图示为一无同步器的五档变速器中四、五两档（四档为直接档，五档为超速档）齿轮示意图，试简述其从高速档换入低速档时的换档过程。<br /> <img src="https://nimg.ppkao.com/2019-04/yuanhuijuan/2019041014494389426.jpg?sign=b7c9a713dc15c800539d269e1b5cd1a5&t=62d70161" />