Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
1998-10-14
2001-04-10
Hurley, Kevin (Department: 3619)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
Reexamination Certificate
active
06213241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power transmitting system in a four-wheel drive vehicle including a hydraulic coupling device comprising a pair of vane pumps.
2. Description of the Prior Art
A power transmitting system in a four-wheel drive vehicle is already known from Japanese Patent Application Laid-open No. 3-104736. In this power transmitting system, an orifice which permits the communication between an intake port and a discharge port in each of the vane pumps, is formed by a small bore provided in a vane. Orifices which permit the communication between the intake ports and the discharge ports in the left and right vane pumps, are formed by clearances between a side plate partitioning rotors of the vane pumps and a cam ring.
In the above known system, since an orifice for communication between the intake port and the discharge port in each of the vane pumps, is formed by the small bore provided in the vane, the manufacturing steps required for providing the orifices in a large number of the vanes are troublesome, and further, it cannot be avoided that variations in size and shape of the orifices in the vanes are generated. For this reason, there is a possibility that the operating characteristics of the hydraulic coupling device are not stable. In addition, since the orifices for communication between the intake ports and the discharge ports in the left and right vane pumps are formed by clearances between the side plate and the cam ring, it is difficult to ensure the dimensional accuracy of the orifices, and there is a possibility that the operating characteristics of the hydraulic coupling device are not stable.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to ensure that the formation of an orifice can be easily performed, and the characteristics of the orifice are stable in a power transmitting system in a four-wheel drive vehicle, including a hydraulic coupling device.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a power transmitting system in a four-wheel drive vehicle, comprising an input shaft driven along with left and right main driven wheels by an engine, a left drive shaft connected to a left subsidiary driven wheel, a right drive shaft connected to a right subsidiary driven wheel, a left vane pump operated in accordance with the difference between the relative rotational speeds of the input shaft and the left drive shaft, and a right vane pump operated in accordance with the difference between relative rotational speeds of the input shaft and the right drive shaft. A left first orifice is provided between an intake port and a discharge port in the left vane pump, a right first orifice is provided between an intake port and a discharge port in the right vane pump, and second orifices are provided between the intake port in the left vane pump and the intake port in the right vane pump and between the discharge port in the left vane pump and the discharge port in the right vane pump. Each of the vane pumps includes a rotor in a space surrounded by a cam ring and a side plate, and the plurality of vanes are radially slidably carried on the rotor in sliding contact at outer ends thereof with the cam ring. The first orifice, which is provided in the side plate, for communication between the intake port and the discharge port, is concavely provided in the side plate of the vane pumps.
With the above arrangement, when there is no difference in the relative numbers of rotation between the main and subsidiary driving wheels, the left and right vane pumps are not operated. Therefore, the transmission of power from the input shaft to the left and right drive shafts is not carried out, whereby the vehicle is brought into a two-wheel drive state. When the main driven wheels slip during starting or sudden acceleration of the vehicle on a low friction coefficient road, a difference in numbers of rotation is generated between the main and subsidiary driven wheels which results in the operation of the left and right vane pumps. Thus, working oil discharged from the vane pumps, is passed through the left and right first orifices, thereby generating a load in the left and right vane pumps. As a result, the transmission of the power from the input shaft to the left and right drive shafts is carried out, whereby a portion of the driving force of the main driven wheels is distributed to the subsidiary driven wheels to achieve a four-wheel drive state of the vehicle, in which both of the main and subsidiary driven wheels are driven.
When tight turning of the vehicle is performed at a low speed, a difference in numbers of rotation is generated between the main and subsidiary driven wheels and hence, the left and right vane pumps discharge different amounts of working oil. The working oil flows via the left and right first and second orifices and for this reason, a large load is prevented from being generated in both of the vane pumps. Consequently, it is possible to alleviate a so-called tight corner braking phenomenon.
Even if the left and right main driven wheels and one of the left and right subsidiary driven wheels fall into a muddy spot and slip, the driving force is transmitted to the other left or right subsidiary driven wheel which is on a road surface of a higher friction coefficient through the vane pump on the side of the other subsidiary driven wheel. Therefore, the function of a differential limiting mechanism is exhibited, thereby enabling the wheels to escape from the muddy spot.
The intake port and the discharge port are concavely provided in the side plate, and the first orifice permitting communication between the intake port and the discharge port is provided in the side plate and therefore, the number of working or machining steps can be reduced, as compared with the case where an orifice is provided in the vane. Further, the working accuracy for the first orifice can be enhanced to stabilize the characteristics of the hydraulic coupling device. In addition, the length of an oil passage connected to the first orifice can be kept to a minimum to reduce the size of the hydraulic coupling device and moreover, the first orifice and the oil passage can be easily formed by working or machining without bringing about an increase in number of parts.
According to a second aspect and feature of the present invention, the left and right vane pumps include a common side plate, and the intake ports and the discharge ports of the vane pumps are provided in opposite sides of the side plate, so that they are opposed to each other, with the bottoms of the intake ports and the bottoms of the discharge ports being in communication with each other through the second orifice extending through the side plate.
With the above arrangement, the common side plate is used for the left and right vane pumps and therefore, the number of parts can be reduced. Moreover, the bottoms of the intake ports as well as the bottoms of the discharge ports in both the vane pumps provided in the opposite sides of the side plate, are in communication with each other through the orifice provided in the side plate. Therefore, as compared with the case where an orifice is formed by a clearance between the cam ring and the side plate, the number of working or machining steps can be reduced, and the working accuracy for the orifice can be enhanced to stabilize the characteristics of the hydraulic coupling device. Moreover, it is possible to prevent the second orifice from being occluded by the vane. In addition, the length of the oil passage connected to the second orifice can be kept to a minimum to reduce the size of the hydraulic coupling device, and moreover, the second orifice and the oil passage can be easily formed by working or machining without bringing about an increase in number of parts.
According to a third aspect and feature of the present invention, a relief valve is provided in parallel to the first orifice and is adapted to be opened in ac
Kita Kanji
Kurokawa Takuya
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Hurley Kevin
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