After the nominal speed, the DC motor speed control is made by modifying the flux and maintaining the armature voltage constant and this is called the field https://www.mrosupply.com/popular_products/thrust-ball-bearings/ weakening zone. To increase the speed, it will suffice to reduce the flow, so that the armature current increases transiently, in order to produce the total torque required by the load. This conjugate increases the speed of the engine and the electromotive force induced in the engine also rises.
The DC motor operates the essentially constant armature current. The level of this current is checked by the load on the shaft. The motor has the ability to actuate the load by exerting a constant torque at any established rotation, which represents the characteristic curves of the DC motors.
The torque can be any up to the nominal value limit, which corresponds to a nominal armature current, defined by thermal aspects of motor design. The transient current falls to an equilibrium point, which corresponds to the maintenance of the torque required by the load. Only during the accelerations caused by the increase of tension that temporarily the current rises to cause the acceleration of the machine, returning then to its original value.