JPH0820213A - Air conditioner for vehicle - Google Patents

Abstract

PURPOSE:To judge operation mode accurately by containing values obtained by temperature-converting set temperature, outside air temperature, and value of solar radiation as variables in temperature calculation equation to be used by an operation mode judging means. CONSTITUTION:A microcomputer 33 is provided with a CPU, a ROM, a RAM, etc., to store a mode judging program in the ROM so that a predetermined signal is sent to a compressor drive circuit 34 and a solenoid valve drive circuit 35. The microcomputer 33 judges operation mode based on start judgement blow-out temperature calculated by an equation comprising values detected by a temperature setting device 28, inside and outside air temperature detectors, and value of solar radiation detectors 30 32 as variables. Here, a value obtained by temperature-converting value of solar radiation and set temperature are used as variables. Consequently, it is possible to judge proper operation mode accurately and prevent unexpected and wasteful mode change-over.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle air conditioner capable of automatically switching operating modes.

[0002]

2. Description of the Related Art Conventionally, in a vehicle air conditioner capable of operating in a cooling mode and a heating mode, TAO = Ks.T
s-Kr, Tr-Kam, Tam-Krad, Trad
It is determined whether or not the target outlet temperature TAO calculated by + C satisfies the conditions set in each of the cooling mode and the heating mode, and the operation mode is automatically switched based on the determination result.

In the above equation, Ts is the set temperature set by the user, Tr is the inside air temperature, Tam is the outside air temperature, and Trad.
Is a value obtained by converting the amount of solar radiation into temperature, Ks is a set temperature coefficient, Kr is an inside air temperature coefficient, Kam is an outside air temperature coefficient, and Kr is a temperature coefficient.
ad is an insolation coefficient, C is a constant, and an appropriate real value is selected for these depending on the size of the target space.

[0004]

By the way, the above-mentioned conventional target outlet temperature TAO is a numerical value at the time of calculation calculated with the inside air temperature Tr as one variable, in other words, it is a numerical value that fluctuates with the inside air temperature, so that proper operation is performed. It is difficult to determine the mode, and for example, when the set temperature is raised while the cooling mode operation is being executed, the heating mode is changed to the heating mode even if the heat load condition allows the operation in the cooling mode. There is a point. In addition, the temperature Tr in the vehicle compartment has a variation in its distribution itself and is easily influenced by external factors such as wind, so that there is a considerable difference in the calculated value of the target outlet temperature TAO depending on the installation position of the temperature detector. As a result, there is a problem that the unstable influence of the inside air temperature Tr strongly appears on the target outlet temperature TAO.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicle air conditioner capable of accurately determining an operation mode.

[0006]

In order to achieve the above object, the invention of claim 1 is an air conditioner for a vehicle equipped with a mode judging means for judging an operation mode based on a temperature calculated by a predetermined formula or the like. The temperature calculation formula used in the mode determination means includes, as variables, a set temperature, an outside air temperature, and a numerical value obtained by converting the amount of solar radiation into a temperature.

According to a second aspect of the invention, in the vehicle air conditioner according to the first aspect, STAO = K as a temperature calculation formula.
s ・ Ts-Kr ・ Ts-Kam ・ Tam-Krad ・ T
rad + C (Ts: preset temperature, Tam: outside air temperature, Tr
ad: Numerical value obtained by converting the amount of solar radiation into temperature, Ks: set temperature coefficient, Kr: inside air temperature coefficient, Kam: outside air temperature coefficient, Kr
It is characterized by using ad: solar radiation amount coefficient, C: constant).

According to a third aspect of the present invention, in the vehicle air conditioner according to the second aspect, the determination of the cooling mode by the mode determination means is a condition of STAO <Tr-a and Tr> Ts + b (Tr: inside air temperature, a , B: constant) is satisfied.

According to a fourth aspect of the invention, in the vehicle air conditioner according to the second aspect, the determination of the heating mode by the mode determination means is STAO> Tr + c, Tr <Ts-d and Tam <Ts (c, d: a constant) is satisfied.

According to a fifth aspect of the present invention, in the vehicle air conditioner of the second aspect, the determination of the cooling dry mode by the mode determination means is STAO when the dry switch is ON.
<Tr−e and Tr> Ts + f and Tam <g condition (e,
f, g: constant) is satisfied.

