GB2364111A - Engine throttle - Google Patents

Abstract

A throttle for an engine, e.g.for a motorbike, includes two walls forming the sides of a square or rectangular section inlet duct, at least one of which is movable relative to the other to vary the throttle opening. In a first embodiment, each wall comprises throttling plates sealed to the main body of the throttle by elastic pieces and is moved by a piston. In another embodiment (Fig.5), pivoted gates act on flexible side walls. In an alternative throttle (Fig.3), an iris diaphragm acts on a rubber tube to vary the throttle opening, and several shutter can be used and geared to close at different rates to alter the section of the inlet duct. In a further throttle (Fig.4), the throttle opening is varied by twisting a tube. The throttles are stated to provide substantially smooth contraction and expansion of air therethrough and to reduce turbulence.

Description

2364111 ENGINE THROTTLE The present invention relates to a throttle body.

A carburettor, or the throttle body of a fuel injector, is a valve to restrict the volume of air that flows into an engine to control the engine speed.

Figures 1 and 2 show in cross-section examples of two existing motorcycle carburettors One is a 'slide type' carburettor, and the other is a 'constant velocity' (CV) type carburettor, sometimes known as a 'Constant Depression' carburettor.

As can be seen, with the slide carburettor, as the device opens, turbulence occurs behind the slide This turbulence limits the volume of air that can flow into the engine, which has a direct relation to the amount of torque that an engine can produce The CV type carburettor has a butterfly valve that rotates along with the slide that lifts Again, turbulence occurs Most car engines use a butterfly only, as do most fuel injectors.

The present invention seeks to provide an improved throttle.

According to an aspect of the present invention, there is provided a throttle of an engine including first and second throttling plates providing substantially smooth contraction and expansion of air therethrough, at least one of said throttling plates being moveable relative to the other.

Preferably, both throttling plates are moveable relative to one another.

The preferred embodiment seeks to optimise the airflow through a motorcycle throttle body The revised throttle body has been realised in the form of a motorcycle carburettor All testing was completed at half throttle and at a total flow pressure of 54 mm of water Initial flow testing results indicate that the throttle body flows air with a pressure loss of approximately 30 % less than that of a standard Keihin carburettor.

Fuel atomisation tests suggest that the throttle body concept would be best suited to a fuel injection system to make full advantage of the system's preferable flow characteristics.

The throttle body can have applications where more power is desired, for example in racing, and/or to increase the efficiency of the vehicle.

An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which:

Figures 1 and 2 are schematic diagrams of prior art throttle bodies; Figure 3 shows in cross-section a view of an embodiment of throttle body; Figure 4 shows in cross-section a view of another embodiment of throttle body; Figure 5 shows in cross-section a view of another embodiment of throttle body; Figure 6 shows in cross-section a view of the preferred embodiment of throttle body; Figure 7 shows the inlet geometry of the preferred embodiment of throttle body of Figure 6; Figure 8 shows in cross-section a test throttle for determining the best inlet and outlet geometries; Figure 9 shows in cross-section a throttle valve body similar to that of Figure 6 designed for use with a hydraulic actuator; Figure 10 shows a smoke tunnel profile of a prior art throttle; Figure 11 shows a smoke profile for the throttle of Figure 6; and Figure 12 is a schematic diagram of an embodiment of development test rig.

The preferred embodiments provide a more efficient inlet passage, particularly at small throttle openings where there is at the moment turbulence around the slide or butterfly.

Some early embodiments are described below.

Referring to Figure 3, the embodiment shown uses an Iris diaphragm which closes around a rubber like tube to provide the restriction Several shutters can be used and geared to close at different rates to alter the section of the inlet tract Fuel delivery is preferably by a type of downstream facing pitot tube This system lends itself to fuel injection quite readily as the pressurised fuel injector can be placed downstream rather than at the point of maximum restriction and therefore lowest pressure.

