The core functions of the transfer case and the differential

Introduction to Transfer Cases and Differentials

The automotive transfer case, as the name suggests, is an important device used to rationally distribute the power of the engine and transmit it to the front and rear axles. In four-wheel drive vehicles, the transfer case plays an indispensable role. Its types vary depending on the four-wheel drive form, mainly including traditional part-time four-wheel drive transfer cases, full-time four-wheel drive transfer cases, on-demand four-wheel drive transfer cases and super select four-wheel drive transfer cases, etc.

In four-wheel drive models, the existence of the transfer case and the differential each plays an indispensable role. The main function of the transfer case is to rationally distribute the power of the engine and ensure that the front and rear axles can receive appropriate driving force. The differential, on the other hand, is mainly responsible for adjusting the speed differences between the front and rear axles as well as among the wheels, to ensure that the vehicle can run smoothly when turning or encountering uneven roads. Although there are essential differences between the two in mechanical structure and specific application, they work together to provide powerful driving force and handling for four-wheel drive models.

Design Challenges and Solutions for Four-Wheel Drive Systems

► Off-road and highway driving challenges

Such a design does indeed demonstrate advantages in off-road environments, but it faces challenges when driving on the highway. What's the reason? When a vehicle is turning, the arc lengths passed by each wheel are different, which in turn leads to variations in the rotational speeds of each wheel during the turning process.

If a rigid connection method is adopted to fixedly transmit power to the front and rear wheels, it will cause the rotational speeds of the front and rear wheels to be consistent. This consistency can interfere with the correct steering trajectory. This kind of interference can be alleviated on slippery or sandy roads with low adhesion through the sliding friction of the wheels. However, on dry roads with high adhesion, this interference will turn into obvious resistance, which is what we often call the steering braking phenomenon.

To overcome this problem, designers ingeniously introduced a differential in the transfer case, which is what we commonly call a central differential. This type of differential belongs to an open differential, and its core function lies in adjusting the speed difference between the front and rear axles. Its basic structure is similar to the differentials equipped on the front and rear axles, and simply adding it to the transfer case constitutes the early design of full-time four-wheel drive.

The application of differential in transfer cases

The importance of the locking mechanism is self-evident. However, such a four-wheel drive system alone does not offer substantial assistance in enhancing the vehicle's off-road performance. This is determined by the characteristics of the open differential. The main function of an open differential is to distribute the engine's power to the wheel with the least resistance. However, if a vehicle is equipped with three such differentials (one for the front and one for the rear axles) to adjust the speed difference, when a certain wheel loses its grip, all the power will be transmitted to this wheel, while the wheel that truly has grip will not be able to obtain power and thus cannot effectively get out of the predicament.

► Limited-slip differential and differential lock

To solve this problem, two main methods are currently adopted: one is to use a limited-slip differential, and the other is to use a differential lock. Although the limited-slip differential can solve the steering problem, it does not significantly improve the vehicle's ability to get out of difficult situations during off-road driving. Next, we will delve into the principles and advantages of these two methods.

Therefore, the core purpose of introducing a differential limiter is to actively apply resistance to the slipping wheels, thereby ensuring that power can be transmitted to the non-slipping wheels. Take the widely used mechanical limited-slip differential as an example. Its structure is similar to that of a clutch device, but it contains multiple sets of clutch plates, so it is often called a multi-plate clutch differential limiter. It is worth mentioning that in high-end models, such differential limiters are regulated through an electronic system, which not only effectively deals with wheel slippage but also enables active power distribution between the front and rear axles. The distribution ratio can even be freely adjusted within the range of 0-100% (in addition, There are also various types such as torque-sensing type, viscous coupling type, helical gear type, ball locking type and active type.

Next, let's briefly understand the differential lock. The differential lock is based on the differential and adds a locking mechanism. Its function is to enable the front and rear axles to be rigidly connected when the vehicle's passability needs to be improved, thereby ensuring that power is distributed to the front and rear axles in a fixed ratio (usually 50:50). In modern four-wheel drive models, the transfer case and the differential have formed a close connection, and each of them undertakes specific tasks during vehicle operation. With the continuous advancement of electronic control technology, driving four-wheel drive vehicles no longer requires special driving skills.

► Maintenance suggestions for transfer cases

Next, let's talk about the maintenance of transfer case oil. To ensure driving safety, it is recommended to have maintenance done every two years or after driving 40,000 to 60,000 kilometers. If a vehicle frequently operates in harsh environments, the maintenance cycle should be shortened and regular inspections should be carried out.

Weifang Ruichi Transmission Machinery Co., Ltd. specializes in transfer cases, gearboxes, clutches, hydrostatic transmissions, lifting cases, etc. For cooperation, please call: 15662499679!