Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2003-03-28
2004-08-24
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S487500, C701S051000
Reexamination Certificate
active
06779540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to corrective control system and method for a liquid pressure control apparatus in, for example, a vehicular automatic transmission which accurately control an output liquid pressure in accordance with a value of an electrical signal and, more particularly, relates to the corrective control system and method which control correctively the output liquid pressure of a control valve unit equipped within the vehicular automatic transmission.
2. Description of the Related Art
In the control valve unit of the vehicular automatic transmission, the electrical signal is used to drive a solenoid so as to produce a signal pressure in accordance with the electrical signal. This signal pressure is used to make a gear shift by controlling a clutch pressure of a frictional element which is the output liquid pressure and a line pressure which is an original pressure of the clutch pressure of the frictional element. At this time, due to a variation in a circuit resistance and a difference in performance between the individual products of frictional elements and solenoids, a relationship between the electrical signal for driving the solenoid and the output liquid pressure cannot accurately be obtained. Both of a shift shock and a response delay in the gear shift easily occur. Thus, desired action and advantages cannot accurately be obtained.
A Japanese Patent Application First Publication No. 2001-116130 published on Apr. 27, 2001 exemplifies a previously proposed corrective control system for a liquid pressure control apparatus in which an actual relationship between the electrical signal for the drive of the solenoid and the output liquid pressure due to the variation in the circuit resistance and difference in performance between individual products of frictional elements and solenoids is compared with each of a plurality of prepared maps having various characteristics. By selecting one of the maps which is least deviation from the actual relationship, an accuracy in the relationship between the solenoid drive electrical signal and the output liquid pressure is improved and an improvement in a controllability can be achieved. Specifically, the actual output pressures with respect to the electrical signals at a plurality of points preset are measured. Thereafter, with a lateral axis as output values on the map and with a longitudinal axis as an actual output liquid pressure, the actual output liquid pressures are plotted. The plotted values are approximated to a first-order function through a least square method. This approximated first-order function has a gradient (gain) and a constant term (offset). These gradient value and constant term are stored. Then, during an actual control procedure, a target output liquid pressure is substituted into the longitudinal axis to calculate an instantaneous map output (liquid) pressure from the stored gain and offset values.
FIG. 7
shows a structure for creating the output liquid pressure which is the clutching pressure of a certain frictional element (or brake) of the automatic transmission from the signal pressure that a solenoid outputs. The previously proposed liquid pressure control apparatus includes: a solenoid valve
40
which creates a spool pilot pressure P
S-PLT
from a pilot pressure P
PLT
and a spool valve
50
outputting a liquid supply pressure P for the frictional element or the brake from line pressure PL which is the spool supply pressure according to the spool pilot pressure P
S-PLT
. In solenoid valve
40
, a movement quantity of a plunger
42
is increased in accordance with a supply current value. A spherical ball
43
is moved which, for example, interrupts pilot pressure P
PLT
and spool pilot pressure P
S-PLT
so that a flow passage
44
is opened. Then, pilot pressure P
PLT
is communicated with spool pilot pressure P
S-PLT
so that a spool pilot pressure P
S-PLT
is increased. On the other hand, in spool valve
50
, a spool supply pressure (line pressure valve) is communicated with a frictional element. This spool
51
is moved together with a pressure increase in spool pilot pressure P
S-PLT
opposed against spool spring
52
and the flow passage is closed so that line pressure PL which is the spool supply pressure reduces the frictional element supplying pressure. Hence, when a current value caused to flow through solenoid valve
40
is large, spool pilot pressure P
S-PLT
and frictional element supplying pressure P is decreased linearly.
In the case of the solenoid valve described above, an output (liquid) pressure characteristic is exhibited which is different from spool pilot pressure P
S-PLT
which is an output (liquid) pressure of the solenoid due to the characteristic of a spool spring
52
.
FIG. 6
shows characteristic graphs representing a static characteristic of the relationship between the drive current to the solenoid and output liquid pressure. As shown in
FIG. 6
, a, so-called, hysterisis characteristic is exhibited between the drive current and the output liquid pressure. Hence, the prepared map is used which is an average output liquid pressure value at each of the same current values from a static characteristic as denoted by a thin dot line shown in FIG.
6
.
SUMMARY OF THE INVENTION
However, at an average output pressure map for each of the respective same current values, a deviation from an actual output liquid pressure characteristic occurs. Consequently, a worsening of a controllability will be introduced.
Especially, in the hysterisis characteristic shown in
FIG. 6
, an output pressure zero point in a first hysterisis loop along which the output pressure value is decreased as the current value is increased, is separated from that in a second hysterisis loop along which the output pressure is increased as the current value is decreased. In this case of characteristic, if the output liquid pressure average value is used, a large influence of the second hysterisis is received in a low hydraulic pressure region. For example, if the current value is once raised and, in the midway through the increase in the current value, the current value is decreased, the output liquid pressure is lowered following the first hysterisis loop of the hysterisis which is a static characteristic of actual output pressure and, thereafter, when the current is lowered, the actual output pressure does not follow the second hysterisis loop but takes a value shifted toward a lower pressure side. Such a phenomenon as described above becomes remarkable when the output liquid pressure is, at one stroke, reduced in accordance with the increase in current value and the output liquid pressure is, at one stroke, increased in accordance with the increase in the output pressure
It is, hence, an object of the present invention to provide corrective control system and method for a liquid pressure control apparatus which are capable of improving the controllability even if a large hysterisis occurs between the electrical signal and output pressure due to a variation in the liquid pressure circuit and solenoid.
The above-described object can be achieved by providing a corrective control system for a liquid pressure control apparatus of a control valve unit, comprising: a liquid pressure controlling section that controls an output liquid pressure of the control valve unit on the basis of a current value which is an electrical signal generated in accordance with an output pressure demand value P* determined according to a calculation process executed within a control unit; an output liquid pressure actually measuring section that outputs respectively separated current values to a solenoid drive circuit of the control valve unit and actually measures the output liquid pressure values for the outputted respective current values; an output pressure theoretical value calculating section that calculates an output liquid pressure theoretical value for each of the current values outputted by the actually measuring section by referring to preset fundamental
Eguchi Tatsuaki
Ishii Shigeru
Nobu Hisao
Suguichi Masashi
Foley & Lardner LLP
Jatco LTD
Krishnamurthy Ramesh
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