Another embodiment, shown in Figure 4, uses a Hyperboloid section A flexible inlet tube is twisted so that it forms a conical restriction This device can be constructed with various media, but again a rubber inlet tract is preferred.

As before, fuel jet and needle placement involves some experimentation, so again it is more suited for fuel injection The device closes by the very ends of the tract rotating in opposite directions to each other A diabolo type shape is produced.

With the inlet gate system shown in Figure 5, two 'doors' close upon each other with the fuel needle sitting centrally between the two As the doors open, the needle lifts and the fuel is metered accordingly The needle carrier is very thin so that it seals on the doors at low throttle openings The needle profile is carefully designed to give the correct mixture at low throttle openings The wall material for this system is flexible in order to form the correct aerodynamic profile.

Another, and the preferred, embodiment was developed following testing on a test rig described below.

To obviate the difficulty of producing a throttle section that varies in three dimensions as it closes (moving vertically to choke the inlet, varying from a tube to a flat section, and the associated changes in length), a square section duct was chosen.

Existing cylinder head designs use round ports to connect the circular section inlet to the round inlet valve The preferred embodiment provides a transition piece to smoothly change the fluid path along the inlet from a square to a round section This causes the component to be longer needing a cylinder head designed with square to round section porting within the cylinder head itself.

The throttle body shown in Figure 3 uses two aerodynamic throttling plates' that close together symmetrically As there is less turbulence, the volume of air that is able to flow into the engine is increased This in turn will lead to the engine producing more torque.

The dimensions shown in Figure 3 are exemplary only.

To keep the restriction mechanism simple, the inlet and exhausting slopes, as well as the top of the jet block are preferably constructed from the same material The edges of the sliding plates need to seal against the carburettor body to stop air leaking around them For this purpose, the plates may be made of PTFE PTFE has a very low coefficient of friction so it slides well against the side of the carburettor body It can also be made a tight enough fit into the body of the carburettor, that no additional sealing is required PTFE is also a very stable material that does not degrade in the presence of petrol.

Small elastic pieces are used to seal the throttling plates to the body walls When the throttle opening is smallest, and the inlet suction is greatest, membranes of the elastic pieces are pulled the tightest As the throttle opening gets larger, the inlet pressure approaches that of atmospheric, and so the decreased tension in the elastic pieces becomes less significant.

These pieces, are preferably constructed from polyurethane, which showed no visual changes and appeared to retain its physical properties After exposure to petrol for three months, the sample had no obvious physical flaws Fluro- Silicon appears to have even greater wear and corrosion resistance properties and is preferred.

Inlet Geometry Research was carried out to determine the correct inlet profile once the layout of the device had been decided To do this, a rig (described below) was constructed with adjustable baffles that could be moved up and down the inlet tract These were moved together in keeping with the design of the device By doing this, different intake and exhausting slopes could be created and assessed Again testing was done at half throttle by area For a sectional view of the inlet geometry test piece, see figure 8.

As all the testing is completed at an area equivalent to half throttle, the height of the sliding baffles had to be determined.

If the full area of the open part of the passageway is simply: = 1,192/2 = 1134 mm 2 So the half throttle area is the above divided by two; = 567 mm 2 As the inlet area reduction is made up in two halves, the area of these sections is 567 mm 2/2, which is = 283 5 mm 2 per baffle.

To calculate the height up from the inlet wall that the webs have to be made to achieve a half throttle equivalent, circle geometry was used as shown in Figure 7.

A linear extrapolation was then embarked upon to solve for O (in radians).

' Using h = r-r cos O/2 LHS target = 1 57 radians.

By using substitution and trial and error:

BRADS LHS of equation 0.6 N 1 8850-sine = 1 8850-0 9511 = 0 9339 0.75 N 2 356-0 7071 = 1 6491 0.74 N 2 3248-0 72960 = 1 5958 0 738 N 2 3185-0 7333 = 1 5852 0.736 N 2 3122-0 7375 = 1 5747 0.735 N 2 3091-0 7396 = 1 5694 By substituting back into: h=r (l-cos 9/2) h=r-r cos 0/2 h=r (l-cos 9/2) 0/2 = 1 154 RADS h= 19 ( 1-0 4043) 11 32 mm .The inlet baffles must sit 11 32 mm up from the passage sidewall to retain a half throttle section area.

