Tire-pressure control apparatus

A tire-pressure control apparatus comprising:

• an air pump which is driven by a rotating wheel so as to supply compressed air to a tire air chamber of the wheel;
• a mechanical control valve device disposed in an air passageway extending between the air pump and the tire air chamber and adapted to control a tire pressure within the tire air chamber, the control valve device being in a permission state where the control valve device permits supply of compressed air from the air pump to the tire air chamber during a period over which the tire pressure increases to an upper limit set value from a lower limit set value after having decreased to the lower limit set value, and being in a prohibition state where the control valve device prohibits supply of compressed air from the air pump to the tire air chamber during a period over which the tire pressure decreases to the lower limit set value from the upper limit set value after having increased to the upper limit set value;
• a valve state detection sensor for detecting whether the control valve device is in the permission state or the prohibition state;
• time measurement means for measuring a prohibition-state retention time, which is a time period starting when the control valve device enters the prohibition state and ending when the control valve device enters the permission state and a permission-state retention time, which is a time period starting when the control valve device enters the permission state and ending when the control valve device enters the prohibition state;
• a wheel speed sensor for detecting rotational speed of the wheel;
• total-discharged-air-quantity calculation means for calculating a total discharged air quantity, which is a total quantity of compressed air supplied from the air pump to the tire air chamber during the permission-state retention time, from a previously obtained quantity of compressed air discharged from the air pump per single revolution thereof and the rotational speed of the wheel which the wheel speed sensor detects during the permission-state retention time measured by the time measurement means;
• and
• average-leaked-air-quantity calculation means for calculating an average leaked air quantity per unit time in a single cycle starting when the control valve device enters the prohibition state and ending when the control valve device again enters the prohibition state after entering the permission state or a single cycle starting when the control valve device enters the permission state and ending when the control valve device again enters the permission state after entering the prohibition state, from the prohibition-state retention time and the permission-state retention time measured by the time measurement means and the total discharged air quantity calculated by the total-discharged-air-quantity calculation means.