ELECTRICAL SYSTEM FOR A MOTOR VEHICLE

Abstract: The object of the present invention is an electrical system for distributing electrical power to the user devices installed on board of a motor vehicle, and, in particular, the wiring of the electrical system located in the area of the dashboard, which is relaized as a sub­ system of multiplex type, comprising three electronic microprocessor control units connected by a communication bus constituted by a serial interconnection line for the transmission of data.

Description: The present invention is concerned with an electrical wiring assembly according to the preamble of claim 1. The dimensions and the complexity of the wiring of the electrical system of motor vehicles have been progressively increasing, with the introduction of a larger and larger number of electrical user devices, in addition to the basic devices, constituted by the engine ignition, the lighting and signalling, and the windscreen wipers. For example, diagnostic equipment is being installed more and more diffusely, which verifies the efficiency of the engine, of the braking system, of the lights, and so forth; auxiliary devices are being more and more used, such as power operated windows, door locks, heated rear windscreen, air conditioners, and so forth; and widely adopted are electronic control systems for the engine ignition and fuel injection, for skidding prevention upon braking, for the suspensions and for four-wheel drives of vehicles. Consequently, increases in weight and in the overall dimensions of the electrical wiring have occurred, and the reliability of the electrical system, as a whole, resulted decreased, in particular due to the increase in number of the connectors. US-A-4 293 947 discloses a wiring assembly according to the preamble of claim 1. In this known device a relatively high number of slave control units is provided and the master control unit scans all the slave units in a sequential manner by transmitting information signals, whereby each of the sequentially called up slave units orderly responds in its turn and transmits data to the master unit. As soon as all the slave units have been scanned a new scanning takes place and so on. This known device requires positioning of slave units at a high number of locations of the vehicle and operates constantly with a pre-established fixed procedure involving increased times for obtaining information as the number of slave units increases. The purpose of the present invention is to provide an electrical wiring assembly which can be structurally integrated inside the dashboard of the vehicle and which is of improved safety and reliability and is capable of providing to the driver critical information from user devices with minimum delay. This purpose is achieved by an electrical wiring assembly having the features claimed in claim 1. By providing the data transmission in two steps according to one of the characteristical features of the present invention, important information or critical states are given to the driver with priority relative to others, and it is no longer necessary to scan each time all of the slave units. The harness in the dashboard area results very simplified, because the usual bundle of electrical power leads is replaced by the subsystem formed by the two slave control units and by the communication bus connecting them. Furthermore, a subsystem is provided, which can be easily adapted to the architecture of the dashboard, and which is also capable of making subsequent expansions possible. Characteristics and advantages of the present invention will be now illustrated by referring to Figures 1, 2 and 3, wherein a preferred practical embodiment of the same invention is shown for exemplifying, non-limitative purposes. Figure 1 shows a diagrammatic view of the dashboard of a motor vehicle, provided with the electrical wiring assembly according to the invention; Figure 2 shows a block diagram of the electrical wiring assembly of Figure 1; Figure 3 shows a detail of the electrical wiring assembly of Figure 2. In Figure 1, the dashboard of a motor vehicle is generally indicated by the reference numeral 10, and by the reference numeral 11 the main control unit, or master control unit, is indicated, and by the reference numerals 12 and 13 the secondary control units, or slave control units, are respectively indicated, which are two in total, namely the left-hand slave control unit and the right-hand control unit. The master control unit 11 is located in the proximity of the control means provided on the dashboard and of the steering column; the slave control units 12, 13 are situated on the sides of the dashboard. By the reference numeral 14, a communication bus is generally indicated, which comprises two leads, 40 and 41, connecting the three control units 11, 12, 13 with one another. As anyone can easily see, the three control units 11, 12, 13 form a subsystem, which can be easily installed in the area of the dashboard of the motor vehicle, in as much as it occupies a small room, and eliminates the usual bundle of leads. The electronic master control unit 11, which is microprocessor-controlled, performs functions of control of the actuation of electrical user devices, not shown in the Figures, of the motor vehicle. The user devices can be the internal lights of the motor vehicle, as well as the external lights, such as the parking lights, the low beams, the high beams, the turning signals and the stop lights, the windscreen wipers, the door locks, the power operated windows, the pilot lamps, the lamps lighting the on-board instruments, the heated rear windshield, the air