8INGLB-PBA8B MOTORS 289 



the maximum torque occurs when the brushes are in the neutral 

 piano, that is at right angles to the flux. No torque would be 

 developed were the brush axis parallel to that of the flux. 



There must be a component of the current in time-phase with the 

 flux (see Par. 103, page 237). If there is 90 time-lag between 

 t he current and the flux, the current is a maximum at the instant 

 the flux is zero, etc., and the average torque is zero. With flux, 

 armature current and brush position all fixed, the maximum 

 torque occurs when the flux and armature current are in time- 

 phase with each other. 



1'nder the conditions shown in Fig. 265, the brush axis is 

 parallel to the resultant flux. That is, the angle between the flux 

 and the brush axis is zero. A consideration of Fig. 265 (a) shows 

 that the current flows in opposite directions in the two equal 

 conductor belts on each side of the brush axis. Although it 

 can be shown that the armature current is nearly in time-phase 

 with the flux, no torque is developed because of the space position 

 of the brushes. 



Hence in this type of motor, no torque is developed when the 

 brush axis is at right angles to the flux, for then there is no cur- 

 rent ; no torque is developed when the brush axis is parallel to 

 the flux, because the ampere-conductors under each pole develop 

 opposite and equal torques. 



It is obvious, however, that if the brushes be placed in some 

 intermediate position, they will be short-circuiting points of the 

 winding between which a difference of potent ial exists and there- 

 urrents will flow in the winding, and also the net ampere- 

 conductors under each pole cannot be zero. It can be shown by 

 a close analysis that the armature current is substantially in 

 time-pha.-e wii), the flux. Tl lerefore, under these conditions 

 the motor develops torque, and if allowed to do so, the armature 

 will rotate. 



<ft) shows the bm>h axis making an'angle with 



the p,|,- judg. The fcTTOWfl in this figure show the direction of 



the armature current at the instant when the upper wire is posi- 



uid th.- current i< increasing positively, I '06 (6) 



>hnw< diagrammatically the g.-ncial direction of tlie>.- currents 



through the armature antl brushes. It will be observed that 



iiTent direction in the conductors under each pole is such 



10 



