Air Conditioning Compressors - Delphi
Air Conditioning Compressors - Delphi
Air Conditioning Compressors - Delphi
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Th e p r e fe rred c o n f i g u r ation fo r a piston<br />
c o m p r e s s o r s o o n m ove d t o a d o u ble acting<br />
s wa s h - p l a t e d e s i g n o f w h ich t h e Harrison<br />
( D e l p h i ) H D 6 i s t y p i c a l . Th e fixe d swash-<br />
p l a t e i s h e l d b e t we e n t h e o p p osing ends<br />
o f t h e d o u b l e p i s t o n by a pair o f s hoes and<br />
t wo s t e e l balls.<br />
S e c t i o n t h r o u g h a n e a r l y f i xe d s wa s h-plate<br />
c o m p r e s s o r, t h e D e l p h i H D 6<br />
A s e c o n d p o s i t i ve d i s p l a c ement c onfigura-<br />
t i o n u s e d i s t h e s l i d i n g va n e . I t o ffers ad-<br />
va n t a g e s o f c o m p a c t n e ss a n d l ow cost but<br />
c a rries t h e p e n a l t y o f ve r y p o o r e fficiency at<br />
h i g h p r e s s u r e r a t i o s .<br />
Th e o t h e r m a i n c o n f i g u r a tion i s t he scroll<br />
c o m p r e s s o r i n w h i ch o n e s c r oll w i th an in-<br />
vo l u t e s u r fa c e o r b i t s i n side a fixe d second<br />
s c r o l l o f t h e s a m e s h a pe. I t can be seen<br />
f r o m t h e f i g u r e t h a t t h e c o n t a c t points of<br />
t h e scrolls enclose a cav it y of reducing size<br />
( s h a d e d green) that move s from the outside<br />
t o t h e c e n t r e a s t h e o n e scroll o r b i ts inside<br />
t h e o t h e r. Th e r e s u l t i s a n i n d u c tion of gas<br />
a t t h e p e r i p h e r y o f t h e scroll a n d deliver y<br />
o f c o m p r e s s e d g a s a t t h e c e n t r e. These<br />
c o m p r e s s o r s a r e ve r y e ff icient a nd quiet<br />
b u t r e p r esent a s i g n i f icant ch allenge for<br />
m a n u fa c tu r e a n d h e n c e fo r c o s t. They have<br />
t h e d i s a d va n t a g e t h a t a l t h o u g h a variable<br />
ve r s i o n o f t h i s c o m p r e s sor i s p o ssible, the<br />
s u p e r i o r e ff i c i e n c y a d va n t a g e is lost.<br />
I l l u s t r a t i o n o f Scroll compression process<br />
Early compressors were all fixed displace-<br />
ment and system control was achieved by<br />
switching the compressor on and off by<br />
means of an electro-mechanical clutch<br />
cont ained within the compressor pulley.<br />
As consideration began to be given to the<br />
application of air conditioning to smaller<br />
vehicles with smaller engines it was found<br />
that the significant and sudden increase in<br />
engine load that resulted from compressor<br />
switching caused problems for the small<br />
engine with result ant issues of drivabilit y.<br />
A compressor with variable displacement<br />
offered the solution to this problem. In 1985<br />
Harrison (<strong>Delphi</strong>) were the first to go into<br />
series production with a variable compres-<br />
sor, the V5, a wobble plate design with five<br />
pistons.<br />
Th e m e ch a n i s m o f a va r i a b l e wo b b l e p l a t e c o m p r e s s o r<br />
Although scroll, vane and piston compres-<br />
sors are all still in use in automotive applica-<br />
tions, the piston compressor is dominant.<br />
Where the combination of efficiency and<br />
controllabilit y is the key requirement, piston<br />
compressors offer the best solution.<br />
P i s t o n C o m p r e s s o r s<br />
The compressor has the t ask of inducing gas<br />
at a low suction pressure and delivering it at<br />
a higher discharge pressure. It achieves this<br />
by using reed valves that operate automa-<br />
tically to control the fluid flow into and out of<br />
the cylinders. St arting with the piston at top<br />
dead centre the pressure in the small clear-<br />
ance volume will be close to the discharge<br />
pressure as the piston has just delivered its<br />
charge. As the piston recedes and the pres-<br />
sure in the clearance volume falls, the delive-<br />
r y reed valve closes automatically, driven by<br />
the discharge pressure. Since the clearance