Variable displacement lubricant pump

The invention is directed to a variable displacement lubricant pump, in particular to a variable displacement vane pump for providing pressurized lubricant.

Vane pumps are well-known for providing pressurized lubricant within a lubrication system of, for example, an internal combustion engine. These vane pumps can be driven directly by the crankshaft of the internal combustion engine, for example by mounting the pump rotor onto the crankshaft.

Because of the co-rotatable connection to the crankshaft of the internal combustion engine, the rotational speed of the vane pump depends on the rotational speed of the crankshaft and not on the required lubrication performance of the internal combustion engine.

The total flow rate of the vane pump is generally proportional to its rotational speed. The flow rate is relatively low at low rotational speed and increases with higher rotational speed. Vane pumps with a variable displacement allow to adapt the pumping flow rate to the requirements of the lubrication system.

A variable displacement vane pump can vary the eccentricity of a radially shiftable control ring enclosing and defining a pumping chamber to thereby adapt the pumping performance independently of the rotational speed of the pump. Examples for these variable displacement lubricant vane pumps are disclosed in WO 2014/141013 Al or in WO 2014/198322 Al.

The variable displacement lubricant pump has generally two operating modes, namely the non-regulation mode and the regulation mode. In the non-regulation mode, the rotational speed is low and eccentricity position of the control ring is at maximum. In the regulation mode at higher rotational speed the eccentricity is varying and is generally decreasing with increasing rotational speed. The regulation mode is initiated at a definite rotational speed, for example at about 30-40% of the maximum rotational speed of the vane pump. In the regulation mode the eccentricity of the control ring is decreasing with increasing rotational speed to limit the flow rate of the vane pump, so that a substantially constant pumping flow rate characteristic with a constant discharging pressure level over the complete rotational speed range of the pump and over the complete operating range of the internal combustion engine is provided.

A disadvantageous effect during the operation of the vane pump is the appearance of eccentricity affecting internal forces. These internal forces result from hydraulic pressure forces in the pumping compartments as a consequence of the volume changes within the pumping compartments during the pump rotation.

These internal forces can unintentionally reduce the eccentricity of the control ring at high rotational speed, causing a significant pressure drop of the discharged lubricant.

It is an object of the invention to provide a cost-effective variable displacement lubricant pump with a reliable discharging pressure level control. This object is achieved by a variable displacement lubricant pump with the features of claim 1.

According to the invention, a variable displacement lubricant pump comprises a pump housing with a first axial sidewall, a pump housing cover with a second opposite axial sidewall and a rotatable rotor hub rotating around a rotational axis. The variable displacement lubricant pump further comprises a non-rotatable and radially shiftable control ring circumferentially enclosing the rotor hub and being arranged with a variable eccentricity with respect to the rotor hub. The shifting direction of the control ring defines an eccentricity axis. The control ring, the rotor hub, the axial sidewall of the pump housing and the axial sidewall of the pump housing cover define a pumping chamber. The variable displacement lubricant pump also comprises a plurality of vanes co-rotating with the rotor hub. The vanes are in sliding contact with the inner cylindrical surface of the control ring, so that the pumping chamber is fluidically separating a plurality of pumping compartments carrying the lubricant through the pumping chamber.

The pumping chamber comprises a suction zone with a suction opening at the axial sidewall of the pump housing and a discharge zone with a discharge opening at the axial sidewall of the pump housing. The suction opening and the discharge opening can alternatively or additionally be provided at the opposite axial sidewall of the pump housing cover. Because of the eccentricity of the control ring, the volumes of the pumping compartments in the suction zone continuously increase in rotational direction and thereby the pressure decreases causing a suction of the lubricant through the suction opening. In the discharge zone, the pumping compartment volumes continuously decrease in rotational direction and thereby the pressure increases causing the discharge of the lubricant through the discharge opening. The pumping chamber is functionally separated by the line of apses into the suction zone and the discharge zone. The apoapsis defines the maximum distance between the outer cylinder surface of the rotor hub and the inner cylinder surface of the control ring, and the periapsis defines the minimum distance. The pumping chamber comprises a neutral zone at the periapsis, which is located in rotational direction behind the discharge opening and before the suction opening. The neutral zone is substantially symmetrically arranged to the line of apses at the periapsis of the pumping chamber. This neutral zone is periodically closed by a passing pumping compartment during the rotation of the rotor hub.

