Communication system for gas engine-driven air conditioner

Abstract

To provide a communication system for a gas engine-driven air conditioner that can reduce component costs.SOLUTION: A communication system 1 for a gas engine-driven air conditioner includes: a transmitter that transmits a differential serial signal; a receiver that receives the differential serial signal; and a communication cable that connects the transmitter and the receiver and includes a pair of electric wires for respectively transmitting a pair of signals constituting the differential serial signal, the pair of electric wires being arranged in parallel. A bit rate of the differential serial signal is set such that a wavelength of a fundamental wave among frequency components constituting the pair of signals is longer than four times a total length of the communication cable.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention is applied to a gas engine driven air conditioner, and relates to a communications system for transmitting and receiving data (serial signals) between a plurality of control devices that constitute the gas engine driven air conditioner. [Background technology]

[0002] For example, as described in Patent Document 1 below, a communication system (hereinafter referred to as a "conventional system") for transmitting and receiving data (serial signals) between multiple control devices is known. In the conventional system, multiple nodes are connected via twisted pair cables. Among the nodes constituting the communication system, a pair of nodes (the two most distant nodes) connected to the ends of the twisted pair cable (communication path) have a termination resistor provided close to their input terminals to suppress deterioration of signal quality (waveform distortion) caused by reflection of the serial signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-028670 A Summary of the Invention

[0004] In general, twisted pair cables are more expensive than cab-tire cables (cables made up of multiple electric wires arranged in parallel), and therefore the component costs of the entire communication system are high.

[0005] An object of the present invention is to provide a communication system for a gas engine driven air conditioner that can reduce parts costs.

[0006] In order to achieve the above object, a communication system according to the present invention is applied to a gas engine driven air conditioner and transmits and receives data between a plurality of control devices of the gas engine driven air conditioner. The communication system includes: A transmitter for transmitting a differential serial signal; A receiving device for receiving a differential serial signal; a communication cable connecting the transmitting device and the receiving device, the communication cable including a pair of electric wires for transmitting a pair of signals constituting the differential serial signal, the pair of electric wires being arranged in parallel; Equipped with. a bit rate of the differential serial signal is set so that the wavelength of a fundamental wave of frequency components constituting each of the pair of signals is longer than four times the overall length of the communication cable; The total length of the communication cable is 1 km or less, and the bit rate is 1 kbps or less. .

[0007] In addition, in a communication system according to another aspect of the present invention, The bit rate of the differential serial signal is set so that the wavelength of the fifth harmonic of the frequency components constituting each of the pair of signals is longer than four times the overall length of the communication cable.

[0009] Here, the electric energy of the AC signal (sine wave) is transmitted as a wave through the communication cable (transmission line). When the total length of the communication cable (transmission line) is longer than 1 / 4 of the wavelength, if the characteristic impedance of the communication cable and the load impedance are not matched, the signal is reflected at the end of the communication cable, and the signal waveform is distorted. In addition, in this case, the communication cable acts as an antenna and radiates electromagnetic noise. In other words, if the wavelength of the signal being transmitted and received is longer than four times the total length of the communication cable, it is hardly affected by the characteristic impedance and the load impedance. Therefore, in the communication system according to the present invention, the bit rate is set so that the wavelength of the fundamental wave of a pair of signals constituting a differential serial signal is longer than four times the total length of the communication cable. That is, the bit rate is set to be sufficiently small (low speed) according to the total length of the communication cable. This makes it possible to adopt an inexpensive cab-tyre cable. Furthermore, no termination resistor is required. Therefore, the component cost of the communication system according to the present invention is lower than that of the conventional system.

[0010] In addition, when a node functioning as a transmitter (master node) simultaneously transmits a signal to multiple nodes functioning as receivers (slave nodes), the number of slave nodes is limited due to the limitation of the output current of the master node. In conventional systems, a termination resistor is used, but the resistance value is relatively small (e.g., 120 ohms). Therefore, the number of slave nodes that can be connected is relatively small.

