Variable mechanical automotive coolant pump

The invention is directed to a variable mechanical automotive coolant pump.

A coolant pump is applicated for providing and regulating the coolant flow cooling an internal combustion engine and thereby preventing an overheating of the engine components. The coolant pump is mechanically coupled with the crankshaft of the internal combustion engine, for example via a belt drive. Due to the constant transmission ratio, the rotational speed of the coolant pump rotor is always proportional to the rotational speed of the crankshaft, but not to the cooling performance requirement of the internal combustion engine. Therefore, variable mechanical automotive coolant pumps become more and more common.

One type of a variable mechanical automotive coolant pump is provided with a switchable clutch to uncouple the drive shaft of the pump from the belt drive driven by the crankshaft of the internal combustion engine, if no coolant circulation is requested.

In WO 2019/042530 Al an alternative pump type of a variable mechanical automotive coolant pump with an axially slidable control sleeve defining a valve is disclosed. For reducing the flow rate of the pump, the axially slidable control sleeve can close the radial discharging area of an impeller wheel within the pump, which is mechanically driven by the crankshaft of the internal combustion engine via a belt drive. The hollow cylindrical control sleeve can be pushed over the impeller wheel covering the radial discharging area of the impeller wheel according to the required coolant flow rate. With this control sleeve the radial discharging area of the impeller wheel can also be closed completely to hydraulically block the coolant pump completely during the cold-start phase of the engine.

The control sleeve is actuated by a hydraulic actuation system provided with pressurized coolant from the pumping chamber. The leakage between the outer cylinder surface of the control sleeve and the inner cylinder surface of the guiding cylinder has to be very low to ensure a constant pressure level within the hydraulic control chamber. Therefore, a small hydraulic gap between the contact surfaces is necessary. Accordingly, the requirements regarding the manufacturing accuracy of the control sleeve and the guiding cylinder are high, resulting in a cost-intensive production of the components.

Due to the high accuracy requirements, the control sleeve is made of a metallic material. The guiding cylinder within the pump housing is also made of a metallic material, so that the wear between the machined metallic contact surfaces is high. The wear can additionally be increased by an inaccurate guiding of the control sleeve resulting in a tilting of the control sleeve with in the guiding cylinder. The tilting of the control sleeve can be caused for example from pressure fluctuations, from pollution particles within the coolant or from an imprecise manufacturing process of the contact surfaces of the components.

To reduce the wear, the inner cylinder surface of the guiding cylinder and the outer cylinder surface of the control sleeve are provided with a wear-resistant coating.

The high accuracy requirements and the additional wear-resistant coating result in a cost-intensive production process of the coolant pump. It is an object of the invention to provide a cost-effective and reliable automotive coolant pump.

This object is achieved by a variable mechanical automotive coolant pump with the features of claim 1.

The variable mechanical automotive coolant pump according to the invention is provided with a rotatable impeller wheel being co-rotatably connected with a rotatable rotor shaft, which is, for example, mechanically driven by the belt drive of an internal combustion engine.

The variable mechanical automotive coolant pump according to the invention is also provided with a non-rotatable and axially slidable control sleeve with a hollow-cylindrical control sleeve body being guided by and within a static guiding cylinder, which is for example machined and defined within a casted static pump housing.

According to the invention, the variable mechanical automotive coolant pump is provided with a separate guiding means, which is guiding the slidable control sleeve within an inner cylinder surface of the static guiding cylinder. The guiding means is substantially surrounding the outer cylinder surface of the control sleeve substantially over the complete circumference, so that the outer cylinder surface of the control sleeve is not in direct contact with the inner cylinder surface of the static guiding cylinder.

Preferably, the radial extension of the substantially cylindrical gap between the outer cylinder surface of the control sleeve and the inner cylinder surface of the static guiding cylinder is at least 0.5 mm. With the application of the separate guiding means, the friction pairing between the sliding surface of the static guiding cylinder and the guiding means is freely selectable, so that both the control sleeve and the guiding means can be provided with the optimal material according to their individual functions. For example, a plastic guiding means providing low friction forces and high sealing characteristics could be combined with a metallic control sleeve of high strength and high form stability.

