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Re: why doesn't LPT have one???? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 24 May 2002 08:26:04
In Reply to: why doesn't LPT have one????, Brian, Fri, 24 May 2002 05:43:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The APC works by reducing the maximum available boost. It can cut it from full to about half. It cuts the boost if it detects knock. The engine is designed so that jwith a mildly degraded engine and 87 octane (US) gas, the engine won't knock at half ("Base") boost.
The LPT engine already runs at this 'base' boost level - that's why its 'low pressure'. So there is no reason to add circuitry and an actuator that would otherwise do nothing.
Turbo boost is limited by a wastegate - basically, there is a lever under the turbo that allows air to bypass the turbo, reducing the output pressure. This lever is driven by a Wastegate Actuator, which is just a piston with a spring. The piston is connected by an air line to the intake manifold. With little or no boost, there is no pressure on the actuator, and it stays put. As the boost pressure increases, the piston moves against the spring. When the pressure is great enough, the piston will move the wastegate on the turbo, reduciing boost.
The APC system works by 'fooling' the wastegate actuator. At the 'base' boost setting, all the pressure from the intake manifold goes to the wastegate actuator. Under normal operation, no knock, the APC energizes the APC solenoid. This solenoid diverts some of the air going to the wastegate actuator. So the wastegate actuator sees a lower pressure than that in the intake manifold - so it allows greater pressure in the intake before it moves the wastegate to limit boost. The APC detects knock, it de-energizes the APC solenoid, and the wastegate actuators sees the 'true' pressure, and limits boost.
With the later Trionic cars, there is more to it, as there always is. But these are the basics.
posted by 140.157.4...
, Fri, 24 May 2002 08:26:04 <-- Viewing This Message
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