Differential and differential assembly method

A differential includes a pinion shaft holder, a differential case, a first side gear, a second side gear, a first spring and a second spring. The differential case includes a first side boss portion and a second side boss portion. The first spring is interposed between the first side boss portion and the first side gear. The second spring is interposed between the second side boss portion and the second side gear. A recessed portion is provided on the pinion shaft holder and is configured to avoid interference with an auxiliary tool. The auxiliary tool maintains one of the first spring and the second spring in the compressed state.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2012-039695 filed on Feb. 27, 2012 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a differential having a spring interposed in a compressed state between a surface of a side boss portion of a differential case and a surface of a side gear. The invention also relates to an assembly method of this differential.

2. Description of Related Art

With a differential according to related art described in Japanese Utility Model Application Publication No. 6-80943 (JP 6-80943 U), disc springs are interposed in a compressed state between surfaces of side boss portions of a differential case and corresponding surfaces of side gears, the surfaces opposing each other in an axial direction of the side gears. In this way, the side gears are pressed against pinion gears by the elastic restoring force of the disc springs, thereby reducing backlash between the side gears and the pinion gears.

This kind of a preload-type differential is difficult to assemble. More specifically, although not described in JP 6-80943 U, first, one side gear and the plurality of pinion gears have been set into the differential case. Then, before pinion shafts are assembled to the pinion gears in the differential case, a disc spring is interposed between the surface of one of the side boss portions of the differential case and the surface of one of the side gears, the surfaces opposing each other in the axial direction of the side gear. In the case when the disc spring is interposed, the disc spring must be compressed.

If the disc spring is not compressed, the side gear will end up being pushed upward toward the pinion gear side, with the disc spring in its natural state. As a result, the center of a center hole in this pinion gear will end up being offset with respect to the center of a through-hole for inserting the pinion shaft in the differential case. Therefore, it will be difficult to push the pinion shaft in so that it extends through both the through-hole in the differential case and the center hole in the pinion gear.

In the related art described above, the pinion shaft must be assembled to the pinion gear while the disc spring is compressed by some method, which is difficult to do and may therefore be time consuming.

SUMMARY OF THE INVENTION

The invention thus provides a differential having a spring interposed in a compressed state between a surface of a side boss portion of a differential case and a surface of a side gear, the surfaces opposing each another in an axial direction of the side gear, as well as an assembly method of this differential.

A first aspect of the invention relates to a differential that includes: a differential case having a first side boss portion and a second side boss portion; first side gear; a second side gear; a plurality of pinion gears; a first spring; a second spring; a plurality of pinion shafts; and a pinion shaft holder. The first spring is interposed in a compressed state between a surface of the first side boss portion and a corresponding surface of the first side gear, the surfaces opposing each other in an axial direction of the first side gear. The second spring is interposed in a compressed state between a surface of the second side boss portion and a corresponding surface of the second side gear, the surfaces opposing each other in an axial direction of the second side gear. Each of the plurality of pinion shafts is inserted from outside of the differential case and extends through a center hole in a corresponding one of the plurality of pinion gears and a corresponding through-hole provided in the differential case. The pinion shaft holder is arranged in a space surrounded by the plurality of pinion gears and has a plurality of through-holes into each of which an axial end portion of a corresponding one of the plurality of pinion shafts fits. The first spring applies a preload for pushing the first side gear against the plurality of pinion gears. The second spring applies a preload for pushing the second side gear against the plurality of pinion gears. Furthermore, recessed portions are provided on the pinion shaft holder and are configured to avoid interference with an auxiliary tool that keeps one of the first spring and the second spring in the compressed state.

With this structure, the possibility is reduced that, when a spring arranged between the side gear and the differential case is compressed and is maintained in this compressed state with an auxiliary tool, the auxiliary tool interferes with the pinion shaft holder that is adjacent to the side gear.

Therefore, by using the auxiliary tool, the centers of the center holes of the pinion gears and the centers of the through-holes of the pinion shaft holder are able to be concentrically aligned with the centers of the through-holes of the differential case.

Thus, the pinion shafts are able to be easily assembled extending through the through-holes of the differential case, the center holes of the pinion gears, and the through-holes of the pinion shaft holder. As a result, the assembly operation of the differential is able to be performed easily and quickly.

In this aspect of the invention, the pinion shafts are able to be assembled relatively easily, so the assembly operation of the differential is able to be performed easily and quickly. Therefore, the manufacturing cost of the differential is able to be reduced.

