Method for estimating drive torque of variable displacement compressor and system for controlling drive source rotation speed

Abstract

The value of an estimated drive torque is prevented from greatly differing from an actual drive torque of a variable displacement compressor immediately after a refrigerating cycle is started. A first estimated drive torque that is calculated based on a physical quantity other than the pressure of a refrigerant and increases with lapse of time after the variable displacement compressor begins to compress the refrigerant and a second estimated drive torque calculated using the pressure of the refrigerant are compared and the one with the value closer to the actual drive torque is employed as an estimated drive torque of the variable displacement compressor.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for estimating a drive torque of a variable displacement compressor used to drive a refrigerating cycle and a system for controlling a rotation speed of a drive source for driving a variable displacement compressor and, more particularly, is suitable for an air conditioner for a vehicle.

2. Description of the Related Art

Conventionally, the drive torque of a variable displacement compressor used for driving a refrigerating cycle is estimated using the pressure on the high-pressure side of the refrigerating cycle (for an example, see Patent document 1).

However, there has been a problem that, if the drive torque is estimated using the pressure etc. on the high-pressure side of a refrigerating cycle in a transient state immediately after the refrigerating cycle is started, the estimated drive torque greatly differs from an actual drive torque.

Further, there has been another problem that when a variable displacement compressor is driven by an engine, which is a drive source, if a target rotation speed of the engine is determined based on an estimated drive torque greatly differing from the actual drive torque during the period of engine idling, it is not possible to harmonize with the control of other devices driven by the engine and, therefore, the target rotation speed of the engine does not stabilize.

[Patent document 1]

Japanese Unexamined Patent Publication (Kokai) No. 2001-180261

SUMMARY OF THE INVENTION

The present invention has been developed to solve the above-mentioned problems and the object thereof is to prevent the value of an estimated drive torque from greatly differing from the actual drive torque of a variable displacement compressor immediately after a refrigerating cycle is started.

In order to attain the above-mentioned object, in a first aspect of the present invention, a refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying the displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing the pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting the pressure of the refrigerant from the variable displacement compressor to the pressure reducing means. In the refrigerating cycle, a method for estimating a drive torque of the variable displacement compressor comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor, which is calculated based on at least a physical quantity other than the pressure of the refrigerant detected by the pressure detection means and gradually increases with lapse of time after the variable displacement compressor begins to compress the refrigerant; and a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using the pressure of the refrigerant detected by the pressure detection means, wherein the first estimated drive torque and the second estimated drive torque are compared and the one with the lower value is employed as an estimated drive torque of the variable displacement compressor.

Due to this, even if the second drive torque estimation means calculates a second estimated drive torque greater than the actual drive torque using the pressure of the refrigerant immediately after the refrigerating cycle starts to operate, a first estimated drive torque calculated by the first drive torque estimation means for calculating an estimated drive torque based on a physical quantity other than the pressure of the refrigerant gradually increases with lapse of time after the variable displacement compressor begins to compress the refrigerant. Therefore, it will be less than the above-mentioned second estimated drive torque during the period of transient immediately after the refrigerating cycle is started, that is, when the variable displacement compressor begins to discharge the refrigerant. As a result, the first estimated drive torque is employed as an estimated drive torque and, therefore, it is possible to prevent the estimated drive torque from greatly differing from the actual drive torque of the variable displacement compressor immediately after the refrigerating cycle is started.

In a second aspect of the present invention, a refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying the displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing the pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting the pressure of the refrigerant from the variable displacement compressor to the pressure reducing means. In the refrigerating cycle, a method for estimating a drive torque of the variable displacement compressor comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor based on at least a physical quantity other than the pressure of the refrigerant detected by the pressure detection means; a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using the pressure of the refrigerant detected by the pressure detection means; and a lapse of time measurement means for measuring the lapse of time after the variable displacement compressor begins to compress the refrigerant are provided wherein, when the lapse of time measured by the lapse of time measurement means is less than a predetermined time, the first estimated drive torque is employed as an estimated drive torque of the variable displacement compressor and when the lapse of time measured by the lapse of time measurement means is equal to or more than the predetermined time, the second estimated drive torque is employed as an estimated drive torque of the variable displacement compressor.

