GB1584353A - Fuel injection system for an engine - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO A FUEL INJECTION SYSTEM FOR AN ENGINE (71) We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to fuel injection system for an engine.

In accordance with the invention there is provided a fuel injection system for an engine, the fuel injection system including a flow meter comprising a body which is engaged by gas flow through the flow meter, and a sensing means, the flow meter being such that the body and/or the sensing means are adapted to be bent backwards and forwards by the gas flow at a frequency corresponding to the flow, and the nsensing means being effective to sense the bending and give an electrical output of a frequency proportional to the bending frequency and therefore the gas flow passing through the flow meter.

The flow meter can be cheaply produced and it provides an effective way of determining gas flow rate, the body producing vortices or air pulses which control the frequency of the bending. The number of vortices or pulses produced is thus proportional to the flow rate.

The sensing means may be a piezoelectric pressure sensing means or a strain gauge.

The piezoelectric pressure sensing means may be made of a piezoelectric ceramic or a piezoelectric platics material. Advantageously, the sensing means is a piezoelectric bimorph.

Usually, the body will be made from a different material to that of the sensing means. However, if desired, the body can be made of the same type of material as the sensing means.

Preferably, the body is a bluff body. The bluff body may be in various shapes such for example as T, square, rectangular, triangular, or oval shapes. The sensing means may advantageously be arranged inside the bluff body.

In the case where the body is T-shaped, then the sensing means can be arranged in the leg of the T-shape. Alternatively, if desired, two sensing means can be employed, with one in each arm of the Tshaped body. Also, if desired, the body can form the cross piece of a T-shaped body with the sensing means being formed as the leg of the T-shaped body.

When the bluff body is formed with a square, rectangular, or triangular shape, for example, it may be cut in one or more appropriate places, or otherwise weakened, to weaken it so that one part of the body can bend about another part of the body.

This bending will then be sensed by the sensing means.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows part of a first fuel injection system in accordance with the invention; Figure 2 shows part of a second fuel injection system in accordance with the invention; Figure 3 shows part of a third fuel injection system in accordance with the invention; Figure 4 shows part of a fourth fuel injection system in accordance with the invention; Figure 5 shows part of a fifth fuel injection system in accordance with the invention; Figure 6 shows part of a sixth fuel injection system in accordance with the invention; and Figure 7 shows part of a seventh fuel injection system in accordance with the invention.

Referring to Figure 1, there is shown part of a first fuel injection system comprising a duct 2 having positioned therein a bluff body 4. The bluff body 4 comprises a cross piece 6 and a leg 8. Provided in the leg 8 is a sensing means in the form of a bimorph 10.

Air passes along the duct 2 in the direction of the arrow 12 and vortices 14 are alternatively formed on either side of the bluff body 4. These vortices 14 act on the leg 8 and cause it to bend to the upper and lower positions shown in dotted lines at 8A and 8B. This bending of the leg 8 to the positions 8A and 8B stresses the bimorph 10. The bimorph 10 generates an electric current proportional to the number of times it bends and therefore proportional to the number of vortices 14 created by the air flow passing over the bluff body 4. Since the number of vortices passing over the bluff body 4 is proportional to the air flow in the duct 2, then the voltages created by the bimorph 10 are also proportional to the air flow in the duct 2.

Referring now to Figure 2, there is shown a duct 20 having therein a T-shaped bluff body 22 having a cross piece 24 and a leg 26.

Two sensing means in the form of bimorphs 28, 30 are inserted as shown in the cross piece 24. Air passes along the duct 20 in the direction of the arrow 32 and causes the ends of the cross piece 24 to bend about the centre leg 26 as shown in the dotted lines.

This bending is sensed by the bimorphs 28 and 30 which, as indicated above, generates an electrical current proportional to the number of vortices 34 being generated and therefore proportional to the air flow in the duct 20.

