Variable Orifice Valve
for Auto A/C Flow Regulation
New valve provides
alternative to FOTs and TXVs
Until now, engineers designing automotive climate control systems had little choice in
expansion devices. They could choose between the fixed orifice tube (FOT), which provides
reliable highway panel discharge temperatures with marginal traffic/idle speed performance
or the more expensive, higher performing thermal expansion valve (TXV).
Bridging this cost and performance gap is a new Variable Orifice Valve (VOV) from Texas
Instruments' Materials & Controls Group, a high-performance, cost-effective expansion
device for automotive refrigerant systems. Located in the liquid refrigerant line between
the condenser and the evaporator in the automobile's A/C loop, the VOV uses thermostatic
bi-metal technology to react to condenser discharge temperatures, controlling variable
restriction levels to provide superior performance for air conditioning systems. To date,
the new VOV is being used on a 1999 model year high-volume sports-utility vehicle produced
by an American automobile manufacturer.
The VOV incorporates a simple fundamental in-line design, unlike the more complex TXV
system. Its features include: a bi-metal coil; a body which houses two flow paths
(variable and fixed); a sleeve spot-welded to the coil to open and close the variable
port; a diffuser filter on the outlet end; an inlet end filter to prevent particles from
entering the VOV; and O-rings which seal the VOV to the internal diameter of vehicle A/C
plumbing.
Unlike the FOT, the VOV's variable restriction levels result in optimal performance
under all driving conditions from highway to city driving to idling. Its low or zero
superheat production results in lower compressor discharge temperatures, which helps
increase compressor life.
Texas Instruments successfully completed an extensive design validation, including
6,000 hours of refrigerant flow through the device and more than 160,000 water thermal
cycles intended to stress the coils.
--KC
For more information, contact Texas Instruments, 34 Forest Street,
Attelboro, MA 02703. 508-236-1158. Circle 753. |