25 Crank Shalt-Fly Wheel Assemblie网商花M 有和民 @R冷大复 窗且冷大置 窗凡冷复 -的 州国有程 4 12 2.5.3 Maus Balancing 2k4 Theoer and firtng5 quences设气直史大 山业皇大物小 出智 TEA 转自 包R冷？ 位月冷子 15 @R杏大司 Page 4Page 4 28 同济大学汽车学院 • Conrod structure: 1 Shaft (连杆体) 2 Conrod bearing (连杆衬套) 3-4 Conrod bearing shell(连杆轴瓦) 5 Conrod cap(连杆盖) 6-7 Bolt （连杆螺栓） A Oil bore • Big-end eye is normally spit perpendicular to the long axis of the conrod. It could also be split at an angle to reduce the maximum width of the conrod • Conrod fracture splitting (连杆大头胀断) describes the separation of the conrod web and the cap by breaking the latter away during processing:  Reducing the number of processing steps  Secured against relative movement with the irregular surfaces  Eliminating the need for any additional guide elements  Easy matching for multi-cylinder engines 2.5.6 Connecting Rod (Conrod) 29 同济大学汽车学院 • The shafts found in multi-cylinder reciprocating engines generally run in plain bearings. The reasons for selecting this type include their great ability to withstand shock and their damping properties, easy division for assembly around the crankshaft, low space requirements, insensitivity to grime (污垢) , and, last but not least, the low costs when compared with rolling bearings (滚动轴承). However, it has higher friction level and the resulting greater oil requirements. 2.5.7 Conrod bearing shell(连杆轴瓦) • Material: Babbit metals(巴氏合金) Aluminum Alloys Copper Alloys 30 同济大学汽车学院 Crankshaft Drive (曲轴) •Function: Crankshaft drive is a functional group that not only efficiently transforms oscillating movement(back￾forth movement) into rotary movement, but is also excellent at converting thermodynamic processes to yield the maximum work, efficiency, and technical feasibility. These advantages are gained at cost of serious disadvantages: Limitation of speed due to free inertia Uneven force transmission Great deal of stress on the crankshaft and high fluctuations Tribological (摩擦学)problems 2.6 Crank Shaft-Fly Wheel Assemblies(曲轴飞轮组) 31 同济大学汽车学院 • The crankshaft drive in automotive engines consists of pistons with rings, piston pins, conrods, a crankshaft with countermass, crank shaft main bearing, and the lubricant 2.6 Shaft-Fly Wheel Assemblies(曲轴飞轮组) 32 同济大学汽车学院 • Function: The piston’s linear movements are converted, with intervention of the conrod, into rotational movement at the crank, thus making torque available for use at the wheels • Loadings: Because of the stains involving forces that change in both time and location, with rotational and flexural (弯曲) torques and the resulting excitation for vibrations, the crankshaft is subject to very high, very complex loads • Components: Crankshaft front end(1), Crankshaft main journal(2), crank pin(3), crank(4), countermass(5),back-end crank(6) • Number of crank pins determines the number of cylinders 2.6.1 Crankshaft(曲轴) 33 同济大学汽车学院 • Crankshaft could be divided into types by different support pattern, the full￾supported crankshaft and partly￾supported crankshaft • The Full-supported type has a better stiffness and bending strength, therefore is used widely in heavy duty engines. However, finished surfaces and number of main bearings of this type of Crankshaft is more than that of the partly-supported type, and the length of engine would also be longer 2.6.2 Crankshaft support pattern(曲轴支承方式) 34 同济大学汽车学院 • Mass balancing is the compensation of imbalances due to construction. The rotating inertial force (惯性力) can be balanced by countermasses (配重) where the static torque of the rotating masses and the balancing masses must correspond. 2.6.3 Mass Balancing (平衡重) Fig.1 Force balance (受力平衡) Fig. 2 Mass balance (设置平衡重) • It is shown in Fig.1 that the force on the crankshaft has balanced with each other, but the torque couple M1-2 and M3-4 generate bending load to the crankshaft. Therefore, countermasses are employed to improve the loading condition of the crankshaft • Countermasses would increase the total mass of crankshaft, therefore increase the centrifugal force and rotating inertial force, which would put more stress on bearing shells 35 同济大学汽车学院 • To obtain a very even torque characteristic, the ignition of the individual cylinders must be evenly distributed over the power cycle. A requirement is that the throws (曲拐) must be evenly distributed over the perimeter (周长). Hence, the following throw spacing results: Four-stroke engines:720°crankshaft/cylinder number • The firing sequence is also determined by the direction of rotation of the crankshaft. Other factors for the firing sequence are:  No or very small free inertial effects  Favorable rotational oscillation behavior  Good supercharging conditions • Take a inline four-cylinder engine for example, favorable firing sequence could be 1-2-4-3 or 1-3-4-2 2.6.4 Throw and Firing Sequences(曲柄及气缸发火顺序) 36 同济大学汽车学院 2.6.4 Throw and Firing Sequences(曲柄及气缸发火顺序)