On-desire AWD systems travel the secondary axle by using an active or passive coupling device or "by an independently powered generate technique". The regular notes that in some cases, the secondary generate technique may also deliver the primary vehicle propulsion. An illustration is really a hybrid AWD car or truck https://groupak.gr/%CE%BF%CF%80%CE%AF%CF%83%CE%B8%CE%B9%CE%BF%CE%B9-%CF%80%CE%AF%CF%83%CF%89-%CF%80%CF%81%CE%BF%CF%86%CF%85%CE%BB%CE%B1%CE%BA%CF%84%CE%AE%CF%81%CE%B5%CF%82