JPH02254024A - Power transmission of four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To prevent tight-corner braking symptom at low speed and large steering angle by, reducing the amount of torque to be transmitted by a viscous coupling with which torque to a center differential is bypassed when a difference in the number of revolutions between front and rear wheel side output shafts is small. CONSTITUTION:The output torque of an engine 1 is transmitted to the output shaft 3 of a transmission 2 and then inputted into the differential pinion 6 of a center differential D through multiple gears 4 and 5. Also, the output torque is transmitted from the first and second side gears 7 and 8 of the center differential D to front and rear wheel side output shafts 11 and 12, respectively. In addition, when a difference in the number of revolutions is produced between respective front and rear wheel side output shafts 11 and 12, the torque from the transmission output shaft 3 to the center differential D is bypassed by the use of a viscous coupling C to the rear wheel side output shaft 12. When the above-mentioned difference in the number of revolutions is small, the amount of torque to be transmitted is reduced by a one-way clutch 33.

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 1] Four-wheel drive systems that can transmit engine torque to the front and rear wheels are well known, but in four-wheel drive vehicles, engine torque can be transmitted to the front and rear wheels using only rigid power transmission means. If the transmission is transmitted to On the other hand, there are problems such as the rear wheels being rotated excessively, making it impossible for the vehicle to run smoothly and causing tire wear.

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, when either the front or rear wheels slip while the vehicle is driving on a low μ road such as a snowy road, the differential operation of the center differential reduces the power output. Most of the power is transmitted to the wheel that slipped, and almost no power is transmitted to the other wheel, so that sufficient reaction force from the road surface cannot be obtained and effective driving cannot be performed.

Therefore, as shown in FIG. 5, for example, the torque of the output shaft 102 of the transmission 101 is transmitted to the differential pinion 106 of the center differential +05 via the main drive gear 103 and the main driven gear 104, and this torque is further transmitted to the differential pinion 106 of the center differential +05.
1st each. In a four-wheel drive vehicle in which power is transmitted to a front wheel output shaft 109 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 104;
Power transmission equipped with a viscous coupling Ill that is substantially composed of outer plates ti+, b attached to the inner peripheral surface of the outer case 111a and an inner plate 111c that rotates integrally with the rear wheel side output shaft 110. A device has been proposed (see, for example, Japanese Patent Application Laid-Open No. 61-81226).

In a four-wheel drive vehicle equipped with such a viscous coupling III, 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 this increase. The rotational speed of the side output shaft 110 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, a part of the torque of the main driven gear 104 is transferred to the viscous cup. Since the signal is transmitted to the rear wheel output shaft 110 via the ring ill, the front wheel output shaft 109
and the rear wheel side output shaft 110 are locked up with a strength corresponding to the 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.

[Problems to be Solved by the Invention] By the way, in a four-wheel drive vehicle as shown in Fig. 5, when the steering angle is increased by slowing down and turning the steering wheel in order to turn the vehicle, the turning radius of the front wheels changes. Since the radius of rotation of the front wheels is larger than that of the rear wheels, the number of rotations of the front wheels is greater than the number of rotations of the rear wheels. For this reason, the main driven gear 104
Although a relatively small difference in rotational speed occurs between the output shaft 110 and the output shaft 110 on the rear wheel side, at such low speeds and large steering angles, the running state of the vehicle falls into the region shown by ■' in Fig. 6. At some point, the front wheel side output shaft 109 (front wheel) and the rear wheel side output shaft 11
O (rear wheel) is in the same state as if it were rigidly connected, and the center differential 105 is locked up and differential operation virtually no longer occurs, making it impossible to absorb the difference in rotation speed between the front and rear wheels. It disappears.

At this time, 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 driven to rotate excessively, making it impossible to turn in a manner commensurate with the turning of the steering wheel.

On the other hand, in the above conventional four-wheel drive vehicle equipped with the viscous coupling Ill, the viscous coupling 1. l
1, the torque transmission amount T is relatively small compared to the rotational speed difference ΔN between the front wheel side output shaft 109 and the rear wheel side output shaft +10, as shown by the curve Gl' in FIG. In this region, the torque transmission amount T increases rapidly as ΔN increases, but when ΔN increases beyond a certain level, the torque transmission amount T increases.
It has the characteristic that the increase in lIk becomes chronic. Therefore, in a low rotational speed difference region where the rotational speed difference ΔN is ΔN, ~ΔN2, the torque transmission amount curve Gl' is in the region 1'
Therefore, when the vehicle turns at a low speed and has a large steering angle, a tight corner braking phenomenon occurs, and even if the steering wheel is turned, a corresponding turn cannot be made.

