This invention relates tα a system far efficient and flexible operation of an internal combustion engine of the Otto type, comprising a supercharging device including a drive train and a clutch for mechanically driving from the engine a positive displacement type supercharger, a dual fuel system and a control system.

BACKGRDUND OF THE INVENTION

As a sαfisticated lifestyle is becoming more common, the demands on efficiency are rising. The efficiency of a process is generally understood as the ratio between what is gained tα what is sacrificed. The process of moving people from one place tα another is a process of great importance. The efficiency of this process when automobiles are utilized is, unfortunately, very low. Tα be able to accomplish the primary task of transporting a suitable number of people a certain distance with today's standards for comfort and speed, much has tα be sacrificed in terms of natural resources and clean environment; also human suffering from accidents caused by inadequate machinery should be remembered in the count of ef iciency-lowering factors.

When people are transported by means αf automobiles, on a level road, with a constant speed, the power needed for the propulsion is relatively low. The time spent during this basic mode of operation is much longer than the time spent for acceleration, thus the maximum power of the engine is used very seldom, typically less than 2% αf the total time. The high power region must, however, be available for the car to be safe in today's traffic. A typical case is the acceleration up tα speed when entering a highway with heavy traffic, or the passing of other vehicles. For that reason ast cars are equipped with rather large and heavy engines, which in turn means that the whole czar is larger and heavier

than if an engine for the basic transportation mode had been used. More material and energy is needed for the construction αf the car, more fuel is needed for the operation αf it — and the negative impact an the environment is greater.

The power exerted by an engine is dependent on its size, the so—called effective mean pressure in the working chambers and the frequency αf the power pulses. Tα obtain high power output from a small engine that last factor must be high. The acceleration αf a wheeled vehicle is, however, dependent on the propulsive force exerted by the driving wheels against the ground. To be able tα utilize the greater power of a high speed engine for acceleration from a cruising mode, the ratio between the speed αf the engine and the speed of the wheels must be increased, i.e. a "shift down" has tα take place. This is a time—consuming and somewhat awkward procedure which is not satisfactory in a critical situation. Furthermore, an engine designed tα operate at high speeds is complicated and expensive, at the same time as efficiency, flexibility and longevity are suffering from such a layout.

An alternative way tα obtain an increase in the propulsive farce is to increase the effective mean pressure in the engine. This is most commonly accomplished by means αf so- called "supercharging" — forcing the engine tα take in more air than it can dα in its naturally aspirated state. Normally some type αf compressor is used in the inlet duct tα increase the density αf the air tα the engine, whereby a larger amount of fuel can be combusted.

A negative effect of the supercharging is, however, that the precα pressed mixture αf fuel and air has a higher tendency far "knack", or "detonation", i.e. a very sudden pressure increase caused by spontaneous ignition. In order tα avoid detonation in the supercharged mode without having tα change fuel, one normally has tα permanently lower the compression ratio in the engine as well .as retard the ignition, as compared tα an engine set up for operation in the naturally aspirated mode only. Bath these measures will lower the

efficiency of the engine. If one wαuld like tα retain the original, advantageous values αf compression ratio and point of ignition, then a fuel with a much higher octane number would have tα be used tα begin with. Such "super-fuels" far basic needs are not readily available and are hard to justi y.

Another, unwanted effect of the supercharging is increased thermal stresses in the engine, especially if an economical "lean" mixture is used, i.e. minimum amount of fuel in the air. Just in order tα avoid overheating and detonation, many supercharged engines are running too "rich", i.e. more fuel than necessary for complete combustion is used, something that is very detrimental for the fuel economy and the environment. (It is understood, that so-called "catalytic a ter-burners" can be employed to lower the obnoxious exhaust emissions, but that fact does not influence the basic thrust αf this invention.) Injection αf water will lower the temperature, but such a system is not a very practical proposition far a small automobile engine. It has also been suggested, e.g. in the German Offεnlεgungsschri 27 14 318, that the mixing of gasoline and methanαl in the same carburatαr could be a way to decrease the risks of detonation and overheating. A system using that as the only power—rising factor wαuld not, hαwever, make the power increase large enαugh to be of interest in this particular case.

