Drive unit for vehicles

#The present invention relates to a drive unit for vehicles, and more particularly, to a structure for lubricating a differential of a transaxle formed by integrating a transmission and a differential.

#In a vehicle, a differential unit is employed to allow right and left driving wheels to rotate at different speeds. A structure of the differential unit used generally will be explained briefly hereafter. A pair of side gears such as bevel gears is disposed in a differential case while being opposed to each other, and a pinion gear is interposed between those side gears. The pinion gear is rotatably mounted on a pinion pin arranged perpendicular to a rotational center axis of the side gears while connected to the differential case. Additionally, a ring gear is arranged around the differential case while meshing with an output gear of a transmission, and power of the transmission is transmitted to the differential unit through the ring gear. The right and left side gears are individually connected to a drive shaft, and power is transmitted to the driving wheels therethrough.

#As described above, said differential unit is mainly composed of the gears to differentiate the rotational speeds of the right and left wheels while increasing a reduction ratio, and therefore subjected to a large torque during running. For this reason, sufficient lubrication is required for the differential unit. As described, the transaxle is formed by integrating the differential unit and the transmission having an oil pump. Therefore, the differential unit of the transaxle may be lubricated by oil discharged from the oil pump during propelling the vehicle by a prime mover such as an engine. For example, Japanese Patent Laid-Open No. 2007-113636 describes a differential device for vehicle in which lubricating oil pressurized by an oil pump is injected to an oil hole of a differential case. An oil passage for letting through the lubricating oil is surrounded by a separate plate and ribs formed on an inner side wall of the differential housing. The differential plate is arranged to divide into an agitating section where the lubricating oil agitated by a ring gear of the differential is temporarily reserved, and a reservoir section where the lubricating oil lifted by the ring gear is reserved. Owing to the separate plate thus formed, an amount of the lubrication oil will not be increased excessively, and an increment of a agitation resistance will be suppressed.

#FIG. 1 a cross-sectional view showing a cross-section of a configuration of the differential plate of the drive unit according to the preferred example along I-I line shown in FIG. 3.

#FIG. 2 is a fractured side view schematically showing the drive unit according to the preferred example.

#FIG. 3 is a side view showing a side of the housing seen from the casing.

#Hereinafter, a preferred example of the present invention will be explained with reference to the accompanying drawings. The drive unit of the present invention is adapted to transmit power of the a prime mover of a vehicle such as an engine to driving wheels while distributing torque to the right and left wheels and allowing those wheels to rotate at different speeds. In addition, the drive unit also have a speed change function. Specifically, the drive unit of the present invention is an transaxle formed by combining a transmission adapted to change a transmission torque or a rotational speed with a differential unit adapted to distribute torque transmitted from the transmission to the driving wheels while allowing the driving wheels to rotate at different speeds. Referring now to FIG. 2, there is schematically shown one example of a transaxle 1. The transaxle 1 shown therein is comprised of a transaxle housing (to be simply called as the “housing” hereinafter) 2 that is connected to a prime mover Eng such as an engine, a transaxle casing (to be simply called as the “casing” hereinafter) 3 that is jointed to the housing 2, and a transaxle rear cover (to be simply called as the “rear cover” hereinafter) 4 that closes a rear end of the casing 3. Thus, the housing 2, the casing 3 and the rear cover 4 forms a sealed housing, and the below-mentioned devices are held therein.

#According to the preferred example, a torque converter 5 is held in the casing 2, and a transmission 6 is held in the casing 3. The torque converter 5 is a conventional fluid coupling in which a turbine runner as an output member is rotated by a spiral oil flow created by a pump impeller as an input member connected to an oil pump 7. The oil pump 7 is activated by the prime mover Eng to establish hydraulic pressure, whereas deactivated to be disabled to establish hydraulic pressure when the vehicle is towed while stopping the prime mover Eng. The transmission 6 is adapted to change a ratio of an output speed to an input speed (i.e., a speed ratio) arbitrarily. For example, a conventional transmission such as a belt-driven continuously variable transmission, a geared transmission comprised of a plurality of planetary gear sets, a geared transmission comprised of a plurality of gear trains, a toroidal continuously variable transmission and so on may be used as the transmission 6.

#A differential unit 8 is also arranged in the transaxle 1 together with the torque converter 5, the transmission 6, and the oil pump 7. The differential unit 8 is comprised of a differential gear unit 9 adapted to distribute the torque of the transmission 6 to the right and left driving wheels (e.g., to the right and left front wheels). The differential gear unit 9 includes a hollow differential casing 10, and a pair of boss portions 11 is formed coaxially on the differential casing 10 to protrude away from each other. One of the boss portions 11 is supported by the housing 2 through the bearing, and the other boss portion 11 is supported by the casing 3 through the other bearing. As described, the housing 2 and the casing 3 are joined together to form a chamber 12, and the differential gear unit 9 is held therein.