Clutch Systems

Compared to rigid flywheels, the DMF effectively reduces torsional and engine vibrations to increase ride comfort. Buses today are often equipped with dual-mass flywheels since both drivers and passengers benefit from its advantages. SACHS is the only brand that offers dual-mass flywheels for buses in OE quality for the aftermarket. Usually, however, trucks have been equipped with rigid flywheels up to now. Apart from rigid flywheels, SACHS also offers dual-mass flywheels for passenger cars and light commercial vehicles.

The truck DMF transmits the engine torque to the clutch pressure plate and the clutch disk. Its primary purpose is to isolate the torsional vibrations generated in the engine, preventing them from passing into the driveline.

The current engine technology places higher and higher demands on clutch systems and the entire driveline. Consumption-optimized truck engines, such as diesel and gasoline engines using direct injection, already develop high torque at low speeds. The usable engine speed range is additionally reduced towards the idling speed level to enable fuel-efficient and low-emission driving. This increases the combustion engine’s rotational irregularities. For the driveline and driver, this means increased vibrations, increased noise and reduced comfort. This is where the DMF comes in as a powerful torsional vibration isolator. It helps protect the driveline against harmful vibration and ensures low-noise and comfortable driving.

The SACHS dual-mass flywheel is installed between engine and transmission, together with the clutch pressure plate and the clutch disk.

The flywheel is divided into a primary and a secondary mass. An extremely powerful multi-spring damping system is installed between the two masses.

Effective compression springs with a multi-stage characteristic curve design ensure optimal vibration isolation.

The SACHS DMF offers numerous advantages, such as optimal vibration isolation across the entire speed range, individual adaptation to the vehicle design, effective noise reduction, smooth setting-off behavior, great shifting and driving comfort, protection of the transmission, excellent start-stop behavior, long service life, reduced installation space requirements, possible pull-type and push-type clutch actuation as well as fuel economy thanks to reduced consumption because vehicles can be operated at lower rpm levels.

A DMF can only be tested on a special test bench for dual-mass flywheels. The workshop can only perform a visual inspection. The visual inspection, however, – similar to the tests on the test bench – only provides a snapshot. The assessment of such an inspection requires a great deal of expertise.

The dual-mass flywheel should be inspected each time the clutch is replaced. If the clutch has already been replaced once, the dual-mass flywheel should be replaced in any case.

At low or regular engine loads, the cooling airflow produced during driving is normally sufficient to dissipate heat from the radiator and work as an engine cooler. In this case, the fan runs at a slow rate or is switched off completely. If the load increases and the vehicle speed drops – e.g. when climbing a hill – there is a risk of heat accumulation due to engine overheating. Thus, the CV fan clutch is engaged to ensure that sufficient air flows through the radiator. The viscous clutch ensures that the fan speed is automatically adjusted to the level necessary to cool down the engine. This reduces both fan noise and fan power consumption, with the pleasant side effect of saving fuel.

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• The fan clutch operates in accordance with the airflow temperature behind the radiator
• The temperature on the outgoing air from the radiator is used to control the fan
• This version is used on passenger cars and small to medium-sized commercial vehicles.

• The vehicle computer receives signals from the engine management sensors and the temperatures at the radiator, charge-air-intercoller/ exhaust cooler, oil cooler etc. and uses them to control the fan clutch
• This version is used for heavy commercial vehicles and agricultural vehicles.

Compared to rigid or simple flywheels, the DMF effectively reduces torsional and engine vibrations for increased ride comfort. That is why dual-mass flywheels are not only installed in buses, but also in other vehicles. SACHS also offers, for example, a high-quality DMF for passenger cars and transporters. Until recently, it is mostly rigid or simple flywheels that have so far been used in trucks, but thanks to the high-quality truck DMF from SACHS ,dual-mass flywheels are also being used increasingly in this segment.

The DMF transmits the engine torque to the clutch pressure plate and the clutch disk. Its primary purpose is to isolate the torsional vibrations generated in the engine, preventing them from passing into the driveline. The DMF is therefore one of the important drive components in coaches and city buses.

The dual-mass flywheel consists of a primary flywheel, secondary flywheel, rotating plain bearing and coupling coil springs.

The current engine technology places higher and higher demands on clutch systems and the entire driveline. Consumption-optimized engines already generate high torque at low speeds. The usable engine speed range is additionally reduced towards the idling speed level to enable fuel-efficient and low-emission driving. This increases the combustion engine’s rotational irregularities. For the driveline, driver and passengers, this means increased vibrations, increased noise and reduced comfort. The SACHS bus DMF steps in here to powerfully isolate the vibrations, which helps protect the driveline against harmful vibration and ensures low-noise and comfortable driving.

The SACHS dual-mass flywheel is installed between engine and transmission, together with the clutch pressure plate and the clutch disk. The axial installation space requirement for a DMF with clutch corresponds to that of a twin plate clutch so that it can usually be integrated into an existing driveline configuration.

The dual-mass flywheel function effectively reduces noise. The flywheel is divided into a primary and a secondary mass. A highly-efficient, grease-filled spring damping system functions between both of the masses. This means the resonance speed of the dual-mass flywheel is below the idling speed of the engine, which is different from a conventional clutch disk that has a torsional vibration damper. Effective compression springs with a multi-stage characteristic curve design ensure optimal vibration isolation in the bus.

The SACHS bus DMF offers numerous benefits, such as optimal vibration isolation across the entire speed range, customized modification to the vehicle design, effective noise reduction, smooth setting-off behavior, great shifting and ride comfort, protection of the transmission, excellent start-stop behavior, long service life, reduced installation space requirements and efficiency through reduction of fuel consumption because vehicles can be operated at lower rpm levels.

A DMF can only be tested on a special test bench for dual-mass flywheels. The repair shop can perform only a visual inspection, which, however, – like the tests on the test bench – just provides a snapshot. Assessing such an inspection requires a great deal of expertise.

Inspect the dual-mass flywheel each time the clutch is replaced. If the clutch has already been replaced once, then also replace the dual-mass flywheel.