Far the creation αf the pressurized air so-called "turbαchargers" have come tα extensive use. A turbαcharger is a dynamic type αf machine, where a pαwer turbine is extracting energy from the exhaust gases for driving a compressor. All automobile engines are _f αf course, of the positive displacement type and the mixing of machines αf dynamic and positive displacement type is generally not good engineering practice. In this particular case the main disadvantage αf this "mis-match" is the fact that at law engine speeds and at low mean pressure levels, there is not enough energy present in the exhaust gases tα accelerate the compressor quickly to the speed where it can give the desired

boast pressure. This phenomenon has been called "turbo lag" and it means that the desired extra torque is not available when called far. It can be stated that the turbo lag, together with the a orementioned disadvantages of lower fuel economy at part load and higher thermal stresses make the turbαcharger unsuitable for the optimized means αf personnel transportation that is the object αf this invention.

Well known in the art αf supercharging are the so-called "mechanical superchargers". These are mechanically driven compressors of some sort, predominantly working according tα the positive displacement principle, like the Roots, rotary vane, scroll αr screw types. The main advantage of having two positive displacement machines coupled together in this manner is, that the boost pressure available is practically independent αf the engine speed. If the compressor is permanently coupled tα the engine, e.g. by means αf V—belts or the like, the "throttle response" will be very gααd, in the sense that an opening of the throttle will result in an almost immediate increase in torque. However, during mast of the operating time there is no need far the compressor, which still absorbs a considerable amount of energy also when running idle, and this is a fact that will make this arrangement unsuitable when fuel economy is one αf the main concerns.

It has been suggested, ε.g in U.S. Pat. No. 4 667 646, tα arrange for energy recovery when the engine is operated with a throttled inlet by means αf a special expansion device, which will feed pαwεr back tα the engine in that made. When supercharging is called far, appropriate valving makes it passible ta operate the same machine as a compressor. Although εlεgant in theory, this principle has not been reduced tα practice due to the difficulty in arriving at a simple, reliable and cast effective design.

Far best fuel economy and longest life αf the compressor, it appears tα be obvious, that the compressor should only be coupled to the engine when there really is a need for

supercharging, and closest at hand wαuld be tα try to use some kind of electromagnetic clutch. Such designs have been suggested, e.g. in Japanese Pat. No. 57-1B3523 (A) and U.S. Pat. Nα. 4,589,396. A typical electromagnetic clutch is not, however, designed for this type αf application. Being αf the dry type, the conditions for heat dissipation as well as wear resistence are poor. When used as intended here, this will lead to overhεating and wεar. It normally also has tαα high polar mass moment αf inertia tα allow a quick engagement.

A typical way tα operate an engine with a de-clutchable superchargεr is tα usε the power resources of the naturally aspirated engine as far as possible and thereafter engage the supercharger tα obtain the "extra" power. In such a case, however, the energy required to bring the compressor up tα speed has tα be taken from thε flywhεel αf the engine, which means a deceleration instead of the desired acceleration. A very elaborate system to overcame that problem is described in the Japanese patent Nα. 58-41224 (A) , where the superchargεr is driven through an electromagnetic clutch and a "variator" - a drive arrangε εnt where the speed ratio can be varied steplessly. In addition to this, a separate intake system with separate inlet valves is provided. Taken all together this gives a very complicated, vulnerable and expensive system.

Tα summarize the prior art it can be said that many schemes are in use and have been suggested tα αbtain a temporary pαwer level that is higher than what the basic engine can deliver, but all these schemes have resulted in a lower efficiency of the pαwer unit when operated in the basic, non- supercharged mode, where most αf the time is spent. Furthermore, the transition from the law ta thε high power level has either required a considerable time, or made use of complicated and unreliable machinery. Thus all prior art solutions have beεn unsatisfactory.

SUMMARY DF THE INVENTION

The present invention is addressing thε nεεd for a better powerplant for the propulsion of vehicles — something that is light, compact and reliable, and which provides good fuel economy at lower pαwer levels together with the availability of a substantial amount of "extra" pαwer when needed, while maintaining good exhaust emission qualities under all operating conditions.

This has been achieved, according tα thε invention, in the use of the engine being designed for best εfficiency when partially throttled, naturally aspirated and operating on a primary fuel of predominantly mineral oil type, a secondary fuel system employing a second fuel tank containing a fuel αf predominantly organic type with a highεr octane numbεr and a highεr latent heat of vaporization than said primary fuel, a oot—operated pedal and an elεctrαnic control system, designed such, that upon signal from said fααt-αperated pedal, said secondary fuel is fed to said engine in a quantity adequate tα prevent detonation without lowering the settings αf said engine with respect tα compression ratio or ignition paint, and said clutch is activated to bring said supercharger in synchronization with said engine.

