Pressure regulating valve

A pressure regulating valve comprising:

• a valve body;
• a bore formed in the valve body, the bore comprising a space portion, a first pressure chamber, and a second pressure chamber;
• a spool which is slidably inserted within the bore, a diameter of an inner circumference of the bore being greater than a diameter of an outer circumference of the spool so as to form a clearance, the first pressure chamber thereby being in hydraulic communication with the space portion, a material of the spool having a lower thermal expansion coefficient than a material of the valve body;
• a supply passage through which hydraulic pressure is supplied to the first pressure chamber from a pressure supply source;
• a drain passage through which hydraulic pressure is drainable from the first pressure chamber;
• a through-passage being formed in the spool through which the space portion and the first pressure chamber are in hydraulic communication;
• and
• an urging member which is disposed in the space portion to apply an urging force to the spool;
• wherein hydraulic pressure in the second pressure chamber pushes the spool to allow draining of hydraulic pressure when hydraulic pressure in the first pressure chamber has risen above a target hydraulic pressure,
• the draining continuing until an equilibrium is reached between the urging force of the urging member and an opposing urging force of hydraulic pressure in the second pressure chamber.

A pressure regulator valve of an automatic transmission, the pressure regulator valve comprising:

• a valve body which comprises
• a cylinder,
• a supply passage which hydraulically connects the cylinder and a pressure supply source,
• a drain passage which hydraulically connects the cylinder and a sump, and
• an inflow-outflow passage which hydraulically connects the cylinder and the sump;
• a spool which is slidably inserted within the cylinder, the spool dividing the cylinder into at least one space portion hydraulically connected to the inflow-outflow passage, a first pressure chamber receiving pressure from the supply passage, and a second pressure chamber receiving pressure from the supply passage, a material of the spool having a lower thermal expansion coefficient than a material of the valve body;
• urging means for applying an urging force on the spool in a direction opposed to an urging force of the second pressure chamber, the spool sliding to allow excess pressure to drain when hydraulic pressure of the second pressure chamber overcomes the urging force of the urging means;
• a clearance through which fluid flows from the first pressure chamber into the space portion;
• a through-passage through which fluid flows from the first pressure chamber into the space portion, the through-passage being formed in the spool;
• and
• restricting means for restricting the flow rate of the inflow-outflow passage,
• the flow rate of the restricting means being less than a combined flow rate of the through-passage and the clearance under a low temperature condition,
• the flow rate of the restricting means being more than a combined flow rate of the through-passage and the clearance under a high temperature condition.