Due to this, when the lapse of time, after the refrigerating cycle is started, is less than the predetermined time, the first estimated drive torque is employed as an estimated drive torque and, therefore, it is possible to prevent the estimated drive torque from greatly differing from the actual drive torque of the variable displacement compressor immediately after the refrigerating cycle is started.

A third aspect of the present invention according to the above-mentioned second aspect is characterized in that the displacement variable mechanism varies the displacement of the refrigerant to be compressed by the compression mechanism section by a control current input from the outside and that the first drive torque estimation means calculates the first estimated drive torque based on the control current.

Due to this, the first drive torque estimation means calculates the first estimated drive torque based on the volume of refrigerant to be compressed by the variable displacement compressor and, therefore, it is possible to more accurately calculate the first estimated drive torque.

A fourth aspect of the present invention according to the above-mentioned first or second aspect is characterized in that the first drive torque estimation means calculates the first estimated drive torque using the lapse of time after the variable displacement compressor begins to compress the refrigerant and the value stored in advance in accordance with the lapse of time. Due to this, it becomes possible to quickly calculate the first estimated torque.

A fifth aspect of the present invention is characterized in that the variable displacement compressor is driven by a drive source and the estimated drive torque calculated by the method for estimating a drive torque of a variable displacement compressor described in any one of the first to fourth aspects is used to control the rotation speed of the drive source.

Due to this, it is possible to optimize the rotation speed of the drive source by using the estimated drive torque, calculated so as not to greatly differ from the actual drive torque, to control the rotation speed of the drive source.

A sixth aspect of the present invention comprises a refrigerating cycle having a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying the displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing the pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting the pressure of the refrigerant from the variable displacement compressor to the pressure reducing means, a drive source for driving the variable displacement compressor, a lapse of time measurement means for measuring the lapse of time after the variable displacement compressor begins to compress the refrigerant, a drive torque estimation means for calculating an estimated drive torque of the variable displacement compressor using the pressure of the refrigerant detected by the pressure detection means, and a rotation speed calculation means for calculating a target rotation speed of the drive source using the estimated drive torque are provided, and is characterized in that, when the lapse of time measured by the lapse of time measurement means is less than a predetermined time, a value, which is an obtained by subtracting a torque calculated by a predetermined calculation from an estimated drive torque calculated by the drive torque estimation means, is used as an estimated drive torque to be used in calculation, and the estimated drive torque calculated by the drive torque estimation means is used as it is in calculation when the lapse of time measured by the lapse of time measurement means is equal to or more than the predetermined time.

Due to this, it becomes possible to optimize the control of the drive source rotation speed by the single drive torque estimation means.

A seventh aspect of the present invention according to the fifth or sixth aspect is characterized in that the rotation speed calculation means calculates a target idle rotation speed of the drive source.

Due to this, it is possible to reduce idling noises and improve the fuel consumption efficiency of the drive source by optimizing the target idling rotation speed.

In an eighth aspect of the present invention, a refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying the displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing the pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting the pressure of the refrigerant from the variable displacement compressor to the pressure reducing means. In the refrigerating cycle, a method for estimating a drive torque of a variable displacement compressor comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor, which is calculated based on at least a physical quantity other than the pressure of the refrigerant detected by the pressure detection means and gradually increases with lapse of time after the variable displacement compressor begins to compress the refrigerant; and a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using the pressure of the refrigerant detected by the pressure detection means, wherein the first estimated drive torque and the second estimated drive torque are compared and the one with the value closer to the actual drive torque is employed as an estimated drive torque of the variable displacement compressor. Due to this, the same effect as that in the first aspect can be obtained.

The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagram showing a configuration in an embodiment of the present invention.

FIG. 2 is a graph showing the drive torque of a variable displacement compressor 1 with respect to the lapse of time in the embodiment of the present invention.