BRIEF DESCRIPTION OF THE DRAWING

Thε drawing discloses a schematic block diagram αf a preferred embodiment of thε supercharging system with a typical Otto type enginε, a positive type αf compressor, a drive train with a clutch, a dual—fuel injection system and an electronic cαntrαl system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring tα the drawing, the components and thε function of the invention will be explained in the following. The new system is conceived to work with an internal combustion engine (1) αf the well known Otto type, where the mixture αf fuel and air is ignited by means of a spark from a spark plug (2) . Thε combustible mixture enters the cylinder through the inlet valve (3) during the inlet stroke and the gas produced by the combustion is expelled through the exhaust valve (4) during the discharge stroke. It is understood, that although the figure shows only one cylinder, the most likεly casε is that the engine has several cylinders. This engine is designed, according to well known principles, for the bεst passible efficiency to be obtained in thε speed and load rεgiαn where it is predominantly used, i.e. somewhere in the middle of the operating range, when it is operating in its naturally aspirated mode and with a prεdαminantly minεral ail based fuel.

The intake system is comprised αf two main parts: the primary system, including the primary inlet duct (5), a first throttling valve (6), a first fuel system with a first fuel tank (7) , a first uel pump (S) , the primary fuel injectors (9) near the inlet valves - and the secondary system, including the secondary inlet duct (10), a second throttling valve (11), a second fuel system with a second fuel tank (12), a second fuel pump (13), the second fuel injectors (14) in thε primary inlet duct and a third injector (15) in the secondary inlet duct, and a positive displacement type compressor (16), prefεrably of the so-called twin-screw type, with suitable proportions. For the prαper function αf thε inlet system, also other valves can bε considered, e.g. an automatic two-way valve (17) and a pressure relief valve (18) .

The compressor is prefεrably drivεn by a pαsitivε typε αf mechanical drive system (19), i.e. non-slipping. The clutch

(20) is preferably of the multi—disk typε, operating in σil for gααd wear characteristics and efficient heat dissipation. The slip torque αf this clutch is adjustable. A servo mechanism, well known for thαsε skilled in thε art, is also envisioned tα αpεrate this clutch upαn a signal from the control system. Due to the viscous drag in this type αf clutch, there will be a slight torque transmitted also in thε de-clutched state, resulting in a slow rotation of the compressor when it is idle. This is advantageous far the life af the compressor in many ways: there will be no risks for bearing— estroying static vibrations or a dried out shaft seal. If a hot compressor is left tα cool down in a completely static cαnditiαn, thεrε is also a risk that the rotors will be deformed due to the uneven cooling, a condition that can cause trouble when the compressor is restarted.

For the control αf the mean pressure in the engine, there is a control system employed, consisting of a oot—operated pedal (21), with its first operating range (22), its second operating range (23) and the position sensor (24) . The farce needed ta operate the foot pedal in the second operating range is at a considerably higher level than in the first operating range. The control system further incorporates a micro computer (25) , which is receiving signals rom the engine and its auxilliaries as required far thε calculation of optimum settings of the valves that control the torque from the engine and the combustion αf the fuel. It also controls the engagement αf the supercharger. Such devices are well known far those skilled in the art and are nαt a part αf this invention. Thε control signals that are most interesting in this context are the signals to the mechanical clutch (20), tα the injectors (9) of the first fuel system, to the injectors (14) and (15) αf the second fuel system, to the throttle valve (6) in the primary system and to the throttling valve (11) in the secondary system.

The significance of this navel system may bε appreciated from the fallowing description af a typical case:

For all "normal" operation of the vehicle, i.e. when there is a mαderatε need for torque to the drive wheels, the foot pedal is used only in its first operating range (22), where thε engine can operate solely in its naturally aspirated mode and on its primary fuel, being predominantly of thε minεral ail typε, typically unleadεd gasoline. Thε throttle valve (6) is nαt allowed tα be opened more than tα approxi atεly two thirds during this mode. The compression ratio in an enginε designed for partly thrαttlεd αpεration can be raised considerably before the "detonation limit" is reached, especially whεn co parεd to an engine set up for operation on gasoline in the supercharged mode. It is also possible to run the engine very "lean" in this mode and to use the optimum ignition setting. Thus, when practicing this invention, the efficiεncy of the engine will bε extremely gααd during mast of the time it is operated.

