1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2006 SAE International All rights reserved. No part of this publication m
3、ay be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org J2057-1 REAF. SEP2006 SURFACE VEHICLE INFORMATION REPORT Issued 1991-06 Reaffirmed 2006-09 Superseding J2057-1 FEB1997 Class A Application/Definition RATIONALE This document has been reaffirmed to comply with the SAE
5、 5-Year Review policy. FOREWORD The Vehicle Network for Multiplexing and Data Communication Subcommittee has defined three classes of communication networks. Perhaps, the least understood, with respect to function and implementation, is the Class A network. A clear understanding of Class A functions
6、 is necessary before any standards for protocol can be established. TABLE OF CONTENTS 1. Scope 2 2. References 2 2.1 Applicable Publication. 2 2.1.1 SAE Publication 2 3 Definitions . 2 3.1 Classification A 2 3.2 Classification B 2 3.3 Classification C . 3 4. Interrelationship of the Three Classes 3
7、4.1 System Speed versus Functional Speed 3 5. Typical Applications of the Classes 3 5.1 Class C Typical Applications. 3 5.1.1 Examples of Class C Applications 3 5.2 Class B Typical Applications. 4 5.2.1 Examples of Class B Applications 5 5.3 Class A Typical Applications. 5 5.3.1 Examples of Class A
8、Devices. 9 6. Parameters of Class A Devices 9 6.1 Input Device Definition 9 6.2 Output Device Definition . 10 6.2.1 Output Device with Feedback (Status) . 10 SAE J2057-1 Reaffirmed SEP2006 - 2 - 7. Class A System Criteria 10 7.1 Latency 11 7.2 Reliability. 11 7.3 Bus and Node Failures . 11 7.4 EMC S
9、usceptibility and Radiation. 11 7.5 Diagnostics 11 7.6 Cost. 11 7.7 Open System 11 7.8 Sensitivity to Environments. 11 7.9 Communications to Other Systems 11 7.10 Electrical Media. 11 7.11 Software Requirements 11 7.12 Node Capabilities 11 7.13 Sleep State Current Drain. 12 8. Preferred Class A Syst
10、em Criteria 12 1. SCOPE This SAE Information Report will explain the differences between Class A, B, and C networks and clarify through examples, the differences in applications. Special attention will be given to a listing of functions that could be attached to a Class A communications network. 2.
11、REFERENCES 2.1 Applicable Publication The following publication forms a part of this specification to the extent specified herein. Unless otherwise indicated, the latest issue of SAE publications shall apply. 2.1.1 SAE Publication Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001
12、, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. SAE J1213/1 Glossary of Automotive Electronic Terms 3. DEFINITIONS SAE J1213/1 defines three classes of communication networks, Class A, Class B, and Class C. 3.1 Class A The Class A network is defined as, “A pot
13、ential multiplex system usage whereby vehicle wiring is reduced by the transmission and reception of multiple signals over the same signal bus between nodes that would have been accomplished by individual wires in a conventionally wired vehicle. The nodes to accomplish multiplexed body wiring typica
14、lly did not exist in the same or similar form in a conventionally wired vehicle.” 3.2 Class B The Class B network is defined as, “A potential multiplex system usage whereby data is transferred between nodes to eliminate redundant sensors and other system elements. The nodes of this form of a multipl
15、ex system typically already existed as standalone modules in a conventionally wired vehicle.” SAE J2057-1 Reaffirmed SEP2006 - 3 - 3.3 Class C The Class C network is defined as, “A potential multiplex system usage whereby high data rate signals typically associated with real time control systems, su
16、ch as engine controls and antilock brakes, are sent over the signal bus to facilitate distributed control and to further reduce vehicle wiring.” 4. INTERRELATIONSHIP OF THE THREE CLASSES A hierarchical relationship exists between the classes of networks. By definition, Class C is a superset of Class
17、 B. Also, Class B is a superset of Class A. It should be noted that this is a functional relationship only. Therefore, it is important to distinguish between the function and the application of the multiplex network. 4.1 System Speed versus Functional Speed Most discussions on multiplexing focus on