In order to prevent this, one possible method is to reduce the torque transmission rate of the viscous coupling 111.
If you do this, the amount of torque transmission will decrease in all regions, so you will not be able to obtain a sufficient amount of torque transmission in the region where ΔN is large.
Driving performance on low μ roads deteriorates.

The present invention has been made in view of the above-mentioned conventional problems, and is designed to suitably lock up the front wheel output shaft and the rear wheel output shaft in driving conditions where the wheels tend to slip, such as when driving on a low μ road. It is an object of the present invention to provide a power transmission device for a four-wheel drive vehicle, which can effectively perform four-wheel drive traveling at low speeds and at large steering angles, and can effectively prevent the occurrence of tight corner braking phenomenon at low speeds and large steering angles.

[Means for Solving the Problems] In order to achieve the above object, the present invention connects a front wheel side neutral power shaft and a rear wheel side output shaft in a differential manner, and connects the torque output from the transmission to the above two output shafts. A center differential that distributes to the shaft, a viscous coupling that transmits torque by bypassing the center differential, and the amount of torque transmitted by the viscous coupling when the rotational speed difference between the front wheel output shaft and the rear wheel output shaft is small. Provided is a power transmission device for a four-wheel drive vehicle, characterized in that it is provided with a torque transmission characteristic changing means for reducing torque transmission characteristics.

[Operations and Effects of the Invention 1] According to the present invention, the viscous coupling that bypasses the center differential and transmits torque is connected, for example, between the center differential human power shaft (transmission output shaft) and one center differential output shaft,
Alternatively, it is provided between the front wheel side output shaft and the rear wheel side output shaft of the center differential. For this reason, basically, while the front wheels and the rear wheels are differentially driven, the front wheel side output shaft (front wheel) and the rear wheel side output shaft (
When a rotational speed difference occurs between the rear wheels (rear wheels), torque is applied between the center differential manual shaft and one center differential output shaft, or between both center differential output shafts via a viscous coupling, depending on this rotational speed difference. can be transmitted. Therefore, under normal driving conditions, while the front and rear wheels are differentially driven,
In the event of a slip, the front and rear wheels can be appropriately locked up to drive the vehicle effectively, improving the running performance of the vehicle.

In a region where the difference in rotational speed between the front and rear wheels is relatively small, where a tight corner braking phenomenon occurs, the torque transmission characteristic changing means prevents the torque transmission of the viscous coupling. Therefore, the torque transmission characteristic of the viscous coupling is such that the amount of torque transmitted is small in a region where the rotational speed difference between the front and rear wheels is small, and the torque transmission amount is large in a region where the rotational speed difference is large. Therefore, the torque transmission characteristic curve (see G in Figure 3) with respect to the difference in rotational speed of the viscous coupling does not fall into the region where tight corner braking occurs (see region ■ in Figure 3), so the low-speed large rudder It is possible to effectively prevent the occurrence of a tight corner braking phenomenon when cornering.

[Example 1 Examples of the present invention will be specifically described below.

FIRST EXAMPLE> As shown in Fig. 1, the output torque of the engine 1 is controlled by changing the speed! ! ! 2, the gear is shifted at a gear ratio according to the shift position and transmitted to the transmission output shaft 3, and the torque of the transmission output shaft 3 is transmitted to the main drive gear 4 having 21 gears attached coaxially thereto, and the transmission output shaft 3. The signal is inputted to the differential pinion 6 of the equally distributed center differential D via the main driven gear 5 having Z number of gears meshing with the main drive gear 4 . Note that the gear ratio R+ "" Z z /Z + of the main driven gear 5 and the main drive gear 4 is set to an appropriate value (for example, 1.0).

