Brush lifting gear for electrical machines

Claim 2

In an electrical machine having a stator, a rotor, a commutator and at least one pair of commutator brushes, brush lifting gear comprising, brush engaging means mounted on said stator and engaging said brushes, said means being displaceable to move said brushes into and out of contact with said commutator, a rotary solenoid mounted on said stator and energizable to displace said brush engaging means, said rotary solenoid comprising radially inner and outer pole pieces rigid with said stator and defining an airgap, a coil supported on said stator and energizable to generate a magnetic flux across said airgap, and an armature coupled to said brush engaging member and rotatably supported on said stator so as to be movable into said airgap in response to energization of said coil, said armature including an auxiliary portion which bridges said airgap to form a low reluctance path across said airgap when the remainder of the armature has entered the airgap, thereby rendering the solenoid insensitive to subsequent fluctuations in the energization level of the coil, and a thin nonmagnetic liner mounted on said armature to prevent said armature from contacting the pole pieces when it bridges the pole pieces.

Claim 3

In an electrical machine having a stator, a rotor, a commutator and at least one pair of commutator brushes, brush lifting gear comprising, brush engaging means mounted on said stator and engaging said brushes, said means being displaceable to move said brushes into and out of contact with said commutator, a rotary solenoid mounted on said stator and energizable to displace said brush engaging means, said rotary solenoid comprising radially inner and outer pole pieces rigid with said stator and defining an airgap, a coil supported on said stator and energizable to generate a magnetic flux across said airgap, and an armature coupled to said brush engaging member and rotatably supported on said stator so as to be substantially in balance about its axis of rotation and to be movable into said airgap in response to energization of said coil, one said pole piece being shaped by a single angular machined cut so that said airgap converges along the direction of motion of said armature into the airgap so as to cause the torque of the solenoid to generally increase as the armature progressively enters the airgap.