Differential device

Abstract

To improve running performance on rough roads while improving cornering acceleration performance.SOLUTION: A differential device (11) comprises a differential mechanism (GS) capable of transmitting rotation of an input member (10) to a first rotary member (30L) and a second rotary member (30R) while allowing differential rotation between the first rotary member and the second rotary member, where the differential mechanism includes a speed-up rotary member (SP) that is drivingly connected to the first rotary member and the second rotary member and that, when a differential rotation occurs between the first rotary member and the second rotary member, rotates at an increased speed relative to the rotation of the input member according to the differential rotation, and has a differential limitation function in which, when the differential rotation occurring between the first rotary member and the second rotary member becomes large, the differential is limited by resistance generated by the increase in speed of the speed-up rotary member.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a differential device mounted on a vehicle or the like. [Background technology]

[0002] In general, a differential device is provided in the transmission path that transmits the driving force from the drive source to the wheels to absorb the difference in rotation speed between the inner and outer wheels when the vehicle turns. In such a differential device, when one wheel is on a low-friction road surface and the other wheel is on a high-friction road surface, for example, on a rough road, if one wheel slips and spins, there is a risk that the driving force will not be transmitted to the other wheel, resulting in a problem of poor rough-road performance. For this reason, various differential devices with a differential limiter (LSD) have been developed.

[0003] Among various types of LSDs, there is a friction plate type LSD that uses friction plates to limit the differential when the wheels are about to spin. This friction plate type LSD increases the differential limiting force by setting a strong initial torque, improving off-road performance, but in situations where differential limiting is not required, there are problems such as poor fuel economy due to drag loss and poor cornering acceleration performance due to understeer during cornering acceleration. For this reason, in recent years, it has been adopted in vehicles used in races, for example, but there is a problem that it is not very suitable for general vehicles. For this reason, a torque-sensing LSD (so-called Torsen LSD (registered trademark)) has also been proposed (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-7505 A Summary of the Invention [Problem to be solved by the invention]

[0005] The system of Patent Document 1 above realizes a differential limiting mechanism using a Ravigneaux type planetary mechanism made up of helical gears, and is effective when the required differential limiting force is small, such as when the vehicle is accelerating while turning. However, when the required differential limiting force is large, such as when the vehicle is traveling on a low-resistance road surface or a road surface with different resistance between the left and right, the differential limiting force is insufficient, resulting in a problem of poor off-road performance.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a differential device which is capable of improving cornering acceleration performance while also improving rough road driving performance. [Means for solving the problem]

[0007] One aspect of the present invention is a differential device comprising an input member to which driving rotation is input, a first rotating member that transmits the driving force to a first wheel, a second rotating member that transmits the driving force to a second wheel different from the first wheel, and a differential mechanism capable of transmitting the rotation of the input member to the first rotating member and the second rotating member while allowing differential rotation between the first rotating member and the second rotating member, wherein the differential mechanism includes an accelerating rotating member that is drivingly connected to the first rotating member and the second rotating member, and that, when a differential rotation occurs between the first rotating member and the second rotating member, rotates at an increased speed relative to the rotation of the input member in accordance with the differential rotation, and has a differential limiting function that limits the differential by the resistance generated by the increase in speed of the accelerating rotating member when the differential rotation generated between the first rotating member and the second rotating member tries to become large. Effect of the Invention

[0008] According to the present invention, cornering acceleration performance can be improved, while rough road running performance can also be improved. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a skeleton diagram showing a differential device according to a first embodiment. [Diagram 2] FIG. 2 is a velocity diagram of the differential device according to the first embodiment. [Diagram 3] FIG. 1 is a schematic cross-sectional view showing a differential device according to a first embodiment. [Figure 4] FIG. 11 is a skeleton diagram showing a differential gear according to a second embodiment. [Diagram 5] FIG. 11 is a velocity diagram of a differential device according to a second embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a differential device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First Embodiment A differential device according to a first embodiment will be described below with reference to FIGS. 1 to 3. FIG.

[0011] [Outline of the differential device according to the first embodiment] First, an overview of a differential device 11 according to the first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a skeleton diagram showing the differential device according to the first embodiment. Fig. 2 is a speed diagram of the differential device according to the first embodiment.

[0012] As shown in FIG. 1, the differential device 11 according to the first embodiment is drivingly connected to a driving force output device 50 that outputs a driving force (driving rotation) using an engine or motor (not shown) as a drive source, and is configured to distribute and transmit the driving force (output rotation) output from the driving force output device 50 to a left wheel 100L, 100R, which serves as a first wheel, while allowing differential rotation between the left wheel 100L, which serves as a first wheel, and a right wheel 100R, which serves as a second wheel different from the first wheel.

