Electric motor fan control system for vehicle

A fan control system of a vehicle for controlling an electric motor fan for cooling a radiator for an engine coolant and a condenser for a refrigerant of an air conditioning system of the vehicle by moving air, comprises a vehicle speed sensor, a sensor for sensing the temperature of the engine coolant, a sensor for sensing a discharge pressure of the refrigerant discharged from the compressor of the air conditioning system, and a controller for controlling the motor fan. In the operating range in which the vehicle speed is lower than a predetermined speed and simultaneously the coolant temperature is lower than a predetermined temperature, the controller holds the motor fan off if the discharge pressure is lower than a predetermined pressure even though the air conditioner switch is on. Therefore, the percentage of running time of the motor fan to the total time is reduced.

BACKGROUND OF THE INVENTION 
The present invention relates to a control system for controlling an 
electric motor fan of a vehicle such as a motor vehicle. 
FIG. 5 shows one conventional fan control system for a passenger car (as 
disclosed in "NISSAN Shingatasha Kaisetsusho (new model maintenance 
manual)", Vol. U12-2, pages B-48 and B-95, Oct. 1989). This system 
includes a vehicle speed sensor 1, a temperature sensor 2 for sensing the 
temperature of an engine cooling water, an air conditioner switch SW1, and 
a control circuit 3 for controlling electric fan motors M1 and M2 for 
moving air toward a radiator of the engine coolant and a condenser of an 
air conditioning system, through motor relays Ry1 and Ry2. 
When the vehicle is in motion, the radiator and condenser receive a flow of 
cool outside air due to the vehicle motion. Therefore, the control system 
stops the fan motors M1 and M2 when the vehicle speed is higher than 80 
km/h and the engine cooling water temperature is lower than 105.degree. 
C., as shown in FIG. 6. When the vehicle speed is lower than 80 km/h and 
the water temperature is lower than 95.degree. C., this control system 
turns off the motors M1 and M2 if the air conditioner switch SW1 is off. 
When the air conditioner switch SW1 is on, a clutch for an air 
conditioning compressor is engaged, and the air conditioning system is in 
an operative state. Therefore, this control system runs the motors M1 and 
M2, regardless of the vehicle speed and the water temperature, when the 
air conditioning system is working. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a vehicle electric 
motor fan control system which can operate an electric motor fan more 
efficiently. 
According to the preset invention, a fan control system for a vehicle 
comprises a cooling means, four sensing means and a controller means. 
The cooling means comprises an air-cooled heat exchanger system for 
removing heat from an engine coolant for cooling an engine of the vehicle 
and a refrigerant of an air conditioning system of the vehicle. The 
cooling means further comprises an electric motor fan for cooling the heat 
exchanger system by directing air to the heat exchanger system. In an 
illustrated embodiment of the invention, the heat exchanger system 
comprises a heat exchanger in the form of a radiator for the engine 
coolant, and another heat exchanger in the form of a condenser for the air 
conditioning refrigerant. The cooling means may include the whole of the 
engine cooling system and the whole of the air conditioning system. 
Among the four sensing means, the first one is a means for sensing a 
vehicle speed. The second sensing means is a means for sensing a cooling 
power of the engine coolant. In the illustrated embodiment of the 
invention, the second sensing means is a temperature sensing means for 
sensing the temperature of the engine coolant. The third sensing means is 
a means for determining whether the air conditioning system is in an 
operative state or in an inoperative state. In the illustrated embodiment 
of the invention, an air conditioner switch SW1 serves as the third 
sensing means. The fourth sensing means is a means for sensing a discharge 
pressure of the refrigerant discharged from a compressor of the air 
conditioning system. In the illustrated embodiment, the fourth sensing 
means takes the form of a pressure switch SW2. 
The controller means switches off the motor fan and holds the motor fan in 
the off state if the discharge pressure is lower than a predetermined 
pressure value, regardless of whether the air conditioning system is in 
the operative state or not, when the vehicle speed is lower than a 
predetermined first speed value (80 km/h, for example) and the cooling 
power of the engine coolant is higher than the a predetermined value. 