A second aspect of the invention relates to a differential that includes: a differential case having a side boss portion; a side gear; a pinion gear; a spring; a pinion shaft and a pinion shaft holder. The spring is interposed in a compressed state between a surface of the side boss portion and a corresponding surface of the side gear, the surfaces opposing each other in an axial direction of the side gear. The pinion shaft is inserted from outside of the differential case and extends through a center hole of the pinion gear and a through-hole of the differential case. The pinion shaft holder is a cylindrical member and has a through-hole into which an axial end portion of the pinion shaft fits. Then, a recessed portion is provided in an axial end portion of the pinion shaft holder and is recessed toward an axial center of the pinion shaft holder. The spring applies a preload for pushing the side gear against the pinion gear.

A third aspect of the invention relates to an assembly method of a differential. The differential includes a differential case having a side boss portion, a side gear, a pinion gear, a pinion shaft, a spring, and a pinion shaft holder that is a cylindrical member. The spring is interposed in a compressed state between a surface of the side boss portion and a corresponding surface of the side gear, the surfaces opposing each other in an axial direction of the side gear. Also, the pinion shaft holder has a through-hole into which an axial end portion of the pinion shaft fits. The recessed portion is recessed toward an axial center of the pinion shaft holder, on both axial end portions of the pinion shaft holder. Further, the through-hole passes through a cylindrical portion of the pinion shaft holder in a radial direction. Then, the assembly method includes: inserting an auxiliary tool from outside of the differential case into a center hole of the side boss portion; compressing the spring by hooking the auxiliary tool onto a surface of the side gear that faces the pinion shaft holder; maintaining the spring in the compressed state by the auxiliary tool; and while the spring is in the compressed state, inserting the pinion shaft from outside of the differential case so that the pinion shaft extends through a center hole provided in the pinion gear and a through-hole provided in the differential case.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, example embodiments of the invention will be described in detail with reference to the accompanying drawings.

FIGS. 1 to 10are views of one example embodiment of the invention. The general structure of the differential of the invention will be described with reference toFIG. 1.

In the drawing, the overall differential is denoted by reference character1. This differential1transmits rotative power input from a transmission or the like, not shown, to left and right driving wheels via a pair of left and right drive shafts, also not shown.

The differential1described in this example embodiment is configured as a three-pinion type differential. That is, the differential1mainly includes a differential case2, three pinion gears3(only two are shown inFIG. 1), three pinion shafts4(only two are shown inFIG. 1), one corresponding to each of the three pinion gears3, one pinion shaft holder5, and two side gears6and7and the like. In this specification, portions of the differential1may be referred to in the singular to facilitate understanding. For example, although the differential1includes the three pinion gears3, one pinion gear among them may be referred.

The differential case2is a case with a spherical space therein, and has a two piece construction in which a body21and a cover22are joined together by bolts, not shown.

Although not shown, the pair of left and right drive shafts is rotatably inserted into and supported, via roller bearings, by a side boss portion21aof the body21and a side boss portion22aof the cover22.

Through-holes21binto which axial outer ends of the pinion shafts4are inserted and by which the pinion shafts4are supported, are formed in a plurality of locations (three locations in this example embodiment) on the outer periphery near the joining surface of the body21. Here, the term “outer end” refers to an end portion positioned on a relatively outer side with respect to the radial direction of the spherical space.

The pinion shafts4are supporting shafts for the pinion gears3, and each is configured so as to be supported at both ends by the axial outer end being inserted into the through-hole21bof the body21and the axial inner end being inserted into a through-hole5aof the pinion shaft holder5. Hereinafter, the term “inner end” refers to an end portion positioned on a relatively inner side with respect to the radial direction of the spherical space. These pinion shafts4are inserted into center holes3aof the pinion gears3.

Each pinion shaft4is prevented from slipping out in the axial direction, as well as prevented from rotating, by a pin8. This pin8is inserted extending through a pin insertion hole21cprovided intersecting the through-hole21bin the body21, as well as through a through-hole4ain the pinion shaft4. This pin8is prevented from slipping out by the joining surface of the cover22.

The pinion shaft holder5is arranged inside a space surrounded by the three pinion gears3and the two side gears6and7, i.e., is housed in the space on the radial inside of the spherical space. Hereinafter, this space may be referred to as the radially inner space. This pinion shaft holder5is a cylindrical member having a smaller diameter than inscribed circles of a space surrounded by the three pinion gears3, as shown inFIGS. 2 and 3. Through-holes5athat pass through in the radial direction are provided in a plurality of locations (three locations in this example embodiment) on the circumference of a cylindrical portion of the pinion shaft holder5. The axial inner end sides of the pinion shafts4fit loosely into these through-holes5a.