[0011] In contrast, in the communication system according to the present invention, no termination resistor is required. That is, the input impedance of the slave node is relatively large and the current consumption of the slave node is relatively small. Therefore, according to the present invention, it is possible to increase the number of slave nodes that can be connected. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a configuration of a communication system according to an embodiment of the present invention; [Diagram 2]FIG. 2 is a circuit diagram showing the internal structure of a transceiver and the configuration of a filter circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The communication system 1 for a gas engine driven air conditioner according to one embodiment of the present invention will be described below. The communication system 1 has a function for transmitting and receiving various data (for example, data for controlling indoor temperature and indoor humidity) between multiple control devices C (such as a microcomputer that controls an outdoor unit, a microcomputer that controls multiple indoor units) that make up the gas engine driven air conditioner.

[0014] 1, the communication system 1 includes a plurality of transceivers 10 corresponding to a plurality of control devices C, respectively, and a plurality of cabtyre cables 20 connecting these transceivers 10. The control devices C and the transceivers 10 are mounted on a printed wiring board PB.

[0015] As shown in Fig. 2, the transceiver 10 is an integrated circuit that supports a so-called half-duplex communication protocol. That is, the transceiver 10 has a built-in driver 11 and a receiver 12. The transceiver 10 has a terminal D / R, a terminal DI, a terminal RO, a terminal A, and a terminal B. The driver 11 and the receiver 12 are sealed inside a body BD made of a synthetic resin material. One ends of the terminal D / R, the terminal DI, the terminal RO, the terminal A, and the terminal B are located inside the body BD, and the other ends are located outside the body BD. The transceiver 10 complies with the well-known communication protocol "RS485".

[0016] The driver 11 includes an input terminal 111 and output terminals 112 and 113. The receiver 12 includes input terminals 121 and 122 and an output terminal 123.

[0017] The input terminal 111 is connected to a terminal CTx of the control device C via a terminal DI. The output terminal 112 and the output terminal 113 are connected to a terminal A and a terminal B, respectively. Furthermore, the input terminal 121 and the input terminal 122 are also connected to a terminal A and a terminal B, respectively. Moreover, the output terminal 123 is connected to a terminal CRx of the control device C via a terminal RO.

[0018] The driver 11 converts a single-ended serial signal Tx input to its input terminal 111 into a serial signal DS (differential signal) consisting of two signals D+ and D- whose logical levels are opposite (opposite phase). The receiver 12 converts the signals D+ and D- respectively input to its input terminals 121 and 122 into a single-ended serial signal Rx.

[0019] Furthermore, the driver 11 has an input terminal 114. When the logic level of the input terminal 114 is "H", the driver 11 outputs a signal D+ and a signal D- from the output terminals 112 and 113, respectively. On the other hand, when the logic level of the input terminal 114 is "L", the output terminals 112 and 113 are disconnected from the internal circuitry of the driver 11. That is, in this case, the output terminals 112 and 113 are in a high impedance state.

[0020] The receiver 12 includes an input terminal 124. When the logic level of the input terminal 124 is "L", the receiver 12 outputs a serial signal Rx from an output terminal 123. On the other hand, when the logic level of the input terminal 124 is "H", the output terminal 123 is disconnected from the internal circuitry of the receiver 12. That is, in this case, the output terminal 123 is in a high impedance state.

[0021] The input terminal 114 and the input terminal 124 are connected to a terminal EN of the control device C via a terminal D / R.

[0022] A selection signal SEL is output from a terminal EN of the control device C. The selection signal SEL is supplied to the driver 11 and the receiver 12 via terminals D / R. That is, when the logic level of the selection signal SEL is "H", the driver 11 is in a state where it can output a serial signal DS, and the receiver 12 is in a state where it cannot output a serial signal Rx. That is, in this case, the transceiver 10 functions as a transmitting device. On the other hand, when the logic level of the selection signal SEL is "L", the driver 11 is in a state where it cannot output a serial signal DS, and the receiver 12 is in a state where it can output a serial signal Rx. That is, in this case, the transceiver 10 functions as a receiving device.

[0023] The input impedance of the transceiver 10 is 12 kohm. The maximum output current of the transceiver 10 is 250 mA.

