Dodge Durango (DN). Manual — part 79
Fig. 24 Regulator Valve in Drive Position
Fig. 25 Regulator Valve in Reverse Position
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DESCRIPTION AND OPERATION (Continued)
KICKDOWN VALVE
When the throttle valve is as far over to the left as
it can go, the maximum line pressure possible will
enter the throttle pressure circuit. In this case, throt-
tle pressure will equal line pressure. With the kick-
down valve (Fig. 26) pushed into the bore as far as it
will go, fluid initially flows through the annular
groove of the 2–3 shift valve (which will be in the
direct drive position to the right).
After passing the annular groove, the fluid is
routed to the spring end of the 2–3 shift valve. Fluid
pressure reacting on the area of land #1 overcomes
governor pressure, downshifting the 2–3 shift valve
into the kickdown, or second gear stage of operation.
The valve is held in the kickdown position by throttle
pressure routed from a seated check ball (#2). Again,
if vehicle speed is low enough, throttle pressure will
also push the 1–2 shift valve left to seat its governor
plug, and downshift to drive breakaway.
KICKDOWN LIMIT VALVE
The purpose of the limit valve is to prevent a 3–2
downshift at higher speeds when a part–throttle
downshift is not desirable. At these higher speeds
only a full throttle 3–2 downshift will occur. At low
road speeds (Fig. 27) the limit valve does not come
into play and does not affect the downshifts. As the
vehicle’s speed increases (Fig. 28), the governor pres-
sure also increases. The increased governor pressure
acts on the reaction area of the bottom land of the
limit valve overcoming the spring force trying to
push the valve toward the bottom of its bore. This
pushes the valve upward against the spring and bot-
toms the valve against the top of the housing. With
the valve bottomed against the housing, the throttle
pressure supplied to the valve will be closed off by
the bottom land of the limit valve. When the supply
of throttle pressure has been shut off, the 3–2 part
throttle downshift plug becomes inoperative, because
no pressure is acting on its reaction area.
1–2 SHIFT VALVE
The 1–2 shift valve assembly (Fig. 29), or mecha-
nism, consists of: the 1–2 shift valve, governor plug,
and a spring on the end of the valve. After the man-
ual valve has been placed into a forward gear range,
line pressure is directed to the 1–2 shift valve. As the
throttle is depressed, throttle pressure is applied to
the right side of the 1–2 shift valve assembly. With
throttle pressure applied to the right side of the
valve, there is now both spring pressure and throttle
pressure acting on the valve, holding it against the
governor plug. As the vehicle begins to move and
build speed, governor pressure is created and is
applied to the left of the valve at the governor plug.
Fig. 26 Kickdown Valve–Wide Open Throttle
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DESCRIPTION AND OPERATION (Continued)
Fig. 27 Kickdown Limit Valve-Low Speeds
Fig. 28 Kickdown Limit Valve-High Speeds
Fig. 29 1–2 Shift Valve-Before Shift
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DESCRIPTION AND OPERATION (Continued)
When governor pressure builds to a point where it
can overcome the combined force of the spring and
throttle pressure on the other side of the valve, the
valve will begin to move over to the right. As the
valve moves to the right, the middle land of the valve
will close off the circuit supplying the throttle pres-
sure to the right side of the valve. When the throttle
pressure is closed off, the valve will move even far-
ther to the right, allowing line pressure to enter
another circuit and energize the front servo, applying
the front band (Fig. 30).
The governor plug serves a dual purpose:
• It allows the shift valves to move either left or
right, allowing both upshifts and downshifts.
• When in a manual selection position, it will be
hydraulically “blocked” into position so no upshift can
occur.
The physical blocking of the upshift while in the
manual “1” position is accomplished by the directing
of line pressure between both lands of the governor
plug. The line pressure reacts against the larger land
of the plug, pushing the plug back against the end
plate overcoming governor pressure. With the combi-
nation of the line pressure and spring pressure, the
valve cannot move, preventing any upshift.
1–2 SHIFT CONTROL VALVE
It contains a valve with four lands and a spring. It
is used as both a “relay” and “balanced” valve.
The valve has two specific operations (Fig. 31):
• Aid in quality of the 1–2 upshift.
• Aid in the quality and timing of the 3–2 kick-
down ranges.
When the manual valve is set to the Drive position
and the transmission is in the first or second gear
range, 1–2 shift control or “modulated throttle pres-
sure” is supplied to the middle of the accumulator
piston by the 1–2 shift control valve. During the 1–2
upshift, this pressure is used to control the kickdown
servo apply pressure that is needed to apply the kick-
down and accumulator pistons. Thus, the 1–2 shift
point is “cushioned” and the quality is improved.
During a WOT kickdown, kickdown pressure is
applied between the kickdown valve and the 1–2
shift control valve. This additional pressure is
directed to the 1–2 shift control’s spring cavity, add-
ing to the spring load on the valve. The result of this
increased “modulated” throttle pressure is a firmer
WOT upshift.
2–3 SHIFT VALVE
The 2–3 shift valve mechanism (Fig. 32) consists of
the 2–3 shift valve, governor plug and spring, and a
throttle plug. After the 1–2 shift valve has completed
its operation and applied the front band, line pres-
sure is directed to the 2–3 shift valve through the
connecting passages from the 1–2 shift valve. The
line pressure will then dead–end at land #2 until the
2–3 valve is ready to make its shift. Now that the
vehicle is in motion and under acceleration, there is
throttle pressure being applied to the spring side of
the valve and between lands #3 and #4.
As vehicle speed increases, governor pressure
increases proportionately, until it becomes great
enough to overcome the combined throttle and spring
pressure on the right side of the valve. When this
happens, the governor plug is forced against the shift
valve moving it to the right. The shift valve causes
land #4 to close the passage supplying throttle pres-
sure to the 2–3 shift valve. Without throttle pressure
present in the circuit now, the governor plug will
push the valve over far enough to bottom the valve in
its bore. This allows land #2 to direct line pressure to
the front clutch.
Fig. 30 1–2 Shift Valve-After Shift
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DESCRIPTION AND OPERATION (Continued)
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