Referring now to Figure 3, there is shown a duct 50 having therein a bluff body 52 in the form of a cross member. Attached to the bluff body 52 is a pressure sensitive device in the form of a bimorph 54. The bluff body 52 and the bimorph 54 form as illustrated an overall T shape. An air flow passes along the duct 50 in the direction of the arrow 56 and vortices 58 are formed.

These vortices cause the bimorph 54 to bend as shown by the dotted lines and this bending causes an electric current to be generated which, as indicated above, is proportional to the number of vortices generated and therefore is proportional to the air flow in the duct 50.

Referring to Figure 4, there is shown a square shaped bluff body 80 which has been provided with two slots 82, 84. The two slots 82, 84 do not meet and they are separated by a bridge 86. Positioned in the bridge 86 is a sensing means in the form of a bimorph 88. As air passes over the bluff body 80 in the direction of the arrow 90, vortices 92 are created which end the rear portion 80B of the body about the bridge 86 as shown by the dotted lines. This bending is sensed by the bimorph 88 which produces an electrical current proportional to the number of vortices 92 generated and therefore proportional to the air flow over the bluff body 80.

In Figure 5, similar parts to those shown in Figure 4 have been given the same ref erence numerals in order to avoid undue length of description. The operation of the device illustrated in Figure 5 is basically the same as that illustrated in Figure 4. In Figure 5, the bluff body 80 is triangular in shape but it will be seen that it is still provided with slots 82, 84 so that the rear portion 80B of the bluff body 80 can bend about the slots 82, 84 as shown by the dot ted lines to cause an appropriate current to be generated from the bimorph 88.

In Figure 6, similar parts have been again given the same reference numerals as in Figure 4. In Figure 6, two bimorphs 88 are employed as shown and the front part 80A of the bluff body 80 is caused to bend as shown by the dotted lines and this bending is again sensed by the two bimorphs 88 which generate appropriate electrical currents.

All the flow meters shown in Figures 1 to 6 are of the vortex shedding type, i.e.

vortices are shed, as shown, by the bluff body. In Figure 7, the flow meter is of the oscillating jet type, in which an air flow passes along a flow meter 100 in the direction of an arrow 102. The flow meter 100 is similar to a fluidic jet device and the air can pass either along passages 104, 108 or along passages 106, 110. The air in the passages 108 and 110 passes over an oval body 112 which is provided with slots 114, 116 as shown. These slots 114, 116 define between them a bridge 118 and provided in this bridge 118 is a sensing element in the form of a piezoelectric bimorph 120. By appropriately securing the front half 1 12A or the rear half 112B of the body 112, one portion of the body 1 12A or 1 12B can be arranged to bend about the bridge 118.This bending is sensed as mentioned above by the bimorph 120 which generates an electrical current proportional to the number of oscillations passing along the passages 108, 110 and therefore proportional to the air flow in the flow meter 100.

By knowing the amount of air passing along an air duct leading to the engine, then appropriate use can be made of the electrical signals generated by the pressure sensing means to appropriately 'activate fuel injection means to give exactly the required amount of fuel to mix with the air. The precise fuel injection means can be of a known type such for example as a fuel injector having a ball valve normally closing a fuel injection orifice and arranged to be vibrated by means of a piezoelectric device.

The vibrations cause the ball valve to be moved off its seat and thus allow fuel injection to take place through the orifice.

It is to be appreciated that embodiments of the invention described above have been given by way of example only and that modifications may be effected. Thus, by way of example, it is mentioned that although bimorphs have been shown, strain gauges could also be employed. Also, if desired, the various slots in the bodies shown in Figures 4 to 7 could be filled with some form of resilient material to reduce unwanted air disturbances caused by the slots.

In all cases it is advisable to secure the body, to the walls of the flow meter duct with a form of resilient mounting. The securing of the body assists in the bending taking place along the whole length of the body, thereby reducing the chances of complex stress patterns being set up in the body. The securing of the body may also be effective to reduce the chances of ducting vibrations being picked up by the sensor.