FIG. 3 is a flow chart showing a method for determining an estimated torque in the embodiment of the present invention.

FIG. 4 is a graph showing the drive torque variation with respect to the lapse of time when the variable displacement compressor 1 varies the discharge displacement in an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments

Embodiments of the present invention are explained below. FIG. 1 is diagram showing a connection relationship of a refrigerating cycle Rc having a variable displacement compressor 1 driven by an engine, not shown, through a belt, an ECU 2 for controlling the refrigerating cycle Rc and the engine, and a sensor group (8 to 12), to be described later, relating to input and output of the ECU 2.

The variable displacement compressor 1 which is a widely known, comprises a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying the displacement in which the refrigerant is compressed by the compression mechanism section and the displacement variable mechanism is controlled by a displacement control signal input from the ECU 2.

The refrigerating cycle Rc comprises the above-mentioned variable displacement compressor 1, a condenser 3 for condensing a refrigerant compressed by the variable displacement compressor 1, a gas-liquid separator 4 for separating the refrigerant condensed by the condenser 3 into gas and liquid, an expansion valve 5, which is a pressure reducing means, for reducing in pressure the liquid refrigerant separated by the gas-liquid separator 4, an evaporator 6 for evaporating the refrigerant reduced in pressure by the expansion valve 5, and a refrigerant pipe 7 for connecting the variable displacement compressor 1, the condenser 3, the gas-liquid separator 4, the expansion valve 5, and the evaporator 6, and further comprises a high pressure sensor 8 for detecting the pressure of the refrigerant from the variable displacement compressor 1 to the expansion valve 5. The expansion valve 5 is a thermostatic expansion valve for reducing the pressure of the liquid refrigerant separated by the gas-liquid separator 4 by setting an opening of the valve in accordance with the pressure of a gas in a temperature-sensitive cylinder 5a arranged downstream of the evaporator 6 so as to expand the liquid refrigerant.

To the ECU 2, a high pressure signal detected by the above-mentioned high pressure sensor 8, an inside air temperature signal from an inside air temperature sensor 9 for detecting the temperature in a vehicle compartment space of a vehicle, not shown, an outside air temperature signal from an outside air temperature sensor 10 for detecting the temperature at the outside of the vehicle, a solar radiation signal from a solar radiation sensor 11 for detecting the quantity of solar radiation that comes into the vehicle compartment, and an evaporator temperature signal from an evaporator temperature sensor 12 attached to the surface of the evaporator 6 for detecting the temperature of the evaporator 6 are input via an A-D converter 13. To the ECU 2, an engine rotation speed signal from an engine rotation speed detection means 14 for detecting the rotation speed of an engine, an air conditioner ON/OFF signal issued when a passenger operates an air conditioner operation panel 15 arranged in the vehicle compartment, and an IG signal from an IG switch 17 for controlling conduction of a current to a vehicle-mounted battery 16 are also input.

Then, the ECU 2 controls the displacement variable mechanism of the variable displacement compressor 1, a condenser fan 18, an air conditioner blower fan 19, and the opening of an idle adjustment valve 20 based on the above-mentioned signal group.

Here, the idle adjustment valve 20 is provided to a bypass pipe path 23 that bypasses a throttle valve 22 arranged in an engine air-suction pipe 21. During the period of engine idling, the ECU 2 adjusts the idling rotation speed by adjusting the flow rate of the sucked air to be supplied to the engine by controlling the opening degree of the idle adjustment valve 20.

The optimum idle rotation speed during the period of engine idling differs depending on the drive torque of an auxiliary device driven by the engine through a belt and, therefore, the ECU 2 determines a target idle rotation speed by estimating the drive torque of the variable displacement compressor 1 and determines an opening of the idle adjustment valve 20 based on the idle rotation speed.

