Adaptive control for motor vehicle

In order to achieve adaptive correction of any undesired variance of servo activating hydraulic fluid pressure due to the change in ambient condition, a ratio (K.sub.Q) of actual mass airflow rate of engine intake air to standard airflow rate is determined. This ratio is used in deriving a judgment as to the ambient condition or modifying standard servo activating hydraulic fluid pressure.

BACKGROUND OF THE INVENTION 
The present invention relates to an adaptive control for a motor vehicle. 
Engine output is affected by ambient conditions. At high altitude, since 
the air density drops, the engine output also drops. During a ratio shift, 
servo activating hydraulic fluid pressure supplied to engage on-coming 
friction device, such as a clutch or a brake, is determined in response to 
throttle opening degree. Thus, if the engine output drops due to an 
increase in altitude, a shift quality also drops. For adaptive correction 
of such an insufficiency, it is necessary to detect a change in ambient 
condition of the motor vehicle. One measure is to install a barometer to 
detect a change in altitude. This measure is costly, however, and thus, 
not acceptable. 
Accordingly, an object of the present invention is to provide an economical 
measure to detect a change in ambient condition of a motor vehicle without 
installation of an additional equipment. 
A specific object of the present invention is to provide an adaptive 
control for a motor vehicle wherein the setting of an automatic 
transmission is automatically adjusted to a new ambient condition. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a system for an 
adaptive control of a motor vehicle including an engine, wherein an 
airflow ratio between an airflow rate of intake air admitted to the engine 
and a standard airflow rate predetermined for a power demand on the engine 
is used to determine a change in ambient altitude in which the engine is 
operating. in ambient condition. 
According to one aspect of the present invention, there is provided a 
method of checking an ambient condition in which a motor vehicle is 
operating, the motor vehicle including an engine with a throttle valve 
which opens in degrees, the method comprising the steps of: 
detecting a throttle opening degree of the throttle valve; 
detecting an airflow rate of intake air admitted to the engine; 
comparing said throttle opening degree detected with said airflow rate 
detected; and 
deriving a judgement as to the ambient condition from a result of said 
comparing step. 
According to a specifict aspect of the present invention, there is provided 
a method of checking an ambient condition in which a motor vehicle is 
operating, the motor vehicle including an engine with a throttle valve 
which opens in degrees, the method comprising the steps of: 
detecting the throttle opening degree; 
detecting engine speed; 
setting data containing standard airflow rate values versus throttle 
opening degree values and engine speed values; 
determining a standard airflow rate versus said throttle opening degree and 
engine speed from said data set; 
detecting an airflow rate of intake air admitted to the engine; 
calculating an airflow ratio of said airflow rate detected to said standard 
airflow rate determined; 
averaging said airflow ratio calculated; and 
deriving a judgement as to the ambient condition from said airflow ratio 
averaged. 
According to another aspect of the present invention, there is provided a 
method of adaptive correction of servo activating hydraulic fluid pressure 
of an automatic transmission of a motor vehicle including an engine with a 
throttle valve which opens in degrees, the method comprising the steps of: 
detecting the throttle opening degree; 
detecting the engine speed; 
setting data containing standard airflow rate values versus throttle 
opening degree values and engine speed values; 
determining a standard airflow rate versus said throttle opening degree 
detected and said engine speed detected from said data set; 
detecting an airflow rate of intake air admitted to the engine; 
determining an airflow ratio of said airflow rate detected to said standard 
airflow rate determined; 
determining a standard servo activating hydraulic fluid pressure in 
response to said throttle opening degree detected; and 
modifying said standard servo activating hydraulic fluid pressure in 
response to said airflow ratio determined.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the accompanying drawings, an embodiment according to the 
present invention is described in FIGS. 1 to 12. 
FIG. 1 shows a motor vehicle power train including an automatic 
transmission 12 and an engine 14. 
The automatic transmission 12 includes a torque converter, a gear train, 
and various friction or torque establishing devices, such as clutches and 
brakes. The torque converter includes a pump impeller drivingly connected 
to output shaft of the engine, a turbine runner, and a stator. The pump 
impeller is in driving connection with a pump. The turbine runner is 
connected to an input shaft of the gear train. The gear train has an 
output shaft 34. 
