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TitleJATCO CVT
TagsMachines Transmission (Mechanics) Automobiles Motor Vehicle Automotive Industry
File Size1.4 MB
Total Pages6
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Page 1

38 GEARS March 2007

DDaimlerChrysler has joined the ranks of many manufactur-ers offering a Continuously
Variable Transmission (CVT). The
2007 Jeep Compass, Patriot, and Dodge
Caliber come equipped with an option-
al CVT produced by JATCO. According
to a local Dodge dealership, they can’t
keep the CVT Calibers in stock. This
dealer sold the first fifty Calibers with-
in a month and is anxiously waiting for
more.

This CVT isn't new technology;
in fact, the unit is similar to the CVT
found in many Nissans since 2002. In
this article, we’ll focus on the mechan-
ical and hydraulic operation of the
JATCO CVT used in DaimlerChrysler
vehicles. In the next issue, we’ll look
into the electronic and computer con-
trol systems.

It all begins with the basics, and
nothing gets more basic than check-
ing fluid, right? The CVT uses a spe-
cial fluid, designated CVTF+4, which
is specifically designed for the CVT.
According to DaimlerChrysler, the unit
requires this special fluid because of the
“higher pressure, special metal alloys,
and the critical need to prevent belt
slippage.” For ID purposes, the fluid is
green and, according to the manufactur-
er, even a small amount of regular ATF
will cause severe damage to the CVT.
The one-quart bottle is part number
05191184AA and the five-gallon jug is
part number 05191185AA.

Checking the fluid in the CVT
isn’t straightforward. In fact, the pro-

cedure follows along the same lines
as the NAG (722.6) and even the new
62TE. There’s no dipstick; customers
are encouraged to take their vehicle to
a repair facility every 15,000 miles to
have a trained technician check their
fluid. A special tool, Miller part number
9336, is used to check the level, which
depends on fluid temperature. Since the
fluid level can change almost 12mm
from 70ºF to 190ºF, the level must be
checked with the 9336 dipstick and
cross-referenced to a chart or table.
From the bottom of the internal stop the
fluid level should be:

Temperature High Low
77ºF 38mm 25mm
138ºF 42mm 29mm
191ºF 46mm 34mm

The fluid is expected to last the life
of the vehicle, but maintenance sched-
ule B (which pertains to most vehicles)
would require the fluid to be changed
every 60,000 miles. According to
DaimlerChrysler, schedule B includes
vehicles driven under any of these con-
ditions:

• At temperatures below 32ºF
(0ºC).

• Stop and go.
• Extensive engine idling.
• Dusty conditions.
• Short trips of less than 10

miles (16 km).
• More than 50% at sustained

high speeds during hot weath-
er, above 90ºF (32ºC).

• Trailer towing.
• Taxi, police or delivery service

(commercial service).
• Off-road or desert operation.
• Heavy loading

Mechanical: External
A quick look at the CVT reveals

two Hall Effect speed sensors (ISS
and OSS), a transmission range sensor
(TRS), a water-to-oil cooler, and a mul-
titude of pressure taps. The components
are labeled on the following pictures
(Figures 1, 2 & 3, see next page).

There are pressure taps all over this
transmission, but don't just plug any
pressure gauge into these ports. Use a
gauge that’s rated for at least 1000 psi.
Typical operating pressures can eas-
ily approach 800 – 900 psi to ensure
necessary side force on the CVT belt
(Figure 4, see page 40).

When montoring pressures, you’ll
see the secondary variator pressures
peak momentarily when rolling to a
stop. This lowers the effective ratio
before the vehicle comes to a com-
plete stop. Once the transmissions stops
rotating, the CVT can’t change ratios,
because the variators need to rotate to
change ratios; more on that later.

Refer to Table A for typical pres-
sures.

Mechanical: Internal
The secrets of the CVT are found

within the transaxle. Here you will
find two variators (pulleys), a steel
belt, a high-pressure oil pump, a valve

JATCO CVT and JATCO CVT and
DaimlerChrysler,DaimlerChrysler,

by Sean Boyle

An Overview and a
Look at Power FlowPart 1

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Page 2

1. Line Pressure
2. TCC Release
3. Primary Variator
4. Forward Clutch
5. TCC Apply
6. Input Speed Sensor
7. Water-to-Oil cooler
8. Pass-Through Electrical Connector
9. Secondary Variator
10. Reverse Clutch
11. Trans Range Sensor
12. Output Speed Sensor

GEARS March 2007 39

Figure 1

Figure 2

Figure 3

JATCO CVT ID

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Page 3

body loaded with solenoids, a planetary
gearset (oh yes, these units still have
a gearset for reverse operation), and a
couple clutch packs (for forward and
reverse)(Figure 5).

A quick study of the CVT shows
that its operation is as simple as the
sprockets of a typical bicycle. Instead of
a chain, the CVT uses a belt that rides
on the pulley surfaces (sheaves) of the
variators. To change ratios, the variators
change their effective diameter.

The primary variator connects to
the input shaft through the forward
clutch assembly, which applies in all
forward ranges. The primary variator
pushes the secondary variator with a
special segmented steel belt. The TCM
is in control of the ratios by modulating
solenoids that modify hydraulic pres-
sure at each variator.