18、two issues; system speed and system complexity. Confusion arises from associating functional speed with system speed and complexity. As described in 3.3, Class C is defined as high speed and real time control. Intuitively, high function speed requires high system speeds and perhaps complexity. The C
19、lass B definition also makes no reference to the speed of the network or the function but places an emphasis on the type of function, “data communications“. Class A defines the functions as being individually wired and not normally connected to intelligent nodes within the vehicle. Here again, no me
20、ntion is made about the system speed or complexity required to achieve the function. Networks operating at high or medium speeds, therefore, must not be excluded from consideration as a Class A network. 5. TYPICAL APPLICATIONS OF THE CLASSES Table 1 lists some characteristics of the three classes of
21、 multiplex networks. The real functional purpose is shown for each. In addition, the type of information and the timeliness of its distribution is noted. TABLE 1 - CHARACTERISTICS OF MULTIPLEX NETWORKS Class A Class B Class C Purpose Sensor/Actuator Control Information Sharing Real-Time Control Info
22、rmation Real Time Occasional Real TIme Latency Response Time Wide Window Varying Window Narrow Window System Multiple Systems Multiple Systems System Specific Information Lost or Corrupted Nuisance Nuisance or Failure Failure 5.1 Class C Typical Applications Systems that require real time, high spee
23、d control normally require a significant amount of information to function properly. This information must be available within a narrow time window that cannot vary. A delay of information longer than the specified time window may cause reduced operation or in extreme cases could result in the vehic
24、le becoming inoperable. Figure 1 illustrates a Class C application. 5.1.1 Examples of Class C Applications AntiLock Brakes, Steer by Wire, Traction Control. SAE J2057-1 Reaffirmed SEP2006 - 4 - FIGURE 1 - TYPICAL CLASS C APPLICATION 5.2 Class B Typical Applications Many systems within the vehicle re
25、quire information that is common to other systems. While redundant sensors and actuators as well as parallel circuitry, would support acceptable operation, multiplex data sharing of this information could result in simpler, more reliable systems. The shared information on a Class B network is not cr
26、itical to the operation of all of the systems to which it is connected. The delay of a specific piece of information will not cause a critical failure in any of the systems. Therefore, the response window in the Class B network is not nearly as narrow as in the Class C. In fact, the response time ma
27、y be variable, depending on the application. Another characteristic of Class B network is its interconnection of dissimilar systems. Figure 2 illustrates a Class B application. FIGURE 2 - CLASS B MULTIPLEX APPLICATION SAE J2057-1 Reaffirmed SEP2006 - 5 - 5.2.1 Examples of Class B Applications A typi
28、cal Class B network could connect Engine Control Modules, Body Computers, and System Diagnostic Modules. 5.3 Class A Typical Applications Figure 3 illustrates the zone locations referenced in Tables 2A through 2D. Tables 2A through 2D list typical applications that could be considered for Class A ne
29、tworks. The chart is by no means complete, and will vary from application to application. It serves, however, to illustrate the numerous devices that can be serviced through a Class A network. It contains information on the device type, its anticipated latency requirements and the severity of damage
30、, should the device fail. FIGURE 3 - APPLICATION ZONES SAE J2057-1 Reaffirmed SEP2006 - 6 - TABLE 2A - TYPICAL CLASS A APPLICATIONS, OPERATOR INPUT SWITCHES Zone Description Latency(1)Typical(2)Number of Functions Fault Category(3)2 Headlights B 2 A 2 Park Lamps B 2 B 2 Turn Signal B 3 A 2 Sunroof C
31、 3 C 2 Trunk Release C 2 C 2 A/C with 4 Speed Fan C 10 C 2 Seat Heater C 2 C 2 Rear Defogger C 2 C 2 Front Defogger C 2 B 2 Windshield Wiper C 2 B 2 Windshield Washer C 2 B 2 Courtesy Lamps/Overhead C 2 C 2 Radio Controls B 12 C 2 Horn B 2 A 2 Hazard C 2 A 2 Fog Lamps C 2 C 2 Fuel Door Opener B 2 C