The automatic transmission 12 has a control valve assembly 13 provided with 
a line pressure solenoid 37, a first shift solenoid 38, and a second shift 
solenoid 39. These solenoids 37, 38, and 39 are controlled by a 
microcomputer based control unit 10 including a central processor unit 
(CPU), a read only memory (ROM), a random access memeory (RAM) and an 
input/output interface circuit (I/O). 
An engine speed sensor 15 detects engine speed (engine rpm) of the engine 
and generates pulses indicative of engine speed detected. Mounted within 
an intake passage 16 is a throttle valve 18 which opens in degrees. A 
throttle sensor 20 detects the opening degree of the throttle valve 
(throttle position) 18 and generates an analog signal indicative of the 
throttle opening degree detected. The analog signal of the throttle sensor 
20 is supplied to an analog-to-digital converter (A/D) 21. Upstream of the 
throttle valve 18 is arranged a mass air flow meter 24 which detects mass 
air flow rate of intake air inducted by the engine 14, and generates an 
analog signal indicative of the mass airflow rate. This analog signal is 
supplied to an analog-to-digital converter (A/D) 25. The mass airflow 
meter 24 can be of the well-known hot wire film type. An engine coolant 
temperature element 28 detects the temperature of engine coolant and 
generates an analog signal indicative of the engine coolant temperature 
detected. This analog signal is supplied to an analog-to-digital converter 
(A/D) 29. 
An output shaft speed sensor 36 detects revolution speed of the output 
shaft 34 and generates pulses indicative of the output shaft speed 
detected. The output shaft speed sensor 36 serves as a transmission mount 
vehicle speed sensor. Another vehicle speed sensor is mounted in a vehicle 
speed meter within a passenger compartment of the vehicle. An automatic 
transmission fluid (ATF) temperature sensor 40 detects the temperature of 
automatic transmission fluid and generates an analog signal indicative of 
the ATF temperature detected. This analog signal is supplied to an 
analog-to-digital (A/D) converter 41. 
In FIG. 1, A/D converters 21, 25, 29 and 41 are illustrated as being 
separated from the control unit 10 for ease of explanation in the 
following description. Actually, the functions of these analog-to-digital 
converters are incorporated in the I/O interface circuit of the control 
unit 10. 
Except the mass airflow meter 24, the motor vehicle power train illustrated 
in FIG. 1 is substantially the same as described in a publication "NISSAN 
FULL-RANGE AUTOMATIC TRANSMISSION RE4R03A TYPE, SERVICE MANUAL, (A261c10)" 
issued on March 1988 by NISSAN MOTOR COMPANY LINITED. For a detailed 
description, reference should be made to this publication. 
Referring to FIGS. 2, 7, 8, and 9, FIG. 9 shows a routine for determining 
an appropriate gear position in accordance with one of a plurality of 
shift point mapping tables selected in response to a judgement regarding 
altitude at which the motor vehicle is operating. FIG. 7 shows a routine 
for deriving the judgement regarding altitude after comparing an airflow 
ratio K.sub.Q with predetermined values Q.sub.1 and Q.sub.2. FIG. 2 shows 
a routine for determining the airflow ratio K.sub.Q. Lastly, FIG. 8 shows 
a routine for determining whether the execution of FIG. 7 routine is 
justified or not. 
Referring to FIG. 3, execution of this program is repeated at regular 
intervals of 5 msec. In FIG. 3, at step 60, analog output signal of 
throttle sensor 20 is converted to digital signal by A/D converter 21 to 
store the result at TVO in RAM. 
Referring to FIG. 5, execution of this program is repeated at regular 
intervals of 5 msec. In FIG. 5, at step 86, analog output signal of mass 
airflow meter 24 is converted to digital signal by A/D converter 25 to 
store the result at Qa.sub.-- AD in the RAM. 
Actual mass airflow rate detected by the mass airflow meter 24 has a 
predetermined relationship with the output signal thereof. This 
predetermined relationship is illustrated by the characteristic curve 
shown in FIG. 6. In FIG. 6, the vertical axis indicates actual mass 
airflow rate, while the horizontal axis indicates digital signal produced 
after analog to digital conversion of the output signal of mass airflow 
meter 24. 