[0013] In detail, the differential device 11 has a gear set GS as a differential mechanism in which all gears (four pinion gears and four sun gears) have tooth surfaces facing the axial direction and are made up of helical gears. That is, the gear set GS as a differential mechanism of the differential device 11 configures the first planetary gear PR1, second planetary gear PR2, third planetary gear PR3, and fourth planetary gear PR4 as single pinion planetary gears by arranging a common step pinion gear SP as a speed-increasing rotation member or planetary pinion gear straddling the four planetary gears.

[0014] The step pinion gear SP in the gear set GS has, as step pinions, a first pinion gear P1 as a fourth gear, a second pinion gear P2 as a fifth gear, a third pinion gear P3 as a sixth gear, and a fourth pinion gear P4 as a fourth gear, each of which is a helical gear. The second pinion gear P2 is formed to have a larger diameter than the first pinion gear P1 and the fourth pinion gear P4, and conversely, the third pinion gear P3 is formed to have a smaller diameter than the first pinion gear P1 and the fourth pinion gear P4.

[0015] The differential device 11 also includes a case 10 serving as a so-called differential case that houses the gear set GS, and the case 10 is drivingly connected to an output member (e.g., a countershaft) of the driving force output device 50 via a differential ring gear 11 (see FIG. 3), and constitutes an input member to which the driving rotation from the driving force output device 50 is input. A sun gear S1 of a first planetary gear PR1 as a first gear and a sun gear S4 of a fourth planetary gear PR4 are provided in the case 10 so as to rotate integrally, and these sun gears S1 and S4 are formed of helical gears and mesh with the first pinion gear P1 and the fourth pinion gear P4, respectively. The first sun gear S1 and the fourth sun gear S4 are formed with the same number of teeth, and the first pinion gear P1 and the fourth pinion gear P4 are also formed with the same number of teeth. In other words, although the step pinion gear SP is drivingly connected to the case 10 in a form that branches off at both axial ends thereof, there is only one path for transmitting the rotation of the driving force output device 50 to the step pinion gear SP.

[0016] The second pinion gear P2 is meshed with a second sun gear S2 as a second gear to which a left wheel 100L as a first wheel is drivingly connected, and the third pinion gear P3 is meshed with a third sun gear S3 as a third gear to which a right wheel 100R as a second wheel is drivingly connected. The second sun gear S2 is formed with a smaller diameter than the first sun gear S1 and the fourth sun gear S4, and conversely, the third sun gear S3 is formed with a larger diameter than the first sun gear S1 and the fourth sun gear S4.

[0017] As shown in FIG. 2, the gear ratio (Zp2 / Zs2) of the second pinion gear P2 to the second sun gear S2 is larger than the gear ratio (Zp1 / Zs1 or Zp4 / Zs4) of the first pinion gear P1 (fourth pinion gear P4) to the first sun gear S1 (fourth sun gear S4), and the gear ratio (Zp3 / Zs3) of the third pinion gear P3 to the third sun gear S3 is smaller than the gear ratio (Zp1 / Zs1 or Zp4 / Zs4) of the first pinion gear P1 (fourth pinion gear P4) to the first sun gear S1 (fourth sun gear S4).

[0018] In the first embodiment, for example, the number of teeth of the first sun gear S1 and the fourth sun gear S4 is set to "32", the number of teeth of the second sun gear S2 and the sun gear S3 is set to "40", the number of teeth of the first pinion gear P1 and the fourth pinion gear P4 is set to "10", the number of teeth of the second pinion gear P2 is set to "13", and the number of teeth of the third pinion gear P3 is set to "12", and the number of teeth of each pinion gear is set so that the speed ratio (speed increase ratio) of the rotational speed of the step pinion gear SP to the rotational speed of the first sun gear S1 and the fourth sun gear S4 is "20" to "30", preferably "25". Note that in the speed diagram shown in Fig. 2, the lateral distance (spacing) between the third sun gear S3 and the step pinion gear SP is shown short due to the size of the drawing, but in reality it becomes longer according to the above speed ratio (speed increase ratio).

[0019] [Detailed configuration of the differential device according to the first embodiment] Next, a detailed configuration of the differential device 11 according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic cross-sectional view showing the differential device according to the first embodiment.

[0020] The differential device 11 includes a case 10 to which the above-mentioned differential ring gear 11 is fixed integrally. The case 10 includes a main case 10A, a left side cover 10B fixed to one end of the main case 10A in the axial direction by a snap ring 14, and a right side cover 10C fixed to the other end of the main case 10A in the axial direction by a snap ring 15. A first sun gear S1 is integrally formed at the tip portion on the inner periphery side of the side cover 10B, and a fourth sun gear S4 is integrally formed at the tip portion on the inner periphery side of the side cover 10C. The first sun gear S1 and the fourth sun gear S4 and the first pinion gear P1 and the fourth pinion gear P4 are each formed of a helical gear, but the thrust forces generated during rotation are canceled out by each other via the case 10.