The compressor of the air conditioning system acts to circulate the 
refrigerant in the refrigeration cycle. The pressure of the gas 
refrigerant is low on the inlet side of the compressor, and high on the 
discharge outlet side. The refrigerant pressure on the discharge side of 
the compressor becomes higher as the rotational speed of the compressor 
(i.e. the engine speed) becomes higher, the temperature of air flowing 
through the evaporator becomes higher, and the amount of airflow produced 
by a blower fan becomes greater. In other words, the refrigerant discharge 
pressure of the compressor is proportional to the heat load of the 
passenger compartment of the vehicle. The discharge pressure is increased 
as the heat load increases, and decreased as the heat load decreases. The 
refrigerant discharge pressure becomes minimum when the heat load 
continues to be low. In this case, therefore, the control system according 
to the present invention ceases the air cooling of the condenser by 
stopping the motor fan. When the discharge pressure is low, the motor fan 
is held in the off state even if the air conditioner switch is turned on. 
Thus, the present control system can reduce the running time of the motor 
fan.

DETAILED DESCRIPTION OF THE INVENTION 
A fan control system according to one embodiment of the present invention 
is shown in FIGS. 2-4. 
As shown in FIG. 2, the fan control system for a vehicle includes an air 
conditioner switch SW1 for switching on and off an air conditioning system 
of the vehicle, a vehicle speed sensor 1 for sensing the speed V of the 
vehicle, a water temperature sensor 2 for sensing the temperature T of an 
engine cooling water, and a pressure switch SW2. 
In this embodiment, the vehicle speed sensor 1 serves as a first sensing 
means 101 (shown in FIG. 1) for sensing the vehicle speed, and the water 
temperature sensor 2 serves as a second sensing means 102 (shown in FIG. 
1) for sensing a cooling power of the engine coolant. The air conditioner 
switch SW1 serves as a third sensing means 103 (shown in FIG. 1) for 
determining whether the air conditioning system of the vehicle is in an 
operative state or in an inoperative state, and for producing a first 
switch-on signal when the air conditioning system is in the operative 
state and a first switch-off signal when the air conditioning system is in 
the inoperative state. The pressure switch SW2 serves as a fourth sensing 
means 104 (shown in FIG. 1) for sensing a discharge pressure of a 
refrigerant. 
The pressure switch SW2 is provided at an outlet of a compressor 131 (shown 
in FIG. 1) of the air conditioning system, and constructed to sense the 
pressure Pd of a refrigerant discharged from the compressor 131. The 
pressure switch SW2 of this embodiment is in an off state to produce a 
second switch-off signal when the refrigerant discharge pressure Pd is 
equal to or lower than a predetermined pressure value K. When the 
refrigerant discharge pressure Pd is higher than the predetermined value 
K, the pressure switch SW2 is put in an on state, and produces a second 
switch-on signal. 
The control system further includes a control circuit 3 which receives 
signals from the air conditioner switch SW1, the vehicle speed sensor 1, 
the water temperature sensor 2 and the pressure switch SW2, and which 
controls fan motors M1 and M2. The control circuit 3 of this embodiment is 
composed of a microcomputer mounted on the vehicle, and peripheral 
components. The motors M1 and M2 are connected with a battery BAT through 
first and second relays Ry1 and Ry2. When the first relay Ry1 is on, then 
the motors M1 and M2 are driven at a low speed (LOW) with power supplied 
from the battery BAT. The control circuit 3 can drive the motors M1 and M2 
at a high speed (HIGH) by further turning on the second relay Ry2. The 
control circuit 3 serves as a controller means 105 (shown in FIG. 1) for 
controlling the fan motors M1 and M2 in accordance with signals supplied 
from the switches SW1 and SW2 and the sensors 1 and 2. 
The control circuit 3 of this embodiment performs a fan control program 
shown in FIGS. 3A and 3B. 
At a step S1 shown in FIG. 3A, the control circuit 3 determines whether the 
vehicle speed V sensed by the vehicle speed sensor 1 is lower than 20 km/h 
(which is a predetermined second speed value) or not. From the step S1, 
the control circuit 3 proceeds to a step S2 if V &lt;20 km/h, and to a step 
S9 shown in FIG. 3B through a first connector point X if it is not. 