[0024] In addition, a pair of connectors CN1, CN2 (pin headers) are mounted on the printed wiring board PB. The connectors CN1, CN2 are connected in parallel. That is, pins Pa and Pb of one connector CN1 are connected to pins Pa and Pb of the other connector CN2. Furthermore, pins Pa and Pb are connected to terminals A and B of the transceiver 10, respectively.

[0025] The cabtyre cable 20 includes a main body 21 and a pair of housings 22, 22. The main body 21 includes an electric wire 21a corresponding to a signal D+ and an electric wire 21b corresponding to a signal D-. The main body 21 further includes a sheath 21c that covers the electric wire 21a and the electric wire 21b. In the sheath 21c, the electric wire 21a and the electric wire 21b are arranged approximately parallel to each other. The housings 22, 22 are provided at both ends of the main body 21. The housing 22 incorporates pins 22a, 22b that correspond to pins Pa, Pb of the connector CN, respectively. The ends of the electric wires 21a, 21b are connected to the pins 22a, 22b. The housing 22 is fitted into the connector CN. In this state, the pins 22a, 22b are in contact (conductive) with the pins Pa, Pb.

[0026] One end and the other end of the cab-tyre cable 20 are connected to a connector CN1 mounted on one of the two printed wiring boards PB and a connector CN2 mounted on the other printed wiring board PB, respectively. That is, a plurality of transceivers 10 (and a control device C) are connected in a daisy chain. A communication path CP for transmitting and receiving various data is configured by a plurality of cab-tyre cables 20. In this embodiment, the total length of the communication path CP (the total length of all the cab-tyre cables 20) is approximately "1 km". Also, in this embodiment, no termination resistor is provided as in the conventional system. Also, the communication speed (the bit rate of the serial signal Tx, the serial signal Rx, and the serial signal DS) is "9600 bps".

[0027] When the gas engine driven air conditioning apparatus is started, each control device C executes a predetermined initialization program, and as a result, one predetermined control device C connected to the communication path CP is set as a master node (transmitting node), and the other control devices C are set as slave nodes (receiving nodes). In other words, the logic level of the selection signal SEL output from the control device C (control device Cm) that is the master node is "H", and the logic level of the selection signal SEL output from the control device C (control device Cs) that is the slave node is "L". After that, various data are transmitted and received between each node. When it becomes necessary to transmit data from a node that is a slave node, that node is set to function as a master node, and the other nodes (including the node that was previously the master node) are set to function as slave nodes.

[0028] The single-ended serial signal Tx output from the terminal CTx of the control device Cm of the master node is supplied to the input terminal 111 of the driver 11 via the terminal DI. The driver 11 converts the serial signal Tx into a serial signal DS (D+ and D-), and outputs it from the output terminals 111 and 112. Then, this serial signal DS (D+ and D-) is transmitted to another transceiver 10 (the transceiver 10 of the slave node) via the terminals A, B and the cab tire cable 20.

[0029] The serial signal DS (D+ and D-) transmitted from the master node is supplied to the input terminals 121 and 122 of the receiver 12 via the terminals A and B of the transceiver 10 of the slave node. The receiver 12 converts the serial signal DS (D+ and D-) into a single-ended serial signal Rx, and outputs it from the output terminal 123. Then, this serial signal Rx is supplied to the terminal CRx of the control device Cs of the slave node via the terminal RO.

[0030] Here, the electrical energy of an AC signal (sinusoidal wave) is transmitted as a wave through a communication cable (transmission line). When the total length L0 of the communication cable (transmission line) is longer than 1 / 4 of the wavelength L1 (L1 / 4 < L0), in a state where the characteristic impedance of the communication cable and the load impedance do not match, signal reflection occurs at the end of the communication cable, and the signal waveform is distorted. Also, in this case, the communication cable acts as an antenna and electromagnetic noise is radiated. Conversely, if the wavelength L1 is longer than four times the total length L0, it is hardly affected by the characteristic impedance and the load impedance.

