JPH08247255A - Differential device - Google Patents

Abstract

PURPOSE: To sharply reduce eccentric abrasion and seizure on a helical gear. CONSTITUTION: This device consists of a diff case 21 which is rotating-driven by an engine, output side helical side gears 37, 39, a helical pinion gear 67 whose gear part 71 is engaged with the gear 39, and a helical pinion gear 69 whose gear part 77 is engaged with the gear 37, and it is provided with a pinion gear group whose gear parts 73, 79 of the gears 67, 69 are engaged with each other, and housing holes 63, 65 for slidably and rotatably housing the gears 67, 69. In the case where the twist angle of tooth trace which is brought in contact with the housing hole 65 at the time of running of a vehicle in the pinion gear 69 is reduced by reaction applied in respective gear parts 77, 79, the tooth length of the center part of the pinion gear 69 is formed smaller than that of both end parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle differential device.

[0002]

2. Description of the Related Art Japanese Unexamined Utility Model Publication No. 6-43401 discloses a differential device 201 as shown in FIG. This differential device 201 includes a differential case 203.
And long and short helical pinion gears 205 and 207, and output side helical side gears 209 and 211. The helical pinion gears 205 and 207 are slidably and rotatably housed in housing holes 213 and 215 of the differential case 203. . The driving force of the engine that rotates the differential case 203 is transmitted from the helical pinion gears 205 and 207 to the wheel side via the side gears 209 and 211.

While transmitting the torque, each helical pinion gear 205, 207 is connected to the helical side gear 209,
Each tooth tip is stored in the storage hole 213 by the reaction force of engagement with 211.
The frictional force is generated by being pressed against the wall surface of 215, and the meshing thrust force of the helical gear causes a space between the helical side gears 209 and 211, or between the respective helical pinion gears 205 and 207 and the helical side gear 2.
Friction resistance occurs between the 09, 211 and the differential case 203, and the differential limiting force is obtained by these friction resistances.

[0004]

SUMMARY OF THE INVENTION The differential device reduces the oil inside the differential case to a low temperature where the oil flow is poor,
With the differential rotation speed and input torque set to predetermined values, after giving a few cycles of differential rotation corresponding to the left and right turns of the vehicle, disassemble and investigate burning and galling of sliding parts. The test is conducted. As a result, it was found that short helical pinion gears were worn only at the central portion in the axial direction and at both ends.

The cause of this is analyzed as follows.

FIG. 7 is a transverse cross-sectional view of the differential device 201. The short helical pinion gear 207 is arranged so as to revolve after advancing in the rotational direction 200 of the differential case 203 of the differential device 201 during forward movement. FIG. 8 shows a meshing portion between the short helical pinion gear 207 and the helical side gear 211 and a meshing portion between the short helical pinion gear 207 and the long helical pinion gear 205. FIG. 8 shows a side surface portion of the short helical pinion gear 207 seen from the Y direction in FIG. A tooth trace 219 and the like are shown. 9 shows the end face of the helical pinion gear 207, the left half of which is the end face in the A direction of FIG.
The right half part is the end surface in the B direction in FIG. EA and E of FIGS.
B indicates an axial end portion of a portion (contact portion with the differential case 203) that receives a force F (FIG. 7) due to rotation of the differential case 203, and N indicates a central portion in the axial direction.

As shown in FIG. 7, when the vehicle travels forward (in the direction of arrow 217), the helical pinion gear 207 receives a force F from the wall surface of the housing hole 215 due to the rotation of the differential case 203, and the helical side gear 211 and the helical pinion gear 205. Are pressed, and the reaction forces f1 and f2 are received from them. As shown in FIG. 8, these reaction forces f1 and f2 have different axial positions of the points of action, so the helical pinion gear 20
Forces 221 and 221 about the midpoint N act on 7 and the moments cause the ends EA and EB to move toward the arrow 22 in FIG.
It acts in the direction of 3,225. In this way, the helical pinion gear 207 falls in the direction in which the twist angle θ of the tooth trace 219 becomes smaller, as indicated by the broken line 227 in FIG. 8, and between the tooth tips of the helical pinion gear 207 and the wall surface of the storage hole 215 as shown in FIG. 10. There is a gap x in the differential case 203.
Drive torque to the pinion gear 207 from the wall of the storage hole
Is input over the entire length of the pinion gear 207, and the pinion gear 207 receives a high reaction force at each meshing portion and contacts the wall surface of the storage hole 215.

