Active vibration insulator

1. An active vibration insulator, comprising:

a first member attached to an engine;

a second member attached to an engine frame;

a main rubber elastic body elastically connecting the first member and the second member;

a vibratable plate forming a pressure receiving chamber with the main rubber elastic body, the pressure receiving chamber receiving a vibration from the engine;

an electromagnetic actuator including a core, around which a coil is wound, attached to the second member and a plunger attached to the vibratable plate and reciprocating relative to the core, the electromagnetic actuator generating vibrating forces depending on electric-current supplies;

a controller for carrying out vibrating-forces generation control in which the electric-current supplies are made variable so as to actively inhibit vibrations generated by an on-vehicle vibration generating source of a vehicle from transmitting to a specific part of the vehicle based on cyclic pulsating signals output from the on-vehicle vibration generating source, thereby letting the electromagnetic actuator generate the vibrating forces;

an acceleration sensor fixed to the second member and detecting a vibration of the second member; and

a bad-roads processor for judging whether or not the vehicle is traveling on a bad road based on the vibration detected by the acceleration sensor and for stopping the vibrating-forces generation control effected by the controller when the vehicle is judged to be traveling on the bad road.

2. The active vibration insulator as claimed in claim 1 , wherein the bad-roads processor stops the vibrating-forces generation control when the vehicle enters bad roads, and resumes the vibrating-forces generation control when the vehicle returns ordinary roads out of the bad roads.

3. The active vibration insulator as claimed in claim 2 , wherein the bad-roads processor comprises:

a first judge for judging whether the vehicle enters bad roads based on a first condition;

a second judge for judging whether the vehicle returns onto ordinary roads out of bad roads based on a second condition, which differs from the first condition; and

a control-stop processor for stopping the vibrating-forces generation control by the controller when the first judge judges that the vehicle enters bad roads, and resuming the vibrating-forces generation control by the controller when the second judge judges that the vehicle returns onto ordinary roads out of bad roads.

4. The active vibration insulator as claimed in claim 1 , wherein the bad-roads processor controls actuating voltages, which the controller applies to the electromagnetic actuator when the vehicle travels on bad roads, to zero.

5. The active vibration insulator as claimed in claim 1 , wherein the bad-road processor controls actuating voltages, which is applied to the electromagnetic actuator by the controller when the vehicle is traveling on the bad road, to be a constant value to fix an actuation of the electromagnetic actuator.

6. The active vibration insulator as claimed in claim 3 , wherein the first judge judges that the vehicle enters bad roads when the vibrations of the second member, which the acceleration sensor detects, exceed a predetermined threshold value at least at a predetermined time within each of plural predetermined continuous periods of time.

7. The active vibration insulator as claimed in claim 3 , wherein the second judge judges that the vehicle returns onto ordinary roads out of bad roads when the vibrations of the second member, which the acceleration sensor detects, do not exceed a predetermined threshold value within each of plural predetermined continuous periods of time.