[0021] On the inner circumferential sides of side covers 10B and 10C, there are arranged a left shaft coupling portion 30L as a first rotating member to which a left drive shaft (not shown) is drivingly coupled to transmit driving force to wheel 100L, and a right shaft coupling portion 30R as a second rotating member to which a right drive shaft (not shown) is drivingly coupled to transmit driving force to wheel 100R. The above-mentioned second sun gear S2 is formed integrally with the left shaft coupling portion 30L, and similarly, the above-mentioned third sun gear S3 is formed integrally with the right shaft coupling portion 30R.

[0022] The left shaft connecting portion 30L is rotatably supported by a needle bearing B1 with respect to the side cover 10B, and is supported by a thrust bearing B3 so as to be immovable in the axial direction but rotatable. Similarly, the right shaft connecting portion 30R is rotatably supported by a needle bearing B2 with respect to the side cover 10C, and is supported by a thrust bearing B5 so as to be immovable in the axial direction but rotatable. A thrust bearing B4 is disposed between the left shaft connecting portion 30L and the right shaft connecting portion 30R in the axial direction. As a result, the left shaft connecting portion 30L and the right shaft connecting portion 30R are rotatably supported by the case 10, and the thrust force generated by the second sun gear S2 and the third sun gear S3, which are helical gears, during rotation is supported by the case 10, so that they are positioned so as to be immovable in the axial direction.

[0023] Meanwhile, the step pinion gear SP is configured by fitting a first pinion gear P1, a second pinion gear P2, a third pinion gear P3, and a fourth pinion gear P4 in parallel in the axial direction on the outer periphery of the pinion shaft PS. As described above, the first pinion gear P1 is meshed with the first sun gear S1, and the fourth pinion gear P4 is meshed with the fourth sun gear S4. In other words, the step pinion gear SP is supported by the case 10 in a doubly supported manner from the inner periphery side.

[0024] In addition, a roller 21 as a positioning member is fitted to the outer periphery of the pinion shaft PS between the first pinion gear P1 and the second pinion gear P2 in the axial direction, and similarly, a roller 22 as a positioning member is fitted to the outer periphery of the pinion shaft PS between the third pinion gear P3 and the fourth pinion gear P4 in the axial direction. The outer diameter of these rollers 21 and 22 is formed to be larger than the outer diameter of the second pinion gear P2, which has the largest outer diameter among the four pinion gears. A cylindrical member 20 formed in a cylindrical shape as an outer peripheral member is arranged on the outer periphery side of the step pinion gear SP, and the outer periphery surfaces of these rollers 21 and 22 are configured to abut against the inner periphery surface of the cylindrical member 20. As a result, the cylindrical member 20 receives the centrifugal force generated in the step pinion gear SP via the rollers 21 and 22, that is, supports the step pinion gear SP from the outer periphery side. In other words, these rollers 21, 22 position the inner and outer circumferential positions of the step pinion gear SP relative to the cylindrical member 20. Therefore, the step pinion gear SP is supported in a state in which its inner and outer circumferential position is determined relative to the shaft connecting portions 30L, 30R and the case 10.

[0025] The step pinion gears SP are made up of a plurality of pieces (for example, four pieces) and are evenly arranged in the circumferential direction. When rotation is input from the case 10 to the first pinion gear P1 and the fourth pinion gear P4 via the first sun gear S1 and the fourth sun gear S4 and there is no differential rotation between the second sun gear S2 and the third sun gear S3, the step pinion gears SP rotate (spin) at their positions, and the phases of the step pinion gears SP in the circumferential direction do not shift. When a differential rotation occurs between the second sun gear S2 and the third sun gear S3, the step pinion gears SP move slightly in the circumferential direction accordingly, but since the number of teeth of each pinion gear in the step pinion gears SP is the same, the relative positional relationship in the circumferential phase of the step pinion gears SP does not shift.

[0026] [Operation of the differential device according to the first embodiment] Next, the operation of the differential device 11 according to the first embodiment will be described. As shown in Fig. 2, for example, when the vehicle is traveling straight (there is no differential rotation between the left and right wheels 100L, 100R), and the driving force Tin from the driving force output device 50 is input to the first sun gear S1 and the fourth sun gear S4 in the gear set GS, the driving force Ts2 is transmitted to the second sun gear S2 via the common step pinion gear SP, and the driving force Ts3 is transmitted to the third sun gear S3. That is, the driving force is distributed and transmitted approximately equally to the left and right wheels 100L, 100R.