Here, the gap x is calculated according to the example of FIG.

In this example, assuming that the tooth width of the helical pinion gear 207 excluding the chamfered portion is Lmm and the helix angle is θ °, the circumferential length from the end EA to the end EB is L × t.
an θ, and the length in the circumferential direction from each end EA, EB to the midpoint N is ½ thereof.

Further, when the angle formed by each end EA, EB and the center O is α,

## EQU1 ## α = ((L × tan θ) / 2) / (θ × π) × 360 (1)

Next, when the displacement amount of each end portion EA, EB due to the tilting of the helical pinion gear 207 is δ mm and the gap formed between the helical pinion gear 207 and the wall of the housing hole 215 is x, x = sin α ° × δmm Equation (2) is obtained.

As shown in FIG. 10, this clearance xmm is a clearance at each end EA, EB of the tooth line 219, and each end E
As the distance from A and EB approaches the midpoint N, α in the equation (1) becomes smaller, the gap x becomes narrower in the equation (2), and the gap x at the midpoint N becomes zero. Therefore, when the vehicle travels forward, the tooth tip of the helical pinion gear 207 is located near the midpoint N in the storage hole 2.
If it comes into contact with or slides against the wall surface of 15, abrasion will progress. That is, when the drive torque is input to the differential case 203, the contact edge of the pinion gear 207, which is received by the axial length of the wall surface of the storage hole 215, is shortened due to the decrease in the twist angle due to the tilt described above, so that the storage hole 2 is only near the midpoint N.
When the pinion gear 207 comes into contact with or slides against the wall surface of the pinion 15, uniform contact cannot be obtained over the entire tooth width of the pinion gear 207, and the wear increases as the input torque increases.

Further, when the vehicle is traveling in reverse, as shown in FIGS.
Reaction forces f1 and f2 of the
Since the helical pinion gear 207 is tilted in the opposite direction to that in the forward traveling by 229 to increase the twist angle θ, the gap x becomes wider near the midpoint N and becomes 0 at each end EA, EB. Therefore, the end portion E that strongly hits the wall surface of the storage hole 215
Wear progresses in the vicinity of A and EB.

FIG. 11 shows a short helical pinion gear 233 in which the tooth line 231 is formed in the direction opposite to the helical pinion gear 207. The short helical pinion gear 233 is also used in the differential case 203 of the differential device 201, like the pinion gear 207 described above.
It is arranged so as to orbit after the rotation direction 200 of the above. In this case, the tooth trace 231 receives the forces 235 and 235 by the reaction forces f1 and f2 when the vehicle travels forward, and falls in the direction in which the twist angle θ of the tooth trace 231 increases as indicated by the broken line 237, and the vehicle moves backward. When traveling, the vehicle receives the forces 239, 239 in opposite directions and falls in a direction in which the twist angle θ decreases. Therefore, as shown in FIG. 12, when the vehicle travels forward, the gap x becomes wider near the midpoint N as in the case where the vehicle travels backward in the above-described example, and the pinion gear 233 is entirely covered with respect to the wall surface of the storage hole. It is not possible to get even contact with the tooth width,
The vicinity of the end portions EA and EB that come into strong contact with the wall surface of the storage hole 215 is worn away, and when traveling in reverse, as in the case of traveling forward in the above example,
Around the midpoint N wears.

As described above, the wear of the helical gear occurs at different portions depending on the direction of the tooth trace and the traveling direction of the vehicle.

Therefore, an object of the present invention is to provide a differential device which is composed of a helical gear and in which uneven wear and seizure of the gear are significantly reduced.

[0017]

According to another aspect of the present invention, there is provided a differential device including: a differential case which is rotationally driven by a driving force of an engine; a pair of output side helical side gears;
A helical pinion gear in which the first gear portion meshes with one of the helical side gears, and a second gear portion, and a helical gear in which the first gear portion has the first and second gear portions and the first gear portion meshes with the other helical side gear. A pinion gear group consisting of a pinion gear, each second gear part meshing with each other, and a storage hole formed in the differential case for slidably and rotatably storing each helical pinion gear. If the helix angle of the tooth trace is smaller due to the reaction force received by the first and second gears, make sure that the tooth height at the axial center of this helical pinion gear is continuously lower than that at both ends. Characterize.