According to a sixth aspect of the present invention, in the vehicle air conditioner according to the second aspect, the determination of the heating dry mode by the mode determination means is STAO when the dry switch is ON.
> Tr + h, Tam <Ts, Tam ≧ i, and N <j (h, i, j: constant, N: compressor rotation speed) are satisfied.

[0012]

According to the invention of claim 1, the temperature to be subjected to the mode determination is calculated by an expression including a numerical value obtained by converting the set temperature, the outside air temperature and the amount of solar radiation as a variable, in other words, an expression not including the inside air temperature as a variable. To be done.

According to the second aspect of the present invention, the temperature to be subjected to the mode determination is STAO = Ks.Ts-Kr.Ts-Kam.
-Calculated by the formula of Tam-Krad-Trad + C. Other functions are similar to those of the invention of claim 1.

According to the third aspect of the invention, STAO <Tr-a
And the condition of Tr> Ts + b is satisfied, the determination of the cooling mode is made. Other functions are similar to those of the invention of claim 2.

According to the fourth aspect of the present invention, the heating mode is determined when the conditions of STAO> Tr + c, Tr <Ts-d and Tam <Ts are satisfied. Other functions are similar to those of the invention of claim 2.

In the invention of claim 5, the dry switch is O
STAO <Tr-e and Tr> Ts + f and Tam <g at N
When the condition of is satisfied, the determination of the cooling dry mode is made. Other functions are similar to those of the invention of claim 2.

In the invention of claim 6, the dry switch is O
Condition of STAO> Tr + h, Tam <Ts, Tam ≧ i and N <j at N (h, i, j: constant, N: compressor speed)
If the condition is satisfied, the heating dry mode is determined. Other functions are similar to those of the invention of claim 2.

[0018]

1 and 2 show a refrigerant circuit and its control circuit according to an embodiment of the present invention, respectively.

In FIG. 1, 1 is a variable capacity electric compressor, 2 is an outdoor heat exchanger, 3 is a first indoor heat exchanger, 4 is a second indoor heat exchanger, and 5 and 6 are heat-sensitive first heat exchangers. 1, second expansion valve,
7 to 10 are first to fourth solenoid valves, 11 and 12 are first and second
A check valve, 13 is a liquid receiver, and 14 is an accumulator.
Reference numeral 15 is a vehicle interior air conditioning duct, 16 is an outside air intake port, and 17
Is an inside air inlet, 18 is a switching damper for the inlet, 19 is a vent outlet, 20 is a foot outlet, 21 is a differential outlet,
22 is an opening / closing damper for a vent outlet, 23 is an opening / closing damper for a foot outlet, 24 is an opening / closing damper for a differential outlet,
Reference numeral 25 is an air mix damper, and 26 is an electric fan.

The discharge port of the compressor 1 is connected to one end port of the outdoor heat exchanger 2 via the fourth electromagnetic valve 10, and the other end port of the outdoor heat exchanger 2 is received via the first check valve 11. It is connected to the inlet of the liquid container 13. The outlet of the liquid receiver 13 is connected to the one end port of the first indoor heat exchanger 3 via the third solenoid valve 9 and the first expansion valve 5, and the other end port of the first indoor heat exchanger 3 is connected to the accumulator 14. It is connected to the inlet, and the outlet of the accumulator 14 is connected to the inlet of the compressor 1.

The discharge port of the compressor 1 is connected to the one end port of the second indoor heat exchanger 4 via the first electromagnetic valve 7,
The other end of the indoor heat exchanger 4 is connected to the inlet of the liquid receiver 13 via the second check valve 12. Further, a second expansion valve 6 is interposed between the outlet of the liquid receiver 13 and the other end of the outdoor heat exchanger 2, and one end of the outdoor heat exchanger 2 and the accumulator 1 are provided.
A second solenoid valve 8 is interposed between the inlet and the inlet of No. 4.

In FIG. 2, 27 is an air conditioner switch,
28 is a temperature setting device for setting the air conditioning temperature, 29 is a dry switch, 30 is an inside air temperature detector such as a thermistor,
Reference numeral 31 is a similar outside air temperature detector, 32 is a solar radiation amount detector including a photo sensor, 33 is a microcomputer, 34 is a compressor drive circuit, and 35 is an electromagnetic valve drive circuit.