[0027] From this state, for example, if the vehicle turns left, or the right wheel 100R slips when a driving force is transmitted, or the left wheel 100L slips when a braking force is transmitted, the rotation speed of the left wheel 100L becomes lower than the rotation speed of the right wheel 100R, as shown by the dashed line in Fig. 2. That is, the rotation speed of the second sun gear S2 becomes lower than the rotation speed of the third sun gear S3, the rotation speed of the step pinion gear SP becomes higher, and a differential rotation occurs between the second sun gear S2 and the third sun gear S3. Conversely, for example, if the vehicle turns right, or the left wheel 100L slips when a driving force is transmitted, or the right wheel 100R slips when a braking force is transmitted, the relationship of the rotation speeds becomes reversed.

[0028] For example, when a small differential rotation occurs between the left and right wheels 100L, 100R, such as when the vehicle is turning, the step pinion gear SP rotates to absorb the differential rotation, and distributes the driving force Tin from the driving force output device 50 into driving force Ts2 to the second sun gear S2 and driving force Ts3 to the third sun gear S3.

[0029] For example, in a state where a large difference in rotation occurs between the left and right wheels 100L, 100R due to slipping of the right wheel 100R, the speed ratio (speed increase ratio) of the rotation speed of the step pinion gear SP to the rotation speeds of the first sun gear S1 and the fourth sun gear S4 in the gear set GS is set to, for example, "20" to "30" as described above, so that the rotation speed of the step pinion gear SP becomes high even with a small difference in rotation. Also, since the step pinion gear SP receives a reaction force from the road surface of the driving force transmitted to the left wheel 100L that is not slipping, a reaction force of the driving force Ts2 is input in reverse from the second sun gear S2 toward the second pinion gear P2, and the amount of this reaction force is intended to be transmitted to the third sun gear S3. However, because the rotational speed of the step pinion gear SP becomes high, the resistance due to tooth surface friction between the second sun gear S2 and the second pinion gear P2 and the resistance due to tooth surface friction between the third sun gear S3 and the third pinion gear P3 increase and become greater than the reaction force, so that the differential limiting function that automatically limits the differential operates, resulting in a so-called self-differential lock state. Note that, for example, in the case where the left wheel 100L slips, the explanation is omitted since only the direction of rotation and the direction of transmission of the driving force are reversed.

[0030] According to a computer simulation, for example, if the speed ratio (speed increase ratio) of the rotational speed of the step pinion gear SP to the rotational speed of the first sun gear S1 and the fourth sun gear S4 in the gear set GS is set to less than "20", the frictional resistance of the tooth surface is small even if a large differential rotation occurs between the left and right wheels 100L, 100R, so that the differential limiting force is insufficient as in a torque-sensitive LSD composed of helical gears, and there is a risk that the self-differential lock function will not work, for example, when driving on a rough road. On the other hand, if the speed ratio (speed increase ratio) is set to be greater than "30", the frictional resistance of the tooth surface is large when a differential rotation occurs between the left and right wheels 100L, 100R, and the self-differential lock function will work, for example, even when the vehicle is turning, and there is a risk of understeer.

[0031] In the first embodiment, a thrust force is generated between the second sun gear S2 and second pinion gear P2, which are helical gears, and the third sun gear S3 and third pinion gear P3, but the thrust bearings B3, B4, and B5 position and support the components in the axial direction, so that frictional resistance caused by thrust force pressing against each other is not generated. Therefore, the resistance that causes the self-diff-lock function when the differential rotation occurs can be calculated only from the resistance due to the tooth surface friction, and the tooth surface friction can be set simply by the tooth inclination angle, tooth shape (involute curve in this embodiment), lubrication state, etc.

[0032] In addition, in the first embodiment, the thrust bearings B3, B4, and B5 are provided, but it is also possible to eliminate these thrust bearings B3, B4, and B5 and to construct the system so that frictional resistance caused by thrust force is actively generated between the case 10 and the shaft connecting parts 30L and 30R, for example. In this case, it is possible to design the system so that the self-diff-lock mechanism operates based on the sum of the tooth surface resistance and the frictional resistance between the respective parts while precisely controlling the tolerances of the respective parts.

[0033] [Summary of the first embodiment] According to the differential device 11 of the first embodiment described above, when the differential rotation between the shaft connecting portion 30L and the shaft connecting portion 30R becomes large, the differential is limited by the resistance generated by the increase in the speed of the step pinion gear SP, so that when the required differential limiting force is small, the cornering acceleration performance can be improved, while when the required differential limiting force is large, the differential is limited, and thus the rough road performance can be improved.

[0034] Specifically, during differential differential, which generates a differential rotation between the shaft connecting portion 30L and the shaft connecting portion 30R, the step pinion gear SP is accelerated to a rotation speed corresponding to the differential rotation. Therefore, when the differential rotation occurs suddenly from a state where there is no differential rotation, the step pinion gear SP acts in a static friction state with a large tooth surface resistance, resulting in a large resistance, and the differential differential is restricted and locked. In addition, during normal turning, the differential rotation occurs gently, so the step pinion gear SP acts in a dynamic friction state with a small tooth surface resistance, and thus has a normal differential limiting function rather than a locked state. Therefore, a differential device can be provided that can improve cornering acceleration performance and rough road driving performance.

