GB2478716A - Engine coolant pump comprising a planetary gearing - Google Patents

Abstract

A coolant pump for an internal combustion engine comprises an impeller shaft 15, and a planetary gearing 20 driving the impeller shaft. The planetary gearing comprises a sun gear 21 rotationally fixed to the impeller shaft, at least one planet gear 24 meshing with the sun gear, a planet carrier 22 provided for being driven by the engine, an annulus 23 having a ring gear 28 that meshes with the at least one planet gear, and a braking device 40 for apply a variable braking load to the annulus. A pulley 26, driven by an engine belt 27, may be rotationally fixed to the planet carrier. Preferably, the braking device comprises a friction element 41 and a driving device 42 for tightening the friction element against a rotating surface 29 of the annulus. The driving device may comprise a casing (46, fig.4) containing a material (49, fig.4), such as wax, whose volume changes with temperature, where the fiction element moves in response to the expansion and contraction of the material. Alternatively, the braking device may comprise an electric motor (43, fig.3) driving a pinion (45, fig.3) that meshes with a further ring gear (30, fig.3) of the annulus.

Description

cOOLANT JMP INTERNAL 1BUSTION EINES

TEICAL FIElD

The present invention relates to a coolant pump for an internal com-bustion engine, in particular for an internal combustion engine of a motor vehicle.

BUND

It is known that most internal combustion engines of motor vehicles are provided with a liquid coolant circuit for cooling some fixed parts of the engine, such as for exarriple the cylinder block and the cylinder head.

The liquid coolant circuit generally comprises a plurality of chan- nels running through the cylinder block and the cylinder head, a ra-diator connected with said channels through thennostat valve, and a pump for circulating the engine coolant in the circuit, which is con-ventionally defined as coolant pump.

A standard coolant pump comprises an impeller that is driven by the internal combustion engine through a Front End Accessory Drive (FEAD), typically a continuous belt driven by a pulley connected to a front extension of a crankshaft.

In order to allow some thermal management of the engine, this stan-dard coolant pump can be switched ON or OFF during the operation of the engine.

Notwithstanding, when the standard coolant pump is ON, the speed of the impeller is anyway linked to the engine speed through the FEAD speed ratio, so that the engine speed inevitably affects also the coolant flow in the coolant circuit.

As a consequence, the standard coolant pump cannot guarantee an accu-rate thermal management of the engine.

However, the engine thermal management is becoming a crucial strategy to control and optimize the heat exchange among engine components, so as to obtain more efficient engines able to comply with tighter ernis-sian regulations.

Therefore, most car makers are now developing solutions for improving the engine thermal management.

A known solution provides for replacing the standard coolant pump with an Electric Coolant Pump (ECP), whose impeller is driven by a dedicated electric motor, in order to deliver the right coolant flow at the right time, independently from the engine speed.

The ECP is however rather complex and expensive, so that it is now used only on top class series vehicles.

Since the irnpefler is driven by an electric motor, the EPC is gener- ally not failsafe and usually implies high power losses (up to 200-400 Watt).

Moreover, the EPC is cumbersome than a standard coolant pump and re-quires deeply modification of the FEP1D.

?n alternative solution to improve the engine thermal management pro-vides for arranging a variable ratio gearing between the impeller of the coolant pump and the FED, whereby the variable ratio gearing can be commanded to change its speed ratio, in order to adjust the speed of the impeller independently fran the engine speed.

The German patent application DE 10 2006 041 687 discloses a coolant pump having an impeller and an impeller shaft integrally connected with the impeller, which is driven by a crankshaft of the internal combustion engine through a continuous belt drive. A planetary gear-ing is arranged between the impeller shaft and the belt drive. The planetary gearing comprises a planet carrier for a plurality of pla-net gears, which contemporaneously mesh with a sun gear and with a ring gear provided by an external annulus. The planet carrier is ro-tationally fixed to the impeller shaft, while both the sun gear and the arinulus are free to rotate with respect to the impeller shaft.

The ring gear is integral with a pulley of the belt drive. The sun gear is coupled with an electric motor or the like, which is arranged to adjust the speed of the sun gear independently from the speed of the ring gear.

By adjusting the speed of the sun gear, the electric motor changes the speed ratio between the ring gear of the annulus and the planet carrier, in order to achieve a continuous adjustment of the impeller speed independently from the engine speed.

1\n object of the present invention is to improve a coolant pump of this latter kind, namely an engine driven coolant pump having a pla- netary gearing for continuously vary the speed of the impeller, inde-pendently from the engine speed.

Another object of the present invention is to reach this goal with a simple, rational and rather inexpensive solution.

DISCLOSURE

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous fea-tures of the embodiments of the invention.

An embodiment of the invention provides a coolant pump for an inter-nal combustion engine, comprising an impeller shaft and a planetary gearing driving the impeller shaft, wherein the planetary gearing comprises a sun gear rotationally fixed to the impeller shaft, at least a planet gear meshing with the sun gear, a planet carrier pro-vided for being driven by the engine, an arinulus having a ring gear that meshes with the at least a planet gear, and a braking device for apply variable braking load to the annulus.

