Determining clutch fill volume in an automatic transmission
View Patent ↗A method of determining a fill volume of a clutch of an automatic transmission. A clutch fill sequence is observed from measurement of fluid pressure applied to the clutch, wherein the sequence may include a initial rise, a plateau, and a final rise. A fill end time may be identified as corresponding to an intersection of a forward extrapolated portion of the plateau and a backward extrapolated portion of the final rise.
1. A method of determining a fill volume of a clutch of an automatic transmission, the method comprising the steps of:
observing a clutch fill sequence from measurement of fluid pressure applied to the clutch, wherein the sequence includes a initial rise, a plateau, and a final rise;
identifying a fill end time corresponding to an intersection of a forward extrapolated portion of the plateau and a backward extrapolated portion of the final rise; and
wherein the identifying the fill end time step comprises the steps of:
identifying at least one representative point of the plateau;
forward extrapolating a line from the at least one representative point of the plateau;
identifying first and second representative points of the final rise; and
backward extrapolating a line from the first representative point through the second representative point of the final rise.
2. The method of claim 1 further comprising the steps of:
smoothing a raw data pressure trace of the fluid pressure to yield a smoothed pressure trace according to the following equation:
p_sm
(
i
)
=
∑
k
=
i
-
j
i
+
j
p
_raw
(
k
)
/
(
2
j
+
1
)
where p_raw=clutch pressure raw data;
2j+1=width of symmetric smoothing window operation; and
p_sm=smoothed data; and
using the smoothed pressure trace to observe the clutch fill sequence.
3. The method of claim 1 wherein the step of identifying the at least one representative point of the plateau comprises:
generating an RMS trace according to the following equation:
p_rms
(
i
)
=
∑
k
=
i
-
j
i
+
j
(
p_sm
(
k
)
-
p_avg
i
)
2
;
where: p_rms=root mean square pressure;
p_sm=smoothed data
p_avg=average pressure in timeframe defined by “k”
identifying a minimum point on the RMS trace; and
identifying a point on the plateau that corresponds to the minimum point on the RMS trace.
4. The method of claim 1 wherein the step of identifying first and second point of the final rise comprises multiplying a pressure value corresponding to the at least one representative point of the plateau by first and second factors, and referencing the pressure trace to identify pressure values which are the products of the multiplying step.
5. The method of claim 1 wherein the step of identifying first and second points of the final rise comprises selecting first and second empirically determined pressure values and referencing the final rise of the pressure trace to identify the pressure values.
6. The method of claim 1 further comprising the step of determining a begin fill time in the clutch fill sequence.
7. The method of claim 6 further comprising the step of smoothing a raw data pressure trace of the fluid pressure to yield a smoothed pressure trace and wherein the step of determining the begin fill time comprises generating first and second order derivative traces from the smoothed pressure trace, and identifying a first instance where the second order derivative trace crosses zero and where the first order derivative trace is positive, and using a time value corresponding to the first instance.
8. The method of claim 6 wherein the step of determining the begin fill time comprises observing an empirically determined pressure value during the initial rise and referencing the initial rise to identify a time value corresponding to empirically determined pressure value as the begin fill time.
9. The method of claim 6 further comprising calculating a fill volume using the fill begin and end times.
10. The method of claim 9 further comprising the step of performing an error check on at least one of the begin and end fill times or the fill volume.
11. A method of determining a fill volume of a clutch of an automatic transmission, the method comprising the steps of:
observing a clutch fill sequence from measurement of fluid pressure applied to the clutch, wherein the sequence includes a initial rise, a plateau, and a final rise;
identifying a fill end time corresponding to an intersection of a forward extrapolated portion of the plateau and backward extrapolated portion of the final rise;
determining a begin fill time in the clutch fill sequence;
calculating a fill volume using the fill begin and end times; and
wherein the step of calculating the fill volume comprises using the following equations:
V
G
=
∫
t
0
t
e
Q
(
t
)
ⅆ
t
where: V G =volume of the particular clutch, in 3 ; and
Q
(
t
)
in
3
sec
=
P
(
t
)
π
D
2
4
γ
Δ
t
where: Q=flow rate for the particular clutch, in 3 /sec;
P(t)=p_sm=pressure found on the trace, lbf/in 2 ;
γ=oil specific weight, lbf/in 3 ;
t c =clutch fill end time;
D=restrictor orifice diameter for the particular clutch, in; and
Δt=sample time interval P(t) and P(t+Δt), sec.
12. The method of claim 11 wherein the fill volume is further calculated by multiplying
∫
t
0
t
β
Q
(
t
)
ⅆ
t
by an adjustment factor.
13. The method of claim 11 wherein the step of calculating the fill volume comprises using the following equation:
V D =t f *Q
where: Q=known flow rate, in 3 /sec;
V D =volume of the clutch, in 3 ; and
t f =t e −t 0
where: t e =end fill time; and
t 0 =begin fill time.
14. The method of claim 13 wherein the fill volume is further calculated by multiplying t f *Q by an adjustment factor.
15. A method of manufacturing a vehicle having an automatic transmission, comprising the steps of:
applying fluid pressure to a clutch of the automatic transmission;
measuring the fluid pressure; and
determining a fill volume of the clutch including the steps of:
observing a clutch fill sequence from measurement of fluid pressure applied to the clutch, wherein the sequence includes a initial rise, a plateau, and a final rise; and
identifying a fill end time corresponding to an intersection of a forward extrapolated portion of the plateau and a backward extrapolated portion of the final rise; and
wherein the identifying the fill end time step comprises the steps of:
identifying at least one representative point of the plateau;
forward extrapolating a line from the at least one representative point of the plateau;
identifying first and second representative points of five final rise; and
backward extrapolating a line from the first representative point through the second representative point of the final rise.
16. The method of claim 15 further comprising storing the fill volume in association with a serial number of the transmission.
17. The method of claim 16 further comprising installing the transmission into a vehicle.
18. The method of claim 17 further comprising loading the stored fill volume associated with the transmission into a controller of the vehicle, and using the fill volume to control flow of pressurized fluid to the clutch.
19. The method of claim 15 further comprising:
determining a begin fill time in the clutch fill sequence;
calculating a fill volume using the fill begin and end times; and
wherein the step of calculating the fill volume comprises using the following equations:
V
G
=
∫
t
0
t
e
Q
(
t
)
ⅆ
t
where: V G =volume of the particular clutch, in 3 ; and
Q
(
t
)
in
3
sec
=
P
(
t
)
π
D
2
4
γ
Δ
t
where: Q=flow rate for the particular clutch, in 3 /sec;
P(t)=p_sm=pressure found on the trace, lbf/in 2 ;
γ=oil specific weight, lbf/in 3 ;
t c =clutch fill end time;
D=restrictor orifice diameter for the particular clutch, in; and
Δt=sample time interval P(t) and P(t+Δt), sec.
20. The method of claim 15 further comprising:
smoothing a raw data pressure trace of the fluid pressure to yield a smoothed pressure trace according to the following equation:
p_sm
(
i
)
=
∑
k
=
i
-
j
i
+
j
p
_raw
(
k
)
/
(
2
j
+
1
)
where: p_raw=clutch pressure raw data;
2 j+ 1=width of symmetric smoothing window operation; and
p_sm=smoothed data; and
using the smoothed pressure trace to observe the clutch fill sequence.