Tractor

Engine configuration

Invented by Rudolph Diesel in 1897, the first diesel engine developed a power of 14.7 kW.
It has evolved considerably since it was first presented at the 1900 Paris Universal Exhibition.

Engine characteristics

Torque (Nm) is an engine's ability to withstand effort. The higher the torque value, the greater the engine's ability to withstand stress. This concept is important when working the soil.
Torque reserve corresponds to an engine's ability to withstand a one-off increase in workload, without increasing engine speed or changing forward speed. It is expressed in %.
The power (W) is the result of multiplying the torque by the engine speed. Technological developments in engines mean that maximum power can be obtained at an engine speed lower than the nominal (maximum) speed.
Hourly consumption (l/h) is a variable value, since it depends on the engine's rotation speed and the load factor.

Power and hourly consumption - CUMA

Specific consumption (g/kWh) corresponds to the mass of fuel required to produce 1 kW for one hour. This often misunderstood concept can be used, for example, to compare the hourly consumption of different engines of the same power. A fuel-efficient engine has a low specific consumption value.

Power and specific consumption - CUMA

Engine power standards.

There are several standards for quantifying the power of an internal combustion engine (OECD, EEC 80/1269, ECE R24, etc.). Of all the standards used, a distinction must be made between power delivered at the flywheel (gross or net) and power at the power take-off.

The SAE J1995, ISO TR 14396, EC 97/68 and 2000/25/EC standards are referred to as gross power standards. Depending on the standard used, power is measured using an engine without the various accessories, air filter, fan and exhaust silencer (SAE J 1995 corresponds to the American standard).
The ECE R24, CEE 80/1269 and DIN 70020 standards give a net power value. Engine power measurements are more stringent than the previous standards. During measurements, the engine is fitted with the majority of accessories (fan, exhaust system, etc.). The ECE R24 standard corresponds to the European standard.
The OECD standard corresponds to the power delivered at the power take-off.

There is a difference of around 20% between the most generous standard (SAE J1995) and the most stringent (OECD).

As a result, engine manufacturers claim power levels that are difficult to compare from one manufacturer to another. For example, at Massey Fergusson, New Holland, Mc Cormick and John Deere, the advertised power is a gross power corresponding to the ISO TR 14396 standard. Other manufacturers use standards expressing net power, such as Same, Deutz and Fendt.

Table of engine power standards

All this information can be used to choose the right engine for the job in hand (ploughing, traction, etc.). For work requiring traction, a high engine torque will be needed to provide strong pulling power. New-generation engines offer high torque at a relatively low engine speed, so you can get plenty of pulling power without having to accelerate too much. This is known as starting torque. Today, maximum torque is generally obtained at 1500 rpm. This gives high pulling power at low revs. To meet regulatory requirements, engine manufacturers have developed certain engine components.

Injection system

There are three main types of diesel engine. They are classified according to the development of injection systems over the last few decades:

Before 1980: indirect injection

With this type of injection, diesel fuel is injected into a pre-combustion chamber in the cylinder head, where the air is heated by a glow plug. It was used on diesel vehicles until the early 2000s. Some low-cost tractors still use this injection system. Injection pressures are in the region of 100 to 150 bars.

1980 - 2000: direct injection

This technology has become widespread in modern diesel engines. Fuel is injected directly into the cylinder. An injector sprays the fuel directly above the piston. The specific shape of the concave piston creates turbulence that encourages air-fuel mixing. The fuel is injected at relatively high pressures (from 180 bar to 1500 bar).

Since 2000: the common rail

This is a variant of direct injection. Common rail" technology is increasingly used in agriculture to comply with the new standards on limiting pollutant emissions. The fuel is injected under very high pressure (300 to 2000 bar), via a common rail, directly into the cylinders.

Pollution control systems

In response to the development of mechanisation in agriculture, standards were introduced in the 1990s limiting CO2, NOx and fine particle emissions. They are not applied in the same way worldwide, with several countries or groups of countries issuing their own standards. The European Union has adopted a "Stage" system, which is very similar to the American "Tiers" system.

