JPH02254026A - Power transmission of four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To prevent tight-corner braking symptom by switching over the connection of the inner and outer plates of a viscous coupling to either front and rear wheel side output shafts or the input part of a center differential. CONSTITUTION:The output torque of an engine 1 is inputted from a transmitted 2 to the differential pinion 6 of a center differential D, and then transmission from first and second side gears 7 and 8 to front and rear wheel side output shafts 11 and 12, respectively. Also, when a difference in the number of revolutions is produced between the output shafts 11 and 12, the torque is transmitted, for example, between a gear 5 and the output shaft 11 by bypassing the center differential D by the use of a viscous coupling C. In this case, a switch-over clutch 45 is shifted, for example, to a front side soft position to connect the gear 5 to the inner plate 31 of the viscous coupling C through the first switch-over disk 35, etc. Thus, the amount of torque to be transmitted in relation to the difference in the number of revolution is reduced to obtain soft characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power transmission device for a four-wheel drive vehicle.

[Prior Art] Four-wheel drive vehicles that can transmit engine torque to the front and rear wheels are well known. If the transmission is transmitted to On the other hand, the rear wheels are rotated excessively, causing problems such as the vehicle not being able to run smoothly and tires being worn out.

For this reason, four-wheel drive vehicles are usually provided with a differential device, such as a center differential, for differentially driving the front wheels and rear wheels. However, in a four-wheel drive vehicle equipped with such a center differential, if one of the front or rear wheels slips while the vehicle is driving on a low μ road (a road with low road resistance), the differential operation of the center differential As a result, most of the power is transmitted to the wheel that is slipping, and almost no power is transmitted to the other wheel that is not slipping.Therefore, sufficient reaction force from the road surface cannot be obtained and the vehicle cannot be effectively driven. .

Therefore, as shown in FIG. 6, for example, the torque of the output shaft 102 of the transmission lO1 is transmitted to the differential pinion +06 of the center differential 105 via the main drive gear 103 and the main driven gear 104, and this torque is further transmitted to the differential pinion +06 of the center differential 105.
1st each. In a four-wheel drive vehicle in which power is transmitted to ten front wheel output shafts and a rear wheel output shaft 110 via second side gears 107 and 108, the main driven gear 1
04 and the rear wheel side output shaft 110, an outer case 111a that rotates integrally with the main driven gear 04;
A power transmission device including a viscous coupling Ill that is substantially composed of an outer plate 1llb attached to the inner circumferential surface of the outer case 1lla and an inner brake 1-111c that rotates integrally with the rear wheel output shaft 110. Devices have been proposed (for example, Japanese Patent Laid-Open No. 61-81226
(see publication).

In a four-wheel drive vehicle equipped with such a viscous car Z ring ill, when the front wheels slip, for example, the rotation speed of the front wheel side output shaft 109 increases due to the differential operation of the center differential 105, and the rotation speed of the front wheel side output shaft 109 increases by the amount of this increase in rotation speed. The rotational speed of the rear wheel side output shaft NO decreases, and therefore a rotational speed difference occurs between the main driven gear 104 and the rear wheel side output shaft 110, and according to this rotational speed difference, the main driven gear 104
A part of the torque is transmitted to the rear output shaft 110 via the viscous coupling +11, so that the front output shaft 1
09 and the rear wheel side output shaft 11O are locked up with a strength corresponding to the above rotational speed difference.

Therefore, the problem that power is transmitted only to the front wheel output shaft 109 that is slipping does not occur, and sufficient power can be transmitted to the rear wheels that are not slipping, thereby effectively driving the vehicle. be able to.

