机车信号分为哪几种制式？有何作用？
["\u673a\u8f66\u4e0a\u7684\u7535\u5668\u8bbe\u5907\uff0c\u5176\u914d\u7ebf\u53ca\u5f15\u5165\u7ebf\u95f4\u7684\u7edd\u7f18\u7535\u963b\u5e94\u4e0d\u5c0f\u4e8e0.2\u5146\u6b27\u3002\u6d4b\u8bd5\u65b9\u6cd5:\u7529\u5f00\u6574\u673a\u3001\u4fe1\u53f7\u673a\u6784\u548c\u7535\u6e90\uff0c\u7528500V\u5146\u6b27\u8868\u5206\u522b\u6d4b\u8bd5\u7ebf\u95f4\u7edd\u7f18\u7535\u963b\uff0c\u5176\u963b\u503c\u5e94\u6ee1\u8db3\u4e0a\u8ff0\u8981\u6c42\u3002"]