According to another aspect of the present invention, in the differential device, the tooth height at the central portion in the axial direction of the pinion gear that revolves backward in the rotation direction of the differential case when the vehicle is traveling forward is continuous from the tooth height at both ends. 2. The differential device according to claim 1, wherein the differential device is formed low.

A differential device according to a third aspect of the present invention includes a differential case which is rotationally driven by a driving force of an engine, a pair of output side helical side gears, a first gear portion and a second gear portion, and the first gear portion is one side. A helical pinion gear that meshes with the helical side gear, and a helical pinion gear that has first and second gear parts, the first gear part meshing with the other helical side gear, and each second gear part is a pinion gear that meshes with each other. And a storage hole formed in the differential case for slidably and rotatably storing the respective helical pinion gears, wherein the helical pinion gear has a first and a second gear portion with helical twist angles of the tooth contact with the storage hole during traveling. If it increases due to the reaction force received by, the tooth height at the center of the axial direction of this helical pinion gear should be continuous from the tooth height at both ends. Characterized in that the Ku formed.

According to a fourth aspect of the present invention, in the differential device, the tooth height at the central portion in the axial direction of the pinion gear that revolves backward in the rotational direction of the differential case when the vehicle is traveling forward is continuous from the tooth height at both ends. 4. The differential device according to claim 3, wherein the differential device is formed to be high.

[0021]

In the differential device according to the first aspect of the present invention, the helical pinion gear is tilted in the direction in which the twist angle of the tooth line contacting the housing hole is reduced by the reaction force received by the first and second gear portions when the vehicle is running. In order to prevent excessive contact at the center, the tooth height at the center of the helical pinion gear is continuously made lower than the tooth height at both ends, so that the tooth tip and the storage hole are kept at all tooth widths. They are in uniform contact. Therefore, uneven wear or seizure does not occur over the entire tooth width of the helical pinion gear.

A differential device according to a second aspect is the differential device according to the first aspect, wherein the tooth height of the central portion in the axial direction of the pinion gear that revolves backward in the rotation direction of the differential case when the vehicle travels forward is revolved. The tooth tip of the helical pinion gear, which is formed continuously lower than the tooth length of both ends, makes uniform contact with the storage hole, which causes a large torque when traveling backward and causes uneven wear and seizure. It can be effectively prevented.

In the differential device according to the third aspect of the present invention, the helical pinion gear is tilted in the direction in which the twist angle of the tooth trace contacting the housing hole increases due to the reaction force received by the first and second gear portions when the vehicle is running. In order to prevent excessive contact at both ends, the tooth height at both ends of the helical pinion gear is continuously formed lower than the tooth height at the center, so that the tooth tip and the storage hole are kept at all tooth widths. They are in uniform contact. Therefore, uneven wear or seizure does not occur over the entire tooth width of the helical pinion gear.

A differential device according to a fourth aspect is the differential device according to the third aspect, wherein the tooth height of the central portion in the axial direction of the pinion gear that revolves backward in the direction of rotation of the differential case when the vehicle is traveling forward is revolved. The tooth tip of the helical pinion gear, which is formed continuously higher than the tooth height of both ends, makes uniform contact with the storage hole. It can be effectively prevented.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. This embodiment has the features of claims 1 and 2. FIG. 1 shows a longitudinal section of the embodiment, and FIG. 2 shows its gear set. The left and right directions are the left and right directions in FIG.
It should be noted that members and the like to which reference numerals are not given are not shown.

As shown in FIG. 1, the differential case 21 of the differential device 7 which is rotationally driven by the driving force of the engine.
The casing main body 31 and the cover 33 are fixed by bolts 35. Left and right helical side gears 37, 39 (a pair of output side helical side gears) are arranged inside the differential case 21.

Hollow boss 4 of each side gear 37, 39
1, 43 are rotatably supported by bearings 45, 47 of the differential case 21. Thrust blocks 53 are arranged on the large diameter portions 49 and 51 formed inside the boss portions 41 and 43 so as to straddle the inner circumferences of the large diameter portions 49 and 51.
The free ends of 7, 39 are supported and centered.