For the inlet, and to cover the baffles, a suitable material was found.

Inlet construction The inlet tract of the preferred embodiment is of a flexible enough material that it will constrict from its 38 mm full bore down to negligible opening Various rubbers are available with the required amount of flexibility, but not many of these are fuel resistant, and none are available in the required section A mouldable material was selected, and the fluoro-silicone group of rubbers selected for their petrol and oil resistance A '587 ' fluoro-silicone was selected with a Shaw number of sixty chosen for its flexibility and durability.

Inlet Material Testing Samples of the 587-60, some latex sheets and some polyurethane sheets were tested to prove their resistance to fuel, oils and salty water Some imperviousness to oils is desirable as the device may contain mechanisms that need oiling, as well as the possibility of the device coming into contact with oil due to leaks or whilst servicing Salt water may be present on winter roads Fuel will obviously be present in the device so this must not compromise the tract at all.

The result table overleaf shows the various materials tested coped when exposed to different substances.

Material Test 587-60 Latex Polyurethane Clean Engine Oil No effect Badly blisters No visible adverse effects Dirty Engine Oil No effect Severe No adverse blistering and effects other splitting than colour staining Baby Oil No effect Quickly No visible blisters the adverse effects surface badly Petrol No effect One large No visible blister where adverse effects majority evaporation occurs Vaseline No effect Blisters after No visible one month adverse effects GT 85 (Penetrating No effect No visible No visible oil-Water adverse effects adverse effects dispersant) Salt Water No effect No visible No visible adverse effects adverse effects Table 1

Material Selection Latex clearly was not suitable for this application as it degrades quickly upon exposure to any oil based substances.

Polyurethane proved to be very durable upon lengthy exposure and seemed to retain its integrity Upon comparison with the technical specifications for fluoro-silicon materials (research folio two-p l, 2 and 8), Polyurethane was a close second.

The preferred embodiment includes means for controlling and assisting fuel atomisation, due to the proposed smooth choking of the carburettor when compared to a conventional device The engine requires the fuel to be properly atomised and evenly dispersed in the air for combustion to occur The turbulent airflow around a conventional slide or butterfly aids the dispersion of the fuel within the air As the engine was turned over with a prototype device, fuel was tending to emerge in heavy droplets in the airflow, which would collect in pools on the lower throttling plate This was not simply a 'rich mixture' phenomenon where the air is saturated, as the fuel tended to appear on the lower throttling plate only.

An alternative to assisting fuel atomisation is to use a fuel injection system where the advantages of the low flow losses can be utilised in conjunction with a pressurised fuel injector The fuel injector does not rely on a venturi, and the atomisation is achieved by carefully designed spray jets to disperse the fuel.

The preferred embodiment provides four sprigs on the jet- block to return the bottom piston to the closed position when the throttle is released The top piston, preferably also has four sprigs to ensure that the cable splitter does not tend to pull unevenly due to uneven forces It is preferred to replace the sprigs by a hydraulic mechanism By activating each piston hydraulically, the main body can be better sealed, and each piston will move together in unison.

An embodiment in which the throttle is redesigned around a hydraulic master cylinder, in which the bore for this is smaller than a brake master cylinder, as the forces involved are much smaller, as shown in figure 15.

Results from Flow Testing Testing a prior and 38 mm Keihin CV carburettor, at a total test pressure of 54 mm of H 20, gave a suction at the bellmouth of 10 mm of H 20 and a static pressure on the engine side of the device of 102 mm of H 20 This represents a total loss through the device of ( 102-10) = 92 mm of Hi Q.

