Refrigeration – Automatic control – Responsive to vehicle body motion or traction
Reexamination Certificate
2000-09-20
2001-11-27
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Responsive to vehicle body motion or traction
C062S228300, C062S229000
Reexamination Certificate
active
06321545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a variable displacement type compressor for use in vehicle air-conditioners. More particularly, this invention relates to an apparatus for controlling the discharge capacity of a variable displacement type compressor by changing the tilt angle of a cam plate with a control valve.
This type of control apparatus known has a control passage that connects a discharge pressure area to the crank chamber, which houses a cam plate, and adjusts the difference between the pressure in the crank chamber and the pressure in the cylinder bores to change the tilt angle of the cam plate, thereby adjusting the discharge capacity. The adjustment of the difference between the pressure in the crank chamber and the pressure in the cylinder bores is carried out by changing the position of the displacement control valve, which is located in the control passage, under the control of a computer.
Japanese Unexamined Patent Publication (KOKAI) No. Hei 6-341378 discloses a displacement control valve that has a constant differential pressure valve section and an electric driving section. The displacement control valve performs control such that the difference between the pressure of the intake refrigerant gas (hereinafter referred to as the suction pressure), which has a correlation with the pressure in the cylinder bore, and the pressure in the crank chamber becomes equal to a preset value. More specifically, the constant differential pressure valve section adjusts the restriction of the control passage by actuating the valve body to keep the difference between the pressure in the crank chamber and the suction pressure at the preset value. An electric driving section changes a reference set value for the operation of this valve section by adjusting the load acting on the valve body under the control of the computer.
When the suction pressure rises to make the difference between the pressure in the crank chamber and the suction pressure fall below the set value, the valve section actuates the valve body to open the control passage. This increases the amount of the high-pressure refrigerant gas supplied to the crank chamber from the discharge pressure area, thus raising the pressure in the crank chamber. As a result, the difference between the pressure in the crank chamber and the suction pressure is maintained at the preset value.
When the suction pressure falls, making the difference between the pressure in the crank chamber and the suction pressure greater than the set value, on the other hand, the valve section moves the valve body in the direction to close the control passage. This decreases the amount of the high-pressure refrigerant gas supplied to the crank chamber from the discharge pressure area, thus dropping the pressure in the crank chamber. This keeps the difference between the pressure in the crank chamber and the suction pressure at the set value.
The computer compares the temperature detected by a temperature sensor with the temperature set by a temperature setting unit to determine a target value, and controls the electric driving section in such a way that the reference set value for driving the valve section is the target value.
When the cooling load acting on the compressor is heavy, for example, the difference between the temperature detected by the temperature sensor and the temperature set by the temperature setting unit is larger. Based on this large difference, the computer controls the electric driving section to decrease the reference set value for driving the valve section. As a result, the tilt angle of the cam plate increases based on a small difference between the pressure in the crank chamber and the pressure in the cylinder bore, thus increasing the discharge capacity of the compressor in accordance with the heavy cooling load.
When a light cooling load is acting on the compressor, on the other hand, the difference between the temperature detected by the temperature sensor and the temperature set by the temperature setting unit is smaller. Based on this small difference, the computer controls the electric driving section to increase the reference set value for driving the valve section. As a result, the cam plate decreases the tilt angle based on a large difference between the pressure in the crank chamber and the pressure in the cylinder bore via the associated piston, thus reducing the discharge capacity of the compressor in accordance with the light cooling load.
In the above-described compressor, however, moment M in the direction of increasing the tilt angle is acting on a cam plate
102
based on inertial force F of a piston
101
which reciprocates, as shown in FIG.
4
. That is, in addition to the difference between the pressure in the crank chamber and the pressure in the cylinder bore via the piston
101
, the moment M that acts on the cam plate
102
based on inertial force F of the piston
101
greatly affects the determination of the tilt angle of the cam plate
102
. The magnitude of moment M is not always constant. As the rotational speed of the engine increases, the rotational speed of a drive shaft
103
rises too. When the piston
101
reciprocates at a high speed accordingly, the inertial force F of the piston
101
that acts on the cam plate
102
increases, thus making the moment M greater.
FIG. 5
shows a state where the cooling load is constant and the set value for driving the displacement control valve is also constant. In other words,
FIG. 5
shows the state where the difference between the pressure in the crank chamber and the pressure in the inertial force F of the piston
101
cylinder bore via the piston
101
is maintained at a certain value. Even in such state, an increase in the rotational speed of the engine driving the compressor and an increase in the inertial force F of the piston
101
will increase the tilt angle of the cam plate
102
or the discharge capacity of the compressor. Such a low-precision control on the discharge capacity of a compressor without considering variation in the inertial force F of the piston
101
is apt to degrade the cooling performance of the air-conditioning system of a vehicle.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a control apparatus for a variable displacement type compressor that can perform high-precision control of the discharge capacity of the variable displacement type compressor.
To achieve the above object, according to this invention, there is provided a control apparatus for controlling the discharge capacity of a variable displacement type compressor, which has a cam plate supported on a drive shaft to rotate together with the drive shaft in a crank chamber. The apparatus changes the discharge capacity by changing the difference between the pressure in the crank chamber and a suction pressure. The cam plate converts a rotational movement of the drive shaft, which is driven by an engine, to reciprocal movement of the pistons, which compresses gas. The control apparatus includes: a valve for keeping the difference between the pressure in the crank chamber and the suction pressure at a set value; an electric driving mechanism that changes a reference set value, wherein the reference set value is used to operate the valve; an external information detector for outputting information about the temperature of a passenger compartment of the vehicle; a rotational speed sensor for detecting the rotational speed of the engine or a rotational speed related to the rotational speed of the engine; and a computer for determining a target value based on the temperature information and for controlling the electric driving mechanism such that the target value determines the set value, wherein the computer corrects the target value based on rotational speed information from the rotational speed sensor.
REFERENCES:
patent: 5694781 (1997-12-01), Peterson
patent: 5823000 (1998-10-01), Takai
patent: 5924296 (1999-07-01), Takano et al.
patent: 6038871 (2000-03-01), Gutierrez et al.
patent: 6-341378 (199
Adaniya Taku
Kawaguchi Masahiro
Ota Masaki
Tarutani Tomoji
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
Tanner Harry B.
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