Apparatus for controlling automatic transmission for vehicle

In an apparatus for controlling an automatic transmission for a vehicle in which, at the time of gear engagement due to changing over from a reverse range or a neutral range to a forward range, a speed-change stage of the automatic transmission is shifted down to a low-speed stage after once setting it to a predetermined high-speed stage. The apparatus has a detector for detecting an amount of slippage of high-speed stage engaging elements which establish the high-speed stage and a control device for controlling to shift down, at the time of gear engagement, to the low-speed stage after the amount of slippage of the high-speed stage engaging elements has lowered to a predetermined value or smaller.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for controlling an automatic 
transmission for a vehicle and, in particular, to an apparatus for 
reducing a shock at the time of gear engagement or gear meshing. 
BACKGROUND OF THE INVENTION 
As this kind of apparatus, there is conventionally known in Japanese 
Published Examined Patent Application No. 709/1975 an apparatus in which, 
at the time of gear engagement or gear meshing due to changing over from a 
neutral range to a forward range, the speed-change stage of the automatic 
transmission is first set to a predetermined high-speed stage and is then 
down-shifted to a low-speed stage, to prevent a large driving force by the 
low-speed stage from being suddenly transmitted, thereby reducing the 
shock at the time of gear engagement. In this prior art, in order to 
securely perform the down-shifting via the high-speed stage at the time of 
gear engagement, an arrangement is made so that the high-speed stage is 
maintained until a predetermined time has elapsed from the time of gear 
engagement, out of consideration of the time required for engagement of 
frictional engaging elements which establish the above-described 
predetermined high-speed stage. 
However, the time required for the engagement of the frictional engaging 
elements varies with mechanical fluctuations of the automatic 
transmission, oil temperature, rotational speed of an engine, hydraulic 
engaging characteristics of the frictional engaging elements, or the like. 
Therefore, if the time for holding the speed-change stage to the 
high-speed stage is kept constant as described above, there may occur a 
case in which the automatic transmission is down-shifted before the 
frictional engaging elements for the high-speed stage are engaged, with 
the result that the shock at the time of gear engagement are not 
sufficiently reduced. On the other hand, if the time for holding the 
speed-change stage to the high-speed stage is prolonged, the down-shifting 
will be delayed, resulting in a poor starting characteristics. 
Further, in Japanese Published Examined Japanese Patent Application No. 
69018/1991, there is known an apparatus in which, at the time of gear 
engagement, an automatic transmission is maintained at a high-speed stage 
until the rotational speed of a turbine of a torque converter is down to a 
predetermined value. However, since the rotational speed of the turbine 
varies with the rotational speed of the engine, or the like, the 
frictional engaging elements for the high-speed stage may not necessarily 
be sufficiently engaged when the rotational speed of the turbine is down 
to the predetermined value. Further, since the engaging conditions of the 
frictional engaging elements at the time when the rotational speed of the 
turbine has lowered to the predetermined value are different between the 
time when the vehicle is completely stopped and the time when it is not, 
the time of engagement of the frictional engaging elements for the 
high-speed stage cannot accurately be determined from the rotational speed 
of the turbine alone. 
OBJECT AND SUMMARY OF THE INVENTION 
In view of the above-described disadvantages, an object of the present 
invention is to provide an apparatus in which the time of engagement of 
the frictional engaging elements for a high-speed stage can be accurately 
determined and in which the transmission is down-shifted from a high-speed 
stage to a low-speed stage at an appropriate timing, so that the shock at 
the time of gear engagement can securely be reduced without impairing the 
starting characteristics. 
According to the present invention, the foregoing and other objects are 
attained by an apparatus for controlling an automatic transmission for a 
vehicle in which, at a time of gear engagement due to changing over from a 
reverse range or a neutral range to a forward range, a speed-change stage 
of the automatic transmission is shifted down to a low-speed stage after 
once setting it to a predetermined high-speed stage, the apparatus 
comprising: detecting means for detecting an amount of slippage of 
high-speed stage engaging elements which establish a high-speed stage; and 
control means for controlling to shift down, at the time of gear 
engagement, to the low-speed stage after the amount of slippage of the 
high-speed stage engaging elements has lowered to a predetermined value or 
smaller. 
