Differential device

A differential device is provided with: an input case having an axially directed end face; a differential gear set with side gears allowing a differential motion therebetween; dog teeth toothed toward the end face on an output case; a clutch structure engageable with the dog teeth and so structured as to couple the output case or the second side gear with the input case when engaged; an axially movable clutch member including an internal end and an external end exposed to the exterior; an axially movable armature including a magnetic material and in contact with the external end; a solenoid supported away from the end face, the solenoid generating a magnetic flux to attract the armature and, via the clutch member, set the clutch structure in mesh with the dog teeth; and a spring biasing the clutch member in a contrary direction.

TECHNICAL FIELD

The disclosure herein relates to a differential device including a differential device provided with an actuator driven by an attractive solenoid to enable operation of a clutch.

BACKGROUND

When a four-wheel vehicle runs on a rough road, its driving force is more preferably transmitted to all the four wheels than to only front or rear wheels in light of stability of traction. When the vehicle runs on a well-paved road, however, an all-wheel drive (AWD) system is inferior in light of fuel efficiency or other factors. As such, systems that offer drivers selectivity between a two-wheel drive mode and an all-wheel drive mode by mean of the drivers' intentional operation, namely referred to as “part-time AWD” systems, are frequently used.

While various drivetrains that realize part-time AWD are possible, a combination of a differential gear set that enables differential motion between axles and a clutch that temporarily couples an input shaft with the differential gear set is applicable for example. A device referred to as “free-running differential”, which contains such a combination unitarily, is proposed. The PTL 1 listed below discloses an example of a free-running differential.

An actuator for driving the clutch may be a geared motor, a hydraulic device, a solenoid or such, and particularly the solenoid is superior in light of its better response. In the art disclosed in the PTL 1, the solenoid generates magnetic flux forming a loop through the core and makes the magnetic flux bypass it to the plunger to create thrust force on the plunger, thereby driving the clutch. Solenoids of this type, although creating relatively small power, enable low energy consumption operation. Attractive solenoids are, however, preferable in light of its capacity of larger power. The PTLs 2 and 3 listed below disclose examples although it is used not for a free-running differential but for locking up differential motion, in which the solenoid magnetically attracts the armature and the return spring is used for separating it away. As the solenoid, in either case, requires wiring to the vehicle body, the solenoid and related components should be rendered non-rotational whereas the differential revolves.

CITATION LIST

Patent Literature

SUMMARY

As a clutch is also immersed in lubricant oil for lubricating a differential gear set, viscosity of the lubricant oil resists disengagement of the clutch. Further, friction among the engaged clutch teeth, when torque acts thereon, strongly resists disengagement. Thus, to ensure disengagement of the clutch, the return spring must exert considerable repulsive force. The solenoid is in turn required to exert sufficient thrust force against the so-strengthened return spring, and an arrangement where the solenoid attracts the armature is thus advantageous. The armature, however, tends to keep adhering to the solenoid because of its residual magnetization, and therefore the return spring should exert greater repulsive force in order to separate or disengage it. The attractive solenoid and the return spring should therefore be strengthened synergistically.

How to bear the force and its reaction force is itself a technical problem and how to transmit the force to the clutch also requires significant consideration. Further, if larger magnetic flux is to be generated, careful consideration must be given to an influence by leakage of the magnetic flux to the environment. For example, to increase the magnetic path cross-sectional area of the core in order to reduce leakage of the magnetic flux a size of the device must be increased. More specifically, how to arrange and support related components in an attractive solenoid may cause many potential technical problems. The device disclosed hereafter has been created in light of these problems.