In this way, when no braking load is applied on the annulus, the tor- que applied by the engine to the planet carrier is completely trans-mitted to the annulus, so that the sun gear and the impeller shaft remain stationary. On the contrary, when the braking load block the annulus, the torque applied by the engine to the planet carrier is completely transmitted to the sun gear, thereby achieving a maximum speed ratio between the speed of the impeller and the engine speed.

By varying the braking load beneath the value needed to block the an- nulus, the torque applied by the engine to the planet carrier is pro-portionally transmitted to the arinulus and to the sun gear, so that a continuous adjustment of the ratio between the speed of the impeller and the engine speed is effectively possible.

As a consequence, a coolant pump according to the present embodiment of the invention allows to continuously change the impeller speed in-dependently from the engine speed, and/or to maintain the impeller at a desired speed independently from any engine speed variation, in or-der to always meet the best trade off between thermal efficiency and cooling function.

Moreover, a coolant pump according to the present embodiment of the invention is generally easier, cheaper and less cumbersome than an ECP, implies negligible power losses and can be designed so as to be failsafe.

According to an aspect of the invention, the coolant pump comprises a pulley rotationally fixed with the planet carrier, which is provided for being driven by an engine belt.

This aspect of the invention has the advantage that the coolant pump can be effectively driven by the engine FEAD, without deep structural changes of the latter.

According to an embodiment of the invention, the braking device can be a conventional frictional brake, namely cariprising at least a friction element and a driving device for tightening the friction element against a rotating surface of the annulus.

A braking device of this conventional kind has the advantage to be very reliable.

According to an aspect of this embodiment of the invention, the driv- ing device comprises a casing containing a material whose volume va-ries as a function of its temperature, and the friction element is arranged so as to move in response of expansions and collapses of said material.

This driving device has the advantage to be simple and rather inex-pensive.

According to another aspect of this embodiment, the material con-tamed into the casing is wax.

The wax has the advantage to be easily available and rather cheap.

According to still another aspect of this embodiment, the driving de-vice comprises an heater for heating the material into the casing.

This aspect has the advantage of better control the braking load ap-plied on the annulus.

According to a further aspect of this embodiment, the heater corripris-es an electrical resistance.

This heater has the advantage to be very simple and rather inexpen-sive.

According to another embodiment of the invention, the braking device can comprise an electric motor driving a pinion that meshes with a ring gear of the annulus.

As a matter of fact, the electric motor can be supplied with elec-trical power so as to generate an adjustable resistant torque that ccuriteracts the rotation of the annulus.

This electromechanical brake has the advantage to be simply controll-able.

The present invention can also be embodied as a motor vehicle com-prising an internal combustion engine and a coolant pump according to any of the preceding embodiments or aspects, wherein the planet car-rier of the planetary gearing is driven by the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 is a schemetic longitudinal section of a coolant pump ac-cording to an embodiment of the invention.

Figure 2 is the section 11-lI of figure 1.

Figure 3 is the section of figure 1 according to another embodiment of the invention.

Figure 4 is the section of figure 1 according to still another embo-diment of the invention.

DEThILED DESCRIPTION

An embodiment of the invention provides a coolant pump 10 for a liq-uld coolant circuit (not shown) of an internal combustion engine of a motor vehicle.

The liquid coolant circuit generally comprises a radiator connected through Thermostat valve with a plurality of channels running through the cylinder block and the cylinder head.

The coolant pump 10 is located in the liquid coolant circuit in order to circulate the coolant therein.

The coolant pump 10 comprises an external casing 11 having a coolant inlet 12 and a coolant outlet 13, and an impeller 14 rotating inside the casing 11, which draws coolant from the inlet 12 and delivers it under pressure through the outlet 13.

The impeller 14 is rotationally fixed to a coaxial shaft 15 protrud-ing from the casing 11, so that any rotation of the shaft 15 causes an equal rotation of the impeller 14.

As a matter of fact, the impeller shaft 15 could be integrally formed with the impeller 14 or connected to the impeller 14 in a fixed man-ner.

The impeller shaft 15 is driven by a planetary gearing 20 comprising three coaxial members, including a sun gear 21, a planet carrier 22 and an annulus 23.

The corrmon axis of these three members is indicated with X and coin-cides with the rotational axis of the impeller shaft 15.

The sun gear 21 is integral with the portion of the impeller shaft 15 extending from the casing 11.

The planet carrier 22 is free to rotate with respect to the impeller shaft 15 and carries three planet gears 24 (see also figure 2) angu-larly equidistant with each other.

Each planet gear 24 is coupled with the planet carrier 22 by means of a coaxial pin 25, in order to be bound to orbit around the common axis X together with the planet carrier 22 and to be free to spin about its central axis Y. The planet gears 24 globally surround and mesh with the sun gear 21.