[0035] Furthermore, as the step pinion gear SP is accelerated relative to the first sun gear S1 and the fourth sun gear S4, the tooth surface friction at the meshing portion of the second sun gear S2 and the second pinion gear P2 and the tooth surface friction at the meshing portion of the third sun gear S3 and the third pinion gear P3 become greater as resistance generated by the acceleration of the step pinion gear SP, thereby achieving a differential limiting function that automatically fixes the differential.

[0036] Furthermore, since the step pinion gear SP is provided with the rollers 21, 22 and brought into contact with the cylindrical member 20, it is not necessary to provide a carrier for connecting the pinion shaft PS, and the manufacturing process can be simplified to reduce costs.

[0037] <Second embodiment> Next, a second embodiment, which is a partial modification of the first embodiment, will be described with reference to Figs. 4 to 6. In the differential device 11 according to the first embodiment, rotation is input from the first sun gear S1 and the fourth sun gear S4, and rotation is output from the second sun gear S2 to the left wheel 100L and from the third sun gear S3 to the right wheel 100R. In the differential device 12 according to the second embodiment, however, input and output are performed by a ring gear instead of these sun gears. In the description of the second embodiment, the same reference numerals are used for the same parts as in the first embodiment, and the description thereof will be omitted, but the same reference numerals are not intended to limit the same structures and functions.

[0038] [Outline of the differential device according to the second embodiment] First, an outline of the differential device 12 according to the second embodiment will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a skeleton diagram showing the differential device according to the second embodiment. Fig. 5 is a speed diagram of the differential device according to the second embodiment.

[0039] 4, the differential device 12 has a gear set GS in which all gears (three pinion gears and three ring gears) have tooth surfaces oriented in the axial direction and are made up of helical gears. That is, the gear set GS as a differential mechanism of the differential device 11 configures a first planetary gear PR1, a second planetary gear PR2, and a third planetary gear PR3, which are single pinion planetary gears, by arranging a common step pinion gear SP astride the three planetary gears.

[0040] The step pinion gear SP in the gear set GS has a first pinion gear P1 as a fifth gear, a second pinion gear P2 as a fourth gear, and a third pinion gear P3 as a sixth gear, each of which is a helical gear. The third pinion gear P3 is formed to have a larger diameter than the second pinion gear P2, and conversely, the first pinion gear P1 is formed to have a smaller diameter than the second pinion gear P2.

[0041] The differential device 12 also includes a case 10 that houses a gear set GS, and the case 10 is drivingly connected to an output member (e.g., a countershaft) of the driving force output device 50 via a differential ring gear 11 (see FIG. 6). A second ring gear R2 of a second planetary gear PR2 serving as a first gear is provided in the case 10 so as to rotate integrally with the case 10, and this second ring gear R2 is formed of a helical gear and meshes with the second pinion gear P2.

[0042] The first pinion gear P1 is meshed with a first ring gear R1 as a second gear to which a left wheel 100L as a first wheel is drivingly connected, and the third pinion gear P3 is meshed with a third ring gear R3 as a third gear to which a right wheel 100R as a second wheel is drivingly connected. The first ring gear R1 is formed with a smaller diameter than the second ring gear R2, and conversely, the third ring gear R3 is formed with a larger diameter than the second ring gear R2.

[0043] As shown in FIG. 5, the gear ratio (Zp1 / Zr1) of the first pinion gear P1 to the first ring gear R1 is greater than the gear ratio (Zp2 / Zr2) of the second pinion gear P2 to the second ring gear R2, and the gear ratio (Zp3 / Zr3) of the third pinion gear P3 to the third ring gear R3 is smaller than the gear ratio (Zp2 / Zr2) of the second pinion gear P2 to the second ring gear R2.

[0044] In the second embodiment, for example, the number of teeth of the second ring gear R2 is set to "32", the number of teeth of the first ring gear R1 and the third ring gear R3 is set to "40", the number of teeth of the first pinion gear P1 is set to "12", the number of teeth of the second pinion gear P2 is set to "10", and the number of teeth of the third pinion gear P3 is set to "13", and the number of teeth of each pinion gear is set so that the speed ratio (speed increase ratio) of the rotational speed of the step pinion gear SP to the rotational speed of the second ring gear R2 is "20" to "30", preferably "25". Note that in the speed diagram shown in Fig. 5, the lateral distance (spacing) between the third ring gear R3 and the step pinion gear SP is shown short due to the size of the drawing, but in reality it becomes longer according to the above speed ratio (speed increase ratio).