Below is a table summarising the various courses from 1990 to the present day:

Internship	Installation	Changes
I	1999 for certain non-road engines	Basic limits for NOx, CO, HC, PM, depending on power, but not very strict compared with current standards.
II	Between 2001 and 2004 according to powers	Reinforcement of Stage I, reduction of thresholds for pollutants.
III (IIIA et IIIB)	Between 2006 and 2013 according to powers	Arrival of technologies such as EGR valves, turbochargers, catalysts, etc. Significant reductions in particulate matter (PM) and NOx.
IV	2014 to 2017 depending on power	Lower thresholds for NOₓ, CO, HC, PM. Reinforcement of post-treatment techniques (SCR, DPFS, DOC).
V	2019 to 2020 depending on power	Significant reductions in particulate matter (PM) from 25 to 15 mg/kWh. New restrictions (Particulate Number, particle size). No change in NOx levels.

SCR (Selective Catalyst Reduction) technology

This consists of optimising combustion to reduce the production of fine particles. Nox emissions are treated using a catalytic reduction process combined with the addition of a urea-based solution (AdBlue).

Schematic diagram of how SCR technology works © AgroSup Dijon

The diagram above shows the 5 stages in the pollution control process using SCR technology. These are as follows

oxidation catalyst producing H2O
injection of AdBlue required for the following reaction
hydrolysis catalyst ensuring the formation of NH3 by reaction between the nitrogen and water molecules
sCR catalyst converting Nox molecules into nitrogen molecules (N2) and water (H2O)
the final oxidation catalyst, which converts the NH3 molecules produced previously into nitrogen (N2) and water (H2O).

Engine, gearbox and hydraulic oils

Engine oils

There are three types of oil:

Mineral oil: this is at the lower end of the value scale, derived directly from refined crude oil. It is rarely used today.
Semi-synthetic oil: this is the middle of the range. It is made up of 35% synthetic oil and 65% mineral oil. It is recommended for low-efficiency engines.
Synthetic oil: this is the highest performance oil. It is made up of a base and additives. This oil has good adhesion properties and is more resistant to ageing. Oil change intervals are increased.

The role of oil is to protect and cool moving parts. All oils comply with viscosity and quality standards. The most common standards are SAE and API.
SAE = Society of Automotive Engineers is an international organisation that tests and approves the viscosity of oils. A distinction is made between SAE "engine" and SAE "transmission" grades.
API = American Petroleum Institute is a standard classifying the different types of transmission oil.

Viscosity corresponds to the oil's resistance to flow as a function of temperature. As viscosity decreases with increasing temperature, the oil must both retain its role as a protective film and remain sufficiently fluid to circulate freely in the engine.

There are monograde and multigrade oils (which have a range of viscosity depending on temperature).

Monograde oils are rarely or never used. They are intended for the lubrication of simple mechanics, such as old-generation engines.
In the case of multigrade oils, polymer-based additives are added to the composition of the oil. This combination limits differences in viscosity when hot and when cold. As its name suggests, a multigrade oil has a cold grade and a hot grade. The cold grade is indicated by the first number (15W40). This refers to the oil's ability to lubricate the engine when it is not at temperature (cold engine). The second number corresponds to the viscosity of the oil when hot. In other words, the oil's ability to retain its properties at higher or lower temperatures.

The quality of engine oils is established on the basis of a classification that takes into account several parameters (protection, resistance, etc.). Depending on the oil's performance, the following nomenclature is used: SA, SB, SC,..., SL. The higher the second letter in the alphabetical order, the better the performance. For diesel engines, the classification is identical except that the first letter is a C: CA, CB, CC,..., CH4.

Gearbox oils

They have an additional classification that takes into account the viscosity of the oil and its composition. Gearbox oils frequently used in agriculture correspond to the GL4 or GL5 classifications.

