Series connected series motors for independent loads

Claim 1

An industrial truck having first and second independently rotatable traction wheels for driving contact with the road, both of said wheels exhibit substantially same start-up load torque and running-load torque when both have non-slip adhesive friction with the road, each traction wheel being subject to exhibiting a start-up load torque ranging from a threshold-load torque, which is a value of torque required to initiate motion of the truck when there is a non-slip adhesive friction with the road, to a no-load torque when there is no adhesive friction with the road, a DC voltage source, first and second DC series motors which are substantially identical to each other and are connected electrically in series with each other in a series circuit, each of said first and second DC series motors having an armature winding and a field winding connected in series with each other, switching means for connecting said series circuit across said voltage source for energizing said motors, said first and second DC series motors being mechanically coupled independently of each other in driving relation with said first and second wheels, respectively, each motor being capable of developing a predetermined transient driving torque when the wheel coupled to said each motor exhibits said no-load torque and the other wheel coupled to the other motor exhibits said threshold-load torque, said predetermined transient driving torque having a peak value at a time after motor energization, said peak value of said predetermined transient driving torque being greater than said threshold-load torque, whereby said truck is moved by the traction of the wheel which exhibits the threshold-load torque during a time interval that said peak value of torque is greater than the threshold-load torque.