Refrigerating system for use in vehicles

Abstract: In a cooling system including a refrigerant compressor (21) for use in a vehicle for refrigerating a refrigerator compartment, the refrigerant compressor is a hermetic type compressor containing a DC brushless motor (21a) as a compressor driver. An electric generator (40) is actuated by an engine (101) of the vehicle to generate an AC electric power which is, in turn, rectified by a rectifier (30) to produce a DC electric power for driving The DC brushless motor. A switch (50) is provided to switch over from the electric generator to a commercial AC electric power (60) source so that the commercial AC electric power is rectified by the rectifier to supply the DC electric power to thereby enable to drive the compressor by use of the commercial AC electric power source during a time period when the engine is stopped. In order to obtain the accurate temperature control in the refrigerator compartment, during a time period when the engine is driven, generating amount of the AC electric power generated at the electric generator is controlled, and during a time period when the engine is stopped, delivering amount of the rectified commercial electric power which is delivered to the DC electric motor is controlled.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a refrigerating system and, in particular, to a compressor driving system in such a refrigerating system for use in a vehicle with an engine, for example, an automotive refrigerator van. Description of the Prior Art In order to cool, chill or refrigerate food, drinks, and/or others, a refrigerating system is provided in a vehicle, for example, an automobile. A dedicated vehicle is also known as a refrigerator van or chill car for transporting cold, chilled, or refrigerated food. Figure 1 shows a schematic block diagram of a refrigerating system in accordance with one prior art system. The refrigerating system 100 includes refrigerant circuit 200 comprising first compressor 201 for compressing refrigerant, condenser 202, receiver-drier 203, expansion valve 204, evaporator 205 for cooling a refrigerator compartment (not shown) and pipe members 206 for connecting an outlet of each of the elements of the refrigerant circuit to an inlet of each of adjacent elements of the refrigerant circuit. First compressor 201 is provided with electromagnetic clutch 211 for intermittently receiving the driving force thereof from automotive engine 101 through belt 102 by virtue of the intermittent operation of electromagnetic clutch 211. Thereby, first compressor 201 is intermittently driven by automotive engine 101 through electromagnetic clutch 211. Refrigerating system 100 further comprises the so-called standby unit 110 including second compressor 111 and three-phase motor 112 for driving second compressor 111 through belt 113. Outlet port 111a of second compressor 111 is connected to the pipe member between first compressor 201 and condenser 202 through pipe member 206. Inlet port 111b of second compressor 111 is connected to the pipe member between evaporator 205 and first compressor 201 through pipe member 206. Three-phase motor 112 is connected to commercial AC electric power source 114 through power source box 115. Power source box 115 functions as both a rectifier and transformer in order to supply the electric power to an electric equipment incorporated in the elements of the refrigerant circuit, for example, an evaporator fan motor (not shown). But, motor 112 directly receives commercial AC electric power as the input thereof. Furthermore, second compressor 111 is provided with electromagnetic clutch 116 for intermittently receiving the driving force thereof from motor 112 through belt 113 by virtue of the intermittent operation of electromagnetic clutch 116. Thereby, second compressor 111 is intermittently driven by motor 112 through electromagnetic clutch 116. Accordingly, temperature control in the refrigerator compartment is carried out by the intermittent operation of electromagnetic clutch 211 or 116. In this composition of the refrigerating system, during the period when the automobile is driven, first compressor 201 driven by the automotive engine only operates in order to circulate the refrigerant through refrigerant circuit 200. On the other hand, during the period when the automobile stops, for example, when the driver is sleeping through the night, second compressor 111 driven by motor 112 only operates instead of first compressor 201. However, in this prior art, the additional provision of second compressor 111 of standby unit 110 complicates piping of the refrigerant circuit. Further, it is difficult to carry out accurate temperature control in the refrigerator compartment because that the refrigerant compressor is driven by the engine which often varies in the rotational speed when automobile is driven. To eliminate these drawbacks, another refrigerating system is proposed. The refrigerating system comprises a refrigerant circuit including a compressor having a three-phase motor and a compressing mechanism driven by the three-phase motor. The motor and the compressing mechanism are hermetically contained in one casing. In this refrigerating system, during the period when the automobile is driven, the motor of the compressor is connected to an automotive generator driven by the automotive engine so as to receive the AC electric power. Thereby, the compressor is driven by the motor driven by receiving the AC from the generator. On the other hand, during the period when the automobile stops, the motor of the compressor