Referring to FIG. 2, execution of this program is repeated at regular 
intervals. In step 62, the digital data TVO is fetched. In step 64, a 
table look-up operation of FIG. 4 is performed using the data TVO 
(throttle opening degree) to determine standard mass airflow rate. This 
result is stored at Qa' as the mass airflow rate. In step 70, the digital 
data Qa.sub.-- AD is fetched. In step 72, a failure check of the data 
Qa.sub.-- AD is conducted. In step 74, it is determined whether failure 
exists or not. If the inquiry in step 74 results in affirmative, the 
program proceeds to step 76 where failure flag FAIL is set and airflow 
ratio K.sub.Q is not calculated based on the data Qa.sub.-- AD fetched in 
step 70. The airflow ratio K.sub.Q is set equal to 1 (one). If the inquiry 
in step 74 results in a negative response and thus the data Qa.sub.-- AD 
fetched in step 70 is reliable, the program proceeds to step 78. In step 
78, a table look-up operation of the characteristic curve is shown in FIG. 
6 is performed using Qa.sub.-- AD to store the result at Qa in RAM as 
actual mass airflow rate. In step 82, a ratio Qa/Qa' is calculated. In 
step 84, the latest data of Qa/Qa', namely (Qa/Qa')new, is used to update 
an average, namely (Qa/Qa')av. In this embodiment, the average is a 
weighted average which is expressed as, 
EQU (Qa/Qa')av=(1/4).times.(Qa/Qa')new+(3/4).times.(Qa/Qa')av. 
The average is stored at K.sub.Q in RAM. 
Referring to FIG. 8A, the analog output signal of engine coolant 
temperature sensor 28 is converted into a digital signal by A/D converter 
29, to store the result at Tw in RAM. 
Referring to FIG. 8, in step 90, the digital data Tw is fetched. In step 
92, it is determined whether the engine coolant temperature Tw is less 
than a predetermined temperature value Twset or not. If Tw is greater than 
or equal to Twset, i.e., the engine has been warmed-up, the program 
proceeds to step 94 where an interruption register is set to initiate 
execution of FIG. 7 routine. However, if Tw is less than Twset, i.e., the 
engine is cold, the program proceeds to step 96. In step 96, LA (low 
altitude) is set at JUDGEMENT in RAM, and airflow ratio K.sub.Q is set 
equal to 1 (one). 
Referring to FIG. 7, at step 98, the digital data K.sub.Q is fetched. In 
step 100, the content of the JUDGEMENT is checked. The content of 
JUDGEMENT is either LA (low altitude) or HA (high altitude). If the 
content of the JUDGEMENT is HA, the program proceeds to step 102. In step 
102, it is determined whether K.sub.Q is greater than Q.sub.1, or not. If 
the inquiry in step 102 results in a negative determination, the content 
of the JUDGEMENT is not altered. If the inquiry in step 100 results in an 
affirmative determination, the program proceeds to step 104, where the 
content of the JUDGEMENT is altered to LA. If the inquiry in step 100 
results in a JUDGEMENT LA, the program proceeds to step 106. In step 106, 
it is determined whether K.sub.Q is less than Q.sub.2 or not. If the 
inquiry in step 106 is negative, the content of the JUDGEMENT is not 
altered. If the inquiry in step 106 is affirmative, the program proceeds 
to step 108 where the content of the JUDGEMENT is altered to HA. The 
predetermined values Q.sub.1 and Q.sub. 2 are different, and Q.sub.1 is 
greater than Q.sub.2. It is readily seen from the preceding description 
that symbol HA indicates that the motor vehicle is operating at a high 
altitude where air density is less, while symbol LA indicates that the 
motor vehicle is operating at a low altitude, where the air density is 
greater. 
FIGS. 10 and 11 show programs for calculating vehicle speed. Execution of 
the program shown in FIG. 10 is initiated by a pulse generated by output 
shaft speed sensor 36. In step 118, an increment of up-counter C is made. 