Hydraulic oils

These fluids are made from an incompressible mineral base to which additives are added to optimise the fluid's physical properties. Their role is to transmit the energy produced by the pump to a receiver (cylinder, motor, etc.) while lubricating and cooling the components in the hydraulic circuit.
They comply with the ISO/AFNOR standard using the basic classes HH, HL, HM, HV and HG, each with different possible grades. Each grade is identified by a number ranging from 15 to 220. The grade corresponds to a viscosity at a certain operating temperature.

Biodegradable hydraulic oils

Developed more than twenty years ago, rapeseed-based hydraulic fluids are a response to the risks of pollution in the event of hydraulic circuit component failure. Despite a higher purchase price than oil from petroleum products, these oils offer some interesting qualities:

Increased oil change intervals. Unsaturated fluids have an oil change interval of 2000 hours. Saturated fluids have a service life of around 6,000 hours.
Lower energy consumption thanks to optimised lubricity.

There are two main types of biodegradable hydraulic fluids. Both comply with the ISO 15380 standard.

The first is based on Triglyceride (HETG) and is generally used for hydraulic circuits with a working pressure of less than 210 bar.
The second is based on a synthetic ester (HEES) and is recommended for hydraulic circuits with a working pressure of less than 420 bar.

The OECD 301B standard defines the concept of biodegradability. The best fluids on the market offer 75% biodegradability.

Operator station

Driving position of a high-clearance tractor

The driving position has evolved considerably in recent years. It offers greater comfort thanks to the development of ergonomics. The seats are more comfortable thanks to the development of air suspension.

What's more, automatic driving aids are becoming increasingly common in tractors of all power ratings.

Finally, operator protection is optimised with the last cab category (class 4). When buying a tractor, it's important to clearly define the work to be carried out, so that you can choose exactly the components you need for the driver's cab.

Screen

This accessory is becoming an essential part of the driver's cab. Some standard tractor manufacturers offer a touch screen. It provides a wealth of information, helps with driving and facilitates the traceability of operations carried out in the field. Accessory suppliers offer screens that can be fitted to specialist tractors. This technology should be available as standard with the appearance of new-generation vineyard tractors (meeting Stage IV anti-pollution standards).

Joystick or steering wheel

The development of on-board electronics has opened up many new possibilities. Controls are centralised on a joystick. This makes it possible to control the tractor's forward movement and hydraulic functions from a single control. The development of hydrostatic or continuously variable transmissions makes it easier to integrate additional functions on the joystick (management of implement lift and control of hydraulic spool valves).

Joystick

Steering wheel - Driving position

On-board electronics

Although this technology is widely used on standard tractors, it is struggling to make inroads on specialist tractors. Yet on-board electronics make it possible to approach driving in a different way. Whether it's a driving aid, with varying levels of performance depending on the technology used(optical sensor, ultrasound, GPS system, etc.). Or simply by providing information such as instantaneous fuel consumption, work rate/ha, or timed management of hydraulic spool valves.

Filtration system

Designing the filtration system

Depending on the specific nature of the filtration system, the component parts differ from one system to another. To achieve maximum filtration, the system should be designed as follows:

A coarse particle pre-filter made of paper, glass wool or foam, placed upstream of the purification device. This protects against dust.
A very high efficiency aerosol filter (type P3). Standard NF U O3-024-1 guarantees its performance.
A class A activated carbon anti-gas filter, downstream of the aerosol filter, to compensate for any evaporation of the product retained by this filter.

Tightness and pressurisation

This is an important concept, as it limits the introduction of pollutants through openings not intended for ventilation. A cabin is difficult to seal because of the many cable passages. A classification can be used to determine different levels of filtration from 1 to 4.

Level 1: the cab offers no protection at all
Level 2: filtration protects the operator from dust
Level 3: level 2 + aerosol protection
Level 4: level 3 + vapour protection

The highest level of protection (level 4) requires a minimum suppression of 20 Pascals or 0.2 millibars.