[Problem to be Solved by the Invention 1] By the way, in a four-wheel drive vehicle as shown in Fig. 6, when the steering wheel is turned to increase the steering angle while slowing down in order to turn the vehicle, the rotation of the front wheels generally increases. Since the radius is larger than the rotation radius of the rear wheels, the front wheel rotation speed is higher than the rear wheel rotation speed, and a relatively small rotation speed difference occurs between the main driven gear 104 and the rear wheel side output shaft 11O. At such low speed and large steering angle, when the vehicle running condition is in the region shown by 1' in Fig. 7,
The front wheel side output shaft 109 (front wheel) and the rear wheel side output shaft 110 (rear wheel) are almost rigidly connected to each other, resulting in a state similar to that of t;, and the center differential 105 is locked and amplified, and the differential operation is substantially activated. This will no longer occur, making it impossible to absorb the difference in rotational speed between the front and rear wheels. As a result, a so-called tight corner braking phenomenon occurs in which the front wheels are strongly braked by the road surface while the rear wheels are rotated excessively, making it impossible to turn in a manner commensurate with the turning of the steering wheel.

In the conventional four-wheel drive vehicle equipped with the viscous coupling 111, the viscous coupling Ill
The torque transmission iT is such that the rotational speed difference ΔN is relatively large as shown by the curve 61' in FIG. In a small region, the torque transmission iT increases rapidly as ΔN increases, but when ΔN increases beyond a certain level, the torque transmission fkT increases slowly.

Therefore, in the low rotational speed difference region where the rotational speed difference ΔN is between σ and β, the torque transmission state falls within the region There was a problem in that even if the driver turned the steering wheel, the appropriate turn would not occur. However, if the torque transmission rate of the viscous coupling lll is set small so that the torque transmission curve 01' does not fall into the region Sexuality worsens.

In addition, in general, when the road resistance is small, a stronger coupling is required to stabilize running performance, but in the conventional power transmission device mentioned above, the difference in rotational speed in the amount of torque transmitted by the viscous coupling is Since the characteristics with respect to ΔN are fixed, there is a problem in that it is difficult to obtain a lock-up state of appropriate strength depending on the road surface condition.

The present invention has been made in view of the above-mentioned conventional problems, and provides a rotational speed difference ΔN between the front wheel side output shaft and the rear wheel side output shaft.
In the region where ΔN is relatively small, the torque transmission amount of the viscous coupling is reduced, while in the region where the rotational speed ΔN is relatively large, the torque transmission amount is increased to stabilize running performance on low μ roads and to improve low-speed large rudder. To provide a power transmission device for a four-wheel drive vehicle that can prevent the occurrence of tight corner braking when cornering, and can adjust the strength of lock-up between front and rear wheels depending on road surface conditions or driving conditions. The purpose is to

[Means for Solving the Problems] Generally, in a power transmission device for a four-wheel drive vehicle equipped with a center differential and a viscous coupling as described above,
The rotational speed difference between the center differential manual shaft and the front wheel output shaft (or rear wheel output shaft) is smaller than the rotational speed difference between the front wheel output shaft and the rear wheel output shaft (for example, evenly distributed In the case of a center differential, it will be 1/2).

On the other hand, even if the viscous coupling is placed between the center differential input shaft, the front wheel output shaft, and the rear wheel output shaft, when torque is transmitted through the viscous coupling, the amount of torque transmitted is The front wheel side output shaft and the rear wheel side output shaft can be locked up according to the conditions. The amount of torque transmitted by a viscous coupling is a function of the difference in rotational speed between the two shafts connected to the viscous coupling, and as the difference in rotational speed increases, the amount of torque transmitted increases. When the strength of the lockup increases, it has the following characteristics:

Therefore, it is better to insert a viscous coupling between the center differential input shaft and the front output shaft (or the rear output shaft). The amount of torque transmitted relative to the rotational speed difference ΔN between the front wheel output shaft and the rear wheel output shaft, that is, the strength of lockup, is smaller than when the front wheel output shaft is interposed between the front wheel output shaft and the rear wheel output shaft.

Focusing on this fact, in order to achieve the above object, the present invention connects the front wheel side output shaft and the rear wheel side output shaft in a differential manner, and transfers the torque output from the transmission to the above two output shafts. In a power transmission device for a four-wheel drive vehicle that includes a center differential distributed to the shaft and a viscous coupling that transmits torque by bypassing the center differential, one plate of the inner plate and outer plate of the viscous coupling is , is connected to one of the front and rear output shafts, and the other plate of the viscous coupling is connected to the other output shaft of the above-mentioned re-output shaft, or the center differential A power transmission device for a four-wheel drive vehicle is provided, characterized in that it is provided with a torque transmission path switching means for switching whether or not to connect to a torque input section.

