As with any automotive alternator or generator since they were first added to cars about 70 or 80 years ago, there is a regulator. Although there is no clutch and the alternator mechanically turns at any time the engine is running, it is not producing anything electrically unless the regulator determines that it must do so.
Before the invention and application of semiconductors to the automobile, this was done with electromechanical regulators. If the voltage sank to a certain level, a relay contact was energized which completed the circuit between the generator and battery.
Now that we have semiconductor based regulators, there is an active device that conducts electricity to the battery at such a time when the battery becomes low on charge.
So, no mechanical clutch, but there is automatic electrical management to prevent 80 amps from being developed at times when it is not needed or wanted.
Hope this helps,