Execution of the program shown in FIG. 11 is repeated at regular intervals 
of 100 msec. In step 120, the content of counter C is counted and the 
result is used to calculate the vehicle speed. The result of this 
calculation is stored at VSP as vehicle speed. In step 122, counter C is 
cleared. 
Referring to FIG. 9, a step 110, the content of JUDGEMENT (HA or LA) is 
fetched. Two shift point mapping tables as shown in FIG. 12 are stored in 
the ROM, one being suitable for motor vehicle operation at low altitude, 
the other being suitable for motor vehicle operation at high altitude. In 
step 112, an appropriate one of the shift point mapping tables for 
JUDGEMENT fetched in step 110 is selected. In steps 114 and 116, the TVO 
(throttle opening degree) and VSP (vehicle speed) are fetched, 
respectively. In step 124, a table look-up operation of the selected shift 
point mapping table as shown in FIG. 12 is performed to determine a 
desired gear position, and the result is determined at GP as gear position 
desired. In step 126, shift solenoids 38 and 40 are controlled to 
accomplish the gear position stored at GP. 
Referring again to FIG. 2, in step 84, the weighted average of Qa/No is 
calculated. This process, often called "filtering", is preferrable in 
eliminating deviation of Qa/Qa' due to variations in mass airflow rate 
(Qa) so as to minimize its influence on judgements regarding altitude, for 
example. Alternatively, a running average may be used instead of the 
weighted average. The running average is expressed as, 
EQU (Qa/Qa')av=(1/N).times.[(Qa/Qa')old.sub.N +(Qa/Qa')old.sub.N-1 . . . 
+(Qa/Qa')old.sub.1 ], 
where 
N: a number of sampled data; 
(Qa/Qa')old.sub.N ; (Qa/Qa')old.sub.N-1 ; 
(Qa/Qa')old.sub.N-2 ; . . . (Qa/Qa')old.sub.1 : data sampled in previous 
cycles. 
In FIG. 2, standard mass air flow rate (Qa') is determined on the data 
table shown in FIG. 4 as a function of throttle opening degree (TVO) only. 
Alternatively, as shown in FIG. 14, a standard mass airflow rate (Qa') 
data table may be used. This data table is retrievable not only with 
throttle opening degree (TVO), but also with engine speed (Ne). The values 
in this data table are prepared after considering the fact that mass 
airflow rate varies with variation in engine speed. This data table in 
FIG. 14 is used in the routine shown in FIG. 13. 
Referring to FIG. 13, this routine is substantially the same that of FIG. 2 
except that two steps 132 and 140 have replaced the step 64. With the 
programs shown in FIGS. 13A and 13B, the vehicle speed is calculated. 
Execution of the program shown in FIG. 13A is initiated by a pulse 
generated by engine speed sensor 15. In step 134, an increment of 
up-counter C is made. Execution of the program shown in FIG. 13B is 
repeated at regular intervals of 100 msec. In step 136, the content of the 
counter C is counted and the result is used to calculate engine speed. The 
result of this calculation is stored at Ne in the RAM as engine speed. In 
step 138, the counter C is cleared. 
Referring back to FIG. 13, in step 132, the digital data Ne (engine speed) 
is fetched, and in step 140, a table look-up operation of FIG. 14 is 
performed using the data TVO (throttle opening degree) and Ne (engine 
speed) fetched in steps 62 and 132, respectively. 
Referring to FIGS. 16 to 19, another embodiment is described. This 
embodiment is different from the preceding embodiment in that airflow 
ratio K.sub.Q is used as a correction coefficient in modifying standard 
servo activating hydraulic fluid pressure determined in response to 
throttle opening degree. 
Before discussing the embodiment of FIGS. 16 to 19, the mass airflow ratio 
K.sub.Q (=Qa/Qa') is further described in connection with FIG. 15. Since 
engine torque is in proportion to the mass air flow rate, the mass airflow 
ratio K.sub.Q is proportional to a ratio of actual engine torque to 
standard engine torque. FIG. 15 shows this relationship. In FIG. 15, the 
vertical axis indicates the ratio of actual transmission output torque 
(TqB) to standard transmission output torque (TqB'). 
Referring to FIG. 16A, analog output signal of ATF temperature sensor 28 is 
converted to digital signal by A/D converter 29 to store the result at ATF 
as automatic transmission fluid temperature. 