A method for estimating the drive torque of the variable displacement compressor 1 is explained below using FIG. 2 and FIG. 3. FIG. 2 is a graph showing the drive torque variation of the variable displacement compressor 1 with respect to time in the present embodiment, in which graph the time is assumed to be to when an air conditioner ON signal is input to the ECU 2 from the operation panel 15 and the variable displacement compressor 1 begins to be driven. In FIG. 2, the solid line indicates the actual drive torque, the broken line indicates the first estimated drive torque (TrqA) calculated based on a physical quantity other than the pressure on the high-pressure side of the refrigerating cycle by the first drive torque estimation means according to the present invention, and the alternating long and short dashed line indicates the second estimated drive torque (TrqB) calculated using the pressure on the high-pressure side of the refrigerating cycle by the second drive torque estimation means according to the present invention. The first estimated torque (TrqA) in the present embodiment is represented by a line that is an approximation of the drive torque variation of the variable displacement compressor 1 with respect to time and this line shows that the drive torque monotonically increases with the lapse of time after the air conditioner ON/OFF signal is input.

FIG. 3 is a flow chart for determining which estimated drive torque to use to control the engine rotation speed between the above-mentioned first estimated drive torque (TrqA) and the second estimated drive torque (TrqB) in the ECU 2 in the present embodiment.

First, in step S1, the above-mentioned high pressure signal and the engine rotation speed are read and then the flow proceeds to step S2.

In step S2, the first estimated drive torque (TrqA) is calculated based on the map stored in advance in the ECU 2, without using the high pressure signal and then the flow proceeds to step S3. The map stores a relationship between the lapse of time after the air conditioner ON/OFF signal is input and the above-mentioned first estimated drive torque (TrqA).

In step S3, the second estimated drive torque (TrqB) is calculated based on the high pressure signal, the engine rotation speed signal, and the control current value calculated by the ECU 2 for controlling the above-mentioned displacement variable mechanism, and then the flow proceeds to step S4.

In step S4, the first estimated drive torque (TrqA) calculated in step S2 is compared with the second estimated drive torque (TrqB) calculated in step S3 and when the first estimated drive torque (TrqA) is less than the second estimated drive torque (TrqB), the flow proceeds to step S5 and when the first estimated drive torque (TrqA) is greater than the second estimated drive torque (TrqB), the flow proceeds to step S6.

In step S5, a target idling rotation speed during the period of engine idling is determined based on the first estimated drive torque (TrqA) and then the flow proceeds to step S7.

In step S6, a target idling rotation speed during the period of engine idling is determined based on the second estimated drive torque (TrqB) and then the flow proceeds to step S7.

In step S7, the flow returns to step S1.

Next, the effect of the present embodiment is explained. In the present embodiment, the first estimated drive torque (TrqA) that increases with lapse of time after the air conditioner ON/OFF signal is input and the second estimated drive torque (TrqB) calculated based on the high pressure signal, the engine rotation speed signal, and the control current value of the displacement variable mechanism are compared, and the target idle rotation speed is determined based on the smaller estimated drive torque. Therefore, even immediately after the air conditioner ON/OFF signal is input, the second estimated drive torque (TrqB), that is calculated based on the high pressure signal and is greater than the actual one, is not used, but the first estimated drive torque (TrqA) that increases with lapse of time is used. Due to this, it is possible to determine the target idle rotation speed by using the estimated drive torque close to the actual drive torque of the variable displacement compressor 1, as shown in FIG. 2.

Due to this, it is possible to optimize the target idle rotation speed of an engine and therefore, the idling noise can be reduced and the engine fuel consumption efficiency can be improved.

In the present embodiment, the first estimated drive torque (TrqA) is calculated based on the map stored in advance in the ECU 2. However, as shown in FIG. 4, even if the volume of refrigerant that the variable displacement compressor 1 compresses is varied by the displacement variable mechanism, it is unlikely that the actual drive torque varies considerably depending on the volume of refrigerant to be compressed (hereinafter, referred to as a discharge displacement) immediately after the air conditioner ON/OFF signal is input and, therefore, it is possible to use the same single map regardless of the volume of refrigerant to be compressed. As is also obvious from FIG. 4, the period of time (T0 to T1, T0 to T2, T0 to T3) during which a target idle rotation speed is determined using the first estimated drive torque (TrqA) is lengthened depending on the change in discharge displacement.

