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5、vised 2013-10 Superseding J1952 OCT2010 All-Wheel Drive Systems Classification RATIONALE To recommend consistent All-Wheel Drive (AWD) terminology and definition for usage in the AWD community (marketing, press release, engineering, and sales). FOREWORD This Document has been updated to reflect chan
6、ges in nomenclature and classification of AWD Systems within the industry. 1. SCOPE In this SAE Recommended Practice, attention will be given to passenger cars and light trucks (through Class III). 1.1 Purpose The definitions are intended to outline basic nomenclature and to categorize AWD concepts.
7、 The goal is to give those working in the field a common base for discussion regarding the type of AWD systems independent of marketing terminology. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this specification to the extent specified herein. Unless otherwise in
8、dicated, the latest issue of SAE publications shall apply. SAE J2817 Definition and Measurement of Torque Biasing Differentials SAE J2059 All-Wheel-Drive Drivetrain Schematic Symbol Standards SAE INTERNATIONAL J1952 Revised OCT2013 Page 2 of 6 3. DEFINITIONS 3.1 AWD SYSTEM DESCRIPTION A conventional
9、 AWD system consists of a means to distribute torque to all wheels of a vehicle. Based on desired performance, traction and handling characteristics, there are different types of systems to achieve these ends. These AWD systems include 4X4, 6X6, and other configurations. There are three basic types
10、of systems defined below: Part-Time, Full-Time, and On-Demand. Combinations of these systems may also be used. 3.2 PART-TIME AWD SYSTEM DESCRIPTION In a part-time AWD system, driver intervention is required to rigidly couple and decouple primary and secondary axles. When a part-time system is engage
11、d, the primary and secondary axles are rigidly connected through the torque distribution device (i.e., Power Transfer Unit (PTU), transfer case). The primary axle is normally connected unless in neutral mode. The secondary axle(s) is/are engaged in AWD and disengaged in two-wheel drive. The torque d
12、istribution device is commonly referred to as a transfer case in primary rear wheel drive based AWD vehicles. In a primary front wheel drive based vehicle, the torque distribution functions are typically managed in the PTU, transaxle, or secondary axle(s). This basic type of system requires the driv
13、er to select between two-wheel drive and AWD commonly using either a switch or lever. Part-time systems may allow the driver to shift between two-wheel drive and AWD while the vehicle is in motion. Part-time systems may have two speeds - one for normal driving (High-range) and one for improved groun
14、d speed control and increased gradeability (Low-range). Although part-time AWD achieves maximum traction under certain conditions it should be limited to off-pavement usage or on-pavement usage in low traction scenarios. Torque “wind up“ is experienced during on-road dry pavement usage when making m
15、oderate to tight low speed turns. This “wind up“ (also referred to as crow hop or binding) is due to the fact the front and rear axles are rigidly connected (no center differential) and rotating at the same speed but traveling different distances. 3.3 FULL-TIME AWD SYSTEM DESCRIPTION In a full-time
16、AWD system front and rear axles are driven at all times through a center differential. Unlike a part-time system, the full-time system employs a center (inter-axle) differential that allows the front and rear axles to turn at different speeds on wet or dry surfaces. Depending upon the gear ratio in
17、the differential, the input torque can be nominally split to the front and rear axles in a fixed ratio. A 35:65 split means that 35% of the torque is directed to the front axle and 65% to the rear axle. For maximum traction, torque through the center differential must be modulated to distribute powe
18、r to the axles with the greatest traction. Torque modulation can be done passively, actively, with a torque biasing device, or with brake based traction control systems. This type of system can be used on any surface at any speed. SAE INTERNATIONAL J1952 Revised OCT2013 Page 3 of 6 3.4 ON-DEMAND AWD
19、 SYSTEM DESCRIPTION In an on-demand all-wheel drive system, the secondary drive axle may be driven by an active or passive coupling device, or by an independently powered drive system. A secondary drive axle, which is driven by an independently powered drive system, may also provide the primary vehi
20、cle propulsion. In a typical on-demand AWD system, the vehicle operates in two-wheel drive (either front or rear depending upon the basic vehicle architecture) until AWD is required, such as during primary axle slip, yaw correction, or by other control strategies. In the case of secondary axles driv
21、en by an active or passive coupling device, torque transfer from the primary to the secondary axle(s) can be modulated, dependent on driving conditions. Most systems are typically relative speed control devices and activate when there is a speed difference between the primary and secondary axle(s) d
22、ue to slippage; however, pre-emptive slip or other control strategies are common. This type of system can be used on any surface at any speed. 3.5 AWD SYNCHRONIZATION The act of mechanically bringing two or more torque carrying members to the same speed to engage AWD while the vehicle is in motion.
