Improving the partial-load fuel economy of 4-cylinder SI engines by combining variable valve timing and cylinder-deactivation through double intake manifolds

The SI engines in passenger cars run in the partial-load conditions in the most time especially in the urban driving cycles; thus it is particularly important to improve the partial-load fuel economy. Cylinder deactivation (CDA) and variable valve timing (VVT) could be applied to improve the fuel economy in the middle to low load region. Current CDA technologies are realized by deactivating all intake and exhaust valves (CDAV) of the inactive cylinders with special mechanisms increasing system cost and complexity. An innovative CDA method is proposed for 4-cylinder SI engines through double intake manifolds (CDAM). A novel load control strategy combining the CDAM and VVT along with late intake valve closure (LIVC) has been investigated. The results show that the pumping loss decreases by 58.9-65.6% and 24.5-35.3%; and the fuel economy improves by 5.5-17.6% and 3.1-9.2% in the CDA mode at 2000 rpm and 4000 rpm, respectively. The fuel economy in the full-cylinder mode also improves by 0.68-2.95% because of the application of the double intake manifolds. The strategy is more effective in the low speed range and more suitable for the urban driving cycles. Although a less fuel economy improvement than the CDAV method, the CDAM method can be realized with less cost and complexity.