At the step S2, the control circuit 3 determines whether the water 
(coolant) temperature T sensed by the water temperature sensor 2 is lower 
than 95.degree. C. (which is a first temperature value) or not. The 
control circuit 3 proceeds to a step S3 if T &lt;95.degree. C., and to a step 
S6 if it is not. 
At the step S3, the control circuit 3 determines whether the air conditoner 
switch SW1 is on or not. Then, the control circuit 3 proceeds to a step S4 
if the air conditioner switch SW1 is on, and to a step S5 if the air 
conditioner switch SW1 is off. 
At the step S4, the control circuit 3 determines whether the refrigerant 
discharge pressure Pd is equal to or lower than the predetermined value K, 
or not, by checking the signal from the pressure switch SW2. If Pd 
.ltoreq. K, the control circuit 3 proceeds to the step S5. 
At the step S5, the control circuit 3 stops, or hold stationary, the fan 
motors M1 and M2 by turning off the first relay Ry1. The control circuit 3 
of this embodiment produces a fan control signal in an off control state 
to switch off the motors M1 and M2 at the step S5. 
When the answer of the step S2 or step S4 is negative, then the control 
circuit 3 proceeds to the step S6, and determines there whether the water 
temperature T is lower than 105.degree. C. (which is a predetermined third 
temperature value). If T &lt;105.degree. C., then the control circuit 3 
switches on the first relay Ry1 at a step S7, and by so doing, drives the 
motors M1 and M2 at a low speed. At the step S7, the control circuit 3 
produces the fan control signal which is in a first on control state to 
drive the motors M1 and M2 at the low speed. If the water temperature T is 
equal to or higher than 105.degree. C., then the control circuit 3 drives 
the motors M1 and M2 at a high speed by turning on the first and second 
relays Ry1 and Ry2 at a step S8. At the step S8, the control circuit 3 
produces the fan control signal which is in a second on control state to 
drive the fan motors M1 and M2 at the high speed. 
If the vehicle speed V is equal to or higher than 20 km/h, then the control 
circuit 3 proceeds from the step S1 to the step S9 to determine whether 
the vehicle speed V is lower than 80 km/h (which is a first predetermined 
speed value), or not. Then, the control circuit 3 proceeds from the step 
S9 to a step S10 if V &lt;80 km/h, and from the step S9 to a step S17 if V 
.gtoreq.80 km/h. 
At the step S10, the control circuit 3 determines whether the water 
temperature T is lower than 95.degree. C. (first temperature value) or 
not. Then, the control circuit 3 proceeds to a step S11 if T &lt;95.degree. 
C., and to a step S14 if T .gtoreq.95.degree. C. At the step S11, the 
control circuit 3 determines whether the air conditioner switch SW1 is in 
the on state or not. From the step S11, the control circuit 3 proceeds to 
a step S12 if SW1 is on, and to a step S13 if it is not. 
At the step S12, the control circuit 3 checks the output signal of the 
pressure switch SW2 and determines whether the discharge pressure Pd of 
the refrigerant is equal to or lower than the predetermined pressure value 
K. If it is, the control circuit 3 proceeds to the step S13 and produces 
the fan control signal in the off control state to stop the motors M1 and 
M2. If Pd &gt;K, then the control circuit 3 proceeds to the step S14. 
If the answer of the step S10 or S12 is negative, the control circuit 3 
reaches the step S14, and determines whether the water temperature is 
lower than 100.degree. C. (a second predetermined temperature value), or 
not. From the step S14, the control circuit 3 proceeds to a step S15 to 
drive the motors M1 and M2 at the low speed if T &lt;100.degree. C., and to a 
step S16 to drive the motors M1 and M2 at the high speed if T 
.gtoreq.100.degree. C. 
If the vehicle speed is equal to or higher than 80 km/h (the first speed 
value), then the control circuit 3 proceeds from the step S9 to a step S17 
to determine whether the water temperature is lower than 105.degree. C. (a 
third temperature value), or not. From the step S17, the control circuit 3 
proceeds to a step S18 to stop the motors M1 and M2 if T &lt;105.degree. C., 
and to a step S19 to drive the motors M1 and M2 at the high speed if T 
.gtoreq.105.degree. C. 