In a preferred embodiment, the above-described detecting means is arranged 
to detect rotational speeds of an input side and an output side, 
respectively, of the high-speed stage engaging elements and then to 
calculate the amount of slippage of the high-speed stage engaging elements 
from the rotational speeds. In this arrangement, the amount of slippage is 
calculated by the difference or ratio between the rotational speed of the 
input side and the rotational speed of the output side. 
Even if the timing of engagement of the high-speed stage engaging elements 
at the time of gear engagement may vary due to mechanical fluctuations of 
the automatic transmission, or due to changes in the hydraulic oil 
temperature, rotational speed of the engine, or the like, or due to 
whether the vehicle is stopped or not, the timing of gear engagement can 
accurately be determined by checking the amount of slippage of the 
high-speed stage engaging elements. Therefore, by shifting down to the 
low-speed stage after the amount of slippage has lowered to the 
predetermined value or smaller, the low-speed stage can surely be 
established via the high-speed stage at an appropriate timing. 
If the low-speed stage friction engaging elements which establish the 
low-speed stage are not engaged yet when the engagement of the high-speed 
stage engaging elements is released at the time of down shifting, the 
driving force which has so far been increased to a certain degree by the 
high-speed stage will be dropped or decreased and, consequently, the 
effect of speed changing via the high-speed stage will be reduced. In such 
a case, if an arrangement is made to hold the speed-change stage to the 
predetermined high-speed stage until a lapse of a predetermined time after 
the amount of slippage of the high-speed stage engaging elements has 
lowered to the predetermined value, the low-speed stage friction elements 
will be engaged within the predetermined time and, therefore, the 
low-speed stage will be established right after releasing of the 
high-speed stage engaging elements. Therefore, the driving force can be 
increased stepwise without a temporary decrease in the driving force. 
Even if the amount of slippage in the high-speed stage engaging elements is 
lowered to the predetermined value or smaller, there is a possibility that 
the starting characteristics are impaired by sticking to or remaining in 
the high-speed stage if the lowering cannot be detected due to a failure 
in the detecting means, or the like. In order to solve this kind of 
disadvantage, it is preferable to provide means for shifting the 
speed-change stage down to the low-speed stage at a lapse of a 
predetermined time from the time of gear engagement, irrespective of the 
amount of slippage of the high-speed stage engaging elements.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, numeral 1 denotes a transmission for effecting the 
changing or shifting of a vehicle speed to four forward speeds and one 
reverse speed. The transmission 1 comprises: an input shaft 1a which is 
connected to an engine 2 via a fluid torque converter 3; an output shaft 
1b which is connected to driving wheels 4 of the vehicle via a 
differential gear 5; and first- to fourth-speed forward gear trains G1, 
G2, G3, G4 and one reverse gear train GR, all gear trains being disposed 
between the input shaft 1a and the output shaft 1b. In each of the forward 
gear trains, there are interposed hydraulic engaging elements in the form 
of a hydraulic clutch C1, C2, C3, C4 respectively so that, through the 
engagement of each hydraulic clutch, each of the corresponding gear trains 
can be selectively established. There is further provided a one-way clutch 
6 in the first-speed gear train G1 to allow for an overrotation of the 
output side. It is thus so arranged that, even if the first-speed 
hydraulic clutch C1 is engaged, there can be established another 
corresponding gear train when another hydraulic clutch is engaged. In 
addition, the reverse gear train GR and the fourth-speed gear train G4 use 
the clutch C4 in common by providing a selector 7 which operates to 
selectively engage the fourth-speed gear train G4 and the reverse gear 
train GR to the output shaft 1b. According to this arrangement, when the 
selector 7 is in the forward position on the left sidle of the Figure (the 
position as illustrated), the fourth-speed gear train G4 is established 
and, when it is changed over to the reverse position on the right side of 
the Figure, the reverse gear train GR is established. 
The above-described hydraulic clutches C1 through C4 are controlled by a 
hydraulic oil circuit 9 provided with manual valves (not illustrated) 
which are interlocked with a shift lever 8. Solenoid valves which are 
controlled by an electronic control circuit 10 (hereinafter called ECU) 
are integrated into the hydraulic oil circuit 9. The ECU 10 is input by 
signals from engine sensors 11 for detecting throttle valve opening degree 
TH, cooling water temperature TW or the like, speed sensors 12 for 
detecting the vehicle speed V, a position sensors 13 for detecting the 
changeover positions of the shift lever 8. When the shift lever 8 is 
changed over to the D range which is the forward range for automatic speed 
changing, an automatic speed changing from the first speed through the 
fourth speed is arranged to be carried out according to speed-change 
characteristics, as shown in FIG. 3, which are set in advance by selecting 
the throttle valve opening degree TH and the vehicle speed V as 
parameters. 