If maximum acceleration is desired, the driver will press the foot pedal (21) "to the -floor". The position sensor (24) will then instruct the micro computer (25) to arrange for the quickest possible compressor start-up. The throttle valvε (6) is αpεnεd fully at the same timε as a secondary fuel of predominantly organic nature, typically aεthanol or ethanαl or mixtures containing an alcαhαl with a highεr αctanε numbεr than the primary fuεl, is injected through the injector (14). The ratio between thε amount of primary and secondary fuel is given by the requirεmεnt that dεtαnatiαn must bε avoided. It should be appreciated that by this novel arrangεmεπt a considerable amount αf "extra" torquε is released, which can be used far a rapid engagement of the compressor. It is understood, that for a quick and safe compressor acceleration phase, the drive train tα thε compressor must be very robust and the pαlar mass mαment αf inertia αf the rotating elements must be as law as possible. Already with the present state αf the art it is quite feasible tα arrive at satisfactory designs for those elements, and further developments are foreseeable. The fact that thε engine normally is working with a comparatively low rotational speed when the compressor is engaged, will further improve the conditions for a short

and safe start—up period αf thε compressor. As sααn as the increased torquε is made available, the clutch (20) is engagεd and thε second throttle valvε (11) is openεd. Immεdiately thεrεafter, the third injector (15) is beginning tα inject same of the secondary fuel ahead of the compressor (16). As the slip in thε clutch is decreasing, the boost pressure will increase, the two-way valve (17) will open and more of thε sεcαndary fuel will bε injected through the third injector (15). The start—up sequence discribed hεrε takes typically only a few tenths αf a second.

During the time thε εnginε is working in the second made, the ratio between thε amount αf primary ^' and sεcαndary fuεl is constantly monitαrεd, so that detonation is avoided. Thus it is foreseen that the total amount of the primary fuel might have to bε reduced under certain conditions. It should also be appreciated, that the sεcαndary -fuel, being basically an alcαhαl, is a more "clean-burning" fuel than the primary fuel, being basically a sort αf gasoline, having the effect that thε exhaust emissions will be less harmful when the εnginε is αpεrated in thε supεrcharged mσdε than whεn working in the basic mode. With this secondary fuel available, a similar arrangement tα avoid detonation also in thε first operational mode could sometimes be justified, e.g. in thε case αf a sudden increase in torque requirement at a low εnginε speed.

Although it is well known, that the injection αf a fuel with a high latent heat αf vaporization, like an alcohol, ahead of a mechanical supercharger has several beneficial εffεcts, typically mαrε efficient compression, more rεliablε operation αf the compressor and giving a cααler charge, it has not up till now beεπ used outside the realm αf racing. It is only whεn incorporated into a complete system, as in the case αf the present invention, that this becomes a practical proposition. It is also -foreseen, that a small amαunt αf ail of a kind that is harmless tα the environment can bε mixed with the secondary fuel, which will further improve the efficiεncy and reliabilty αf the compressor. These factors.

taken together with the fact that the compressor will be used only during a very limited time, will make a system, built in accordance with the present invention, vεry suitable far basic transportation with many hours αf operation per year. It has the added advantage, that thε drivεr can to a largεr extent than hitherto influencε thε αpεrating costs through his driving pattεrn.

It is also fαreseεn that same "anti—hunting means" should be incorporated, as a situation can arise when the driver has to reduce the pαwer temporarily whεn running in thε supercharged mode, e.g. whεn maneuvering into a "slot" in a fast moving line of cars an a highway. In such a case thε first thrαttle valve (6) and the second throttle valve (11) will work together, at the same time as the injection of the secondary fuel is stoppεd. Thε two thrαttlε valves should bε programmed to ensure that an unduly high pressure is nαt created after the compressor, but for the sake αf safety, a relief valve (18) should be incorporated in thε system. Thus the "extra" torque is immεdiately available as soon as nεεdεd, for a pεriαd αf timε that can be predetermiπεd.

Whilε the invention has bεεn particularly shown and dεscribεd with referencε to a prεferred embαdimεnt thεrεαf, it will bε understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope αf thε invεntion.