JPH0377089B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a power transmission device for an automobile, and more specifically, a power transmission device for an automobile that automatically drives the rear wheels of a front-wheel drive vehicle as appropriate. Regarding.

(Prior technology) Recently, front-wheel drive vehicles have been increasing in number, but since the driving wheels and steering wheels are the same, these front-wheel drive vehicles have low cornering resistance, which means they tend to slip easily, and have extremely strong understeer. This characteristic made it difficult to drive. Among these, front-wheel drive vehicles with a transversely mounted engine have high power transmission efficiency and are oriented toward fuel efficiency, but they have been developed primarily for use in passenger cars that are intended to be driven on roads with good surface conditions, such as paved roads. As a result, the aforementioned understeer became particularly pronounced when cornering on unpaved roads such as gravel roads, as well as snowy and muddy roads.

For this reason, some passenger cars have been designed to enable four-wheel drive driving as needed by manually switching the clutch; This is undesirable from the standpoint of drivability, fuel economy, etc., because four-wheel drive is always performed even when the front wheels do not slip, that is, when four-wheel drive is not required.

(Problems to be Solved by the Invention) The present invention has been made in consideration of the above circumstances, and it automatically switches to four-wheel drive mode when the front wheels slip to some extent when cornering or on a snowy road. To provide a power transmission device for an automobile that eliminates the adverse factors caused by the above-mentioned slip, and to select between front-wheel drive driving and automatic four-wheel drive driving according to the driver's preference. It is possible to switch between
When front-wheel drive driving is selected, the propeller shaft, which is a large component that forms part of the power transmission system to the rear wheels, is prevented from rotating, thereby reducing noise and reducing fuel consumption. This is what I am trying to do.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, in a front wheel drive vehicle, a subclutch is provided closer to the engine than the propeller shaft in the rear wheel drive power transmission system. In addition, the freewheel is included on the rear wheel side of the propeller shaft, and the freewheel transmits rotation from the propeller shaft side to the rear wheel, but does not transmit rotation from the rear wheel to the propeller shaft side. Furthermore, when the front and rear wheels are running straight without slipping and the subclutch is connected, the reduction ratio of the front wheel drive system is made slightly smaller than the reduction ratio of the rear wheel drive system, and the freewheel The number of revolutions on the propeller shaft side, which rotates integrally with the inner ring of the freewheel of the power transmission system, is made slightly smaller than the number of revolutions on the rear wheel shaft side, which rotates integrally with the outer ring of the freewheel.

(Function) With this configuration, when driving straight on a paved road where the front wheels do not slip, front-wheel drive driving is performed without power being transmitted to the rear wheels by the freewheel, and when cornering, When the front wheels slip more than a predetermined amount, power is transmitted to the rear wheels via the freewheel, thereby eliminating the negative factor caused by the slip.

(Example) The present invention will be described below based on drawings showing examples thereof.

In FIG. 1 showing an embodiment of the present invention, a transmission 3 is connected to an engine 1 disposed horizontally at the front of a vehicle body via a main clutch 2. A reduction gear (front differential driven gear) 5 is in mesh. The left front wheel is connected to the front wheel differential mechanism 6 provided on the final reduction gear 5 via the axle 7.
FL is connected, and the right front wheel is connected via axle 8.
FR is connected.

9 is a rear drive shaft, and a manually operated sub-clutch (tooth dog clutch) 31 is connected to the middle portion of the rear drive shaft. A driven gear 11 provided at one end of the drive shaft 9 meshes with the final reduction gear 5 for front wheels, and a drive bevel gear 12 provided at the other end of the drive shaft 9 meshes with the final reduction gear 5 for the front wheels.
It meshes with a driven gear 14 provided at the front end of 3. A freewheel 32 is connected to the rear end of the shaft 13 and the shaft 18 via a universal joint 15, a propeller shaft 16, and a universal joint 17 in this order.

A drive bevel gear 19 is provided at the rear end of the shaft 18, and the gear 19 is disposed within a rear axle housing 20 and meshes with a rear wheel final reduction gear (rear differential driven gear) 21.

