motor drive shaft10to be positioned within the motor drive shaft10and to be arranged coaxially with the motor drive shaft10. The left-rear wheel drive shaft30ato which the left-rear wheel9ais fixed is rotatably supported by a bearing32. The right-rear wheel drive shaft30bis arranged coaxially with the left-rear wheel drive shaft30a. The right-rear wheel drive shaft30bto which the right-rear wheel9bis fixed is rotatably supported by a bearing34. It may be considered that the stator14, the rotor16and the motor drive shaft10, for example, mainly constitute the motor.

The motor unit8includes, as main gears, a counter drive gear40, a counter driven gear50, a final drive gear60, a final driven gear70, and a rear-wheel differential gear (Rr differential)80. The counter drive gear40is arranged at the motor drive shaft10to integrally rotate therewith. The counter driven gear50is arranged at the counter shaft20and is rotatable relative to the counter shaft20in a state engaging with the counter drive gear40. The final drive gear60is arranged at the counter shaft20to integrally rotate therewith. The final driven gear70is arranged at the left-rear wheel drive shaft30ain a state engaging with the final drive gear60. The rear-wheel differential gear80is arranged between the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30b. It may be considered that the counter driven gear50, the counter shaft20, the final drive gear60and the final driven gear70, for example, mainly constitute the decelerator.

The motor unit8further includes a torque limiter90engageable with both the counter driven gear50and the counter shaft20to control torque transmission therebetween.

The torque limiter90includes a first face cam52(seeFIG. 4) provided at the counter driven gear50and a disc spring unit100which is integrally rotatable with the counter shaft20and which includes a second face cam110(seeFIG. 4) configured to mesh or engage with the first face cam52. The disc spring unit100is configured to be deflected or bend so that the second face cam110is displaced in a direction opposite to the first face cam52, i.e., in a direction away from the first face cam52, in a case where a load equal to or greater than a set value (i.e., a predetermined torque) is applied to the disc spring unit100while the second face cam110is being biased to the first face cam52. Accordingly, the torque limiter90may fulfill a function for controlling (specifically, allowing and interrupting) the torque transmission between the counter driven gear50and the counter shaft20. The aforementioned function of the torque limiter90is hereinafter referred to as a “torque connection/disconnection function” for the purpose of explanation.

Specifically, the torque connection/disconnection function is a function for allowing transmission of torque in a case where such torque input to the torque limiter90is smaller than a release torque and for prohibiting transmission of torque in a case where such torque input to the torque limiter90is equal to or greater than the release torque.

The torque limiter90may additionally include a hub200provided at an outer circumference of the counter shaft20, a sleeve300configured to slide in an axial direction of the counter shaft20in a state of engaging with the hub200between a first position P1at which the sleeve300is spline-connected to the disc spring unit100and a second position P2at which the sleeve300is disconnected from (i.e., away from) the disc spring unit100, and a solenoid400controlling the sliding of the sleeve300. The sleeve300serves as a sliding member. Accordingly, the torque limiter90may additionally include a function for controlling (specifically, allowing and interrupting) transmission of the drive force between the counter driven gear50and the counter shaft20. The aforementioned function of the torque limiter90is hereinafter referred to as a “drive force connection/disconnection function” for the purpose of explanation.

Specifically, the drive force connection/disconnection function is a function for allowing the transmission of the drive force from the counter driven gear50to the counter shaft20in a case where the vehicle1is driven in the four-wheel-drive mode and for prohibiting the transmission of the drive force between the counter driven gear50and the counter shaft20in a case where the vehicle1is driven in the front-wheel-drive mode so as to restrain drag torque generated within the motor unit8, for example.

The motor unit8including the aforementioned construction is operated as below. In a case where the vehicle1is driven in the four-wheel-drive mode, the drive force of the motor (the motor drive shaft10) is transmitted to the counter shaft20via the counter drive gear40and the counter driven gear50. The drive force transmitted to the counter shaft20is further transmitted to the final driven gear70via the final drive gear60. The drive force transmitted to the final driven gear70is transmitted to the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30bvia the rear-wheel differential gear80. The rear-wheel differential gear80transmits the drive force to the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30bso that the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30brotate at the same rotation speed (same number of rotations) in a case where the vehicle1is driven forward. The rear-wheel differential gear80also transmits the drive force to the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30bso that the left-rear wheel drive shaft30aand the right-rear wheel drive shaft30brotate at respective rotation speeds (respective number of rotations) appropriately in a case where the vehicle1turns right or left.

In a case where the torque smaller than the release torque is input to the torque limiter90, the torque limiter90operates to allow the torque transmission between the counter driven gear50and the counter shaft20. Specifically, the second face cam110of the disc spring unit100is biased towards the first face cam52provided at the counter driven gear50so as to be meshed with the first face cam52. As a result, the torque limiter90allows the torque transmission between the counter driven gear50and the counter shaft20.

