Differential device with two-step ability to limit differential motion

A differential device is provided with: an input member; a gear set with output gears to transmit torque from the input member to the output gears while allowing differential motion therebetween; a first clutch for limiting the differential motion; a first pressure pressing on the first clutch; a first cam mechanism for pressing the first pressure plate toward the first clutch; a second clutch, when connected, drivingly connecting the output gears with the input member; a second pressure plate for engaging the second clutch; and a rotatable driver disk including a pressing member so coupled with the cam mechanism as to, from a first position to a second position, rotate the first cam mechanism together and to, from the second position to a third position, allow the first cam mechanism to create rotational difference relative to the pressing member, thereby engaging the second clutch.

BACKGROUND

As right and left axles in a vehicle do not necessarily rotate in an equal speed, it is required to allow differential motion therebetween. To transmit torque to both the axles with enabling differential motion therebetween, a differential device is used.

In a case where either a right or left driving wheel loses traction, the differential device will run idle and then lose an ability to transmit torque even to the other driving wheel. To avoid such a situation, some differential devices comprise mechanisms for limiting differential motion. One example thereof is a limited slip differential (LSD) which uses a friction clutch. An electronically controlled LSD could also be used, which uses a device for applying pressure force to its friction clutch and an electronic device for controlling the device in combination. Possible as the pressure device are hydraulic and cam mechanisms.

On the other hand, a so-called free-running differential can controllably connect and shut off a differential device from a propeller shaft, which is for example used for switching between a two-wheel mode and a four-wheel mode. A friction clutch in combination with a pressure device is often used for such connection and shut-off therein. A device in which an electronically controlled LSD is combined with a free-running differential has been proposed, which comprises independent two sets of friction clutches and pressure devices. Published Japanese translation of PCT International Publication for Patent Application No. 2012-512996 discloses a related art.

SUMMARY

The disclosure herein relates to a differential device with a two-step ability to limit differential motion, and in particular to a differential device capable of limiting differential motion at a first step and locking it at a second step.

A friction clutch is suitable for limiting differential motion, whereas it is not adaptable to use for locking a differential device because it starts slippage when it receives torque above its threshold depending on an applied pressure force. In contrast, a dog clutch is suitable for locking a differential device, whereas it cannot be used for limiting differential motion because it cannot allow slippage. Use of these two clutches in combination of driving devices respectively applied thereto may enable a differential device freely selectable between limiting and locking differential motion, but is expected to terribly complicate its structure. A complicated structure is, of course, disadvantageous in terms of reliability and weight.

The following disclosure relates to a device using only one actuator to realize both limiting and locking differential motion.

According to an aspect, a differential device is provided with: an input member receiving torque to rotate about an axis; a gear set including output gears rotatable about the axis, the gear set being so coupled with the input member as to mediate transmission of the torque from the input member to the output gears while allowing differential motion between the output gears; a first clutch so coupled with the input member and the output gears as to limit the differential motion; a first pressure plate axially adjacent to the first clutch and axially movable to press on the first clutch; a first cam mechanism adjacent to the first pressure plate to press the first pressure plate toward the first clutch; a second clutch, when connected, drivingly connecting the output gears with the input member; a second pressure plate axially adjacent to the second clutch and axially movable to engage the second clutch; and a driver disk capable of making a rotational motion from a first position via a second position to a third position, the driver disk including a pressing member so coupled with the cam mechanism as to, from the first position to the second position, rotate the first cam mechanism together and to, from the second position to the third position, allow the first cam mechanism to create rotational difference relative to the pressing member, and in combination with the second pressure plate constituting a second cam mechanism to engage the second clutch.

DESCRIPTION OF EXAMPLARY EMBODIMENTS

Exemplary embodiments will be described hereinafter with reference to the appended drawings. Throughout the following description and the appended claims, an axis means a rotational axis of a differential device, an axial direction means a direction parallel thereto and a radial direction means a direction perpendicular thereto unless otherwise described. The rotational axis ordinarily agrees with rotational axes of cam mechanisms and a driver disk but agreement is not necessary. Further, while distinctions between the right and the left will made for the convenience of explanation, these distinctions do not limit possible embodiments.

While a differential device of a bevel gear type will be described hereafter as an example, what the present specification discloses is generally applicable to any gear device mediating torque transmission from an input member to output gears while allowing differential motion therebetween, such as a differential device of a face-gear type or a planetary gear type.

Referring mainly toFIG. 1, the differential device is generally provided with a casing1as an input member, a differential gear set3which transmits torque while allowing differential motion, a first clutch5for limiting the differential motion, a second clutch7for locking up the differential motion, and an actuator9for putting these clutches in action.

The casing1houses the differential gear set3and as well acts as an input member that receives torque from an engine/motor to rotate about an axis C. The casing1may be so structured as to be dividable into multiple members to expose the interior for convenience of installation of various components therein, and is for example dividable into a main body11and a cover13. For the convenience of coupling the cover13with the main body11, these members may be provided with flanges for example, which radially outwardly spread and are as well applicable to coupling with a ring gear for receiving the torque. Of course, any other structure is applicable to coupling and any other portion of the casing1is applicable to receive the torque.

