Brake technologies, beyond ABS
The Anti-lock Braking System is an automated system which substantially improves the braking efficiency of motor vehicles, especially on poor road surface conditions. For agricultural machinery, mainly tractors, there are some other ways to ensure efficient braking
The circulation of agricultural machinery on public roads, especially tractors, has always attracted the attention of lawmakers due to their great size and weight as well as speed limits. These are built-in factors which can involve danger for the machinery as well as other drivers on the road.
Minimum safety requirements have been repeatedly and progressively been improved. As regards braking, considerable progress has been achieved with increasing speeds of tractors from 30 to 40 km/h by applying mandatory regulations for braking on both axles, that is, all four wheels.
Similar norms have been brought in for trailed machinery, mainly trailers, which must be equipped with braking devices ensuring efficiency in accordance with their maximum size and weight. This means that modern tractors and trailers with brake systems are extremely important for safety on public roads. New European Union regulations enacted introduced strict limits for this purpose with such innovative features as the compatibility of the tractor and trailer. The well known ABS, Anti-lock Braking System, is now required for all new tractors with maximum potential speed of up to 60 km/h or greater and there is the prospect of applying the same requirement for models with speed between 40 and 60 km/h. Thus manufacturers are committed to taking their new products in this direction through work on technical solutions which have been successful in experiments conducted on associated sectors such as truck trailers. Bosch Rexroth has developed the hydraulic power brake with ABS. In substance, this hydraulic brake valves modify fluid pressure on each individual wheel.
On the other hand, the U.S. WABCO has manufactured air brakes widely used in Italy and for some time has produced a modular braking system platform with single our double line completed with a pressure regulator and a load-sensing valve for savings with the entire plant. In the truck category, the Italian company Zaccaria markets air and hydraulic ABS brake systems. Though they operate independently, both the hydraulic and air brake valves active the same shank which works the lever connected to the braking system. In reverse, when pressure lowers to zero a sturdy spring on the rear axle cylinders triggers the parking brake.
Though the ForCon 201, the Force Control by Fliegl Agrartechnik GmbH is not a specific braking system for agricultural trailers, it greatly improves the performance of trailers which are not equipped with one for greater stability in braking, better stability on the road in downgrades and upgrades and provides reduced wear on tires, especially on tight curves. ForCon also ensures greater safety on downgrades and better weight distribution for the tires and forward and reverse towing with no problem with bumps and depressions. Another German manufacturer, Knorr-Bremse, has come out with the Trailer-EBS TEBS G2.1, an electronic braking system built around its own ABS and, for value added, the RPS, Roll Stability Program.
This device detects critical terminal transverse stability and automatically applies the brakes on the single wheels to reduce lateral speed and the ALB thanks to which braking power is modified in proportion with the load.
ABS alternatives
ABS is an expedient and efficient technical component but it is also costly. For this reason, numerous alternatives have been created for agricultural machinery which usually operate indirectly to improve braking efficiency or, more precisely, decelerate the tractor or also the tractor-trailer combination.
All these are well known and widely tried and tested but a new range of techniques have been proved a degree of success become available for making technical progress in the sector.
Automatic reversal of front traction
The first step in this direction came with the automatica reversal of front traction. An example of this solution is called Terralock by New Holland which has been fully tested. Other than changing traction, this can be put to a single use automatically for reversing the front wheels during braking for the resistance of the transmission to counter the forward inertia of the vehicle.
Disc brakes
A further solution for application, direct or indirect, involved all the wheels. The first option to add was was the drive shaft driving the rear wheels but more recently focus was trained on disc brakes, sometimes multiple, on the end of the drive shaft for all the tractor wheels for a substantial increase in braking efficiency. In light of the considerable braking load and the heat generated a cooling oil bath solution was hit on for the brake discs in intercapillary housing for cooling everything.
More recently a direction taken was to go for external discs in pairs on the truncation as is frequent in the automotive field.