[Operations and Effects of the Invention] In the present invention, for example, the outer plate of a viscous coupling is connected to the front wheel output shaft, and the inner plate is selectively connected to the center differential input shaft (torque input part) or the rear wheel output shaft. When the inner plate is connected to the center differential input shaft by the torque transmission path switching means, the torque transmission amount of the viscous coupling with respect to the rotational speed difference ΔN between the front wheel output shaft and the rear wheel output shaft On the other hand, when the inner plate is connected to the output shaft on the rear wheel side, the torque transmission amount is large and null, so two torque transmission characteristics can be set with one viscous coupling. Therefore, on low μ roads, the inner plate is connected to the rear wheel output shaft to increase the amount of torque transmitted to the rotational speed difference ΔN to strengthen lockup, while on high μ roads, the inner plate is connected to the center differential input shaft. By weakening the lock amplifier by reducing the amount of torque transmitted relative to the rotational speed difference ΔN, lock-up can be performed in accordance with the road surface condition or the driving condition, and the driving performance can be stabilized.

In addition, if the inner plate is connected to the center differential input shaft in a region where the rotational speed difference ΔN is small, and the inner plate is connected to the rear wheel side output shaft in a region where the rotational speed difference ΔN is large, the rotational speed difference ΔN is small. A torque transmission characteristic is obtained in which the amount of torque transmission is small in the region where ΔN is large, and the amount of torque transmitted is large in the region where ΔN is large. (See Area I in Figure 2). Therefore, it is possible to effectively prevent the tight corner braking phenomenon at low speeds and large steering angles, and to stabilize the running performance on low μ roads.

In addition, if the outer plate of the viscous coupling is connected to the rear wheel output shaft and the inner plate can be selectively connected to the center differential output shaft or the front wheel output shaft, or the inner plate is connected to the front wheel output shaft. However, it goes without saying that similar actions and effects can be obtained with other combinations of connection methods, such as when the outer plate can be selectively connected to the center differential input shaft or the rear wheel side output shaft.

[Example] Examples of the present invention will be specifically described below.

FIRST EMBODIMENT> As shown in FIG. 1, the output torque of the engine 1 is transmitted to the transmission output shaft 3 after being changed by the transmission 2 at a gear ratio according to the shift position. The torque of No. 3 is input to the differential pinion 6 of the equal distribution center differential DA via a main drive gear 4 coaxially attached to the main drive gear 4 and a main driven gear 5 meshing with the main drive gear 4.

The center differential DA is a bevel gear type ordinary differential device, in which the differential gear 6 revolves around the first side gear 7 and the second side gear 8 while meshing with them, and can also rotate around the differential gear shaft 6a. With such revolution and rotation, the first. The second side gear 7.8 is driven in rotation with equal torque. And the first. When the loads on the second side gears 7°8 are equal, the differential gear 6 revolves but does not rotate; 2nd side gear 78
rotates at the same number of revolutions. However, when the loads on the first and second side gears 7.8 are not equal, the differential gear 6 rotates and revolves, and depending on the ratio of the loads on both side gears 7.8, the side with the lower load is transferred to the other side. It is designed to rotate at a higher rotation speed than the side gear (for differential operation). Note that even when both side gears 7.8 differentially rotate in this way, the total number of rotations of both side gears 7.8 is always equal to twice the number of revolutions of the differential gear 6, as in the case of non-differential rotation.

A front wheel side output shaft 11 is connected coaxially to the first side gear 7 of the center differential DA, and the first side gear 7
The torque is equally distributed to the front differential 15 via the front output shaft 11 and the front bevel gear 14 provided at the front end of the front output shaft 11,
This torque is further transmitted from the front differential 15 to the left and right front axle shafts I6. +7 to the left and right front wheels.

On the other hand, a rear wheel output shaft 12 is connected coaxially with the second side gear 8, and the torque of the second side gear 8 is transmitted between the rear wheel output shaft 12 and the rear side end of the rear wheel output shaft I2. The torque is equally distributed to the rear differential 22 via the rear bevel gear 21 provided at the rear side, and this torque is further transmitted to the rear differential 22
The power is then transmitted to left and right rear wheels 25 and 26 via left and right rear axle shafts 23 and 24, respectively.

