In order to reduce fuel consumption and reduce carbon dioxide emissions, automotive light weight has become one of the focuses of attention. Research shows that the vehicle curb weight. Every 100 reduction in kg, 100 km fuel consumption can be reduced by 0.3~0.6 L. In addition, the car lightweight can also improve the power of the car, save materials and reduce costs. It was expected that by 2010 the average vehicle kerb mass will reduce 17%, namely 250 kg; car servicing quality will be reduced to 1000 kg from the current average of about 1300 kg.
In addition to the above objectives, the light weight of the engine involves the mass distribution of the vehicle (vehicle dynamics). The gasoline engine is changed into a diesel engine, the engine will often make weight (solid structure, turbocharger, turbo air cooler, fuel injection device, etc.) to front axle load increase, making the equilibrium of the vehicle has been destroyed. Therefore, the light weight of car engine has become a problem that can not be ignored in vehicle development.
The way to reduce the weight of engines is to increase the power to reduce the quality of the unit power. The state-of-the-art power density index is approaching 1 kg/kW. Take the car diesel engine as an example, if the power increase in early 1990s is only hovering at 20-30 kW/L, then the upward trend since the end of twentieth Century can be described as "leaps and bounds"". Today, the maximum explosive pressure has reached 20 MPa, and the power has reached 60 kW/L.
Discussion on casting process of aluminum alloy body
The casting process of aluminum alloy body can be divided into many moulds (metal mould) and one mold (sand mould). The method of making sand cores is also different. Nowadays, sand casting and die casting are the most commonly used in mass production. Sand mold gravity casting provides the largest degree of freedom in molding, and closed cylinder head connections (closed top) can be used. Die casting is an economical solution if the number of pieces is higher (with an annual output of more than 200 thousand pieces). Die casting can realize thin-walled casting structure with very short beat, fine surface quality and precise size. However, due to the high mold filling pressure, the sand core can not be used, and the water jacket usually has to be opened up (open top). This means that the cylinder bore lacks radial support. However, even that may not cause severe deformation of the cylinder. Now, even direct injection diesel engines can be made into open roof structures. In addition, the rapid mold filling process leads to the formation of bubbles, so that the mechanical properties can not be improved by thermal aging hardening. This disadvantage can be avoided by squeeze casting because the lower pressure used in the process significantly slows the mold filling process and is likely to make up. In addition, die casting has an indirect effect on the length of the water jacket. Because the diameter of the cylinder, bolt position, sealing flange and the minimum width required is usually 0.5 degrees of taper and other factors, the actual water jacket made of die cast body usually at least cover only the stroke of the piston 70%. This will reduce the heat flow through the piston ring and increase the heat load of the engine oil. In the aspect of airframe structure, die casting has some limitations. However, these can be controlled by technical means. Whether the body adopts die casting process, the first or the production batch.
For heavy duty engines, sand casting is preferred to produce reliable and durable airframe by proper molding process, alloy optimization and heat treatment. From the cost of parts, the full use of sand casting in the molding of greater degree of freedom, but also can be integrated into a variety of functions in the cylinder block, in general to reduce quality and improve economic efficiency.
Problems to be solved for aluminum alloy body structure
The casting of aluminium alloy for grey cast iron cylinder must meet some additional requirements, as described below
1) make sure the cylinder is sliding and the surface is wear-resistant and difficult to deform
2) meet the requirements of the transfer force flow
3) control the expansion of the main bearing clearance
Effect of lower elastic modulus on acoustic and vibration of 4 aluminum alloy
The lightweight of engine block by means of material and structure
1) measures for sliding surfaces of cylinder tubes
2) ensure that the force flow passes and controls the clearance of the main bearing
3) measures to ensure structural dynamic characteristics
Cost performance analysis
The cost performance analysis of the 2 L 4 cylinder engine made of gray iron, vermicular graphite cast iron and aluminum alloy is carried out. The result is shown in table 1.
According to the calculation of annual output of 400 thousand, using vermicular cast iron, raising the cost of 38%, blank cost and machining cost increase to the same extent; the Aluminum Alloy body, raising the cost of 62%, is the main material prices higher. The cost advantages of aluminum alloys in machining are greatly weakened by a variety of hybrid processes.
Cost performance analysis shows that aluminum alloy structure has great potential. Only when the overall arrangement is very compact (the center of the cylinder is small), the material properties of compacted graphite iron will emerge.