A left rear wheel RL is connected via an axle 23 to a rear wheel differential mechanism 22 provided on this rear wheel final reduction gear 21, and a right rear wheel RR is connected via an axle 24. .

In this way, the power transmission elements after the driven gear 11 constitute a power transmission system for driving the rear wheels.

An example of the freewheel 32 is shown in FIGS. 2 and 3.
This is shown in the figure, which includes an inner ring 25 whose outer peripheral surface is a regular polygon, an outer ring 26, and both wheels 25, 26.
It has a plurality of rollers 27 arranged therebetween and a cage 28 holding the rollers 27. Such a freewheel 32 is coupled such that its inner ring 25 rotates integrally with the propeller shaft 16 side, and its outer ring 26 rotates integrally with the shaft 18 side. The cage 28 holds the rollers 27 at appropriate intervals and is slidably fitted into the inner ring 25 with a weak resistance provided by an elastic body or the like. When the rotational speed of the inner ring 25 is higher than the rotational speed of the outer ring 26, the roller 27 wedges between the two wheels 25 and 26 as shown in FIG. On the other hand, if the rotation speed of the inner ring 25 is smaller than the rotation speed of the outer ring 26, the roller 27 becomes free between the two wheels 25 and 26 as shown in FIG. The rotation of 25 is not transmitted to the outer ring 26. Of course, no rotation is transmitted from the outer ring 26 to the inner ring 25. In addition, the structure of such freewheel 32 itself,
Since the operation is well known, further detailed explanation will be omitted.

The power transmission system for the rear wheels mentioned above consists of front and rear wheels FL,
When the FR, RL, and RR are traveling straight without slipping, a small amount of torque is applied between the freewheel 32 and the rear wheels RL and RR so that the driving force (rotational force) is not transmitted to the rear wheels RL and RR via the freewheel 32. It is designed to create a difference in rotational speed. That is, the rotation speed on the engine 1 side (propeller shaft 16) of the freewheel 32 is set to be slightly smaller than the rotation speed on the rear wheels RL, RR side (shaft 18). This can be done, for example, by making the diameters of the front wheels FL, FR and the rear wheels RL, RR different, but preferably,
It is preferable to set the gear ratio before and after the freewheel 32. For this purpose, the reduction ratio X ₁ for the front wheels FL, FR is determined as X ₁ = number of teeth of gear 5/number of teeth of gear 4, while the reduction ratio X ₂ for the rear wheels RL, RR is determined as X ₂ = It is calculated as: Number of teeth of gear 11 / Number of teeth of gear 4 × Number of teeth of gear 14 / Number of teeth of gear 12 × Number of teeth of gear ₂₁ / Number of teeth of gear ₁₉ . Just select the number of teeth for each gear. The rotation ratio before and after the freewheel 32 is 1/1.05 to 1/1.2, preferably 1/1.05 to 1/1.2.
The ratio should be 1.1 to 1/1.2.

Now, to explain how to determine the rotation ratio as mentioned above, the four wheels FL, FR, RL,
Assuming that the tire dynamic radius of the RR is the same and that the front and rear treads are the same, each symbol is defined as follows (see Figure 4).

t: Torezdo 1: Wheelbase NF: Rotational speed of the front wheel drive shaft NR: Rotational speed of the rear wheel drive shaft R: Rear inner wheel turning radius NiF: Front inner wheel rotational speed NiR: Rear inner wheel rotational speed ifF: Front final gear ratio ifR: Rear final gear ratio Under these conditions, NF=√ ² +1 ² +√(+) ² +1 ² /2√R ² +1 ²・ifF・NiF NR=(1+t/2R)ifR・NiR NiF/NiR=√ ² + 1 ² /R. And if η is the rotation ratio between the front and rear wheels, then η=NF/NR=√ ² +1 ² +√(+) ² +1 ² /2(R
+t/2) ・ifF/ifR.