At the time of gear engagement or gear meshing when the shift lever 8 is 
changed over from the N range which is the neutral range or the R range 
which is the reverse range to the D range, a second-speed signal is first 
output from the ECU 10 even if the driving conditions are in such a range 
as to establish the first-speed gear train. In this manner, the 
second-speed gear train G2 is established by supplying oil by the 
hydraulic oil circuit 9 to the first-speed hydraulic clutch C1 and the 
second-speed hydraulic clutch C2. Thereafter, by outputting the 
first-speed signal, the oil is discharged from the second-speed hydraulic 
clutch C2, thereby engaging only the first-speed hydraulic clutch C1 to 
establish the first-speed gear train G1. The driving force to be 
transmitted to the driving wheels 4 is increased stepwise to perform the 
so-called squat control which reduces a shock at the time of gear 
engagement. 
The timing for down-shifting from the second-speed to the first-speed in 
this squat control is to be determined on the basis of an amount of 
slippage of the second-speed hydraulic clutch C2. To detect this amount of 
slippage, signals from a sensor 14 for detecting the rotational speed Nin 
of the input shaft 1a of the transmission 1 and from a sensor 15 for 
detecting the rotational speed Nout of the output shaft 1b are input to 
the ECU 10. Then, an amount of slippage is calculated by a difference or a 
ratio between the rotational speed of the output shaft 1b at the time when 
the second-speed is established and Nout, the rotational speed of the 
output shaft being obtainable by multiplying the Nin by a gear ratio r 
(=output/input) of the second-speed gear train G2. In this embodiment, the 
amount of slippage is calculated as a ratio of slippage ECL by the 
following formula: 
EQU ECL=r.multidot.Nin/Nout 
Details of the squat control are as shown in FIG. 2. First, a determination 
is made in step S1 as to whether or not the shift lever 8 has been changed 
over to the D range. If the shift lever 8 is in a range other than the D 
range, the operation or procedure proceeds to step S2 and set the 
remaining time t1 of a first subtracting timer to a predetermined first 
set time t1s. On the other hand, if the shift lever 8 is in the D range, 
the operation proceeds to step S3 to determine whether the changeover is 
from the N range to the D range or from the R range to the D range. In the 
course of the changeover from the R range to the D range, the shift lever 
8 passes through the N range. However, if the speed of passing 
therethrough is fast enough, a determination is made that the changeover 
is from the R range to the D range. 
When the shift lever 8 is changed over from the N range to the D range, the 
operation proceeds to step S4 to determine whether or not the throttle 
valve opening degree TH is fully closed. When it is not fully closed, the 
operation proceeds to step S5 to determine whether or not the degree of 
increase .DELTA.TH of the throttle opening degree is equal to or above a 
predetermined value .DELTA.THs. It is at the time when a driver depresses 
an acceleration pedal that the relationship .DELTA.TH.gtoreq..DELTA.THs is 
satisfied. Since, at such a time, it is considered that the driver has an 
intention of rapidly starting the vehicle, the squat processing is not 
carried out. When the TH is fully closed or .DELTA.TH&lt;.DELTA.THs, the 
operation proceeds to step S6 to determine whether or not the vehicle 
speed V at the present time is below a first set value V1 which is a 
relatively low speed (e.g., 3 to 5 km/h with hysteresis). If V.ltoreq.V1, 
the operation proceeds to step S7 to determine whether or not the cooling 
water temperature TW is equal to or above a S9 predetermined value TWs. 
Since, at a low temperature condition when TW&lt;TWs, the viscosity of oil is 
high and consequently the clutch pressure gradually increases, there will 
not occur a large shock even if the first-speed gear train G1 is 
established from the beginning at the time of gear engagement. Therefore, 
only when TW.gtoreq.TWs, the operation proceeds to step S8 to carry out 
the squat processing or operation. 