On the other hand, in a case where the torque equal to or greater than the release torque is input to the torque limiter90, the torque limiter90operates to interrupt or block the torque transmission between the counter driven gear50and the counter shaft20. Specifically, the disc spring unit100is configured to be deflected or bend so that the second face cam110is displaced in the direction away from the first face cam52. The torque limiter90thus interrupts the torque transmission between the counter driven gear50and the counter shaft20by releasing meshing between the first face cam52and the second face cam110.

In a case where the vehicle1is driven in the front-rear drive mode, the torque limiter90operates to interrupt the transmission of the drive force between the counter driven gear50and the counter shaft20so as to restrain generation of the drag torque within the motor unit8. Specifically, the sleeve300which is controlled by the solenoid400slides from the first position P1at which the sleeve300is spline-connected to the disc spring unit100during the four-wheel driving of the vehicle1to the second position P2at which the sleeve300is away from the disc spring unit100in a state of engaging with the hub200to thereby release the engagement between the disc spring unit100and the counter shaft20. Accordingly, the torque limiter90may interrupt the transmission of the drive force between the counter driven gear50and the counter shaft20. Alternatively, even in a case where the vehicle1is driven in the front-wheel-drive mode, the torque limiter90may operate to allow the transmission of the drive force between the counter driven gear50and the counter shaft20as necessary. In this case, the sleeve300which is controlled by the solenoid400slides to the first position P1at which the sleeve300is spline-connected to the disc spring unit100in a state of engaging with the hub200. The disc spring unit100and the counter shaft20engage with each other so that the torque limiter90may allow the transmission of the drive force between the counter driven gear50and the counter shaft20.

Next, examples of specific constructions of the aforementioned torque limiter90and components related thereto are explained with reference toFIGS. 3 and 4.

The torque limiter90includes the first face cam52provided at the counter driven gear50which transmits the drive force of the motor and the disc spring unit100integrally rotatable with the counter shaft20and including the second face cam110, the second face cam110facing the first face cam52and being configured to mesh with the first face cam52. The second face cam110is configured to be biased towards the first face cam52. The first face cam52serves as a first meshing portion and the second face cam110serves as a second meshing portion.

Further, the torque limiter90may additionally include the hub200, the sleeve300and the solenoid400as mentioned above.

An example of a specific construction of the counter driven gear50is explained with reference toFIG. 5in addition toFIGS. 3 and 4.

As illustrated inFIG. 5, the counter driven gear50is an annular-formed member as a whole while including a penetration bore51along a center axis of the counter driven gear50. The counter driven gear50is made of metal such as iron, steel, aluminum alloy and titanium alloy, for example. The counter driven gear50includes teeth54at an outer peripheral surface, the teeth54engaging with teeth provided at the counter drive gear40.

A housing void which annularly extends as a whole is provided at an inner portion of the counter driven gear50. The housing void may include, for example, a first void53awhich extends annularly, a second void53bconnected to the first void53aand extending annularly, and a third void53cconnected to the second void53band extending annularly. The first void53ais surrounded by a first outer peripheral wall53dincluding a first diameter and annularly extending and by a first inner peripheral wall53a1including a second diameter which is smaller than the first diameter and annularly extending. The second void53bis surrounded by the first outer peripheral wall53dand by a second inner peripheral wall53b1including a third diameter which is smaller than the second diameter and annularly extending. The third void53cis surrounded by the first outer peripheral wall53dand by a third inner peripheral wall53c1including a fourth diameter which is smaller than the third diameter and annularly extending.

A plate500which annularly extends so as to fill the first void53ais housed and fixed in the first void53a. The plate500is made of metal such as iron, steel, aluminum alloy and titanium alloy, for example. The first face cam52ais provided at a surface510of the plate500facing the disc spring unit100. The surface510serves as a surface of the counter driven gear50, the surface intersecting with an axial direction of the counter driven gear50. The first face cam52aincludes plural teeth520serving as first protruding portions which are arranged so as to be spaced away from one another and which extend radially.

The counter driven gear50illustrated inFIG. 5is rotatable relative to the counter shaft20or rotatable integrally with the counter shaft20in a state where the counter shaft20penetrates through the penetration bore51to be positioned therewithin as illustrated inFIGS. 3 and 4.

In order to enhance a relative rotation between the counter driven gear50and the counter shaft20, a clearance29is formed in a region of the counter shaft20as illustrated inFIGS. 3 and 4, the region extending in a circumferential direction and facing the penetration bore51of the counter driven gear50. In the clearance29, plural bearings (needle bearings)24may be arranged so as to be spaced away from one another. Each of the plural bearings is provided to be rotatable about a center axis which extends in parallel to a center axis of the counter shaft20.

In comparison betweenFIG. 5andFIG. 3(orFIG. 4), the housing void includes the first void53a, the second void53band the third void53cinFIG. 5while the housing void serves as a single void53extending annularly inFIG. 3(orFIG. 4). In this disclosure, the housing void illustrated inFIG. 5and the housing void illustrated inFIG. 3(orFIG. 4) are both applicable.