The planet carrier 22 is rotationally fixed to a coaxial pulley 26, so that any rotation of the pulley 26 causes an equal rotation of the planet carrier 22 about the coirunon axis X. The pulley 26 is provided for being driven by a continuous V-belt 27 that, in turn, is conventionally driven by another pulley (not shown) connected to a front extension of a crankshaft of the internal com-bustion engine.

The annulus 23 is rotatably coupled with a cylindrical portion of the planet carrier 22, in order to be free to rotate with respect to the latter as well as to the sun gear 21.

The annulus 23 comprises a ring gear 28 that globally surrounds and meshes with all the planet gears 24.

The coolant pump 10 further comprises a braking device 40 for exert-ing a variable braking load on the annulus 23 and consequently on the ring gear 28.

In the embodiment shown in figure 1, the braking device 40 generally comprises a plurality of shoes 41, which are individually associated to a double-acting hydraulic cylinder 42 hinged at a stationary support.

The hydraulic cylinders 42 can be cormianded to contemporaneously move the shoes 41 against an inner surface of a rotating drum 29 integral with the annulus 23, thereby generating a friction that brakes the ring gear 28.

This friction is a function of the normal force exerted by the hydraulic cylinders 42, so that the braking load on the ring gear 28 can be varied by adjusting said normal load.

In the embodiment shown in figure 3, the braking device 40 generally comprises a stationary electric motor 43 having a rotating shaft 44 S and a pinion 45 coaxially fixed to the rotating shaft 44.

The pinion 45 meshes with an auxiliary ring gear 30 integral with the rotating drum 29.

The electric motor 43 can be supplied with electrical power in order to exert on the annulus 23 a resistant torque that brakes the ring gear 28.

This resistant torque is a function of the electrical power supplied, so that the braking load on the ring gear 28 can be varied by adjusting said electrical power.

In the embodiment shown in figure 4, the braking device 40 generally comprises a stationary casing 46 with a movable piston rod 47, and a shoe 48 associated to the piston rod 47.

The stationary casing 46 is filled with a material 49, typically wax, whose volume varies as a function of its temperature.

As a matter of fact, when the temperature raises, the material 49 ex- pands into the stationary casing 46 moving the shoe 48 against an in-ner surface of the rotating drum 29, thereby generating a friction that brakes the ring gear 28.

The friction is a function of the temperature of the material 49, so that the braking load on the ring gears 28 increases as the tempera-ture increases.

When the temperature decreases, the material 49 collapses and the shoe 48 moves away from the rotating drum 29 due its own weight, leaving the ring gear 28 free to rotate.

In order to better control the braking load, an electric resistance 50 is located into the stationary casing 46 for selectively heating the material 49.

The operation of a coolant pump 10 according to any of the preceding embodiments is disclosed hereinafter.

If the braking device 40 does not exert any braking load on the annu-lus 23, the ring gear 28 is completely free to rotate, substantially without any counteracting resistance.

As a consequence, the torque generated by the internal combustion en-gine, and transmitted to the planet carrier 22 by means of the V-belt 27 and the pulley 26, is completely transmitted by the planet gears 24 to the annulus 23.

As a matter of fact, the ring gear 28 rotates while the sun gear 21 and the impeller shaft 15 remain stationary, so that the coolant pump does not work.

If conversely the braking device 40 exerts a braking load capable to block the annulus 23, the torque generated by the internal combustion engine, and transmitted to the planet carrier 22 by means of the V-belt 27 and the pulley 26, is completely transmitted by the planet gears 24 to the sun gear 21 and consequently to the impeller shaft 15.

As a consequence, the ring gear 28 remains stationary, while the ira- peller 14 rotates at maximum speed, so that the coolant pump 10 cir-culates a maximum coolant flow.

If the braking device 40 exerts a braking load beneath the maximum value needed to block the annulus 23, the torque generated by the in-ternal combustion engine, and transmitted to the planet carrier 22 by means of the V-belt 27 and the pulley 26, is partially transmitted by the planet gear 24 to the annulus 23 and to the sun gear 21 connected to the impeller shaft 15.

As a consequence, the impeller 14 rotates at a reduced speed, so that the coolant pump 10 circulates a partial coolant flow.

It follows that, by varying the braking load exerted by the braking device 40, it is effectively possible to continuously change the im-peller speed independently from the engine speed, and/or to maintain the impeller 14 at a desired speed independently from any engine speed variation, in order to always meet the best trade off between thermal efficiency and cooling function.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing summary arid detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodirrnt without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERENCE NURAIS

Coolant pump 11 External casing 12 Coolant inlet 13 Coolant outlet 14 Impeller Impeller shaft Planetary gearing 21 Sun gear 22 Planet carrier 23 Annulus 24 Planet gear Pin 26 Pulley 27 V-belt 28 Ring gear 29 Rotating drum Auxiliary ring gear 40 Braking device 41 Shoe 42 Hydraulic cylinder 43 Electric motor 44 Rotating shaft 45 Pinion 46 Stationary casing 47 Piston rod 48 Shoe 49 Material 50 Electric resistance X Common axis Y Spin axis of the planet gears