Honda Acura NSX 1991, Service Manual, Page: 391 / 1420

Description
The automatic transmission is a combination of a 3-element torque converter and a triple-shaft electronically controlled
automatic transmission which provides 4 speeds forward and 1 in reverse. The entire unit is positioned in line with the
engine.
TORQUE CONVERTER, GEARS AND CLUTCHES
The torque converter consists of a pump, turbine and
assembled in a single unit.
They are connected to the engine crankshaft so they turn together as a unit as the engine turns.
Around the outside of the torque converter is a ring gear whi
h meshes with the starter pinion when the engine is being
started. The entire torque converter assembly serves as a flyw e e l while transmitting power to the transmission mainshaft.
The transmission has three parallel shafts, the mainshaft, the countershaft, and the secondary shaft. The mainshaft is
in line with the engine crankshaft.
The mainshaft includes the clutches for Ist, and and gears for Reverse and 1st (3rd gear is integral with
the mainshaft, while reverse gear is integral with 4th gear).
The countershaft includes the clutches for Ist-Hold and
and gears for Reverse and 1st.
The secondary shaft includes the 2nd clutch and gears for 2nd and 3rd.
The 4th and reverse gears can be locked to the countershaft at its center, providing 4th gear or Reverse, depending on
which way the selector is moved.
The gears on the mainshaft and secondary shaft are in constant mesh with those on the countershaft.
When certain combinations of gears in the transmission are engaged by clutches, power is transmitted from the mainshaft
to the countershaft to provide 1, 2, 3, and D.
ELECTRONIC CONTROL
The electronic control system consists of an automatic transmission control unit, sensors, a linear solenoid and 4 solenoid
valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions.
The A/T control unit is located on the insulator center bulkhead, behind the driver’s seat.
HYDRAULIC CONTROL
The valve assembly includes the main valve body, secondary valve body, servo valve body, regulator valve body, lock-up
valve body and the 2nd accumulator body.
They are bolted to the torque converter case as an assembly.
The main valve body contains the manual valve, 1-2 shift valve, 2-3 shift valve, 3-4 shift valve, relief valve, one-way
relief valve and oil pump gears.
The secondary valve body contains the 3-2 kick-down valve, CPC (clutch pressure control) valve, 2nd orifice control
valve, 3rd orifice control valve, modulator valve, 4th exhaust valve, servo control valve, 2nd exhaust valve and 4-3
down valve.
The servo valve body contains the accumulator pistons and servo valve. The throttle valve body includes the throttle
valve which is bolted onto the servo body.
The regulator valve body contains the pressure regulator valve, lock-up control valve and cooler refief valve. Fluid from
the regulator passes through the manual valve to the various control valves.
The lock-up valve body contains the lock-up timing B valve and lock-up shift valve. The 2nd accumulator body contains
the accumulator pistons and LSD relief valve.
The torque converter check valve is located in the torque converter housing, under the main valve body.
The Ist, Ist-Hold, 3rd and 4th clutches receive oil from their respective feed pipes.
SHIFT CONTROL MECHANISM
Input from various sensors located throughout the car determines which shift control solenoid valve the A/T control unit
will activate. Activating a shift control solenoid valve changes modulator pressure, causing a shift valve to move. This
pressurizes a line to one of the clutches, engaging that clutch and its corresponding gear.
LOCK-UP MECHANISM
In 3 or D
in 3rd and 4th. pressurized fluid is drained from the back of the torque converter through an oil
passage, causing the lock-up piston to be held, against the torque converter cover. As this takes place, the mainshaft
rotates at the same speed as the engine crankshaft. Together with hydraulic control, an electronic control unit optimizes
the timing of the lock-up
The lock-up valves control the range of lock-up according to lock-up control solenoid valves A and B, and throttle valve
B. When lock-up control solenoid valves A and B activate, modulator pressure changes. The lock-up control solenoid
valves A and are mounted on the torque converter housing, and are controlled by the A/T control unit.