The first side gear6is set inside the side boss portion21aof the body21of the differential case2such that the center of a center hole in the first side gear6is concentric with the center of a center hole in the side boss portion21aof the body21.

The second side gear7is set inside the side boss portion22aof the cover22of the differential case2such that the center of the center hole in the second side gear7is concentric with the center of a center hole in the side boss portion22aof the cover22.

A disc spring9and a thrust washer10are interposed between an outer end surface of the first side gear6and an inner end surface of the side boss portion21aof the body21that oppose each other in the axial direction of the first side gear6. Also, a disc spring9and a thrust washer10are also interposed between an outer end surface of the second side gear7and an inner end surface of the side boss portion22aof the cover22that oppose each other in the axial direction of the second side gear7.

By having the disc springs9respectively interposed in a compressed state between the first and second side gears6and7and the left and right side boss portions21aand22aof the differential case2, the first and second side gears6and7are pushed against the three pinion gears3by the elastic restoring force of the disc springs9, thereby reducing backlash between them.

The thrust washers10are sliding bearings that reduce the friction resistance of the left and right boss portions21aand22aof the differential case2when the first and second side gears6and7rotate, thus preventing the friction portions from seizing.

The first and second side gears6and7respectively include hollow shaft portions61and71. Gear portions62and72formed by bevel gears are provided on one axial end side of hollow shaft portions61and71, respectively. The gear portions62and72of the first and second side gears6and7are both each in mesh with the three pinion gears3.

The hollow shaft portions61and71are rotatably inserted into the center holes of the side boss portions21aand22aof the differential case2, respectively. Furthermore, small gaps are respectively formed, between inner peripheral surfaces of the center holes and the hollow shaft portions61and71, near the inner side openings of the side boss portions21aand22a. Axial inner end portions of the pair of left and right drive shafts described above, not shown, are spline-engaged with the insides of the hollow shaft portions61and71.

The operation of the differential1having this kind of structure will only be described in brief here.

First, when a vehicle is traveling straight ahead, for example, and rotative force is input to the differential case2, the first and second side gears6and7and the right and left drive shafts, not shown, are rotatably driven by the three pinion gears3revolving together with the differential case2, such that the left and right driving wheels are driven at the same rotation speed.

On the other hand, when there is a difference in the rotation resistance between the left and right rear wheels due to the vehicle traveling along a curve or the like, the three pinion gears3rotate (i.e., spin), and the first and second side gears6and7rotate differentially. As a result, the rotative force input to the differential case2is differentially distributed to the left and right driving wheels via the left and right drive shafts.

Next, before describing an assembly method of the preload-type differential1that uses the disc springs9, the structure and operation of an auxiliary tool30used in this assembly will be described in detail with reference toFIGS. 4 and 5.

The auxiliary tool30includes a guide pin31and a slider32and the like. The guide pin31is fixed inside an outer cylinder33. The slider32is fitted, in a manner relatively displaceable in the axial direction, to the radially outer side of the guide pin31.

The slider32includes an inner cylinder34, a plurality (two in this example embodiment) of movable pieces35, and a plurality of torsion coil springs36of a number equal to the number of moveable pieces35.

The inner cylinder34is fitted, in a manner relatively displaceable in the axial direction and the circumferential direction, to the inner periphery of the outer cylinder33. Recessed portions34aare formed in a plurality of circumferential locations (the same number as the number of moveable pieces35) on the axial inner end side (i.e., the inner end side when the auxiliary tool30is inserted into the differential case2) of the inner cylinder34. The moveable pieces35are attached to the recessed portions34aso as to be displaceable near and far with respect to (i.e., displaceable toward and away from) a central axis of the inner cylinder34. In other words, the moveable pieces35are attached so as to be able to tilt radially inward and outward with respect to the auxiliary tool30. Also, a guide piece34bthat extends in the axial direction is provided between the recessed portions34aprovided on the inner cylinder34.

Although it will be described in detail later, the guide piece34bis provided to make it easier for pawl-like protrusions35aof the moveable pieces35to hook onto an inner end surface of the gear portion62of the first side gear6, when tilting the moveable pieces35radially outward while the two moveable pieces35are inserted in the center hole of the first side gear6. Here, the inner end surface of the gear portion62faces the pinion shaft holder5.

