The present invention relates to a generator for use in a motor vehicle and to an electrical supply circuit of a motor vehicle incorporating such a generator.

It is usual for the loads of a motor vehicle to rely on a regulated DC supply. The supply is typically 12 v. though in certain applications such as trucks the voltage may be higher. The generator is usually an alternator in modern vehicles as this can meet the electrical load requirements at all engine operating speeds and as all the loads requi re a regulated DC supply, it is essential that the rectifying diodes and the regulator be designed to withstand the maximum current load. This leads to a requirement for a larger storage battery, as this forms an essential component of the regulating circuit. As a result, such design of the supply circuit of a motor vehicle has led to increased component cost. Furthermore, in the case of certain loads, examples of which will be described below, it i s not essential to employ a rectified supply nor even a regulated supply and the energy losses associated with rectif ication and regulation cause a reducti on i n ef f i c iency and increased fue l consumption.

The present invention seeks to mitigate the foregoing disad¬ vantages of the prior art and provides in one aspect a supply circuit f or an engi ne dr iven vehi cle, compri s i ng an alternator driven by the engine, a rectif ier for rectifying the current output of the alternator, a voltage regulator for regulating the rectif ied output current without regulating the current in the f ield windings of the alternator, a battery charged by the rectified and regulated current and supplying selected loads of the vehicle with regulated DC current, and a supply circuit for feeding unregulated AC current di rectly f rom the alternator to further selected loads of the vehicle.

Usually, the alternator will be a three phase alternator, in the interest of efficiency and the regulator and the loads will also be three phase.

The invention finds particular application in the case of a motor vehicle having a catalytic converter for reducing exhaust emissions. Such a vehicle employs a catalyst of which the working life is severely impaired by poisoning if allowed to operate at low temperatures. The catalyst is usually heated by the exhaust gases but under certain conditions, notably during over-running of the engine, the catalyst temperature falls at a time when the exhaust emissions are particularly damaging to the catalyst.

According to a preferred feature of the invention, it is proposed to use the unregulated AC supply from the alternator to heat the catalyst electrically especially during periods of deceleration and idling in order to stabilise its tempera¬ ture over its full operating range.

Such a heater is frequency insensitive and furthermore requires the consumption of electrical power only when the engine load is minimal. Thus, it lends itself particularly well to being driven directly from the unregulated AC side of the alternator. No energy is wasted in converting or regulating the heating current and the efficiency of the heating current is maximised. The heating current cannot damage the heating elements because it does not suffice of itself to raise the catalyst temperature to the operating temperature and is being used only to supplement the heating effect of the exhaust gases. The lack of regulation is therefore unimportant the essential requirement being in this case to heat the element as rapidly as possible.

The power consumed by the catalyst heater during over-running results in a breaking force being applied to the engine but this of course is desirable under such conditions as it reduces wear on the brakes. The waste kinetic energy of the

vehicle is being converted into electrical energy by the alternator in order to improve the operation of the exhaust catalyst.

It is further possible to use the unregulated AC supply to power other heaters used at diverse places in a motor vehicle, in particular to heat the passenger compartment and to heat window areas. The invention for example permits rapid demisting of front and rear windshields. The heaters powered from the unregulated AC circuit may be resistive elements which are either used to heat an air supply or are themselves incorporated in the glass. In either event, there is no risk of overheating the elements and the lack of regulation of the AC supply is of no significance.

The lights of a motor vehicle are also heating elements which operate satisfactorily without regulation of the power supply from which they are powered. It will be appreciated that the alternator will always be under load, if only from the DC circuit which will power the ignition and other circuits such are radios which require a regulated DC supply, with the result that within the range of operating speeds of the alternator, the variations of the AC voltage will not be excessive. It is therefore possible to achieve adequate illumination levels at low engine speeds without damaging the filaments at higher engine speeds.

It is seen therefore that the serious loads on the electrical systems can run satisfactorily from the AC unregulated supply and that the DC current requirements may be reduced significantly, permitting the use of a smaller battery capable of meeting the load requirement when the engine is turned off and the use of a smaller regulator and rectifier to charge the battery. The rectification diodes used in a conventional alternator are responsible for a high proportion of the cost and of the bulk of the alternator. The invention can therefore result in simplification of the construction of the alternator and a reduction in its cost.

It is a further advantage of the invention that when the engine i s not running the high current loads normally supplied by the battery are automatically switched off. The risk of eletrically started fire in the event of a collision is therefore reduced.