InFIG. 5, the first face cam52ais formed and provided at the plate500(specifically, at the surface510of the plate500facing the disc spring unit100). On the other hand, inFIG. 3(orFIG. 4), the first face cam52is directly formed and provided at a surface of the counter driven gear50, the surface surrounding the single void53and facing the disc spring unit100. In this disclosure, the first face cam52aillustrated inFIG. 5and the first face cam52illustrated inFIG. 3(orFIG. 4) are both applicable.

An example of a specific construction of the disc spring unit100is explained with reference toFIG. 6in addition toFIGS. 3 to 5. InFIGS. 5 and 6, an external force is not applied to the disc spring unit100.

As illustrated inFIGS. 5 and 6, the disc spring unit100is made of metal with flexibility such as iron, steel, aluminum alloy and titanium alloy, for example. The disc spring unit100mainly includes a disc spring portion120in an annular form and a support portion140in a tubular form integrally and coaxially formed and provided with the disc spring portion120.

In a case where the external force is not applied to the disc spring portion120, the disc spring portion120extends as including a radius which decreases from a first end122to a second end124of the disc spring portion120as illustrated inFIG. 5. The disc spring portion120includes a penetration bore125at the second end124. The second face cam110is provided at a surface126(a reference surface) of the disc spring portion120facing the counter driven gear50. The second face cam110includes plural teeth128(second protruding portions) provided so as to be spaced away from one another and extending radially. An appropriate interval is provided or defined between one of the teeth128and the other one of the teeth128adjacent to each other so that the corresponding tooth520of the first face cam52is arranged between the aforementioned adjacent teeth128. That is, an appropriate interval is provided or defined between one of the teeth520and the other one of the teeth520of the first face cam52adjacent to each other so that the corresponding tooth128of the second face cam110is arranged between the aforementioned adjacent teeth520.

The support portion140extends as including a radius which increases from a first end142to an intermediate portion144of the support portion140and extends as including substantially the same radius from the intermediate portion144to a second end146of the support portion140. That is, the support portion140includes the radius which increases from the first end142to the intermediate portion144, the radius being substantially constant from the intermediate portion144to the second end146. The support portion140includes a penetration bore143at the first end142. The support portion140is connected integrally, at the first end142, to the second end124of the disc spring portion120. Accordingly, the penetration bore143of the support portion140is connected to the penetration bore125of the disc spring portion120.

The support portion140includes plural raised portions148at an outer peripheral surface, the raised portions418being arranged so as to be spaced away from one another and extending in the axial direction.

The disc spring unit100illustrated inFIGS. 5 and 6is mounted to the counter driven gear50in a state where the support portion140(i.e., the second end146thereof, for example) is fixed to the second inner peripheral wall53b1. Specifically, the second inner peripheral wall53b1and the third inner peripheral wall53c1of the counter driven gear50are inserted to the penetration bore125of the disc spring portion120and the penetration bore143of the support portion140. The disc spring portion120is pressed against the plate500until the surface126of the disc spring portion120becomes substantially vertical to the center axis of the counter driven gear50so that the disc spring portion120is arranged within the second void53b. That is, the second end124of the disc spring portion120and the first end142of the support portion140make contact with the second inner peripheral wall53b1.

As illustrated inFIGS. 3 and 4, the disc spring unit100may be fixed to the counter driven gear50by a snap ring S arranged between a cutout which is provided at the second end146of the support portion by extending annularly in the circumferential direction and a groove which is provided at the counter driven gear50by extending annularly in the circumferential direction so as to face the cutout. As a result, the support portion is restricted from moving in a direction away from the first face cam52along the axial direction (i.e., in a right direction inFIGS. 3 and 4).

The disc spring unit100is fixed to the counter driven gear50in the aforementioned manner. In the state where the disc spring unit100is fixed to the counter driven gear50, the second face cam110provided at the disc spring unit100faces the first face cam52provided at the counter driven gear50as illustrated inFIGS. 3 and 4.

In comparison betweenFIG. 5andFIG. 3(orFIG. 4), the support portion140of the disc spring unit100extends as including the radius which increases from the first end142towards the intermediate portion144and extends as including substantially the same radius from the intermediate portion144towards the second end146inFIG. 5. On the other hand, the support portion extends as including substantially the same (i.e., constant) radius from the first end142to the second end146inFIG. 3(orFIG. 4). In this disclosure, the support portion140illustrated inFIG. 5and the support portion illustrated inFIG. 3(orFIG. 4) are both applicable.