The lower pressure in the suction zone and the higher pressure in the discharge zone cause a resulting internal force as a summation of all hydraulic-induced forces within each pumping compartment in the complete pumping chamber. The direction and the magnitude of this internal force depends on the rotational speed of the pump. The angle of the resulting internal force is varying depending on the rotational speed. The magnitude of the internal force is increasing with increasing rotational speed. At low rotational speed a positive component of this resulting internal force acts in shifting direction of the control ring pushing the control ring into a higher eccentricity position. In the regulation mode at higher rotational speed the direction of the resulting internal force is pivoting, so that the force component acting in shifting direction of the control ring becomes negative. As a result, the negative force component acts in opposite direction and pushes the control ring into a lower eccentricity position.

In particular, the periapsis pumping compartment in the neutral zone contributes a component to the eccentricity-reducing internal force. The periapsis pumping compartment in the neutral zone at the end of the discharging process is pressurized with the discharging pressure, until the fluidic connection with the discharge opening is closed by the following vane, so that the hydraulic pressure within the periapsis pumping compartment being almost completely located in the neutral zone is forcing the control ring into a lower eccentricity position as long as the fluidic connection to the discharging opening is open. Simultaneously, the pumping compartment at the opposite apoapsis side of the pumping chamber is pressurized with the suction pressure. The apoapsis pumping compartment keeps the suction pressure as long as the fluidic connection to the discharge opening is not yet open. Once the leading vane of the apoapsis pumping compartment arrives at the discharge opening, the fluidic connection to the discharge opening is open and the pumping compartment pressure equilibrates to the discharging pressure. The resulting hydraulic pressure force causes a counter force component acting against the force component initiated by the pumping compartment at the periapsis. The pressure equilibration in the compartment at the apoapsis caused by the fluidic connection to the discharge opening occurs with a delay. The delay depends on the rotational speed and increases with higher rotational speed. The direction of the hydraulic pressure force rotates with increasing delay, so that the force component acting in shifting direction is decreasing and becomes smaller than the force component on the opposite side of the pumping chamber at the periapsis. As a result, the internal force component in shifting direction pushes the control ring into a lower eccentricity position causing a discharge pressure drop.

The variable displacement lubricant pump also comprises a switchable pressure relief valve at the neutral zone flu id ica lly connecting the discharge opening and the suction opening via a passing pumping compartment, so that the neutral zone is not periodically closed by the passing pumping compartment anymore. The pressure relief valve comprises a valve opening at the axial sidewall of the pump housing and a valve body defined by the control ring. This pressure relief valve allows a controllable leakage flow between the discharge zone and the suction zone via the periapsis pumping compartment passing the neutral zone. The periapsis pumping compartment in the neutral zone is thereby depressurized and the compartment pressure adapts to the suction pressure. As a result, the hydraulic pressure force in this compartment is significantly reduced, so that no relevant internal force component unintentionally reduces the eccentricity of the control ring.

Because of the pressure relief valve, a small amount of the lubricant is branching-off of the discharged flow causing a reduction of the pumping efficiency. This effect is not useful in the non-regulation mode, because the internal force at low rotational speed is not significantly affecting the eccentricity of the control ring, so that the valve opening of the pressure relief valve needs not to be permanently open.

The valve opening is arranged such that it is covered or not covered depending on the eccentricity value of the control ring. At a maximum eccentricity value at lower rotational speed, the valve opening is completely covered and closed by the control ring to ensure a maximum pump flow rate at low rotational speed.

At a minimum eccentricity value at high rotational speed, the valve opening is completely uncovered, so that the total valve opening area is open. The provided fluidic connection depressurizes the pumping compartment at the periapsis and reduces the internal forces affecting the eccentricity of the control ring.

Preferably the pressure relief valve fluidically connects the suction opening with the periapsis pumping compartment being located in the neutral zone. The valve opening is preferably fluidically extending the suction opening, so that the pressure relief valve allows a fluidic connection of the suction opening with the discharge opening via the pumping compartment passing the neutral zone. Accordingly, the fluidic connection is only open, as long as the periapsis pumping compartment is not completely located within the neutral zone and as long as the periapsis pumping compartment is still fluidically connected to the discharge opening. However, after completely having passed the discharge opening, the periapsis pumping compartment in the neutral zone is fluidically connected to the suction opening, only.

In a preferred embodiment of the invention, the uncovered valve opening area depends on the eccentricity value of the control ring. The valve opening area increases with decreasing eccentricity of the control ring in the regulation mode. As a result, the allowed leakage flow through the valve opening increases with decreasing eccentricity of the control ring and is normally relatively high at higher rotational speed. The leakage flow thereby autonomously adapts to the increasing hydraulic pressure forces in the regulation mode.