The left and right rear axles (not shown) penetrate the boss portions 55 and 57 of the differential case 21, respectively, and the side gear 3
The bosses 41 and 43 of 7, 39 are spline-connected, and abut against each other via a thrust block 53. Thrust washers 59 are arranged between the side gears 37, 39 and the differential case 21, respectively, and between the side gears 37, 39 (outer peripheral side of the thrust block 53).
A thrust washer 61 is arranged in the.

The differential case 21 has long and short storage holes 63, 6
A plurality of sets 5 are formed in the circumferential direction. These storage holes 6
3 and 65 have long and short helical pinion gears 6 respectively.
7, 69 are stored so as to be slidably rotatable.

The long pinion gear 67 comprises first and second gear portions 71, 73 and a small diameter shaft portion 75 connecting them, and the first gear portion 71 meshes with the right side gear 39. The short pinion gear 69 is composed of first and second gear portions 77 and 79, the first gear portion 77 meshes with the left side gear 37, and the second gear portion 79 meshes with the second gear portion 73 of the pinion gear 67. ing.

As shown in FIG. 1, the opening 8 is formed in the differential case 21.
1, 83, 85 are provided, and spiral oil grooves 87, 87 are formed on the inner periphery of the boss portions 55, 57. When the rear differential 7 rotates, the oil splashed from the oil sump flows into and out of the differential case 21 through the openings 81, 83, 85 and the oil grooves 87, 87, and the meshing parts of the gears and the sliding parts are moved. Lubricate.

The driving force of the engine for rotating the differential case 21 is from the pinion gears 67, 69 to the side gears 37, 3.
It is distributed to the left and right rear wheels 13, 15 via 9. Further, when a drive resistance difference occurs between the rear wheels due to one wheel idling on a rough road, the driving force of the engine is differentially distributed to the left and right sides by the rotation of the pinion gears 67 and 69.

During transmission of torque, each pinion gear 67, 6
The tooth tip of 9 is pressed against the wall surfaces of the housing holes 63 and 65 by the reaction force of meshing with the side gears 37 and 39, so that frictional resistance is generated. Further, the mesh thrust force of the helical gears causes the end faces of the pinion gears 67 and 69 to interfere with the differential case 21.
A frictional resistance is generated between the side gears 37, 39 and the differential case 21 via the thrust washer 59.
Further, the side gears 37, 39 are inserted through the thrust washers 61.
Friction resistance occurs between the two. These frictional resistances provide a torque sensitive differential limiting function.

Each gear portion 71 of the pinion gears 67, 69,
The teeth of the teeth 73, 77, 79 are formed in the directions shown in FIG. An arrow 89 indicates the direction of rotation of the differential case 21 when the vehicle travels forward. At this time, the short pinion gear 69 that revolves around the rotational direction 89 of the differential case 21 revolves around the force F from the wall surface of the storage hole 65. The second gear portion 7 of the pinion gear 67 is the same as the force F in FIG.
3 and the left side gear 37.

As described above with reference to FIGS. 7 to 10, this is because the pinion gear 69 tilts in the direction in which the helix angle θ of the tooth trace becomes smaller when the vehicle travels forward, and the center portion of the pinion gear 69 hits the housing hole 65 strongly. As shown in FIG. 3, the tooth height hN at the center of the pinion gear 69 is equal to the tooth height hE at both ends as shown in FIG.
Molded continuously lower than A and hEB. In the present embodiment, the difference between the tooth height hN and the tooth heights hEA and hEB corresponds to the dimension of the bearing clearance between the pinion gear 69 and the storage hole 63.
It is set as 0.03 mm. Therefore, this difference size varies depending on the size of the pinion gear 69 of the differential device 7 and the size of the storage hole 65 of the differential case 21, but can be easily set by polishing the tooth crests. Therefore, in the pinion gear 69, the tip of the tooth and the storage hole 65 are brought into uniform contact with each other over the entire tooth width during forward traveling in which a larger force is applied during backward traveling, and uneven wear and seizure are prevented.

Thus, the differential device 7 is constructed.

When the differential device 7 is applied to a vehicle, the behavior of the vehicle body when a large torque is applied such as at the time of starting or accelerating is stabilized by the torque sensitive differential limiting function and the maneuverability is improved.

