,It is important to appreciate(知道) that the choice of gear ratios in a transmission is often dictated(限制）, in practice, by what is available or what is already in production. This situation occurs because of the large expense involved in engineering new gear sets, and installing or modifying the manufacturing plant to make the new parts. There are some cases that do necessitate a change, however. These may include a change in the engine, for example, from petrol to diesel, or a signicant change to the weight of the vehicle in which the gearbox is to be installed.,Chapter 11 Automotive Design 11.1 Changing Ratios Matching of The Transmission to The Vehicle,Where changes can be accommodated, they may be limited to one or two gear ratios, leaving the intermediate ratios as is(原样，照原来样子）, hence not necessarily optimized. Finally, before looking at how the ideal ratio may be chosen, the other limitation on ratio choice is the gear design itself. An example is a rst gear pair where there could be a limit on how small the drive pinion might be in order to withstand the shock loading which can occur in the gearbox. There are a number of decisions that need to be made when deciding what gear ratios should be tted in a particular transmission unit.,Chapter 12 Automotive Manufacturing,补充：Car Design Process 12.1 Vehicle Architecture Design and manufacturing 车辆结构的设计与制造 12.2 Injection Moulding 注射成型技术 12.3 Joining For Lightweight Vehicles 轻量化汽车的连接技术,学习内容,本次课学习内容、目标和重点难点,学习目标,难点重点,Automotive Design Car Design Process 12.1 Vehicle Architecture Design and manufacturing,1.掌握汽车设计的九个步骤 2.掌握汽车车身设计的特点,1.重点：汽车设计术语；长句翻译方法； 相关术语的记忆 2.难点：长句翻译,自学补充材料汽车设计过程,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and anufacturing,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and anufacturing,New Words,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and anufacturing,New Words,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and manufacturing,New Words,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and manufacturing,The automotive industry utilizes a wide spectrum of manufacturing processes to effectively and economically accommodate different vehicle production volumes. In order to develop the most cost effective production strategy, investment in tooling (fixed cost) must be balanced with variable cost for a given volume. For very low-volume production, minimization of investment is paramount. This is usual in the specialty car industry, where the annual production volumes may be less than 1000 units. In these cases, more expensive materials and somewhat longer cycle times can be tolerated to minimize investment in tooling and equipment.,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and manufacturing,For more medium-volume production (in the order of 25 000 units per year), the use of automation is the key enabler in achieving competitive costs and cycle times. For high-volume production (such as vehicles where the total volume over a six-year cycle can be several million vehicles), the fixed cost is spread over the millions of vehicles produced. Therefore, minimizing variable costs are critical; lower cost materials and rapid cycle times are crucial to the economic success of the product. Thus, the need to manage in vestment in tooling and equipment with variable cost has a significant effect on how a vehicle body is designed.,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and manufacturing,In response to this, several approaches to vehicle design exist, including body-on-frame, monocoque, space frame, and unibody. The original method for vehicle body design, body-on-frame, is mostly used today for trucks. It is well suited to high volume production and is based on a body structure attached to (but independent of) the chassis system. In monocoque construction, a vehicle structure is made from extrusions and relatively simple stampings or break forms. This creates a very simple, tub-like(木盆形） structure which offers attachment points for the chassis, the front end, and the closure panels. Because this method minimizes the number of stampings and castings, the number of expensive dies for forming and casting is also minimized; thus, monocoque construction is a very low-investment method for body design.,Chapter 12 Automotive Manufacturing 12.1 Vehicle architecture design and manufacturing,In the space frame approach, frame members are typically fabricated from extrusions. These extrusions are usually joined together by castings called nodes. This frame is then used to carry the loads and offer attachment points for the outer panels（Figure 12-1）. This approach is well designed for low- to medium volume vehicle production runs. In the unibody approach, the vehicle body is composed mostly of stampings joined together to integrate the body and the chass