Each of these moveable pieces35has a band plate-shaped and has a pawl-like protrusion35a. The pawl-like protrusion35aprotrudes in a direction orthogonal to a length direction of the moveable piece35and is provided on one end side in the length direction. The other end sides of the moveable pieces35in the length direction are attached to the recessed portions34aof the inner cylinder34.

More specifically, a spindle portion35bis provided on both ends in the width direction, on the other axial end side of each of the moveable pieces35. A tension coil spring36is wound around each of these spindle portions35b. One end side of this tension coil spring36catches on the inner cylinder34side, and the other end side of the tension coil spring36catches on the moveable piece35, such that the tension coil spring36is placed in a compressed state. The two moveable pieces35are urged closer to the central axis of the inner cylinder34, i.e., so as to tilt radially inward, by the elastic restoring force from the compression of the tension coil springs36.

That is, the two moveable pieces35are configured such that circumscribed circle diameters of the pawl-like protrusions35aof the two moveable pieces35become smaller than the inside diameter of the inner cylinder34and the inside diameters of the center holes of the first and second side gears6and7, by the two moveable pieces35being urged so as to constantly tilt radially inward from the spring force of the tension coil spring36(seeFIG. 6, for example).

Also, when a tip end side of the guide pin31that is inserted into the inner cylinder34is pushed into the space surrounded by the two moveable pieces35and the one guide piece34b, the moveable pieces35move away from the central axis of the inner cylinder34, i.e., tilt radially outward, against the spring force of the tension coil spring36. As a result, when the moveable pieces35tilt radially outward, a diameter of a circle contacting pawl-like protrusions35aof the two moveable pieces35becomes larger than the inside diameter of the inner cylinder34and the inside diameters of the center holes of the first and second side gears6and7(seeFIG. 8, for example).

In order to make it easier to push the guide pin31in, a tapered guide surface35cis provided on an inside surface of each of the two moveable pieces35. Also, positioning means (not denoted by a reference character) for positioning the guide pin31in the axial direction is provided midway in the length direction of the guide pin31and midway in the length direction of the inner cylinder34.

This positioning means includes a circumferential groove31a, a through-hole34c, and a ball41and a compression coil spring42that are inserted into the through-hole34c. The circumferential groove31ais provided midway in the length direction of the guide pin31. The through-hole34cis provided along the radial direction midway in the length direction of the inner cylinder34of the slider32, and an opening on a radially outer side of the inner cylinder34increases in diameter.

More specifically, the ball41and the compression coil spring42are housed in this order from the radial inside to the radial outside into the through-hole34cof the inner cylinder34. The compression coil spring42is in a compressed state by being pressed on (i.e., retained) by the outer cylinder33so as not to protrude radially outward. Therefore, the ball41is urged radially inward by the elastic restoring force of this compression coil spring42.

Here, when a portion of the ball41is engaged with the circumferential groove31aof the guide pin31, the guide pin31and the slider32are positioned so as not to be relatively displaced in the axial direction. When positioned in this way, the guide pin31is not pushed into the space surrounded by the two moveable pieces35and the one guide piece34b(seeFIG. 6, for example). In this state, a diameter of a circle contacting the pawl-like protrusions35aof the two moveable pieces35becomes smaller than the inside diameter of the inner cylinder34and the inside diameters of the center holes of the first and second side gears6and7. This state, shown inFIG. 6, will be referred to as an “inoperative state”.

Also, when the guide pin31and the slider32are relatively displaced in the axial direction by a slightly strong force, the ball41is pushed radially outward at an opening edge of the circumferential groove31a. Therefore, the compression coil spring42is compressed further by the ball41, and the ball41slips out of the circumferential groove31a. As a result, relative displacement in the axial direction between the guide pin31and the inner cylinder34is possible. When relative displacement is possible in this way, the guide pin31is pushed into the space surrounded by the two moveable pieces35and the one guide piece34b(seeFIG. 8, for example). Also, the diameter of the circle contacting the pawl-like protrusions35aof the two moveable pieces35become larger than the inside diameter of the inner cylinder34and the inside diameters of the center holes of the first and second side gears6and7against the spring force of the tension coil spring36. This state, shown inFIG. 8, will be referred to as an “operative state”.

Next, the way in which the auxiliary tool30described above is used, together with the assembly method of the differential1, will be described in detail with reference toFIGS. 6 to 10.

