GB2363168A

GB2363168A - Engine oil lubricated servo vacuum pump

Info

Publication number: GB2363168A
Application number: GB0013564A
Authority: GB
Inventors: Michael Graham Bilney
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2000-06-05
Filing date: 2000-06-05
Publication date: 2001-12-12
Anticipated expiration: 2020-06-05
Also published as: GB0013564D0; WO2001094794A1; GB2363168B

Abstract

The pump comprises a single diametrically sliding vane 14 vacuum pumping element 10, 12 driven by an electric motor 24 for supplying vacuum 18 to servo assisted vehicle brakes. In order that the pump may run continuously, internal combustion engine lubricating oil is drawn 28 from the engine sump by the pump vacuum, used for pump lubrication and returned with pump exhaust air to the engine sump. Electric pump drive allows the rotational speed and its position within the engine bay to be independent of the engine. Using pump vacuum to suck the oil reduces the load on the engine oil pump, permits use of low pressure lines and prevents line failure interfering with engine lubrication. Power consumption may be reduced by chopping motor voltage supply.

Description

2363168 - -L - VACUUM PUMP

Field of the invention

5 The present invention relates to a vacuum pump principally for automotive vehicle applications.

Background of the invention

10. Vehicles often comprise 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 15 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 any variant of a vehicle fitted with a diesel engi-ne there is no manifold vacuum, because diesel engines operate with wide open throttle and 20 load is varied not by throttling the air intake but by metering the quantity of fuel directly or indirectly injected into the cylinders. 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.

Pumps that are directly driven by the engine have to operate within the same dynamic range of speeds as the engine. In order to enable the brakes to be operated while the vehicle is travelling down a long hill, the displacement 35 of the pump must be sufficiently large to provide an adequate vacuum supply even with the engine operating at idling speed. This however means that the vacuum pump places an unnecessary drag on the engine, when it is operating at high speed. The provision of decoupling means such as a slipping clutch in the drive to the pump would mitigate this problem but would increase cost and reduce 5 reliability. Depending on the layout of the engine compartment, it may also be difficult to find a suitable place to mount such an engine driven pump.

Electrically driven vacuum pumps do not suffer from the 10 same problem as pumps driven by the engine because they can operate at a speed that is independent of the engine speed and they do not need to be mounted near a rotating element of the engine, such as a camshaft or crankshaft pulley. They do however suffer from durability problems in that they 15 have hitherto been designed as sealed self-contained units. The internal lubrication of such pumps presents a problem, which has in the past been addressed by appropriate selection of the materials used for making the pumping elements. Despite the use of self-lubricating materials, the 20 requirement for durability has precluded continuous operation of an electrically driven pump. It has instead been necessary to resort to a costly control system to switch the electrically driven pump on and off to limit its duty cycle while coping with the varying vacuum demand 25 generated by such consumers in the vehicle as the brake servo (also termed a booster).

Object of the invention 30 The present invention seeks therefore to provide a vacuum pump for use in an automotive vehicle that mitigates the problems previously encountered with engine driven vacuum pumps and electrically driven vacuum pumps.

- 3 Summary of the invention

According to the present invention, there is provided a vacuum pump for an automotive vehicle driven by an oil 5 lubricated internal combustion engine, the vacuum pump comprising a pumping element, an electric motor for driving the pumping element, and means for drawing oil for interior lubrication of the vacuum pump from oil used to lubricate the engine of the vehicle.

The invention in its broadest aspect overcomes the problems of the prior art by providing a pump that is electrically driven but which is engine oil lubricated. The pump may therefore be mounted where desired (conventionally,

15 but not essentially, within the vehicle engine compartment) and operated at constant speed but it is neverthelessoil lubricated and can therefore be allowed to operate at all times that the vehicle engine is running without its durability being compromised.

