How much salary should a car cost?

SUVs on rally

Driving on a rocky road. Increased ground clearance and underbody protection are noticeable. Cables are stretched to protect the windshield from branches

Overcoming a water obstacle.
On board the SUV paddle

- the ability of a vehicle to move on low-quality roads and outside the road network, as well as to overcome artificial and natural obstacles without the use of aids[1].
Cross-country ability
is one of the component characteristics of vehicle mobility; as a rule, it is specified when designing equipment based on its intended purpose, taking into account economic feasibility [1][2].
According to cross-country ability
, transport equipment is divided into vehicles of normal, increased and high cross-country ability:

• off-road vehicles
  - general-purpose vehicles with regular tires and a non-locking differential, designed for driving on highways and dirt roads[1],
• off-road vehicles
  , which include mainly military vehicles with a wheel arrangement of 4×4, 6×4, 6×6, 8×8, wide-profile tires, a tire pressure regulation system, partially or fully locking differentials, the main purpose of which is to work on roads and areas without roads[1],
• All-terrain vehicles
  (
  all-terrain vehicles
  [3]) are tracked vehicles and all-wheel drive vehicles, which, in addition to the above, are equipped with ultra-low pressure tires, pneumatic rollers, arched tires or non-traditional types of propulsion [1].

Content

• 1 Typical types of obstacles 1.1 Rough roads
• 1.2 Point obstacles
• 1.3 Ascents and descents
• 1.4 Loose soil
• 1.5 Brody
• 1.6 Soft and destructible barriers
• 1.7 Ditches and threshold obstacles

How to measure ground clearance?

Of course, no one crawls under the car and measures all possible low points to determine the lowest one. It has long been known that the lowest part of a car, as a rule, is its front part, because that’s where the engine is located, and it weighs a lot. They count from him.

But there are some nuances here too. So, in most cars, a plastic or metal protection is also attached to their bottom, the main purpose of which is to protect the engine crankcase from breakdowns. It is, of course, a good thing, but it still hides a couple of centimeters of ground clearance.

By the way, when you choose a car, don’t forget to ask the seller what point he measured the ground clearance from. The fact is that some sellers, even though the car has protection installed, call the ground clearance measured not from it, but from the bottom of the engine. As a result, without clarifying this nuance, the buyer in the future may be very disappointed in his purchase. Indeed, in reality, the ground clearance turns out to be 1–2 centimeters less.

However, cars with normal ground clearance are not always able to overcome this or that obstacle, especially for tuned cars in which the front overhang of the bumper is located below the bottom of the engine. Therefore, this should also be taken into account when determining the vehicle’s throughput capabilities.

Typical types of obstacles

Rough road

Driving on uneven roads reduces the life of the vehicle. If the vehicle's traction is insufficient, it may get stuck. In order for the car to cope with uneven roads, the following measures are used:

• Off-road vehicles are significantly stronger than road vehicles. They have a more durable body and frame, plus reinforced suspension.
• High engine torque. All-wheel drive and differential lock are desirable.
• High ground clearance.
• Soft springs, long suspension travel.
• Winch for pulling out a stuck car.

Point obstacles

The car must pass small but high obstacles (stones, stumps, hummocks) under the bottom. For this it is important:

• High ground clearance.
• To prevent obstacles from damaging the engine, the engine compartment below is protected by a durable tray.
• Equal
  
  velocity
  joints
  CV
  
  joints
  with rubber boots are vulnerable . CV joints are protected so that the boot cannot be broken by a snag, or a dependent front suspension is used, in which the CV joint is located inside a metal fist.

Ascents and descents

When driving uphill, the engine may stall. If there is not enough tire grip, the car may fall down. When driving across a slope, the vehicle may tip over. When moving from an uphill or downhill slope to level ground, the car may catch on the body and get stuck. Control measures:

• High engine torque, low gears in the transmission.
• High ground clearance. High longitudinal flotation angle. High overhang angles.
• Tires designed for driving on the ground.
• Four-wheel drive.
• Wide track.

Loose soil

A car caught on loose soil may get stuck in it and not get out. Control measures:

• Reduced ground pressure (mainly due to an increase in the diameter and width of the wheels and the number of axles, as well as a decrease in tire pressure).
• Four-wheel drive.
• Differential lock.
• Using a winch for self-pulling.