In a preferred embodiment of the invention, the valve opening angle is larger than 5% of the neutral zone angle. Referring to the rotational axis of the rotor hub the valve opening angle defines the angular extent of the valve opening. The valve opening angle and the radial position of the valve opening describe the circumferential arc-length of the valve opening with respect to the rotational axis of the rotor hub. Accordingly, the neutral zone angle defines the angular extent of the neutral zone behind the discharge opening and before the suction opening with reference to the rotational axis of the rotor hub. This neutral zone angle depends on the number of vanes or the number of pumping compartments and is generally larger than the pumping compartment angle defined by two adjacent vanes. In a particularly preferred embodiment of the invention, the valve opening angle is larger than 10% of the neutral zone angle, so that the angular extent of the valve opening is at least 1/10 of the angular extent of the neutral zone.

Preferably the valve opening angle is larger than 4°. In a particularly preferred embodiment of the invention the valve opening angle is larger than 7°. Preferably the valve opening angle is smaller than the angle between the opening edge of the suction opening, seen in rotational direction of the rotor, and the eccentricity axis of the control ring.

In a preferred embodiment of the invention, the valve opening is defined by an arc-shaped groove in the axial sidewall of the pump housing. This arc-shaped groove is, for example, machined out of the casted pump housing. Preferably the arc-shaped groove is connected to the suction opening. The arc-shaped groove is preferably concentrically arranged with respect to the rotor hub. The nominal radius of the centreline of the preferably circular arc-shaped groove is substantially equal to the radius of the inner cylinder surface of the control ring

In a preferred embodiment of the invention, the arc-shaped groove is provided with a substantially constant cross-sectional area of 0.5-5.0 mm ² . Preferably, the depth of the groove is significantly lower than the radial width of the groove. For example, the depth of the groove can be 0.5 mm and the corresponding width of the groove can be 5 mm. The small cross-section of the groove provides a throttling effect to reduce the leakage flow through the pressure relief valve.

Alternatively, the valve opening can also be defined by a linear groove. This linear groove is preferably arranged in a circle chord-type orientation with respect to an auxiliary circle being concentrically arranged to the rotational axis of the rotor hub.

In a further embodiment of the invention, the vane pump is provided with a second separate pressure relief valve comprising a separate valve opening at the axial sidewall of the pump housing cover. The functionality and the features of this pressure relief valve are identical with the first valve at the axial sidewall of the pump housing. With a second valve, the cross-sectional area of each groove can be reduced to improve the throttling effect of the groove shape, but without affecting the total valve opening area. In addition, a second valve improves the reliability, if one of the grooves is blocked, for example, by pollution with particles.

With the pressure relief valve the pressure conditions within the pumping chamber and especially the pressure conditions within the periapsis pumping compartment in the neutral zone are changed such that no relevant internal hydraulic pressure force component is pushing the control ring into a lower eccentricity position. The loss of the discharged lubricant flowing through the pressure relief valve is substantially lower than the losses caused by the pressure drop resulting from the reduced eccentricity, so that the total flow rate at higher rotational speed is generally significantly increased. Further, the extended suction opening increases the total suction volume of the vane pump at higher rotational speed, so that the discharged flow rate of the pump is additionally increased.

An embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 shows a total schematic cross-sectional view of a variable displacement lubricant pump with a pressure relief valve according to the invention at a minimum eccentricity value with an open pressure relief valve, figure 2a shows an enlarged schematic cross-sectional view of the variable displacement lubricant pump of figure 1 at a maximum eccentricity value with a closed pressure relief valve, figure 2b shows an enlarged schematic cross-sectional view of the variable displacement lubricant pump of figure 1 at a minimum eccentricity value with an open pressure relief valve, and figure 3 shows a schematic longitudinal sectional view through the open pressure relief valve of the variable displacement lubricant pump of figure 1 without the control ring.

Figure 1, 2a and 2b show a variable displacement lubricant pump comprising a pump housing 12 with an axial sidewall 13, a rotatable rotor hub 35, which rotates around a rotational axis rA, a non-rotatable and linearly slidable control ring 15 and a not shown pump housing cover 16 with an axial sidewall 17, which is shown in figure 3 only. The control ring 15 is arranged linearly slidable to vary the eccentricity e of an inner cylinder surface 14 of the control ring 15 with respect to the rotatable rotor hub 35. The sliding direction defines an eccentricity axis eA. One side of the control ring 15 is pushed by a spring 60 being supported at the inner side of the pump housing 12 to force the control ring 15 into a maximum eccentricity position eVmax. On the opposite side of the control ring 15, the control ring 15 and the pump housing 12 define a hydraulic control chamber 70. The control chamber 70 can be pressurized, for example, by pressurized lubricant to force the control ring 15 against the spring force into a lower eccentricity position or into a minimum eccentricity position eVmin. The variable displacement lubricant pump 10 further comprises a pumping chamber 25 defined by the inner cylinder surface 14 of the control ring 15, an outer cylinder surface 36 of the rotor hub 35, the first axial sidewall 13 of the pump housing 12 and the second axial sidewall 17 of the pump housing cover 16. The variable displacement lubricant pump 10 also comprises, for example nine radially oriented vanes 30 being co-rotatably connected to the rotor hub, each vane 30 being guided linearly slidable within a corresponding and radially oriented guiding groove 38 in the rotor hub 35. The vanes 30 are proximally supported by a circular spring ring 75 pushing the vanes 30 radially outwards, so that the vanes 30 are distally in sliding contact with the inner cylinder surface 14 of the control ring 15. The vanes 30 fluidically separate the pumping chamber 25 into, for example nine pumping compartments 40 rotating within the pumping chamber 25.

