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Check valve for a vacuum pump

Check valve for a vacuum pump description/claims

The present invention relates to vacuum pumps having forced oil lubrication principally for automotive vehicle applications and in particular to a check valve for such a vacuum pump.

Vehicles often have components that are vacuum operated, an important example being servo-assisted brakes. In a vehicle having a conventional spark-ignition engine, a partial vacuum is present in the part of the intake manifold downstream of the main throttle and no special steps need to be taken to provide a vacuum source. There are, however, several cases when manifold vacuum cannot be relied upon as a vacuum source. For example, in diesel engines there is little or no manifold vacuum, because load is varied not by throttling the air intake but by metering the quantity of fuel directly or indirectly injected into the cylinders. For emission control purposes, it is desirable to provide exhaust gas recirculation into the intake gases of a diesel engine. Thus, modern diesels are equipped with a throttle to cause a vacuum in the intake to allow a portion of exhaust gases to flow into the intake. Even so, the pressure depression needed to obtain the desired exhaust gas flow is less than what is encountered in a spark-ignition engine in which the throttle is used for load control. Thus, it is often insufficient to operate accessories. Likewise, electrically driven vehicles and vehicles with hybrid drive systems may not always have a vacuum source available at all times.

For these reasons, vacuum pumps for use in automotive vehicles have been proposed previously and these fall into two categories, namely engine driven pumps and electrically driven pumps.

It is known to provide an oil check valve to prevent the backflow of oil from the vacuum pump to the oil supply from the engine. Such a check valve is shown in FIG. 6 of the accompanying drawing.

The check valve has a housing 2 supported by a shaft 3 connected to a rotor of a sliding vane vacuum pump. A positive oil supply passage 4 communicates with a valve chamber 6 defined by the housing 2 when a valve member in the form of a check valve ball 7 is moved away from its seat. A spring 8 located in a spring housing 9 is used to bias the check valve ball 7 against a seat as shown in FIG. 6. An oil inlet passage 5 is also in fluid communication with the valve chamber 6.

The oil inlet passage 5 supplies oil to interior components of the vacuum pump and so, when the pump is operating, is maintained at a pump operating vacuum, e.g., approximately 20 kPa gauge pressure. The 20 kPa gauge vacuum is given by way of example and not intended to be limiting.

Therefore during normal running of the vacuum pump the check valve ball is subject to the positive pressure P1 of the oil feed in the oil supply passage 4 to one side and the pump operating vacuum in the inlet supply passage 5 to the other side. This differential pressure is sufficient to move the valve check ball 7 away from its seat to permit oil to flow to the interior of the vacuum pump. The arrangement of the check valve is such that such when such pressure differential is sufficient to lift the valve check ball 7 from its seat, as the vacuum pump starts to operate, oil can be drawn in through the inlet passage 5 even when the pressure in the oil supply passage is at or close to atmospheric pressure.

It is a problem with this arrangement that even after the pump is stopped, the pressure in the oil inlet passage 5 can remain at pump operating vacuum for a long time. Therefore, even when the oil feed pressure P1 in the oil supply passage 4 drops to zero, the check valve ball 7 could still be in a partially open position for some time due to the pump operating vacuum in the inlet passage 5. Consequently, oil can be drawn into the vacuum pump for a long period of time causing hydraulic lock within the vacuum pump. The next time the vacuum pump is started, damage to the vacuum pump will often occur.

According to an aspect of the invention there is provided a check valve for a vacuum pump having a rotary pumping element connected to an oil supply wherein the check valve is rotatable with the rotary pumping element and has a valve member moved against the action of a spring by centrifugal force when the rotary pumping element rotates so as to selectively open an oil inlet passage to the vacuum pump.

The valve member may have an end face and is moved against the action of the spring by a combination of centrifugal force and the oil supply pressure acting upon the end face of the valve member.

The rotary pumping element may be rotatable about an axis of rotation and the check valve may further comprise a valve housing rotatable about the axis of rotation, the valve member is slidingly supported in a valve chamber formed by the valve housing so as to be slideable along a slide axis, the spring biases the valve member into a closed position where it closes off the oil inlet passage to the vacuum pump and the slide axis of the check valve is inclined relative to the axis of rotation of the rotary pumping element.

Preferably, the slide axis may be arranged at a right angle with respect to the axis of rotation so as to maximise the centrifugal force on the valve member.

The spring may react between an end cap fastened to the valve housing and the valve member.

The valve member may have an end face and a tubular body portion extending away from the end face and the spring may be located within the tubular body portion of the valve member.

The end cap may have a vent passage formed therein so that the interior of the tubular body portion of the valve member is maintained at atmospheric pressure.

The oil supply may be connected to the valve chamber by an oil supply passage and, when the valve member is in the closed position, the valve chamber may remain in fluid communication with the oil supply passage.

A second end cap may be fastened to the valve housing to provide an end stop for the valve member thereby determining the closed position of the valve member.

According to a second aspect of the invention there is provided a vacuum pump for a motor vehicle driven by an oil lubricated internal combustion engine, the vacuum pump comprising a rotary pumping element, a drive means for driving the rotary pumping element, an oil supply from the engine for interior lubrication of the vacuum pump and a check valve constructed in accordance with said first aspect of the invention.

The rotary pumping element may comprise a rotor and at least one sliding vane.

The drive means may comprises one of a chain drive from the engine of the motor vehicle, a belt drive from the engine of the motor vehicle, a hydraulic motor, a pneumatic motor and an electric motor.

• Provisional Patent
• Utility Patent

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