Downshift: principle, types. SUVs with low gear and differential lock

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

First of all, let's say that the gears of any transmission are designed to regulate the speed of torque transmission from the engine to the drive wheels. They are divided into straight lines, as well as increasing torque and reducing it. Here we will talk more about the last look.

Downshift and its purpose

In other words, a downshift is the one that is in the transfer case, or otherwise - an additional box that distributes torque between the two drive axles. When it is turned on, the speed of the car drops, and the torque and power increase. This gear is often used when overcoming obstacles such as ice, fords, steep descents or inclines, sand, mud, rocky roads and heavy off-road conditions.

It is activated by a button or a lever with the designation L and LO, which means short for low - "low". The principle of downshifting is that when it is turned on, the speed of the SUV drops, but at the same time it becomesstronger and more capable of overcoming obstacles. The amount of speed drop depends on the gear ratio in the gears. The car moves at high speeds when downshifting.

For example, consider a situation where, during a long climb in third gear, the motor does not have enough power, and when the second gear is engaged, the number of revolutions becomes too high. In this case, the inclusion of a lower gear helps to cope with the situation: the car is moving at low speed, but at the same time at high speeds. Thanks to the increase in torque on the wheels, overcoming obstacles on the road becomes much easier. The number of revolutions of the bridge increases along with the gear ratio of the secondary shaft. Due to this, the car can more easily overcome severe off-road, water obstacles, descents and ascents and other obstacles.

Demomultiplier

The demultiplier is structurally included in the transfer case circuit or is performed as a separate unit. In the "machines" the transfer case may not be present, and its functions are performed by some parts and assemblies in the gearbox. An additional gearbox, in which there is a reduction gear (demultiplier), is designed to increase traction on the wheels. The demultiplier is a transmission mechanism that is designed to increase torque. It is installed, as a rule, on those cars that are designed for operation in poor road conditions. In this case, the usual number of gears in the boxwill not be enough, getting an intermediate gear ratio in the transmission will help here.

Consider this situation: in fourth gear at a certain speed, the motor runs under specific conditions with an overload, in lower gear, third, the engine is "twisted". In this case, an additional gearbox will help.

How to downshift?

It is necessary to stop the car, after that the main gearbox lever is moved to the neutral position, and the additional gearbox lever to the “downshift” position. Then we squeeze the clutch. Not all transmissions have a separate transfer case. In this case, a conventional gearbox has a special lever with which this gear is engaged. If the downshift is switched on in the normal mode, then in this case there is a high risk of overloading both the engine and the transmission. As a result, both units may fail.

Application of underdrive and differential lock

So, as we have already understood, downshift is an additional gear that reduces the number of wheel revolutions at constant engine speeds. Usually it is installed in the transfer case. Having it makes an SUV more expensive, heavier and more difficult. But on economy class cars, it is not always installed; instead, the power take-off shaft is connected to the rear axle gearbox in the gearbox, in the downshift housing. Recently, frame SUVs are getting smaller, and crossovers are getting closer.with city cars. These cars often lose downshifts as well. Now there has been such a trend that the priority is the presence of comfortable conditions in the car, rather than its off-road qualities. Most manufacturers are switching to a load-bearing body, and the frame structure remains a thing of the past. True jeeps are still those SUVs that have a reduction gear and differential lock, so they are not afraid of any obstacles.

Differential lock needed to improve flotation. The differential itself is divided into interwheel and interaxle. Previously, cars did not have such technologies, so their absence had a negative impact on the safety of elements in the design. The cross-axle differential allows the wheels to rotate at different speeds, this is necessary, for example, if the car makes a turn. But its presence can lead to the fact that when slipping, the power of the motor will go only to the wheel that is stuck, while the other will be motionless. When the differential is locked, the engine energy will be distributed equally between the wheels, and thus the car will be able to overcome the obstacle.

The center differential is similar in its principle of operation: it allows the front and rear axles to move at different speeds and along different trajectories. But in some situations, this can significantly complicate management: if the front wheels are stuck, the rear ones will be inactive. Locking the center differential can successfully solve this problem. SUVs, known for their excellent cross-country ability,as a rule, they are equipped with three locks: rear, front and center differential.

SUVs with low gear and differential lock

Currently, there are still real off-road conquerors, equipped with all the necessary equipment in order to feel as comfortable as possible on any surface. Among these vehicles are, for example, Chevrolet Trailblazer, Hummer H3, Land Rover Dicovery.

"Trailblazer" has a large body, frame construction and just a huge list of technical advantages. He has a bright and brutal appearance. In 2015, the model received quite significant updates both in the exterior and in the technical "stuffing". The suspension is soft, but this fact introduces some drawback to the control of the SUV: a slight roll appears during sharp turns. The car pleases with the quality of the trip that it can provide with a complete set of necessary systems.

Now let's move on to the American model of a true off-road conqueror - the Hummer. At the heart of the production of this car, the concern used to a greater extent military technology. It is not surprising that he was able to create a real brutal SUV. Its serial production was stopped back in 2010, and last year it was announced that the Hummer H3 can only be purchased by special order. The car is distinguished by its huge ground clearance, large engines, magnificent wheels, shodoff-road tires, and, importantly, it is equipped with one of the best low gear and differential lock systems that are borrowed from the military industry.

"Discovery" remains one of the few British SUVs that have retained the frame structure. It is distinguished not only by excellent external data, but also by increased comfort, as well as cross-country ability. The range of engines, although not distinguished by a rich choice, looks impressive. Locking is available on it in several modes, and the car also boasts good all-wheel drive. The reliability and quality of the car is truly impressive.

Such jeeps can be successfully operated in urban conditions, but still their true purpose as large and heavy vehicles is real off-road. At the same time, it should be noted that such cars cannot be called economical, and they are also equipped with a large list of features that are not useful for using a jeep on paved roads.

Types of reduction gears

Worm gears are used as reduction gears, less often cylindrical and planetary. The worm gear is one of the gears with intersecting shaft shafts. The movement in them is carried out on the principle of a screw pair. Its main properties are low noise level due to the gearing features, relatively low efficiency, small dimensions and large gear ratio. Compared with a spur gearbox, a worm gearprovides better running smoothness. This type of transmission has a much greater potential for increasing torque and reducing speed than gearboxes with other types of gears. Cylindrical gears are used in mechanisms with parallel shafts. This type requires increased accuracy due to design features.

Gear transmissions are reliable and durable subject to the permissible level of loads, one of the minuses is the fact that at a high rotation speed such a mechanism has a high noise level, and also cannot respond flexibly to a changing load. A variety of gears are planetary. They have gear wheels with movable axles. Such gears are lightweight, easy to assemble, produce less noise compared to conventional gears, and also have the ability to obtain large gear ratios. Among the shortcomings can be called a large number of parts, increased requirements for the accuracy of installation and manufacturing.