Dual-voltage control for an electrical load

Abstract: In one embodiment of the present invention, a daytime running lamp (DRL) system for a motor vehicle includes a switchable connection from the headlamps (42,44) of the vehicle to the neutral connection (18) of the vehicle's alternator (10). Compared with the full system voltage of the vehicle, the neutral connection (18) of the alternator (10) is a lower-voltage source which can drive the headlamps (42,44) at reduced brightness. Such reduced brightness is a typical characteristic of DRL systems. The system disclosed herein can be more cost-effective and provide greater energy efficiency than alternative DRL systems.

Description: The present invention relates to electrical systems having dual-voltage control for an electrical load, according the preamble of claim 1. A feature which is increasingly provided on motor vehicles is daytime running lamps (DRL). In a vehicle with DRL, the headlamps of the vehicle are normally illuminated when the vehicle's engine is running. This illumination is generally with reduced brightness with respect to the full brightness of the headlamps. In a DRL system, manually turning on the vehicle's headlamps will override the DRL system and provide full-brightness illumination of the headlamps. Further, a manual override function is frequently provided such that the vehicle can be idled without the DRL system turning on the headlamps. This manual override function is sometimes provided by the driver of the vehicle setting the vehicle's parking brake. A challenge in the design of DRL systems is providing the reduced illumination intensity of the headlamps. A number of ways to do this have been proposed. In one, a dropping resistor is selectively inserted into the headlamp feed circuit when DRL illuminates the headlamps. This dropping resistor provides the reduced-brightness illumination of the headlamps which is characteristic of DRL systems. In another DRL configuration, an electronic module pulse-width-modulates power supplied for illumination of the headlamps. When the headlamps are illuminated in DRL mode, the module provides a voltage of reduced duty cycle. The headlamps thus are illuminated with reduced brightness. In yet another DRL configuration, the headlamps are switchably connected in series when illuminated in DRL mode. This series connection, as opposed to the normal parallel connection of the headlamps, provides reduced illumination intensity of the headlamps. Each of the proposed designs detailed above, although effective in providing a DRL function, has shortcomings. The dropping resistor design can waste a substantial amount of electrical energy. Further, the pulse-width-modulation design and the headlamps-in-series design are expensive designs, each having an electronic module for controlling the DRL function. US-3,706,005 discloses an electrical system according the preamble of claim 1 comprising a polyphase alternator having a first output connection from only one phase winding of the alternator and a second output with an average voltage greater than an average voltage at said first output connection; an electrical load in the form of a motor vehicle headlamp; and first switching means for switchably coupling and decoupling said electrical load to said output of said alternator. The present invention provides an electrical system comprising an electrical system comprising a polyphase alternator having a first output connection and having a second output with an average voltage greater than an average voltage at said first output connection; an electrical load in the form of a motor vehicle headlamp; and first switching means for switchably coupling and decoupling said electrical load to said output of said alternator; characterised by said first output connection being a neutral connection; second switching means responsive to said first switching means for coupling said neutral connection of said alternator to said electrical load if said output of said alternator is decoupled from said electrical load by said first switching means; a parking brake switch; and third switching means responsive to said parking brake switch for coupling and decoupling said electrical load to said neutral connection in response of said parking brake switch. Daytime running lamp systems embodying the present invention can be more energy efficient and cost effective than alternative daytime running lamp systems. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an electrical schematic of a portion of an automotive electrical system according to one embodiment of the present invention. Referring to Figure 1, a portion of an automotive electrical system according to one embodiment of the present invention will be described. The system includes an alternator 10. Alternator 10 includes three-phase stator windings 12, 14 and 16, which generate three-phase alternating current (AC) power. Stator windings 12, 14 and 16 are coupled together at a neutral connection 18. Alternator 10 also includes rectifier 20. Rectifier 20 includes four pairs of diodes (22A and 22B, 24A and 24B, 26A and 26B, and 28A and 28B). Stator winding 12 is coupled between diodes 22A and 22B, stator winding 14 is coupled between diodes 24A and 24B, and stator winding 16 is coupled between diodes 26A and 26B. These connections provide rectification of the three-phase power generated in stator windings 12, 14 and 16 such that at output 30, direct-current (DC) power is provided. Diodes 28A and 28B form a fourth pair of diodes which is only present in some prior-art alternator rectifiers. Neutral connection 18 is coupled between these diodes 28A and 28B. This fourth pair of diodes rectifies a third-harmonic voltage component which is present at neutral connection 18, providing increased power output from alternator 10. This increased power output comes at the cost of providing diodes 28A and 28B. Among the electrical loads coupled to output 30 of alternator 10 is battery 32, which is charged by current provided by alternator 10. Coupled to output 30 of alternator 10 is headlamp switch 34. As can be seen, headlamp switch 34 has three positions. In the OFF position, headlamps and parking lamps of the vehicle are off. In the PARK position, only parking lamps are on. (The connection from the PARK position of headlamp switch 34 to the parking lamps is conventional and will therefore not be shown here for clarity of presentation.) In the HEAD position of headlamp switch 34, the headlamps of the vehicle are powered. (Typically, the parking lamps are powered as well.) When headlamp switch 34 is in the HEAD position, headlamp switch 34 provides power to high/low beam selector switch 36. When high/low beam selector switch 36 is in the LO position, high/low beam selector switch 36 provides power to low beam filaments 38 and 40 of headlamps 42 and 44. When high/low beam selector switch 36 is in the HI position, high/low beam selector switch 36 provides power to high beam filaments 46 and 48 of headlamps 42 and 44. High beam filaments 46 and 48 are coupled to neutral connection 18 of alternator 10 via normally closed contacts 50 and 52 of relays R1 and R2, respectively. It should be noted that the neutral connection of an alternator is not generally provided for external connection. An output 53 of alternator 10, to which neutral connection 18 is coupled, would need to be added should a particular alternator not already have external access to neutral connection 18. The coil 54 of relay R1 is coupled such that coil 54 is energised (opening contact 50 of relay R1) if headlamp switch 34 is in the HEAD position. Coil 56 of relay R2 is coupled such that when the parking brake of the vehicle is applied, as sensed by the closing of parking brake switch 58, coil 56 is energised. This opens contact 52 of relay R2. The system illustrated in Figure 1 provides a cost-effective daytime running lamp (DRL) feature, whose function is as follows. When headlamp switch 34 is not in the HEAD position, indicating that the driver of the vehicle is not affirmatively selecting his headlamps to be on, coil 54 of relay R1 is not energised. Thus, normally closed contact 50 is closed. Further, if the parking brake of the vehicle is not applied, parking brake switch 58 will be open. Coil 56 of relay R2 will thus not be energised, leaving contact 52 of relay R2 closed. Thus, high beam filaments 46 and 48 of headlamps 42 and 44 will be coupled to neutral connection 18 of alternator 10. It has been demonstrated in a particular alternator 10 tested by the inventors that when alternator 10 is operating, neutral connection 18 has a AC voltage with an average value of about 6.7 volts. This is in contrast to the typical DC voltage at output 30 of alternator 10, which is around 14 volts. Thus, by connecting high-beam filaments 46 and 48 to neutral connection 18, those filaments will operate at reduced brightness when compared to connection of these filaments to output 30 of alternator 10. This reduced brightness provides a DRL feature. The reduced brightness DRL feature is active at all times when the engine of the vehicle is running, except when headlamp switch 34 is in HEAD position or when the parking brake switch 58 is closed. Either of these events will open a normally closed contact 50 or 52, decoupling high beam filaments 46 and 48 from neutral connection 18. Headlamp switch 34 being in the HEAD position indicates that the driver wishes full-function headlamps. The overriding feature provided when parking brake switch 58 is closed provides the driver a method to override his daytime running lights feature if he wishes to idle his vehicle without his headlamps on. Headlamp switch 34 is a "high-current" switch. That is, headlamp switch 34 carries the current from output 30 of alternator 10 to headlamps 42 and 44. However, other known headlamp control systems employ a "low-current" headlamp switch which is an input to an electronic controller. The electronic controller has a high-current output to drive the headlamps (that is, to couple the headlamps to output 30 of alternator 10). In such a system, relay coil 54 of relay R1 can be coupled in either the "low-current" portion of the system (that is, coupled to the headlamp switch) or coupled in the "high-current" portion of the system (that is, coupled at the output side of the electronic controller). It should be noted that while relays R1 and R2 are described herein as electromechanical relays, those skilled in the art recognise that solid-state relays can be employed in place of either of relays Rl and R2. Such solid-state relays typically include field-effect transistors (FETs) or other semiconductor devices.