It would be possible for oil to be drawn from a passage in the engine that is pressurised by the engine oil pump and for the oil to be returned from the vacuum pump to the engine sump. This however is not preferred because high 25 pressure hydraulic lines would be needed to connect the vacuum pump to the engine. Furthermore, accidental damage to or disconnection of these lines could interfere with proper lubrication of vital engine components such as crankshaft and camshaft bearings. It is also noted that under such 30 circumstances, the vacuum pump constitutes yet another customer for the oil pump to support and therefore is seen to trespass on the potential capability of the engine lubrication system.

35 Instead, it is preferred to use the vacuum generated by the vacuum pump to draw its own oil directly from the engine sump without assistance from the engine oil pump. In this case, the oil lines to connect the engine to the vacuum pump need not be high pressure lines and their failure would not interfere with engine lubrication in any way. Hence it is advantageous for the pump to be provided with an oil supply 5 connector which is connectable to an engine oil supply pipe and which communicates with a pumping chamber of the vacuum pump by way of one or more passages that serve to distribute oil to internal surfaces of the vacuum pump that are prone to wear.

It is particularly preferred that the vacuum pump should be of the type having a rotor mounted eccentrically within a generally cylindrical housing and having vanes extending radially from the rotor into sealing contact with 15 the inner surface of the housing.

Such vane pumps, when connected to a pressurised oil supply, often use the oil supply to provide the force necessary to maintain the vanes in sealing contact with the 20 inner surface of the housing. It is preferred however not to adopt such an approach as this would call for an oil supply under positive pressure.

Instead, it is preferred for the pumping element to 25 comprise a single vane of constant length the opposite ends of which are both in constant sealing contact with the inner surface of the housing, the vane moving radially relative to the rotor in synchronism with the rotation of the rotor relative to the housing on account of the eccentricity of 30 the rotor.

An advantage of the vacuum pump being located off the engine is that it is capable of running continuously, for as long as the vehicle is in operation. The load on the 35 electric motor will depend on the amount of air pumped but once the desired vacuum pressure has been reached in the brake booster, the current requirement of the motor will be - minimal. If desired, it would at this time be possible to chop or pulse width modulate the voltage supply to the motor to prevent speeding of the motor. For example, a centrifugally operated switch or governor may be used to 5 interrupt the electrical supply to the motor when a certain speed is reached. This may also be feasible electronically by means of a current sensing device which would respond to the reduction in power demand. However, when vacuum is used up by any connected consumer and the load on the motor 10 increases, the response of the pump will be virtually instantaneous as it will not be necessary to bring the motor of the pump up to speed. Consequently, it is not necessary to provide a control system that responds to the vacuum demand nor a large vacuum reservoir to cope with rapid 15 fluctuations in vacuum demand by the connected consumers.

Brief description of the drawings

The invention will now be described further, by way of 20 example, with reference to the accompanying drawings, in which:

Figure 1 is a transverse section through the pumping element of a known single vane vacuum pump, and Figure 2 is a schematic axial section through a motor 25 driven vacuum pump of the invention.

Detailed description of the preferred embodiment

Figure 1 shows a single vane vacuum pump comprising a 30 rotor 10 mounted eccentrically within a housing 12 having an inner surface 16 which is not a right circular cylinder but a geometrically generated 'oblong' form. A single flat vane 14 is slidably mounted diametrically with a close running clearance within the rotor 10 and the shape of the surface 35 16 is such that its opposite ends make sealing contact with the surface 16 in all angular positions of the rotor 10, to form an instantaneous chord to the arc it subtends. The outer surface of the rotor 10 also makes sealing contact with the surface 16 at the six o'clock position as shown in Fig. 1. The pump has an air inlet, or suction port 18 containing an anti-oil migration valve which, for a pump in 5 which the rotor 10 is driven counterclockwise (as represented by the arrow in Figure 1), communicates with the variable volume working chamber defined to the right of the rotor 10. The pump also has an exhaust port 20 that communicates with the working chamber to the left of the 10 rotor as viewed. A non-return valve (shown schematically in Figure 2), which is preferably a reed valve, is arranged in the exhaust port 20.