Referring to FIG. 16, in step 150, the data ATF (automatic transmission 
fluid temperature) is fetched. In step 152, it is determined whether or 
not ATF is lower than a predetermined temperature value L, for example 
60.degree. C. If this inquiry is affirmative, the program proceeds to step 
154 where a table look-up operation of a line pressure table for low 
temperature is performed using the throttle opening degree to give the 
duty duration D(P1). Then, the program proceeds to step 164. In step 164, 
the OFF duty duration per ON-OFF cycle of line pressure solenoid 37 (see 
FIG. 1) is modulated in response to the duty D(Pl) given by the 
predetermined line pressure control strategy in step 154. If the inquiry 
in step 152 is negative, the program proceeds to step 156, where it is 
determined whether or not automatic transmission 12 is in a stable state, 
after comparing a desired gear position with an actual position. If the 
desired gear position is equal to the actual gear position, a ratio shift 
is not required, and thus the transmission 12 is in stable state, and thus 
the inquiry in step 156 results is affirmative. In this case, the program 
proceeds from step 156 to step 154. In step 154, a table look-up operation 
of a line pressure table for the usual temperature is performed using 
throttle opening degree (TVO) to give the duty duration D(P1). Then, in 
step 164, the line pressure solenoid 37 is controlled on the duty D(P1) 
obtained in step 54 to give a stable-state line pressure vs., throttle 
opening degree characteristic. The line pressure control performed in step 
154 is substantially the same as the conventional line pressure control 
described on Pages I-29 to I-30 of the publication "NISSAN FULL-RANGE 
AUTOMATIC TRANSMISSION RE4R03A TYPE, SERVICE MANUAL, (A261C10)." 
If the inquiry is step 156 results in negative, and a ratio shift is 
required, the program proceeds to steps 200, 202, and 204 to carry out a 
servo activating hydraulic fluid pressure control based on the airflow 
ratio K.sub.Q determined by executing the routine shown in FIGS. 2 or FIG. 
13. In step 200, a table look-up operation of the standard servo 
activating hydraulic pressure table shown in FIG. 17 is performed using 
data TVO, i.e., throttle opening degree, fetched in step 62 in FIG. 2 or 
13 to store the result at PI(s) in a RAM. The data stored at PI(s) is 
called standard servo activating hydraulic pressure. In step 202, the 
standard servo activating hydraulic fluid pressure PI(s) is corrected with 
the airflow ratio K.sub.Q by performing multiplication K.sub.Q 
.times.PI(s), for example, to store the result at PI. In step 204, this 
pressure data PI is increased by a predetermined value PI.sub.OFS. In step 
162, a table look-up operation of a duty conversion table shown in FIG. 18 
is performed using pressure data PI to give the duty duration D(Pl). Then, 
in step 164, line pressure solenoid 37 is controlled in response to duty 
D(Pl) determined in step 162. Referring to step 204, the predetermined 
value P1.sub.OFS is a value determined for athe force of a return spring 
of a servo of an on-coming friction device to be engaged during the ratio 
shift. As shown in FIG. 19, ON-OFF cycle of line pressure solenoid 37 is 
repeated 50 times per second. Thus, one cycle is 20 msec, its frequency is 
50 Hz. OFF duration in one cycle is determined by duty D(Pl). The 
relationship between servo activating hydraulic pressure (line pressure) 
and duty D(Pl) is such that the hydraulic fluid pressure is in proportion 
to duty D(Pl). 
Referring to FIGS. 20A and 20B, these describe the influence on a ratio 
shift of variance in the atmospheric pressure, and referring to FIGS. 21A 
and 21B, these described how the influence is removed due to correction of 
the servo activating hydraulic pressure according to the embodiment 
described in connection mainly with FIG. 16. 
In determining servo activating hydraulic fluid pressure for a ratio shift, 
for example, 1-2 upshift, it is the conventional practice to use a 
pressure table, as shown in FIG. 17, which contains optimum servo 
activating hydraulic pressure values for 1-2 upshift versus different 
throttle opening degree values. The pressure values of the table are set 
for optimum performance of an on-coming friction device during the upshift 
under standard conditions where the upshift is initiated at a preset 
vehicle speed for a given throttle opening degree in accordance with a 
shift point mapping for drive range, at low altitude, and at medium 
ambient temperature. 
