GB2277618A

GB2277618A - Multiplexed data transmission for motor vehicle

Info

Publication number: GB2277618A
Application number: GB9308748A
Authority: GB
Inventors: Paul James Rockley
Original assignee: Henlys Group PLC
Current assignee: Henlys Group PLC
Priority date: 1993-04-28
Filing date: 1993-04-28
Publication date: 1994-11-02
Anticipated expiration: 2013-04-28
Also published as: GB2277618B; GB9308748D0

Abstract

A multiplexed data transmission system for use in a motor vehicle comprises a central control means 1 linked by data bus 2 to a plurality of control nodes 3 distributed around the vehicle, each control node being operatively linked to at least one adjacent switch means adapted to control the electrical power supply to a local electrical power-consuming component 4 and further adapted to break the supply of power to said component if the current exceeds a pre-determined value, whereby control data supplied by the central control means is transmitted to a selected control node via the data bus and subsequently brings about the switching of selected switch means and thus the selective operation of an associated power-consuming component. Monitoring means remains dormant while receiving a regular monitoring signal from the central control means 1, and sends switching signals to the switch means in response to cessation of the monitoring signal for a pre-determined time. <IMAGE>

Description

MOTOR VEHICLE Field of the Invention This invention relates to a motor vehicle, for example a public service vehicle such as a coach or bus, having a multiplexed data transmission system to effect control of various electric power-consuming components of the vehicle, for example lights, ventilation fans and the like.

Background to the Invention As the number of electrical components in motor vehicles increases, the complexity of the wiring loom needed to interconnect them also increases, and with it the cost. A further problem with complex wiring looms is that relatively high currents can be carried in them to all parts of the vehicle, increasing the risk of short circuit through insulation failure at any point, with the consequential risk of fire.

Providing the necessary protection for all circuits by way of fuses gives rise to complex central fuse boxes in the vehicles. With public service vehicles such as coaches and buses, the problems are even greater than with motor cars, because the distances over which the wiring extends is much greater, and the number of power-consuming components is also much larger. For example on some coaches, each passenger seat may be provided with its own overhead lamp. Multiplexed data transmission systems have been proposed as a way of overcoming these problems, by distributing power separately from the signals controlling its switching. Thus, a common data highway or bus is established to link local switching nodes for the components to a central controller which then sends individually addressed data messages to the nodes to cause switching of power from a common supply to the selected components at or adjacent to the point of use. One such system is described in WO 89/02141.

A problem with such systems is the need to protect the individual power-consuming components from short-circuit failures. Provision of dispersed fusing arrangements is costly and inconvenient when fuse replacement is required.

A further difficulty is the provision of a satisfactory fail-safe control system which will permit the vehicle to operate in the event of a microprocessor failure or the like.

Summarv of the Invention One aspect of the invention provides a motor vehicle having a plurality of electrical power-consuming components distributed around the vehicle body and/or chassis, switch means adjacent to each said component, the switch means being supplied with electrical power from a central power supply and being arranged to break the supply of power to a component if the current exceeds a predetermined value, at least four control nodes distributed around the vehicle and linked by a data bus to a central control means, each control node being operatively linked to a respective group of said switch means adjacent to said node, the central control means being arranged to send switching signals via said data bus to a selected one of said nodes to signal a switch means to switch power to a selected component.

The central control means may serve to gather information from all the other nodes, and from its own inputs and outputs. This information is then processed to determine which outputs should be turned on or off in the system. The central control means will preferably be located as close to the chassis electrical distribution centre as possible, to permit it to derive some of its inputs therefrom. This may or may not be close to the driver.

Another aspect of the invention provides a motor vehicle having a plurality of electrical power-consuming components distributed around the vehicle body and chassis, switch means adjacent to each said component, the switch means being supplied with electrical power from a central power supply, at least four control nodes distributed around the vehicle and linked by a data bus to a central control means, each control node being operatively linked to a respective group of said switch means adjacent to said node, the central control means being arranged to send switching signals via said data bus to a selected one of said nodes to signal a switch means to switch power to a selected component, and monitoring means connected to said central control means and to at least some of said switch means and arranged to remain dormant while receiving a regular monitoring signal from the control means and to send switching signals to said switch means in response to cessation of said signal for a predetermined time.

Preferably, the monitoring means receives from the control means a pulsed signal and is arranged to detect the change in voltage associated with the pulses. The absence of the change is used to trigger the default state operating predetermined switch means.

More preferably, the monitoring means is arranged to restore control of the switching means to the central control means when said monitoring signal is again received.

Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a diagram illustrating the layout of the data transmission system in a vehicle; Figure 2 is a block diagram of the monitoring means of the vehicle and system of the invention; Figure 3 is a more detailed diagram of the monitoring means illustrated in Figure 2; and Figure 4 is a timing diagram for the operation of the monitoring means.

Detailed Description of the Illustrated Embodiments Referring to Figure 1, a motor vehicle such as a coach has an electrical system comprising a central controller 1 conveniently located adjacent to the driver of the vehicle and connected to a data bus 2 linking four control nodes 3, each comprising a slave controller and a plurality of smart switches controlling the supply of electrical power to individual components 4, such as lights. Each node 3 is supplied with electrical power from the vehicle's 24 volt battery 5 by way of a power cable 6.

Smart switches are semiconductor devices which combine signal processing capabilities with power control. An example is that sold by Siemens under the trade mark "PROFET". This is a rugged N-channel power MOSFET which has integrated protective functions against destruction through short-circuit, over-temperature, overload and electrostatic discharge, and has a status pin to provide an indication if a fault has occurred. The device automatically shuts down if a short circuit occurs.

The controller 1 comprises a microprocessor signalling over the data bus using the controller area network protocol (CAN) developed by Bosch for in-vehicle data transfer and put forward to ISO as a draft standard. The CAN is designed to cope with data transfer rates that cover the entire field of all real time (e.g. engine management) and multiplex applications (e.g. driver lights) at rates from 10 kbps to 1 Mbps. It has complex error detection and correction capabilities, thus giving high error immunity. The CAN protocol uses a bus configuration with only one logical bus line. The transfer medium may be simply a twisted pair, which may be screened or unscreened according to the application. The protocol operates as a multi-master system on a single bus, where each controller gains access to the bus by bit-wise arbitration. The message with the lowest numerical identifier field has priority over the other controllers trying to access the bus. The controller which is unable to gain access to the bus on its first attempt will keep retransmitting when the bus is idle untii it has control of the data bus. The data frame is broken down into the startof-frame to synchronise all controllers, the arbitration field to indicate the priority of the data, the control field to indicate how much data there is, the data field itself (0 to 8 bytes), the CRC (cyclic redundancy check) field to check that the message has not been corrupted, the ACK field for receivers to acknowledge successful receipt of data, and finally the end-of-frame to mark the end of the message. The protocol has various error checking methods to ensure that data is of the correct logic and that a receiver has successfully detected the data.

Thus, the controller 1 introduces a message onto the data bus containing the address of the individual node together with the necessary information in the data field to turn on the correct smart switch.

Each node contains a CAN chip, a microcontroller, a RAM chip and a ROM chip. In the illustrated embodiment, this is true for the central controller and for each of the other nodes. The microcontroller in a "slave" node may turn the smart switches on or off by writing to an address location on its own data bus, not the CAN data bus. By control from the software, the slave node controller reads the data from the receive data register of the CAN chip, and if a Remote Transmission Request (RTR) bit is present, the Input/Output (I/O) status of that slave is sent to the Master or central controller via the CAN bus. If the RTR bit is not present, the received data is used either to turn on or to turn off the smart switches. If a change occurs in the I/O status, this information is also sent to the Master via the CAN bus.

It is possible that intelligence at the slave node may become unnecessary, by providing a node circuit in which the data content of the message received on the CAN bus causes registers to be written to, thereby switching the appropriate output. There would thus be no need to use the RTR bit, as a separate bit has been allocated to determine the direction of the data to or from the slave node.

It will be appreciated that the number and distribution of the nodes will be determined by the vehicle design.

Referring now to Figures 2 and 3, to provide failure monitoring of the system, the microcontroller 20 forming part of the controller 1 is arranged to emit regular pulses to a pulse monitor 21. While the pulse is present, the pulse monitor 21 enables the microcontroller to continue with its normal function. Should the pulse output of the microcontroller fail because of failure of the microcontroller itself or the software operating it, the pulse monitor sends a control signal to selected ones of the smart switches to switch them on, thus providing a basic lighting set, for example, as a default on failure of the controller.

Referring to Figure 3, the pulse monitor comprises a retriggerable monostable 30 which is fed, via a NAND gate 31, with the pulse generated from P1.0 of the microcontroller. Each time the falling edge of the software-generated pulse is detected, the monostable is retriggered. While /Q1 (pin 4 Monostable) is low, the RST output is always low, and so the microcontroller is in normal operation. If the software fails, then after a period of time determined by C1 and R1, /Q1 goes high, therefore resetting the microcontroller via NAND gates 32 and 33. The duration of the resetting pulse is determined by C3, R4 and R3. After this pulse, the software has a period of time determined by R3 and C3 to recover. The trip pulse coincides with the reset pulse and on the rising edge of the first trip pulse the not Q output of the first flip-flop 34 goes low. On the rising edge of the second trip pulse the not Q output of the first flip-flop 34 goes high and the not Q output of the second flip-flop 35 goes low, therefore activating the default outputs.