Engine braking
The function of engine braking has been applied to trucks for some time and has progressively become widespread in the automotive sector, especially for diesel engines and obviously for agricultural tractors for which they are useful especially for lengthy transport on downgrades while towing substantial loads for gradually slowing forward speed to the limited speed or maintaining speed without need to use the parking brake to avoid overloading the entire plant which decreases braking efficiency by up to 40%. The operation is Choking, or slowing down the flow of exhaust gas through the silencer. By using a control the butterfly valve is closed and this generated counter pressure reducing the engine rpm. With this step engine exhaust and compression becomes passive and this increases braking on all the wheels obviously with the help of the transmission.
Fuel falls to zero electronically by disactivating the acceleration controls of the engine usually when rps decline to 1100-1200 rpm or forward speed drops under 10 km/h.
It must be noted that full braking efficiency is reached only when engine rpm are high and also in this case (opposed to usual considerations) fuel consumption drops to zero. The entire system is managed by air and often linked to the brake circuit via the compressed air for the trailer to favor combined operations.
Introducing hydraulic services
Yet another option designed for the same engine braking results, that is, creating force of resistance capable of opposing the engine of the vehicle. This solution is activating what is necessary for one or more services managed by hydraulics for increasing overall braking efficiency. For models which are equipped, this is done by exploiting the cooling fan theeth wheel and/or entire hydraulic plant to use in this case as a negative brake.
Installing hydrostatic traction
This is an option not now available for almost all agricultural tractors because what is involved is an integrated mechanical transmission. But for self-propelled machines, especially large ones such as combine harvesters and mower-mulcher-loaders with combined mechanical-hydraulic transmissions this is always serviceable to use. In this case, once unloading is started the hydraulic part for the vehicle's forward drive shows great efficiency for slowing down. For many years this solution has been considered so valid that it is given official type-approval as the main brake plant, that is a service brake.
A variation on the theme is the expectation of the same functional situation which, however, acts on the hydraulics motor applied directly on the wheels as occurs for example on self-propelled grape harvesters.
The future
As almost always happens, in the tractor field the vehicle type applications are transposed to what has already been introduced in other sectors such as the automotive sector. This means that in the near future we can also see self-propelled agricultural machinery with hydrostatics replaced by electricity for recovering braking energy and braking adapting emergency assistance, smart cruise control, that is control adapted to the speed of cruising. In any case, the evolution of technology for improving safety of vehicles on the road is praiseworthy as well as it is for agricultural machinery now showing various criteria of respect in all categories as regards the benefits of global improvement for work conditions.
ABS (Anti-lock Braking System
This safety system allows all four tires of the vehicle to maintain traction for the driver on the road surface to avoid blocking the brakes and locking the wheels in the case of excessive braking. When the ABS Electronic Control Unit, ECU, sensors detect the wheels coming close to locking, possibly causing uncontrolled skidding, the systems steps in with hydraulic valves to reduce hydraulic press on the brake of the wheel rotating much more slowly than the speed of the vehicle to prevent blocking. To ensure ABS efficiency, internal phonic and speed sensors are installed on at least one axle of the vehicle. The wheel speed sensor, usually magnetic type, detects rotation speed according the rotation of a toothed ring. To guarantee precise speed of rotation the number of the teeth must correspond to the size of the wheel rotating. As an example, a 1.4 m tire would require a ring with 120 teeth.
For multi-axle trailers a different logic is applied, the independent side solution calls for four wheels equipped with directly controlled sensors and two modulators, one on each side. With this arrangement, the pressure on the left and right sides are controlled independently. In practice, the pressure on the brake components of each wheel on one side is modulated by signals arriving from the slower rotation rates.
ABS is not usually used to reduce the distance required for braking in low traction conditions but sometimes often to improve traction and stability of the vehicle on the road or even more for vehicle towing implements.
The development of ABS and ESP, Electronic Stability Program, which incorporates the ABS and ASR, which further reduces reaction time and thus the braking distance as well. Also considered are the wear on tires and cruise control speed on downgrades and are of use for towing heavy trailers.