conditioner, and so forth. The control unit 11 receives the input signals, which represent the requests for actuation of the above user devices, coming from the control means located on the dashboard and on the steering column; these control means are represented by the block 15, and are connected with the control unit 11 by means of the lines 16. The secondary control units (slave control units) 12 and 13 are microprocessor-controlled, and perform functions of actuation of the user devices, as above listed, with which they are operatively connected. The control unit 12 contains the power stages and the protection means, not shown, for the actuation of the user devices located on the left-hand side of the motor vehicle; the control unit 13 contains the power stages and the protection means for the actuation of the user devices located on the right-hand side of the motor vehicle. The power stages and the protection means of the control unit 12 receive electrical power from the battery, not shown in the Figures, through the block of the key switch 17, and the interconnection line 18, and those of the control unit 13 receive electrical power from the control unit 12, through the interconnection line 19. With the power stages of the control unit 12, the power leads are connected, which supply electrical power to the user devices actuated by the same control unit; some power leads are represented by the arrows 20s, 21s, 22s, 23s. Similarly, with the power stages of the control unit 13, the power leads are connected, which supply electrical power to the user devices actuated by the same control unit; some power leads are represented by the arrows 20d, 21d, 22d, 23d. With the two slave control units 12, 13 also the input leads, represented by the arrows 38s, 39s and 38d, 39d, are connected, which convey the signals generated by sensors designed to perform functions of measurement and of monitoring of some devices of the motor vehicle. By the reference numeral 24, an instrument panel is indicated, which is installed on the dashboard, wherein the speedometer 25, the revolution counter 26, the fuel level gauge 27, the engine coolant liquid temperature gauge 28 and the oil pressure gauge 29 are collected. The signals of speedometer and revolution counter actuation come from the control unit 12, through the interconnection line 30, and the signals of actuation of the fuel level gauge, of the coolant temperature gauge, and of the oil pressure gauge come from the control unit 13, still through the interconnection line 30; these signals are directly supplied to the instruments of the instrument panel 24 via the interconnection lines 31 and 32. In any case, also these instruments can be actuated under control by the master control unit 11. As inputs to the instrument panel 24, through the line 33, also the signals are supplied, which serve for feeding the lamps of lighting of the same instrument panel and the fuel level pilot lamp, the coolant temperature pilot lamp, the oil pressure pilot lamp. The lines 32 and 33 are connected, in their turn, with the master control unit 11, which is connected, in its turn, through the line 34, with the panelboard 35 on which other pilot lamps are installed, such as the external lights pilot lamps, and so forth. The master control unit 11 performs also the function of actuation of warning pilot lamps, indicating the operative status of pre-selected devices, such as the door opening/shutting, the level of the engine lubricant liquid and the level of the engine coolant liquid, the level of the windscreen cleansing liquid, the level of the brake liquid, the wear of the brake pads, and so forth. These pilot lamps are grouped on the control panelboard 36, which is connected with the master control unit 11 through the line 37. To the master control unit 11, the signals relevant to the warning pilot lamps are sent, through the communication bus 14, by the slave control units 12 and 13, which receive them as inputs form the leads 38s, 39s, 38d, 39d. The communication bus 14 which connects the control units 11, 12, 13 is formed by a serial interconnection line, comprising two leads 40 and 41, which are visible in Figure 3. The leads 40 and 41 are twisted to a plait configuration, in order that an identical path and an identical behaviour in case of disturbances is secured. The leads 40 and 41 are connected with the microprocessor slave control unit 12 through a transmission interface, generally indicated by 42 and, through resistances 43 and 44, with a reception interface, generally indicated by the reference numeral 45. The transmission interface 42 is constituted by NAND gates 46 and 47 and by an inverter 48; the reception interface 45 is constituted by NAND gates 50, 51, 52, 53, which form a bi-stable multivibrator (flip-flop). The leads 40 and 41 are also connected with the control units 11 and 13 through reception interfaces 54 and 55 which are identical to interface 45, and transmission interfaces 56 and 57, which are identical to interface 42. The communication bus 14 can also comprise reserve leads, capable of transmitting between the control units the data relevant to user devices in the motor vehicle which are of basic importance, and hence critical, such as parking lights, emergency lights, windscreen wipers, stop lights. The access by each control unit to the communication bus 14 is managed by the master control unit 11 with a communication protocol, which calls up the slave control units 12, 13 for receiving and collecting data therefrom and establishes the access modalities according to priorities assigned to the same control units. The transmission