In operation, as the rotor 10 turns counterclockwise, 15 the volume of the working chamber to the right of the rotor 10 bounded by the rotor 10, the surface 16 and the vane 14 increases and draws air in from the suction port. In the other working chamber, the same air is compressed and forced out of the exhaust port 10 past the non-return valve. Such a 20 pumping element is generally well known and need not therefore be described in further detail in the present context. Indeed, though the described single vane pumping element is preferred, the invention can alternatively be applied to pumps with alternative designs of pumping 25 element.

As shown in Figure 2, the pumping element in the present invention is driven by an electric motor 24. This enables the vacuum pump to be located where desired within 30 the engine compartment and also allows the pump to run at a speed that is independent of the engine speed. However, instead of being a self- contained sealed unit, the vacuum pump is connected to the lubrication circuit of the engine. In particular, a connector 28 is provided for connection to 35 a low pressure oil supply pipe, to draw oil from the engine sump. Within the pump, the oil drawn from the engine sump passes through various passages that ultimately communicate with the vacuum side of the rotor 10. The flow passages may either be intentionally machined grooves as illustrated or they may be clearances inherently present between the stationary and moving components. In this way, the vacuum 5 generated by the pump serves to draw oil from the engine sump into the pump, the oil passing over the bearing of the motor drive shaft 26 and the end surfaces of the rotor 10. The oil will ultimately be atomised into a fine mist carried by the pumped air to lubricate all moving parts of the pump.

The exhausted oil and air mixture is returned to the engine sump through a further connector 20 which in use is connected to the engine sump by a return line. The nonreturn valve 22 is shown schematically in Figure 2 as being 15 a reed valve but other forms of non-return valve (such as a spring biased ball valve) may alternatively be used.

The advantage of the engine oil lubricated electrically driven pump of the invention is that it does not need to be 20 operated intermittently but can be left to run at all times that the engine is in operation. This avoids the need for a control system and for a vacuum reservoir, thereby reducing system cost and weight. The power drawn by the motor when no pumping work is being done is small so that little engine 25 power is wasted in driving the pump. The volumetric flow of the air/oil exhaust ultimately returned to the engine crankcase is also not excessive and will not result in raised crankcase pressure.

30 The power consumption of the motor can be reduced still further by chopping the voltage supply to drive the electric motor 24 with a pulse width modulated supply voltage. This may be achieved by the use of a governor that interrupts the electrical supply to the electric motor 24 each time the 35 vacuum pump speed exceeds a predetermined value.

Claims

A vacuum pump for an automotive vehicle driven by an oil lubricated internal combustion engine, the vacuum 5 pump comprising a pumping element, an electric motor for driving the pumping element, and means for drawing oil for interior lubrication of the vacuum pump from oil used to lubricate the engine of the vehicle.

10
2. A vacuum pump as claimed in claim 1, wherein in operation the vacuum generated by the vacuum pump serves to draw into the vacuum pump oil from the engine.
3. A vacuum pump as claimed in claim 2, wherein the is pump comprises a first connector for an oil supply pipe from the engine, which connector communicates with a pumping chamber of the vacuum pump by way of one or more passages that serve to distribute oil to surfaces of the vacuum pump that move relative to one another and a second connector for 20 an oil return pipe to return a mixture of oil and air to the engine.
4. A vacuum pump as claimed in any preceding claim, wherein the pumping element comprises a rotor mounted 2s eccentrically within a generally cylindrical housing and having vanes extending radially from the rotor into sealing contact with the inner surface of the housing.
S. A vacuum pump as claimed in claim 4, wherein the 30 pumping element comprises a single vane of constant length the opposite ends of which are both in constant sealing contact with the inner surface of the housing and which moves radially relative to the rotor in synchronism with the rotation of the rotor relative to the housing on account of 35 the eccentricity of the rotor.
A vacuum pump as claimed in any preceding claim, wherein the pump is connected in use to be electrically powered continuously at all times that the vehicle engine is in operation.
7. A vacuum pump as claimed in claim 6, wherein the power supply to the electric motor of the pump is modulated to limit the speed of the pump when operating under reduced load. 10
8. A vacuum pump constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.