Maintenance

Regular maintenance is required to maintain the performance of the filtration system.

The dust filter must be cleaned regularly and replaced according to the manufacturer's recommendations.
Activated carbon cartridges can be used in different ways. Either it is removed between each treatment, or it remains in place. The first solution avoids saturating the filter element too quickly. However, successive installation and removal can damage the seals, encourage preferential air flow and reduce filtration efficiency. When the cartridge is dismantled, it must be stored in an airtight container, away from plant protection product storage areas, in accordance with the same rules as respirator cartridges. We strongly recommend replacing them every year.

To ensure optimum working comfort, the cab and its components must be kept in good condition. It is important to check the condition of door and window seals frequently. Replace them when they no longer perform their function.

Air conditioning

An essential part of any cab, air conditioning must be maintained so that the cab enclosure can be heated in a matter of minutes. The temperature difference between inside and outside must be controllable. It is important not to direct cold draughts towards the driver, to protect his or her health.
Maintain the air conditioning system regularly, in accordance with the manufacturer's recommendations. Particular attention should be paid to evaporator and condenser maintenance. Checking the liquid charge, the oil level in the compressor and replacing the drier filter should be carried out by trained and equipped personnel.

Transmission

The transmission has never stopped evolving. The first tractors were equipped with a rudimentary transmission with only three speeds and reverse gear. Gear changes often required the tractor to come to a complete stop. The 1970s saw the introduction of synchronised gearboxes on agricultural tractors. This technological development simplified gear changes.

There is now a wider choice of transmissions on tractors, including :

Mechanical transmission (standard manual gearbox)

How it works

Based on gears and pinions that the driver shifts manually via gear lever(s).
Often with double clutch or dry clutch.

Features

Robust, simple and inexpensive to maintain.
Used mainly on low- to medium-power tractors.

Disadvantages

Less comfortable to use, requiring the engine speed to be lowered to change up or down a gear.
Less precise gearing, especially for precision work.

Semi-powershift or full powershift transmission

How it works

Electro-hydraulic system allows several gear ranges to be shifted without the need for a clutch.
Allows you to change gears under load, without stopping.

Benefits

Excellent balance between comfort and efficiency.
Ideal for work with varying loads.
Saves time and improves efficiency in the field.

Examples

24/24 powershift transmission = 24 forward / 24 reverse speeds with several robotised gears in each range.

Continuously variable transmission

Historically, tractor manufacturer Fendt has long dominated this market, with its famous VARIO. Recently, however, many manufacturers have followed suit with different names (AutoPowr, MLT, CVT...).

How it works

No fixed gears. Continuously variable transmission between 2 speed limits (e.g. 0 to 30 km/h).
Electronic management, often hydrostatic + mechanical planetary.

Benefits

Maximum comfort, very smooth.
Automatically maintains optimum engine speed in relation to forward speed.
Ideal for precision work (spraying, sowing, etc.)

Disadvantages

More complex and therefore more expensive.

Automated transmission

How it works

Mechanical or powershift type, but gear changes are managed automatically by electronics.
Resembles a robotised or Autoshift gearbox

The benefits:

Less expensive than a CVT, but offers greater comfort.
Less manual intervention by the driver

Hydrostatic transmission

How it works

Transmission by pressurised oil circulation (pump + hydraulic motor).
Often used on compact tractors, vineyard tractors or agricultural loaders.

Benefits

Very smooth, precise, easy to drive.
Precise control at low speeds.

Disadvantages

Less efficient in pure traction.
More limited for heavy agricultural work.

Pneumatic

Tyres provide the link between the tractor and the ground. There are two categories of tyre on the market: diagonal and radial structures.

Tyre structures

Radial tyres are more square in shape. Developed by Michelin in the 1970s, it is more versatile. The sidewalls and tread work independently. Load distribution is optimised, generating less settling.
The bias-ply tyre has a rounded shape. They are best suited to low-speed transport operations. As the tread is integral with the sidewall, this type of tyre offers good lateral stability. However, the load distribution is not optimal, so it is less suited to ploughing work.