By the way, when a rotational speed difference ΔN occurs between the front output shaft 11 and the rear output shaft 12, the center differential DA is bypassed and the main driven gear 5 and the front output shaft +1
A substantially cylindrical viscous coupling C that transmits torque between the front wheel output shaft 11 and the rear wheel output shaft 12 has an axis line that is connected to the front wheel output shaft 11 (rear wheel output shaft 12
) is arranged parallel to the axis of the This viscous coupling C essentially includes a substantially cylindrical outer case 27 forming a housing thereof, and the outer case 2.
a plurality of annular outer plates 28 attached to the inner circumferential surface of 7; and a connecting shaft 29 arranged between each outer plate 28.
The outer case 27 is composed of a disk-shaped inner plate 31 coaxially attached to the outer case 27, and the outer case 27 is filled with oil.

When the outer plate 28 and the inner plate 31 rotate at different rotational speeds, torque is transmitted between the plates 28 and 31 according to the difference in rotational speed due to the viscosity of the oil. In this way, when torque is transmitted between both plates 28, 31, the front wheel output shaft 11 and the rear wheel output shaft 12 are gradually locked up more and more as the amount of torque transmission increases. ing.

A first bypass gear 32 is attached coaxially to the outer circumferential surface near the front end of the outer case 27, and this first bypass gear 32 is connected to a second bypass gear 32 coaxially attached to the front output shaft 11. It meshes with gear 33.

Further, an inner plate disk 34 is coaxially attached to the rear 1 m end of the connecting shaft 29 extending from inside the outer case 27 toward the rear side. A first switching disk 35 is arranged on the front side of the inner plate disk 34 so as to have the same axis as the inner plate disk 34, and the first switching disk 35 is a tubular pipe that coaxially accommodates the connection @29 in the hollow part. It is connected to a third bypass gear 37 via a shaft 36, and this third bypass gear 37 meshes with the main driven gear 5. On the other hand, a second switching disc 39 is arranged on the rear side of the inner plate disc 34 so as to have the same axis as the inner plate disc 34, and this second switching disc 39 has a connection shaft that is arranged on the same axis as the connecting shaft 29. 41 to a fourth bypass gear 42, and this fourth bypass gear 42 meshes with a fifth bypass gear 43 coaxially attached to the rear wheel side output shaft 12.

The first switching disk 35 and the inner plate disk 3
4 and the second switching disk 39 are each formed into a disk shape having the same radius, and are arranged closely in this order from the front side to the rear side.

A switching clutch 45 is provided on the outside of the outer circumferential surface of each of these discs 35, 34, 39 in close proximity thereto, and the set position of this switching clutch 45 can be switched by an actuator 47 via a link mechanism 46. When the switching clutch 45 is set to the front side position (the switching clutch 45 in FIG. 1 shows this state), the inner plate disc 34
and the first switching disc 35 are connected, and when the switching clutch 45 is set to the rear side position, the inner plate disc 34 and the second switching disc 39 are connected.

When the switching clutch 45 is set to the front side position (hereinafter, this clutch position is referred to as the soft position), the main driven gear 5 and the inner plate 31 are sequentially connected to the third bypass gear 37, the pipe shaft 36, and the first switching position. The disk 35, the switching clutch 45, the inner plate disk 34, and the connecting shaft 29 are connected to each other.

This t; main driven gear 5 and front wheel side output shaft 11
are connected via a viscous coupling C, and at this time, torque is transmitted between the main driven gear 5 and the front output shaft 11 in accordance with the rotational speed difference ΔN', but the center differential DA transmits torque, etc. Since it is a distribution type, the above rotation speed difference ΔN' is between the front wheel side output shaft 11 and the rear wheel side output shaft 1.
This is 1/2 of the rotational speed difference ΔN between the two. therefore,
In this case, the torque transmission amount with respect to the rotational speed difference ΔN becomes small, and the torque transmission amount has a soft characteristic in which the increase in the torque transmission amount with respect to an increase in ΔN is small, as shown by curve F in FIG.