The above-mentioned center differential D is a bevel gear type ordinary differential device, and the differential gear 6 revolves around the first side gear 7 and the second side gear 8 while interacting with them, while also being able to rotate around the differential gear 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 7.
8 rotates at the same number of rotations. However, when the loads on the first and second side gears 7.8 are not equal, the differential gear 6
revolves while rotating on its own axis, and the side gear with a lower load is rotated at a higher rotational speed than the other side gear according to the ratio of the loads on both side gears 7.8 (for differential operation). Note that even when both side gears 7.8 differentially rotate in this manner, the total number of rotations of both side gears 7.8 is equal to twice the revolution number 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 D, and the torque of the first side gear 7 is transmitted between the front wheel side output shaft 11 and the front wheel side output shaft 1.
1 is transmitted to the equally distributed front differential 15 via a front bevel gear 14 provided at the front end of the
This torque is further transmitted from the front differential 15 to the left and right front wheels 18,197 via left and right front axle shafts 16,17, respectively.

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 end of the rear wheel output shaft 12. 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
From there, the power is transmitted to left and right rear wheels 25, 26 via left and right rear axle shafts 23, 24, respectively.

By the way, when a difference in rotational speed occurs between the front wheel output shaft 11 and the rear wheel output shaft 12, the center differential D is bypassed and torque is transmitted between the transmission output shaft 3 and the front wheel output shaft 11. A viscous coupling C is provided. This viscous coupling C essentially includes a substantially cylindrical outer case 27 that forms a housing and has the same axis as the transmission output shaft 3, and a plurality of annular outer plates 28 attached to the inner peripheral surface of the outer case 27. and a disc-shaped inner plate 29 disposed between each outer plate 28 and coaxially attached to the transmission output shaft 3.
The outer case 27 is filled with oil. When the outer plate 28 and the inner plate 29 rotate at different rotation speeds, both plates 28.
Torque is transmitted between 29 and 29. In this way, when torque is transmitted between both plates 28 and 29, the front wheel output shaft 11 and the rear wheel output shaft 12 gradually become more strongly locked up as the amount of torque transmission increases. ing.

Further, a first bypass gear 31 having a number of Z gears is attached coaxially to the outer peripheral surface of the outer case 27, and a second bypass gear 31 having a number Z of gears meshing with the first bypass gear 31 is attached coaxially therewith.
A bypass gear 32 is provided. Gear ratio R between second bypass gear 32 and first bypass gear 31! (Z 4/
Zs) is a value slightly smaller than the gear ratio R1 between the main driven gear 5 and the main drive gear 4 (for example, 0
．． 9). And second bypass gear 3
2 is connected to the front wheel side output shaft 11 via a one-way clutch 33
is coaxially connected to. This one-way clutch 33
When the rotation speed of the front wheel side output shaft 11 is higher than the rotation speed of the second bypass gear 32 when the vehicle is moving forward, torque is transmitted from the front wheel side output shaft 11 to the second bypass gear 32; When the rotational speed of the side output shaft 11 is lower than the rotational speed of the second bypass gear 32, the side output shaft 11 idles, and no torque is transmitted between the front wheel side output shaft 11 and the second bypass gear 32. Note that the one-way clutch 33 corresponds to the torque transmission characteristic changing means described in claim 1 of the present application. One-way clutch 33 above
is not provided, the viscous coupling C
The amount of torque transmitted is between the front wheel side output shaft 11 and the rear wheel side output shaft 1.
The characteristic for the rotational speed difference ΔN between the two is as shown in the curve F in FIG. Torque transmission does not occur in the portion (where the rotational speed of the front wheel side output shaft 11 is lower than the rotational speed of the second bypass gear 32), and the characteristic of the torque transmission amount with respect to ΔN at this time is as shown by the curve G2 in Fig. 3. Become.

Well, the reason why the point where the torque transmission amount is O on the curve F1 is shifted by ΔN is because, as will be explained in detail later, the gear ratio R2 (for example, 0.9) is changed from the gear ratio R1 (for example, 1. 0
) is set smaller. If the gear ratio R, and the gear ratio R2 are equal, then the characteristic of the torque transmission amount of the viscous coupling C versus ΔN will be as shown by the curve F2 in Fig. 2, and when the rotational speed difference ΔN is 0. Sometimes the torque transmission amount becomes 0.

The torque transmission effect in the above configuration will be explained below.
For ease of understanding, the rotation speed of the transmission output shaft 3 is lo
oOrpm is constant, gear ratio R1 is 1.0,
The explanation will be made assuming that the gear ratio R2 is 0.9.