The pumping chamber 25 has a suction zone S with a suction opening 18 at the axial sidewall 13 of the pump housing 12 and has a discharge zone D with a discharge opening 19 at the axial sidewall 13 of the pump housing 12. The pumping chamber 25 also defines a neutral zone N, which is located, seen in rotational direction, behind the discharge opening 19 and before the suction opening 18. The angular extent of the neutral zone N is defined by a neutral zone angle B. The neutral zone angle B is marginally larger than the compartment angle C defined by two adjacent vanes 30, so that the neutral zone N is periodically closed by a passing periapsis pumping compartment 40'. In this embodiment the variable displacement lubricant pump 10 comprises nine pumping compartments 40 with a compartment angle of 40° each. The number of vanes 30 can alternatively be more or less than nine. In the suction zone S, the volume of each pumping compartment 40 continuously increases to thereby suck-in the lubricant through the suction opening 18. In the discharge zone D, the volume of each pumping compartment 40 continuously decreases to thereby discharge the lubricant through the discharge opening 19.

The neutral zone N is provided with a switchable pressure relief valve 50 comprising a valve opening 52 defined by an arc-shaped groove 55 at the axial sidewall 13 of the pump housing 12 and comprising a valve body 56 defined by the control ring 15. The arc-shaped groove 55 is fluidically connected to the suction opening 18 and is thereby extending from an opening edge 18' of the suction opening 18 in counter-rotational direction of the rotor hub 35. The angular extent of the arc-shaped groove 55 referring to the connecting point with the suction opening 18 has a valve opening angle b, which is marginally smaller than the angle D between the eccentricity axis eA and the opening edge 18' of the suction opening 18. According to the compartment angle of 40°, the valve opening angle b can be for example 18°. The radial width w of the arc-shaped groove 55 is, for example 5 mm and the depth t is, for example 0.5 mm.

The variable displacement lubricant pump 10 operates in two operating modes namely the non-regulation mode and the regulation mode. In the non-regulation mode, the eccentricity value eV of the control ring 15 is at maximum eccentricity eVmax. In the regulation mode the control ring 15 is at a non-maximum eccentricity value eVn and the eccentricity value eV varies and decreases with increasing rotational speed to the minimum eccentricity value eVmin.

In the non-regulation mode at lower rotational speed the control ring 15 is at a maximum eccentricity value eVmax of, for example 3.1 mm, so that the arc-shaped groove 55 is completely covered by the control ring 15 and the pressure relief valve 50 is thereby closed, as shown in figure 2a.

Figure 1 and figure 2b show the variable displacement lubricant pump 10 in the regulation mode. The control ring 15 is at a minimum eccentricity position eVmin of, for example 0.1 mm. In this eccentricity position, the pressure relief valve 50 is completely open and the valve opening 52 defined by the arc-shaped groove 55 is not at all covered by the control ring 15. In the regulation mode, the valve opening area 53 depends on the eccentricity value eV and the valve opening area 53 increases with increasing rotational speed.

The open pressure relief valve 50 thereby provides a fluidic connection between the discharge opening 19 and the suction opening 18 before the following vane 30a of the periapsis pumping compartment 40' arrives at the neutral zone N and before the leading vane 30b arrives at the actual suction opening 18, as shown in figure 3. The neutral zone N is not completely closed by the passing periapsis pumping compartment 40'. The resulting leakage flow LF is bypassing the leading vane 30b and thereby causes a pressure relief of the periapsis pumping compartment 40' in the neutral zone N reducing the pumping compartment pressure from discharge pressure to approximately suction pressure. The second pressure relief valve 50' additionally reduces the pumping compartment pressure by allowing a second leakage flow LF' bypassing the leading vane 30b through the valve opening 54.

Because of the variable valve opening area 53, the leakage flow LF autonomously adapts to the increasing hydraulic pressure forces. As a result, the lower hydraulic pressure in the periapsis pumping compartment 40' passing the neutral zone N reduces the resulting internal force component acting in sliding direction of the control ring 15, so that the internal force component is not forcing the control ring 15 into a lower eccentricity position.