On the other hand, when the switching clutch 45 is set to the rear side position (hereinafter, this clutch position is referred to as the hard position)
, the rear wheel output shaft 12, the inner plate 31, the fifth bypass gear 43, the fourth bypass gear 42, the connecting shaft 41, the second switching disc 39, the switching clutch 45, the inner plate disc 34, and the connecting shaft 29. are connected via. For this reason, the rear wheel side output shaft 12 and the front wheel side output shaft 11
are connected via a viscous coupling C, and at this time, torque is transmitted between the rear wheel side output shaft 12 and the front wheel side output shaft 11 in accordance with the rotational speed difference ΔNi between them.
In this case, since the difference in rotational speed between the outer plate 28 and the inner plate 31 is large (ΔN), the amount of torque transmitted accordingly increases, and as shown by the curve F1 in FIG. It becomes a hard characteristic with a large increase in quantity.

By the way, a control unit 48 is provided to control the actuator 47, and the control unit 48 has left and right front axle shafts 1, respectively.
The rotation speeds of each front wheel 18.19 and each rear wheel 25.26 detected by the first to 5th rotation speed sensors 5] to 54 provided for the rear axle shaft 23.6.17 and the rear axle shaft 23.24 are input. It is now possible to do so. And the first. The average value of the detection values of the second rotation speed sensors 51 and 52 is regarded as the front wheel rotation speed (front wheel side output shaft rotation speed), and the third. The average value of the detection values of the fourth rotation speed sensor 53 and 54 is regarded as the rear wheel rotation speed (rear wheel side output shaft rotation speed), and the switching clutch is set based on the difference between these front wheel rotation speed and rear wheel rotation speed. Soft 45/
I'm trying to switch to hard.

A method of controlling the torque transmission mechanism by the control unit 48 will be described below.

The switching clutch 45 is set to the soft position in normal driving conditions with little wheel slip, such as when driving on a high μ road, that is, in a region where the rotational speed difference ΔN between the front and rear wheels is small. Then, by entering a low μ road, etc., the rotation speed difference ΔN becomes a predetermined value Δ.
When N1 is exceeded, the switching clutch 45 is switched from the soft position to the hard position as shown by the broken line H2 in FIG. Then, when the rotational speed difference ΔN decreases to ΔNI' as the vehicle enters a high μ road again, the switching clutch 45 is switched from the hard position to the soft position as shown by the polygonal line H2 in FIG.

Here, when switching the switching clutch 45 to the hard side and when switching to the soft side, hysteresis is provided by making a difference in the switching rotation speed.
This is to prevent frequent switching of the switching clutch 45 when the rotational speed difference ΔN increases or decreases near the switching rotational speed.

When the switching clutch 45 is controlled in this way, the amount of torque transmitted by the viscous coupling C with respect to the rotational speed difference ΔN is as shown by the curve J1 in FIG. becomes smaller, and the rotational speed difference ΔN
In the region where is large, the torque transmission amount becomes large. Therefore, the torque transmission state of the viscous coupling C does not fall into the region I where the tight corner braking phenomenon occurs at low speeds and large steering angles. Therefore, during normal driving, the front and rear wheels are differentially operated, and when driving on low μ roads, the front and rear wheels are appropriately locked up according to the degree of slip to stabilize the vehicle's drive, and at low speeds and with large steering angles, the front and rear wheels are locked up appropriately. Since the corner braking phenomenon can be effectively prevented from occurring, the running performance of the vehicle can be improved.

Furthermore, when it is desired to weaken the strength of the lock-up when driving on a high μ road, etc., the driver can change the rotation speed difference between the hard side and the soft side as shown by the polygonal lines Hs and H4 in Fig. 3. ΔN2. By making it possible to increase ΔN to 8', the torque transmission characteristics can be changed over a wider range. Therefore, since the torque transmission characteristic can be selected according to the road surface condition or the driving condition, it is possible to further improve the driving performance. In this case, the characteristic of the torque transmission amount with respect to the rotational speed difference is as shown by the curve J2 in FIG. 4.