The microcomputer 33 has a CPU, a ROM, a RAM, etc., and stores a program for controlling the rotational speed of the compressor and a program for determining a mode, which will be described in detail later, in the ROM. This microcomputer 33 operates signals of the air conditioner switch 27, the temperature setter 28 and the dry switch 29, and the inside air temperature detector 30, the outside air temperature detector 31 and the solar radiation amount detector 32.
A predetermined signal based on the detection signal of each drive circuit 34, 3
5

The compressor drive circuit 34 controls the rotation speed of the compressor 1 based on the rotation speed signal from the microcomputer 33 and changes its capability. The solenoid valve drive circuit 35 is the microcomputer 3
Based on the mode signal from 3, the opening / closing of each solenoid valve 7-10 is controlled to switch the refrigerant cycle.

Next, the operation modes that can be executed by the above air conditioner will be described. The device of the embodiment can be operated in four modes of cooling, cooling dry, heating and heating dry by switching the first to fourth electromagnetic valves 7 to 10.

In the cooling mode operation, as shown in FIG. 3, the compressor 1 is operated with the first and second solenoid valves 7 and 8 closed and the third and fourth solenoid valves 9 and 10 opened. It is executed by As shown by the solid arrows in FIG. 4, the compressor 1
The refrigerant discharged from the refrigerant flows into the outdoor heat exchanger 2 through the fourth electromagnetic valve 10 to be condensed, and the first check valve 11 and the liquid receiver 1
The gas flows into the first expansion valve 5 and the first indoor heat exchanger 3 through the third and third electromagnetic valves 9, evaporates, and is sucked into the compressor 1 through the accumulator 14.

That is, in the same mode operation, the heat absorption of the first indoor heat exchanger 3 can be utilized to cool the vehicle interior.

In the cooling dry mode operation, as shown in FIG. 3, the compressor 1 and the electric motor are operated with the first, third and fourth solenoid valves 7, 9, 10 opened and the second solenoid valve 8 closed. Fan 2
It is executed by activating 6. As shown by the solid line arrow in FIG. 5, a part of the refrigerant discharged from the compressor 1 flows into the outdoor heat exchanger 2 through the fourth solenoid valve 10 and is condensed, so that the first check valve 11, the liquid receiver 13 and the first check valve 11 are received. The three solenoid valves 9 flow into the first expansion valve 5 and the first indoor heat exchanger 3, evaporate, and are sucked into the compressor 1 through the accumulator 14. The remaining part of the refrigerant flows into the second indoor heat exchanger 4 through the first electromagnetic valve 7 to be condensed, passes through the second check valve 12, and then merges with the refrigerant.

In other words, in the same mode operation, the first indoor heat exchanger 3 and the second indoor heat exchanger 4 respectively exert the heat absorbing action and the heat radiating action, and by utilizing both actions, the air blowing temperature is not lowered. It is possible to dehumidify the interior of the vehicle, and the temperature and dehumidification amount at this time can be controlled by adjusting the discharge capacity of the compressor 1 and the opening degree of the air mix damper 25. Further, the outdoor heat exchanger 2 is the air mix damper 2
8 is zero (the amount of air passing through the second indoor heat exchanger 4 is zero)
It releases the excess heat amount under the condition close to, and maintains the proper balance between heat absorption and heat dissipation.

In the heating mode operation, as shown in FIG. 3, the compressor 1, the electric fan and the first, second and third solenoid valves 7, 8 and 9 are opened and the fourth solenoid valve 10 is closed. It is carried out by activating 26. As shown by the solid line arrow in FIG. 6, the refrigerant discharged from the compressor 1 flows into the second indoor heat exchanger 4 through the first electromagnetic valve 7, is condensed, and passes through the second check valve 12 and the liquid receiver 13. After that, a part of the refrigerant is separated and a part of the refrigerant is passed through the third solenoid valve 9 and the first expansion valve 5 and the first expansion valve 5.
The accumulator 1 flows into the indoor heat exchanger 3 and evaporates.
4 is sucked into the compressor 1. The remaining portion of the refrigerant flows into the second expansion valve 6 and the outdoor heat exchanger 2 to evaporate, passes through the second electromagnetic valve 8, and then merges with the refrigerant at the inlet portion of the accumulator 14.