is connected to the commercial AC electric power source instead of the automotive generator so as to receive the commercial AC electric power from the AC electric power source. Thereby, the compressing mechanism of the compressor is driven by the motor which is driven by receiving the commercial AC electric power. Furthermore, temperature in the refrigerator compartment is controlled by the turning on-off operation of the generator or the commercial AC electric power source. That is, temperature in the refrigerator compartment is controlled by the intermittent operation of the motor of which rotational speed is maintained at the certain value. However, since the temperature in the refrigerator compartment is controlled by the intermittent operation of the motor of which rotational speed is maintained at the certain value, it is still difficult to carry out accurate temperature control in the refrigerator compartment. Another known system is shown in US-A-3885398. In this system, two refrigerant compressors are provided, one mechanically driven from the vehicle's engine, and the other electrically driven either from an on-board generator powered by an auxiliary engine, or from an external mains supply. SUMMARY OF THE INVENTION Accordingly, it is an object of the preferred embodiment of the present invention to carry out accurate temperature control in the refrigerator compartment. It is another object of the preferred embodiment of the present invention to reduce the fuel consumption of the automotive engine when the compressor is driven by the motor which is driven by AC electric power supplied from the automotive generator. According to the present invention, there is provided a system for driving a refrigerant compressor in a refrigerator system for use in a vehicle having an engine, which comprises: an electric generator to be mounted on said vehicle and driven by said engine for generating AC electric power, selecting means having a first input port coupled to said electric generator for receiving AC electric power therefrom, a second input port to be connected to an AC electric power source external of the vehicle for receiving AC electric power therefrom and an output port, said selecting means selecting either electric power from said generator or AC electric power from said external AC electric power source to deliver the selected AC electric power to said output port; and characterised by rectifying means coupled to said output port of the selecting means for rectifying said selected AC electric power to produce DC electric power; a DC electric motor to be driven by said DC electric power and mechanically coupled to said refrigerant compressor; sensing means for sensing a temperature within a refrigerator compartment mounted on said vehicle, said sensing means producing a first signal which represents said sensed temperature of said refrigerator compartment; setting means for setting a temperature of said refrigerator compartment, said setting means producing a second signal which represents said set temperature of said refrigerator compartment; calculating means coupled to said sensing means, said setting means and said selecting means so as to receive said first and second signals and a third signal which indicates which of said AC electric power from said electric generator or said AC electric power from said external AC electric power source is delivered as the selected AC electric power to said output port, said calculating means calculating a differential between said sensed temperature of said refrigerator compartment and said set temperature of said refrigerator compartment, and producing a fourth signal representing said differential between said sensed temperature of said refrigerator compartment and said set temperature of said refrigerator compartment, duty ratio control means coupled to said calculating means for receiving said third and fourth signals, said duty ratio control means including pulsating means for producing a pulse as a fifth signal, the duty ratio of the pulses being varied in response to change in said fourth signal when said duty ratio control means receives said third signal indicating that said AC electric power from said external AC electric power source is delivered to said output port, said duty ratio being maintained at 100% when said duty ratio control means receives said third signal representing that the AC electric power from said electric generator is delivered to said output port; and delivering means coupled to said duty ratio control means for receiving said fifth signal, said delivering means delivering said DC electric power to said DC motor with intermissions, the duration of which is varied in response to change in said duty ratio. The calculating means may be further coupled to said DC motor so as to receive a sixth signal representing a rotational speed of said DC motor so that said calculating means produces said fourth signal in consideration of said sixth signal. Amperage control means may be coupled to said calculating means for receiving said third and fourth signals, said amperage control means being further coupled to said electric generator so as to control a direct current supplied to a field coil thereof in response to said fourth signal. Said delivering means may be coupled to said amperage control means so as to send a seventh signal representing a voltage of said DC electric power so that said amperage control means controls said field current in response to both said fourth signal and said seventh signal. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described merely by way of example with reference to the remainder of the drawings, wherein Figure 2 is a schematic diagram of a refrigerating system in accordance with one embodiment of the present invention. Figure 3 is a block diagram of a control system which is used for controlling the rotational speed of a DC brushless motor of a refrigerant compressor of the refrigerating system. Figure 4 is a graph showing a relation between the electric power generated at an automotive generator and the rotational speed of the DC brushless motor of the refrigerant compressor. Figure 5 is a graph showing voltage-amperage characteristic of the AC electric power generated at the automotive generator and a generating efficiency of the automotive generator when the rotational speed of the automotive generator is maintained at a certain value. Figure 6 is a graph showing a relation between a value of the duty ratio signal generated at a duty ratio circuit and the rotational speed of the DC brushless motor of the refrigerant compressor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 2 shows a schematic block diagram of a refrigerating system in accordance with one embodiment of the present invention. In the drawing, same numerals denote the corresponding elements shown in Figure 1 so that substantial explanation thereof is omitted. With reference to Figure 2, the refrigerating system 10 includes refrigerant circuit 20 comprising compressor 21, condenser 202, receiver-drier 203, expansion valve 204, evaporator 205 and pipe members 206. Compressor 21 includes DC brushless motor 21a and scroll type compressing mechanism 21b driven by motor 21a. Motor 21a and compressing mechanism 21b are hermetically contained in one casing (not shown). DC brushless motor 21a is connected to circuit 30 which includes a rectifying device (not shown). Circuit 30 is further connected to terminals 50a of electromagnetic changeover switch 50 which includes an electromagnetic device (not shown). Generator 40 is mounted on an automotive engine compartment, and is driven by automotive engine 101 through belt 41. Generator 40 is connected to terminals 50b of switch 50. Plug 61 is connected to terminals 50c of switch 50. During the period when the automobile stops, plug 61 is inserted in commercial AC power source 60 so that the electromagnetic device is energized. Thereby, terminals 50a is connected to terminals 50c. Consequentially, the commercial AC electric power is supplied to circuit 30. On the other hand, during the period when the automobile is driven, plug 61 is detached from commercial AC power source 60 so that the electromagnetic device is not energized. Thereby, terminals 50a is disconnected to terminals 50c, and is simultaneously connected to terminals 50b as shown in Figure 2. Consequentially, the AC electric power generated at generator 40 is supplied to circuit 30. Accordingly, the AC electric power generated at generator 40 and the commercial AC electric power are selectively supplied to circuit 30 in response to the connection and disconnection of plug 61 to commercial AC power source 60, and is rectified thereat. The rectified electric power at circuit 30 is supplied to DC brushless motor 21a of compressor 21 with intermission of which value varies in response to change in an value of later mention duty ratio signal. Thermo-sensor 71 is disposed in a refrigerator compartment (not shown)so as to sense the real temperature in the refrigerator compartment, and is connected to arithmetic circuit 70 so as to send a first signal representing the real temperature in the refrigerator compartment to arithmetic circuit 70 therefrom. Device 72 for setting the certain temperature in the refrigerator compartment is also connected to arithmetic circuit 70 so as to send a second signal representing the set temperature in the refrigerator compartment to arithmetic circuit 70 therefrom. Arithmetic circuit 70 is further connected to both duty ratio control circuit 80 and amperage control circuit 90 so as to send later mention third and fourth signals to each of circuits 80 and 90 therefrom. Arithmetic circuit 70 is still further connected to electromagnetic changeover switch 50 so as to receive a third signal from switch 50. The third signal represents that whether the electromagnetic device of switch 50 is energized. Duty ratio control circuit 80 is further connected to circuit 30 so as to send the later mention duty ratio signal to circuit 30 therefrom. Amperage control circuit 90 is further connected to a field coil (not shown) of generator 40, and is still further connected to DC power source 91, such as a DC battery, so as to supply various amperage of the DC electric power to the field coil of generator 40 therefrom. With reference to Figure 3 additionally, arithmetic circuit 70 receives the first, second and third signals from thermo-sensor 71, temperature setting device 72 and electromagnetic changeover switch 50, respectively. When arithmetic circuit 70 receives these three signals, the first and second signals are compared so as to calculate a fourth signal which represents the differential between the real and set temperatures. After that, the third and fourth signals are sent to both amperage control circuit 90 and duty ratio control circuit 80 therefrom. Duty ratio control circuit 80 includes a pulsating device which generates a pulse as a fifth signal. When duty ratio control circuit 80 receives the third signal representing that the electromagnetic device of changeover switch 50 is not energized, duty ratio control circuit 80 generates a pulse as a