1. Field of the Invention
The present invention relates to an air conditioner having a hot gas bypass function of heating air when a gas refrigerant of high temperature and pressure, which has been discharged from a refrigerant compressor, is decompressed and introduced into a refrigerant evaporator and the refrigerant evaporator is used as a radiator from which the heat of the gas refrigerant is radiated. More particularly, the present invention relates to an air conditioner for vehicle use which is preferably mounted on a vehicle.
2. Description of the Related Art
In a conventional air conditioner for vehicle use, warm water (engine coolant) is circulated in a heat exchanger used for heating in winter, and air to be conditioned is heated by this heat exchanger for heating while the warm water is used as a heat source. In this case, when the temperature of the warm water is low, air at low temperature is blown out into a passenger compartment, that is, it is impossible to provide a sufficiently large heating capacity.
In order to solve the above problems, conventionally, an air conditioner is proposed in which the heating capacity is exhibited by providing a hot gas bypass. In this conventional air conditioner, when the temperature of warm water is low in the case of starting an engine, gas refrigerant (hot gas) compressed by a compressor in the refrigerating cycle is introduced into an evaporator which bypasses a condenser, and heat is emitted from the gas refrigerant to air to be conditioned by the evaporator, so that a heating function can be exhibited. However, the hot gas cycle in which gas refrigerant of high temperature and pressure in the refrigerating cycle is used, the heating capacity is greatly affected by whether or not a sufficiently large quantity of refrigerant is charged into the air conditioner. For example, when a sufficiently large quantity of refrigerant is not charged, the heating capacity is lowered, and when an excessively large quantity of refrigerant is charged, the compressor is too frequently turned on and off, and the durability of the magnet switch of the compressor is deteriorated.
In order to solve the above problems, Japanese Unexamined Patent Publication No. 5-272817 discloses the following techniques. A high pressure on the discharging side of the compressor is detected, and it is judged whether a quantity of circulating refrigerant is sufficient or insufficient in the heating mode conducted by the hot gas bypass. In the case where the quantity of refrigerant is too large, the refrigerant is discharged onto the condenser side. In the case where the quantity of refrigerant is too small, the residing refrigerant is recovered from the condenser side. Recovery of the residing refrigerant is specifically conducted in such a manner that the entry side of the condenser is opened and the entry side of the hot gas bypass path is closed, that is, the air conditioner is set in the normal cooling mode, and then the compressor is operated.
However, in the heating mode conducted by the hot gas bypass, high pressure on the discharging side of the compressor fluctuates by factors such as a heat load in the cycle, rotary speed of the compressor, throttle diameter of the decompression means in the hot gas bypass path and so forth. Therefore, it is difficult to appropriately judge only by the high pressure whether the quantity of refrigerant is sufficient or insufficient.
In addition to that, after the hot gas bypass operation has been started, in order to stabilize the operation of high pressure, it takes a long time. At least 5 minutes is required to stabilize the operation at high pressure. In this period of time, the heating capacity is insufficient due to lack of the refrigerant. Further, a sufficiently large quantity of oil is not returned to the compressor, which causes a failure of lubrication of the compressor.
When the residing refrigerant is recovered in the case of heating in winter, the outside temperature is low and a heat load for cooling is very light. Therefore, a difference between high and low pressure in the refrigerating cycle is very small. For the above reasons, in the case where a variable displacement type compressor, in which a displacement of the compressor is changed by utilizing a difference between high and low pressure in the refrigerating cycle, is used for the compressor, the displacement is not increased, that is, the displacement is kept small because the difference between high and low pressure in the refrigerating cycle is small. Accordingly, it becomes impossible to recover the residing refrigerant.
In order to solve the above problems, the present applicant has proposed the refrigerating cycle disclosed in U.S. Pat. No. 6,105,375. In this conventional refrigerating cycle device, when the heating mode conducted by the hot gas bypass is started, when the compressor is operated while both the entry side of the condenser and that of the hot gas bypass path are closed, the residing refrigerant existing on the condenser side is forcibly recovered onto the evaporator side.
However, in the case where recovery control of recovering the residing refrigerant is conducted as described above, as the compressor is continuously driven under the condition that only a small quantity of refrigerant and oil exist in the hot gas cycle, it becomes impossible to supply a necessary quantity of oil to the compressor for a long period of time. In this case, failure of lubrication is caused in the compressor, which leads to abrasion or breakdown of parts of the compressor. In the worst case, the compressor is locked.
Conventionally, in the case where hot gas bypass operation is conducted for more than a predetermined period of time, there is a possibility that refrigerant leaks from the electromagnetic valve to the condenser side. In this case, the quantities of refrigerant and oil in the hot gas cycle are decreased, and the hot gas capacity is lowered and, further, abrasion of the compressor is caused due to a reduction in the quantity of oil circulated.
The present invention has been accomplished to solve the above problems. It is an object of the present invention to provide an air conditioner capable of effectively recovering refrigerant and oil, which reside in a condenser, immediately before the start of hot gas operation, by driving a compressor for a short period of time.
It is another object of the present invention to provide an air conditioner capable of preventing a reduction of the hot gas capacity and also preventing abrasion of a compressor caused by a decrease in quantities of refrigerant and oil in the hot gas cycle in the case where hot gas bypass operation is conducted for more than a predetermined period of time.