The second face cam110provided at the disc spring portion120is explained below. As illustrated inFIG. 6, the plural teeth128(protruding portions) constituting the second face cam110are provided at the annularly-formed surface126of the disc spring portion120. Each of the teeth128includes a main surface606, a first inclination surface608, a second inclination surface610, a third inclination surface612and a fourth inclination surface614. The main surface606extends in a radial direction from a first end602to a second end604in parallel to the surface126towards an outer circumferential edge of the surface126. The first inclination surface608extends in the radial direction by connecting between the main surface606and the surface126. The second inclination surface610extends in the radial direction by connecting between the main surface606and the surface126while sandwiching the main surface606with the first inclination surface608. The third inclination surface612extends in the radial direction towards the center axis of the disc spring portion120from the first end602of the main surface606and inclines towards the surface126. The fourth inclination surface614extends in the radial direction towards the outer peripheral edge of the disc spring portion120from the second end604of the main surface606and inclines towards the surface126. In the present embodiment, the main surface606includes a width increasing from the first end602to the second end604. Alternatively, the main surface606may include a width decreasing from the first end602to the second end604or substantially the same width from the first end602to the second end604, for example.

FIG. 7schematically illustrates the configuration of each of the teeth128as viewed from the outer circumferential edge of the disc spring portion120illustrated inFIG. 6towards the center axis. An angle α1formed by the first inclination surface608relative to the surface126is selectable in a range from zero degrees (exclusive) to 45 degrees (inclusive) (i.e., 0<α1≤45). An angle α2 formed by the second inclination surface610relative to the surface126is also selectable in a range from zero degrees (exclusive) to 45 degrees (inclusive) (i.e., 0<α2≤45). In addition, an angle α3 (not illustrated inFIG. 7) formed by the third inclination surface612relative to the surface126is also selectable in a range from zero degrees (exclusive) to 45 degrees (inclusive) (i.e., 0<α3≤45). In the same manner, an angle α4 (not illustrated inFIG. 7) formed by the fourth inclination surface614relative to the surface126is selectable in a range from zero degrees (exclusive) to 45 degrees (inclusive) (i.e., 0<α4≤45). In the embodiment, each of the angles α1 to α4 is specified to 45 degrees. Alternatively, the angles α1 to α4 are not necessarily the same as one another and may be differently specified from one another.

In a state where the first face cam52and the second face cam110engage with each other (i.e., a state illustrated inFIG. 3), one of the teeth520of the first face cam52is arranged at a region between the two adjacent teeth128of the second face cam110. That is, one of the teeth128of the second face cam110is arranged at a region between the two adjacent teeth520of the first face cam52. Thus, each of the teeth520of the first face cam52desirably includes a configuration so that each of the teeth520is appropriately arranged at the region between the two adjacent teeth128of the second face cam110and that each of the teeth520appropriately engages with the two adjacent teeth128. In the embodiment, each of the teeth520of the first face cam52may include the same configuration as each of the teeth128of the second face cam110. Specifically, each of the teeth520may include a main surface, a first inclination surface, a second inclination surface, a third inclination surface and a fourth inclination surface. The main surface extends in a radial direction from a first end to a second end in parallel to the surface510(seeFIG. 5) towards an outer circumferential edge of the surface510. The first inclination surface extends in the radial direction by connecting between the main surface and the surface510. The second inclination surface extends in the radial direction by connecting between the main surface and the surface510while sandwiching the main surface with the first inclination surface. The third inclination surface extends in the radial direction towards the center axis of the counter driven gear50from the first end of the main surface and inclines towards the surface510. The fourth inclination surface extends in the radial direction towards the outer peripheral edge of the counter driven gear50from the second end of the main surface. In a state where the first face cam52and the second face cam110engage with each other, the first inclination surface of the tooth520faces or makes contact with the first inclination surface608of the tooth128and the second inclination surface of the tooth520faces or makes contact with the second inclination surface610of the tooth128. Thus, an angle formed by the first inclination surface of the tooth520relative to the surface510and an angle formed by the second inclination surface of the tooth520relative to the surface510are desirably equal to the angle α1 formed by the first inclination surface608and the angle α2 formed by the second inclination surface610of the tooth128respectively.

An example of a specific construction of the torque limiter90for exercising the drive force connection/disconnection function is explained below. As illustrated inFIGS. 3 and 4, the hub200is provided at an outer peripheral surface of the counter shaft20. The hub200includes plural splines serving as a dog clutch and provided so as to be spaced away from one another in the circumferential direction along the outer peripheral surface of the counter shaft20. InFIGS. 3and4, one of the splines in the plural splines of the hub200is illustrated. The hub200may be made of metal such as iron, steel, aluminum alloy and titanium alloy, for example.

The sleeve300is provided to be slidable in the axial direction of the counter shaft20in a state of engaging with the hub200. The sleeve300includes plural splines serving as a dog clutch and provided so as to be spaced away in the circumferential direction along the outer peripheral surface of the counter shaft20. InFIGS. 3 and 4, one of the splines in the plural splines of the sleeve300is illustrated. The sleeve300engages with the hub200in a state where the plural splines of the sleeve300are meshed with the plural splines of the hub200. The sleeve300may be also made of metal such as iron, steel, aluminum alloy and titanium alloy, for example.

