Controlled Deceleration Device: Operation

The Boost Controlled Deceleration Device (BCDD) contains 2 diaphragms. When vacuum in the intake manifold exceeds a pre-determined value, diaphragm I opens the vacuum control valve. This allows manifold vacuum into a vacuum chamber in the BCDD and actuates diaphragm II. When actuated, diaphragm II opens the air control valve, allowing additional air into the manifold to maintain required operating pressure.

The amount of air entering the manifold is controlled by the servo-action of the air control valve and vacuum control valve. This servo-action maintains manifold vacuum at the predetermined operating pressure.

Fig 1: Datsun Maxima BCDD System Schematic

Courtesy of NISSAN NORTH AMERICA, INC.

Intake manifold operating pressure (vacuum) changes depending on altitude at which the vehicle is being operated. To compensate for this, an altitude compensator is incorporated in the BCDD of 280ZX models. The altitude compensator automatically adjusts the operating pressure in response to altitude.

Fig 2: Datsun Stanza BCDD System Schematic

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Fig 3: Datsun 280ZX BCDD System Schematic

Courtesy of NISSAN NORTH AMERICA, INC.