In this case, main driven gear 5 and main drive gear 4
Since the gear ratio R is 1.0, the rotational speed of the transmission output shaft 3 and the revolution speed of the differential gear union 6 are always equal.

When the front wheels 18.19 and the rear wheels 25.26 are rotating at the same rotation speed, such as when the vehicle is traveling straight with almost no slipping of any of the wheels, that is, when the front wheel side output shaft 11 and the rear wheel side When the rotational speed of the output shaft 12 is the same, the transmission output shaft 3, the front wheel output shaft 11, and the rear wheel output shaft 12 all rotate at the same rotational speed of 11000 rpm. At this time, the inner plate 29 and outer plate 28 of the viscous coupling C are rotating together with the transmission output shaft 3 at approximately Iooorpm. Therefore, the first bypass gear 31 has a rotational speed of 11 approximately equal to that of the transmission output shaft 3.
It is rotating at 000 rpm. Since the gear ratio R2 between the second bypass gear 32 and the first bypass gear 31 is set to 0.9, the rotation speed of the second bypass gear 32 is 110 rpm of the rotation speed of the first bypass gear 31, which is 11000 rpm.
．． 9 times, or 1111 rpm. In this case, since the rotation speed (1000 rpm) of the front wheel side output shaft 11 is smaller than the rotation speed (1111 rpm) of the second bypass gear 32, the one-way clutch 33 idles, and therefore the transmission output shaft 3 and the front wheel output shaft 11 are connected to each other. No torque is transmitted between them, the front output shaft 11 and the rear output shaft 12 are not locked up at all, and the transmission of power to both output shafts 11 and 12 is regulated only by the center differential D.

When the load on the front wheels decreases due to slippage of the front wheels 8 and 19, the rotation speed of the front output shaft 11 increases as the load on the front wheels decreases due to the differential operation of the center differential D. However, as mentioned above, the sum of the rotation speed of the front wheel side output shaft 11 and the rotation speed of the rear wheel side output shaft 12 is 2 times the revolution speed of the differential pinion 6 (the rotation speed of the transmission output shaft 3).
It is constant at 200 rpm, that is, 200 rpm. At this time,
As mentioned above, the second bypass gear 32 is l 111 r
pm, so if the rotation speed of the front output shaft 11 is less than lllrpm, the one-way clutch 33 will idle, and no torque will be transmitted between the transmission output shaft 3 and the front output shaft 11. The front wheel side output shaft 11 and the rear wheel side output shaft 12 are not locked up at all, and both output shafts 11, 12
The transmission of power to is regulated only by the center differential D. In addition, at this time, the rotation speed of the rear wheel side output shaft 12 is 889.
rpm (200Orpm-1111rpm=88
9 rpm), and the rotational speed difference ΔN is 222 rpm (1
111 rpm - 839 rpm = 222 rpm). Therefore, when the rotational speed difference ΔN is 222 rpm or less, the torque transmission action of the viscous coupling C is canceled.

Here, the load on the front wheel side further decreases, and the rotation speed of the front wheel side output shaft 11 decreases to 1. When the rotation speed exceeds l lrpm, the one-way clutch 33 does not idle, and a portion of the torque of the front wheel side output shaft 11 on the high rotation side is transmitted to the second bypass gear 32 on the low rotation side, that is, the transmission output shaft 3. When torque is transmitted from the front wheel output shaft 11 to the transmission output shaft 3 in this way, the front wheel output shaft 11 and the rear wheel output shaft 12 are gradually and strongly locked up as the amount of torque transmission increases. Ru. This phenomenon occurs when the transmission output shaft 3
Viscous coupling C
The rotational speed difference ΔN0 at which torque transmission begins is the transmission output shaft 3
The higher the rotation speed, the larger it becomes.

Therefore, when the rotation speed of the front wheels 18.19 becomes higher than the rotation speed of the rear wheels 25.26 in this way, the torque transmitted from the front wheel side output shaft ll to the transmission output shaft 3 via the viscous coupling C is , the third
As shown by curve G in the figure, when the rotational speed difference ΔN is ΔN or less (in the above specific example, ΔN-N-222rp, the torque transmission amount is 0, and when the rotational speed difference ΔN exceeds ΔN0, It shows a characteristic that the torque transmission amount increases rapidly as ΔN increases.For this reason, the torque transmission characteristic curve G of the viscous coupling C with respect to the rotational speed difference ΔN
, does not fall into the region I where the tight corner braking phenomenon occurs, so the tight corner braking phenomenon does not occur even at low speeds and large steering angles. In addition, in the conventional viscous coupling, the torque transmission characteristic curve falls within region I, as shown by curve G1 in FIG.