Each of the splines of the sleeve300slides in the axial direction between the first position P1at which the spline is positioned (i.e., spline-connected) between the two adjacent raised portions148provided at the support portion140of the disc spring unit100so that the disc spring unit100is integrally rotatable with the counter shaft20and the second position P2at which the spline disengages and separates from the aforementioned two adjacent raised portions148so that the disc spring unit100is rotatable relative to the counter shaft20.

The aforementioned sliding of the sleeve300(specifically, each of the splines thereof) between the first position P1and the second position P2is achievable by the solenoid400serving as an example of an actuator.

In a state where each of the splines of the sleeve300is arranged at the first position P1as illustrated with a solid line inFIGS. 3 and 4, the rotation of the counter driven gear50causes the raised portions148provided at the support portion140of the disc spring unit100to make contact with the corresponding splines of the sleeve300so that the raised portions148press the corresponding splines of the sleeve300in the circumferential direction. Accordingly, the disc spring unit100(the counter driven gear50) is integrally rotatable with the counter shaft20.

On the other hand, in a state where each of the splines of the sleeve300is arranged at the second position P2as illustrated with a dotted lineFIGS. 3 and 4, the raised portions148provided at the support portion140of the disc spring unit100are inhibited from making contact with the corresponding splines of the sleeve300. Accordingly, the disc spring unit100(the counter driven gear50) is rotatable relative to the counter shaft20.

Next, the operation of the torque limiter90including the aforementioned construction in a case where the torque limiter90exercises the torque connection/disconnection function is explained with reference toFIGS. 8A, 8B, 8C, 8D, 8E and 8F.

A positional relationship between the first face cam52and the second face cam110before completion of mounting of the disc spring unit100to the counter driven gear50(i.e., in a free state of the torque limiter90during assembly operation of the disc spring portion120on the counter driven gear50) is illustrated inFIG. 8A. A positional relationship between the first face cam52and the second face cam110in a state where the disc spring unit100is mounted to the counter driven gear50(i.e., in a normal state of the torque limiter90) is illustrated inFIG. 8C. A positional relationship between the first face cam52and the second face cam110in a state where the release torque is input to the second face cam110(or the first face cam52) is illustrated inFIG. 8E. Each graph inFIGS. 8B, 8D, and 8Fshows a relationship between a load applied to the disc spring portion120and a stroke (an amount of displacement) of the disc spring portion120corresponding to each of the positional relationships between the first face cam52and the second face cam110illustrated inFIGS. 8A, 8C and 8E.

In the free state of the torque limiter90where the external force is not applied to the disc spring portion120of the disc spring unit100as illustrated inFIG. 8A, the surface126of the disc spring portion120is inclined so that the first end122is positioned closer to the first face cam52than the second end124. In the aforementioned state, because no load is applied to the disc spring portion120, the stroke of the disc spring portion120is zero as illustrated inFIG. 8B.

In the state where the disc spring unit100is mounted to the counter driven gear50as illustrated inFIG. 8C, the load is applied to the disc spring portion120in a direction opposite to the first face cam52. Thus, the surface126of the disc spring portion120extends substantially in parallel to a vertical direction. In such state, a load L1is applied to the disc spring portion120opposite to the first face cam52along the axial direction, so that a stroke D1of the disc spring portion120is obtained.

As illustrated inFIG. 8E, the release torque is input to the second face cam110(or the first face cam52). In a case where torque in the circumferential direction is applied to the second face cam110or the first face cam52, each of the teeth128receives a force (a load) opposite to the first face cam52along the axial direction because each of the teeth128of the second face cam110and each of the teeth520of the first face cam52make contact with each other via the inclined surfaces (i.e., the first inclination surface608and the second inclination surface610of each of the teeth128and the first and second inclination surfaces of each of the teeth520). When the torque input to the second face cam110or the first face cam52reaches the release torque, the load L1is applied to the disc spring portion120opposite to the first face cam52along the axial direction as illustrated inFIG. 8F, so that a stroke D2of the disc spring portion120is obtained. Accordingly, the surface126of the disc spring portion120is inclined so that the first end122is positioned further away than the second end124from the first face cam52. The first face cam52and the second face cam110disengage from each other to interrupt the torque transmission between the first face cam52and the second face cam110.

As illustrated inFIGS. 8B, 8D and 8F, the amount of stroke which increases with increase of load by a certain amount (fixed amount) is relatively small in a range where the load applied to the disc spring portion120is zero to L1. On the other hand, in a range where the load applied to the disc spring portion120is L1to L2, the amount of stroke which increases with increase of load by the certain amount (fixed amount) is relatively large. With the disc spring portion120including the aforementioned characteristics, the second face cam110keeps engagement with the first face cam52until input torque reaches the release torque and the engagement between the second face cam110and the first face cam52may be immediately released at the time the torque equal to or greater than the release torque is input.

