牵引电动机的主要作用是什么？
["\u7275\u5f15\u7535\u673a\u662f\u673a\u8f66\u8fdb\u884c\u673a\u68b0\u80fd\u548c\u7535\u80fd\u76f8\u4e92\u8f6c\u6362\u7684\u91cd\u8981\u90e8\u4ef6\u3002\u5b83\u5b89\u88c5\u5728\u673a\u8f66\u8f6c\u5411\u67b6\u4e0a\uff0c\u901a\u8fc7\u4f20\u52a8\u88c5\u7f6e\u4e0e\u8f6e\u5bf9\u76f8\u8fde\u3002\u673a\u8f66\u5728\u7275\u5f15\u72b6\u6001\u65f6\uff0c\u7275\u5f15\u7535\u673a\u5c06\u7535\u80fd\u8f6c\u6362\u6210\u673a\u68b0\u80fd\uff0c\u9a71\u52a8\u673a\u8f66\u8fd0\u884c\u3002\u5f53\u673a\u8f66\u5728\u7535\u6c14\u5236\u52a8\u72b6\u6001\u65f6\uff0c\u7275\u5f15\u7535\u673a\u5c06\u5217\u8f66\u7684\u673a\u68b0\u80fd\u8f6c\u5316\u4e3a\u7535\u80fd\uff0c\u4ea7\u751f\u5217\u8f66\u7684\u5236\u52a8\u529b\u3002"]