As described above, the differential device 7
Is stored in the storage hole 65 when the vehicle travels forward with a large force.
Since the tooth length of the central portion of the short helical pinion gear 69 that strongly hits is made lower than the tooth height of both end portions, the tooth tips and the storage holes 65 uniformly contact with each other across the entire tooth width, and uneven wear or seizure does not occur.

Next, a second embodiment will be described with reference to FIGS. This embodiment has the features of claims 3 and 4. FIG. 4 shows the gear portion used in this embodiment. In this embodiment, members having the same functions as those of FIG. 1 are referred to by the same reference numerals, and description of these members having the same functions is omitted.

As shown in FIG. 4, this gear portion is composed of a pair of output side helical side gears 91 and 93 and a plurality of sets of long and short helical pinion gears 95 and 97. The side gears 91 and 93 are rotatably supported by the differential case 21.

The long pinion gear 95 includes the first and second gear portions 99 and 101 and the small-diameter shaft portion 103 that connects them.
And the first gear portion 99 meshes with the side gear 93. The short pinion gear 97 includes first and second gear portions 105 and 107, the first gear portion 105 meshes with the side gear 91, and the second gear portion 107 meshes with the second gear portion 101 of the pinion gear 95. .

Each gear portion 99 of the pinion gears 95, 97,
The tooth traces of 101, 105 and 107 are formed in the directions shown in FIG. Further, an arrow 109 indicates the rotation direction of the differential case 21 when the vehicle travels forward, and at that time, the short pinion gear 97 that revolves around the rotational direction 109 of the differential case 21 and revolves receives a force F from the wall surface of the storage hole 65. It is pressed against the second gear portion 101 of the pinion gear 95 and the side gear 91 by (the same as the force F in FIG. 7).

As described above with reference to FIGS. 11 and 12, this is because the pinion gear 97 is tilted in the direction in which the helix angle θ of the tooth trace is increased when the vehicle is traveling forward, and both ends are accommodated in the storage hole 6.
5, the tooth heights hEA and hEB at both ends of the pinion gear 97 are continuously formed lower than the tooth height hN at the central portion as shown in FIG. In the present embodiment, the difference between the tooth height hN and the tooth heights hEA, hEB corresponds to the dimension of the bearing clearance between the pinion gear 69 and the storage hole 63, and is 0.
It is set as 03 mm. Therefore, this difference size is determined by the pinion gear 69 of the differential device 7 and the differential case 2.
Although it varies depending on the size of the first housing hole 65, it can be easily set by polishing the tooth crest surface. Therefore, in the pinion gear 97, the tooth tip and the storage hole 65 are brought into uniform contact with each other over the entire tooth width during forward traveling, which requires a force larger than during backward traveling, and uneven wear or seizure is prevented.

In the first and second embodiments described above, in the short helical pinion gears 69 and 97 as shown in FIGS. 2 and 4, these pinion gears 96 and 9 are used.
The line 100 parallel to the rotation axis of 7 is the pinion gear 69,
When it is temporarily pulled toward the tooth tip of 97, there is a contact P with the short storage hole 65, but this contact P is the pinion gear 69,
The rotation of 97 causes it to move in the axial direction. When the contact P is offset toward the one end side in the axial direction, the first and second gear portions 77, 79
The reaction force applied to the pinion gears 69 and 97 causes the tilting of the pinion gears 69 and 97 themselves to increase, so that the pinion gears 69 and 97 come into contact with the storage hole 65 more strongly.
That is, regardless of the number of contacts between the tooth tips of the pinion gears 69 and 97 and the storage holes 65 (contacts generated due to the relationship between the length of the pinion gear and the twist angle of the pinion gear) and the deviation thereof, the present invention uses the pinion gears 69 and 97. The tooth tip and the housing hole 65 can be brought into uniform contact with each other over the entire tooth width.

As described above, the differential device of the present invention is applied to the rear differential (rear wheel side axle differential), the front differential (front wheel side axle differential), and the center differential (differential device for distributing the driving force to the front and rear wheels). Used.

[0046]

According to the differential device of claim 1,
Since the helical pinion gear falls in the direction in which the twist angle of the tooth trace contacting the housing hole is reduced by the reaction force received by the first and second gear portions when the vehicle is traveling, excessive contact at the central portion is prevented. In order to prevent uneven wear and seizure, the tooth length at the center of this helical pinion gear is continuously made lower than the tooth height at both ends, and the tooth tips and the storage holes are in uniform contact over the entire tooth width. ing.