The disc spring unit100performing the aforementioned torque connection/disconnection function is configured to be deflected or bend so that the second face cam110is displaced in the direction opposite to the first face cam52. Thus, the disc spring unit100operates to release the engagement between the second face cam110and the first face cam52. The disc spring portion120of the disc spring unit100is integrally formed and provided with the support portion140which is restricted from sliding in the direction opposite to the first face cam52along the axial direction. Thus, in the entire disc spring unit100, a portion which slides relative to the other components (i.e., a sliding portion), specifically, the counter driven gear50, merely exists. The release torque is therefore restrained from variating or fluctuating because of magnitude of friction force which may result from the sliding portion in the disc spring unit100.

Because the disc spring unit100does not substantially include any portion which slides relative to the other component as mentioned above, the disc spring unit100also does not substantially include a sliding member with a large inertia mass. Thus, even when a high-frequency impact load is input to the disc spring unit100, the disc spring unit100may securely release the engagement between the second face cam110and the first face cam52. The release torque is restrained from variating or fluctuating because of magnitude of friction force which may result from the sliding portion in the disc spring unit100.

The second face cam110and the disc spring portion120are integrally formed, i.e., the second face cam110is formed at the disc spring portion120itself, thereby decreasing the number of components. In addition, the support portion140supporting the disc spring portion120is also integrally formed in addition to the second face cam110and the disc spring portion120, thereby further decreasing the number of components. Cost reduction may be achieved for obtaining the torque limiter.

In a case where the disc spring portion120operates to release the torque transmission (i.e., performs a torque release operation), a radially outer region and a radially inner region of the second face cam110release the engagement, in the mentioned order, relative to the first face cam52in the process of deflection of the disc spring portion120to which the torque is input so that the second face cam110is displaced in the direction opposite to the first face cam52. The aforementioned state is clearly understood in comparison between the disc spring portion120inFIG. 8Cand the disc spring portion120inFIG. 8E. With the torque release operation by the disc spring portion120, the torque transmission between the first face cam52and the second face cam110moves to the inner diameter side to decrease transmissive torque. Accordingly, torque increase from the start to the end of the torque release operation may be reduced. While the torque transmission required before the start of the torque release operation is secured, the release torque may be reduced.

As mentioned above, the radially outer region and the radially inner region of the second face cam110release the engagement, in the mentioned order, relative to the first face cam52in the process of deflection of the disc spring portion120to which the torque is input so that the second face cam110is displaced in the direction opposite to the first face cam52. Thus, at a moment immediately before the second face cam110completely releases the engagement with the first face cam52, only the inner diameter region of the second face cam110engages with the first face cam52. In this case, the inner diameter region of the second face cam110may possibly locally receive a large torque.

In order to eliminate the aforementioned possibility, the disc spring portion120may include a second face cam900as illustrated inFIGS. 9 and 10according to another embodiment.

A difference of the second face cam900serving as the second meshing portion from the second face cam110illustrated inFIGS. 5 and 6is explained below.

As illustrated inFIGS. 9 and 10, the second face cam900includes plural teeth910(second protruding portions) provided so as to be spaced away from one another and extending radially. Each of the teeth910includes the main surface606, the first inclination surface608, the second inclination surface610, a third inclination surface912and the fourth inclination surface614. The main surface606extends in the radial direction from the first end602to the second end604in parallel to the surface126towards the outer circumferential edge of the surface126. The first inclination surface608extends in the radial direction by connecting between the main surface606and the surface126. The second inclination surface610extends in the radial direction by connecting between the main surface606and the surface126while sandwiching the main surface606with the first inclination surface608. The third inclination surface912extends in the radial direction towards the center axis of the disc spring portion120from the first end602of the main surface606and inclines towards the surface126. The fourth inclination surface614extends in the radial direction towards the outer peripheral edge of the disc spring portion120from the second end604of the main surface606and inclines towards the surface126.

An angle β3 formed by the third inclination surface912relative to the surface126is specified smaller than the angle α1 formed by the first inclination surface608relative to the surface126, the angle α2 formed by the second inclination surface610relative to the surface126and the angle α4 formed by the fourth inclination surface614relative to the surface126. Thus, each of the teeth910includes a thickness which is constant from the second end604to a center portion and which decreases from the center portion towards the center axis of the disc spring portion120. At a moment immediately before the second face cam900completely releases the engagement with the first face cam52, a situation where only the inner diameter region of the second face cam900engages with the first face cam52may be inhibited from occurring. A large torque is restrained from being locally applied to an inner diameter region of the second face cam900.

In the aforementioned embodiments, the torque limiter includes both the torque connection/disconnection function and the drive force connection/disconnection function. Because the torque limiter does not necessary include the drive force connection/disconnection function, the drive force connection/disconnection function may be omitted.

A difference of the torque limiter according to still another embodiment illustrated inFIG. 11from the torque limiter illustrated inFIG. 3is explained below.

