Truck braking system
A truck brake system is divided into different areas in accordance with EC Directive 98/12 / EC. A distinction is made between the braking system of the towing vehicle or the braking system of the trailer and a combination of both vehicles . The legally required three brake systems FBA, BBA, HBA or, if applicable, the DBA required as the 4th brake system must be functional, as otherwise the truck can no longer be operated safely.
Solo truck or towing vehicle
This chapter describes the function of the braking system of a solo truck or towing vehicle without taking trailer operation into account.
Parking brake system (FBA)
The parking brake system (FBA) is used to secure the parked truck and was previously transferred to the rear wheels of the vehicle in a simple manner, as in a car with a cable brake. It must function mechanically so that the function of the FBA is not impaired even in the case of auxiliary power brake systems when the auxiliary power is lost (usually loss of compressed air). Today, the system of a spring brake cylinder is generally used in trucks .
mechanical cable pull unbraked
mechanical cable braked
Spring accumulator released with compressed air (unbraked)
Spring accumulator operated without compressed air (braked)
Spring accumulator unbraked
Spring accumulator braked
When the spring accumulator is released, the compressed air holds the accumulator spring back via the brake piston. The actuated spring accumulator is vented via a valve so that the accumulator spring actuates the brake piston (mechanical effect).
If the spring accumulator is used instead of the cable on the other side of the brake lever, braking can be initiated by extending the brake piston (venting the spring accumulator - applying the mechanical force of the accumulator spring).
A renewed pressurization of the spring accumulator consequently releases the braking again.
Service brake system (BBA)
The service brake system (BBA) in a truck is used to comply with the legal requirements for minimum braking.
The reference value (= 100%) for the deceleration is the acceleration due to gravity (9.81 m / s²). The service brake system must provide at least a certain percentage of deceleration, see deceleration z in the following table. The values are determined during the main inspection and safety inspection and entered in the test report .
| Vehicle class | Vehicle type | First registration | Service brake system deceleration z ≥ [%] |
Hand force FH ≤ [daN] |
Foot force FF ≤ [daN] |
Parking brake system deceleration z ≥ [%] |
Hand force FH ≤ [daN] |
Foot force FF ≤ [daN] |
|---|---|---|---|---|---|---|---|---|
| N2, N3 | Truck / tractor / motorhome > 3.5t | before 01/01/1991 | 43 3 | --- | 70 | 15th | 60 | 70 |
| from 01/01/1991 and before 07/28/2010 | 45 | 16 | ||||||
| from 07/28/2010 | 50 | |||||||
| M2, M3 | Bus | before 01/01/1991 | 48 | --- | 70 | 15th | 60 | 70 |
| from 01/01/1991 | 50 | 16 |
Source: HU brake guidelines, as of 2012
The service brake system (BBA) is intended to bring the vehicle to a safe stop during operation (i.e. while driving). For this purpose, legal values must be complied with, which in the EU refer to EC Directive 98/12. In today's trucks, versions of the BBA are usually disc brakes that are controlled by diaphragm brake cylinders. The forerunners of the space-saving diaphragm brake cylinders were piston brake cylinders, which may still be present in older trucks.
Piston brake cylinder unbraked without air
Piston brake cylinder braked with air
Diaphragm brake cylinder unbraked without air
Diaphragm brake cylinder braked with air
Auxiliary braking system (HBA)
A better designation would be emergency braking system , as there is also the term auxiliary power braking system in the brake systems, but this has a different meaning. The task of the HBA is actually simple, namely to enable the vehicle to be braked if the BBA fails. The implementation of the HBA is also regulated by EC Directive 98/12. In the case of trucks / KOM (power buses ), the HBA is usually triggered via the actuation mechanism (handbrake lever / actuation valve of the parking brake ), for this the parking brake is applied, which can be vented once again if the BBA fails, so the release path of the parking brake lever is relatively long so that the required gradability of the HBA can at least theoretically be achieved. Bleeding the spring accumulator should only be used with caution in an emergency, as a spring accumulator that is deflated too quickly could lead to the rear axle locking.
Continuous braking system (DBA)
Retarder system or retarder is a generic term for the so-called wear-free brakes. These are supposed to relieve the BBA. DTAs are prescribed for trucks with a gross vehicle weight of 9 t or more or COM with a gross vehicle weight of 5.5 t or more. Typical representatives of the DBA are dynamic pressure brakes or retarders . DBAs installed today are usually integrated into the anti-lock braking system (ABS) so that locking of the rear axle is prevented, but overbraking is still possible with some DBAs if the actuation device of the DBA is switched too quickly to the maximum level of performance.
pendant
In general, similar requirements are made of the trailer's braking functions, but they are sometimes implemented differently.
Parking brake system (FBA)
In principle, there are the same designs as for the towing vehicle. In other words, cable brakes, which in the so-called linkage brakes (usually drum brakes ) act in some way on the linkage of the brake system so that it is triggered. In many trailers, disc brakes are now also installed, in which mostly a spring accumulator in the form of a combination brake cylinder (formerly known as a tristop cylinder) comes into operation.
Service brake system (BBA)
Again, similar to the towing vehicle, but the FFS can be operated directly or indirectly. The indirect actuation is mostly an overrun brake . In the case of hydraulic systems (tractor), direct actuation can either be transmitted to the trailer via hydraulic lines. However, the standard for trucks today is the dual-line brake system, in which the trailer is connected to the towing vehicle via two air lines (red supply line / yellow brake line) and the trailer's BBA can be triggered virtually at the same time when the tractor’s BBA is activated.
Auxiliary braking system (HBA)
Triggering of the HBA when the trailer is torn down, so that it does not continue to drive without braking. In the case of trailers with overrun brakes, a tear-off rope is attached to the towing vehicle, which then triggers the FBA when it is demolished. In the trailer with compressed air brakes, this is done by the trailer control valve, which triggers the so-called forced braking of the FFFS in the trailer when the red supply line is torn off. Since the FFFS relies on supply air, emergency braking only takes place as long as there is a supply of compressed air in the trailer - but this should normally be sufficient to bring the trailer to a standstill.
Continuous braking system (DBA)
If DBA are installed in the trailer, the eddy current brake system is usually used here .
See also
Web links
literature
- LKW - A textbook and reference work, pages 133-236. Kirschbaum Verlag, Bonn 2008, ISBN 978-3-7812-1702-7 .
- Commercial vehicle technology, pages 215 - 227. Vieweg + Teubner Verlag, Wiesbaden 2008, ISBN 978-3-8348-0374-0 .
credentials
- ↑ Directive 98/12 / EG (PDF) includes a. also sources for the article
- ^ Hans-Hermann Braess, Ulrich Seiffert: Vieweg handbook automotive technology. 2nd edition, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden, 2001, ISBN 3-528-13114-4