According to an aspect, a differential device is provided with: an input case rotatable about an axis and having an end face directed in a direction of the axis; a differential gear set including first and second side gears respectively rotatable about the axis and allowing a differential motion between the first and second side gears; dog teeth toothed toward the end face on an output case supporting the differential gear set or on the second side gear; a clutch structure engageable with the dog teeth and so structured as to couple the output case or the second side gear with the input case when engaged; a clutch member movable in the direction of the axis and including an internal end in communication with the clutch member and an external end exposed through the end face to an exterior of the input case; an armature movable in the direction of the axis, the armature being at least formed of a magnetic material and in contact with the external end; a solenoid supported away in the direction of the axis from the end face, the solenoid configured to generate a magnetic flux in the direction of the axis to attract the armature and, via the clutch member, set the clutch structure in mesh with the dog teeth; and a spring biasing the clutch member in a direction to disengage from the dog teeth.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Exemplary embodiments will be described hereinafter with reference to the appended drawings. Throughout the following descriptions and appended claims, unless otherwise described, an axis means a rotation axis of a differential device, an axial direction means a direction parallel to the axis and a radial direction means a direction perpendicular thereto. In the following description, distinctions between right and left are given, but are only for convenience of explanation. Embodiments where right and left are reversed could occur, of course.

Referring first toFIG.1, the differential device is usable for a purpose of allowing differential motion between both axles rotating about an axis C and as well temporarily transmitting torque from an input shaft to the axles (it could be referred to as “free-running differential” or such). The differential device could be used for embodying a part-time AWD vehicle although its application is, of course, not limited thereto.

The differential device is in general composed of an input case1that receives torque from the input shaft, a clutch11for operating a differential gear set7, and an actuator21for driving the clutch11. The differential device may be provided with an output case5supporting the differential gear set7, and the output case5is rotatable relatively to the input case1. The input case1and the output case5are mutually coaxial and nested, and normally but not indispensably the former houses the latter.

The input case1steadily or continuously connects with the input shaft to receive the torque and thereby rotate about the axis C. The input case5is provided with dog teeth13to constitute the clutch11, and the transmitted torque is, when the clutch11is disengaged, not transmitted to the output case5, thereby allowing the output case5to freely rotate about the axis C. If the actuator21makes the clutch11engaged, the input case1drivingly connects with the output case5to transmit the torque to the output case5, thereby rotating together.

Alternatively, as shown inFIG.6, one77of side gears of the differential gear set7may be, on the back face of its gear teeth, provided with the dog teeth13to constitute the clutch11. The differential gear set7in this example is, not via the output case5, directly supported by the input case1. If the clutch11is engaged, the side gear77is coupled with the input case1. When one77of the side gears is fixed, the other77cannot make differential motion, thus the clutch11according to this example is used for the purpose of locking/unlocking the differential motion by the differential gear set7. A differential device according to this example can be referred to as a “Lock-up differential” or such.

Referring back toFIG.1, the input case1is in general in the form of a cylinder and end faces closing its both ends roughly isolate the interior from the exterior. The connection between the input case1and the input shaft may be established by a ring gear for example and a flange radially projecting the cylinder may be usable for connection to the ring gear, although another embodiment is applicable thereto, of course.

Respectively further from both the end faces of the input case1, boss portions project axially outward, and the input case1is thereby supported by a carrier81. Between the input case1and the carrier81, bearings83such as roller bearings may be interposed, while ball bearings or any bearing devices may be substituted for the roller bearings. The actuator21is disposed around one3of the end faces.

The output case5is provided with the differential gear set7and is therefore capable of outputting torque to both the axles with allowing differential motion therebetween. According to the example illustrated inFIG.1, the differential gear set7is of a bevel gear type and is provided with pinion gears71rotatably supported by a pinion shaft73and side gears75,77in mesh therewith. Of course, any other proper type such as a face gear type or a planetary gear type is applicable thereto. The side gears75,77may be, on these inner peripheries, provided with splines for coupling with the axles although any other form may be used for coupling.

The output case5is, on one end9, provided with dog teeth13toothed axially and toward the end face3of the input case1. The dog teeth13constitute the clutch11, which drivingly connects the output case5with the input case1when engaged as described already. The clutch structure for drivingly connecting the output case5with the input case1may be, as exemplarily shown inFIG.1, established by means of a clutch member15, or alternatively the input case1may be provided with corresponding dog teeth to, in combination with the dog teeth13, constitute the clutch11.

