An alternating current latching relay is provided which employs a latching-type, mechanically operated snap-action switch mechanism with a set of electric contacts that are selectively latched either in the open or closed condition in a snap-action manner upon successive actuations of the snap-action mechanism by suitable push rod means for initiating its operation. At least one alternating current excited bender-type piezoelectric drive member has one end secured to a common base member with the latching-type snap-action switch mechanism and the remaining free end engaging the push rod means. An alternative current electric excitation signal is directly applied to the piezoelectric plate elements of the bender- type drive member for mechanically vibrating the bender-type drive member in a manner such that its amplitude of vibration quickly builds up to a value where it repeatedly strikes the push rod means with sufficient force to selectively actuate the snap-action switch mechanism to the opposite one of its two operating conditions from that in which it originally was set. A tuning mass in the form of a slug element is secured to the end of the bender-type drive member to reduce the natural resonant frequency of vibration of the bender-type drive member to substantially the frequency of the alternating current excitation signal to thereby increase the amplitude of its vibrations to a maximum. Additionally, the tuning mass increases the impulse delivered by the bender-type drive member to the push rod for actuating the snap-action mechanism.

A direct current latching relay comprised of bender-type piezoelectric drive members each of which is a three terminal member formed of two piezoelectric plate elements separated by a conductive plane. Each piezoelectric plate element is separately electrically charged with an input pulsed d.c. switching signal of the same polarity as the pre-poling field previously induced in the piezoelectric plate element. By electrically charging one of the piezoelectric plate elements with a switching signal electric field of the same polarity as the pre-poling field, the bender-type drive members are member made to bend in one direction. Alternatively, by charging the opposite plate of the drive member again with a direct current electric charging field of the same polarity as the pre-poling field previously induced in the plate, the bender-type drive member can be caused to bend in the opposite direction. The bender-type peizoelectric drive member whe bent engages and drives a push rod which actuates a snap-action switching contact mechanism from either an open circuit state or to a closed circuit state or vice versa. Pulsed direct current charging fields are applied to the piezoelectric plate element of the bender-type drive member and a high resistance discharge resistor is connected across each of the piezoelectric plate members so asto automatically dischargethe plate members shortly after their excitation. As a result, no long term depolarization of the piezoelectric plate members occurs and because of the pulsed short term nature of the charging fields, no long term deformation (creep) develops in the plate elements over extended periods of usage of the relay.

A switch assembly includes first and second contact members which are operatively provided to take one of two positions, a break-position in which the first and second contact members are separated from each other, and a make-position in which the first and second contact members are electrically connected with each other. Magnetic members are provided operatively in association with the first and second contact members to define a closed magnetic loop with a current path extending through the loop, when the first and second contact members are turned to the make-position. The magnetic members attract each other by the magnetic flux through the closed loop to maintain the first and second contacts in the make-position when the current flowing through the current path is not zero. Thus, the first and second contact members are permitted to return to the break-position at a zero crossing point of a.c. current flowing through the contacts.