FIGS. 20A and 20B show torque curves during the upshift occurring at the 
same shift point with the same throttle opening degree but at different 
altitudes. In these torque curves, reference characters TqB and TqM denote 
torque before shift and torque during shift, respectively. Reference 
character t denotes a time interval of inertia phase. Torque TqM is mainly 
determined by servo activating hydraulic fluid pressure supplied to the 
on-coming friction device, and thus remains invariable over variance in 
torque TqB due to change in air density since servo activating hydraulic 
fluid pressure determined for the same throttle opening degree is fixed. 
Quality of shift may be evaluated by a ratio TqB/TqM. This ratio is optimum 
in FIG. 20A, since the servo activating hydraulic fluid pressure is so 
adjusted as to provide a good shift at low altitude. At high altitude with 
low atmospheric pressure, air density drops to cause a drop in engine 
output. 
As seen from FIG. 20B in comparison with FIG. 20A, torque TqB drops at high 
altitude where air density is low. However, energy to be absorbed during 
the inertia phase and torque TqM remains invariable. Thus, the time 
interval t for inertia phase becomes short at high altitude, and ratio 
TqB/TqM deviates from the optimum value. 
Adaptive correction of variance in shift quality due to altitude 
variability is described in connection with FIGS. 21A and 21B. 
FIG. 21A shows a torque curve during 1-2 upshift under the same condition 
as in FIG. 20A. Similarly, FIG. 21B shows a torque curve during the 
upshift under the same condition as in FIG. 20B. Referring to FIG. 21B, 
since airflow ratio K.sub.Q is multiplied with the standard hydraulic 
fluid pressure, torque TqM determined by the servo activating hydraulic 
fluid pressure corrected drops as torque TqB drops the due to a change in 
air density. Thus, ratio TqB/TqM is kept optimum at high altitude. 
Let us now consider 1-2 upshift at different vehicle speeds with the same 
throttle opening degree. FIGS. 22A, 22B, and 22C show torque curves during 
the upshift when servo activating hydraulic fluid pressure is determined 
in response to throttle opening degree. FIGS. 23A, 23B, and 23C show 
torque curves during the upshift when servo activating hydraulic fluid 
pressure is corrected with airflow ratio K.sub.Q. 
As readily seen from FIGS. 22A and 22C in comparison with FIG. 22B, torque 
TqB becomes large at low vehicle speed L, while it becomes small at high 
vehicle speed H. Thus, torque TqB is in inverse proportion to vehicle 
speed. 
Energy to be absorbed during inertia phase is in proportion to vehicle 
speed, and a difference in torque before and after the shift is in 
proportion to torque TqB. However, the time interval t for the inertia 
phase remains almost unchanged since torque TqB is in inverse proportion 
to vehicle speed. 
Ratio TqB/TqM is optimum in FIG. 22B since servo activating hydraulic fluid 
pressure is so adjusted as to provide a good shift at the preset vehicle 
speed. In FIGS. 22A and 22C, this ratio deviates from the optimum value 
since torque TqM remains the same even though torque TqB becomes large at 
low vehicle speed (FIG. 22A) and becomes small at high vehicle speed (FIG. 
22C). This variance in shift quality is difficult to correct if servo 
activating hydraulic fluid pressure is determined only in response to 
throttle opening degree. 
Referring to FIGS. 23A, 23B, and 23C, adaptive correction of variance in 
shift quality due to shift point variability is described. Torque curves 
shown in FIGS. 23A, 23B, and 23C result from varying torque TqM by 
correcting servo activating hydraulic fluid pressure with airflow ratio 
K.sub.Q. FIGS. 23A, 23B, and 23C correspond to FIGS. 22A, 22B, and 22C, 
respectively, in that they show torque curves during the upshift at the 
three different shift points. As will be appreciated from comparing FIG. 