Referring toFIG.2Afor example in combination withFIG.1, the clutch member15is a generally ring-like member loosely fitting in the inner face of the input case1and is movable in the direction of the axis C. Its internal end17is in interior of the input case1to communicate with the clutch structure. From the face opposed to the internal end17, a plurality of legs projects axially outward and respective external ends19thereof pass through the end face3and are exposed to the exterior of the input case1. As openings on the end face3are engaged with the legs of the clutch member15, the clutch member15is capable of transmitting torque from the input case1to the output case5.

The internal end17may be provided with second dog teeth14and the dog teeth13and the second dog teeth14are so structured as to mesh together, thereby forming the clutch11in combination. The clutch structure in this case is as described already in a unitary form with the clutch member15.

The external ends19may be further provided with a contact plate27for communicating with the actuator21. The contact plate27is of a plate-like shape forming a ring generally continuous in the circumferential direction, and may be provided with a part bent and raised properly for fastening with the external ends19and/or any proper projection for being in contact with the actuator21. A material applied to the contact plate27may be, although not particularly limited, differentiated from materials applied to the input case1and the clutch member15, and as well an armature23and a core53described later.

The actuator21is in general composed of an armature23, a solenoid25and a return spring31. The armature23is at least partly of a magnetic material and is thus attracted by magnetic flux generated by the solenoid25. The armature23is disposed to be in contact with the external ends19and is thereby capable of driving the clutch member15in the direction of the axis C. The return spring31biases the clutch member15in the opposing or counter direction.

The entirety of the solenoid25is circular around the axis C and is provided with a coil51that generates magnetic flux in the direction of the axis and a core53that surrounds the coil51to conduct the magnetic flux. The coil51is a wound lead line made of a good conductor such as copper, where the direction of winding is preferably so directed as to generate magnetic flux strongest in the direction of the axis C. The core53may be made of a high magnetic permeability material such as ferrite so that the magnetic flux is conducted with high efficiency to improve energy efficiency and as well reduce negative effect originated from leakage of the magnetic flux to the environment. The core53surrounds a most part of the coil51but leaves a part facing the armature23open axially, thereby effectively directing the magnetic flux toward the armature.

The armature23is provided with a radial face41that receives the aforementioned magnetic flux and is attracted thereby, which may be a disk-like face expanding in the radial direction. To broaden the area for receiving the magnetic flux, as shown inFIG.2B, it may be further provided with a bevel45inclining toward the core53and the bevel45may be not only on the radial inside but also on the outside. The core53may be in a form complementary to the bevels.

The armature23is further provided with an axial section43so elongated as to be in contact with the external ends19or the contact plate27and thus transmit the driving force thereto. The axial section43may be, as exemplarily shown inFIG.3Ain combination withFIGS.2A and2B, for example, a cylindrical rim rising in the axial direction from the outer periphery of the radial face41. The rim at least partly covers the core53and passes over its outer side to reach the external ends19or the contact plate27. This shape can be formed unitarily by pressing or drawing a flat plate and is thus easy for production. Of course, its production may be done by casting or forging, or an axial section43as a separate body may be joined with a flat radial face41. While such a shape is thin, it is sufficient to drive the clutch member15and is beneficial as the cross section of the core53need not be reduced.

The armature23, alternatively, may be provided with columns49, as illustrated inFIG.4, in place of or in addition to the cylindrical rim. The columns49penetrate the solenoid25, in particular the core53, and extend axially to be in contact with the external ends19or the contact plate27. The columns49may pass over the radial inside relative to the coil51as shown or over the outside. In these embodiments, as the columns49anti-rotate, i.e., prevent rotation of, the armature23, a cut-out such as described later may be omitted. Further alternatively, the columns49may detour the core53around its outer periphery. In this case, the columns49may be anti-rotated by engagement with a pin85described later or may have an independent anti-rotation means.