A disc spring unit700included in a torque limiter800illustrated inFIG. 11is spline-connected to plural projecting portions28provided at the counter shaft20in a manner being spaced away from one another along the outer circumference of the counter shaft20so that the counter driven gear50and the counter shaft20are connected to be integrally rotatable with each other. Specifically, the disc spring unit700includes the disc spring portion120which may include the same construction as the disc spring portion120illustrated inFIGS. 3, 5 and 6, and a support portion710integrally connected to the disc spring portion120. The support portion710includes a tubular form in the same manner as the aforementioned support portion140and includes plural recess portions714at an end portion, the recess portions714being arranged to be spaced away from one another in the circumferential direction of the support portion710. Each of the recess portions714engages with the corresponding projecting portion28in the plural projecting portions28provided at the counter shaft20. Accordingly, when the counter driven gear50rotates, the projecting portions28provided at the counter shaft20make contact with the respective recess portions714provided at the support portion710of the disc spring unit700to press the respective recess portions714. As a result, the disc spring unit700(the counter driven gear50) is integrally rotatable with the counter shaft20.

As illustrated inFIG. 11, the support portion710of the disc spring unit700is restricted from moving in a direction away from the first face cam52along the axial direction (i.e., in a right direction inFIG. 11) by the snap ring S, in the same way as the support portion140illustrated inFIG. 3. Thus, also in the torque limiter800illustrated inFIG. 11, the disc spring portion120of the disc spring unit700is integrally formed and provided with the support portion710which is restricted from moving in the direction opposite to (i.e., away from) the first face cam52along the axial direction. Thus, in the entire disc spring unit700, a portion which slides relative to the other components (i.e., a sliding portion), specifically, the counter driven gear50, merely exists. In a case where the release torque as intended at a time of designing the torque limiter800is actually input to the disc spring unit700, the disc spring unit700may securely release the engagement between the second face cam110and the first face cam52.

As mentioned above, the support portion710of the disc spring unit700is restricted from moving in the direction away from the first face cam52along the axial direction by the snap ring S. Thus, each of the projecting portions28provided at the counter shaft20and each of the recess portions714provided at the support portion710hardly slide to each other in the axial direction.

In the torque limiter according to the aforementioned embodiments performing the torque connection/disconnection function (and the drive force connection/disconnection function) between the input shaft and the output shaft, the counter driven gear50is employed as the input shaft and the counter shaft20is employed as the output shaft. At this time, technical thought in this disclosure is also applicable in a case where the torque connection/disconnection function (and the drive force connection/disconnection function) is obtained between any input shaft and any output shaft transmitting a drive force of an engine or a motor.

According to the aforementioned embodiments, the torque limiter90,800includes the first meshing portion (first face cam)52provided at the surface510of the input shaft (counter driven gear)50which transmits the drive force of the motor, the surface510intersecting with an axial direction of the input shaft50, and the disc spring portion120including the second meshing portion (second face cam)110,900which is arranged facing the first meshing portion52in the axial direction and which is configured to mesh with the first meshing portion52, the disc spring portion120being integrally rotatable with the output shaft (counter shaft)20which is provided coaxially with the input shaft50and which is rotatable relative to the input shaft50, the disc spring portion120being deflected to displace the second meshing portion110,900in a direction opposite to the first meshing portion52in a case where a load equal to or greater than a set value is applied to the disc spring portion120while the second meshing portion110,900is being biased towards the first meshing portion52.

Accordingly, in a case where the load equal to or greater than the set value (i.e., a predetermined torque) is input to the disc spring portion120, the disc spring portion120is deflected to displace the second meshing portion (second face cam)110,900provided at the disc spring portion120in the direction opposite to the first meshing portion (first face cam)52provided at the input shaft (counter driven gear)50. As a result, meshing between the first meshing portion52and the second meshing portion110,900is released to interrupt torque transmission between the input shaft50and the output shaft (counter shaft)20. The torque limiter90,800which realizes the torque connection/disconnection function may be thus obtained.

The torque limiter90,800further includes the support portion140,710integrally provided with the disc spring portion120and including a tubular form, the support portion140,710including the plural raised portions148at an outer peripheral surface, the plural raised portions148extending in the axial direction and being spaced away from one another in a circumferential direction. The output shaft (counter shaft)20includes the sliding member (sleeve)300sliding in the axial direction between the first position P1at which the sliding member300is positioned within the plural raised portions148so that the disc spring portion120is integrally rotatable with the output shaft20and the second position P2at which the sliding member300is away from the plural raised portions148so that the disc spring portion120is rotatable relative to the output shaft20.

Accordingly, the support portion140,710which is integrally provided with the disc spring portion120allows transmission of the drive force between the input shaft (counter driven gear)50and the output shaft (counter shaft)20by engaging with the sliding member (sleeve)300provided at the output shaft20to be slidable in the axial direction and prohibits the transmission of the drive force between the input shaft50and the output shaft20by releasing the engagement with the sliding member300. The torque limiter90,800which realizes the drive force connection/disconnection function may be thus obtained.

