Improved CAN system for vehicles

Abstract

The invention comprises a capacitive network coupling 23a,b, network data reconstruction circuit (Fig. 4; 40 & 50), network data processing (Fig. 4; 40), output circuit (Fig. 4; 60) and voltage regula

Description

Field of the Invention The present invention relates to controlled area network (CAN) bus systems, and in particular to an apparatus that is capable of reading signals transmitted on the CAN bus system of vehicles. Background of the Invention It is common for vehicles to be equipped with a CAN bus system. The CAN bus system is used to transmit signals to devices forming part of the vehicle or attached to the vehicle. For example, a signal to illuminate a direction indicator would be transmitted from a controller upon receipt of a signal by the controller from the driver controls. It is often desirable to retro-fit devices to a vehicle, or to customise operation of elements of the vehicle after construction of said vehicle. In order to operate such retro-fitted devices or to customise operation of elements of the vehicle it is necessary to obtain a signal from the CAN bus. In some cases systems are available to programme the CAN bus, but typically vehicle manufacturers do not authorise modification of the vehicle’s CAN bus because there is a possibility that a third party may choose a code that has already been allocated to a different function, which could compromise safety of the vehicle. The solution for providing access to the CAN bus signals that is currently available involves mirroring the signals sent on the CAN bus using a contactless CAN reader. A CAN reader is placed between the CAN high and CAN low wires of a CAN bus system. The CAN reader reads signals passing on the CAN high and CAN low wires. The CAN reader is a capacitive reader. One product that is available commercially is known as CANcliq and is available from Squarell BV. In order to use a CAN signal read by a CAN reader, the read signal is transmitted by a processor in the CAN reader to a CAN interface which is situated some distance from the CAN reader, the CAN reader and the CAN interface being connected together by wire. Similar systems are described in GB2516236 and US2009 / 0279645. The output of the CAN reader is a single ended square wave where the low point of the square wave is nominally 0 volts and the high point of the square wave is nominally 5 volts. The signal is susceptible to noise. As such the CAN interface requires signal processing features in order to remove the noise from the signal. It would be desirable to provide an apparatus capable of reading signals flowing on a CAN bus system and providing control outputs in a single component. Summary of the Invention According to an aspect of the invention there is provided a CAN bus reader and signal generating apparatus comprising: a capacitive network coupling; a network data reconstruction circuit; a network data processing and logic unit; at least one output circuit; and a voltage regulator, the voltage regulator receiving an input voltage and providing an output voltage lower than the input voltage, the output voltage providing a potential difference across the capacitive network coupling, the network data reconstruction circuit and the network data processing and logic unit, characterised in that, the capacitive network coupling comprises a pair of spaced apart capacitive sensor plates and a long tailed pair circuit, wherein each of the spaced apart capacitive sensor plates is configured for alignment with a respective one of a CAN low and a CAN high wire of a CAN bus of a machine; the network data reconstruction circuit receives, amplifies and reshapes the output signal from the long tail pair; the network data processing and logic unit receives the digital signal output from the network data reconstruction circuit and is programmed to generate output signals based on signals detected on the machine CAN bus; and the at least one output circuit is connected to an electrical circuit of the machine which includes a commanded device, and wherein the or each output circuit is configured to switch current flowing through the electrical circuit of the machine to the commanded device on and off. The CAN bus reader and signal generating apparatus may be a CAN bus reader and signal generating apparatus as specified in Claim 1. According to another aspect of the invention, there is provided a machine comprising a CAN bus and CAN bus reader and signal generating apparatus as specified in Claim 13. Other features of the invention are set out in the claims dependent on Claims 1 and 13, in the description and drawings. Brief Description of the Drawings In the Drawings, which illustrate the prior art and preferred embodiments of the invention, and which are by way of example: Figure 1 is a schematic representation of a CAN reader system of the prior art; Figure 2 is a schematic representation of a CAN system according to the invention; Figure 3 is a circuit diagram illustrating the circuits of the invention; Figure 4 is a schematic representation of a circuit board mounting the circuits illustrated in Figure 3; Figure 5 is a flow diagram illustrating the generation of output signals in the CAN system illustrated in Figures 2 to 4; Figure 6 is a flow diagram illustrating the processing of signals read from the CAN bus; Figure 7 is a schematic representation view from above of an alternative embodiment of part of the CAN system of the invention; and Figure 8 is a schematic representation view from below of the part of the CAN system of the invention illustrated in Figure 7. Detailed Description of the Preferred Embodiments Referring now to Figure 1, there is shown a system