The axial section43or the columns49may be of the same material as that of the radial face41and also formed as a unitary body therewith, but nevertheless may be of a non-magnetic material and formed as separate bodies. In a case of the non-magnetic material, leakage of the magnetic flux can be reduced and its negative effect can be suppressed.

Further between the axial section43or the columns49and the external ends19or the contact plate27, a bush as a separate body from them may be interposed. The bush is ring-like and therefore, when the case1rotates, keeps contact with both these members. The bush may be of a non-magnetic material and further of a resin having a low friction coefficient, for example, to reduce friction.

As the internal periphery of the core53fits on the boss portion57, the totality of the actuator21is supported thereby. Except the internal periphery, the core53is set away from the input case1and particularly kept between the back face of the core53and the end face3of the input case1is a considerable gap. This is helpful in reducing leakage of the magnetic flux from the core53toward the end face3. The boss portion57may be provided with a shoulder59slightly expanding radially outward in order to place the core53in position. The extent of the shoulder59is at least short of the back face of the coil51and therefore the gap is kept at least at the radially outer side of the internal periphery of the coil51.

The internal periphery of the core53may be elongated axially in a direction opposite to the shoulder59as shown inFIGS.2A and4. This elongated section may substantially form a cylindrical shape and is usually formed in a unitary body with the core53but may be a separate body fixed to the core53. Its end may abut on the bearing83and be thereby prevented from falling off. Alternatively the boss portion57may be provided with a fall-off prevention member in order to prevent the core53from falling off. Such a member is for example a ring engaging with the boss portion57and may be of a non-magnetic material in order to prevent leakage of the magnetic flux. The internal periphery of the core53may not necessarily be, however, throughout its face in contact with the boss portion57. To reduce the contact area, any groove or recess may exist on the internal periphery of the core53. This is also helpful in reducing leakage of the magnetic flux and also helpful in reducing slide drag between the core53and the boss portion57.

The armature23may fit on the boss portion57, but instead may fit on its elongated section of the core53. In any case, they are in a slidable fitting relation and therefore the armature23is axially movable. As both the armature23and the core53are non-rotational and the former fits on the latter, it is advantageous in smoothing its axial travel. To prevent the armature23from falling off, a ring33engaging with the core53or the boss portion57may be used. The ring may be of a non-magnetic material to reduce leakage of the magnetic flux.

Alternatively, a support member35for supporting the core53and the armature23may be provided as shown inFIG.2B. The support member35is substantially in the form of a cylinder for example and its end may abut on the bearing83so as to be prevented from falling off. The support member35is in contact with the core53and both are non-rotational, and it can prevent the core from falling off. The support member35may alternatively establish tight-fitting on the boss portion57or have a structure for engaging with the boss portion57. The armature23may slidably fit on the support member35, thereby being helpful in suppressing leakage of the magnetic flux from the armature23to the boss portion57. To prevent the armature23from falling off, the support member35may be provided with any fall-off prevention structure and an example thereof is a short flange formed by bending the end thereof outward as shown. The support member35may be also of a non-magnetic material in order to reduce leakage of the magnetic flux.

The return spring31may be disposed in the gap kept between the back face of the core53and the end face3of the input case1. It may be interposed particularly between the contact plate27and the end face3. The return spring31may be slightly compressed in advance to bias the clutch member15in a direction to promote its disengagement.

While the return spring31is rotational along with the contact plate27and such, the armature23and the solenoid25are non-rotational and are preferably anti-rotated, i.e., held in place to prevent rotation. The core53may be provided with a pin85projecting radially outward, as shown inFIG.3Afor example, and the anti-rotation of the solenoid25may be realized by latching the pin85on the carrier81. The armature23may be provided with any structure engaging with the solenoid25, which may be a cut-out on the axial section43for engaging with the pin85. Alternatively applicable are pins87elongated from the core53to penetrate the armature23as shown inFIG.3B. In any case the armature23along with the solenoid25may be anti-rotated, i.e., secured, by pins85and87. The pins85and87may be formed in a unitary body with the core53but may be a separate body made of a non-magnetic material. In the case where it is of a non-magnetic material, leakage of the magnetic flux can be reduced and its negative effect can be suppressed.

