THROTTLE VALVE
In all gear positions the throttle valve (Fig. 40) is
being supplied with line pressure. The throttle valve
meters and reduces the line pressure that now
becomes throttle pressure. The throttle valve is
moved by a spring and the kickdown valve, which is
mechanically connected to the throttle. The larger
the throttle opening, the higher the throttle pressure
(to a maximum of line pressure). The smaller the
throttle opening, the lower the throttle pressure (to a
minimum of zero at idle). As engine speed increases,
the increase in pump speed increases pump output.
The increase in pressure and volume must be regu-
lated to maintain the balance within the transmis-
sion. To do this, throttle pressure is routed to the
reaction area on the right side of the throttle pres-
sure plug (in the regulator valve).
The higher engine speed and line pressure would
open the vent too far and reduce line pressure too
much. Throttle pressure, which increases with engine
speed (throttle opening), is used to oppose the move-
ment of the pressure valve to help control the meter-
ing passage at the vent. The throttle pressure is
combined with spring pressure to reduce the force of
the throttle pressure plug on the pressure valve. The
larger spring at the right closes the regulator valve
passage and maintains or increases line pressure.
The increased line pressure works against the reac-
tion area of the line pressure plug and the reaction
area left of land #3 simultaneously moves the regu-
lator valve train to the right and controls the meter-
ing passage.
The kickdown valve, along with the throttle valve,
serve to delay upshifts until the correct vehicle and
engine speed have been reached. It also controls
downshifts upon driver demand, or increased engine
load. If these valves were not in place, the shift
points would be at the same speed for all throttle
positions. The kickdown valve is actuated by a cam
connected to the throttle. This is accomplished
through either a linkage or a cable. The cam forces
the kickdown valve toward the throttle valve com-
pressing the spring between them and moving the
throttle valve. As the throttle valve land starts to
uncover its port, line pressure is “metered” out into
the circuits and viewed as throttle pressure. This
increased throttle pressure is metered out into the
circuits it is applied to: the 1–2 and 2–3 shift valves.
When the throttle pressure is high enough, a 3–2
downshift will occur. If the vehicle speed is low
enough, a 2–1 downshift will occur.
Fig. 40 Throttle Valve
21 - 34
42RE AUTOMATIC TRANSMISSION
WJ
DESCRIPTION AND OPERATION (Continued)