23A with FIG. 22A, and comparing FIG. 23C with FIG. 22C, torque TqM is 
increased in FIG. 23A and decreased in FIG. 23C since servo activating 
hydraulic fluid pressure is corrected with airflow ratio K.sub.Q. Since 
K.sub.Q is in proportion to torque TqB, relative to torque TqB in FIG. 
23B, torque TqM is in proportion to TqB. Thus, ratio TqB/TqM is kept 
optimum over a wide range of shift point variability. 
Energy to be absorbed during inertia phase is in proportion to vehicle 
speed, and a difference in torque before and after the shift is determined 
in response to torque TqB. Thus, as shown in FIGS. 23A, 23B, and 23C, the 
time interval t for the inertia is short at low vehicle speed (see FIG. 
23A), while it is long at high vehicle speed (see FIG. 23C). 
Energy to be absorbed during inertia phase is the same if the shift point 
is the same. Since torque TqM becomes larger in FIG. 23A than in FIG. 22A, 
the time interval t becomes shorter in FIG. 23A than in FIG. 22A. 
Similarly, since TqM becomes smaller in FIG. 23C than in FIG. 22C, the 
time interval t becomes longer in FIG. 23C than in FIG. 22C. 
From the preceding description in connection with FIGS. 23A, 23B, and 23C, 
it will now be understood that servo activating hydraulic fluid pressure 
during the ratio shift is corrected such that ratio TqB/TqM is always 
optimum. Thus, good shift quality is maintained over a wide range of shift 
point variability. 
FIGS. 24A, 24B, and 24C, describe the influence on ratio shift due to 
variance in ambient temperature, and FIGS. 25A, 25B, and 25C describe how 
such influence is removed according to the servo activating hydraulic 
pressure corrected with airflow ratio K.sub.Q. 
As mentioned, according to conventional practice, servo activating 
hydraulic fluid pressure is determined in response to throttle opening 
degree and so adjusted as to provide a good shift at medium ambient 
temperature. Air density increases as ambient temperature decreases in 
winter, while it decreases as ambient temperature increases in summer. 
Engine output increases in response to an increase in air density, while 
it decreases in response to a decrease in air density. FIGS. 24A, 24B, and 
24C show torque curves during 1-2 upshift occurring at the same shift 
point with the same throttle opening degree but at different ambient 
temperatures. As seen from FIG. 24A in comparison with FIG. 24B, torque 
TqB increases at low temperature, while as seen from FIG. 24C in 
comparison with FIG. 24B, torque TqB decreases at high temperature. Since 
torque TqM remains invariable, ratio TqB/TqM deviates from the optimum 
value in FIGS. 24A and 24C. 
Adaptive correction of a variance in shift quality is described in 
connection with FIGS. 25A, 25B and 25C. 
FIG. 25B shows a torque curve during 1-2 upshift under the same condition 
as in FIG. 24B. Similarly, FIGS. 25A and 25C show torque curves during the 
upshift under the same condition as in FIG. 24A and 24C. Referring to 
FIGS. 25A and 25C, since K.sub.Q is in proportion to a ratio of torque TqB 
relative to standard torque TqB as shown in FIG. 25B, torque TqM 
determined by servo activating hydraulic fluid pressure corrected with 
K.sub.Q varies in accordance with air density variability. Thus, ratio 
TqB/TqM is kept optimum over wide range of ambient temperature 
variability. 
Referring again to FIGS. 21A and 21B, it is seen that the trailing edge of 
the torque curves are rounded, as denoted by the reference characters r. 
This is caused by the fact that K.sub.Q drops in response to a reduction 
in intake airflow near the end of shift, and servo activating hydraulic 
fluid pressure also drops. The same characteristic is seen in FIGS. 23A, 
23B, 23C, 25A, 25B, and 25C. This characteristic improves shift quality. 
If a turbo charged engine is used, turbo lag is unavoidable. With the same 
throttle opening degree, a ratio shift with turbo in operation and the 
same shift with turbo not yet in operation show different shift qualities 
when servo activating hydraulic fluid pressure is determined in response 
to throttle opening degree. This is because there is a difference in 
torque TqB. This variance in shift quality is corrected by effecting shift 
on servo activating hydraulic fluid pressure corrected with airflow ratio 
K.sub.Q.