23、3.6 SPEED DIFFERENTIATION A difference in speed between two or more driven members. 3.7 LONGITUDINAL TORQUE DISTRIBUTION 3.7.1 Fixed Torque Distribution Output torque distribution is fixed by the design of the device. Typical examples include open center differentials. 3.7.2 Variable Torque Distribu
24、tion Output torque distribution is variable by the design of the device. Typical examples include couplings and torque biasing devices. 3.7.3 IndetermInate Torque Distribution Output torque distribution is not determined by the device but by the input torque and tractive capability. Typical examples
25、 include part-time AWD systems. 3.8 COUPLING DEVICE Primary functions are to connect input and output elements (analogous to series power flow) and vary torque (continuously or discretely). SAE INTERNATIONAL J1952 Revised OCT2013 Page 4 of 6 3.9 ACTIVE CONTROL Possesses variable tuning based on exte
26、rnal control feedback. Actively controlled systems typically incorporate an electronic control unit. Active systems include electronically controlled electro-magnetic, electro-mechanical and electrohydraulic actuated wet clutches. Active systems can be integrated with other vehicle control systems t
27、o improve traction and/or stability. 3.10 PASSIVE CONTROL Possesses preset tuning without external control feedback. Passively controlled systems do not incorporate an electronic control unit and thus do not sense non-driveline variables or interact with other vehicle control systems. Passive device
28、s include viscous couplings and hydraulically activated clutch pack couplings without external controls. 3.11 POWER TRANSFER UNIT (PTU) In a transverse mounted drivetrain based vehicle, this term refers to the drive mechanism that distributes power towards the secondary axle. Its primary function is
29、 to change the direction of power flow. The PTU may also contain torque management devices. Typically, PTUs are utilized in front wheel drive based applications. NOTE: A Power Take Off Unit (PTO), not the same as a PTU, is a device whose primary function is to drive accessories (a PTO is not utilize
30、d to propel the vehicle). 3.12 TORQUE BIASING DEVICE A coupling device in parallel with a differential. 3.13 TRANSFER CASE In a longitudinal mounted drivetrain based vehicle, this term refers to the drive mechanism that distributes power to the front and rear axles. Its primary function is to offset
31、 the power flow. The transfer case may also contain torque management devices. SAE INTERNATIONAL J1952 Revised OCT2013 Page 5 of 6 3.14 AWD SYSTEMS CLASSIFICATION DIAGRAM Full-Time Variable Torque Active System On-Demand Synchro Variable Torque Passive System On-Demand Synchro Variable Torque Active
32、 System On-Demand Independently Powered Variable Torque Active System N/A Yes Indeterminate Active Type Synchronization Capable Longitudinal Speed Differentiation Capable Longitudinal Torque Distribution Capable Torque Modulation (Passive/Active) Designation Part-Time Full-Time On-Demand No Yes N/A
33、Yes No Yes Yes Indeterminate Fixed Variable Variable N/A N/A Passive Passive Part-Time Non Synchro System Part-Time Synchro System Full-Time Fixed Torque System Full-Time Variable Torque Passive System Active Active SAE INTERNATIONAL J1952 Revised OCT2013 Page 6 of 6 4. NOTES 4.1 Marginal Indicia A
34、change bar (l) located in the left margin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document, including technical revisions. Change bars and (R) are not used in original publications, nor in documents that contain editorial changes only. PREPARED BY THE SAE ALL WHEEL DRIVETRAIN STANDARDS COMMITTEE