Other Embodiments

In the present embodiment, the first estimated drive torque (TrqA) is calculated based on the map of the estimated torque that is stored in advance in the ECU 2 and which rectilinearly increases with lapse of time after the air conditioner ON/OFF signal is input. However, the present invention is not limited to this, and it may be calculated by any method provided the first estimated drive torque (TrqA) is calculated without using the high pressure signal, and the first estimated drive torque (TrqA) may be calculated based on the control current value of the displacement variable mechanism. Due to this, it is possible to more accurately calculate the first estimated drive torque (TrqA).

Further, in the above-mentioned embodiment, which one of the first estimated drive torque (TrqA) and the second estimated drive torque (TrqB) is used is determined depending on the magnitude of the first estimated drive torque (TrqA) and the second estimated drive torque (TrqB), however, the present invention is not limited to this, and which one of the first estimated drive torque (TrqA) and the second estimated drive torque (TrqB) is used may be determined based on the lapse of time measured by a lapse of time measurement means provided for measuring the lapse of time after the air conditioner ON/OFF signal is input. Alternatively, it may also be possible to use the first estimated drive torque (TrqA) until a predetermined time elapses after the air conditioner ON/OFF signal is input and then use the second estimated drive torque (TrqB) after the predetermined time elapses.

Furthermore, in the above-mentioned embodiment, the optimum target idle rotation speed is determined while preventing the estimated drive torque from greatly differing from the actual drive torque by providing plural drive torque estimation means, however, the present invention is not limited to this. It may also be possible to determine a target idle rotation speed by using a single drive torque estimation means for calculating an estimated drive torque based on the high pressure signal, by including the above-mentioned lapse of time measurement means, and by using a value, which is obtained by subtracting the torque calculated by a predetermined calculation from the estimated drive torque calculated by the drive torque estimation means, until a predetermined time elapses.

The high-pressure sensor 8 may be installed at any place provided that it can detect the pressure of the refrigerant from the variable displacement compressor 1 to the expansion valve 5 and it may be installed to the main body of the variable displacement compressor 1 or it may be installed to the refrigerant pipe 7.

In the above-mentioned embodiment, a single map is used in order to calculate the first estimated drive torque, however, the present invention is not limited to this, and plural maps may be used.

In the above-mentioned embodiment, the first estimated drive torque and the second estimated drive torque are compared and the one with the smaller value is employed as an estimated drive torque of the variable displacement compressor, however, the present invention is not limited to this, and it may also be possible to compare the first estimated drive torque and the second estimated drive torque and employ the one with the value closer to the actual drive torque as an estimated drive torque of the variable displacement compressor.

While the invention has been described by reference to specific embodiments chosen for the purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.

Claims

1. A method for estimating a drive torque of a variable displacement compressor included in a refrigerating cycle, wherein the refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying a displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting pressure of the refrigerant from the variable displacement compressor to the pressure reducing means, and wherein the method comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor, which is calculated based on at least a physical quantity other than pressure of refrigerant detected by the pressure detection means and which gradually increases with lapse of time after the variable displacement compressor begins to compress the refrigerant; and a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using pressure of refrigerant detected by the pressure detection means, and the first estimated drive torque and the second estimated drive torque are compared and the one with the lower value is employed as an estimated drive torque of the variable displacement compressor.

2. A method for estimating a drive torque of a variable displacement compressor included in a refrigerating cycle, wherein the refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying a displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting pressure of the refrigerant from the variable displacement compressor to the pressure reducing means, and wherein the method comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor based on at least a physical quantity other than pressure of refrigerant detected by the pressure detection means; a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using pressure of refrigerant detected by the pressure detection means; and a lapse of time measurement means for measuring lapse of time after the variable displacement compressor begins to compress the refrigerant, and when the lapse of time measured by the lapse of time measurement means is less than a predetermined time, the first estimated drive torque is employed as an estimated drive torque of the variable displacement compressor and when the lapse of time measured by the lapse of time measurement means is equal to or more than the predetermined time, the second estimated drive torque is employed as an estimated drive torque of the variable displacement compressor.

