Power plants – Pressure fluid source and motor – Pneumatic motor with gas supply or removal device
Patent
1994-06-17
1996-05-14
Ryznic, John E.
Power plants
Pressure fluid source and motor
Pneumatic motor with gas supply or removal device
60411, 60412, 417 12, 417 442, F16D 3102, F04B 4900
Patent
active
055156762
DESCRIPTION:
BRIEF SUMMARY
This application is a Rule 371 of PCT/GB92/02346 filed Dec. 17, 1992.
This invention relates to vacuum pump motor control apparatus and particularly to apparatus for controlling an electrically driven vacuum pump of a motor vehicle. The invention also relates to a method of controlling an electrically driven vacuum pump.
For many years the partial vacuum created in the inlet manifold of a petrol engine has been utilized to exhaust the reservoir of a vacuum brake servo, thereby to provide power assistance for the vehicle brakes. Such a system is simple and extremely reliable.
The vacuum available from the inlet manifold of a petrol engine may however be insufficient to meet brake servo demand in certain conditions of use. Furthermore the vacuum source may also be required for operation of other devices such as exhaust gas recirculation (EGR) valves.
Diesel engines have an unthrottled air supply and thus the partial vacuum in the inlet manifold is only marginally below atmospheric pressure; consequently a useful vacuum source is not available. Accordingly mechanically operated vacuum pumps have been proposed for cars and light trucks equipped with a conventional vacuum brake servo. Such pumps are typically driven from the engine camshaft by for example a follower or a belt.
Vacuum pumps are not required for medium and heavy weight trucks because these vehicles are usually equipped with spring brakes actuated by a high pressure pneumatic control system.
The space available under the bonnet of a car or light truck is usually limited, and the installation of a vacuum pump can cause difficulties if the vehicle design has been optimised for a petrol engined variant. In any event, the difficulty of installing an engine driven pump is exacerbated by the use of overhead camshaft engines because the pump mounting may tend to increase the vehicle bonnet height and reduce access to other parts of the engine. It may also be difficult to arrange adequate lubrication for a mechanically driven pump mounted at the top of an engine.
Electrically driven vacuum pumps are suitable for installation in any convenient space in the engine compartment, and may advantageously be located in an area not subject to extremes of temperature cycling.
Electrically driven vacuum pumps may be used to meet the entire vacuum demand or, in conjunction with the vacuum available from the inlet manifold of a petrol engine, to meet peak demands only.
One problem with conventional vacuum pumps is that they are usually designed to work continuously throughout the speed range of the engine, their performance must thus be specified for the minimum engine speed and thus such pumps take a significant amount of energy to run at higher speeds; this results in an unnecessary increase in vehicle fuel consumption, especially where on a motorway journey of several hundred miles the vehicle driver may only use the brakes once or twice and other vacuum demands are low.
Hitherto vacuum pumps for vehicle installations have been designed for continuous operation and are thus overspecified for the actual service duty. Typically a vacuum pump needs to operate for around 10 seconds in order to exhaust a brake servo reservoir and, as noted above, the pump may be required to operate very infrequently.
According to one aspect of the invention there is provided vacuum pump control apparatus for an electrically driven vacuum pump, the apparatus comprising a pressure switch for indicating a predetermined level of vacuum in a reservoir, said switch having two states, and control means responsive to a first state of said switch indicative of vacuum below said predetermined level to cause the electrical drive of said pump to run at a given speed, and responsive to a second state of said switch indicative of vacuum above said predetermined level to cause said electrical drive to run at a lower speed than said given speed or to stop, said control means further including delay means operable to delay slowing or stopping of said electrical drive in response to said second state of
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Ryznic John E.
WABCO Automotive (UK) Limited
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