Testing the throttle body of Figure 6 or 9, open to the same cross sectional area and at the same test pressure, gave 26 mm of H 20 at the bell-mouth and 90 mm of H 20 on the engine side of the device This represents a total loss through the device of ( 90-26) = 64 mm Hiz.

Calculating this as a percentage, the preferred throttle body flows with less pressure loss in the region of 30 %.

All readings were taken at points of the same cross sectional area, with the throttle at half way, and at the same test flow pressure (total pressure) to eliminate calculations and to make the results immediately comparative.

Smoke Tunnel Results By looking at figures 10 and 11, it can clearly be seen that the preferred throttle body has a much smoother flow passage than the profile of the slide type carburettor, in this case an Amal MKI Concentric The profile of the preferred throttle retains near laminar flow through the venturi, where the Amal profile starts to produce a vortices both behind and under the slide Both profiles were tested at the same flow speed of approximately 8 ms-1.

The smoke tunnel results show that the preferred profile is more aerodynamic than that of a slide type carburettor.

There is clearly a vortex forming in the low-pressure area behind the slide, causing some reversed flow, and a smaller vortex forming under the slide This second vortex may indeed aid the atomisation of fuel and allow the engine to run much more effectively It does also limit the volume flow through the device.

It can be seen that in order for a carburettor to function as a carburettor, development has gone down the road that it has to ensure adequate fuel mixing As mixing with the aid of a venturi and a spray tube is not an issue with fuel injection, a move away from turbulent slides and butterflies is justifiable Indeed, it is the lack of turbulence that has caused the Orpheus device to produce a mixture too heavy to successfully ignite.

Figure 12 shows an embodiment of test rig which was developed to design the throttle body.

It was decided that the rig would show comparative information about the flow resistance caused by one device compared to another However, the volumetric flow rate and flow pressure must be comparable to what is produced by an actual bike Running the engine with a vacuum gauge attached yielded this information The test pieces were then connected to a tuned output vacuum device via a tube This tube is of the same dimensions as the inlet of the test bike.

In reality, the flow rates will not be even due to the piston pulses Further from that, valve closure sends pulses in the reverse direction It is for this reason that the results are taken as comparative.

The static flow pressures before and after the device is recorded by water filled manometers All the testing is completed at a constant and consistent flow pressure This is read from another manometer that measures the total flow pressure The total flow pressure manometer has one end connected to the static tapping downstream of the device, and the other end connected to a fine pitot tube that sits in the middle of the flow path The power setting on the vacuum device was also noted, as it provides an easy ballpark reference to how well a particular device flows If the vacuum device needs to be turned up a long way, then the resistance of the device is high and more power is needed to achieve the test flow pressure.

Claims (13)

1 A throttle of an engine including first and second throttling plates providing substantially smooth contraction and expansion of air therethrough, at least one of said throttling plates being moveable relative to the other.

2 A throttle according to claim 1, wherein both throttling plates are moveable relative to one another.

3 A throttle according to claim 1 or 2, including an iris diaphragm which closes around a tube to provide a throttle restriction.

4 A throttle according to claim 1 or 2, including a hyperboloid section.

A throttle according to claim 4, including a flexible inlet tube twisted to form a substantially conical restriction.

6 A throttle according to any preceding claim, including an inlet gate system provided with two doors which close upon each other with a fuel needle sitting centrally between the two.

7 A throttle according to claim 6, including a carrier which carries the needle, the carrier being of a thickness to seal on the doors at low throttle openings.

8 A throttle according to any preceding claim, wherein the components of the throttle are substantially all formed from the same materials.

9 A throttle assembly including a throttle according to any preceding claim and a substantially square or rectangular inlet duct to the throttle.

A throttle assembly according to claim 9, including means for controlling and assisting fuel atomisation.

11 A throttle assembly according to claim 9 or 10, including a fuel injection system.

12 A motorcycle engine including a throttle according to any one of claims 1 to 7 or a throttle assembly according to any one of claims 9 to 11.

13 A throttle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.