3.2 Evaluation test of electronically controlled hydraulic-driven fuel injection system and exhaust valve system
In this study, the following values are targeted.
* Fuel injection system :
injection pressure＞120 MPa (currently 70 MPa)
injection duration＜18 deg.
* Exhaust valve system :
opening/closing valve speed＞3 m/s
In the design of the fuel injection system and the exhaust valve system, the dimensions and particulars are planned considering the actual use in the performance test by the single cylinder test engine.
3.2.1 Basic design of system
(1) Fuel injection system
Fig. 7 shows the construction of the fuel injection system. The pressure in the accumulator is supplied to the lower side of the booster piston by opening the open side logic valve through the 5-port electromagnetic spool valve. The plunger of the fuel injection pump is lifted thereby to achieve the injection. After the required injection, the close side logic valve is opened to release the pressure of the booster piston, and at the same time, the open side logic valve is closed, and the supply of the hydraulic pressure is stopped to complete the injection.
Fig. 7 Construction of fuel injection system
The system is designed based on the accumulation pressure of Pacc=35 MPa. The injection is 12.8 cc/cycle from the engine requirement. The boosting ratio 120/35=3.42 is necessary from the ratio of the target injection pressure of 120 MPa to the accumulation pressure. In an actual condition, the efficiency is estimated to around 85% taking into consideration the reduction in the volume elasticity during the operation and the drop of the accumulation pressure. As a result, the plunger diameter should be 27.5 mm when the booster piston diameter is 55 mm. So, the plungers of 28 mm and 26 mm in diameter are prepared for the test. The diameter of the injection pipe is 4.5 mm from the calculation considering the total area of injection nozzle holes. Table 3 shows the principal particulars of these injection systems.
Fig. 8 Construction of exhaust valve system
(2) Exhaust valve system
Fig. 8 show the construction of the exhaust valve system. The supply of the accumulating oil pressure is controlled by the open side electromagnetic spool valve and the close side one which are independently provided. When the open side electromagnetic spool valve is operated and the open side logic valve is opened. the hydraulic pressure is supplied to the actuator, and the piston is pushed down to open the exhaust valve. The piston of the actuator is double-staged, and at the beginning of the opening of the valve. the hydraulic pressure is supplied to the large diameter part to open the valve at high speed. After that, as the hydraulic is supplied only to the small diameter piston part and the valve opening speed is reduced, the quantity of the working fluid and the hydraulic power are saved.