In the differential device according to the third aspect of the present invention, the helical pinion gear is tilted in the direction in which the twisting angle of the tooth trace contacting the housing hole is increased by the reaction force received by the first and second gear portions when the vehicle is running, so both ends In order to prevent excessive contact between the teeth, the tooth height of both ends of the helical pinion gear is continuously lower than the tooth height of the central part, and the tooth tips and storage holes are evenly contacted over the entire tooth width. This prevents uneven wear and seizure.

According to a second aspect and a fourth aspect of the present invention, in the differential device of the first aspect and the third aspect, respectively, the helical revolving rearward of the pinion gear group revolves in the rotational direction of the differential case when the vehicle travels forward. The tooth tips of the pinion gear are in uniform contact with the storage holes, and it is possible to effectively prevent uneven wear and seizure during forward traveling, which requires a larger torque than during backward traveling.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a perspective view of a gear unit used in the first embodiment.

FIG. 3 is a sectional view of a short helical pinion gear used in the first embodiment.

FIG. 4 is a perspective view of a gear portion used in a second embodiment of the present invention.

FIG. 5 is a sectional view of a short helical pinion gear used in the second embodiment.

FIG. 6 is a sectional view of a conventional example.

7 is a cross-sectional view of the conventional example of FIG.

FIG. 8 is a side view for explaining tilting of the helical pinion gear.

FIG. 9 is an end view for explaining tilting of a helical pinion gear.

FIG. 10 is a cross-sectional view showing a difference in gap amount between the accommodation hole and each part of the helical pinion gear.

FIG. 11 is a side view for explaining tilting of a helical pinion gear having a twist angle direction different from that of FIG. 8;

12 is a cross-sectional view showing the difference in the amount of clearance between the accommodation hole and each part of the helical pinion gear in the example of FIG.

[Explanation of symbols]

7 Differential device 21 Differential case 37, 39, 91, 93 Output side helical side gear 63, 65 Storage hole 67, 95 Long helical pinion gear (helical pinion gear) 69, 97 Short helical pinion gear (helical pinion gear) 71, 77, 99, 105 1st Gears 73, 79, 101, 107 Second gear hN Center tooth height hEA, hEB End tooth height

Claims (4)

[Claims] 1. A helical pinion gear having a differential case rotationally driven by a driving force of an engine, a pair of output side helical side gears, a first gear portion and a second gear portion, and the first gear portion meshing with one helical side gear. And a helical pinion gear having first and second gear parts, the first gear part meshing with the other helical side gear,
The second pinion includes a pinion gear set in which the second gear parts mesh with each other, and a storage hole formed in the differential case for slidably and rotatably storing each helical pinion gear. When the angle becomes small due to the reaction force received by the first and second gear portions, the gear height of the axial center portion of the helical pinion gear is continuously lower than the gear heights of the both end portions. . 2. The tooth height of the central portion in the axial direction of the pinion gear of the pinion gear set, which revolves backward and revolves with respect to the rotation direction of the differential case when the vehicle is traveling forward, is formed continuously lower than the tooth heights of both end portions. Item 1. The differential device. 3. A differential case rotatably driven by a driving force of an engine, a pair of output side helical side gears, a first gear portion and a second gear portion, and the first gear portion meshes with one helical side gear. A helical pinion gear, a helical pinion gear having first and second gear parts, the first gear part meshing with the other helical side gear, each second gear part forming a pinion gear set meshing with each other, and a differential case Each helical pinion gear has a storage hole for slidingly and rotatably storing the helical pinion gear. When the vehicle is running, the helical pinion gear has a large helix angle of the tooth contact with the storage hole due to the reaction force received by the first and second gears. In this case, the helical pinion gear is characterized in that the tooth height at the central portion in the axial direction is continuously higher than the tooth height at both ends. RENTAL DEVICE. 4. The tooth height of the central portion of the pinion gear that revolves around the rear of the pinion gear set in the rotational direction of the differential case when the vehicle is traveling forward is continuously higher than the tooth heights of both end portions. Item 3. The differential device.