The cross-axle differential refers to the transmission mechanism that distributes torque between the drive shafts. In addition, this mechanism allows the wheels to rotate with different angular velocities. This moment is especially noticeable when cornering. In addition, this design makes it possible to safely and comfortably move on a dry hard surface. In some cases, when driving on a slippery track or off-road, the device in question can play as a stopper for a car. Consider the features of the structure and operation of cross-axle differentials.
The differential is designed to distribute torque from the cardan shaft to the drive wheel axles in front or rear, depending on the type of drive. As a result, the cross-axle differential makes it possible to rotate each wheel without slipping. This is the direct purpose of the mechanism.
When moving in a straight line, when the load on the wheels is uniform with identical angular velocities,the unit in question functions as a transfer compartment. In the event of a change in driving conditions (slipping, turning, turning), the load indicator changes. The axle shafts tend to rotate with different speed parameters, it becomes necessary to distribute the torque between them in a certain ratio. At this stage, the cross-axle differential begins to perform its main function - guaranteeing the safety of vehicle maneuvers.
The layout of the considered automotive devices depends on the working drive axle:
- On the gearbox housing (front wheel drive).
- On the drive rear axle housing.
- Cars with all-wheel drive are equipped with an interwheel differential on the skeletons of both axles or transfer boxes (they transfer the working moment between the wheels or axles, respectively).
It is worth noting that the differential on the machines appeared not so long ago. On the first models, "self-propelled" crews had poor maneuverability. Turning the wheels with an identical angular speed parameter led to slippage of one of the elements or loss of adhesion to the road surface. Soon, engineers developed an improved modification of the device, which allows leveling the loss of control.
Prerequisites for creation
Cross-axle differentials of cars were invented by the French designer O. Pekker. In a mechanism designed to distribute a rotatingmoment, gears and working shafts were present. They served to transform the torque from the engine to the drive wheels. Despite all the advantages, this design did not completely solve the problem of wheel slip when cornering. This was expressed in the loss of adhesion of one of the coated elements. The moment was especially pronounced in icy areas.
Slipping in such conditions led to unpleasant accidents, which served as an additional incentive to develop an improved device that could prevent the vehicle from skidding. The technical solution to this problem was developed by F. Porsche, who came up with a cam design that limits wheel slippage. The first cars to use a simulated cross-axle differential were Volkswagens.
The limiting node works on the principle of a planetary gearbox. The standard design of the mechanism includes the following elements:
- semi-axle gears;
- associated satellites;
- working body in the form of a bowl;
- main gear.
The skeleton is rigidly connected to the driven gear, which receives the torque from the analogue of the main gear. The bowl through the satellites transforms the rotation to the drive wheels. The difference in speed modes of angular parameters is also provided with the help of accompanying gears. At the same time, the value of the working moment remains stable. The rear cross-axle differential is focused on the transfer of speed to the drive wheels. Transportall-wheel drive vehicles are equipped with alternative mechanisms that act on axles.
The indicated types of mechanisms are divided according to structural features, namely:
- conical versions;
- cylindrical options;
- worm gears.
In addition, differentials are divided by the number of teeth of the gears of the axle shafts into symmetrical and asymmetrical versions. Due to the optimal distribution of torque, the second versions with cylinders are mounted on the axles of vehicles with all-wheel drive.
Machines with front or rear drive axle are equipped with symmetrical conical modifications. The worm gear is universal and can be aggregated with all types of devices. Conical units are capable of working in three configurations: straight, rotary and slip.
Scheme of work
In straight-line movement, the electronic imitation cross-axle differential lock is characterized by an equal distribution of the load between the wheels of the vehicle. In this case, an identical angular velocity is observed, and the body satellites do not rotate around their own axes. They transform the torque on the axle shaft using a static gear and the driven gear of the main gear.
When cornering, the vehicle experiences variable resistance forces and loads. Parameters are distributed as follows:
- The smaller radius inner wheel gets more drag than the outer counterpart. An increased load indicator causes a decrease in rotation speed.
- The outer wheel moves along a larger path. At the same time, an increase in the angular velocity contributes to a smooth turn of the machine, without slipping.
- Given these factors, the wheels must have different angular speeds. The satellites of the inner element slow down the rotation of the axle shafts. The same, in turn, through a conical gear element, increase the intensity of the external counterpart. At the same time, the torque from the main gear remains stable.
Slippage and stability
Car wheels can receive different load parameters, slipping and losing traction. In this case, excessive force is applied to one element, and the second one works "idle". Because of this difference, the movement of the car becomes chaotic or stops altogether. To eliminate these shortcomings, use the system of exchange rate stability or manual blocking.
In order for the moment of torsion of the axle shafts to even out, the action of the satellites should be stopped and the rotation from the bowl to the loaded axle shaft should be transformed. This is especially true for MAZ cross-axle differentials and other heavy-duty vehicles with all-wheel drive. A similar feature is due to the fact that if you lose grip at one of the four points, the amount of torque will tend to zero,even if the machine is equipped with two interwheel and one interaxle differential.
Electronic self block
To avoid the troubles mentioned above, partial or complete blocking allows. For this, self-locking analogues are used. They distribute torsion taking into account the difference on the axle shafts and the corresponding speed conditions. The best way to solve the problem is to equip the machine with an electronic cross-axle differential lock. The system is equipped with sensors that monitor the required performance while the vehicle is moving. After processing the received data, the processor selects the optimal mode for correcting load and other effects on wheels and axles.
The principle of operation of this node consists of three main stages:
- At the beginning of the drive wheel slippage, the control unit receives pulses from the rotation speed indicators, after analyzing them, a decision is automatically made on the operation method. Next, the valve-switch closes and the high-pressure analogue opens. The pump of the ABS unit creates pressure in the working circuit of the brake cylinder of the slipping element. The slipping drive wheel is braked by increasing the pressure of the brake fluid.
- At the second stage, the self-block simulation system maintains the braking force by maintaining the pressure. Pump action and wheel slip stop.
- The third stage of the operation of this mechanism includes the completion of the wheel slipwith simultaneous pressure relief. The switch opens and the high pressure valve closes.
KamAZ cross-axle differential
Below is a diagram of this mechanism with a description of the elements:
1 - Main shaft.
2 - Seal.
3 - Carter.
4, 7 - Support type washers.
5, 17 - Case bowls.
6 - Satellite.
8 - Lock indicator.
9 - Filler plug.
10 - Pneumatic chamber.
11 - Fork.
12 - Stop ring.
13 - Gear clutch.
14 - Lockup clutch.
15 - Drain cap.
16 - Middle axle drive gear.
19 - Rear axle gear.
20 - Fixing bolt.
21, 22 - Cover and bearing.
The cross-axle differential is designed to provide a safe and comfortable ride on roads of various purposes. Some of the disadvantages of the mechanism under consideration, indicated above, are manifested during dangerous and aggressive off-road maneuvering. Therefore, if the machine is provided with a manual override mechanism, it must only be operated under appropriate conditions. It is very difficult and unsafe to use high-speed cars without the specified mechanism, especially at high speeds on the highway.