Brody

To prevent water from entering the car, the lower part of the engine compartment and body are sealed. On special vehicles (for example, military vehicles), to increase reliability, a pump can also be installed to pump out water, pumping out water that gets into the car due to damage (when bullets, shrapnel, etc. hit the vehicle). The air intake into the engine is set as high as possible.

The engine air intake located above is called the “snorkel”. There are factory snorkels for popular SUVs. Many SUV owners make their own snorkel by installing a “closed” barrel air filter on the car, for example, from a Volga GAZ-3110 or Moskvich-2141, to which a plastic or metal thin-walled pipe running along the rack is attached through a rubber corrugation windshield up. A monocyclone or other water filter can be installed at the top, or the end of the pipe can be “bent” in various ways onto the roof of the SUV to prevent water droplets from raining and splashing.

Also, to overcome fords, cars are equipped with “hydroprotection” - all the breathers of the units (engine, gearbox, transfer case, axles) are supplemented with flexible hoses that extend as high as possible. It is not recommended to route the hoses into the snorkel, because the vacuum created by the engine is also transmitted to the units, helping water to penetrate through the seals into the units. On the contrary, in some cases, increased air pressure can be used in the crankcases of transmission units, for example, by connecting an inflated chamber to the breather.

When overcoming a ford, it is recommended to remove the cooling fan belt (often this is also the generator belt if the fan does not operate through a viscous coupling) to avoid damage to the impeller.

Soft and destructible barriers

Bushes, branches, etc. In themselves are not harmful, but among the pliable branches there may be a hard trunk or stump that can crush the radiator, tear off the windshield wipers and even break the windshield. In addition, branches constantly lashing the glass interfere with your view. For protection, the car is equipped with a guard and branch breaker cables.

Moats and threshold obstacles

The ability to overcome such obstacles is important for military vehicles. A two-axle all-wheel drive vehicle can overcome a ditch approximately equal in width to the radius of the wheel (if the drive is on one axle, it is even narrower). Multi-axle and tracked - from a third to a half of the wheelbase. To overcome wider ditches, bridges are sometimes used either with the help of improvised means, for example, bundles of brushwood, or a path is made by destroying the walls of the ditch using an entrenching tool, or by detonating an explosive charge.

Threshold obstacles (scarps and counter-scarps) are vertical steps. Sometimes, with a height of more than 1 m and a wall made of hard materials, such obstacles can even stop a tank. Such ledges are usually forced using improvised means, for example, bundles of brushwood, or a path is made by destruction using an entrenching tool, or by detonating an explosive charge, or by artillery fire. A wheeled vehicle with one axle drive can overcome a ledge with a height of 2/3 of the wheel radius, and with all-wheel drive - the radius of the wheel.

KAMAZ manufactured the first vehicle in the line of Samson mining dump trucks

Photo: KAMAZ PJSC

The KAMAZ Scientific and Technical Center developed and manufactured the first vehicle in a new line of mining dump trucks - KAMAZ-65805, intended for use in medium and small quarries.

The vehicle, named "Samson", was created for transporting rock and ore in the open air in areas with temperate and cold climates. The dump truck has increased permissible loads on the axles (12 tons) and drive axles (21 tons). Tires are also used in quarry versions.

“KAMAZ-65805 is the first representative of a new family of vehicles in the new line of KAMAZ-Samson mining dump trucks. The family will consist of mining dump trucks with a wheel arrangement of 8x4 and 10x6, with a carrying capacity of 45 to 70 tons,” said Sergei Nazarenko, chief designer of innovative vehicles at the Scientific and Technical Center.

Dump truck length – 11040 mm, width – 2530 mm, height – 3950 mm. Compliance of the dimensions with the requirements of traffic regulations allows the vehicle to move without a load on public roads.

Under the hood of KAMAZ-65805 there is a new in-line 12-liter KAMAZ R6 diesel engine with a power of 500 hp. The gearbox is a hydromechanical automatic, which is the most suitable solution for quarry equipment in this load capacity class, because allows you to change gears without interrupting the power flow. The gearbox has a built-in retarder (mountain brake). The volume of the fuel tank is 400 l, the maximum speed of the dump truck without load is 90 km/h, with load – 50 km/h.