First, the disc spring9and the thrust washer10are arranged on the inside surface of the side boss portion21ain the body21of the differential case2, and then the first side gear6is set in. Furthermore, the three pinion gears3are set so as to be in mesh with this first side gear6, as shown inFIG. 6. Next, the pinion shaft holder5is set into the radial inner space surrounded by the three pinion gears3.

In this step, the disc spring9is in a natural state in which it is not compressed, so the first side gear6is lifted upward. That is, the first side gear6is lifted upward with respect to the direction of gravitational force. Therefore, centers200of the center holes3aof the pinion gears3and centers300of the through-holes5aof the pinion shaft holder5are radially offset such that they are not concentrically aligned with centers100of the through-holes21bof the body21.

In such a state, the two moveable pieces35and the one guide piece34bis inserted from the outside into the center hole of the side boss portion21aof the body21of the differential case2while the auxiliary tool30is placed in the inoperative state shown inFIG. 6. At this time, the pawl-like protrusions35aof the two moveable pieces35are away from, above, the inner end surface of the gear portion62of the first side gear6, as shown inFIG. 7.

Next, the auxiliary tool30is placed in the operative state. That is, the tip end of the guide pin31is guided along the tapered guide surfaces35cof the two moveable pieces35by fixing the guide pin31and sliding the slider32down as shown by the arrow inFIG. 7. Thus, the tip end of the guide pin31is inserted into the space surrounded by the two moveable pieces35and the one guide piece34b.

As a result, the two moveable pieces35are tilted radially outward against the spring force of the tension coil springs36, and the pawl-like protrusions35aof the two moveable pieces35are hooked onto the inner end surface of the gear portion62of the first side gear6, as shown inFIG. 8.

In this kind of state, by sliding the slider32further downward as shown by the arrow inFIG. 8, the disc spring9is compressed by the first side gear6when the first side gear6is lowered together with the slider32.

As a result, the pinion shaft holder5and the three pinion gears3that are in mesh with the first side gear6move downward by their own weight. Thus, the centers200of the center holes3aof the pinion gears3and the centers300of the through-holes5aof the pinion shaft holder5become concentrically aligned with the centers100of the through-holes21bof the body21, as shown inFIG. 9.

In this state, by inserting the pinion shafts4into the through-holes21bof the body21from the outside, the pinion shafts4are able to be inserted into both the center holes3aof the pinion gears3and the through-holes5aof the pinion shaft holder5, as shown by the arrow inFIG. 9.

Then, the pins8are inserted into the pin insertion holes21cprovided intersecting the through-holes21bof the body21and the through-holes4aof the pinion shafts4, as shown inFIG. 10. Further, the second side gear7, the disc spring9, and the thrust washer10are assembled to the body21, and the cover22is attached by a bolt to the body21.

Then, as shown by the arrow inFIG. 10, the tip end of the guide pin31is withdrawn from the space surrounded by the two moveable pieces35and the one guide piece34bby sliding the guide pin31downward with respect to the slider32in the auxiliary tool30. As a result, the two moveable pieces35tilt radially inward by the elastic restoring force of the tension coil springs36. Accordingly, the pawl-like protrusions35aof the two moveable pieces35separate from the inner end surface of the gear portion62of the first side gear6and are pulled to the radial inside of the center hole of the first side gear6.

Next, the auxiliary tool30is pulled out the first side gear6and the side boss portion21aof the body21by pulling the entire auxiliary tool30downward.

In this way, the auxiliary tool30is used to compress the disc spring9that is interposed between the surface of the side boss portion21aof the body21of the differential case2and the surface of the gear portion62of the first side gear6, and then keep the disc spring9in this compressed state, before the pinion shafts4are assembled to the three pinion gears3when assembling the differential1. In particular, with the auxiliary tool30having a structure such as that described in this example embodiment, once the disc spring9has been compressed, the compressed state is able to be maintained relatively easily.

In this example embodiment, recessed portions5bare provided on the pinion shaft holder5. Therefore, in the assembly process described above, the possibility is reduced that the pawl-like protrusions35aof the auxiliary tool30interfere with the pinion shaft holder5when the pinion shaft holder5is assembled with the pawl-like protrusions35ahooked onto the inner end surface of the gear portion62of the first side gear6.

