Four-wheel drive system for vehicles

Details Four-wheel drive system for vehicles Four-wheel drive system for vehicles

2002-07-15

2004-04-27

Hurley, Kevin (Department: 3611)

Planetary gear transmission systems or components

Plural power paths to planetary gearing

Plural planetary units

C180S248000

Reexamination Certificate

active

06726591

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a four-wheel drive system for vehicles which rotationally drives all four wheels of a vehicle by transmitting a rotational driving force from a driving source (engine or the like) to the front wheels and rear wheels, and more particularly relates to a four-wheel drive system for vehicles which is constructed so that the rotational driving force from the driving source is divided and transmitted to the front and rear wheels via a center differential mechanism.
BACKGROUND OF THE INVENTION
Four-wheel drive vehicles in which both the front wheels and rear wheels are driven have been generally known in the past, and four-wheel drive vehicles in which a center differential mechanism is installed between the front wheels and rear wheels, and the vehicle is constructed so that the rotational driving force of the engine is divided and transmitted to the front and rear wheels via a center differential mechanism, are also known. In such four-wheel drive vehicles as well, axle differential mechanisms that are used to absorb the difference in rotation between the left and right wheels are installed on the front and rear wheels. Accordingly, in four-wheel drive vehicles of this type, a center differential mechanism and axle differential mechanisms for the front and rear wheels are required, so that a total of three differential mechanisms must be installed.
In cases where three differential mechanisms are thus separately installed, the power transmission system of the vehicle is increased in size, and the number of parts required is also increased, so that there is an increase in the cost of the vehicle. Accordingly, systems in which either the front or rear axle differential mechanism and the center differential mechanism are constructed as an integral unit have been proposed (for example) in Japanese Patent No. 2615086, Japanese Patent No. 3047016 and Japanese Patent No. 2621680. In the systems disclosed in these patents, the axle differential mechanism on the side of the front wheels and the center differential mechanism are constructed as an integral unit; accordingly, it is conceivable that the overall construction of the power transmission system could be reduced in size.
However, in the case of the system disclosed in Japanese Patent No. 2615086, the center differential mechanism is constructed with a pair of double planetary gears, and has a construction in which a bevel gear type axle differential mechanism is installed adjacent to this; accordingly, this system suffers from the problem of an extremely complicated and expensive construction. Furthermore, an integrated system is constructed by installing the bevel type axle differential mechanism inside a two-part casing that accommodates the center differential mechanism, and then connecting the two-part casing by means of bolts; as a result, the number of constituent parts required in the respective mechanisms is increased, and the number of places where shim adjustment is required is increased, so that the system is poor in terms of assembly characteristics. Moreover, a construction is used in which the system that is integrally constructed in this manner is supported by the transmission housing via a pair of left and right bearings so that rotation is possible; accordingly, the forces that act on the input gear members to the center differential mechanism and the output gears members to the rear wheel side must be supported by this pair of bearings, so that the bearing load is increased.
Furthermore, in the system disclosed in Japanese Patent No. 3047016, a hydraulic clutch that performs on-off operation of the center differential mechanism is installed, so that a portion of the system has a double-shift structure, thus resulting in a complicated overall structure. Moreover, the system disclosed in Japanese Patent No. 2621680 is constructed by installing two sets of planetary gear trains adjacent to each other; this system has a construction in which the rotational driving force from the engine is divided and transmitted to the left front wheel and the second planetary gear train by the first planetary gear train, and the rotational driving force that has thus been transmitted to the second planetary gear train is divided between the right front wheel and the rear wheels by the second planetary gear train. Accordingly, the gear ratios of these two sets of planetary gear trains with respect to the left and right front wheels must be set at the same value, so that the degree of freedom in design is low, and the setting of the gear ratios is difficult.
SUMMARY OF THE INVENTION
The present invention was devised in light of such problems. It is an object of the present invention to provide a simple and compact four-wheel drive system in which the center differential mechanism and either the front or rear axle differential mechanism are constructed as an integral unit.
In the present invention, in order to achieve such an object, a four-wheel drive system for vehicles is constructed with a center differential mechanism that divides and transmits a rotational driving force from a driving source (e.g., the engine E in the embodiment) to the front wheel side and rear wheel side, and an axle differential mechanism that divides and transmits the rotational driving force that has been divided by the abovementioned center differential mechanism to the left and right wheels on either the front wheel side or the rear wheel side. Furthermore, the center differential mechanism is constructed from a single pinion type first planetary gear device which has a first carrier member (e.g., the first carrier
13
in the embodiment) that is rotationally driven by the rotational driving force from the driving source, a first sun gear member (e.g., the first sun gear
11
in the embodiment) that is connected to the axle differential mechanism, and a first ring gear member (e.g., the first ring gear
14
in the embodiment) that is connected to the other of the two sides, i.e., either the front wheel side or rear wheel side, and the axle differential mechanism is constructed from a double pinion type second planetary gear device which has a second ring gear member (e.g., the second ring gear
24
in the embodiment) that is connected to the first sun gear member, a second sun gear member (e.g., the second sun gear
21
in the embodiment) that is connected to either the left or right wheel, and a second carrier member (e.g., the second carrier
23
in the embodiment) that is connected to the other of the two wheels, i.e., either the left or right wheel. These first and second planetary gear devices are installed adjacent to each other in a coaxial configuration.
In the four-wheel drive system constructed in this manner, the rotational driving force is divided and transmitted to the front wheel side and rear wheel side by the center differential mechanism, and the rotational force that has thus been divided is divided and transmitted to the left and right wheels by the [abovementioned] axle differential mechanism. Accordingly, the construction that divides and transmits the driving force is simple, and can easily be designed. Furthermore, since the single pinion type first planetary gear train that constitutes the center differential mechanism and the double pinion type second planetary gear train that constitutes the axle differential mechanism are disposed adjacent to each other in a coaxial configuration, the connecting structures of the respective elements can be simplified, and the overall construction can be made compact.
Furthermore, in another invention of the present application, a four-wheel drive system for vehicles is constructed with a center differential mechanism that divides and transmits a rotational driving force from a driving source (e.g., the engine E in the embodiment) to the front wheel side and the rear wheel side, and an axle differential mechanism that divides and transmits the rotational driving force divided by this center differential mechanism to the left and right

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