for reading and mirroring the signals sent on a CAN bus system, for example the CAN bus 1 of a vehicle. The vehicle CAN bus 1 comprises a pair of twisted copper wires. One of the pair of wires carries a CAN bus high signal and the other a CAN bus low signal. A CAN bus reader 2 is mounted on the vehicle such that the wires of the vehicle CAN bus 1 pass between capacitor plates 3a, 3b of the CAN bus reader 2. Where the wires pass between the capacitor plates 3a, 3b the wires are separated so that the CAN low wire is aligned with the capacitor plate 3a and the CAN high wire is aligned with the capacitor plate 3b such that the capacitor plate 3a senses the signal in the CAN low wire, whilst the capacitor plate 3b senses the signal in the CAN high wire. A second CAN bus 5 is connected to a CAN interface which comprises a processor 10, the processor 10 being located remote from the CAN bus reader 2. The processor 10 has an input / output interface 10a, which receives the wires of the second CAN bus 5 and outputs signals via output wires 11 to output ports 12. The arrangement illustrated in Figure 1 may be used to provide an output that the vehicle would not be able to generate itself without the presence of the apparatus illustrated in Figure 1. For example, the vehicle may have a sensor that recognises that the hand brake is either on or off. The vehicle may also have sensors that sense that the door is open or closed. However, the vehicle may not be configured to provide a warning that the door is open and that the parking brake is off. It has been found that drivers of delivery vans often leave their vehicles running and the driver’s door open, as this reduces the time taken to access the vehicle and move off. Drivers may mistakenly omit to apply the parking brake. In the context of a delivery van, a condition in which the parking brake has not been applied and the driver’s door is open, would indicate a likelihood that the van driver has left or is likely to leave the vehicle without applying the parking brake. By providing the apparatus illustrated in Figure 1 and connecting the outputs 12 to a device that can emit a warning signal, such as a loud speaker, the driver of the vehicle may be provided with a warning that the vehicle is in an unsafe condition. The apparatus may also be used to monitor driver behaviour, whether a warning device is connected to the outputs 12 or not. Data may be logged by connecting a data logger to the output ports 12. The apparatus illustrated in Figure 1 in effect creates a mirrored version of the vehicle CAN bus 1 and through the CAN interface allows signals to be issued based on signals detected on the vehicle CAN bus 1, without creating direct connections with the vehicle CAN bus 1. A number of problems are associated with the above-mentioned arrangement, including lack of space to mount the apparatus on a vehicle, the possibility of noise interfering with signals transmitted on the wires of the second CAN bus 5 and the requirement to replicate the whole vehicle CAN bus 1 in the second CAN bus 5. The apparatus 20 illustrated in Figures 2 does away with the need for two separate spaced apart electronic elements (namely the CAN Bus reader 2 and the CAN interface in the form of processor 10 illustrated in Figure 1) joined by a second CAN bus. A vehicle on which the apparatus 20 is mounted includes a CAN bus 1. The CAN bus 1 includes a pair of twisted copper 4 wires, one of which carries CAN low electrical signals and the other CAN high electrical signals. The apparatus 20 is mounted on the vehicle such that the wires of the vehicle CAN bus 1 pass between capacitor plates 23a, 23b of the apparatus. In the region where the CAN bus 1 passes between the plates 23a, 23b the wires carrying the CAN low and CAN high signals are separated from each other with each one of the wires being arranged next to a respective one of the CAN low and CAN high plates 23a, 23b. The capacitor plate 23a senses the signal in the CAN low wire, whilst the capacitor plate 23b senses the signal in the CAN high wire. The CAN low wire and the CAN low plate 23a each form one of the plates of a capacitor. Similarly, the CAN high wire and the CAN high plate 23b each form one of the plates of a capacitor. The apparatus 20 receives electrical power from the vehicle electrical system through the power input terminals 24a, 24b (for example, connected to +9 -32 volts and ground Ov) and outputs electrical signals to the vehicle electrical system through power outputs 25a, 25b. Figures 7 and 8 illustrate another embodiment of the invention where the wires 1 a 1 b of the vehicle CAN bus 1 are separated above and below capacitor plates 23a, 23b, rather than lying in the same plane and being spaced apart laterally as described with reference to Figures 2-6. Otherwise, the apparatus 20 illustrated in Figures 7 and 8 is the same as described with reference to Figures 2 to 6. In the illustrated example, the apparatus 20 comprises five distinct circuits mounted on a single circuit board as illustrated in Figures 3 and 4. Figure 3 illustrates the circuits mounted on the circuit board in most detail, whereas Figure 4 illustrates the circuit board. Referring now to Figure 3 in particular: Long Tailed Pair The first circuit is a long tailed pair 30. The signals from the capacitor plates 23a, 23b form inputs (HIGH)(LOW) to the long tailed pair which transforms the two signals into a single output signal (OUT). This output signal forms the input for the next part of the circuit. Logic Amp and Shutdown The (OUT) signal from the long tailed pair circuit 30 forms the input to the logic amp and shutdown circuit 40. The function of the first part of the circuit 41 is to amplify the