fifth signal of which duty ratio is maintained 100 %, and then sends the fifth signal to circuit 30 therefrom. When circuit 30 receives the duty ratio 100% signal from duty ratio control circuit 80, the rectified electric power supplied through circuit 30 from generator 40 is continuously supplied to DC brushless motor 21a. At the same time, amperage control circuit 90 controls the amperages of the DC electric power which is supplied from DC power source 91 to the field coil of generator 40 in response to change in the fourth signal. Thereby, generator 40 generates the various AC electric power in response to change in the amperage of the DC electric power supplied from DC power source 91, that is, generator 40 generates the various AC electric power in response to change in the fourth signal. The various AC electric power is supplied to circuit 30 so as to be the corresponding rectified electric power. Therefore, the rotational speed of DC brushless motor 21a of compressor 21 can be proportional to the value of the AC electric power generated at generator 40 as shown in Figure 4. During the period when DC brushless motor 21a of compressor 21 is driven, a sixth signal representing the rotational speed of motor 21a is fed back from motor 21a to arithmetic circuit 70 through a wire (not shown in Figure 2). Accordingly, arithmetic circuit 70 calculates the fourth signal in consideration of the sixth signal. Further, a seventh signal representing the voltage of the rectified electric power is fed back from circuit 30 to amperage control circuit 90 through a wire (not shown in Figure 2). Accordingly, circuit 90 controls the amperage of the DC electric power which is supplied from DC power source 91 to the field coil of generator 40 in response to change in the fourth signal and in consideration of the seventh signal. Figure 5 is a graph showing voltage-amperage characteristic of the AC electric power generated at automotive generator 40 and a generating efficiency of automotive generator 40 when the rotational speed of generator 40 is maintained at a certain value. In the graph, curves A, B and C show the voltage-amperage characteristic of the AC electric power generated at generator 40 in each of certain three amperages of the DC electric power supplied from DC power source 91 to the field coil of generator 40. Furthermore, curves A′, B′ and C′ show the generating efficiency of generator 40 in each of the above-mentioned three amperages. The amperage which generates curves C and C′ is greater than the amperage which generates curves B and B′, which is greater than the amperage which generates curves A and A′. With reference to Figure 5, when the AC electric power of which value is G is generated in each of the above-mentioned three amperages, the generating efficiency of generator 40 varies to eta 1, 2 and 3, respectively. Specifically, the generating efficiency of generator 40 corresponding G of curve A is greater than the generating efficiency of generator 40 corresponding G of curve C by delta (eta), that is, by (eta 1 - eta 3). Accordingly, automotive generator 40 can always generate the AC electric power with the best generating efficiency by selectively varying amperage of the DC electric power supplied from DC power source 91 to the field coil of generator 40. Therefore, amperage control circuit 90 is designed to be able to control amperage of the DC electric power which is supplied from DC power source 91 to the field coil of generator 40 in order to let generator 40 always generate the AC electric power with the best generating efficiency during the period of the operation of generator 40. In the event, the fuel consumption of the automotive engine is effectively reduced when brushless motor 21a of compressor 21 is driven by receiving the rectified electric power through circuit 30 from automotive generator 40. When plug 61 is inserted in commercial AC power source 60, that is, the electromagnetic device of electromagnetic changeover switch 50 is energized so as to supply the commercial AC electric power to circuit 30, duty ratio control circuit 80 receives the third signal which represents that the electromagnetic device is energized from arithmetic circuit 70. Simultaneously, duty ratio control circuit 80 also receives the fourth signal from arithmetic circuit 70. When duty ratio control circuit 80 receives the third signal representing that the electromagnetic device is energized from arithmetic circuit 70, duty ratio control circuit 80 generates the duty ratio signal as the fifth signal of which value is varied in response to change in the fourth signal, and then sends the fifth signal to circuit 30 therefrom. When circuit 30 receives the various value of the duty ratio signal from duty ratio control circuit 80, the rectified electric power is supplied to DC brushless motor 21a from circuit 30 with intermission of which value is varied in response to change in the value of the duty ratio signal. Therefore, the rotational speed of DC brushless motor 21a varies in response to change in the value of the duty ratio signal as shown in Figure 6. Accordingly, in both during the period when the automobile stops and during the period when the automobile is driven, output of compressor 21 is varied in response to change in the rotational speed of DC brushless motor 21a of compressor 21. Thereby, the temperature in the refrigerator compartment is controlled by virtue of varying the rotational speed of DC brushless motor 21a of compressor 21 so that the accurate temperature control in the refrigerator compartment can be carried out.