Therefore, during normal driving, the front and rear wheels are differentially operated, and when slipping, the front and rear wheels are appropriately locked up according to the degree of slip to drive the vehicle effectively, and at low speeds and with large steering angles, the tight corner braking phenomenon is prevented. Since this can be effectively prevented from occurring, it is possible to improve the running performance of the vehicle.

Note that, instead of comprising the torque transmission characteristic changing means of the viscous coupling with a one-way clutch as in the first embodiment, it may be constructed with an actuator that electrically controls the torque transmission of the viscous coupling.

<Second Embodiment> Hereinafter, a second embodiment of the present invention will be described with reference to FIG. The same reference numerals are used to omit the explanation, and only the parts different from the first embodiment will be explained.

As shown in FIG. 4, in the second embodiment, the front wheel side output shaft i
t and the rear wheel side output work 2 are connected via a viscous coupling C, and torque is transmitted between them according to the rotational speed difference between both output shafts 11.12.
I'm trying to lock it up. That is, a first bypass gear 42 having a number of gears Zl is attached to the front end of a connecting shaft 41 coaxially attached to the inner plate 29 of the viscous coupling C, and the first bypass gear 42 is connected to the one-way clutch 33. It meshes with a second bypass gear 32, which has 21 gears and is connected to the front wheel side output shaft 11 via the second bypass gear 32.

Then, a third bypass gear 43 having 21□ gears is attached to the outer periphery of the outer case 27 of the viscous coupling C, and a fourth bypass gear 44 having the number Zll of gears that meshes with the third bypass gear 43 is output to the rear wheel side. It is attached coaxially to the shaft 12. And the first bypass gear 42
and the gear ratio of the second bypass gear 32 RIff=Z14/
z13 is the third bypass gear 43 and the fourth bypass gear 4
The gear ratio Rr r −Z Ix/Z r + is set larger than the gear ratio Rr r −Z Ix/Z r +.

In the above configuration, Rrz>R The one-way clutch 33 spins idly.

When the rotational speed difference ΔN between the front wheel output shaft 11 and the rear wheel output shaft 12 exceeds a predetermined value ΔN0 due to slipping of the front wheels 18, 19, etc., the rotational speed of the front wheel output shaft 11 becomes the second rotation speed. The rotation speed becomes higher than that of the bypass gear 32, the one-way clutch 33 engages, and a portion of the torque of the front output shaft 11 is transmitted to the rear output shaft 12 via the viscous coupling C, and both output shafts 11, 12 is now locked up. In this case, the action/effect is the first
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. FIG. 3 is a diagram showing the characteristics of the torque transmission amount of the viscous coupling shown in FIG. 1 with respect to the rotational speed difference, and the operating range where the tight corner braking phenomenon occurs. FIG. 4 is a schematic diagram of a four-wheel drive vehicle showing a second embodiment of the present invention. FIG. 5 is a schematic diagram of a conventional four-wheel drive vehicle equipped with a viscous coupling that transmits torque by bypassing the center differential. FIG. 6 is a diagram showing the characteristics of the torque transmission amount of the viscous coupling of the four-wheel drive vehicle shown in FIG. 5 with respect to the rotational speed difference. C...Viscous coupling, D...Center differential,
DESCRIPTION OF SYMBOLS 1... Engine, 2... Transmission, 3... Transmission output shaft, 4... Main drive gear, 2... Main driven gear, 6... Differential gear, 7.8... First ．．
2nd side gear, Il...front wheel side output shaft, 12...
Rear wheel side output shaft, 28... Outer plate, 29...
Inner plate, 31...first bypass gear, 32...
...Second bypass ear, 33...One-way clutch. 42... First bypass gear, 43... Third bypass gear, 44... Fourth bypass gear.

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. The present invention is characterized in that it is provided with a viscous coupling and a torque transmission characteristic changing means that reduces the amount of torque transmitted by the viscous coupling when the rotational speed difference between the front wheel output shaft and the rear wheel output shaft is small. Power transmission device for four-wheel drive vehicles.