Referring to Figure 4, the timing stages in the operation of the monitoring means are as follows: O Power on, monostable cleared by R2/C2, CPU reset 1 Monostable triggered by rising edge of CLR. CPU starts.

2 Monostable retriggered by software (P1.0 falling edge) 3 Monostable retriggered by software (P1.0 falling edge) 4 Monostable retriggered by software (P1.0 falling edge) 5 Software failure - P1.0 not toggled 6 Monostable times-out, RST goes high forcing P1.0 high. CLR removed from trip counter.

7 RST goes low enabling CPU restart. Rising edge of TRIP clocks trip counter.

8 Software does not recover during ti - CPU reset once more.

8a Defaults activated by second rising edge of TRIP.

9 Software recovery - falling edge detected on P1.0. /Q1 goes low forcing reset of trip counter, deactivating default outputs and returns control to software.

10 Normal operation - Monostable retriggered with tw.

11 Normal operation - Monostable retriggered with tw.

12 Normal operation - Monostable retriggered with tw.

13 Normal operation - Monostable retriggered with tw.

(Note: The second D type bistable can be triggered from Q or /Q. This will allow default mode to be entered immediately a software failure is detected or if triggered from /Q will allow one reset/recovery cycle before activation.) In the above: tw = 0.25 R1C1(1+0.7/R1) for LS devices (tw = RlC1 for HC) th Determined by R3//R4C3 ti Determined by R3C3 CPU power on reset time determined by R2C2.

Claims

1. A multiplexed data transmission system for use in a motor vehicle comprising: a plurality of electrical power-consuming components distributed around the vehicle body and/or chassis, switch means adjacent to each said component, the switch means being supplied with electrical power from a central power supply, a plurality of control nodes distributed around the vehicle and linked by a data bus to a central control means, each control node being operatively linked to respective group of said switch means adjacent to said node, the central control means being arranged to send switching signals via said data bus to at least a selected one of said nodes to signal a switch means to switch power to a selected component.

2. A system according to Claim 1 wherein said switch means are arranged to break the supply of power to a component if a current exceeds a pre-determined value.

3. A system according to Claim 1 or Claim 2 wherein a monitoring means is connected to said central control means and to at least some of said switch means and arranged to remain dormant while receiving a regular monitoring signal from the control means and to send switching signals to said switch means in response to the cessation of said monitoring signal for a pre-determined time.

4. A system according to Claim 3 wherein said switching signals, via said switch means, set said power-consuming components to a default status.

5. A system according to Claim 3 wherein a re-set signal is sent by said monitoring means to said central control means on cessation of said regular monitoring signal.

6. A system according to Claim 5 wherein said re-set signal is repeatedly sent to said central control means during cessation of said regular monitoring system.

7. A system according to Claims 3, 4, 5 and 6 wherein said central control means resumes control of all components on recovery.

8. A system according to Claim 7 wherein the monitoring means is arranged to restore control of the switching means to the central control means when said monitoring signal is again received.

9. A system according to any preceding Claim wherein said central control means gathers information from all the nodes in the system and from its own inputs and outputs.

10. A system according to any preceding Claim wherein the central control means is located close to the chassis electrical distribution centre.

11. A system according to Claims 3 to 10 wherein the monitoring means receives from the central control means a pulse signal and is arranged to detect a change in voltage associated with the pulse.

12. A system according to Claim 11 where an absence or change in signal is used to trigger a default state operating predetermined switch means.

13. A system according to any preceding Claim wherein the central control means is adapted to communicate with the control nodes using a protocol that enables the use of simple wiring such as a twisted pair.

14. A system according to Claim 13 wherein said protocol is a controller area network protocol.

15. A system according to any preceding Claim wherein said switches are 'smart' switches.

16. A system according to any preceding Claim wherein said control nodes comprise a means for recognizing and/or monitoring a fault or a failure.

17. A motor vehicle comprising a data transmission system in accordance with any preceding Claim.

18. A multiplexed data transmission system as substantially herein described and/or with reference to the accompanying Figures.

19. A motor vehicle comprising a multiplexed data transmission system as substantially herein described and/or with reference to the accompanying Figures.