These recessed portions5bare provided recessed toward the axial center of the pinion shaft holder5on both axial end portions of the cylindrical pinion shaft holder5, as shown inFIGS. 2 and 3. Also, the recessed portions5bare provided in regions corresponding to the center holes of the first and second side gears6and7. In particular, in this example embodiment, the recessed portions5bare provided in regions between the three through-holes5aprovided in the pinion shaft holder5, i.e., regions in three locations.

When the recessed portions5bare provided in this way, the pinion shaft holder5is bilaterally symmetrical with respect to a plane orthogonal to the axial center of the pinion shaft holder5. The reason for making the pinion shaft holder5bilaterally symmetrical in this way is so as to not limit the arrangement phase of the through-holes5aor the assembly direction when assembling the pinion shaft holder5inside the body21of the differential case2, as well as to improve the weight balance of the pinion shaft holder5when the pinion shaft holder5rotates as the three pinion gears3revolve.

The lengths of the recessed portions5bin the axial direction of the pinion shaft holder5are set to dimensions such that the tip ends of the two moveable pieces35(i.e., the pawl-like protrusions35a) will not interfere with the pinion shaft holder5when the two moveable pieces35and the one guide piece34bare inserted into the center hole of the first side gear6and the first side gear6is slid downwards, as shown inFIG. 8, for example.

Also, the lengths of the recessed portions5bin the circumferential direction of the pinion shaft holder5are set to dimensions such that the recessed portions5bwill not interfere with the pawl-like protrusions35athat move as a result of the two moveable pieces35of the auxiliary tool30tilting radially outward.

Setting the dimensions in this way makes it possible to reliably avoid the auxiliary tool30interfering with the pinion shaft holder5while the disc spring9is maintained in the compressed state by the auxiliary tool30.

As described above, in the example embodiment to which the invention has been applied, the recessed portions5bare provided on the pinion shaft holder5to prevent the pawl-like protrusions35afrom interfering with the pinion shaft holder5that is placed on the inner end surface of the first side gear6, while the pawl-like protrusions35aof the two moveable pieces35of the auxiliary tool30are hooked onto the inner end surface of the gear portion62in the process of assembling the differential1.

Also, the disc spring9is arranged between the surface of the first side gear6and the surface of the side boss portion21aof the body21that oppose each other in the axial direction of the first side gear6. Then, the disc spring9is compressed and maintained in this compressed state by the auxiliary tool30, before the pinion shafts4are assembled to the three pinion gears3. In this compressed state, because the recessed portions5bare provided on the pinion shaft holder5, the possibility is reduced that the pawl-like protrusions35aof the moveable pieces35of the auxiliary tool30interfere with the pinion shaft holder5.

Therefore, by using the auxiliary tool30, the centers200of the center holes3aof the three pinion gears3and the centers300of the three through-holes5aof the pinion shaft holder5are able to be concentrically aligned with the centers100of the three through-holes21bof the body21.

Thus, the assembly operation is able to be performed easily and quickly, e.g., the pinion shafts4are able to be easily assembled extending through the through-holes21bof the body21, the center holes3aof the pinion gears3, and the through-holes5aof the pinion shaft holder5. As a result, the manufacturing cost of the differential1is able to be reduced.

The invention is not limited to only the example embodiments described above. That is, the invention also includes all modifications and applications that are within the scope, and meanings equivalent to the scope, of the claims for patent. Hereinafter, another example embodiment of the invention will be given as an example.

In the example embodiment described above, the differential1includes the three pinion gears3, but the invention is not limited to this. That is, the number of pinion gears3used may be set appropriately as long as it is two or more.

In the example embodiment described above, the auxiliary tool30includes the two moveable pieces35, but the invention is not limited to this. For example, as long as the auxiliary tool30is configured to hook the pawl-like protrusions35aof the moveable pieces35cm the inner end surface of the gear portion62of the first side gear6when compressing the disc spring9, the structures of the details of the auxiliary tool30are not particularly limited.

In the example embodiment described above, a case in which the spring used for applying a preload to the differential1is the disc spring9is given as an example, but the invention is not limited to this. That is, the type of this spring is not particularly limited.

The invention may be applied to a differential having a structure in which a spring that applies a preload for pushing a side gear against a plurality of pinion gears is interposed in a compressed state between a surface of a first side boss portion of a differential case and a corresponding surface of a first side gear, the surfaces opposing each other in the axial direction of the first side gear, and between a surface of a second side boss portion of the differential case and a corresponding surface of a second side gear, the surfaces opposing each other in the axial direction of the second side gear, as well as to an assembly method for this differential.