Second Embodiment> The second embodiment of the present invention will be described below with reference to FIG. 5, but the same components as the first embodiment shown in FIG.
The same numbers as in the first embodiment are given, and the explanation thereof is omitted.
Only the parts that are different from the embodiment will be explained.

As shown in FIG. 5, in the second embodiment, an unequal distribution center differential DB using a planetary gear train is provided as a differential device between the front and rear wheels. In this center differential DB, the torque of the main driven gear 5 is input to the carrier 61, and the torque of the carrier 61 is distributed unequally (for example, 7:3) between the ring gear 62 and the sun gear 63. Then, the ring gear 62 is connected to the rear wheel side output shaft l? connected to
A side sun gear 63 is connected to the front wheel side output #111. In the second embodiment, the first bypass gear 32 attached to the outer peripheral surface of the outer case 27 of the viscous coupling C meshes with the second bypass gear 33 attached to the rear wheel side output shaft 12, and the first bypass gear 32 is attached to the connecting shaft 41. The attached fourth bypass gear 42 meshes with the fifth bypass gear 43 attached to the front wheel side output shaft 11. For this reason, the viscous coupling C and each switching disk 34, 35
Although the arrangement of the angle 39 and the switching clutch 45 is reversed from that of the first embodiment, these structures are substantially the same as those of the first embodiment.

In the above configuration, for example, if the torque distribution ratio between the ring gear 62 and the sun gear 63 of the center differential DB is 7:3, the rotation speed difference between the main driven gear 5 and the front output shaft +1 is equal to This is 3/10 of the rotational speed difference between the output shaft 12 and the rear wheel side output shaft 12, so the torque transmission characteristic at the soft position becomes softer (becomes smaller) as shown by curve F in FIG. Therefore, the torque transmission characteristics of the viscous cuff spring C can be adjusted over a wider range.

Other than these points, the functions and effects of the second embodiment are the same as those of the first embodiment.
Since this is the same as in the embodiment, the explanation thereof will be omitted.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a four-wheel drive vehicle showing a first embodiment of the present invention. FIG. 2 is a diagram showing general characteristics of the torque transmission amount of the viscous coupling with respect to the rotational speed difference between the front wheel side output shaft and the rear wheel side output shaft. The third factor is a diagram showing the switching characteristics of the switching clutch between the hard side and the soft side. FIG. 4 is a diagram showing the characteristics of the torque transmission amount of the viscous coupling with respect to the rotational speed difference between the front and rear wheels when the switching clutch shown in FIG. 3 is switched. 5th [1!7] is a schematic diagram of a four-wheel drive vehicle showing a second embodiment of the present invention. FIG. 6 is a schematic diagram of a conventional four-wheel drive vehicle equipped with a viscous coupling that transmits torque torque by bypassing the center differential. FIG. 7 is a diagram showing the characteristics of the torque transmission amount of the viscous coupling of the four-wheel drive vehicle shown in FIG. 6 with respect to the rotational speed difference. C...Viscous coupling, DA...Equal distribution center differential, DB...Unequal distribution center differential, l...Engine, 2...Transmission, 3...Transmission output shaft, 4...
・Main drive gear, 5... Main driven gear,
6... defbinion, 7, 8... 1st. 2nd side gear, 11... Front wheel side output shaft, 12... Rear wheel side output shaft, 28... Outer plate, 31... Inner plate, 34... Inner plate disc, 35...
First switching disk, 39...Second switching disk, 45
...Switching clutch, 47...Actuator, 48
...Control unit, 51-54...1st-
4th rotation speed sensor. Figure 5

Claims (1)

[Claims] (1) A center differential that differentially connects the front and rear output shafts and distributes the torque output from the transmission to both output shafts, and a center differential that bypasses the center differential to transmit torque. 4 with viscous coupling
In a power transmission device for a wheel drive vehicle, one plate of the inner plate and the outer plate of the viscous coupling is connected to one of the output shafts of the front wheel side and the output shaft of the rear wheel side, and the viscous cup A four-wheel drive characterized by providing a torque transmission path switching means for switching between connecting the other plate of the ring to the other output shaft of the two output shafts or to the torque input section of the center differential. Car power transmission device.