In a preferred embodiment of the invention, the axial position of the control sleeve regulating the discharging flow rate of the impeller wheel is continuously adaptable.

The actuation of the control sleeve can be achieved by different types of actuation systems and is preferably provided with a hydraulic actuation system. The hydraulic actuation system is provided with a hydraulic control chamber being fluidically effective to an axial end surface of the control sleeve. The hydraulic pressure force axially pushes the control sleeve over the impeller wheel thereby closing the radial discharging area of the impeller wheel. The high hydraulic pressure for hydraulically actuating the control sleeve is preferably provided by an additional side channel pump rotor arrangement at the backside of the impeller wheel. Because of this high hydraulic pressure, the control quality of the hydraulic control chamber substantially depends on the sealing quality of the separate guiding means, so that the guiding means hydraulic quality is essential for a precise hydraulic actuation of the control slider.

The return mechanism of the control sleeve can be realised by a spring-supported return mechanism or by providing a second hydraulic control chamber, for example defined by an inner static supporting means and an axial end surface on the opposite side of the first axial end surface of the control sleeve. Thus, the pump can be actuated purely hydraulically, so that no additional electric motor is necessary providing the high actuation forces.

In a preferred embodiment of the invention, the guiding means is defined by a non-closed ring-shaped guiding means body, which is provided with a compensation slit. This compensation slit allows an adaption of the total circumference of the ring-shaped guiding means body to geometric inaccuracies of the sliding surfaces. To equalize tolerance-related inequalities the shape and the dimensions of the guiding means body can adapt to the shape and the dimensions of the inner guiding cylinder surface. The compensation slit also allows to adapt to geometric variations resulting from thermal expansion differences between the control sleeve and the static guiding cylinder.

In a preferred embodiment of the invention, the axial extension of the guiding means is smaller than 25% of the total axial extension of the control sleeve, so that the control sleeve is not being guided over the complete outer cylinder surface. This results in a reduction of the sliding contact surface, so that the friction between the guiding means and the static guiding cylinder is relatively low. The low friction forces allow relatively low hydraulic actuation forces, so that the power consumption of the actuation system of the coolant pump is reduced resulting in an increased efficiency of the pump. Further, the lower hydraulic actuation forces result in a lower hydraulic pressure in the hydraulic control chambers, which increases the sealing efficiency of the guiding means and reduces the leakage over the guiding means.

In a preferred embodiment of the invention, the control sleeve is guided by two separate guiding means and preferably by exactly two guiding means for providing a statically determined system with one degree of freedom in the sliding direction. The guiding means are preferably arranged with a distance to each other of at least the axial extension of one guiding means between the two guiding means. The application of two distant guiding means avoids a relevant tilting of the control sleeve within the static guiding cylinder.

Preferably, the guiding means body is provided with a labyrinth-type compensation slit. This labyrinth-type compensation slit comprises two axially oriented slit parts each extending from both axial end surfaces of the guiding means body and a circumferentially oriented slit part connecting the two axially oriented slit parts. The slit width of the circumferentially oriented slit part is very small, to avoid relevant leakages of the coolant over the guiding means. The slit width of the circumferentially oriented slit part also can be substantially zero. The slit width of the axially oriented slit parts is larger than the slit width of the circumferentially oriented slit part to allow the adaption of the ring-shaped guiding means body to manufacturing inaccuracies and thermal expansion differences between the control sleeve and the static guiding cylinder.

