Apparatus for driving a cooling fan

TECHNICAL FIELD

The invention relates to a device for driving a cooling fan of a combustion engine, comprising a gear between the cooling fan and a drive shaft of the engine.

BACKGROUND

Engines, e.g. engines of vehicles, usually have the cooling fan connected directly to the engine's crankshaft, in which case it runs at the same speed as the engine. With a view to reducing fuel consumption, it is desirable that the engine be run at relatively low speed. In state of the art engines, this entails the speed of the fan having to be geared up to achieve sufficient air flow for satisfactory cooling. To this end, a belt drive is often used to impart to the fan a higher speed than the engine, so that the fan has sufficient capacity at low engine speeds. At high speeds, however, the fan will then require more energy from the engine, which is disadvantageous for the engine's fuel consumption. A quickly rotating fan also generates disturbing noise and shortens the service life of the belts. A belt drive has the further disadvantage that belts, guide pulleys and tensioning pulleys hinder the fan's cooling air flow through the engine space. A belt-driven fan may certainly be run intermittently to achieve a desired average fan capacity, but only by a low gear ratio can it be protected against too high powers.

A known practice from, for example, DE1101051 is to arrange between the belt drive and the fan a hydraulic connection which provides automatic slippage when the load on the fan rises.

SUMMARY OF THE INVENTION

An object of the invention is to further develop the state of the art and propose a compact device of the kind indicated in the introduction which does not hinder

the fan's cooling flow and makes it possible to run the fan in a desired speed range according to the load.

This is achieved by the features indicated in the claims set out below.

According to a version of the invention, the drive is a hydrodynamic gear of the type which comprises fixed guide vanes and is adapted to responding to a lower engine speed at a lower load on the fan by providing a step-up gear ratio between the drive shaft and the fan and to responding to a higher engine speed at a higher load on the fan by applying slippage to reduce the gear ratio between the drive shaft and the fan.

This makes it possible for the whole drive device to be arranged in a small amount of space entirely behind the fan without disturbing the cooling air flow. It also makes it possible for the fan to be run at sufficient rotation speed to provide good cooling power even at low engine speed. At higher load on the fan, the device advantageously reduces the gear ratio by applying slippage. Although the efficiency of the device is thereby diminished, a fuel saving is still achieved as compared with a belt-driven fan.

An increasing speed increases also the load torque and hence the slippage, thereby reducing the gear ratio. The power loss which then occurs may be expressed as slippage X speed X torque. The increased slippage also causes the fan not to fully match the speed increase. Hence the fan will draw somewhat less power. The power decrease is clearly greater than the power loss caused by the slippage.

The device's gear ratio step-up between the drive shaft and the fan may in an embodiment be about 1.4:1 at a specified low speed and a specified low load.

The device may also be connected to an adjustable hydraulic source in order to vary a fullness coefficient of the gear. The gear ratio of the gear can thus be varied as necessary.

Other features and advantages of the invention may be indicated by the claims and the description of an embodiment example set out below.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a schematic sideview, partly in section and with portions cut away, of a vehicle engine with a fan and a fan drive device according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT EXAMPLE

In the schematic depiction in FIG. 1 , items with the same function have the same reference numerals throughout. The drawing depicts a forward end of a vehicle engine (combustion engine) 10 with a protruding end 14 of a shaft driving the engine, e.g. the crankshaft 12 of the engine 10. The crankshaft end 14 is connected via a fixed connection 16 to a fan 60 via a hydraulic gear 30.

The hydraulic gear 30 is of a hydrodynamic type and comprises in a conventional manner a stationary housing 32 with fixed guide vanes 34. The housing 32 is firmly connected to the forward side of the engine 10 by a retainer 20 which is coaxial to the crankshaft 12. In the example depicted, the retainer 20 is provided with a radial annular flange 22 which is connected to the forward side of the engine 10 and an annular flange 24 which is coaxial to the crankshaft 12 and which surrounds and is firmly connected to the outside of the stationary housing 32.

An input shaft 36 to the gear 30, which is driven by the crankshaft end 14, bears in the housing 32 a pump wheel 38 with pump blades 40, while an output shaft 42 in the housing 32, which drives the fan 60, bears a turbine wheel 44 with turbine blades 46.

The hydraulic gear 30 is also of the type at which, at low load, i.e. low fan speed, provides a gear ratio step-up between the input shaft 36 and the output shaft 42. A gradually increasing load causes slippage of the turbine wheel 44 in the

housing by internal friction of the hydraulic fluid, resulting in a gradually decreasing gear ratio between the input shaft 36 and the output shaft 42.

The gear 30 is engaged and disengaged respectively and has its speed regulated by the supply and removal of hydraulic fluid via a line 48 from a schematically depicted hydraulic source 50, comprising in the example a double- acting pump 52 driven by a motor 54. The speed of the fan 60 can therefore be controlled as necessary by the fullness with hydraulic fluid of the housing 32. When there is no fan requirement, the housing 32 is drained completely. To this end, the hydraulic source 50 may be controlled by, for example, an undepicted engine temperature sensor via a control unit 56.

At low engine speed and consequently small load on the fan 60, the maximum gear step-up ratio of the gear 30 may typically be about 1.4:1.

The description set out above is primarily intended to facilitate comprehension and no unnecessary limitations of the invention are to be inferred therefrom. The modifications which will be obvious to one skilled in the art from perusing the description may be implemented without departing from the concept of the invention or the scope of the claims set out below.