[0045] [Detailed configuration of the differential device according to the second embodiment] Next, a detailed configuration of the differential device 12 according to the second embodiment will be described with reference to Fig. 6. Fig. 6 is a schematic cross-sectional view showing the differential device according to the second embodiment.

[0046] The differential device 12 includes a case 10 to which the above-mentioned differential ring gear 11 is fixed integrally, and the case 10 includes a main case 10A, a left side cover 10B fixed to one end of the main case 10A in the axial direction by a snap ring 14, and a right side cover 10C fixed to the other end of the main case 10A in the axial direction by a snap ring 15. A second ring gear R2 is formed integrally with the main case 10A at the central portion in the axial direction on the inner circumferential side.

[0047] On the inner circumferential side between the side covers 10B and 10C, there are disposed a left shaft coupling part 30L which is drivingly coupled with a left drive shaft (not shown) to transmit driving force to the wheel 100L, and a right shaft coupling part 30R which is drivingly coupled with a right drive shaft (not shown) to transmit driving force to the wheel 100R. A first ring gear R1 is integrally formed at the tip of a support plate part formed in a flange shape toward the outer circumferential side of the left shaft coupling part 30L, and similarly, a third ring gear R3 is integrally formed at the tip of a support plate part formed in a flange shape toward the outer circumferential side of the right shaft coupling part 30R.

[0048] The left shaft connecting portion 30L is supported by the side cover 10B so as to be rotatable but immovable in the axial direction by a ball bearing B6 serving as a first bearing. Similarly, the right shaft connecting portion 30R is supported by the side cover 10C so as to be rotatable but immovable in the axial direction by a ball bearing B7 serving as a second bearing. As a result, the left shaft connecting portion 30L and the right shaft connecting portion 30R are supported by the case 10 so as to be rotatable, and the thrust force generated by the first ring gear R1 or the third ring gear R3, which are helical gears, during rotation is supported by the case 10, so that they are positioned so as to be immovable in the axial direction.

[0049] On the other hand, the step pinion gear SP is formed in a step shape in the axial direction by the above-mentioned first pinion gear P1, second pinion gear P2, and third pinion gear P3, and is rotatably supported via needle bearings B8 and B9 on the pinion shaft PS fixedly supported by the carrier CR.

[0050] As described above, in the differential device 12 according to the second embodiment, the case 10 rotatably supports the shaft connecting portion 30L via the ball bearing B6 and rotatably supports the shaft connecting portion 30R via the ball bearing B7, and is configured to contain the first ring gear R1, the third ring gear R3, and the step pinion gear SP. In other words, since the gear set GS as a differential mechanism is covered and contained within the case 10, other members (for example, members connected to a device that performs vectoring torque) are not drivingly connected to any of the members of the gear set GS, and the gear set GS can be enclosed in the case 10. In addition, it can be said that the gear set GS is enclosed in the case 10 by integrally forming the second ring gear R2 as internal teeth on the inner peripheral side of the main case 10A of the case 10. By structuring the gear set GS in this manner, the differential device 12 can be made compact, safety can be ensured against the intrusion of foreign matter, and the lubrication structure can be simplified.

[0051] In addition, in the differential device 12 according to the second embodiment, the above-mentioned other members are not drivingly connected to any of the members of the gear set GS, so that the first ring gear R1, the second ring gear R2, and the third ring gear R3 can be arranged adjacent to each other in the axial direction, and compactness can be achieved. In particular, when configuring a vectoring torque type differential device, a configuration in which a member for applying vectoring torque to the carrier CR is connected is considered, and in that case, it is considered to connect the members from between the ring gears to prevent the members from intersecting. However, in this embodiment, the carrier CR is separated from the other members inside the case 10 and rotates independently, so that the carrier CR can be made to have a simple structure and compactness can be achieved.

[0052] [Operation of the differential device according to the second embodiment] Next, the operation of the differential device 12 according to the second embodiment will be described. As shown in Fig. 5, for example, when the vehicle is traveling straight (there is no differential rotation between the left and right wheels 100L, 100R), and the driving force Tin from the driving force output device 50 is input to the second ring gear R2 in the gear set GS, the driving force Tr1 is transmitted to the first ring gear R1 via the common step pinion gear SP, and the driving force Tr3 is transmitted to the third ring gear R3. That is, the driving force is distributed and transmitted approximately equally to the left and right wheels 100L, 100R.

