Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid controlled mechanical clutch or brake
Reexamination Certificate
2001-09-18
2003-02-18
Estremsky, Sherry (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid controlled mechanical clutch or brake
C477S155000
Reexamination Certificate
active
06520882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in a shift control system for an automatic transmission, and more particularly, to a shift control system for an automatic transmission, which has a plurality of frictional elements and can shift the transmission by engaging at least a frictional element by increasing the pressure of a hydraulic fluid.
2. Description of the Prior Art
An automatic transmission is so constructed as to determine a power transmission path (shift gear or stage) of a gear shift system by selectively actuating a plurality of frictional elements, such as clutches and brakes, based on the fluid pressure and change the shift by switching the frictional elements to be actuated. It is well known that in an automatic transmission having a plurality of frictional elements, a shift for the transmission can be made by engaging at least a frictional element by increasing the pressure of a hydraulic fluid.
As discussed after, a shift control of the present invention can be adapted for an automatic transmission which has one or more frictional elements to be engaged (the number of engaging-side frictional elements may be equal to or greater than one, and a releasing-side frictional element may not be required or the number of releasing-side frictional elements may be equal to or greater than two), and is not limited to a so-called interchange shift which has a single releasing-side element and a single engaging-side element (also called a 1-to-1 interchange shift). The background of the invention will become apparent from the following description of the exemplified case of automatic transmission. In case of such a shift, an automatic transmission makes its shift through a so-called interchange of frictional elements, in which one frictional element is released by reducing the hydraulic (fluid) pressure while the other frictional element is engaged by increasing the hydraulic fluid pressure.
Note that a frictional element to be switched to a released state from an engaged state at the time of carrying out the interchange shift is called a releasing-side frictional element and its hydraulic fluid pressure to be applied to the frictional element is called a releasing-side hydraulic (fluid) pressure, and that a frictional element to be switched to an engaged state from a released state is called an engaging-side frictional element and its hydraulic fluid pressure to be applied to the frictional element is called an engaging-side hydraulic (fluid) pressure.
In the case of the interchange shift, for example, at the time of executing the interchange shift, the interchange shift can be accomplished under releasing/engaging control in which the engaging-side frictional element is engaged by increasing the engaging-side hydraulic fluid pressure while the releasing side frictional element is being released by reducing the releasing-side hydraulic fluid pressure. As a engaging-side control (for engaging-side frictional element), it is known to independently and sequentially carry out a so-called piston stroke control and a so-called volume control, as disclosed in Japanese Patent Provisional Publication No. 7-286663(Document 1) which is referred hereinafter as a conventional technique. Accordingly, a control needed for the piston stroke and a control needed to secure a volume (of hydraulic fluid to be supplied to the frictional element) are performed independently (it is possible to independently perform learning etc.)
In consideration of the following points, therefore, a shift control for an automatic transmission still has been required to be improved.
(A) Because the progress of the shift can not be controlled on the engaging-side (frictional element) in drive-down (Driv Down) shift, the timing at which the volume is needed is determined irrespective of the volume of the hydraulic fluid to be supplied to the engaging-side frictional element itself. Depending on the situation, therefore, the volume may become necessary while an engaging-side frictional element is doing a piston stroke; however, it is difficult to deal with such a case.
This will be explained with reference to
FIG. 8
which shows the relationship between a turbine speed N
t
or the number of rotations (per unit time) of the input shaft of the transmission and the volume needed by the engaging-side frictional element. The progressing speed of an inertia phase is determined mainly by the releasing-side hydraulic pressure (the progress of the inertia phase is managed by controlling the releasing-side frictional element). In this case, however, while a volume (or a necessary volume which is required for carrying out the shift) needed by the engaging-side frictional element is also determined by the degree of the progress of the inertia phase, what timing and when the volume becomes necessary cannot be controlled by the engaging-side hydraulic pressure itself. As the timing at which the engaging-side frictional element needs the volume cannot be controlled by the engaging-side frictional element itself, there may occur the aforementioned situation where it is difficult to provide the necessary volume.
(B) Unless the end of the piston stroke is detected by some kind of means, a wasteful time is certainly produced. It is not therefore possible to cope with the shift that demands, for example, a high response (such as the shift made upon a drive-down).
FIG. 9
is a diagram which is also referred to in the later description of an embodiment of the present invention. As apparent from this diagram, linkage between the piston stroke control and the volume control is needed and leads to a wasteful time. (The control to link the two controls causes a lag.) The necessity of such a link control means that it is difficult to secure the necessary volume promptly after the piston stroke ends. The piston stroke control may be carried out using a timer. The use of a timer inevitably requires a certain extra or surplus time, thus producing a wasteful time. (The extra time causes a lag.)
(C) A supplementary explanation of the aforementioned problems will now be given. From the viewpoint of the performances or the like needed for the engaging-side hydraulic pressure for the drive-down shift, the following points are to be considered.
(1) In the latter half of the inertia phase, the volume becomes necessary.
(2) As the degree of the progress of the inertia phase cannot be controlled by the engaging-side frictional element (as discussed referring to
FIG. 8
, the degree of the progress of the inertia phase is controlled in the drive-down shift mainly by the releasing-side hydraulic pressure), the time when the volume becomes necessary is irrelevant to the status of the engaging-side frictional element.
(3) As the control is used in the drive-down shift, the unnecessary lag is ideally not allowable and the volume is to be increased to the required level as fast as possible.
If shift control depends on the control of the engaging-side frictional element as shown in
FIG. 9
even in the case of
FIG. 8
where the shift progresses irrespective of the engaging-side volume (or the volume of the hydraulic fluid to be supplied to the engaging-side frictional element), this case is similar to the situation (2) so that the volume may become necessary during piston stroke control but cannot be coped with. Further, because the employment of a timer control (using the timer) to end the piston stroke inevitably produces a wasteful time (see FIG.
9
), the timer control is not suitable for the shift that demands a response for the reason given in the paragraph (3).
It is therefore difficult to both surely finish the piston stroke within an intended time even if it is unclear when the volume becomes necessary and promptly secure the necessary volume after the completion of the piston stroke at the same time.
(D) It is desirable that even when the shift progresses irrespective of the engaging-side volume, the completion of the piston stroke and securing of the necessary volume are to be satisfied
Estremsky Sherry
Foley & Lardner
Jatco Transtechnology Ltd.
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