Thereafter, the control circuit 3 returns to the step S1 to repeat the 
program. 
FIG. 4 shows the operations of the control system according to this 
embodiment of the present invention. When the vehicle speed V is lower 
than the first predetermined speed value (80 km/h) and simultaneously the 
water temperature T of the engine cooling water is lower than the first 
temperature value (95.degree. C.), the control circuit 3 holds the fan 
motors M1 and M2 off if either or both of the switches SW1 and SW2 is off, 
and switches on the fan motors M1 and M2 only if both switches SW1 SW2 are 
on. Therefore, the controller means 105 (shown in FIG. 1) of this 
embodiment corresponding to the control circuit 3 comprises a 
discriminationg means 105b (shown by broken line in FIG .1) for producing 
a discrimination signal only when the vehicle speed is lower than the 
first speed value (80 km/h) and simultaneously the water temperature is 
lower than the first temperature value (95.degree. C.), and a (AND) logic 
operating means 105a (shown by a broken line in FIG. 1) for holding the 
fan control signal in the off control state if at least one of the 
switches SW1 and SW2 is off when the discriminating signal is present. 
When the vehicle speed V is higher than the first speed value (80 km/h) or 
the water temperature T is higher than the first temperature value 
(95.degree. C.), the control circuit 3 produces the fan control signal 
independently of the switches SW1 and SW2. Therefore, the control circuit 
3 of this embodiment comprises a second operating means for producing the 
fan control signal independently of the switches SW1 and SW2. In the 
example shown in FIG. 1, the discriminating means 105b includes the second 
operating means. Therefore, the discriminating means 105b is connected 
with the first and second sensing means 101 and 102, and produces the 
discrimination signal and the fan control signal in accordance with the 
vehicle speed and the coolant temperature. The logic operating means 105a 
receives the output signals of the air conditioner switch SW1 and the 
pressure switch SW2, and produces the fan control signal by functioning 
like an AND gate only when the discrimination signal is present. 
In this way, the control system of this embodiment holds the fan motors M1 
and M2 in the off state even if the air conditioner switch SW1 is switched 
on, as long as the refrigerant discharge pressure Pd is equal to or lower 
than the predetermined value when the vehicle speed is in the medium or 
low range and the engine coolant temperature is low. Therefore, this 
control system can reduce the percentage of working time to total time of 
the motors M1 and M2, and improve the durability, and the vibration and 
noise reducing characteristics of the fan motors. 
This embodiment employs a three step control system in which the fan speed 
assumes one of three discrete values which are zero, a predetermined low 
speed and a predetermined high speed. However, it is optional to employ an 
on-off control system in which the fan motor is turned on or off. For 
example, the fan speed is always equal to a high speed when the motor is 
switched on. 
In the illustrated embodiment, the engine is a water-cooled type. However, 
the cooling system of an engine used in the present invention may be 
arranged to utilize the latent heat of vaporization of a coolant such as 
alcohol. The compressor of the air conditioning system may be a constant 
displacement (or capacity) type or may be a variable displacement 
(capacity) type. 
As shown in FIG. 1, the fan control system according to the illustrated 
embodiment of the invention comprises the cooling means 100, the first, 
second, third and fourth sensing means 101-104, and the controller means 
105. The cooling means 100 comprises at least one electric motor 110 
drivingly connected with at least one fan 112. The fan 112 is directed to 
the radiator 120 of the cooling system of the engine 121, and to the 
condenser 130 of the air conditioning system of the vehicle. The radiator 
130 and condenser 120 constitutes an air-cooled heat exchanger system. The 
radiator 120 is used to remove heat from the engine coolant circulating in 
the engine cooling system. The condenser 130 is used to remove heat from 
the refrigerant circulating in the air conditioning system which comprises 
the condenser 130, compressor 131 and evaporator 132. The controller means 
105 is connected with the four sensing means 101-104 so as to receive 
signals, and produces the fan control signal to control the fan motor 110 
in accordance with the signals supplied from the sensing means 101-104. 
The controller means 105 may comprise the relays Ry1, and Ry2, or some 
means functioning as these relays may be connected between the controller 
means 105 and the motor 110.