Engine exhaust gas energy recovery device

An engine exhaust gas energy recovery device comprising:

• an exhaust gas turbocharger comprising a turbine and a compressor, the turbine being driven by the exhaust gas discharged from the engine, the compressor compression-transporting outside air to the engine body by driving the turbine;
• a first exhaust pipe connecting the exhaust gas turbocharger to an exhaust manifold of the engine;
• a power turbine being driven by the exhaust gas;
• a second exhaust pipe connecting the exhaust manifold to the power turbine;
• a gas flow-rate control valve being provided on the way of the second exhaust pipe so as to control the flow-rate of the exhaust gas fed to the power turbine;
• a bypass pipe being connected to the second exhaust pipe which is provided on the upstream side of the gas-flow rate control valve so as to bypass the power turbine;
• an exhaust gas bypass control valve which is provided on the way of the bypass pipe and which controls the flow-rate of the exhaust gas bypassing the power turbine;
• an engine load detecting sensor which detects the load of the engine;
• an engine speed detecting sensor which detects the speed of the engine;
• a cylinder pressure detecting sensor which detects a cylinder pressure of the engine;
• and a control device which comprises a database computing the optimal compression pressure and the optimal cylinder maximum pressure at which a fuel consumption rate of the engine becomes the optimum operating state on the basis of each value detected by the engine load detecting sensor and the engine speed detecting sensor,
• wherein the control device controls an exhaust valve closing timing so that a compression pressure agrees with the computed optimal compression pressure, and controls a fuel injection timing so that a cylinder maximum pressure agrees with the computed optimal cylinder maximum pressure.