In a preferred embodiment of the invention, the guiding means is embedded in the control sleeve body. For fixing the guiding means the control sleeve body is preferably provided with a ring groove in the outer cylinder surface of the control sleeve body. The guiding means body is radially extending the outer cylinder surface of the control sleeve by at least 20% of the radial thickness of the guiding means body, so that the guiding means is not completely embedded in the control sleeve. The guiding means thereby prevents the control sleeve from contacting the static guiding cylinder. The groove ground surface supports the guiding means radially and the sidewalls of the groove prevent the guiding means from sliding axially along the outer cylinder surface of the control sleeve. The groove sidewalls also increase the sealing efficiency by providing an additional labyrinth-type gap between the guiding means and the groove surfaces in axial direction. The sealing efficiency is ensured by the sidewalls of the groove, even if the guiding means is not completely contacting the groove ground surface resulting from the adaption of the guiding means to the inner cylinder surface of the guiding cylinder.

In a preferred embodiment of the invention, the guiding means is made of a plastic material. Many plastic materials are characterised by good sliding characteristics and a low friction coefficient in combination with metallic materials, which reduces the sliding friction and the resulting wear of the sliding contact surfaces of the components. The good sliding characteristics of a plastic guiding means also results in low hydraulic actuation forces, so that the hydraulic pressure in the hydraulic control chambers is reduced.

Many plastic materials are provided with a high elastic deformability, so that a plastic guiding means easily adapts to the shape and the dimensions of the inner cylinder surface of the static guiding cylinder thereby increasing the guiding quality and the sealing efficiency. As a result, the manufacturing precision of the static guiding cylinder can be reduced to save the production costs of the coolant pump.

The application of a plastic guiding means instead of a cost intensive wear resistant coating in combination with lower manufacturing precision requirements results in a significantly increased cost-efficiency of the manufacturing process of the coolant pump.

In a preferred embodiment of the invention, the slidable control sleeve is made of an aluminium-based material. Aluminium-based materials are characterised by a low density resulting in a low weight, which reduces the weight of the coolant pump. Aluminium-based materials are also provided with a high strength and high form stability. An embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 shows a schematic longitudinal cross section of a variable mechanical automotive coolant pump comprising a control sleeve according to the invention, and figure 2 shows a schematic perspective view of the control sleeve of figure 1.

Fig. 1 shows a variable mechanical automotive coolant pump 10, for example for providing an internal combustion engine with liquid coolant. The coolant pump 10 comprises an impeller wheel 20 being co-rotatably connected to a rotor shaft 30. The rotor shaft 30, for example, is driven by the belt drive of the internal combustion engine. The coolant pump 10 further comprises a non-rotatable and axially slidable control sleeve 40, with a hollow cylindrical control sleeve body 45 comprising two separate plastic guiding means 60,60' defined by a non-closed and ring-shaped guiding means body 61 each. The guiding means body 61 slidably supports the control sleeve 40 within and at a static guiding cylinder 70. The coolant pump 10 also comprises a static inner supporting cylinder 50 guiding the radial inside of the control sleeve 40.

The impeller wheel 20 is arranged within a pumping chamber 25 and comprises a circular disc-type impeller body 22 with a plurality of integrally formed impeller blades 26, which are substantially radially oriented in a fan-type arrangement. The axial front suction side 23 of the impeller wheel 20 is partially covered by a cover ring 28 being co-rotatably connected to the impeller blades 26. At the axial front suction side 23 the cover ring 28 is provided with a cylindrical protrusion 27 defining an axial central inlet for the liquid coolant. The rotating impeller blades 26 suck liquid coolant from the axial front suction side 23 of the pump through the cylindrical protrusion 27 within the cover ring 28. Due to the centrifugal forces, the impeller blades 26 accelerate the liquid coolant radially outwardly. The liquid coolant is discharged through a radial discharge ring-opening 24 defined by the cover ring 28 and the impeller body 22 into the outlet volute 29 circumferentially enclosing the impeller wheel 20.

The axially slidable control sleeve body 45 is provided with two supporting ring grooves 46,46' for radially supporting and axially fixing the non-closed ring-shaped guiding means body 61. The two guiding means 60, 60' guide the control sleeve 40 within the static guiding cylinder 70 and fluidically separate a first hydraulic control chamber 100 and the pumping chamber 25.