[0053] From this state, for example, if the vehicle turns left, or the right wheel 100R slips when a driving force is transmitted, or the left wheel 100L slips when a braking force is transmitted, the rotation speed of the left wheel 100L becomes lower than the rotation speed of the right wheel 100R, as shown by the dashed line in Fig. 5. That is, the rotation speed of the first ring gear R1 becomes lower than the rotation speed of the third ring gear R3, the rotation speed of the step pinion gear SP becomes higher, and a differential rotation occurs between the first ring gear R1 and the third ring gear R3. Conversely, for example, if the vehicle turns right, or the left wheel 100L slips when a driving force is transmitted, or the right wheel 100R slips when a braking force is transmitted, the relationship of the rotation speeds becomes reversed.

[0054] For example, when a small differential rotation occurs between the left and right wheels 100L, 100R, such as when the vehicle is turning, the step pinion gear SP rotates to absorb the differential rotation, and distributes the driving force Tin from the driving force output device 50 to a driving force Tr1 to the first ring gear R1 and a driving force Tr3 to the third ring gear R3.

[0055] For example, in a state where a large difference in rotation occurs between the left and right wheels 100L, 100R due to slipping of the right wheel 100R, the speed ratio (speed increase ratio) of the rotation speed of the step pinion gear SP to the rotation speed of the second ring gear R2 in the gear set GS is set to, for example, "20" to "30" as described above, so that the rotation speed of the step pinion gear SP becomes high even with a small difference in rotation. Also, since the reaction force of the driving force transmitted to the left wheel 100L that is not slipping is received from the road surface, the reaction force of the driving force Tr1 is input in reverse from the first ring gear R1 toward the first pinion gear P1, and the reaction force is intended to be transmitted to the third ring gear R3. However, because the rotational speed of the step pinion gear SP becomes high, the resistance due to tooth surface friction between the first ring gear R1 and the first pinion gear P1 and the resistance due to tooth surface friction between the third ring gear R3 and the third pinion gear P3 increase and become greater than the reaction force, so that the differential limiting function that automatically limits the differential works, resulting in a so-called self-differential lock state. Note that, for example, in the case where the left wheel 100L slips, the explanation is omitted since it is only the rotation direction and the direction of transmission of the driving force that are reversed.

[0056] According to a computer simulation, for example, if the speed ratio (speed increase ratio) of the rotational speed of the step pinion gear SP to the rotational speed of the second ring gear R2 in the gear set GS is set to less than "20", the frictional resistance of the tooth surface is small even if a large difference in rotation occurs between the left and right wheels 100L, 100R, so that the differential limiting force is insufficient as in a torque-sensitive LSD composed of helical gears, and there is a risk that the self-differential lock function will not work, for example, when driving on a rough road. On the other hand, if the speed ratio (speed increase ratio) is set to be greater than "30", the frictional resistance of the tooth surface is large when a difference in rotation occurs between the left and right wheels 100L, 100R, and the self-differential lock function will work, for example, even when the vehicle is turning, and there is a risk of understeer.

[0057] In addition, in this second embodiment, thrust forces associated with driven rotation are generated between the first ring gear R1 and first pinion gear P1, the second ring gear R2 and second pinion gear P2, and the third ring gear R3 and third pinion gear P3, which are helical gears. Since the thrust forces of these gears are not received by thrust bearings or the like, the resistance due to friction on the tooth surfaces can be made large, and the sensitivity with which the self-diff-lock function occurs can be increased.

[0058] It is also possible to apply resistance that generates the self-differential-locking function by using a thrust force to move the carrier CR together with the step pinion gear SP in the axial direction and pressing it against the shaft connecting portion 30L or the shaft connecting portion 30R to generate a frictional force. Conversely, it is also possible to design the carrier CR and the step pinion gear SP so that they are positioned and supported in the axial direction by a thrust bearing or the like, so that the resistance that generates the self-differential-locking function can be calculated based only on the resistance due to the tooth surface friction.

[0059] [Summary of the second embodiment] The differential device 12 of the second embodiment described above also has a differential limiting function in which the differential is limited by the resistance generated by the increase in speed of the step pinion gear SP when the differential rotation between the shaft connecting portion 30L and the shaft connecting portion 30R becomes large. Therefore, when the required differential limiting force is small, it is possible to improve cornering acceleration performance and prevent deterioration of fuel efficiency, while when the required differential limiting force is large, the differential is limited, thereby improving rough road performance.

[0060] Furthermore, as the step pinion gear SP is accelerated relative to the second ring gear R2, the resistance generated by the acceleration of the step pinion gear SP, namely, the tooth surface friction at the meshing portion between the first ring gear R1 and the first pinion gear P1 and the tooth surface friction at the meshing portion between the third ring gear R3 and the third pinion gear P3, becomes greater, thereby achieving a self-diff-lock function that automatically fixes the differential.

[0061] Furthermore, by using a structure in which each component of the gear set GS is enclosed within the case 10, the differential device 12 can be made compact, safety can be ensured against the intrusion of foreign matter, and the lubrication structure can be simplified.