of the data takes place by cycles, coordinated by the master control unit 11, which are structurally equal, and are periodically repeated. Each cycle is constituted by two steps, the first step being dedicated to the selection of the control unit(s) which must transmit data, and to the collection of the requests for transmission, which are ordered according to the highest pre-established priority. During the second step, access is given to the communication bus 14 and the true transmission takes place according to the pre-established priority, and the master control unit 11 dedicates a pre-established time interval to the reception of a data from another control unit, or to the transmission of a data towards another control unit. Each transmitted data comprises a certain number of linear sequences (bytes), each composed by a pre-established number of bits. For example, the binary sequences can be six, wherein the first binary sequence relates to the address of the control unit which must transmit and to the type of data to be transmitted; the following three binary sequences define the true data, the last two binary sequences are check sequences to check the correctness of the transmission of data, by means of a mathematic operation carried out by dividing the first four binary sequences by a preselected polynomial expression. The check of the correctness of the transmission is also carried out on each bit of each transmitted binary sequence; this is made possible by the two leads 40 and 41 of the bus 14 and by the transmission and reception interfaces shown in Figure 3. The correctly transmitted data are finally validated and acquired by the receiving control unit. The transmission interface (42 or 56 or 57) sends simultaneously, on band base, a signal corresponding to the data to be transmitted in the form of a binary sequence on the lead 40, and, on the lead 41, a signal in the form of a sequence, which is the complement to one (high level) of the first signal; the reception interface (45 or 54 or 55) verifies that the individual bits which are simultaneously present in the two leads are of different level, i.e., the one low, and the other high, or vice-versa, and only when a difference exists and corresponds to a pre-established value, the reception interface allows the first signal to pass to the control unit and the bit present in the lead 40 is acquired by the control unit. By means of this solution, a wiring assembly is provided, which is extremely functional and reliable, besides having a small weight and a low cost.

Claims: Electrical wiring assembly for the distribution of electrical power to user devices installed aboard a motor vehicle equipped with a dashboard (10), comprising electronic microprocessor control units (11,12,13) operatively connected with a source of electrical power and interconnected with one another by means of a multiplex communication bus (14), said control units including a master control unit (11) for performing control functions and slave control units (12,13) for performing actuation functions, said master control unit (11) being operatively connected with signalling means (instrument panel 24) which signal the requests for actuation of said user devices and said slave control units (12,13) being operatively connected with said user devices and at least containing power stages for the actuation of said user devices, wherein the communication bus (14) between the control units (11,12,13) comprises a serial interconnection line, the access of each control unit (11,12,13) to the communication bus (14) and the transmission of data being managed and coordinated by the master control unit (11) which calls up the slave control units (12,13) for receiving and collecting data from the slave control units (12,13), and further comprising means (42,45,54-57) for verifying the correctness of the transmission of data, characterised in that said slave control units include in total two slave control units and said master and two slave control units (11,12,13) are located in the area of the dashboard (10) of the motor vehicle, and in that the transmission of data between said control units (11,12,13) comprises a first step of selecting among the control units (11,12,13) the control unit(s) which must transmit data and of ordering the transmission requests thereof according to a pre-established priority, and a second step of giving access to the communication bus (14) for carrying out the transmission of data according to said pre-established priority, whereby correctly transmitted data are finally validated and acquired by the receiving control unit (11,12,13). Electrical wiring assembly according to claim 1, characterised in that the communication bus (14) comprises two leads (40,41) connected with the control units (11,12,13) through transmission interfaces (42,56,57) and reception interfaces (45,54,55), wherein the transmission interfaces (42,56,57) are provided for sending to one (40) of said leads a signal corresponding to the data to be transmitted and for sending to the other (41) of said leads a signal complementary to the first signal, and wherein the reception interfaces (45,54,55) are provided for checking whether a difference exists between the two signals and if this difference exists and corresponds to a pre-established value, the reception interfaces (45,54,55) allow the first signal to pass to the control unit(s).

Inventors: BASSI, ALDO, FIORAVAZZI, SILVIO, GUELFI, GIORGIO, POLI, ALBERTO, PRISTERA, RAFFAELE, ROGORA, EDOARDO
Applicants: FIAT AUTO S.P.A.
Application year: 1987
Main classification: B60R16
IPC codes: G05B19, B60R16