When it is necessary to measure flows at very low velocities, the pressure difference across the sensing means may not be sufficient to cause a high enough output. In this case a thermally sensitive device may be used in conjunction with the sensing means. The thermally sensitive device may be a hot wire thermistor or a thermally sensitive resistive point. The thermally sensitive device may operate to detect the vortices or pulses generated at these low velocities.

The electronic circuitry associated with the flow meter would be set up so as to decide at what frequency the output from the two pressure sensing means and the thermally sensitive device should be combined or switched over.

WHAT WE CLAIM IS: 1. A fuel injection system for an engine, the fuel injection system including a flow meter comprising a body which is engaged by gas flow through the flow meter, and a sensing means, the flow meter being such that the body and/or the sensing means are adapted to be bent backwards and forwards by the gas flow at a frequency corresponding to the flow, and the sensing means being effective to sense the bending and give an electrical output of a frequency proportional to the bending frequency and therefore the gas flow passing through the flow meter.

2. A fuel injection system according to claim 1 in which the sensing means is a piezoelectric pressure sensing means.

3. A fuel injection system according to claim 2 in which the sensing means is a piezoelectric bimorph.

4. A fuel injection system according to any one of the preceding claims in which the sensing means is arranged inside the body.

5. A fuel injection system according to claim 4 in which the body is T-shaped and the sensing means is arranged in the leg of the T-shape.

6. A fuel injection system according to any one of the preceding claims in which the body is weakened so that one part of the body can bend about another part of the body.

7. A fuel injection system according to any one of the preceding claims in which the body is a bluff body.

8. A fuel injection system according to claim 7 including a thermally sensitive device for detecting generated gas vortices or pulses at frequency levels at which the sensing means is not operative.

9. A fuel injection system substantially as herein described with reference to any one of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. bimorphs have been shown, strain gauges could also be employed. Also, if desired, the various slots in the bodies shown in Figures 4 to 7 could be filled with some form of resilient material to reduce unwanted air disturbances caused by the slots. In all cases it is advisable to secure the body, to the walls of the flow meter duct with a form of resilient mounting. The securing of the body assists in the bending taking place along the whole length of the body, thereby reducing the chances of complex stress patterns being set up in the body. The securing of the body may also be effective to reduce the chances of ducting vibrations being picked up by the sensor. When it is necessary to measure flows at very low velocities, the pressure difference across the sensing means may not be sufficient to cause a high enough output. In this case a thermally sensitive device may be used in conjunction with the sensing means. The thermally sensitive device may be a hot wire thermistor or a thermally sensitive resistive point. The thermally sensitive device may operate to detect the vortices or pulses generated at these low velocities. The electronic circuitry associated with the flow meter would be set up so as to decide at what frequency the output from the two pressure sensing means and the thermally sensitive device should be combined or switched over. WHAT WE CLAIM IS:

1. A fuel injection system for an engine, the fuel injection system including a flow meter comprising a body which is engaged by gas flow through the flow meter, and a sensing means, the flow meter being such that the body and/or the sensing means are adapted to be bent backwards and forwards by the gas flow at a frequency corresponding to the flow, and the sensing means being effective to sense the bending and give an electrical output of a frequency proportional to the bending frequency and therefore the gas flow passing through the flow meter.

2. A fuel injection system according to claim 1 in which the sensing means is a piezoelectric pressure sensing means.

3. A fuel injection system according to claim 2 in which the sensing means is a piezoelectric bimorph.

4. A fuel injection system according to any one of the preceding claims in which the sensing means is arranged inside the body.

5. A fuel injection system according to claim 4 in which the body is T-shaped and the sensing means is arranged in the leg of the T-shape.

6. A fuel injection system according to any one of the preceding claims in which the body is weakened so that one part of the body can bend about another part of the body.

7. A fuel injection system according to any one of the preceding claims in which the body is a bluff body.

8. A fuel injection system according to claim 7 including a thermally sensitive device for detecting generated gas vortices or pulses at frequency levels at which the sensing means is not operative.

9. A fuel injection system substantially as herein described with reference to any one of the accompanying drawings.