According to the drive system described above, the transition to four-wheel drive occurs when η = 1, so the limit turning radius when switching to four-wheel drive is
It is sufficient to set R ₀ (see FIG. 4) and determine the ratio of ifF/ifR so that η=1 at this time. this
R ₀ exists from infinity (straight running) to the minimum turning radius, so within this range, R ₀ can be determined by experiment, taking into account errors in tire manufacturing, air pressure, shared loads, vehicle tread differences, etc. All you have to do is set .
At this time, if R ₀ is too large, the system will unnecessarily switch to four-wheel drive when turning at high speeds and with a large radius on paved roads, which is undesirable. If R ₀ is too small, the ratio of shifting to four-wheel drive will be small. Therefore, R ₀ should be set by taking into consideration the purpose of use of the vehicle (for example, whether the vehicle will be primarily driven on paved roads or unpaved roads). Then, by integrating the above, ifF/ifR is 1/1.05 to 1/1.2, preferably 1/1.
It may be set to 1.1 to 1/1.2. Note that 0 in FIG. 4 is the turning center.

Next, the operation of the above configuration will be explained. When the vehicle travels straight on a paved road, the front wheels FL and FR do not slip, so the rear wheel power transmission system connects the freewheel 32 to the propeller shaft 16.
The rotation speed of the shaft 18 (the inner ring 25 of the freewheel 32) is smaller than the rotation speed of the shaft 18 (the outer ring 26 of the freewheel 32). Therefore, the output of the engine 1 (rotation of the propeller shaft 16) is not transmitted to the rear wheels beyond the freewheel 32, but is transmitted to the front wheels.
Only FL and FR are used to drive the vehicle.

Now, when the vehicle makes a sharp turn and the front wheels FL and FR slip more than a predetermined amount, the rotation speed of the propeller shaft 16 increases in response to this slip, and the rotation speed of the propeller shaft 16 increases.
The number of revolutions will be higher than that of 8. As a result, the output of the engine 1 is transferred to the rear wheels via the freewheel 32.
The information is also transmitted to RL and RR, automatically switching to four-wheel drive. During this turn, when driving only with the front wheels FL and FR, the understeer becomes stronger due to slipping, but by shifting to the four-wheel drive driving described above, that is, due to the oversteer tendency due to the drive of the rear wheels RL and RR, the understeer becomes weaker. It will be done.

Furthermore, when driving on snow-covered roads or other slip-prone surfaces, the front wheels FL and FR will slip even when driving straight, so if this slip exceeds a certain level, the vehicle will automatically shift to four-wheel drive for the reasons mentioned above. I will do it.

Of course, in any driving condition, the front wheels FL,
If the FR does not slip more than the specified level, the front wheel FL,
Automatically shifts to FR-only driving. Also,
By disengaging the sub-clutch 31, the driver can always drive with only the front wheels FL or FR, but if necessary, the driver can engage the sub-clutch 31 to achieve four-wheel drive, which automatically switches between front-wheel drive and driving. It is possible to travel by running. When the subclutch 31 is disengaged and the vehicle is running in front wheel drive, the rotation of the propeller shaft 16 is stopped, which is advantageous in terms of fuel efficiency and noise prevention.

As is clear from the above description, the present invention is suitable for people who mainly drive around town or on expressways (disengage the sub-clutch 31), and occasionally drive on mountain roads or snowy roads (connect the sub-clutch 31). It is also extremely desirable for those with advanced driving skills who want to enjoy sporty driving while actively slipping the front wheels FL and FR without driving the rear wheels RL and RR. Become.
Note that if a normal synchronizing mechanism is added to the sub-clutch 31, clutch switching can be performed smoothly while the vehicle is running.