Low-pressure tyres are frequently used in large-scale cultivation, and are now becoming increasingly popular on grape harvesters and fruit tractors. This type of tyre has the particularity of having a large air volume, essentially thanks to a wider tread. This makes it possible to support heavy loads at moderate pressures, reducing ground pressure and therefore the risk of compaction and rutting.

The tracked undercarriage is another alternative that limits soil compaction. Manufacturers such as Track Equipement offer innovative technical solutions that can be adapted to a wide range of tractor models. The height of the tractor and its ground clearance remain the same, so there are no changes to the way in which implements are attached. Only flanges are added, but these can be easily removed. When the tracks are removed, the tractor returns to its original configuration.
As far as maintenance is concerned, in line with the manufacturing principle, it simply involves cleaning and regular greasing.

How do you read the marking on a tyre?

13.6	Flange size (in inches)
R	Radial tyre
28	Rim diameter (in inches)
SUPER VINE	Type of structure
123	Load capacity index
A8	Speed symbol

Hydraulic circuit

The hydraulic circuit is an essential part of the agricultural tractor, and is being used more and more to carry out various functions such as steering, braking and transmission, as well as operating the implements attached to the tractor via hydraulic distributors.

Hydraulic circuit: single pump

Hydraulic circuit: double pump

Components of a hydraulic circuit

A hydraulic circuit is made up of several key elements:

Hydraulic pump

This is the heart of the system. Generally driven by the engine via the gearbox.

Types :

Gear pump (constant flow, less expensive, common on simple models)
Piston pump (variable flow, more efficient, on top-of-the-range tractors)
Vane pump (rare in agriculture)

Oil tank

Contains the hydraulic oil used in the circuit.
It can be integrated into the transmission housing (combined system) or separate.

Filtration

Filters protect the circuit from clogging (limits wear, prevents breakdowns).
There are return, suction and sometimes high-pressure filters.

Distributors

Control the flow of oil to hydraulic cylinders or motors. They can be :

Mechanical (manual).
Electro-hydraulic (via solenoid valves, often with in-cab or joystick controls).
Proportional (for precise control of flow and position).

Hydraulic cylinders and motors

Cylinders: convert pressure into linear movement (e.g. lifting arms).
Hydraulic motors: convert pressure into rotary motion (e.g. augers).

Flow regulators / pressure valves

They protect the circuit against overpressure and allow the speed of the cylinders to be controlled.

Hydraulic outlets (external)

Located at the rear and sometimes at the front of the tractor;
Standardised (ISO) for easy connection of implements
Different numbers depending on the model: from 2 to 8 spool valves or more

Types of hydraulic circuits on a tractor

Open centre circuit

The oil circulates continuously when the spool valves are not actuated.
Simple and economical, but less efficient under load.
Typical of older or basic tractors.

Closed centre circuit

The oil only circulates when a control is activated.
The variable flow pump adapts to demand.
More energy-efficient.
Standard on modern tractors (e.g. load sensing systems)

Load Sensing (LS)

Sophisticated version of the closed-centre circuit.
Pressure is adjusted automatically according to tool demand.
Optimised consumption, rapid pressure build-up, improved responsiveness.
Example: PFC system (Pressure Flow Compensated)

Lifting gear hydraulic circuit

The rear (and sometimes front) 3-point linkage is an independent circuit or is integrated into the general hydraulic system.
It is controlled by a spool valve or a specific lever.
Includes a single-acting or double-acting cylinder, depending on the configuration.
Often works with :

Position control
Force control (adjusts depth according to tool resistance)
Mixed control

Operation synchronised with the transmission

On some tractors, particularly those with a continuously variable transmission (CVT) or intelligent systems, the hydraulic circuit is integrated into the tractor's overall electronic management system (ISOBUS, TIM, etc.). This allows :

Automatic regulation of flow rates and pressures
Feedback from the implement to the tractor

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