Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid controlled mechanical clutch or brake
Reexamination Certificate
2000-10-03
2003-01-21
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid controlled mechanical clutch or brake
C475S122000, C475S136000, C477S046000
Reexamination Certificate
active
06508735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic control system for a transmission in which a driving rotary member, a driven rotary member and a transmission member are controlled in their contact pressures by a higher oil pressure and in which frictional engagement elements are controlled in their applications/releases by a lower oil pressure.
2. Related Art
Generally, a discontinuous transmission capable of controlling gear ratios stepwise (or discontinuously) and automatically is provided with a gear speed change mechanism having a plurality of planetary gear mechanisms, a plurality of frictional engagement elements for changing the torque transmission lines of the gear speed change mechanism and a hydraulic control system for controlling the applications/releases of those frictional engagement elements with oil pressure. In this discontinuous transmission, the frictional engagement elements are controlled in their applications/releases to change the gear ratios by controlling the oil pressures acting on the frictional engagement elements on the basis of predetermined conditions. Since output pressure of an oil pressure source of the hydraulic control system is set higher than a line pressure or an initial pressure of the entire hydraulic circuit, there arises a problem of the so-called “shift shock” when the output pressure of the oil pressure source is used as it is as the pressure for applying the frictional engagement elements. In Japanese Patent Laid-Open No.
8-285067
(JP-A-8-285067), therefore, there is disclosed an example of a hydraulic control system for an automatic transmission, in which the output pressure of the oil pressure source is not used as the pressure for applying the frictional engagement elements before it is lowered to a predetermined level.
The automatic transmission, as disclosed in the Laid-Open, is arranged on the output side of an engine and is provided with a torque converter, a gear speed change mechanism having a plurality of planetary gear mechanisms, a plurality of frictional engagement elements and a hydraulic control system. This hydraulic control system is provided with: an oil pump as the oil pressure source; a primary regulator valve for regulating the output pressure of the oil pump to a line pressure according to the vehicle speed and the throttle opening; a manual valve for receiving the line pressure to output an oil pressure in a manner to correspond to each shift position; and a modulator valve for lowering the oil pressure, as outputted from the manual valve, in a shift position requiring an engine braking force, to a pressure to be fed to the hydraulic servos of the frictional engagement elements. When the shift position requiring the engine braking force is selected, moreover, the shift shock at the engine braking can be suppressed by feeding the frictional engagement elements with the oil pressure which is made lower than the oil pressure to be fed to the frictional engagement element to be applied when a predetermined gear stage is set.
Here, the transmission capable of controlling the gear ratios automatically is exemplified not only by the discontinuous transmission disclosed in the Laid-Open but also by a continuously variable transmission capable of controlling the gear ratios without any stage (i.e., continuously). As an example of this continuously variable transmission, there can be enumerated the belt-type continuously variable transmission which is provided with a driving pulley (primary pulley), a driven pulley (secondary pulley) and a belt. In the outer circumferences of the driving pulley and the driven pulley, there are individually formed V-shaped grooves, in which the belt is wound. On the other hand, a hydraulic control system is provided for controlling the widths of the grooves of the driving pulley and the driven pulley.
By controlling the groove width of the driving pulley, moreover, the winding radius of the belt (i.e., the effective radius of the pulley) is changed to control the gear ratio. By adjusting the groove width of the driven pulley, i.e., the clamping force for the belt, on the other hand, the tension of the belt is controlled. Thus, the contact pressures between the driving pulley and the driven pulley, and the belt can be controlled to retain the torque to be inputted to the continuously variable transmission and the torque transmission capacity according to the gear ratio.
In the belt type continuously variable transmission, on the other hand, the driving pulley and the driven pulley are restricted in their external diameters by the relation between the positions of the driving pulley and the driven pulley, and those of the parts to be arranged around the driving pulley and the driven pulley. These positional relations limit the enlargement in the control range of the gear ratio, as controlled only by the belt type continuously variable transmission. Thus, there has been proposed a layout in which the control width of the gear ratio is enlarged by arranging the belt type continuously variable transmission and a transmission having the planetary gear mechanism and the frictional engagement elements, as disclosed in the Laid-Open, in tandem in the torque transmission line leading from the engine to the wheels. In the vehicle adopting this layout, the oil pressure sources for outputting initial pressures of the oil pressure for controlling the groove width of the driven pulley and the oil pressure for controlling the applications/releases of the frictional engagement elements are desired to be common for suppressing the number of parts of the hydraulic control system and for reducing the size/weight of the hydraulic control system.
Here will be compared the belt type continuously variable transmission and the transmission having the gear speed change mechanism. The oil pressure for establishing a clamping pressure for the belt and the oil pressure necessary for applying the frictional engagement elements are made different by the difference in the power transmission manners. In the belt type continuously variable transmission, more specifically, the torque transmission capacity is retained by the frictional contacts between the driving pulley and the driven pulley of relatively smaller diameters and a portion of the belt. In the transmission having the gear speed change mechanism, on the contrary, the torque transmission capacity is retained by the frictional contact of the entirety of the annular frictional faces of the frictional engagement elements having relatively larger external diameters. As a result, the oil pressure necessary for controlling the groove width of the driven pulley in the belt type continuously variable transmission needs to be higher than the oil pressure necessary for applying the frictional engagement elements in the automatic transmission having the gear speed change mechanism.
When an output pressure of the oil pressure source is controlled to a high level and a high oil pressure (i.e., a high output pressure) is fed to the frictional engagement elements, however, the components of the hydraulic circuit leading to the frictional engagement elements are required to have the strength for resisting the high oil pressure, thus causing a problem that the hydraulic control system is enlarged in its size, increased in its weight and raised in its manufacture cost. Additionally, the output pressure of the oil pressure source acts as it is on the frictional engagement elements so that the frictional engagement elements have to be protected against the high oil pressure. As a result, the frictional engagement elements may also be enlarged in their size, increased in their weight and raised in their manufacture cost and may be damaged.
SUMMARY OF THE INVENTION
An object of the invention is to provide a hydraulic control system for a transmission, which can be reduced in size and weight and lowered in cost while preventing frictional engagement elements in advance from being damaged.
Another object of the invention is to red
Kojima Shin-ichi
Murakami Akira
Ohtake Masanori
Ho Ha
Marmor Charles A
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