[0062] Other configurations, operations, and effects of the second embodiment are similar to those of the first embodiment, and therefore description thereof will be omitted.

[0063] <Possibilities for other embodiments> In the first and second embodiments described above, the differential device has been described as, for example, a front differential that distributes driving force to the left and right wheels 100L, 100R while limiting the differential between them. However, the present invention is not limited to this, and the device may also be used in a center differential, for example, that distributes driving force to the front and rear wheels while limiting the differential between them.

[0064] The differential device described in the first and second embodiments may be used in any vehicle, such as an automobile using an internal combustion engine as a drive source, a hybrid automobile using an internal combustion engine and a rotating electric machine as a drive source, an electric automobile using a rotating electric machine as a drive source, etc. Furthermore, the differential device may be incorporated as a part of an automatic transmission, a hybrid drive device, an electric drive device, etc.

[0065] In the first embodiment, the cylindrical member 20 is disposed on the outer periphery of the step pinion gear SP as an outer peripheral member, and the rollers 21, 22 are disposed on the step pinion gear SP as positioning members, but the shapes and structures of these members are not limited to this. In particular, since the contact position between the cylindrical member 20 and the rollers 21, 22 is fixed regardless of the rotation of the step pinion gear SP, the outer peripheral member does not necessarily have to be cylindrical like the cylindrical member 20, and does not have to be circular as viewed in the axial direction as long as the positions at which the outer peripheral member contacts the rollers 21, 22 are the same. However, an endless shape that goes around once as viewed in the axial direction is preferable so that it can receive centrifugal force. [Explanation of symbols]

[0066] 11, 12...Differential device / 10...Case (input member) / 30L...Shaft coupling portion (first rotating member) / 30R...Shaft coupling portion (second rotating member) / 100L...Left wheel (first wheel) / 100R...Right wheel (second wheel) / B6...Ball bearing (first bearing) / B7...Ball bearing (second bearing) / CR...Carrier / GS...Gear set (differential mechanism) / P1 in Figs. 1 to 3...1st pinion gear (4th gear) / P2 in Figs. 1 to 3...2nd pinion gear (5th gear) / P3 in Figs. 1 to 3...3rd pinion gear (6th gear) / Fig. 1 P4 in Fig. 3: first pinion gear (fourth gear) / P1 in Figs. 4 to 6: first pinion gear (fifth gear) / P2 in Figs. 4 to 6: second pinion gear (fourth gear) / P3 in Figs. 4 to 6: third pinion gear (sixth gear) / SP: step pinion gear (speed-increasing rotation member, planetary pinion gear) / S1: first sun gear (first gear) / S2: second sun gear (second gear) / S3: third sun gear (third gear) / S4: fourth sun gear (first gear) / R1: first ring gear (second gear) / R2: second ring gear (first gear) / R3: third ring gear (third gear)

Claims

1. an input member to which driving rotation is input; a first rotating member that transmits a driving force to a first wheel; a second rotating member that transmits a driving force to a second wheel different from the first wheel; a differential mechanism capable of transmitting rotation of the input member to the first rotating member and the second rotating member while allowing differential rotation between the first rotating member and the second rotating member, The differential mechanism includes: a speed-increasing rotation member that is drivingly connected to the first rotation member and the second rotation member, and that, when a differential rotation occurs between the first rotation member and the second rotation member, is rotated at an increased speed relative to a rotation of the input member in response to the differential rotation, The differential limiting function limits the differential by the resistance generated by the speed increase of the speed-increasing rotating member when the differential rotation generated between the first rotating member and the second rotating member becomes large. Differential device.

2. The input member has a first gear, The first rotating member has a second gear, the second rotating member has a third gear, the speed-increasing rotation member is a planetary pinion gear including a fourth gear meshing with the first gear, a fifth gear meshing with the second gear, and a sixth gear meshing with the third gear, the planetary pinion gear being integrally formed with the fourth gear, As the planetary pinion gear is accelerated relative to the first rotating member, the tooth surface friction at the meshing portion between the second gear and the fifth gear and the tooth surface friction at the meshing portion between the third gear and the sixth gear become larger as the resistance.

2. The differential device according to claim 1.

3. the first gear is a second ring gear, the second gear is a first ring gear, the third gear is a third ring gear, A carrier is provided to rotatably support the planetary pinion gear, the input member is a case that contains the first ring gear, the third ring gear, and the carrier, The carrier is separated from other members inside the case and rotates independently.

3. The differential device according to claim 2.

4. the first gear is a second ring gear, the second gear is a first ring gear, the third gear is a third ring gear, the input member is a case having the second ring gear, the case rotatably supports the first rotating member via a first bearing and rotatably supports the second rotating member via a second bearing, and contains the second ring gear, the third ring gear, and the planetary pinion gear; 3. The differential device according to claim 2.

Images