signal from the long tailed pair 30 millivolts to approximately 5 volts. The second part of the this circuit 42 reshapes the amplified signal to a digital signal CAN RX. Processor The output CAN RX of the logic amp and shutdown circuit 40 forms the input to the processor circuit 50. The function of the processor is to generate an output signal when a certain signal or combination of signals is detected on the vehicle CAN bus. The processor IC is programmed with a configuration file. The processor circuit 50 is programmed with a configuration file which when run causes the desired signal on the vehicle CAN bus to be identified and the appropriate output signal to be generated. The processor circuit 50 has a quiescent mode and an active mode, and switches to quiescent mode if the processor detects that the CAN bus has become inactive. The other parts of the circuit remain active to allow the processor circuit 50 to sense when the CANbus becomes active again. As the processor circuit represents the majority of the current draw for the device, being able to put it into a low power quiescent mode saves a significant amount of power. Positive Outputs The positive outputs 60 in this example provide two outputs circuits 61,62. Each device that is to be controlled, such as a loudspeaker or an indicator lamp, has its own positive output circuit 61,62. The electrical signal operating the controlled device must be at the vehicle voltage. OUT 1P of the processor 50 forms an input to output circuit 61 and OUT 2P of processor 50 from an input to circuit 62. The the positive outputs circuits 61,62 converts the 5 volt signal output of the processor 50 to the vehicle voltage, typically between 12 volts and 28 volts depending on the vehicle. The positive output circuits 61,62 also includes a shutdown function which protects the apparatus from short circuits that might occur in the vehicle circuits to which the apparatus is connected. Regulator The circuit includes a regulator 70. The function of the regulator 70 is to provide a current at 5 volts from the vehicle electrical system, which as stated above, operates for example between 12 and 28 volts, depending on the vehicle type. The 5 volt output of the regulator is connected to the long tail pair circuit 30, the processor circuit 50 and the logic amplifier and shutdown circuit 40. Figure 4 illustrates a circuit board on which the circuits described above are mounted. The CAN low and CAN high plates 23a and 23b are attached to the circuit board 80. The CAN low capacitor plate 23a is visible in the Figure, with the CAN high plate 23b being located beneath the CAN low plate and hence not being visible. Figure 5 illustrates the circuits of the circuit board shown in Figures 2 and 3 in block diagram form. Referring now to Figure 6, the flow diagram illustrates how signals read from the CAN bus are processed by the apparatus 20. The apparatus 20 (the integrated unit in the flow chart of Figure 6) is powered on at step 100. The processor 50 is loaded with a configuration file at step 101. In this example the configuration This configuration file defines which signals passing on the CAN bus are to be monitored, and produces desired output signals when those signals are detected on the CAN bus. The example signal in the flow chart is the status of the ignition. The processor 50 determines whether the ignition is on or off in step 101 a. The raw CAN bus data to be read as required by the configuration file is read through capacitor plates 23a, 23b in the manner described above in step 102. The output of processor 50 is amplified in step 103 and shaped in step 104. A decision point step 105 an asks whether a new CAN frame has been received or not. If no CAN Frame has been received, the process returns to step 102. If a new CAN Frame has been received the processor 50 extracts the CAN ID from the signal in step 106. In step 107 the processor 50 is programmed to identify whether the CAN ID extracted in step 106 matches a target CAN ID (identified in the configuration file) or not. If the CAN ID does not match a target CAN ID the process returns to step 102. If the CAN ID does match a target CAN ID the process moves to step 108. In step 108 the processor 50 examines the target Byte and the target Bit of the signal having a target CAN ID as per the configuration file (see step 101 a). In step 109 the processor 50 reads the current state of the Target Bit (e.g. Bit 5) which is 1, indicating that the ignition is ON (see step 101a). Step 110 is another decision point. The processor 50 compares the current state of the Target Bit with the previous stored state for the same output (the status of the ignition in this example). If there is no change in the current state (i.e. the ignition is still ON, the process returns to step 102). If a change is detected in the current Bit state read in step 109 as compared to the previous Bit state, the process moves to step 111, which asks what the change is. Does the current Bit state = 1? If yes (the ignition has moved from On to Off - Bit = 0 instead of 1), At step 111 the processor 50 asks if the Current Bit state matches the “Condition for ON” in step 112. If the answer is yes, the processor 50 sets its output pin OUT1P to HIGH (on). If the answer is no, the processor 50 sets the output pin OUT1P to LOW (off) in step 113. At step 114 the new Bit state is stored as a previous Bit state for OUT 1P. The CAN bus reader and signal generating apparatus of the invention does away with the requirement for a replicated CAN bus. Instead, only those signals required are read from the vehicle CAN bus. The apparatus of the invention consumes less power, is less susceptible to noise and requires less space.