Claims: A system for driving a refrigerant compressor (21b) in a refrigerator system for use in a vehicle having an engine (101), which comprises: an electric generator (40) to be mounted on said vehicle and driven by said engine for generating AC electric power, selecting means (50) having a first input port (50b) coupled to said electric generator for receiving AC electric power therefrom, a second input port (50c) to be connected to an AC electric power source (60) external of the vehicle for receiving AC electric power therefrom and an output port (50a), said selecting means selecting either electric power from said generator or AC electric power from said external AC electric power source to deliver the selected AC electric power to said output port; and characterised by rectifying means (30) coupled to said output port of the selecting means for rectifying said selected AC electric power to produce DC electric power; a DC electric motor (21a) to be driven by said DC electric power and mechanically coupled to said refrigerant compressor (21b); sensing means (71) for sensing a temperature within a refrigerator compartment mounted on said vehicle, said sensing means producing a first signal which represents said sensed temperature of said refrigerator compartment; setting means (72) for setting a temperature of said refrigerator compartment, said setting means producing a second signal which represents said set temperature of said refrigerator compartment; calculating means (70) coupled to said sensing means, said setting means and said selecting means so as to receive said first and second signals and a third signal which indicates which of said AC electric power from said electric generator or said AC electric power from said external AC electric power source is delivered as the selected AC electric power to said output port, said calculating means calculating a differential between said sensed temperature of said refrigerator compartment and said set temperature of said refrigerator compartment, and producing a fourth signal representing said differential between said sensed temperature of said refrigerator compartment and said set temperature of said refrigerator compartment, duty ratio control means (80) coupled to said calculating means (70) for receiving said third and fourth signals, said duty ratio control means including pulsating means for producing a pulse as a fifth signal, the duty ratio of the pulses being varied in response to change in said fourth signal when said duty ratio control means (80) receives said third signal indicating that said AC electric power from said external AC electric power source is delivered to said output port, said duty ratio being maintained at 100% when said duty ratio control means receives said third signal representing that the AC electric power from said electric generator is delivered to said output port; and delivering means (included in 30) coupled to said duty ratio control means (80) for receiving said fifth signal, said delivering means delivering said DC electric power to said DC motor with intermissions, the duration of which is varied in response to change in said duty ratio. A system as claimed in claim 1, characterised in that said calculating means (70) are further coupled to said DC motor (21a) so as to receive a sixth signal representing a rotational speed of said DC motor so that said calculating means produces said fourth signal in consideration of said sixth signal. A system as claimed in claim 1 or 2, characterised by amperage control means (90) coupled to said calculating means (70) for receiving said third and fourth signals, said amperage control means being further coupled to said electric generator (40) so as to control a direct current supplied to a field coil thereof in response to said fourth signal. A system as claimed in Claim 3, wherein said delivering means (30) is coupled to said amperage control means (90) so as to send a seventh signal representing a voltage of said DC electric power so that said amperage control means controls said field current in response to both said fourth signal and said seventh signal.

Inventors: ISOBE TOSHIMI, SAKANO RIICHI, ISOBE, TOSHIMI, SAKANO, RIICHI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1990
Main classification: B60H1
IPC codes: F25D3, F25D11, H02J9, G05D23, B60H1, F25B27