This invention relates to apparatus for and a method of regulating the rate of delivery of an additive to a fluid flow.

In fuel management control systems it is known to use electronically controlled fuel injection. In such a system several engine parameter measurements (eg. engine speed, air flow, throttle position, engine load etc.) are evaluated. The amounts of fuel and air, and their ratio are then either derived from a look-up table or calculated in real time. The control signal used to control the delivery of the air and fuel is based on the evaluation of the measured parameters. This control signal is commonly used to contol the actuation of a throttle, regulating the delivery of the air, and an electrically actuated fuel injector.

However, such rates of delivery and a ratio for the air/fuel mixture can only be based on a theoretical assumption of those required for a given set of many parametric conditions.

There is currently considerable interest in the use of water as a cleansing emulsion additive in diesel fuel to assist in minimising the emmission of pollutants from the internal combustion engine. Clearly, the amount of water added is critical. If the ratio is too high, it will impair the performance of the engine too greatly. If the ratio is too low, the exhaust from the engine will not be optimally cleaned. Thus, there is a need for a means of regulating accurately and

responsively the amount of additive water introduced to the flowing fuel to keep the water/fuel ratio at or very near its optimum.

According to the present invention there is provided apparatus for regulating the rate of delivery of additive to a fluid flow, the apparatus including sensing means for monitoring the fluid flow rate and producing a signal representative of the fluid flow rate and delivery means operable to deliver the additive to the fluid flow in response to the signal from the sensing means.

Thus, by using a flow sensor as the sensing means and the source of control of the delivery means, the present invention is able to regulate the amount of additive to, for example, a fuel line, a fuel/air mixture or air in direct response to the actual fluid flow rate. The flow sensor may measure volumetric flow or the speed of the fluid. This provides a simple, cost effective and yet directly responsive means of controlling the rate at which an additive is applied to the flowing fluid.

Also according to the present invention there is provided a method of regulating the rate of delivery of an additive to a fluid flow, the method comprising sensing the fluid flow rate and controlling the rate of delivery of the additive to the fluid in response to the sensed fluid flow rate.

Preferably, the output of the sensing means is a pulse train having a pulse rate related, for example proportional, to the fluid flow rate. A particularly convenient form of sensing means are a Hall-effect flow sensor. This may comprise an impellor which rotates in the fluid flow at an angular velocity related to the flow rate and a Hall-effect device arranged to produce a pulse output as the blades of the impellor pass the Hall-effect device.

Alternatively, it is equally possible to use a pulse width modulated output from the sensor or pulse amplitude modulation.

It is desirable that the output of the sensing means is conditioned, for example by applying it to the input of a pulse generator arranged to produce a conditioned pulse output actuating signal, possibly of predetermined duration, representative of the output of the sensing means. The duration of the conditioned pulse output may be adjustable to vary the ratio of additive delivered to the fluid by varying the duration for which the delivery means are commanded to deliver additive to the fluid. As before, the output of a conditioning circuit could equally well provide a pulse width modulated or pulse amplitude modulated actuating signal.

The invention may also include threshold means, as a cut-out or cut-in, arranged to inhibit or enable the actuating input to the delivery means above and/or below predetermined thresholds of fluid flow rate. For example, the threshold may be related to the output of

the flow sensor or the speed of an engine to which the apparatus is fitted. The cut-out or cut-in effect may, for example, control the supply of fuel to the engine or control a by-pass to a direct fuel-line.

The invention may also include means for varying the ratio of delivered additive to fluid dependant on the fluid flow rate. For example, the output of the sensing means may be fed to a frequency-to-voltage converter which is arranged to output a variable voltage applied to a voltage control pin on a multivibrator, forming part of the conditioning circuit, which is arranged to vary the output pulse width of the multivibrator.

In some circumstances it may be desirable to compensate for the over- or under-capacity of the delivery means in a particular situation. This is particularly so when the signal from the sensing means is a pulse train and the delivery is dependent on a series of strokes to inject the additive, as with an injector. To achieve this it may be preferable to multiply or divide the signal from the sensing means to apply a greater or lesser number of actuating pulses per transmitted signal pulse to account for the capabilities of the delivery means.

The invention is particularly applicable to regulating the delivery of a liquid additive, for example water or other cleaning agent to a liquid fuel, for example a petroleum-based fuel such as diesel oil.

The present invention can be put into practice in various ways one of which will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a block diagram of apparatus according to the invention;

Figure 2 is a circuit diagram of part of the apparatus in Figure l; and

Figure 3 is a block diagram of the same part of the apparatus of Figure 1 in a fuel line.

