If a towing vehicle begins to brake, the trailer pushes it with its mass, elongating the stopping distance of the vehicle combination. An overrun brake is a device which uses the inertial mass of a trailer to actuate the trailer’s brake system and so assures its autonomous braking. It is a reliable mechanical principle. Furthermore, it is automatically and smoothly controlled. An overrun brake system is applicable to trailers with a load capacity of up to 3500 kg and in some cases of agricultural low-speed trailers it can be even more. KNOTT offers either mechanical overrun brakes (wheel brakes controlled by brake cables) or hydraulic ones (wheel brakes controlled by hydraulic circuit). There are also several designs available with different drawbar mounting methods, or even compete drawbars with an integrated overrun brake in them. Next, there is a stand-alone group of height adjustable drawbars that allow hitching the trailer to vehicles with a different height of towing device.
The force acting horizontally between a towing vehicle and a trailer at braking pushes a drawtube into the overrun brake body, thereby actuating a transmission mechanism of the trailer’s brake system, connected to the wheel brakes by brake cables, thus the braking effect occurs.
The operation principle is the same as with the mechanical variant with one difference, being the drawtube pushing through the transmission mechanism directly at the hydraulic brake cylinder, located in the overrun brake. With the help of hydraulic fluid, this cylinder controls the expanding brake cylinders in the wheel brakes.
With drawbars of round or square cross-section (KNOTT overrun brake types KR & KV respectively), it is possible to integrate the whole overrun brake system directly into the drawbar itself, creating a very compact design. The individual components of the overrun brake are thus ideally protected against the unfavourable outdoor conditions. Such an overrun brake is delivered as a homologated assembly with drawbar length according to the customer’s request.
A KNOTT overrun brake of the KRV type can be mounted onto a drawbar of rectangular cross-section by the means of a bolted connection. Thanks to several adapters available, the same KRV overrun brake may be attached to various rectangular drawbar dimensions, assuring the versatility of its use.
We have overrun brakes of the types KF, KFG & KFGL with a corresponding flange available for mounting to V-shaped drawbars.
This simple drawbar is made of a standard straight tube of round or rectangular cross-section.
A round or rectangular drawbar tube can be bent into the shape of a swan neck to increase the height of a coupling point to a towing vehicle. The magnitude of this height-displacement depends on the homologation of the particular drawbar and ranges from 50 mm to 220 mm. This drawbar type is mostly used in cases, when adhering to the legally specified trailer coupling height is problematic or the demand for integrating the overrun system into the trailer drawbar is present.
A V-shaped drawbar, designated by us as the ZHL type, is a popular one. It is a strength-optimised solution, which is either bolted to the trailer frame or, with the help of adapters, connects directly to the axle.
If one trailer should be towed by personal vehicles as well as freight vehicles, it is necessary for its drawbar to be able to adapt to different heights of coupling devices. Height-adjustable drawbars serve this purpose. We have the following drawbar types in our product range for such use case:
KHD
A unique innovation of KNOTT Slovakia. Very comfortable and simple operation of the stepless height-adjustment by the means of a single handle. All parts of the mechanism, and in the case of a braked version, all parts of the overrun brake system as well, are effectively hidden and protected inside the drawbar. This elegant solution was awarded by the National Design Award in 2005. A version without an overrun brake is designated as the KHDU type.
KHA
A traditional height-adjustment system with two toothed knuckles. Simpler in design, but much more demanding in operation, than the height-adjustment system used in the KHD drawbar type. To make the height-adjustment easier, we offer an auxiliary lifting mechanism with a gas strut as an optional accessory. The brake cable for the overrun brake is led sideways, outside the drawbar.
KHV
Operation principle is the same as with the KHA drawbar type, but this type of drawbar lacks the overrun brake. It can be used to solve the height-adjustment for trailers with a load capacity of up to 6500 kg, where the brake control is already realised by a pneumatic brake system.
If the drawbar of a parked trailer takes an undesired space (e.g. a mobile retail stand, by which the owner pays for the total area taken by the trailer), it is favourable to use a drawbar that can be folded away or easily dismounted. KNOTT offers two solutions here. Either it is the use of a toothed knuckle allowing the drawbar to fold up or dismount if needed, or it is a pin-lock system allowing the front drawbar section to fold 90° sideways in both directions.