The wheel formula of the car is 10x6. Three rear axles are driven. In this case, the first two axles and the last rear axle are steerable. This solution allows you to increase the maneuverability of the vehicle when working in a quarry. In terms of maneuverability, the car is not inferior to cars with an 8x4 wheel arrangement. The Samson's drive wheels account for more than 72% of the vehicle's weight, which is higher than that of 8x4 road dump trucks and almost reaches the performance of 6x4 dump trucks. This ensures high vehicle cross-country ability, including on wet or snowy roads inside the quarry.

The rear drive axles, with the ability to lock differentials, are a full-fledged tridem, that is, the distribution of torque occurs in equal proportions between them. Hydropneumatic axle suspension makes it possible to implement the so-called hydraulic balancer - equal distribution of the load on all drive axles. Also, using the suspension, a system for correcting roll from uneven loading or uneven unloading area is implemented. In addition, the dump truck is equipped with an overload control system and a secure front and rear view video camera.

“At the moment, the dump truck is assembled as Autonomous Ready, that is, the used dump truck units are completely ready to turn it into an unmanned one. All that remains is to install elements of machine vision, sensors, communications and a decision-making unit so that Samson can independently work in quarries without driver participation. This will significantly minimize the risks to people’s lives and health,” explained Sergei Nazarenko.

The dump truck is supposed to be equipped with a driver condition monitoring system (fatigue monitoring), as well as a system for preventing collisions and vehicle falls in quarries from a height. Also available as an option will be a warning system for the vehicle approaching power lines, a tire pressure monitoring system, an alcohol lock, a centralized lubrication system for components and assemblies, and a 360-degree video surveillance system around the vehicle.

A dump platform with a bottom and sides made of special steel of increased thickness is used for loading large and hard blocks of rock. Thanks to its heating by engine exhaust gases, the issue of freezing of wet winter soil has been resolved. The body, which has an inclination angle of 50 degrees, has a special protective canopy above the cabin that protects the driver, units and components of the dump truck from falling rocks. The volume of the rock dumping platform is 26 cubic meters.

The dump truck's load capacity is 60 tons, and its total weight reaches 87 tons. “In terms of its load capacity, KAMAZ-65805 can compete with the lower class of mining two-axle dump trucks of the BELAZ type,” Nazarenko is sure. – Among its advantages are a higher average speed, a lower price of the car due to the widespread use of units, much better fuel efficiency, lower cost of maintenance and spare parts, longer maintenance intervals, a significantly more comfortable cabin of the latest generation, lower costs for the development of technological roads , since the KAMAZ-Samson dump truck (mod. 65805) is narrower compared to BELAZ, and there is no need for wide roads.”

It is also worth noting the lower costs of moving such dump trucks between quarries. If, after working out one quarry, there is a need to move to another, the dump truck can move under its own power along public roads - there is no need to disassemble the vehicle or special escort during the haul.

Before launching into mass production, KAMAZ's new product will undergo tests that will last a year and a half: in July of this year, tests will begin at the company's Scientific and Technical Center, then test operation is planned in Kuzbass quarries. It is planned that the model will be launched into mass production in 2022.

Parameters related to cross-country ability

Dimensions

Ground clearance (clearance)

In a simplified sense, a car's ground clearance is the distance from the lowest part of the car to the surface of the earth. In technical descriptions, ground clearance is usually indicated for the vehicle in running order, which indicates that the declared ground clearance is the maximum operating level.

and may decrease when the vehicle is loaded.

The amount of ground clearance is one of the key factors affecting the vehicle's cross-country ability. In off-road vehicles with dependent suspension, the lowest point is most often the differential housing, less often the lower shock absorber brackets, spring struts, and transfer case housing. With a classic axle design, the ground clearance of such cars is low and fluctuates around 200 mm (for standard wheels). With an independent suspension, the lowest point can be either the suspension arms, shock absorber brackets, transfer case housing, engine crankcase and differentials (rarely), as well as elements of the exhaust system, parts of the anti-roll bar (if equipped), a frame or spar element. In general, this design allows you to significantly increase the ground clearance of the car. If additional equipment is used, such as underbody protection, a towbar, additional sills, running boards, as well as bumper covers, etc., this can become the lowest part of the car.

