Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
1998-02-22
2001-05-15
Cuchlinski, Jr., William A (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C701S031000, C714S025000, C714S030000, C714S046000
Reexamination Certificate
active
06233509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle diagnostic system.
2. Description of the Related Art
Modern vehicles incorporate complex electronic and electromagnetic active components such as engine management systems, fuel delivery control systems, and brake control system. It is desirable that these active components intercommunicate and as a result it is now becoming conventional to equip vehicles with a serial data communication bus linking active vehicle components and in particular components known as Electronic Control Units (ECU's). There are several widely used serial communication protocols which are accepted as industry standards, one such high speed and high performance protocol being known as CAN (that is Controller Area Network). The term CAN bus is used herein to mean any bus linking active components of a vehicle and conveying data representative of the performance of those components.
It is conventional practice to communicate between diagnostic equipment and a vehicle over its diagnostic bus. However, a CAN bus is not primarily intended for diagnostics and is not designed to allow for the connection of additional cable lengths to the vehicle's wiring system. The addition of a length of cable to a vehicle's CAN bus may cause data corruption.
The active components transmit to and receive data from the CAN bus to which they are connected at a high data rate, for example 1 Mbps. Such a high data rate ensures that the large volume of data can be handled, but also means that propagation delays on the bus must be minimized. Propagation delays of more than 20 ns are not acceptable on a conventional CAN bus. Accordingly, each active element must be carefully designed to present no more than a predetermined electrical load to the bus.
In order to gain access to data on a CAN bus for diagnostic purposes, it is conventional practice to connect a gateway terminal to the bus. The gateway terminal is permanently connected to the bus and in effect represents an additional active component. The gateway terminal monitors data on the CAN bus, and records fault conditions or other diagnostic related parameters. This diagnostic data may later be downloaded to appropriate diagnostic equipment. The data available at the output of the gateway terminal is limited in scope as compared with that on the bus, the nature of the data being determined largely by regulatory demands, e.g. regulations imposed by particular political bodies. Typically a gateway terminal is designed to meet an agreed standard such as ISO9141. Unfortunately, although regulations may change over the life of a vehicle, it is not possible to readily modify a gateway terminal to reflect such changes. Furthermore, problems can arise in a vehicle which cannot be readily diagnosed using the signals output by a conventional gateway terminal, especially where the data rate on the vehicle side of the gateway is much higher than that on the output side of the gateway.
A CAN bus is generally in the form of a twisted pair cable linking the active components. It is sometimes desirable to connect diagnostic equipment to the cable to gain direct access to the data on the bus rather than relying upon a gateway terminal. Unfortunately, diagnostic equipment is generally located in cabinets and cannot readily be positioned close to a vehicle under test. It has been discovered by the applicants that it is not possible to connect a cable between a CAN bus and a remote diagnostic station as signal reflections arise which result in corruption of data on the bus. In a typical CAN system the maximum acceptable length of a stub connection to the bus is limited to 30 centimeters. This makes a direct connection between a CAN bus and many types of diagnostic equipment impractical.
BRIEF SUMMARY OF THE INVENTION
According to present invention, there is provided a vehicle diagnostic system comprising a connector which may be coupled to a CAN bus, and an analyzer incorporating test equipment linked to the connector by a cable, wherein the connector comprises a buffer located between the bus and the cable to isolate the electrical load represented by the cable from the bus and to communicate signals transmitted from the analyzer to the bus and received from the bus to the analyzer.
Preferably the buffer comprises a converter circuit arranged to interface bi-directional signals on the buffer with unidirectional transmit and receive signals. The buffer and analyzer each comprise a line driver and receiver circuit arranged to convert signals from the buffer converter and test equipment to a protocol suitable for transmission on a cable, and to convert signals from the cable to signal suitable for applications to the buffer converter and test equipment.
The test equipment used can be of conventional form, as can the buffer converter circuit, the novelty lying in the separation of these two components such that one of the components is in the connector at one end of the cable and the other component is in the analyzer at the other end of the cable. The line driver and receiver circuit ensure that data is not corrupted during its transmission through the cable. The signals from the test equipment and the buffer converter may be converted to RS422 levels for transmission along the cable.
REFERENCES:
patent: 5905885 (1999-05-01), Richter
patent: 2217029A (1989-10-01), None
Arthur Gertrude
Cuchlinski, Jr. William A
Genrad Limited
Piper Marbury Rudnick & Wolfe
LandOfFree
Electronic diagnostic system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronic diagnostic system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronic diagnostic system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2529107