That is, in the same mode operation, the interior of the vehicle compartment can be heated by utilizing the heat radiation effect exhibited by the second indoor heat exchanger 4, and the heat absorption effect by the outdoor heat exchanger 2 and the first indoor heat exchanger 3 can be achieved. It is possible to simultaneously perform dehumidification of the vehicle interior by utilizing the heat absorption effect of the first indoor heat exchanger 3,
The heating capacity and the dehumidifying amount at this time can be controlled by adjusting the discharge capacity of the compressor 1 and the opening degree of the air mix damper 25.

In the heating dry mode operation, as shown in FIG. 3, the compressor 1 and the electric motor are operated with the first and third solenoid valves 7 and 9 opened and the second and fourth solenoid valves 8 and 10 closed. Fan 2
It is executed by activating 6. As shown by the solid line arrow in FIG. 7, the refrigerant discharged from the compressor 1 flows into the second indoor heat exchanger 4 through the first electromagnetic valve 7 and is condensed.
It flows into the first expansion valve 5 and the first indoor heat exchanger 3 through the second check valve 12, the liquid receiver 13 and the third electromagnetic valve 9, evaporates, and is sucked into the compressor 1 through the accumulator 14.

That is, in the same mode operation, the interior of the vehicle can be heated by utilizing the heat radiation effect exhibited by the second indoor heat exchanger 4, and the heat absorption effect exhibited by the first indoor heat exchanger 3 can be utilized. It is possible to simultaneously dehumidify the interior of the vehicle, and the heating capacity and the dehumidifying amount at this time can be controlled by adjusting the discharge capacity of the compressor 1 and the opening degree of the air mix damper 25.

Next, a mode determining method in the above air conditioner will be described. The apparatus of the embodiment has an equation in which the set temperature, the outside air temperature, and the amount of solar radiation are variables, STAO = Ks · T
s-Kr / Ts-Kam / Tam-Krad / Trad
The operation mode determination is performed based on the start determination blowout temperature (STAO) calculated by + C and the like. The start determination blowout temperature STAO is calculated by the microcomputer 33 at any time.

In the above equation, Ts is a set temperature set by the user, Tam is an outside air temperature, Trad is a value obtained by converting the amount of solar radiation into temperature, Ks is a set temperature coefficient, Kr is an inside air temperature coefficient, and Kam is an outside air temperature. Coefficient, Krad is the solar radiation coefficient, C
Is a constant, which is different from the conventional formula for calculating the target outlet temperature TAO in that the set temperature Ts is used as a variable of two items.

Here, an example of a program flow relating to mode determination will be described with reference to FIG. In addition, all of a to j in the following conditions are constants defined by real values.

First, after the air conditioner switch 27 is turned on, the ON / OFF state of the dry switch 29 is determined (steps ST1 and ST2).

When the dry switch 29 is OFF, it is then determined whether or not the conditions of STAO <Tr-a and Tr> Ts + b are satisfied, and if these conditions are satisfied, cooling is performed. A mode is selected (steps ST3-5).

If the condition of step ST3 is not satisfied, then it is judged whether or not the conditions of STAO> Tr + c, Tr <Ts-d and Tam <Ts are satisfied, and these conditions are satisfied. If so, the heating mode is selected (steps ST6 to ST9).

On the other hand, in step ST2, the dry switch 2
When 9 is ON, STAO <Tr-
It is determined whether or not the conditions of e and Tr> Ts + f and Tam <g are satisfied, and if these conditions are satisfied, the cooling dry mode is selected (steps ST10 to ST1).
3).

If the condition of step ST10 is not satisfied, then it is judged whether or not the conditions of STAO> Tr + h, Tam <Ts, Tam ≧ i and N (compressor rotation speed) <j are satisfied. If these conditions are satisfied, the heating dry mode is selected (step ST14).
To 18). Further, even if the conditions of steps ST14 and ST15 are satisfied, if one of the conditions of steps ST16 and ST17 is not satisfied, the heating mode is selected (step ST18).

When the condition of step ST1 is not satisfied, the air blowing mode is selected (step ST20), and the electric fan 26 is operated to blow air into the passenger compartment.