32、2 Illumination Control C 2 A 2 Telephone Control B 20 C 2 Cruise Control (Set. - Res.) B 4 B 2 Convertible Top C 2 C 3 Window with Lockout and Express B 14 C 3 Mirror Left/Right B 7 C 3 Seat with Memory B 12 B 3, 4 Vent Window B 3 C 3, 4, 7, 8 Door Lock B 3 C 4 Seat without Memory B 9 B 4, 7, 8 Wind
33、ow B 3 C 5, 6 Recliner B 3 C 5, 6 Lumbar B 4 C 9 Wagon Rear Window B 3 B 1. Latency, A: 150 ms Reliability T.B.D. T.B.D. = Non-Multiplexed Systems Bus Failure No Effect on Driveability Limited Effect on some Functions Required Redundancy Node Failure No Effect on Function Function Fails Safe Functio
34、n Fails, Other Function not Affected EMC Susceptibility 30 dBm (field strength) Margin Over OEM Specification T.B.D. 0 dBm (field strength) Margin Over OEM Specification EMC Radiation Ambient T.B.D. 0 dBm (field strength) Margin Over OEM EMC Specification Node Diagnostics Automatic Continuous Automa
35、tic Periodic Only on Controls Only on Demand Bus Diagnostics Automatic Continuous Self Regulation None Cost Decrease from Non-Multiplexed System Same as Non-Multiplexed System 10% Increase Additional FunctionsOpen System Public Domain Free License License at Minimal Fee Sensitivity to Environments I
36、nsensitive to Environment 85% of Applications Separate Networks for Each Car Environment Communications to Other Networks Direct Subset of SAE J1850 Via SAE J1850 Microcomputer Separate Gateway Electrical Media 1 Wire and Ground 1 Twisted Pair Shielded Twisted Pair Software Requirements Central CPU;
37、 5 K per node Node Capabilities Multiple “I” and “O” per Node One “I” and “O” per Node Only One “I” or One “O” per Node System Capability 250 Functions per Network T.B.D. 64 Functions per Network Sleep State Current Drain 0 Amps T.B.D. = OEM Specifications 1. T.B.D. = To Be Determined SAE J2057-1 Re
38、affirmed SEP2006 - 11 - 7.1 Latency For Class A applications, latency is the total time required for a system to respond to a request. This includes the time to sense an input, process the information and energize the controlled device. This does not include the additional time for the output device
39、 being controlled to reach its final state. 7.2 Reliability This criterion is for the entire system including redundancy of any kind as specified by the system designer. 7.3 Bus and Node Failures This notes what happens to the operation of the devices on the network in the event of bus or node failu
40、res. 7.4 EMC Susceptibility and Radiation The systems generation of and susceptibility to EMI RFI noise. 7.5 Diagnostics The ability of a system to determine if failures are present in the system and relay this information for appropriate action. 7.6 Cost This is the total system cost for the Class
41、A network. It should be relative to the anticipated cost, per function, of a non-multiplexed vehicle. 7.7 Open System This criterion indicates the proprietary position of the network being evaluated. 7.8 Sensitivity to Environments The entire systems ability to withstand the various environments wit
42、hin a motor vehicle. It must consider all of the hardware associated with the network. 7.9 Communications to Other Systems The ability of the network to communicate with other networks that are likely to be in the motor vehicle. Refer to Table 2D for an illustration of Class A applications that comm
43、unicate to Class B modules. 7.10 Electrical Media The requirements for transmission media for the Class A network at the EMI RFI levels specified in 7.4. 7.11 Software Requirements The size of memory required to operate the number of functions indicated in 7.12. Specifications must be given for dist
44、ributed software as well as a centrally controlled system. 7.12 Node Capabilities The maximum number of nodes and functions that can be controlled by the network. SAE J2057-1 Reaffirmed SEP2006 - 12 - 7.13 Sleep State Current Drain The amount of current drain of each node of the system when the syst
45、em is in its mode of least activity. This mode is commonly referred to as the “sleep state“. 8. PREFERRED CLASS A SYSTEM CRITERIA Table 3 lists the preferred characteristics for each of the criterion listed in Section 7. Because it is unlikely that any one Class A network can satisfy all of the criteria, this table will serve only as a benchmark from which all potential Class A multiplex systems can be judged. PREPARED BY THE SAE VEHICLE ARCHITECTURE FOR DATA COMMUNICATIONS STANDARDS COMMITTEE
