| With car sales rising year by year,fuel cars continued to increase,the harm to the environment of automobile exhaust gas is more obvious.Both engine manufacturers and researchers are eager to find a new type of internal combustion engine which can not only have good power and fuel economic performance,but also have excellent discharge performance.Under this background,the engine variable technology arises at the historic moment.Through comprehensive adjustment of engine performance parameters(such as gas distribution timing,compression ratio,intake pipe length,etc.)engine variable technology make the engine in each kind of different conditions work in the best state,play to the engine’s maximum potential and have excellent economy and emissions.Variable compression ratio technology has great potential.In this paper,the structural design of the crankshaft connecting rod of the four-cylinder VCR engine is completed with reference to the parameters of a Fiat engine.The structure and motion principle of the VCR engine are analyzed in detail,and the parameters of the important structure are analyzed and checked.Completed the check of VCR engine connecting rod of ultimate strength conditions,the results show that the VCR engine and parts meet the strength requirements.This paper designs the hydraulic system of VCR engine crankshaft connecting rod,analyzes the control requirements and characteristics of hydraulic system,and calculates and selects the components such as servo valve,hydraulic pump and bidirectional hydraulic lock.Design of crankshaft connecting rod hydraulic system control circuit,including:control chip,power distribution circuit,input signal conditioning circuit and analog voltage output circuit.Based on the AMESim software platform,the motion characteristics of the hydraulic system are simulated to verify the feasibility and effectiveness of the hydraulic system in the operation stability,the closed loop control of the servo valve and the two-way fast locking of the neutral function.By using the uniform design method,the power,economy and emptivity of the VCR engine designed in this paper are analyzed in the GT-POWER software.The VCR engine optimal compression ratio is obtained by the quadratic polynomial stepwise regression method under the typical operating conditions.The BP neural network algorithm is used to establish the hydraulic oil density prediction model to realize the accurate prediction of density under different temperature and pressure.According to the requirements of the hydraulic control system,the hydraulic system working process is established and the control system model is built by Simulink.The simulation results show that the hydraulic control system can adjust the length of the crankshaft connecting rod of the VCR engine in real time to achieve the best engine compression ratio under different working conditions. |
