Smart Fluid Systems

Oil Lines

Modern combustion engines equipped with exhaust gas turbochargers are highly complex machines with a variety of moving components which must be lubricated efficiently. The same applies to gearboxes. COHLINE manufactures lines needed to supply the various units with lubricating oil. While doing its work, oil often heats up to a considerable extent and must be cooled accordingly. In order to transport the oil to cooler and tight installation spaces, COHLINE develops the ideal solution together with you.

Engine oil lines

Engine oil lines are used in vehicles with large engines. Due to the high power of the engine, part of the power must be dissipated in heat via coolers to prevent overheating of the system and thus failures. Engine oil is usually cooled by means of oil/air heat exchangers, located either in the front end or in the wheel housing. The lines must compensate for tolerances of the components to each other and also vehicle/engine movements.

Depending on the requirements, the materials used for engine oil lines consist of different nominal sizes and material combinations,. Pipe components are made of steel, stainless steel, aluminium or even plastics. Hose sections are made of elastomers such as AEM and, depending on requirements, are designed with an appropriate pressure carrier braid. Tolerance and movement compensation is ensured either by a hose part or the geometry of the line in the case of plastic lines.

The interface to the motor as well as to the cooler are sealed by an O-ring, which can be located on a swivel part, an upset or in a connector.

In the case of plastic lines, the connecting components (gear unit connection, plug connector) are either pushed in or welded on.

Transmission oil lines

Transmission oil lines carry transmission oil from the gear unit to the corresponding cooler, oil/water heat exchanger or oil/air heat exchanger and back to the gear unit. An oil/water heat exchanger is usually located near the transmission. It is usually a heat exchanger made up of individual plates, which,between oil and water, are able to alternately flow and transfer heat. The oil/air heat exchanger is usually located in the front end, directly in the airflow of the airstream. Lines for an oil/air heat exchanger are longer, as they run from the transmission past the engine to the front end. Here, not only tolerances, but also vehicle / engine movements must be compensated for.

Materials used for transmission oil lines are of different nominal sizes and material combinations, depending on the requirements. Pipe sections are made of steel, stainless steel, aluminium or even plastics. Hose sections are made of elastomers such as AEM and, depending on requirements, are designed with an appropriate pressure carrier braid. Tolerance and movement compensation is ensured either by a hose part or the geometry of the line in the case of plastic lines.

The interfaces to the gear unit and cooler are sealed by an O-ring, which can also be located in a connector.

Oil dipstick guide tubes

Oil dipsticks allow the level of the engine oil to be checked. To perform the measurement, they must extend into the oil pan located under the engine, while also being easily accessible from above. Over time, paths that the dipstick must take have become more and more tortuous, as engine compartments have become more complex. COHLINE develops and manufactures appropriate dipstick guide tubes from various materials and, on request, also the matching oil dipsticks.

Turbocharger lines

Turbocharger lines convey oil and cooling water to and away from the turbocharger to cool and lubricate its bearing bracket. Depending on the exhaust gas temperature, it is necessary to additionally flow cooling water through the bearing bracket. This procedure is necessary, since heat dissipation via the oil flow, which mainly serves to lubricate the bearing of the air compressor and exhaust gas turbine shaft, is not sufficient.

Since turbocharger lines are located close to the exhaust tract, high-temperature-resistant materials are used here. In addition to elastomer hoses, hoses made of PTFE with stainless steel braiding are also used. In addition, the components can be protected from heat radiation by heat protection hoses, heat protection mats or heat protection sheets, which are applied to the lines. If all the aforementioned protection measurements are not sufficient, flexible stainless steel components, stainless steel bellows tube or corrugated stainless steel hose are used to dampen and compensate for the tolerances and the vibrations and thermal expansions of the components.

Power steering

Power steering systems are hydraulic steering assistance systems that have now been largely replaced on passenger cars by electrically assisted steering systems. They consist of a suction line that carries the power steering oil from the reservoir to the pump, an expansion hose that carries oil from the pump to the steering gear, and two return lines which carry oil from the steering gear back to the oil reservoir via the oil cooler.

The suction line usually consists of a pure molded hose, if the oil reservoir can be located near the pump in the engine compartment. When longer distances need to be covered between the oil reservoir and the pump, a pipe/hose combination is employed.

An expansion hose usually consists of several hose sections with various fittings to dampen vibrations caused by the pump, to assure that they are not transmitted to the vehicle body. So-called resonators and chokes are used here and, in combination with the increase in volume of the hose, "acoustics" can be tuned to suit the specific vehicle.

Line types

  • Expansion hose lines
  • Pressure range: 120 bar operating pressure
  • Return lines, suction lines
  • High-pressure lines
  • Pressure range: 180 bar operating pressure
  • Oil cooler for power steering
  • Smooth bore pipe
  • CSC tube (upset)
  • finned tube (various fin heights possible)

The two return lines usually consist of pipe/hose sections that are connected to the oil cooler with connectors. Connectors are used, since the cooler is pre-assembled on the front end, i.e. on the vehicle side, and all other lines are pre-assembled on the engine. When the vehicle is "married", the power steering system can then simply be connected to the radiator using the two connectors.

The oil cooler used in such systems is a tube, which can be designed with different cooling levels. For example, it can be a pure smooth aluminium tube, which is mounted directly in the driving air intake in front of or below the main cooling package in the front end of the vehicle. More cooling capacity can be achieved by applying bellows-flares onto the tube. By doing so the "radiator" receives more surface area, resulting in higher heat dissipation. Turbulence is created in the volume flow of the servo oil in the cooler, which serves to improve heat transfer from the medium to the tube wall.

A further increase in performance is possible by using so-called finned tubes. These consist of thick-walled aluminium tubes into which correspondingly high fins can be rolled, depending on the cooling capacity required. Here, too, the internal geometry can be designed in such a way that turbulence of the medium occurs and heat can be exchanged more effectively.