Observations, ZF 8 HP, no fluid torque converter

[meep]

This is pretty wild. After a few weeks in the Tacoma hybrid, I’ve noticed that sometimes if I need to launch quicker, it had the same feel of a stick as the driver would release the clutch under load until it hooks. Did some reading - there is no liquid torque converter in this transmission. The bell housing is filled with the motor/generator instead.

Under gentle launch, the motor seems to provide launch to 3-4 mph and the engine “starts” and the vibration felt during starting probably includes some form of clutch engagement. Under harder launch, it’s all happening at the same time - electric launch, engine starting but reaching for higher revs, with the sensation of a clutch locking it in.

Upon reading that there is no TC, it must be the case where the computer essentially “clutches in” gear, which may actually be second under those conditions - first or second. It’s an interesting setup. At least all that is happening in a wet clutch system.

Theres not much out on this unit - anyone have any experience with it?

 

[MCompact]

The BMW and Jeep PHEVs use the 8HP with the same powertrain layout.

 

[Jetronic]

This is pretty wild. After a few weeks in the Tacoma hybrid, I’ve noticed that sometimes if I need to launch quicker, it had the same feel of a stick as the driver would release the clutch under load until it hooks. Did some reading - there is no liquid torque converter in this transmission. The bell housing is filled with the motor/generator instead.

Under gentle launch, the motor seems to provide launch to 3-4 mph and the engine “starts” and the vibration felt during starting probably includes some form of clutch engagement. Under harder launch, it’s all happening at the same time - electric launch, engine starting but reaching for higher revs, with the sensation of a clutch locking it in.

Upon reading that there is no TC, it must be the case where the computer essentially “clutches in” gear, which may actually be second under those conditions - first or second. It’s an interesting setup. At least all that is happening in a wet clutch system.

Theres not much out on this unit - anyone have any experience with it?

Are there gears at all? oh yes, zf 8 hp...

This type of setup is used on geared cars, but if only one gear forward, the engine tends to drive a generator that in turn runs an electric motor until the vehicle speed is high enough for a direct connection through a clutch. I guess that'w what yours does too, but with gears, the "high enough vehicle speed" is 3-4 mph, instead of 30-40 mph.

 

[Skippy722]

The Grand Cherokee 4xe used a very similar system. I don’t know if it was how I drive, the Jeep’s programming, or what but occasionally mine would feel more like someone just dropping the clutch.