The most common way to increase the vehicle's ground clearance, regardless of the type of suspension, is to install larger diameter wheels. For dependent suspension, it is also practiced to relocate the shock absorber mounting points and locate the springs above the bridge. It is rare to re-equip an SUV with axles with final drives (if they were not provided for by the factory design).

To be able to install wheels of larger diameter, they resort to the “lift” procedure. A lift (English lift - rise) is a technical intervention in the design of a car in order to increase the distance between the body and the axis of rotation of the wheels. In practice, a suspension lift and a body lift (body lift) are used.

When using a lift of independent suspension designs, an increase in ground clearance can occur without the use of larger wheels (from the point of view of improving cross-country ability, such an operation is ineffective, while remaining quite labor-intensive).

Overhang angles

Let us assume that a car enters an overpass with an angle of inclination α. The front overhang angle (approach angle) is the maximum α at which a car can drive its front wheel onto a slope without hitting the overpass with any part of the body (marked in red in the diagram). Similarly, the rear overhang angle (departure angle) is the maximum α at which you can drive the rear wheel onto a slope (marked in green in the diagram). The angle of the rear overhang is usually made larger so that the driver is confident that if the car is not stuck in the front, the rear will pass.

Vehicles designed for off-road driving (SUVs) have a greater approach and departure angle than conventional passenger cars. For example, the Defender SUV has a fairly high off-road angle: the front off-road (entry) angle is 49°, the rear off-road (departure) angle is 47°.

Overhang angles

Longitudinal flotation angle (Ramp angle, Roll angle)

Rollover angle - The maximum angle at which a car can move from a slope to the horizontal part of an overpass without hitting anything with its bottom. Ramp angle (Roll angle) - The maximum angle between the tangents to the front and rear wheels and the bottom point of the car. These angles characterize the steepness of the obstacles that the car can overcome.

Pitch angle

Angle of transverse static stability

The angle by which the car must be tilted around its longitudinal axis for it to tip over.

Traction parameters

type of drive

All-terrain vehicles have all-wheel drive, plus some measures to avoid wheel slipping (for example, differential locks, mechanical and electronic multipliers). The engine is usually diesel, as it works more reliably in water and has more torque.

The transmission must have low gears that allow you to climb steep slopes and move on soft ground.

Power density

The ratio of a car's power to its weight.

Thrust-to-weight ratio

The ratio of traction force to vehicle mass.

Traction parameters

Specific ground pressure

The first off-road vehicles, as well as their successors for military and commercial purposes, traditionally used automobile tires with high specific ground pressure with developed lugs. On the one hand, the small width of the rubber helped to reduce rolling resistance, which increased the speed of movement on hard soil and improved fuel efficiency. On the other hand, narrow wheels, due to higher specific pressure, provided better traction on shallow viscous and loose soils. Overcoming obviously impassable terrain with deep viscous soils (swamps, loose sandstones, virgin snow) without auxiliary technical means was not part of the tasks of such vehicles. Other types of self-propelled vehicles were oriented towards performing such tasks - multi-wheeled and tracked all-terrain vehicles, etc.

As soon as off-road vehicles began to be actively used on paved roads, a new level of requirements for their active safety appeared; To improve handling and braking capabilities, wider wheels were used. The design of such cars began to include more powerful power units, due to which the increased rolling resistance was partially offset.

However, on off-road vehicles that are not designed for constant use on paved roads, they try to install wheels that have the lowest possible specific ground pressure due to their increased diameter and width. In the presence of developed lugs, this wheel design allows movement on relatively deep, viscous soils. The increased diameter allows you to overcome obstacles of greater height, including improving the vehicle's track rolling ability and increasing the vehicle's ground clearance.

Pneumatic all-terrain vehicles use wheels of extra-large diameter and width with low internal pressure. Low specific pressure on the ground allows them not to damage soil surfaces and plants, and also provides buoyancy (with sufficient internal volume of the pneumatic tire). Developed lugs are rarely used, since in fact, their role is played by an elastic tire that repeats the shape of the soil at the contact patch and, due to this, increases the friction force.

Suspension type

The specifics of use impose the following requirements on off-road vehicles: increased ground clearance compared to road-modified vehicles, greater energy consumption and durability of elastic and damping elements, large suspension travel, as well as resistance of suspension elements to mechanical influences (impacts on the ground, obstacles) .