In the air conditioner of an aspect of the present invention, it is possible to conduct a normal cooling mode operation and a heating mode operation performed by a hot gas bypass in which a condenser is bypassed. Immediately before this heating mode operation, after cooling mode operation has been turned on for a predetermined period of time, it is turned off for a predetermined period of time, and then heating mode operation is started. Due to the foregoing, refrigerant residing in the condenser can be effectively recovered into the hot gas cycle in a short period of time. Therefore, it becomes possible to prevent the occurrence of abrasion or breakdown of parts of the compressor caused by lack of lubrication in the compressor.
In the air conditioner of another aspect of the present invention, a second decompression device for decompressing refrigerant discharged from a compressor is arranged in a hot gas bypass path, and the hot gas bypass path is connected with a portion between a first decompression device and an evaporator. Concerning the system constitution of the hot gas cycle, there are provided two types. One is a type in which one decompression device is used for both the cooling mode and the heating mode (type B). The other is a type in which two different decompression devices are used for both the cooling mode and the heating mode (type A). This aspect is limited to the constitution of the hot gas cycle system of type A. In this aspect, the same operation and effect as that of the above aspect can be provided.
In the air conditioner of the present invention, cooling mode operation conducted for a predetermined period of time immediately before the start of heating mode operation by the hot gas bypass may be turned on and off a plurality of times. Due to the foregoing, an operation conducted when a quantity of refrigerant in the hot gas cycle is small, can be reduced to as short as possible. Therefore, the occurrence of abrasion and breakdown of parts of the compressor caused by lack of lubrication can be further reduced.
In the air conditioner of the present invention, a predetermined period of time to turn on and off the cooling mode operation, which is conducted immediately before the start of heating mode operation by the hot gas bypass, can be determined by a quantity of refrigerant recovered from a condenser for each temperature of the outside air. The quantity of refrigerant recovered is changed according to the temperature of outside air when a compressor is operated. Accordingly, the recovery time to ensure a quantity of refrigerant necessary for the hot gas cycle is determined by the temperature of outside air.
In the air conditioner of the present invention, a predetermined period of time to turn on and off the cooling mode operation, which is conducted immediately before the start of heating mode operation by the hot gas bypass, can be determined by a difference in pressure between the high pressure side and the low pressure side. When the difference in pressure reaches a predetermined value, the compressor is turned off, so that refrigerant can be recovered by the difference in pressure. Compared with the recovery of refrigerant conducted according to the operation time of the compressor, this method is advantageous in that a state of operation can be positively detected and it becomes unnecessary to set a refrigerant recovery time which is necessary for each temperature of outside air.
In the air conditioner of the present invention, a predetermined period of time to turn on the cooling mode operation, which is conducted immediately before the start of heating mode operation by the hot gas bypass, can be determined by a rotary speed of an engine. As a quantity of refrigerant to be recovered is changed by a flow rate of refrigerant in the hot gas cycle, when the rotary speed of the engine is detected, it is possible to estimate the flow rate of refrigerant. Therefore, when the rotary speed of the engine, which represents the rotary speed of the compressor, is detected, the refrigerant recovery time is determined for each rotary speed.
In the air conditioner of the present invention, in the case where refrigerant recovery control is conducted after a heating mode operation conducted by the hot gas bypass has been continued for a predetermined period of time, when pressure in a condenser becomes higher than pressure on the low pressure side of the hot gas cycle by a predetermined pressure difference P1, refrigerant is recovered by the second OFF mode in which a compressor is turned off and the entry side of a condenser is opened. Due to the foregoing, refrigerant flows from the condenser into the hot gas cycle, and refrigerant can be recovered from the condenser.
In the air conditioner of the present invention, when an operation of the cooling mode is conducted for a predetermined period of time after the completion of operation of the heating mode, a state of a predetermined pressure difference P1 can be formed.
In the air conditioner of the present invention, after the completion of the heating mode, the first OFF mode, in which a compressor is turned off and the entry side of a condenser is opened, is conducted for a predetermined period of time, and then a cooling mode operation is conducted. In this way, a predetermined pressure difference P1 may be made. When the first OFF mode is conducted for a predetermined period of time before a cooling mode operation, after pressure in the condenser is once made to be equal to pressure on the low pressure side of the hot gas cycle, a predetermined pressure difference P1 can be made. Therefore, a period of time required for making the predetermined pressure difference P1 can be reduced, o. When the compressor is turned on, an operation is conducted while DUTY is set at a value higher than zero. In this variable displacement type compressor, it is possible to conduct a refrigerant recovery operation by the cooling mode in which DUTY to the compressor is gradually increased after a difference in pressure has been somewhat reduced. Therefore, the period of time of the first OFF mode can be reduced.
In the air conditioner of still another aspect of the present invention, in the case where a heating mode switch is turned off in heating mode operation and turned on again in a predetermined period of time, first, after the first OFF mode, in which a compressor is turned off and then the entry side of a condenser is opened, is conducted for a predetermined period of time, refrigerant is recovered by conducting a cooling mode operation. Due to the foregoing, no refrigerant is recovered under the condition that pressure in a condenser is lower than pressure on the low pressure side of the hot gas cycle. Accordingly, refrigerant can be effectively recovered.
The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.