In the casing1, the main body11, for example, is on its periphery provided with through-holes for coupling with a shaft15, which is secured to the main body11by means of a pin or such. In the casing1, the cover13, for example, is on its side face provided with through-holes17,19for communicating the clutches5,7with the actuator9.

The differential gear set3is in general provided with a plurality of pinions31and side gears33,35respectively meshing with the pinions31. The pinions31are so supported by the shaft15in a way as to be rotatable thereabout, and receive torque via the shaft15from the casing1.

The side gears33,35are output gears, which respectively have structures such as splines in order to couple with axles, to output the torque to both the axles. More specifically, the differential gear set3, via engagements among the gears, mediates transmission of the torque from the casing1as an input member to the side gears33,35as output gears while allowing differential motion therebetween.

One of the side gears33,35, a boss portion35B of the left side gear35for example, is preferably elongated in the axial direction to serve for coupling with the first clutch5, particularly for engagement in the circumferential direction with inner plates53or pressure plates55described later.

Referring toFIG. 2Ain combination withFIG. 1, the first clutch5is preferably a friction clutch composed of a pair of, or more, friction plates mutually applying friction, and is for example a multi-plate clutch comprising a plurality of outer plates51, a plurality of inner plates53and a pressure plate55. Plural pairs of the outer plates51and the inner plates53, although only one pair is visible inFIG. 2A, are alternately arranged in the axial direction, where the outer plates51are engaged with the casing1by means of lugs or such and the inner plates53the boss portion35B. In addition, the plates51,53,55are all slightly movable in the axial direction, and the pressure plate55is axially adjacent to and thereby capable of pressing the plates51,53. When the pressure plate55slightly moves toward the plates51,53and then applies pressure thereto, the plates51,53come to frictionally brake the side gear35relative to the casing1and therefore limit its differential motion.

In the casing1further housed is a clutch member75, which is movable in the axial direction. A face of the clutch member75, which faces the pressure plate55, is toothed to form first clutch teeth71, and a combination thereof and second clutch teeth73in mesh therewith constitutes the second clutch7. The second clutch teeth73may be formed on a component separate from the pressure plate55or formed on and as a unitary body with the pressure plate55. In any case, the separate component or the pressure plate55becomes engaged with the boss portion35B of the side gear35by means of lugs or such.

From a face of the clutch member75opposed to the first clutch teeth71, plural legs77stand axial-symmetrically and extend in the axial direction, which respectively fit in and engage with the through-holes19of the cover13, as best shown inFIG. 7in particular. Respective ends of the legs pass through the through-holes19to get exposed to the exterior and may be combined with a ring107outside the casing1by mean of bolts or such. The ring107serves for communication with a second cam mechanism101as will be described later.

When the clutch member75moves in the axial direction toward the pressure plate55and consequently the clutch teeth71,73get engaged mutually, the second clutch7by means of the engagement of the legs77with the cover13makes the side gear35drivingly combine with the casing1, whereby prohibiting differential motion (locking up the differential gear). To promote disengagement, any return spring may be interposed between the ring107and the cover13.

Referring toFIG. 2Bin combination withFIGS. 1 and 2A, the actuator9is in general provided with a first cam mechanism91for driving the first clutch5, the second cam mechanism101for driving the second clutch7, and a driver disk95for putting them into action.

Any cam mechanism that creates relatively great pressure force can be applied to the first cam mechanism91. The first cam mechanism91according to the example shown in the drawings is generally provided with a cam plate81rotatable about the axis, a plurality of cam balls83arranged to be axially symmetrical, and an anti-rotated counter plate85. The cam plate81and the counter plate85are, respectively, in general ring-like or disk-like, and the cam balls83are put in therebetween and thus capable of rolling thereon. In place of the balls, any rollers capable of rolling, such as columns or truncated cones, are applicable, or cam projections formed on any one or both of the cam plate81and the counter plate85may be used.

The cam plate81has a plurality of cam faces81F respectively corresponding to the cam balls83and each cam face81F has a bottom elongated and slanted gently in the circumferential direction. In addition thereto or in place thereof, the counter plate85may also have corresponding cam faces. The cam plate81is further provided with a pair of grips81G for coupling with the driver disk95. The grips81G engage with the driver disk95of itself or a pressing member as will be described later, thereby being driven into rotational motion.

As best shown inFIG. 4, when the cam plate81is driven by the driver disk95and then set into a rotational motion RD, the cam balls83roll on the cam faces81F to go up the slanted bottoms to impart a pressure force F1to the counter plate85.

Referring again toFIGS. 1, 2A and 2B, mainly toFIG. 2B, to serve as a mediation between the first cam mechanism91and the first clutch5, a medial member37may be used. The medial member37is generally ring-like for example and is provided with a plurality of axial-symmetric projections37P toward the first clutch5and the projections37P pass through the through-holes17of the cover13to come adjacent to the pressure plate55. To equalize the pressure forces respectively applied by the projections37P, and to absorb relative rotation before limiting differential motion, any intervening members103may be interposed between the projections37P and the pressure plate55. The intervening members103are a thrust bearing and/or a ring plate for example. Further, a thrust-bearing/ring-plate105may be interposed also between the medial member37and the first cam mechanism91.

