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Getting Power to the Pavement
Published in Patrick Hossay, Automotive Innovation, 2019
When incorporated in an AWD system, the effect is impressive. For our purposes here, let’s make a distinction between AWD and 4WD. Four-wheel drive relies on a transfer case to provide torque to the front axle. However, there is no differential rotation possible between the two axles. This makes it unsuitable for dry road conditions, since the necessary relative slip of the tires on a turn would significantly increase wear and decrease road holding. All-wheel drive, on the other hand, utilizes a central differential, allowing differentiated rotation at each wheel and axle (Image 3.21). So, when combined with torque vectoring this allows for the delivery of a precise torque at each wheel. During hard acceleration or cornering, an AWD system that normally distributes 90% of torque to the front and 10% to the rear, might even the torque to a 50/50 split; and the bulk of that rear torque would be sent to the outside wheel, ensuring a more controlled turn. The challenge in AWD is typically efficiency, as driving both axles entails much more mechanical friction. However, the addition of torque vectoring can address this by permitting disengagement of an axle entirely, effectively allowing the drivetrain efficiency to approach that of a two wheel drive vehicle when the all-wheel drive is not needed.
Automotive Transmissions and Drive Trains
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
A transfer case is required with most four-wheel drive vehicles in order to provide a second output shaft to drive the second axle. A transfer case may also provide a power takeoff to drive accessory equipment such as a hoist. In some heavy equipment, a transfer case is not required because the main transmission is provided with both front and rear outputs.
Prediction and optimization of lubrication performance for a transfer case based on computational fluid dynamics
Published in Engineering Applications of Computational Fluid Mechanics, 2019
LiQing Chen, PanPan Ma, JunLiang Tian, XiuTian Liang
A transfer case is a key component for power distribution in modern four-wheel-drive vehicles. It is a gear train whose input shaft is connected to the second shaft of the transmission directly or through a universal joint, and the output shaft is connected to each of the drive axles via a universal joint, the characteristics of which have a considerable influence on the dynamic performance of the vehicle. The mechanical characteristic and control strategies of the transfer case have been the focus of research for many years. An adaptive reconfiguration design system for transfer cases based on the adaptive reconfiguration design theory was constructed, including the modules of the design scheme, adaptable design, and intelligent assembly of the components, and these provide a new method for the design of transfer case component parts (Chen, 2015). Asgari and Hrovat (1997) developed a model of an electronically controlled on-demand four-wheel-drive transfer case; it was validated using the available test data. This facilitated the design and evaluation of a suitable control system. Chen, Chen, Wang, Hu, and Huang (2013) analyzed the strength of the transfer case shell; the results can be used as a reference for further optimization. Wang, Wang, and Chen (2015) solved the problem of distortion of the transfer case housing – a problem that could not be solved by traditional design methods – and set up a multiobjective optimal model of the transfer case based on a multiobjective satisfaction method. Panzani et al. (2010) proposed new driveline structures with torque-biasing devices, including an active differential and active transfer case, which contribute to an active-control system that can alter the vehicle behavior by changing the mechanical layout. So far, however, there has been little discussion about the lubrication performance and optimal lubricant volume for transfer cases.