Referring back toFIG.1, the differential device may be provided with any suitable means for detecting whether the clutch11is or is not engaged; one example is a contactless sensor91. Examples of the contact less sensor91include, but are not limited to, a sensor using high-frequency oscillation to detect proximity of metal, a sensor detecting change of electrostatic capacitance, electric field or magnetic field, and a sensor using optical means. These contactless sensors can avoid energy loss caused by contact between rotating components.

The contactless sensor91may be disposed where it can detect whether the contact plate27is close thereto or away therefrom. As will be understood from the preceding descriptions, the contact plate27is exposed out of the outer periphery of the differential device and moves in the gap between the core53and the input case1, therefore the contactless sensor91can execute precise detection without any disturbance by ambient components. While the contact plate27is rotational but ring-like as described already, during rotation, it steadily or continuously faces the contactless sensor91and is therefore available for detection of its axial position. Further as described already, as any arbitrary material is applicable to the contact plate27, it is allowed to select a material appropriate for detection by the contactless sensor91. Of course, instead of the contact plate27, any other part of the clutch member15could be selected as a subject for detection or, as illustrated inFIG.5A, any part of the armature23may be selected as the subject for detection. The armature23, being non-rotational, steadily or constantly opposes the equally non-rotational contactless sensor91and is thus available for detection of the position. Further, these components could additionally include any proper member for convenience of detection.

The contactless sensor91is described above to approach an axially moving component in the orthogonal direction but the contactless sensor91may be directed in the axial direction as illustrated inFIG.5B. The subject of detection may be the armature23or, as shown, the contact plate27. In the latter case, in order to avoid interference by the armature23and the core53, these components may be partly cut out. It is unnecessary to totally cut out them as the armature23and the core53are non-rotational components and instead only a part in question could be cut out. Of course, in place of forming cut-outs, the contact plate27may be expanded in diameter so as to project radially outward from outer edges of the armature23and the core53.

Alternatively, in place of the contactless sensor, as shown inFIG.5C, a contact sensor93is also applicable. The contact sensor93could be a mechanical push switch or a pull switch. Of course, a sensor using electric, magnetic or optical means may be used. The subject of detection includes the armature23and the contact plate27as described above, or any other part of the clutch member15may be the subject.

Further, in place of or in addition to any of the aforementioned sensors, a speed sensor or any other sensor may be provided for the differential device. The contact plate27may be correspondingly provided with notches or teeth formed on its peripheral edge, which cause the sensor to create pulses corresponding to its speed. As the contact plate27is a rotational member rotating in synchronous with the input case1, it is available for not only detecting whether the clutch11is engaged but also obtaining the rotational speed.

In the differential device described herein, leakage of the magnetic flux from the solenoid to the input case, particularly from the side face of the core to the end face of the input case, is reduced. In attractive solenoids, as the magnetic flux is densest in this direction and thus potently attracts the input case, it may cause prominent energy loss by friction if the back face of the core and the end face of the input case are mutually in contact. Further, as the input case rotates in the direction orthogonally to the magnetic flux, creation of induced current as well causes energy loss and this loss could increase as the magnetic force increases. The differential device described herein can reduce both these energy losses. Further, as it is unnecessary to increase the cross sectional area of the core to address leakage of the magnetic flux, the device could be designed in a more compact form. On the other hand, as the relatively broad gap between the back face of the core and the end face of the input case is available for the return spring, greater freedom of design about the return spring could be enjoyed and it is helpful to ensure sufficient repulsive force and a sufficient length of expansion and contraction. Further, as the contact plate is exposed radially outward in the gap, it is easy to detect the state of the clutch by means of sensors.

Although certain exemplary embodiments are described above, modifications and variations of the embodiments will occur to those skilled in the art, in light of the above teachings.