At step S8 a determination is made as to whether or not the remaining time 
t1 of the first subtracting timer has become zero, i.e., whether the first 
set time t1s has elapsed after the time when the changeover to the D range 
was made. If the above-described time has not lapsed, the operation 
proceeds to step S9 to determine whether or not the ratio of slippage ECL 
of the second-speed hydraulic clutch C2 is below a predetermined value 
ECLs. If EC1&gt;ECLs, the operation proceeds to step S10 to first set the 
remaining time t2 of a second subtracting timer to a predetermined set 
time t2s and then proceeds to step S11 to carry out the processing of 
establishing the second-speed gear train G2 by outputting a second-speed 
signal. According to this arrangement, the second-speed clutch C2 is 
supplied with hydraulic oil and its engaging force is gradually increased. 
As a consequence, the slipping in the second-speed clutch C2 is gradually 
decreased to perform a torque transmission by the second-speed gear train 
G2. When ECL.ltoreq.ECLs, the operation proceeds to step S12 to determine 
whether or not the remaining time t2 of the second subtracting timer has 
become zero, i.e., whether the above-described predetermined time t2s has 
lapsed from the time when the condition ECL.ltoreq.ECLs was attained. If 
this time has not lapsed yet, the operation proceeds to step S13 to 
continue the operation of establishing the second-speed gear train G2 and, 
if this time has lapsed, this operation is stopped. According to this 
arrangement, a first-speed signal is output according to the speed-change 
characteristics shown in FIG. 3 and hydraulic oil is discharged from the 
second-speed hydraulic clutch C2. At this time, even if the clutching 
pressure of the first-speed hydraulic clutch C1 has not sufficiently been 
increased or boosted at the time when ECL has lowered to ECLs, the 
clutching pressure will sufficiently be increased within the 
above-described predetermined time t2s. The engagement of the first-speed 
clutch C1 will, therefore, be almost completed and, as a result of 
decrease in the clutching pressure of the second-speed clutch C2, the 
first-speed gear train G1 will quickly be established. In this manner, the 
driving force to be transmitted to the driving wheels 4 is increased 
stepwise without causing a temporary dropping at the time of down-shifting 
from the second-speed gear train G2 to the first-speed gear train G1, 
thereby reducing the shock at the time of gear engagement. In order to 
prepare for a possibility that the relationship ECL.ltoreq.ECLs is not 
attained until after the lapse of a long period of time due to a failure 
in the second-speed clutch C2 or a failure in the sensors 14, 15, or the 
like, the following arrangement is made. Namely, when a determination has 
been made at step S8 that t1=0 after the lapse of the setting time t1s of 
the first subtracting timer from the time of gear engagement, the squat 
control is stopped. Instead, a first-speed signal according to the 
speed-change characteristics in FIG. 3 is output so that the starting of 
the vehicle at the first-speed gear train G1 can be made. 
At the time of changing over from the R range to the D range, the operation 
proceeds from step S3 to step S14 to determine whether or not the throttle 
valve opening degree TH is fully closed. If it is found not fully closed, 
the operation proceeds to step S15 to determine whether or not the degree 
.DELTA.TH of increase in the throttle opening is above the predetermined 
value .DELTA.THs. When the throttle valve opening degree TH is either 
fully closed or .DELTA.TH&lt;.DELTA.THs, the operation proceeds to step S16 
to determine whether the vehicle velocity V is below a second setting 
value V2 (e.g., 7-8 km/h with hysteresis) which is set higher than the 
above-described first setting value V1 When V.ltoreq.V2, the operation 
proceeds to step S7 to determine the cooling water temperature TW and, 
when TW.gtoreq.TWs, the squat processing as described in step 8 and 
downwards is carried out. It is generally when the shift lever 8 is 
rapidly changed over from the R range to the D range in order to escape or 
come out of a muddy field or the like that a determination is made that 
the changeover in question is from the R range to the D range. In such a 
case, since the vehicle speed V to be detected becomes high to a certain 
degree due to racing of the driving wheels 4, the second setting value V2 
is set at a relatively high value as described above. 
In the above-described embodiment, it has been arranged that the 
second-speed gear train G2 is established by the squat processing. 
However, a gear train of a higher speed other than the second speed may 
also be established. Furthermore, the present invention can also be 
applied to an automatic transmission of a planetary gear type. 
It is readily apparent that the above-described apparatus for controlling 
an automatic transmission for a vehicle meets all of the objects mentioned 
above and also has the advantage of wide commercial utility. It should be 
understood that the specific form of the invention hereinabove described 
is intended to be representative only, as certain modifications within the 
scope of these teachings will be apparent to those skilled in the art. 
Accordingly, reference should be made to the following claims in 
determining the full scope of the invention.