3. The method for estimating a drive torque of a variable displacement compressor as set forth in claim 2, wherein: the displacement variable mechanism varies the displacement of the refrigerant to be compressed by the compression mechanism section by a control current input from an outside; and the first drive torque estimation means calculates the first estimated drive torque based on the control current.

4. The method for estimating a drive torque of a variable displacement compressor as set forth in claim 1, wherein the first drive torque estimation means calculates the first estimated drive torque using the lapse of time after the variable displacement compressor begins to compress the refrigerant and a value stored in advance in accordance with the lapse of time.

5. A system for controlling a drive source rotation speed, wherein the variable displacement compressor is driven by a drive source and the estimated drive torque calculated by the method for estimating a drive torque of a variable displacement compressor as set forth in claim 1 is used to control rotation speed of the drive source.

6. A system for controlling a drive source rotation speed, comprising a refrigerating cycle having: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying a displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means and the evaporator; and a pressure detection means for detecting the pressure of the refrigerant from the variable displacement compressor to the pressure reducing means, a drive source for driving the variable displacement compressor, a lapse of time measurement means for measuring lapse of time after the variable displacement compressor begins to compress the refrigerant, a drive torque estimation means for calculating an estimated drive torque of the variable displacement compressor using pressure of refrigerant detected by the pressure detection means, and a rotation speed calculation means for calculating a target rotation speed of the drive source using the estimated drive torque, wherein when the lapse of time measured by the lapse of time measurement means is less than a predetermined time, a value, which is obtained by subtracting a torque calculated by a predetermined calculation from an estimated drive torque calculated by the drive torque estimation means, is used as an estimated drive torque to be used in calculation, and the estimated drive torque calculated by the drive torque estimation means is used, as it is, in calculation when the lapse of time measured by the lapse of time measurement means is equal to or more than the predetermined time.

7. The system for controlling a drive source rotation speed as set forth in claim 5, wherein the rotation speed calculation means calculates a target idle rotation speed of the drive source.

8. A method for estimating a drive torque of a variable displacement compressor in a refrigerating cycle, wherein the refrigerating cycle comprises: a variable displacement compressor having a compression mechanism section for compressing a refrigerant and a displacement variable mechanism for varying a displacement of the refrigerant to be compressed by the compression mechanism section; a condenser for condensing the refrigerant compressed by the variable displacement compressor; a pressure reducing means for reducing pressure of the refrigerant condensed by the condenser; an evaporator for evaporating the refrigerant reduced in pressure by the pressure reducing means; refrigerant pipes for connecting the variable displacement compressor, the condenser, the pressure reducing means, and the evaporator; and a pressure detection means for detecting pressure of refrigerant from the variable displacement compressor to the pressure reducing means, wherein the method comprises: a first drive torque estimation means for calculating a first estimated drive torque of the variable displacement compressor, which is calculated based on at least a physical quantity other than pressure of refrigerant detected by the pressure detection means and gradually increases with lapse of time after the variable displacement compressor begins to compress the refrigerant; and a second drive torque estimation means for calculating a second estimated drive torque of the variable displacement compressor using pressure of refrigerant detected by the pressure detection means, and the first estimated drive-torque and the second estimated drive torque are compared and the one with the value closer to an actual drive torque is employed as an estimated drive torque of the variable displacement compressor.

9. The method for estimating a drive torque of a variable displacement compressor as set forth in claim 2, wherein the first drive torque estimation means' calculates the first estimated drive torque using the lapse of time after the variable displacement compressor begins to compress the refrigerant and a value stored in advance in accordance with the lapse of time.

10. A system for controlling a drive source rotation speed, wherein the variable displacement compressor is driven by a drive source and the estimated drive torque calculated by the method for estimating a drive torque of a variable displacement compressor as set forth in claim 2 is used to control rotation speed of the drive source.

11. The system for controlling a drive source rotation speed as set forth in claim 6, wherein the rotation speed calculation means calculates a target idle rotation speed of the drive source.