The mode determination of cooling, cooling dry, heating, and heating dry is continuously performed until the air conditioner switch 27 is turned off, whereby the operation mode is automatically changed according to the current environment.

As described above, in the above-described vehicle air conditioner, the set temperature Ts, the outside air temperature Tam, and the numerical value Trad obtained by converting the amount of solar radiation into temperature are used as variables, that is, the inside air temperature is not included as a variable. Is calculated to be the same as the set temperature Ts, the start determination blow-out temperature STAO to be the target of the mode determination is calculated. It is possible to prevent an inadvertent and useless mode switching by accurately determining an appropriate operation mode without being changed to a heating mode by the start determination outlet temperature STAO that is the target of the mode determination. There is an advantage that the unstable influence of the inside air temperature can be eliminated.

Further, the set temperature Ts, the outside air temperature Tam, and the numerical value Trad obtained by converting the amount of solar radiation into temperature are converted into coefficients Ks, Kr, and
Since the correction is performed using Kam, Krad, and C, there is an advantage that the start determination blowout temperature STAO to be determined can be accurately calculated and the above mode determination can be performed more accurately.

Furthermore, since temperature conditions other than the start judgment temperature STAO are prepared for each operation mode, the cooling mode, the cooling dry mode, the heating mode and the heating dry mode can be clearly distinguished without being confused with each other. A comfortable air conditioning can be realized.

Since the third solenoid valve 9 is opened in all operation modes, it is not always necessary to execute the four mode operation as in the above embodiment, but the solenoid valve in the heating mode is not necessary. If the third solenoid valve 9 is closed in the switching state, all the refrigerant after passing through the liquid receiver 13 will be in the second state.
It is made to flow into the expansion valve 6 and the outdoor heat exchanger 2 to be evaporated,
It is also possible to eliminate the heat absorbing action in the first indoor heat exchanger 3 and perform the operation in the simple heating mode that does not use dehumidification together,
Energy-saving operation of heating can be performed under conditions that do not require dehumidification.

Further, brine may be circulated in the second indoor heat exchanger 4, and as shown in FIG. 9, the refrigerant passage inlet / outlet of the brine refrigerant heat exchanger 36 is connected to the first solenoid valve 7 and the second reverse valve. If it is connected to the stop valve 12 and the brine passage inlet / outlet of the heat exchanger 36 is connected to the second indoor heat exchanger 4 via the pipe line provided with the electric pump 37, each of cooling dry, heating and heating dry In the mode operation, the brine 39 heated by the brine refrigerant heat exchanger 36 may be circulated by the pump 37 so that the heat exchanger 36 can exhibit a heat radiation effect.

Further, in the refrigerant circuit of FIG. 9, an auxiliary heat source for heating the brine sent to the second indoor heat exchanger 4, for example, an auxiliary heat source 38 such as an electric heater is arranged in the brine passage in the brine refrigerant heat exchanger 36. Alternatively, an auxiliary heat source 3 such as an electric heater or a combustor may be provided in the brine inflow conduit of the second indoor heat exchanger 4.
If 9 is additionally provided, the brine can be heated by these auxiliary heat sources 38 and 39 to compensate for the insufficient heat radiation amount in the second indoor heat exchanger 4 to improve the capacity, and the outside air temperature is low and the refrigerant circuit can operate normally Even when it does not operate or when the operation of the compressor 1 is forcibly stopped, it is possible to execute the simple heating mode in which heating is simply performed by circulating the heating brine.

Furthermore, the solenoid valve in the embodiment may be capable of controlling the flow rate. In this case, the flow control of each valve controls the intake / exhaust amounts of the outdoor heat exchanger and both indoor heat exchangers. Each can be controlled. Further, both check valves may be replaced by an opening / closing valve or a flow control valve as long as the flow direction can be controlled.

As described above, the present invention is not limited to the devices described in the embodiments, but can be variously applied as long as it is a vehicle air conditioner capable of operating at least the cooling mode and the heating mode, and the same effect can be obtained.