The TCM can change the dimen-
sion between the two variator pulley
surfaces. This allows the belt to ride low
in the primary variator (simulate small
gear) or ride high in the primary varia-
tor (simulate large gear). By chang-
ing the variator position, the TCM can

Typical when
when Idling
Min - Max (or Lockup
Pressures for TCC
(psi) Apply)
Line Pressure . . . . . . . . . . . . . . . . . . . . 72 – 870 . . . . . . . . . . . . 72 – 218
Forward Clutch . . . . . . . . . . . . . . . . . . 15 – 218 . . . . . . . . . . . . 72 – 145
Primary Variator. . . . . . . . . . . . . . . . . . 15 – 870 . . . . . . . . . . . . 15 – 218
Torque Converter Apply. . . . . . . . . . . . . 0 – 145 . . . . . . . . . . . . . 0 – 102
Torque Converter Release . . . . . . . . . . . 0 – 145 . . . . . . . . . . . . . 0 – 102
Secondary Variator. . . . . . . . . . . . . . . . 15 – 870 . . . . . . . . . . . . 15 – 218
Reverse Brake . . . . . . . . . . . . . . . . . . . 15 – 218 . . . . . . . . . . . . 72 – 145

Table A

40 GEARS March 2007

JATCO CVT and DaimlerChrysler, Part 1

Figure 4

Figure 5

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Page 4

GEARS March 2007 41

acheive any gear ratio between 2.349:1
and 0.394:1.

The only component connecting
the variators is the belt. Similar to the
Honda CVT, the belt assembly is made
up of many ridged segments shaped
like wedges and held together by a
layered steel belt. The belt is a pusher,
not a puller, which means the primary
variator uses the belt to push the sec-
ondary variator.

The concept involves the fact that
steel cannot be compressed, so the
belt shouldn’t wear (and definitely not
stretch) over time. Since the segments
are designed with interlocking dowels,
it acts like a solid steel structure when
transfering torque from one variator to
the other. This design is very different
from the ZF design, which uses a chain
and pins where one variator pulls the
other.

With all CVT designs, pressure
is the key component to making them
survive. Belt slip within the sheaves
(pulley surfaces) will quickly destroy
the belt. This is why CVTs have such
incredibly high pressures and special
fluids.

Powerflow
Powerflow comes down to the

basic concept of “a small gear driving a
big gear equals underdrive” and so on,
except in this case, there are no gears
to speak of. Sure, there’s a planetary
gearset, but it’s only used to get the
sheaves to rotate in the opposite direc-
tion for reverse.

In reverse, the forward clutch is
released and the reverse clutch applied,
holding the carrier to the case. Power
flows clockwise through the input shaft
to the annulus gear. Since the car-
rier is held, the sun gear will be forced
to rotate counter-clockwise. The sun
gear is connected to the primary varia-
tor and, as simple as that, you have
reverse.

The pulley ratio is locked in reverse
to prevent overacceleration. This is
necessary since the potential is there
for the engine to remain at a constant
speed while the transmission changes
ratios. A customer may not realize it,
but the vehicle could (if allowed) accel-
erate faster in reverse than in forward
range. This is why they lock the ratio
in reverse: to prevent highway speed

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Page 5

42 GEARS March 2007

driving in reverse (Figure 6).
With the selecter in drive or low,

power flows from the torque converter,
through the input shaft, through the
applied forward clutch, to the sun
gear/hub assembly. The sun gear/hub is
splined to the primary variator, so the
input basically bypasses the planetary
gearset. Since nothing is held, the gear-
set just idles as in neutral.

As previously mentioned, the TCM
is in complete control of the ratios.
During acceleration, when the driver
wants power and speed, the TCM com-
mands a lower ratio, which increas-
es engine RPM to provide maximum
torque and horsepower. Once the driver

lets off the throttle and enters cruise,
the TCM commands a higher ratio
to reduce engine RPM and improve
efficency and economy.

If the driver holds the thottle steadi-
ly from a standstill, the TCM will allow
engine speed to increase to a point, then
hold it there. The vehicle will simply
continue to accelerate.

It's a pretty interesting experience
to drive a CVT-equipped vehicle for
the first time. Not only do you expect a
shift, but sometimes you lose perspec-
tive of how fast you’re driving, since the
engine isn’t connected directly to the
drivetrain through a specific gear ratio.
I’ve grown accustom to hearing the
engine hum, which I can subconciously
translate into vehicle speed. With a
CVT, the engine could be humming at
that same RPM all day with the vehicle
cruising at a variety of speeds. It just
takes a little getting used to.

After the torque flows through the
variators, it’s multiplied through an idler
gear assembly and final drive assembly.
The idler gear assembly multiplies the
torque by 1.72; the final drive multiplies
the torque by 3.55. The overall ratio
range is 14.34 for low, and 2.44 for high.
This is pretty typical from one extreme
to the other in comparison to a conven-
tional transmission (Figures 7 & 8).

That’s enough for now; in the next
issue of GEARS, we’ll look at the con-
trol system of the JATCO CVT, includ-
ing the valve body, electronic controls,
and the computer codes related to diag-
nosing this new transmission.

JATCO CVT and DaimlerChrysler, Part 1

Figure 6

Figure 7

Figure 8

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