Rotation detection device

1. A rotation detection device, comprising:

an on-time power supply connected to a battery mounted on a vehicle and to an ignition switch, and is configured to generate a first constant voltage when the ignition switch is on;

an off-time power supply connected to the battery and configured to generate a second constant voltage lower than the first constant voltage, when the ignition switch is off;

a rotation sensor configured to output a detection signal corresponding to rotation information that depends on a rotation operation of the vehicle;

a controller configured to calculate on-time rotation information on the vehicle when the ignition switch is on, by using the detection signal output from the rotation sensor that is generated based on the first constant voltage, to control a motor for the vehicle; and

a calculator connected to the off-time power supply and configured to:

control the off-time power supply to intermittently supply the second constant voltage to the rotation sensor when the ignition switch is off, at an intermittent interval;

calculate off-time rotation information on the vehicle by using the detection signal output from the rotation sensor that is generated based on the intermittently supplied second constant voltage;

store the off-time rotation information into a memory; and

transfer the off-time rotation information stored in the memory to the controller when the ignition switch is set on again,

wherein, in the controlling the off-time power supply to intermittently supply the second constant voltage to the rotation sensor when the ignition switch is off, the calculator is further configured to:

update a set value of the intermittent interval, at which the second constant voltage is to be supplied intermittently, so that the set value becomes smaller, when the off-time rotation information contains information indicating rotation of the motor, and

update the set value, so that the set value becomes larger, when the off-time rotation information on the vehicle does not contain the information indicating rotation of the motor.

2. The rotation detection device according to claim 1 , wherein, when the ignition switch is off, the rotation sensor outputs the detection signal as a signal with a higher resolution, as the intermittent interval becomes smaller.

3. The rotation detection device according to claim 1 , wherein the rotation sensor is configured to output the detection signal as a signal with a higher resolution, as a value of the second constant voltage becomes larger.

4. The rotation detection device according to claim 1 ,

wherein the motor for the vehicle includes a motor having phase windings,

wherein the rotation detection device further comprises a monitor circuit configured to detect a state in which a voltage of each of winding terminals of the motor for the vehicle exceeds an allowable voltage value set in advance, and

wherein the calculator is configured to start an operation of intermittently supplying the second constant voltage to the rotation sensor when the monitor circuit has detected the state in which the allowable voltage value is exceeded.

5. The rotation detection device according to claim 1 ,

wherein the calculator is configured to generate rotation information for comparison by intermittently using a detection signal output from the rotation sensor when the ignition switch is on, and sequentially transfer the rotation information for comparison to the controller, and

wherein the controller is configured to:

compare the on-time rotation information on the vehicle generated by the controller with the rotation information for comparison; and

determine that the on-time rotation information on the vehicle has been generated normally when a difference between the on-time rotation information on the vehicle and the rotation information for comparison falls within an allowable range set in advance.

6. The rotation detection device according to claim 1 ,

wherein the rotation sensor includes a single detection circuit in which a power supply voltage supplied from an outside is one system,

wherein the rotation detection device further comprises a selector configured to select any one of the first constant voltage and the second constant voltage in accordance with an external command, and supply a selected power supply voltage to the rotation sensor, and

wherein the calculator is configured to:

generate the external command so as to supply the first constant voltage to the rotation sensor when the ignition switch is on;

generate the external command so as to supply the second constant voltage to the rotation sensor when the ignition switch is off; and

execute control of switching the selector.

7. The rotation detection device according to claim 1 , wherein the on-time power supply is connected to the battery mounted via the ignition switch and configured to receive power from the battery when the ignition switch is on, and

the off-time power supply is directly connected to the battery and configured to receive power from the battery when the ignition switch is on and when the ignition switch is off.