The actuator9is further provided with a second pressure plate93, which is, although having the ring107interposed as described above, adjacent to the second clutch7. The second pressure plate93is provided with a plurality of legs93L extending opposite to the second clutch7, namely toward the driver disk95, which are as well arranged axially symmetrically. As corresponding thereto, the driver disk95is provided with cam faces99, and each cam face99, as shown inFIG. 5, includes a bottom slanted in the circumferential direction. The slope therein may be made relatively steep. The combination of the legs93L and the cam faces99constitutes the second cam mechanism101.

The cam plate81is, as corresponding to the legs93L, provided with perforations81H, and as shown inFIG. 5the legs93L pass through the perforations81H to get exposed to the cam faces99, respectively. When the driver disk95is in the rotational motion RDand makes a difference in rotation relative to the cam plate81, the legs93L follow the cam plate81. Then, as the legs93L slide on the cam faces99and go up the bottoms thereof, the second pressure plate93moves in the axial direction and, via the ring107, engages the second clutch7.

Referring toFIG. 3in combination withFIG. 2B, the actuator9is provided with the driver disk95, which is laid on the cam plate81. The driver disk95is generally in a shape in which a half disk nearly equal in radius to the cam plate81is combined with a larger half disk. The larger half may be provided with gear teeth, which are applicable to coupling with a motor at the exterior. Alternatively, the driver disk95may by itself constitute a rotor of the motor or, still alternatively, may be driven by any driver device other than the motor or constitute a part of the driver device. The driver disk95is coaxial with and rotatably supported by the casing1. A ball bearing111may be used for the purpose of rotatable support.

In addition, by using the larger half, it may be combined with the pressing member97for driving the first cam mechanism91. In the example shown in the drawing, the pressing member97is a coil spring and the driver disk95is provided with a semi-cylindrical hollow95S in which the coil spring fits. Both ends of the pressing member97butt against, and are supported by, both ends of the hollow95S, and further a bracket or such is applicable thereto in order to prevent displacement. In addition, both the ends of the pressing member97of the coil spring respectively butt against grips81G, thereby rotating the cam plate81along with the driver disk95.

Referring mainly toFIG. 6A, while the driver disk rotates from its initial position (first position) to a certain position (second position), as the repulsive force by the coil spring overcomes the reaction force applied by the cam plate81, the driver disk95rotates the cam plate81together and the first cam mechanism91exerts a pressure force in accordance with its rotational angle on the first clutch5, thereby putting the first clutch5in action. The first cam mechanism91is beneficial to operation of the first clutch5which is a friction clutch, as it uses the cam balls rolling on the gently slanted faces to create a relatively large pressure force.

Referring mainly toFIG. 6B, when rotating beyond the second position, as the repulsive force yields to the reaction force and then the coil spring becomes compressed, a difference in rotation between the driver disk95and the cam plate81is created. As stated already, when a rotational difference is created, the legs93L go up the cam faces99so that the second pressure plate93moves in the axial direction, thereby moving the clutch member75in the axial direction.

When the driver disk95rotates beyond the second position to reach the third position, the second clutch7becomes engaged. While the pressure force by the second cam mechanism101is weaker than that by the first cam mechanism91, such a relatively low pressure force is sufficient because it is unnecessary to counter the reaction force. Further, as shown inFIG. 7, after engagement, side faces of the legs77come into contact with side faces of the through-holes19to retain its state; a relatively large pressure force is not required to retain the engagement.

Further, the side faces of the legs77and the side faces of the through-holes19may be correspondingly gently oblique in the circumferential direction. This structure converts a rotational motion RDof the cover13into a pressure force F2and is thus beneficial to retention of engagement.

While the rotational motion progresses from the second position to the third position, the cam balls83hardly roll over, or rather stand still, in the first cam mechanism91. Because the cam balls83do not move further in depth in the cam faces, they can immediately move back to the initial positions when the driver disk95reverses its rotation.

The second position is determined uniquely by a balance between the repulsive force by the coil spring and the reaction force. More specifically, the second position can be arbitrarily set by regulation of a spring modulus of the coil spring, and the pressure force by the first cam mechanism91, which determines the upper limit of the braking power by the first clutch5, can be also arbitrarily set thereby.

According to the present embodiment, the first clutch which limits the differential motion and the second clutch which prohibits the differential motion are both put in action only by the single driver disk. As the actions thereof are controlled only by the rotational angle of the driver disk, control of the actions of the first and second clutches is readily carried out. As the first clutch in advance limits the differential motion by the time the second clutch becomes engaged, any relative rotation between these clutch teeth is eliminated and therefore engagement therebetween is not disturbed.

Although the pressing member97is described above as the coil spring, any other repulsive member is applicable thereto. Alternatively, in place thereof or in addition thereto, applicable is any latch mechanism or a ratchet mechanism which retains engagement from the first position to the second position and releases engagement at the second position. Still alternatively, it may be so constituted that a constitution of the cam faces, not any pressing member, delays action of the second cam mechanism behind action of the first cam mechanism.

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.