[0031] As described above, the total length L0 of the communication path CP in this embodiment is approximately "1 km". Therefore, if the wavelength L1 (wavelength of the fundamental wave) of the serial signal DS is longer than "4 km", it is hardly affected by the characteristic impedance and the load impedance. When the bit rate of the serial signal DS is "115.2 kbps", the wavelength of the signal is "5.208 km (= 300,000 km / (115200 / 2))". Therefore, by setting the bit rate of the serial signal DS to "115.2 kbps" or less, the effects of the characteristic impedance and the load impedance can be almost ignored.

[0032] However, the serial signal DS is a square wave. The square wave is composed of a fundamental wave and odd-order harmonics. Therefore, it is advisable to consider not only the fundamental wave but also the influence of the harmonics from the characteristic impedance and the load impedance. For example, it is advisable that the wavelength of the fifth harmonic (a harmonic having a frequency five times that of the fundamental wave) is longer than four times the total length L0. Therefore, in this embodiment, the bit rate is set to "9600 bps". That is, according to this, the wavelength of the fifth harmonic is "12.5 km (= (300,000 km / (9600 / 2)) / 5)", which is sufficiently longer than four times the total length L0 ("4 km"). Therefore, the fifth harmonic (and components of lower orders) are hardly influenced by the characteristic impedance and the load impedance. In addition, the intensity of components of orders higher than the fifth harmonic is relatively small, so these influences can be almost ignored. Therefore, in this embodiment, an inexpensive cab-tire cable can be adopted. Furthermore, no termination resistor is required. Therefore, the component costs of the communication system 1 according to this embodiment are lower than those of the conventional system.

[0033] In addition, in the conventional system, a termination resistor is used, but its resistance value is relatively small (for example, 120 ohms). Here, if the output voltage of the driver 11 is "12V" and the safety factor is "0.7", the maximum output current of the driver 11 of the master node is 250mA, so the maximum number of slave nodes is "35 = (250mA / (12V / (12kohm / / (120ohm / 2))) × 0.7".

[0034] On the other hand, as described above, in this embodiment, no termination resistor is required. That is, the input impedance of the slave node is relatively large, and the current consumption of the slave node is relatively small. Therefore, according to this embodiment, the maximum number of connectable slave nodes can be increased. Specifically, the maximum number of connectable slave nodes in this embodiment is "175 units (= 250 mA / (12 V / 12 kΩ) × 0.7".

[0035] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the object of the present invention.

[0036] For example, in the above embodiment, the transceiver 10 is employed in which the driver 11 and the receiver 12 are enclosed (packaged) in one body BD, but instead, the driver 11 and the receiver 12 may be configured as separate entities. Also, for example, the above embodiment is an example in which the present invention is applied to a communication system that complies with "RS485" as an example of a differential serial communication protocol, but the present invention is also applicable to communication systems that comply with other differential serial communication protocols (for example, RS422). [Explanation of symbols]

[0037] 1...communication system, 10...transceiver, 11...driver (transmitting device), 12...receiver (receiving device), 30...cab-tyre cable (communication cable), C...control device, CN...connector, DS...serial signal, LF...low-pass filter, CP...communication path

Claims

1. A communication system for a gas engine driven air conditioner, which is applied to a gas engine driven air conditioner and transmits and receives data between a plurality of control devices of the gas engine driven air conditioner, comprising: A transmitter for transmitting a differential serial signal; A receiving device for receiving a differential serial signal; a communication cable connecting the transmitting device and the receiving device, the communication cable including a pair of electric wires for transmitting a pair of signals constituting the differential serial signal, the pair of electric wires being arranged in parallel; Equipped with a bit rate of the differential serial signal is set so that a wavelength of a fundamental wave of frequency components constituting each of the pair of signals is longer than four times the total length of the communication cable; A communication system for a gas engine driven air conditioner, wherein the total length of the communication cable is 1 km or less, and the bit rate is 1 kbps or less.

2. 2. The communication system for a gas engine-driven air conditioner according to claim 1, A communication system for a gas engine-driven air conditioning unit, wherein the bit rate of the differential serial signal is set so that the wavelength of the fifth harmonic of the frequency components that make up each of the pair of signals is longer than four times the total length of the communication cable.

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