In most cases, a dependent suspension design improves the vehicle's cross-country ability on rough terrain due to greater articulation capabilities compared to an independent one. In other words, at breaks in the ground profile, wheels with such a suspension design are more likely to be able to maintain contact with the ground surface. In cars with dependent suspension, under such conditions, the wheel hangs out, which leads to the car losing mobility. The dependent suspension axle housing often serves as protection for the engine crankcase, which is important when overcoming surfaces with protruding elements (logs, stones, etc.). On the other hand, independent suspension, due to the high-mounted differential housing, increases the vehicle's ground clearance. Also, an independent suspension has a larger number of loaded moving elements, which reduces its reliability and increases the cost of manufacturing and maintenance.

However, there is also a type of dependent suspension that can significantly increase the vehicle's ground clearance, while maintaining the main advantages of the dependent design - axles with wheel reducers. The axle beam in them is located above the axis of rotation of the wheels, the differential is traditionally located on the beam itself, but the gear mechanisms are located directly at each wheel. The most famous cars using a similar design are Unimog and UAZ. Bridges of this design are called “portal”. Disadvantages may include increased vibration and noise load, increased weight, loss in dynamics, and, of course, rarity and high cost.

From a handling point of view, when traveling at high speed over rough terrain, an independent suspension design is most preferable. First of all, this is due to its smaller volume of unsprung masses, higher energy consumption and less tendency to roll. It is this design that is used on most passenger cars for rally raids, including the famous Paris-Dakar.

Tire grip coefficient

The higher it is, the lower the risk of falling off a slope or causing the car to slip. To increase traction, use tires with developed lugs; on asphalt, however, such tires have worse grip and create increased noise.

To increase the coefficient of tire adhesion, snow chains and anti-skid sectors can be used. You can also replace the wheels with tracks.

What is the geometric cross-country ability of a car?

Owners of serious SUVs criticize modern crossovers for their low cross-country ability – including geometric ones. And often, I must say, quite deservedly. What is geometric cross-country ability, and what does it affect?

Geometric cross-country ability is a set of geometric parameters of a car that affect its ability to overcome obstacles.

If we talk about full geometric cross-country ability, then it consists of several groups of parameters that can be conventionally designated as basic and off-road.

Basic parameters are the actual overall dimensions of the car: length, width, height and wheelbase size. Both direct cross-country ability and geometric off-road parameters depend on them.

As mentioned above, the geometric cross-country ability is largely determined by the car’s parameters: the overall length and length of the wheelbase, the height and width of the car, as well as the track width and the length of the front and rear overhangs. The length, width and height of the car do not need explanation, but a few words can be said about the rest. Thus, the length of the wheelbase is the distance between the axles of the front and rear wheels, the track width is the distance between the centers of the wheels of one axle in the contact patch with the surface, the front overhang is the distance between the axle of the front wheels and the extreme forward point of the car, and the rear overhang is accordingly, the distance between the axle of the rear wheels and the rearmost point of the car.

Typically, when talking about geometric cross-country ability, five main parameters are considered:

• clearance, or ground clearance of the car;
• approach angle;
• departure angle;
• ramp angle, or longitudinal angle of passability;
• tipping angle.

Let us briefly explain each of these quantities. Ground clearance, or ground clearance , is the distance from the lowest element of the car to the surface of the ground. According to GOST, this distance is measured in the central part of the car, but often the lowest located element can be offset relative to the center: for example, it could be a muffler resonator or a shock absorber bracket. Therefore, clearance is usually considered to be the distance from this lower point to the horizontal surface on which the car stands.

The approach angle is the angle between the horizontal surface and the line drawn between the contact patch of the front wheels and the lowest point of the front of the car. In other words, this is the maximum angle of the ramp that a car can enter without the front of the vehicle touching it. It’s easy to guess that it depends on the ground clearance and the length of the front overhang: the higher the ground clearance and the smaller the front overhang, the higher the approach angle will be.

Departure angle is the same thing, but for the rear: the angle between the horizontal surface and the line drawn between the contact patch of the rear wheels and the bottom point of the rear of the car. In other words, this is the maximum angle of the ramp that a vehicle can enter when reversing without the rear of the vehicle touching it. It obviously depends on the ground clearance and the length of the rear overhang: the higher the ground clearance and the smaller the rear overhang, the greater the departure angle will be.

