Articulation angle control

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The articulation angle control is a system that enables the controlled transmission of the thrust force to the vehicle in an articulated bus and prevents the vehicle from rolling or swerving in unfavorable road conditions. With the articulation angle control, which is usually operated by two hydraulic cylinders, it is achieved that the vehicle cannot buckle further in uncontrolled manner than corresponds to the specified angle between the front and rear vehicle, depending on the steering angle of the steered front wheels. In particular, articulated sliding buses , in which the drive takes place on the trailing axle, are absolutely dependent on this system. If there is a risk of uncontrolled buckling, the two-part vehicle will automatically stretch when the impulses from the articulation angle controller act on the wheel brakes of the rear axle. By braking the left or right drive wheel, a torque is generated around the vertical axis that counteracts the bending movement.

The articulation angle control should not be confused with the articulation lock, which is also known colloquially as an anti - buckling mechanism . While the articulation angle control is used almost exclusively in push or pusher articulated buses and ensures stable vehicle running as soon as a steering movement takes place, kink protection is also used in so-called puller vehicles. This prevents damage to the joint from excessive steering angles by stopping the vehicle as soon as the joint goes into the end stop.

Development and history

Until the end of the 1970s, articulated buses had the engine in the front of the car and the drive was on the second axle. The disadvantage was that at higher speeds, rolling movements could occur in the trailer. The vehicle workshops Falkenried (FFG) and Hamburg-Consult (HC), both subsidiaries of Hamburger Hochbahn AG (HHA), developed an electronic articulation angle control with financial support from the Federal Ministry of Research and presented it in 1975.

From two HHA buses of the standard Mercedes-Benz O 305 bus type , the world's first articulated pusher bus was created in 1977, the motor and drive of which were in the trailer. The then Daimler-Benz AG (today Daimler AG ) acquired the license rights to the control and from then on was no longer dependent on third-party manufacturers such as Vetter Fellbach for articulated bus production .

The advantage of the rear-wheel drive is that the front car does not have to accommodate an engine and the car floor and entrances can be built with low floors. The rear engine is also more easily accessible for maintenance work.

At MAN and Magirus-Deutz , an articulated bus was temporarily manufactured in which the engine was also located in the rear, but powered the rear axle of the front end of the car via a homokinetic shaft running through the joint . The axle in the trailing axle was designed as a single-tire and steered trailing axle . These vehicles were usually one meter shorter and, thanks to the steered axle, a little more manoeuvrable, which gave them a certain advantage over articulated pusher buses. In addition to the complex drive shaft guidance, however, a disadvantage of these vehicles was that the drive axle in the middle was not sufficiently loaded when the vehicle was empty, which meant that the drive wheels spun faster. Cornering under load also led to increased wear and tear on this cardan shaft construction. In the mid-1980s, MAN added articulated pusher buses to its range; the previous design of rear engine and center-axle drive was hardly in demand.

Layout and function

One or two hydraulic cylinders are installed in the slewing ring area of ​​the joint . They are connected via lines to a hydraulic block that can limit the flow from one cylinder to the other. The system is under permanent overpressure . A nitrogen bubble compensates for temperature fluctuations.

During normal cornering, the hydraulic oil is displaced through the lines and the hydraulic block by the movement of the cylinders. From a certain angle, the hydraulic block narrows the cross-section and thus increases the pressure in the system. Buckling is dampened. If the mechanical stop is reached, a warning signal sounds for the driver, the system intervenes in the engine control and reduces the speed so that the vehicle can only roll at walking speed.

In the case of articulated buses pulled from the front of the vehicle , the articulation must be protected when reversing. When maneuvering, the vehicle can buckle and the turntable can be damaged. The system also cushions buckling here. From an angle (usually max. 47 °) it reduces the engine speed and also applies the bus stop brake to bring the vehicle to a standstill immediately.

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Individual evidence

  1. ↑ Low-floor articulated bus . Technical description of the FFG Falkenried Hamburg, September 1978