Claims: An electrical system comprising: a polyphase alternator (10) having a first output connection (18) and having a second output (30) with an average voltage greater than an average voltage at said first output connection; an electrical load in the form of a motor vehicle headlamp (42,44); and first switching means (34) for switchably coupling and decoupling said electrical load (42,44) to said second output (30) of said alternator (10) ; characterised by said first output connection (18) being a neutral connection; second switching means (50,54) responsive to said first switching means (34) for coupling said neutral connection (18) of said alternator (10) to said electrical load (42,44) if said second output of said alternator (10) is decoupled from said electrical load (42,44) by said first switching means (34); a parking brake switch (58); and third switching means (52,56) responsive to said parking brake switch (58) for coupling and decoupling said electrical load (42,42) to said neutral connection (18) in response to positions of said parking brake switch (58). An electrical system as claimed in Claim 1, wherein said headlamp comprises a first filament and a second filament, said first switching means couples and decouples said first filament to said second output of said alternator, and said second switching means couples and decouples said neutral connection of said alternator to said second filament. An electrical system as claimed in Claim 2, wherein said first switching means comprises a high-current headlamp switch. An electrical system as claimed in any preceding claim, wherein the second switching means is a first relay having a contact responsive to said headlamp switch such that said contact couples said neutral connection of said alternator to said headlamp when said headlamp switch decouples said output of said alternator from said headlamp. An electrical system as claimed in any preceding claim, wherein the third switching means is a second relay having a contact responsive to a position of said parking brake switch and in series with said contact of said first relay. An electrical system as claimed in any one of the preceding claims, wherein said second output of said alternator is a direct-current output of a rectifier which rectifies alternating-current power produced by said alternator.

Inventors: BUSH THOMAS ALEXANDER, DEOL SATVIR SINGH, NASSER AHMAD MUSTAPHA, BUSH, THOMAS ALEXANDER, DEOL, SATVIR SINGH, NASSER, AHMAD MUSTAPHA
Applicants: FORD MOTOR CO, FORD MOTOR COMPANY
Application year: 1996
Main classification: B60Q1
IPC codes: B60R16