U.S. patent number 3,794,896 [Application Number 05/319,795] was granted by the patent office on 1974-02-26 for control circuit for cooling fans.
This patent grant is currently assigned to Joseph Lucas (Electrical) Limited. Invention is credited to William David Holt.
United States Patent |
3,794,896 |
Holt |
February 26, 1974 |
CONTROL CIRCUIT FOR COOLING FANS
Abstract
A control circuit for an electrically driven cooling fan has a
relay for switching the fan in and out. Associated with the relay
is resistance means for reducing the differential between the on
and off points of the fan.
Inventors: |
Holt; William David (Colne,
EN) |
Assignee: |
Joseph Lucas (Electrical)
Limited (Birmingham, EN)
|
Family
ID: |
9721013 |
Appl.
No.: |
05/319,795 |
Filed: |
December 29, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Dec 1, 1972 [GB] |
|
|
1,380/72 |
|
Current U.S.
Class: |
318/471; 361/24;
318/473; 361/106 |
Current CPC
Class: |
F01P
7/08 (20130101) |
Current International
Class: |
F01P
7/08 (20060101); F01P 7/00 (20060101); G05d
023/30 () |
Field of
Search: |
;318/471,472,473
;317/13B,13C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dobeck; B.
Attorney, Agent or Firm: Holman & Stern
Claims
I claim:
1. A control circuit for an electrically driven cooling fan,
comprising in combination a resistor the value of which is
dependent in use on the temperature of an apparatus cooled by the
fan, a relay winding having a contact which when the winding is
de-energised serves to operate the fan, an amplifier coupled to
said resistor and responsive to the value of said resistor, said
amplifier having an output decreasing with rise in temperature of
the apparatus whereby when the temperature of the apparatus falls
to a predetermined level the amplifier output energises said relay
winding, and resistance means which is coupled to the amplifier by
way of the relay contact when the relay winding is energised, the
resistance means serving when the relay is energised to reduce the
current flowing in the relay winding by an amount insufficient to
cause the relay winding to become de-energised, so reducing the
required increase in the temperature of the apparatus before the
relay winding is again de-energised to cause the fan to operate.
Description
This invention relates to a control circuit for an electrically
driven cooling fan.
A control circuit according to the invention comprises in
combination a resistor the value of which is dependent in use on
the temperature of an apparatus cooled by the fan, a relay winding
having a contact which when the winding is de-energised serves to
operate the fan, a control circuit responsive to the value of said
resistor for energising the relay winding when the temperature of
the apparatus falls to a predetermined level, and resistance means
which is coupled to the control circuit by way of the relay contact
when the relay winding is energised, the resistance means reducing
the required increase in the temperature of the apparatus before
the relay winding is again de-energised to cause the fan to
operate.
The accompanying drawing is a circuit diagram illustrating one
example of the invention.
Referring to the drawing, a road vehicle incorporates a battery 9
having its negative terminal connected to an earth supply line 10,
and its positive terminal connected to a supply line 11 through a
series circuit including the vehicle ignition switch 8, diode 30
and a resistor 13. The road vehicle is driven by an internal
combustion engine indicated at 17, the engine being cooled by flow
cooling water within a conduit 16.
Located within part of the conduit 16 is a
temperature-sensitive-resistor 15 one end of which is connected to
the line 10, and the other end of which is connected through a
temperature gauge 14 to the line 11. A junction of the gauge 14 and
resistor 15 is connected through a resistor 24 to the line 10, and
a variable point on the resistor 24 is connected to the base of an
n-p-n transistor 25, the emitter of which is connected to the base
of an n-p-n transistor 26 having its emitter connected to the line
10. The transistors 25, 26 have their collectors connected to the
line 11 through a relay winding 22 bridged by a freewheel diode 31,
and the winding 22 serves when it is energised to move a contact 23
out of engagement with a contact 21 into engagement with a contact
28. The contact 28 is connected through a variable resistor 29 to
the base of the transistor 25, and the contact 21 is connected to
the positive battery terminal through a fan motor 19, which when it
is operating drives a fan 18 providing cooling air through a part
16a of the conduit 16.
In operation, when the engine temperature is low, the resistor 15
has a high value, and current flowing through the gauge 14 turns on
the transistors 25, 26 energising the winding 22 so that the
contact 23 moves into engagement with the contact 28 and the fan
motor 19 is not energised.
When the engine temperature is high, the resistor 15 has a low
value, and the transistors 25, 26 do not conduct sufficiently to
energise the winding 22, so that the contact 23 is in engagement
with the contact 21 and the fan motor 19 is energised.
Assuming that the fan motor 19 is operating then as the temperature
of the resistor 15 falls, an increase in base current flows to the
transistor 25, until at a predetermined temperature, the
transistors 25, 26 conduct sufficiently to energise the winding 22,
thereby moving the contact 23 back into engagement with the contact
20a and stopping the motor 19. However, the contact 23 now couples
the base of the transistor 25 to the line 10 by way of the resistor
29, so reducing the base current of the transistor 25, and reduces
the current flowing in the winding 22. This reduction is
insufficient to de-energise the winding 22, so that the contact 23
remains in engagement with the contact 28.
As the fan motor 19 is not now operating, the temperature of the
resistor 15 increases, and the current flowing to the winding 22
decreases, until at a predetermined temperature the winding 22 is
de-energised, and the contact 23 moves into engagement with the
contact 21 again to operate the motor 19.
It will be appreciated that the relay 22, 23 has the usual property
in that the current requires to energise the winding 22 is greater
than the current at which the winding 22 becomes de-energised. In
effect, the resistor 29 serves when the winding 22 is energised to
decrease the current flowing through the winding 22 by an amount
less than the differential between the turn-on and turn-off
currents of the winding 22.
The diodes 30, 31 are incorporated to protect the transistors 25,
26 against transients. The settable resistors 24, 29 determine the
operating points of the fan 19.
* * * * *