Ramp angle , or longitudinal flotation angle, is the maximum angle that a car can overcome without touching the surface with its bottom. It, in turn, depends on the combination of ground clearance and wheelbase length: the higher the ground clearance and the shorter the wheelbase, the larger the ramp angle. Its change, for example, can be clearly seen in the three-door and five-door versions of the Lada 4X4: their approach and departure angles are the same, but the ramp angle of the three-door is greater because it has a shorter wheelbase.

Rollover angle , or angle of lateral static stability, is the maximum angle of rotation of the vehicle around the longitudinal axis at which it may not tip over on its side. It depends on a combination of the vehicle's width and height, its track width, as well as its center of gravity: the wider the vehicle and its track, the smaller the height and the lower the center of gravity, the higher the rollover angle.

In addition to these basic parameters of geometric cross-country ability, there are some more that are definitely related to geometry, but are not directly related to the dimensions of the car. These are the maximum surmountable slope, wading depth, suspension travel and suspension articulation.

The maximum surmountable slope is the maximum angle relative to the horizon of the surface on which a car can move without assistance, that is, the maximum steepness of the slope that a car can drive onto.

The fording depth is the maximum depth of a water obstacle that a vehicle can overcome without negative consequences for its technical part. The depth of fording is primarily limited by the height of the engine air intake point: if water rises to it, it will penetrate into the intake tract and further into the cylinders, which can cause water hammer and serious engine damage. In conventional cars, the air intake point is located under the hood, which limits the maximum fording height. Specially prepared SUVs are equipped with a snorkel - a pipe that brings the air intake point to the roof level, which allows you to overcome deeper fords without the risk of water hammer.

Suspension travel is the maximum distance that a wheel can travel in the vertical direction from the point of maximum compression of the suspension until it is completely unloaded on the verge of lifting off the surface. To evaluate this parameter, the car can be driven with one of the front wheels onto an obstacle of such a height that the rear wheel on the same side comes off the surface - this is called diagonal hanging, since the second front wheel in this case will also be on the verge of lifting off the ground. Well, the distance along the vertical axis between the lift height of the front and rear wheels on one side of the car in this position is the articulation of the suspension . Wheel suspension travel and articulation have an indirect effect on geometric cross-country ability.

Above, we outlined and explained almost all the parameters that characterize the geometric cross-country ability of a car. In practice, in the “everyday” understanding and quick comparison, geometric cross-country ability is usually understood as four of them: ground clearance, as well as approach, departure and ramp angles. Automakers use these numbers to describe the capabilities of their crossovers and SUVs - and by and large, they quite comprehensively characterize the vehicle's performance.

However, the key words here are “operational indicators”: geometric cross-country ability figures are far from the only thing that determines real cross-country ability. It is no less influenced by the type of drive (and if the drive is four-wheel drive, then the type of its technical implementation , the presence of inter-axle and inter-wheel locks , as well as the characteristics of the tires used. And as practice shows, it is the latter that become the main limitation of the off-road capabilities of modern production cars.

Source

Examples

The main parameters related to the cross-country ability of some passenger cars:

(*) In an unloaded state.

Notes

1. ↑ 12345
   Cross-country ability of vehicles // Military Encyclopedia / Grachev P. S. - Moscow: Military Publishing House, 2003. - T. 7. - P. 66. - ISBN 5-203-0187-X.
2. Cross-country ability // Soviet military encyclopedia. - Moscow: Military Publishing House of the USSR Ministry of Defense, 1978. - T. 6. - P. 610.
3. All-terrain vehicle // Military encyclopedia / Grachev P. S. - Moscow: Military Publishing House, 1994. - T. 2. - P. 30. - ISBN 5-203-00299-X.
4. Cars of the UAZ-469 family. Manual. MO 1985
5. [1] Operating manual for UAZ Patriot 2005
6. [2] Renault Duster. Off-road characteristics.
7. [3] Volkswagen Touareg. Chassis and all-wheel drive.
8. [4] Defender 90-11-130. Owner's Handbook.
9. GAZ-24-95 - exclusive Volga 4x4