Pressure control system for automotive pneumatic pressure supply line

A pressure control system for a pneumatic pressure supply line installed in a vehicle, the supply line including a compressor driven by an engine of the vehicle and an accumulator communicated with the compressor through a pressure supply conduit, characterized by comprising:

• an unloading pressure control valve selectively urging a spring-loaded intake valve of the compressor to an open position;
• a pressure feedback conduit communicating the accumulator to the unloading pressure control valve;
• a solenoid operated valve disposed in the pressure feedback conduit to block and unblock the communication of the accumulator to the unloading pressure control valve;
• a load sensor responsive to a load acting on the engine;
• a pressure sensor responsive to an accumulator pressure;
• and
• a control unit controlling the solenoid operated valve in response to an output signal of the load sensor and that of the pressure sensor, the control occurring, for a heavy load engine operation, in a first mode wherein the solenoid operated valve opens at a first predetermined level of accumulator pressure during an elevation of the accumulator pressure while closing at a second predetermined level of accumulator pressure which is lower than the first predetermined level by a substantial amount during a drop of the pressure, and, for a light load engine operation, in a second mode wherein the second predtermined level is at least closer to the first predetermined level than in the first mode.