The support portion140,710is restricted from moving in the axial direction by being fixed to the input shaft (counter driven gear)50.

Because the disc spring portion120and the support portion140,710are integrally provided with each other and the support portion140,710is fixed to the input shaft (counter driven gear)50in a state where the support portion140,710is restricted from moving in the axial direction, the disc spring portion120and the support portion140,710are substantially inhibited from generating a friction force which may result from a sliding with other components such as the input shaft50, for example. Accordingly, the torque limiter90,800which restrains fluctuation or variation of release torque may be obtained.

The first meshing portion (first face cam)52includes the plural first protruding portions (teeth)520arranged to be spaced away from one another and radially extending. The second meshing portion (second face cam)110,900includes the plural second protruding portions (teeth)128,910arranged to be spaced away from one another and radially extending.

Accordingly, the first meshing portion (first face cam)52including the plural first protruding portions (teeth)520may be securely meshed with the second meshing portion (second face cam)110,900including the plural second protruding portions (teeth)128,910. The torque limiter90,800which realizes the torque connection/disconnection function may be thus obtained.

The plural second protruding portions (teeth)128,910is provided at the reference surface (surface)126in an annular region of the disc spring portion120, each of the plural second protruding portions128,910including the main surface606which extends in a radial direction from the first end602to the second end604in parallel to the reference surface126towards an outer circumferential edge of the annular region, the first inclination surface608which extends in the radial direction by connecting between the main surface606and the reference surface126, and the second inclination surface610which extends in the radial direction by connecting between the main surface606and the reference surface126while sandwiching the main surface606with the first inclination surface608.

Because the plural second protruding portions (teeth)128,910constituting the second meshing portion (second face cam)110,900are meshed with the plural first protruding portions (teeth)520constituting the first meshing portion (first face cam)52via the first inclination surface608and the second inclination surface610, the second meshing portion110,900(or the first meshing portion52) is pressed in the direction opposite to the first meshing portion52(or the second meshing portion110,900) in a case where the load equal to or greater than the set value (i.e., the predetermined torque) is input to the disc spring portion120. Accordingly, the torque limiter90,800which realizes the torque connection/disconnection function may be thus obtained.

Each of the plural second protruding portions (teeth)910includes the third inclination surface912which extends in the radial direction towards a center axis of the disc spring portion120from the first end602of the main surface606and inclines towards the reference surface126. The third inclination surface912forms the angle β3 relative to the reference surface126, the angle β3 being smaller than the angle α1, α2 formed by each of the first inclination surface608and the second inclination surface610relative to the reference surface126.

Because each of the plural second protruding portions910constituting the second meshing portion (second face cam)900includes the third inclination surface912which extends in the radial direction towards the center axis of the disc spring portion120, a situation where torque is locally applied to an inner region of each of the plural second protruding portions910of the second meshing portion900is restrained.

The disc spring portion120includes the radius which decreases from the first end122to the second end124in a state where an external force is inhibited from being applied to the disc spring portion120, the disc spring portion120including the penetration bore125at the second end124.

Accordingly, in a case where the load equal to or greater than the set value (i.e., a predetermined torque) is input to the disc spring portion120, the disc spring portion120is deflected to displace the second meshing portion (second face cam)110,900provided at the disc spring portion120in the direction opposite to the first meshing portion (first face cam)52provided at the input shaft (counter driven gear)50. As a result, meshing between the first meshing portion52and the second meshing portion110,900is released to interrupt torque transmission between the input shaft50and the output shaft (counter shaft)20. The torque limiter90,800which realizes the torque connection/disconnection function may be thus obtained.

The second meshing portion (second face cam)110,900including the plural second protruding portions (teeth)128,910is provided at the surface126of the disc spring portion120, the surface126facing the first meshing portion (first face cam)52including the plural first protruding portions (teeth)520. One of the plural second protruding portions128,910and the other one of the plural second protruding portions128,910adjacent to each other in the plural second protruding portions128,910define an interval therebetween, the interval at which one of the plural first protruding portions520is configured to be arranged.

Accordingly, the first meshing portion (first face cam)52including the plural first protruding portions (teeth)520may be securely meshed with the second meshing portion (second face cam)110,900including the plural second protruding portions (teeth)128,910. The torque limiter90,800which realizes the torque connection/disconnection function may be thus obtained.

The support portion140,710includes the radius which increases from the first end142to the intermediate portion144of the support portion140,710, the radius being constant from the intermediate portion144to the second end146of the support portion140,710.

Accordingly, the support portion140,710which is integrally provided with the disc spring portion120allows transmission of the drive force between the input shaft (counter driven gear)50and the output shaft (counter shaft)20by engaging with the sliding member (sleeve)300provided at the output shaft20to be slidable in the axial direction and prohibits the transmission of the drive force between the input shaft50and the output shaft20by releasing the engagement with the sliding member300. The torque limiter90,800which realizes the drive force connection/disconnection function may be thus obtained.