Claims

1. A CAN bus reader and signal generating apparatus comprising:a capacitive network coupling;a network data reconstruction circuit;a network data processor;at least one output circuit; anda voltage regulator, the voltage regulator receiving an input voltage and providing an output voltage lower than the input voltage, the output voltage providing a potential difference across the capacitive network coupling, the network data reconstruction circuit and the network data processor,characterised in that,the capacitive network coupling comprises a pair of spaced apart capacitive sensor plates and a long tailed pair circuit, wherein each of the spaced apart capacitive sensor plates is configured for alignment with a respective one of a CAN low and a CAN high wire of a CAN bus of a machine;the network data reconstruction circuit receives, amplifies and reshapes the output signal from the long tail pair;the network data processor is programmed with a configuration file, the network data processor receiving the digital signal output from the network data reconstruction circuit and is programmed through the configuration file to generate output signals based on the signals detected on the machine CAN bus and identified in the configuration file; andthe at least one output circuit is connected to an electrical circuit of the machine which includes a commanded device, and wherein the or each output circuit is configured to switch current flowing through the electrical circuit of the machine to the commanded device on and off.

2. A CAN bus reader and signal generating apparatus according to Claim 1, wherein the capacitive network coupling, the network data reconstruction circuit, the network data processor, the at least one output circuit, and the voltage regulator are mounted on one or more circuit boards.

3. A CAN bus reader and signal generating apparatus according to Claim 1 or 2, wherein the at least one output circuit includes a short circuit detection circuit configured to detect short circuits in the vehicle electrical circuit.

4. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the at least one output circuit is formed of discrete components.5 A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the electrical circuit of the machine includes a plurality of commanded devices, and wherein the CAN bus reader and signal generating apparatus includes a plurality of output circuits, one for each respective commanded device.

6. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the machine is a vehicle.

7. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the input voltage to the voltage regulator is between 12 volts and 28 volts.

8. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the output voltage of the voltage regulator is 5 volts.

9. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the apparatus has a quiescent state and an active state and wherein in the quiescent mode the current is lower than the active mode.

10. A CAN bus reader and signal generating apparatus according to Claim 10, wherein in the quiescent mode the current is in the range of 3-5mA.

11. A CAN bus reader and signal generating apparatus according to Claim 10 or 11, wherein in the active mode the current is in the range of 12-14mA.

12. A CAN bus reader and signal generating apparatus according to any of Claims 9 to 11, wherein the network data processor is programmed to switch from the active mode to the quiescent mode when no signals are detected on the machine CAN bus for a pre-determined period of time.

13. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the network data processor is programmed through the configuration file to extract only signals detected on the machine CAN bus and identified in said configuration file, wherein the network data processor is programmed through the said configuration file to generate the output signals based on the signals detected on the machine CAN bus and identified in the configuration file.

14. A CAN bus reader and signal generating apparatus according to any preceding claim, wherein the network data processor is a network data processing and logic unit.

15. A CAN bus reader and signal generating apparatus according to any preceding claim, comprised in a single unit.

16. A machine comprising a CAN bus and a CAN bus reader and signal generating apparatus according to any of Claims 1 to 15.

17. A machine according to Claim 16, wherein the machine is a vehicle.

18. A machine according to Claim 17, wherein the CAN bus reader and signal generatingapparatus is programmed with the configuration file to read at least one signal identified in the configuration file and transmitted on the CAN bus and to provide an output to a commanded device according to the status of at least one signal.

19. A machine according to Claim 18, wherein the CAN bus reader and signal generating apparatus is programmed to read a plurality of signals transmitted on the CAN bus and to provide an output to a commanded device according to the status of the plurality of signals.T +44(0)30 0300 2000A

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