The control sleeve 40 is actuated by pressurizing a first hydraulic chamber 100 with pressurized coolant entering through an inlet 102 in the axial end surface 75 of the static guiding cylinder 70, so that a hydraulic pressure force at an axial end surface 101 of the control sleeve 40 is applied. The applied high hydraulic pressure force pushes the hollow-cylindrical control sleeve body 45 in closing direction over the impeller wheel 20, so that the radial discharge ring-opening 24 is closed to hydraulically block the coolant pumping.

The inside of the control sleeve 40 is supported by an inner static supporting cylinder 50 defining a second hydraulic control chamber 105 within the control sleeve body 45. The second hydraulic chamber 105 is sealed by two sealing rings 58,59. One sealing ring 58 is arranged in a corresponding groove 53 at the outer cylinder surface 52 of the inner supporting cylinder 50. The second sealing ring 59 is arranged in a corresponding groove 54 at the inner cylinder surface 49 of the control sleeve body 45. For actuating the control sleeve 40 the second hydraulic control chamber 105 can be pressurized with coolant entering through an inlet 56 connected with an eccentric and axially oriented bore 55 within the supporting cylinder 50 to provide an opposite hydraulic pressure force at a second axial end surface 106 of the control sleeve body 45. This opposite hydraulic pressure force pushes the control sleeve 40 in opposite opening direction for opening the radial discharge ring-opening 24 of the impeller wheel 20.

The hydraulic pressure for actuating the control sleeve 40 is provided by a side channel pump 90 defined by and at the backside of the impeller wheel 20 and by the opposite axial end surface 51 of the inner supporting cylinder 50. The pressurized coolant is flowing through a ring channel 95 between the inner static supporting cylinder 50 and the rotating rotor shaft 32 to two electromagnetic pressure control valves 80,85 being fluidically connected in parallel. The control valves 80,85 regulate the hydraulic pressure within each hydraulic control chamber 100, 105 to adapt the axial position of the control sleeve 40 to the cooling performance requirements of the cooling system. The first pressure control valve 80 fluidically connects the inlet 102 of the first hydraulic control chamber 100 with the ring channel 95 being provided with pressurized coolant from the side channel pump 90. The second pressure control valve 85 fluidically connects the inlet 56 of the second hydraulic control chambers 105 with the ring channel via a bore 55 in the supporting cylinder 50.

Fig.2 shows the schematic perspective view of the control sleeve 40 with the hollow cylindrical control sleeve body 45 and the two guiding means 60 and 60' defined by a non-closed ring-shaped guiding means body 61. The guiding means body 61 is made of a plastic material, for example "iglidur H370". Each guiding means body 61 is arranged within a corresponding supporting groove 46,46' at the outer cylinder surface 42 of the aluminium control sleeve body 45 to radially support the guiding means body 61 and to axially secure the guiding means body 61 against axial displacement. The two guiding means 60,60' are arranged with an axial distance d of about 150% of the axial extension e of the guiding means body 61.

The guiding means body 61 is provided with a labyrinth-type compensation slit 65 comprising two axially oriented slit parts 65,66 and a circumferentially oriented slit part 68. Each axial oriented slit part 65, 66 extends axially from one of the two axial end surfaces of the guiding means body 61. The circumferential oriented slit part 68 is connecting the two axial oriented slit parts 65,66, so that the guiding means body 61 is not completely mechanically closed. The slit width of the axial oriented slit parts 65,66 is larger than the width of the circumferentially oriented slit part 68. The axial oriented slit parts 65,66 allow an adaption of the circumferential dimension of the guiding means body 61 to compensate geometric variations resulting from imprecise manufacturing and thermal expansion between the control sleeve 40 and static guiding cylinder 70. The circumferentially oriented slit part 68 is very small or can be substantially zero to avoid relevant leakages over the guiding means 60,60'. As a result, the mechanically not closed and thereby adaptable guiding means body 61 is, however, closed hydraulically.