Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
2000-10-02
2002-05-14
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
Reexamination Certificate
active
06386834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control valve used for a displacement variable compressor that is capable of changing its displacement based on a control pressure, which acts on a displacement variation mechanism.
A cooling circuit of a vehicle air conditioner generally includes a condenser, an expansion valve, which is used as a pressure reducing device, an evaporator and a compressor. The compressor draws refrigerant gas from the evaporator, compresses it and discharges the compressed gas to the condenser. The evaporator receives heat from the passenger compartment air and heats the refrigerant gas that flows in the cooling circuit. In accordance with the magnitude of the heat load and the cooling load, the heat of air that passes through the evaporator is transferred to the refrigerant that flows within the evaporator. Thus, the refrigerant gas pressure at the outlet or the downstream side of the evaporator reflects the magnitude of the air conditioning load.
A variable displacement swash plate type compressor, which is typically used in vehicles, includes a displacement control mechanism for controlling the outlet pressure of the evaporator (referred to as the suction pressure Ps) to maintain a desired target value (referred to as the set suction pressure). The displacement control mechanism performs feed back-control of the discharge displacement, that is, the angle of the swash plate, using the suction pressure Ps as the control index to achieve a flow rate of the refrigerant that corresponds to the magnitude of the cooling load. A typical example of such a displacement control mechanism is called an internal control valve. By sensing the suction pressure Ps with a pressure sensing member such as bellows, a diaphragm or the like in the internal control valve and using the motion of the pressure sensing member for positioning a valve body, the pressure (crank pressure Pc) in the swash plate chamber (also called the crank chamber) is controlled to determine the swash plate angle.
Further, since a simple internal control valve, which can have only a single preset suction pressure, cannot address fine air conditioning control needs, there are control valves that can change the preset suction pressure by external electrical control. Such control valves effect the change of the preset suction pressure by employing an actuator, such as an electromagnetic solenoid or the like, to apply force to the valve body.
A compressor to be used in a vehicle is generally driven by the vehicle engine. The compressor generally consumes the most engine power (or torque) of the several auxiliary machines that are driven by the engine. Thus, there is no doubt that the compressor is a large load on the engine. Accordingly, a typical vehicle air conditioner has a program for reducing the engine load by minimizing the discharge displacement of the compressor when engine power is needed for other purposes, such as accelerating the vehicle or driving the vehicle uphill. In an air conditioner using the variable displacement compressor including the above-described suction pressure varying valve, substantial displacement reduction is realized by changing the preset suction pressure of the control valve to a value higher than a usual preset suction pressure.
The operation of the variable displacement compressor with a preset suction pressure variable valve was analyzed in detail. As a result, it has been found that, as long as a suction pressure Ps-indexed feedback control is involved, the expected displacement reduction (that is, a decrease in the engine load) will not be necessarily realized. The graph of
FIG. 14
conceptionally shows the relationship between the suction pressure Ps and the discharge displacement Vc of the compressor. As can be seen from this graph, the curve (characteristic line) between the suction pressure Ps and the discharge displacement Vc is not one kind. There are a plurality of curves in accordance with the magnitude of the heat load in the evaporator. Thus, even if a certain pressure Ps
1
is given as the preset suction pressure Pset, which is a target value of the feedback control, a constant variation (&Dgr;Vc in the graph) is generated by the conditions of the heat load on the actual discharge displacement Vc that results from the operation of the control valve. For example, when the heat load in the evaporator is very high, even if the preset suction pressure Pset is increased sufficiently, the actual discharge displacement Vc may not be decreased enough to sufficiently reduce the engine load.
Further, as long as the above-described displacement limiting control is temporary, it is necessary to return the discharge displacement Vc of the compressor to the discharge displacement Vc that existed before the displacement limiting procedure. When the return of the displacement occurs very rapidly, an uncomfortable shock or noise is experienced by the vehicle passengers. Accordingly, it is preferred that the discharge displacement Vc be returned to normal gradually.
The graph of
FIG. 15
shows various patterns of the displacement Vc of the compressor, which correlates with the load torque, over time before and after the displacement limiting control procedure. The patterns shown by the solid lines in this graph are substantially ideal linear return processes. On the contrary, as long as the control procedure is based on the suction pressure Ps, gentle linear return patterns as shown in
FIG. 15
by the solid lines cannot be realized by monotonously controlling (that is, a monotonous return to the previous amount of energization of the electromagnetic solenoid) the preset suction pressure Pset. Thus, the displacement Vc abruptly increases along one of two return patterns as shown by broken lines in FIG.
15
.
One pattern is a pattern in which the discharge displacement Vc immediately rises, and the other pattern is a pattern in which the discharge displacement Vc immediately rises after a considerable delay. These patterns are phenomena that are derived from the fact that the suction pressure Ps and the discharge displacement Vc of the compressor have no definite relationship. Thus, in trying to achieve a more ideal pattern for the displacement return after reducing the displacement, there was a limit based on the conventional suction pressure Ps control.
The technique of controlling the discharge displacement Vc of the displacement variable compressor based on the suction pressure Ps, which reflects the heat load in the evaporator, was an appropriate technique in attaining the original purpose of stabilizing and maintaining the compartment temperature. However, to achieve a rapid reduction in the discharge displacement and then to return to the original discharge displacement Vc in a pattern that avoids shock or noise, control must be based on something other than the suction pressure Ps.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a control valve for a displacement variable compressor that is capable of controlling the discharge displacement of a compressor for stabilizing and maintaining the compartment temperature, of rapidly changing the discharge displacement and returning the displacement to normal. Specifically, the object of the present invention is to provide a control valve that accurately controls the displacement in the vicinity of the lowest discharge displacement and that permits direct control of the discharge displacement over a wide range.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve for a cooling apparatus is provided. The apparatus has a compressor, which includes a displacement mechanism, an external refrigerant circuit, which is connected to the compressor to form, together with the compressor, a cooling circuit. The control valve changes the discharge displacement of the compressor by controlling a control pressure that acts on the displacement variable mechanism. The valve includes a housing, an internal passage pr
Adaniya Taku
Kawaguchi Masahiro
Kimura Kazuya
Suitou Ken
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
Robinson Daniel
Walberg Teresa
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