SAE (Society of Automotive Engineers)，汽车工程师学会对于汽车的四驱系统（准确讲应该是多轮驱动系统）的分类是有它的一套推荐的做法的，先放一张图：
下面是维基百科中 SAE 关于四驱系统分类的说明：
Per the SAE International standard J1952, AWD is the preferred term for all the systems described above. The standard subdivides AWD systems into three categories.
根据 SAE J1952 标准，AWD 是对下面描述的所有四驱系统的推荐术语。该标准将 AWD 系统细分为三类。
Part-Time AWD systems require driver intervention to couple and decouple the secondary axle from the primarily driven axle and these systems do not have a center differential (or similar device). The definition notes that part-time systems may have a low range.
分时四驱系统需要驾驶员介入来接通和断开第二驱动轴和主驱动轴的连接，并且这些系统没有中央差速器（或者类似的装置）。该定义指出分时系统可能有低速档。
Full-Time AWD systems drive both front and rear axles at all times via a center (inter-axle) differential. The torque split of that differential may be fixed or variable depending on the type of center differential. This system can be used on any surface at any speed. The definition does not address inclusion or exclusion of a low range gear.
全时四驱系统通过中央差速器同时驱动前轴和后轴。根据中央差速器的不同类型，扭矩分配可能是固定的也可能是可变的。全时四驱系统可以在任何路面任何速度下使用。该定义没有规定需要包含或者不包含低速档。
On-Demand AWD systems drive the secondary axle via an active or passive coupling device or 'by an independently powered drive system'. The standard notes that in some cases the secondary drive system may also provide the primary vehicle propulsion. An example is a hybrid AWD vehicle where the primary axle is driven by an internal combustion engine and secondary axle is driven by an electric motor. When the internal combustion engine is shut off the secondary, electrically driven axle is the only driven axle. On-demand systems function primarily with only one powered axle until torque is required by the second axle. At that point either a passive or active coupling sends torque to the secondary axle.
适时四驱系统通过一个主动或者被动的耦合装置来驱动第二驱动轴，或者用一套独立的动力系统来驱动第二驱动轴。标准指出在某些情况下第二驱动轴也会承担起驱动车辆的主要角色。一个例子就是混合动力 AWD 汽车，它的主驱动轴是由内燃机驱动的，第二驱动轴是又电机驱动的，当内燃机停机时，由电机驱动的第二驱动轴就成了车辆的唯一驱动轴。适时四驱系统主要是由主驱动轴来提供动力，直到第二驱动轴也需要扭矩，此时再主动或者被动的将扭矩分配给第二驱动轴。
In addition to the above primary classifications the J1952 standard notes secondary classifications resulting in a total of eight system designations:
除上述主要分类外，J1952 标准还注明了二级分类，总共有八个子类：
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