Most transmission shops don’t have the facilities to cut open a converter to see what’s going on in there. There’s the odd occasion when you send a converter out to get it cut open so the whole shop can see what’s going on and perhaps understand the mystery of the converter clutch better, but that’s the exception; not the rule.
In this issue of Fun with Transmissions, we’re going to see what’s happening inside the new Honda 6-speed torque converter. And we’re going to examine what makes it different — and possibly more durable — than previous design Honda/Acura converter clutches. Honda doesn’t make substantial changes in their designs very often, so when they do it’s newsworthy.
The previous design Honda converter has been used in every Honda lockup application since the early eighties. The design works like so many other OE converter clutches: The clutch plate is splined to the turbine (figure 1). Converter charge oil keeps the converter clutch away from the face of the converter housing while the converter clutch is off (figure 2).
The apply circuit works similar to a 4L60E: An on/off solenoid controls the shift valve (converter clutch on/off), and a pulse width modulated (PWM) solenoid controls the rate of apply (figure 3). When the computer commands lockup, the shift valve moves to allow the converter clutch to apply; the pulse width modulated solenoid controls the rate of apply. This way the computer can control the “feel” of the converter clutch apply.
The new Honda/Acura 6-speed was first introduced in Acuras in 2010. Honda introduced it in the Odyssey in 2011. The new 6-speed torque converter clutch has a clutch drum with friction plates, steel plates, a pressure plate, and a retaining snap ring (figure 4). The turbine has a clutch hub welded to it that splines to the friction plates (figure 5).
With the piston turned over, you can see how the piston splines to the cover to keep it from turning when it applies the clutches (figure 6).
The previous design converter clutch is applied by draining oil from the front of the converter. So when we say the computer controls the rate of apply, what’s really happening is the computer controls the rate of drain, which, in turn, controls the rate of apply.
The 6-speed converter clutch works the same as any other clutch drum in the transmission. Where the previous design converter used three valves for lockup, the 6-speed has two:
1. Shift solenoid C controls the lockup shift valve (converter clutch on/off).
2. Clutch pressure control (CPC) solenoid D, a pulse width modulated solenoid, controls the converter clutch drum’s rate of apply.
When the computer commands lockup, the shift valve strokes; this allows the converter clutch to apply. The CPC D solenoid pulses on to move the lockup control valve to the left, opening the passage to feed oil to the clutch drum (figure 7).
Lockup can occur in all forward ranges while accelerating and in 2nd through 6th while decelerating.
That’s all there is to it; a fairly simple system designed to improve converter clutch durability and performance. And once you understand how the system works, it’s easy to understand. And that makes it easy to have fun with transmissions!