Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Patent
1991-03-08
1993-12-21
Pellinen, A. D.
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
320 33, 324433, H02H 718, H02J 700
Patent
active
052723801
DESCRIPTION:
BRIEF SUMMARY
The invention relates to electrical supply control systems for motor vehicles and is concerned particularly with safeguarding an electrical storage battery in a vehicle from excessive discharge.
There is an increasing tendency to equip motor vehicles with electrically operated facilities which take power from the vehicle battery with the vehicle unattended. Typical examples are memories for preferred positions of electrically adjustable devices such as seats and mirrors and memories for radio tuning. Other examples are clocks and alarm systems. In addition to these facilities which can not normally be isolated from the electrical supply under the control of a driver, other electrical facilities may be left on accidentally when a vehicle is unattended or fail to a condition where they draw current inadvertently.
As a result of this drain on the battery, a battery which is in poor condition or which has a low state of charge may become discharged when the vehicle is left for a few hours to such an extent that the battery is unable to start the engine. In a typical installation with a nominal 12 volt battery, the normal quiescent battery potential is approximately 12.7 volts. The battery is unlikely to be able to start the vehicle engine in favourable conditions at voltages below 10.5 volts, but in adverse conditions such as low temperatures this minimum voltage may rise to 11.5 or even 11.75 volts.
Another problem which can arise even with a well charged battery in good condition if it is left for several days is that the battery can become discharged to the level where the battery deteriorates significantly by sulphation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a control system for the electrical supply of a motor vehicle which reduces the risk of excessive battery discharge.
In accordance with the present invention there is provided a control system for the electrical supply of a motor vehicle, the motor vehicle incorporating an electrical storage battery and electrical system including at least one facility which normally consumes current when the vehicle is left unattended and driver operable facilities such that a first switching operation normally occurs when the driver leaves the vehicle and a second switching operation normally occurs when the driver returns to the vehicle; the control system comprising means for generating a first relatively low reference voltage and a second relatively high reference voltage, each selected to conform to a pre-selected battery condition; a first timing means operable for a relatively short period and a second timing means operable for a relatively long period; means responsive to said first switching operation to start the timers, first voltage comparison means arranged to compare the actual battery voltage with the first reference voltage after said relatively short period and thereafter to provide a low battery signal if the actual voltage is below the first reference voltage; second voltage comparison means arranged to compare actual battery voltage with the second reference voltage after said relatively long period and thereafter to provide a low battery signal if the actual voltage is below the second reference voltage; means for isolating the battery from the electrical system in response to either low battery signal and means for reconnecting the battery to the electrical system in response to said second switching operation.
With such an arrangement, electrical units such as memory devices remain effective when the vehicle is left standing provided that the battery is in an appropriate condition. If battery voltage drops to a predetermined level selected as the limit of acceptability, the battery is isolated from its loads with a view to preventing further discharge. By providing two different reference battery voltage levels at which the battery may be isolated and making these reference voltages effective after different time delays the system can be set so that good battery protection is provided in conjunction with a
REFERENCES:
patent: 3395288 (1968-07-01), Von Brimer
patent: 3522481 (1970-08-01), Terzic
patent: 3852732 (1974-12-01), Yorksie et al.
patent: 4080560 (1978-03-01), Abert
patent: 4493001 (1985-01-01), Sheldrake
Elms Richard
Jaguar Cars Limited
Pellinen A. D.
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