Although resistive loads only have been di scussed above, it is foreseen that the AC unregulated supply may be used to power other devi ces and loads in a motor vehi cle i f appropriately designed. It is for example conceivable that three phase motors may be used for various purposes, such as in window winding mechanisms, seat adjustment motors, air conditioning compressors, heater fans and so forth.

The fact that the speed of such motors may depend upon the prevailing engine speed may be unimportant in certain appli- cations. Alternatively, constant speed drives may be employed though currently their cost would be prohibitive.

It is a particular advantage of the invention, that power may be taken f rom the alternator at lower engine speeds than is carried out in present practice. Apart from enabling large loads such as the catalyst heater to be powered at such engine speeds , thi s results i n a reaction f orce bei ng experienced by the engine crank and this helps prevent the creep which one often encounters with automatic transmissions when the engine is idling. The load on the crank can also be beneficial when tuning the engine.

According to a second aspect of the invention, there is provided a three phase alternator having a recti fying arrangement, there bei ng provided two sets of output terminals the first set connected to the rectified DC supply and the second set being directly connected to the phase windings of the alternator.

The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a circuit diagram of a vehicle supply incorporating a regulated DC circuit and an unregulated AC circuit.

Referring to the drawing, an alternator 2 has an armature represented schematically at 4, and a field winding 6. The armature winding is three phase. A star winding may be used as an alternative to the illustrated delta winding. The field winding 6 is supplied with unregulated DC from the battery though as described later the DC supply to the field winding 6 may be switched.

The three phase outputs A, B and C are available directly and unrectified at terminals 8, 10 and 12, respectively. The three phase outputs A, B and C are also connected to a rectifying bridge arrangement 14. Each phase output is connected to the junction between a respective pair of diodes such as 16 and 18, the six diodes being arranged to produce a full-wave rectified output at terminals 20 and 22. The output of the bridge at terminal 22 is also connected to a terminal 24 to serve as a neutral N for the three phase supply. A capacitor 26 is used to smooth the rectified DC output.

The generator is installed in a motor vehicle (not shown) to be driven by the vehicle's engine. Terminals 20 and 22 are connected to a voltage regulator, not shown, which regulates the voltage and supplied DC for charging a battery and to those circuits, such as parking lights, which require power when the engine is not running. The generator charges the battery and powers these circuits when the engine is running, but when the engine is stopped, the circuits are powered by the battery. This is the conventional arrangement and thus the battery is kept charged to operate the starter motor amongst other loads.

The voltage regulator cannot be a conventional regulator controlling the current in the field winding 6 as this would reduce the AC supply as well as the DC supply. The regulator of the DC supply is required to prevent discharge of the battery during low engine speeds and overcharging at high engine speeds. In a simple form, this regulator may comprise a bank of zener diodes to limit the voltage at high engine speeds and series connected diodes to prevent reverse current flow through the battery at low engine speeds. More complex and efficient circuitry employing thyristors is also known to achieve similar objectives and can readily be adapted to meet the needs of the voltage regulator in the present embodiment.

Normally, all the electrical circuits of a motor vehicle would be powered from the regulated DC supply. In the present arrangement, however, selected loads are powered directly from the AC unregulated supply. The loads connected to the unregulated AC supply are preferably resistive high current loads such as heater elements but motors including fan motors may be powered in this manner.

The loads connected to the three phase AC supply should be balanced, that is to say they should draw equal currents from the three phases. It is possible for each load in itself to be balanced or for loads to be switched on simultaneously to be connected to the different phases. For example, the rear windscreen demister may be connected to one phase and be ganged with two further heating elements associated with the front winscreen and each connected to a respective phase.

In a vehicle employing a catalytic exhaust converter, the catalyst is preferably heated by an element connected to the unregulated AC supply. This enables the catalyst to be maintained at a temperature higher than that at which it can be poisoned by the gases and it is believed that the step of electrically heating the catalyst may further enable to amount of catalyst required to be reduced.

If the total electrical load on the engine both AC and DC is particularly light, then it may be unncessary to allow the maximum field winding current to flow through the alternator. It is possible therefore to include in addition to the DC regulator means for switching off or reducing the f ield winding current when the electrical load drops, for example when the battery is in a high state of charge and no AC load is switched on.

It i s of course important to note that only loads which are not required to operate when the engine is turned off should be connected to the AC supply. However, many of the loads and in particular those with high current requirement, can be connected to the AC supply. The remaining loads driven from the DC supply place les s onerous requi rements on the rectifier and regulator, thus allowing lower rated components to be used, with a resultant saving in cost and bulk of the system.