Air pressure circuit for tire testing device
A pneumatic circuit of a tire testing apparatus includes: a piping configured to guiding air from an air supply source to a tire; a control part configured to output a target command pressure; a pressure proportional control valve part; and a constant-flow air discharge part. The pressure proportional control valve part supplies and discharges the air of a flow rate proportional to a differential pressure between the target command pressure and an internal pressure of the tire so that the internal pressure of the tire becomes the target command pressure, and has a dead band in which the air is not supplied and discharged within a predetermined range. The constant-flow air discharge part is formed between the tire and the pressure proportional control valve part, and is configured to discharge the air of an inside of the piping to an outside at a constant flow rate.
1. A pneumatic circuit of a tire testing apparatus for measuring uniformity of a tire, comprising:
a piping configured to guide air from an air supply source to the tire;
a control part configured to output a target command pressure which is a value of a predetermined air pressure;
a pressure proportional control valve part which is formed on the piping and supplies and discharges the air of a flow rate proportional to a differential pressure between the target command pressure and an internal pressure of the tire so that the internal pressure of the tire becomes the target command pressure and has a dead band in which the air is not supplied and discharged within a predetermined range including the differential pressure of zero; and
a constant-flow air discharge part which is formed between the tire and the pressure proportional control valve part in the piping and is configured to discharge the air of an inside of the piping to an outside at a constant flow rate.
2. The pneumatic circuit of the tire testing apparatus according to claim 1 , wherein
the constant-flow air discharge part discharges the air to the outside at a flow rate at which the dead band is positioned to an air discharge side when an air temperature of an inside of the tire is increased at the time of measuring the uniformity.
3. The pneumatic circuit of the tire testing apparatus according to claim 1 , wherein
a mass flow rate Q (kg/s) of the air discharged to the outside by the constant-flow air discharge part is larger than a value expressed by the following formula (1):
Q =( V/RT )γ (1)
here, V is volume (m 3 ) of the inside of the tire and the inside of the piping from the tire to the pressure proportional control valve part, and T is an absolute temperature (K) of the air of the inside of the piping, and R is a gas constant (J/kg/K) of dry air, and γ is an increment (Pa/s) per second in the internal pressure of the tire at the time of stopping operation of the constant-flow air discharge part and the pressure proportional control valve part in a state in which the internal pressure of the tire is a test pressure at the time of measuring the uniformity.
4. The pneumatic circuit of the tire testing apparatus according to claim 3 , wherein
the mass flow rate Q (kg/s) of the air discharged to the outside by the constant-flow air discharge part is expressed by the following formula (2):
Q =( V/RT )γ+(αΔ Ph/ 2) (2)
here, α is a ratio (kg/Pa) of a change in air supply mass to a change in the differential pressure of an air supply side of the pressure proportional control valve part, and ΔPh is a range (Pa) of the differential pressure of the dead band.