[0052]

As described in detail above, according to the first aspect of the invention, an expression in which a numerical value obtained by converting the set temperature, the outside air temperature, and the amount of solar radiation into a temperature is used as a variable, in other words, the inside air temperature is not included as a variable. The temperature that is the target of the mode judgment is calculated assuming that the inside air temperature is the same as the set temperature by the formula, so under the heat load condition that it can be operated in the cooling mode as in the past. It is possible to prevent an inadvertent and unnecessary switching of modes by accurately determining the proper operating mode without being changed to the heating mode, and the instability of the inside air temperature from the temperature subject to the mode determination. The effect can be eliminated.

According to the second aspect of the present invention, since the numerical values obtained by converting the set temperature, the outside air temperature, and the amount of solar radiation into temperature are corrected by the respective coefficients and constants, the temperature to be judged is accurately calculated and the above-mentioned values are calculated. The mode can be judged more accurately. The other effects are the same as those of the invention of claim 1.

According to the inventions of claims 3 to 6, since temperature conditions other than the start judgment temperature are prepared for each operation mode, each mode is judged more accurately to realize comfortable air conditioning according to the environment. it can. Other effects are similar to those of the invention of claim 2.

[Brief description of drawings]

FIG. 1 is a diagram showing a refrigerant circuit of a vehicle air conditioner according to the present invention.

FIG. 2 is a diagram showing a control circuit of the vehicle air conditioner according to the present invention.

FIG. 3 is a diagram showing a solenoid valve switching state in each operation mode.

FIG. 4 is a diagram showing a refrigerant cycle in a cooling mode.

FIG. 5 is a diagram showing a refrigerant cycle in a cooling dry mode.

FIG. 6 is a diagram showing a refrigerant cycle in a heating mode.

FIG. 7 is a diagram showing a refrigerant cycle in a heating dry mode.

FIG. 8 is a diagram showing a program flow for mode determination.

FIG. 9 is a diagram showing another example of a refrigerant circuit.

[Explanation of symbols]

1 ... Compressor, 2 ... Outdoor heat exchanger, 3 ... 1st indoor heat exchanger, 4 ... 2nd indoor heat exchanger, 5 ... 1st expansion valve, 6 ... 2nd
Expansion valve, 7 ... First solenoid valve, 8 ... Second solenoid valve, 9 ... Third solenoid valve, 10 ... Fourth solenoid valve, 11 ... First check valve, 12 ... Second check valve, 33 ... Microcomputer , 34 ... Compressor drive circuit, 3
5 ... Solenoid valve drive circuit, 36 ... Brine refrigerant heat exchanger, 3
7 ... Pump.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Fujita 20 Kotobukicho, Isesaki City, Gunma Sanden Co., Ltd.

Claims (6)

[Claims] 1. In a vehicle air conditioner having a mode determining means for determining an operation mode based on a temperature or the like calculated by a predetermined formula, the temperature calculating formula used by the mode determining means is a set temperature and an outside air temperature. A vehicle air conditioner characterized in that it includes, as a variable, a numerical value obtained by converting the amount of solar radiation into a temperature. 2. STAO = Ks · Ts as a temperature calculation formula
-Kr / Ts-Kam / Tam-Krad / Trad +
C (Ts: set temperature, Tam: outside air temperature, Trad: numerical value obtained by converting the amount of solar radiation into temperature, Ks: set temperature coefficient, Kr:
The air conditioner for a vehicle according to claim 1, wherein an inside air temperature coefficient, Kam: outside air temperature coefficient, Krad: solar radiation coefficient, C: constant) is used. 3. The cooling mode determination by the mode determination means is a condition (T0 <Tr-a and Tr> Ts + b) (T
The air conditioner for a vehicle according to claim 2, wherein the temperature is lowered when r: inside air temperature, a, b: constant) are satisfied. 4. The heating mode determination by the mode determination means is STAO> Tr + c, Tr <Ts-d and Tam <T.
The air conditioner for a vehicle according to claim 2, wherein the condition is satisfied when the condition (c, d: constant) of s is satisfied. 5. The determination of the cooling dry mode by the mode determination means is STAO <Tr-e when the dry switch is ON.
And Tr> Ts + f and Tam <g are satisfied when the conditions (e, f, g: constants) are satisfied, The vehicle air conditioner according to claim 2. 6. The heating dry mode is judged by the mode judging means when the dry switch is ON and STAO> Tr + h.
And Tam <Ts, Tam ≧ i and N <j conditions (h, i,
j: a constant, N: the number of rotations of the compressor).