题目内容
数据库应用系统开发一般应包括两个方面的内容，它们是结构特性设计和______特性设计。
查看答案
搜索结果不匹配？点我反馈
更多问题
证券清算、交割、交收业务应遵循钱货两清和货银对付两条原则。( )
牙齿稀疏松动，齿根外露，多为( )
能泻火存阴的药物多具有( )
There are many innovations turning up in the latest experimental and production electric cars, affecting everything from batteries to motors to control systems. The need to make them all work together is prompting a complete rethink about the way cars should be designed and manufactured, and it is unclear which technologies will dominate as the constraints imposed by internal combustion engines give way to the new limits and possibilities associated with electric propulsion. (46) But one group of engineers have stuck their necks out and declared that a particular technology, the electric hub motor, is likely to become the most widely used drive system.At this week’s Deutsche Messe technology show in Hanover, researchers at the Fraunhofer Institute displayed an electric vehicle which they are using as a test platform to investigate new vehicle systems. (47) It includes electric hub motors, which they have developed to be markedly more powerful than any such motors currently available. The motors have all the necessary power and control systems integrated into the wheel hub, greatly reducing the number of connections between the hub motors and the rest of the vehicle.(48) Because hub motors can deliver power independently to each wheel, tricks like four-wheel-drive are possible, and with software monitoring each wheel, stability and traction control can also be built-in. Besides dispensing with the traditional engine bay on a car, hub motors save space and weight because there is no need for a mechanical transmission, with its driveshafts and differential units.(49) Some critics of the technology think having heavy electric motors in the wheels of cars will have a negative effect on vehicle handling. But Hermann Pleteit, a project manager with one of the 33 Fraunhofer research centres that have teamed up to work on the experimental car, says the chassis and many other parts of the vehicle can be configured in such a way to compensate for this.Several carmakers and component suppliers are interested in hub motors. Michelin, for one, is developing a system it calls the Active Wheel. (50) As well as an electric motor to drive the wheel, it contains a second electric motor to operate an active suspension system that is also built into the wheel hub. Michelin reckons this arrangement, which is now being tested in cars, could make other conventional parts, like shock absorbers, unnecessary. Because hub motors can deliver power independently to each wheel, tricks like four-wheel-drive are possible, and with software monitoring each wheel, stability and traction control can also be built-in.
微信支付 
支付宝支付