FIG. 5 shows a modification of the present invention, in which a pair of freewheels 41 and 42 are used for the same purpose as the freewheel 32, and the pair of freewheels 41 and 42 constitute a rear wheel differential mechanism. It has become a thing of the past. That is, a freewheel housing 43 is rotatably held within the rear axle housing 20, and the rear wheel final reduction gear 21 is also attached to the housing 43 so as to rotate integrally therewith. A left rear wheel axle 23 is connected to this freewheel housing 43 via a first freewheel 41, and a second
Right rear wheel axle 2 via freewheel 42
4 is connected. An example of the first and second freewheels 41, 42 is shown in FIG.
It has a roller 46 interposed therebetween and a cage 47 holding the roller. The function of such freewheels 41 and 42 is similar to that of the freewheel 32, but rotation can be transmitted from the outer ring 45 to the inner ring 44, but the rotation can be transmitted from the inner ring 44 to the outer ring 45.
The only difference is that rotation cannot be transmitted to the freewheel 32, that is, the direction of rotation transmission is opposite to that of the freewheel 32. And inner circle 4
4 is fitted with a subline so as to rotate integrally with the axle 23 or 24, and the outer ring 45 is attached to the freewheel housing 43 so as to rotate integrally therewith.

In such a configuration, the freewheel 4
1 and 42 is the same as the case of FIG. 1 described above. In terms of turning, the first and second freewheels 4
1 and 42, an appropriate rotational speed difference is given between the rear wheels RL and RR. That is,
When turning to the right in FIG. 5, the left rear wheel RL needs to rotate at a higher rotation speed than the right rear wheel RR, but this difference in rotation speed is due to the rotation speed of the first freewheel 41 for the left rear wheel RL. This is achieved by allowing the inner ring 44 to rotate more freely and faster than the outer ring 45. Of course, in the case of a left turn, the differential action is provided by the second freewheel 42 in the same way as in the case of a right turn.

Furthermore, even if only one of the rear wheels RL and RR slips in mud, the driving force is always transmitted to the other rear wheel, providing a so-called non-slip differential function.

The differential operation of the two freewheels 41 and 42 is also clear from, for example, Japanese Patent Publication No. 15245/1982, so a more detailed explanation will be omitted.

(Effects of the Invention) As is clear from the above, according to the present invention, the vehicle automatically shifts to four-wheel drive only when the front wheels slip more than a predetermined amount, thereby eliminating the negative factor caused by the front wheels slipping. While it can be automatically removed, four-wheel drive is not required unnecessarily, which is preferable from the standpoint of fuel efficiency and the like.

In addition, the driver can select between two-wheel drive driving with only the front wheels and four-wheel drive driving which is automatically switched, and when driving with only the front wheels selected, the rear wheel drive Since the propeller shaft remains stationary, this is preferable from the viewpoint of fuel efficiency and noise prevention.

[Brief explanation of drawings]

FIG. 1 is a simplified overall system diagram showing one embodiment of the present invention, and FIGS. 2 and 3 show examples of the freewheel used in FIG. 1, showing different operating modes. Fig. 4 is a diagram showing the turning radius of each wheel when the vehicle turns, Fig. 5 is a simplified main part system diagram showing a modification of the present invention, and Fig. 6 is an example of the freewheel used in Fig. 5. FIG. 1... Engine, 32, 41, 42... Freewheel, 16... Propeller shaft, 31...
Sub clutch, FL, FR...Front wheel, RL, RR...
Rear wheel.

Claims (1)

[Scope of Claims] 1. In a front-wheel drive vehicle, a rear wheel power transmission system for driving the rear wheels is configured to include a propeller shaft, and a subclutch is provided in the power transmission system at a position closer to the engine than the propeller shaft. A freewheel is connected to the power transmission system on the rear wheel side of the propeller shaft, so that rotation is transmitted from the propeller shaft side to the rear wheel side, but rotation is transmitted from the rear wheel side to the propeller shaft side. In addition, the reduction ratio of the front wheel drive system is made slightly smaller than the reduction ratio of the rear wheel drive system when the subclutch is engaged and the front and rear wheels are traveling straight without slipping. With the freewheel as a boundary, the rotational speed of the propeller shaft side, which rotates integrally with the inner ring of the freewheel, is slightly smaller than the rotational speed of the rear wheel shaft side, which rotates integrally with the outer ring of the freewheel. A power transmission device for an automobile.