Referring to Figure 1 additive delivery regulating apparatus for regulating the addition of, for example, water to a flow of diesel oil in a fuel line comprises a flow sensor 10 for monitoring the rate of volumetric fluid flow in the fuel line. The sensor 10 transmits a signal proportional to the rate of fluid flow to a monostable multivibrator pulse generator 12. The output of the multivibrator 12 is a train of conditioned pulses which are amplified by an amplifier 14. The output of the amplifier 14 is applied directly to the input of a solenoid actuated delivery valve 16 which is arranged to control the delivery of the water additive to the fuel line. The solenoid valve 16 is conveniently constituted by a valve similar to those commonly used on electronic fuel injection (EFI) systems on current motor vehicles.

To provide continual variation of the output of the multivibrator 12 a frequency-to-voltage converter (FVC) 15 is connected from the output of the flow sensor 10 to a control voltage input of the multivibrator 12. The FVC 15 adjusts the output pulse width, i.e. duty cycle, of the multivibrator according to the frequency of the sensor output signal.

A threshold circuit 17 is also connected to the output of the sensor 10. The threshold circuit is responsive to the pulse frequency of the sensor output to open a switch 19 in the power rail of the amplifier. Thus, when the frequency drops below a predetermined value the threshold circuit opens the switch to inhibit the addition of water as an emulsifier to the engine fuel.

Part of this circuit is shown in more detail in Figure 2. The threshold and frequency-to-voltage convertor circuits are omitted for the sake of clarity. The flow sensor 10, the multivibrator 14 and the solenoid valve 16 are all supplied with electrictal power from between positive and negative electrical supply rails V+ and V-. Most conveniently for a vehicular application, this power supply is derived from the 12 volt battery supply in the vehicle. As the voltgage supplied to both the sensor 10 and the multivibrator 14 may influence, to a certain extent, the outputs therefrom and, therefore, their accuracy, the supply V+ is regulated by a voltage regulator 18 to provide a stable supply voltage.

The output of the flow sensor is connected between a resistor Rl and resistors R2 and R3 which are all serially connected between the regulator 18 and the negative supply rail V-. The resistor Rl is provided as a pull-up for the output of the sensor 10. The resistors R2 and R3 act as biasses for a transistor Tl which has its base connected between them. The output of the transistor Tl is conditoned by two resistors R4 and R5 which are both connected to the positive regulated supply rail V+ and to either side of a capacitor Cl. The side of the capacitor Cl connected to the resistor R4 is also connected to the collector of the transistor Tl. The emitter of the transistor Tl is connected directly to the negative supply rail V-.

The resistors R2, R3, R4 and R5, the transistor Tl and the capacitor Cl are used to detect the rising edge of the pulsed sensor output signal to produce a negative-going voltage spike as an indication of the rising edge. The spike is used an an unambiguous trigger for the multivibrator 12 which is a proprietory 555 type monostable integrated circuit component. Of course, any other suitable timer could be used to equal effect.

The time constant of the multivibrator 12 is conventionally set by a resistor R6 and capacitor C2. The resistor R6 and capacitor C2 are serially connected between the supply rails. The junction between the resistor R6 and the capacitor C2 is connected to a pair of setting inputs of the multivibrator 12. Thus, the output of the multivibrator 12 is a positive pulse of a duration set by the values of the resistor R6 and the

capacitor C2. This output is amplified by a transistor T2 sufficient to actuate the solenoid delivery valve 16.

Referring now to Figure 3 the invention is illustrated in a fuel line application for a motor vehicle in which it is required to deliver water at a very precise ratio to the volumetric flow of diesel fuel. The flow sensor 10A is a conventional Hall-effect type connected in the path of a fuel line 20. The sensor 10A has an impellor 22 which rotates at an angular velocity related to the flow rate of fuel in the fuel line 20. The blades of the impellor also pass a Hall-effect device 24 and cause a voltage to be induced as each one passes. Thus, the sensor 10A produces a series of output pulses at a rate in proportion to the flow rate of the fuel in the line 20.

The fuel line 20 is connected to the main input of a mixing chamber 26. The solenoid valve is an injector 16A mounted on the chamber 26 for injection of the additive water through an input 28. The output of the mixing chamber 26 carries the fuel and additive mixture to the internal combustion engine (not shown) .

The variable rate pulse train output of the Hall-effect device 24 of the sensor 10A is applied to the input of the circuitry comprising the pulse conditioning circuit. The monostable multivibrator 12, the amplifier 14 and the voltage regulator 18 of Figure 2 are shown generally by the block 30 in Figure 3. The output of the circuitry 30 is a conditioned pulse train which actuates the injector 16A to pass water at a rate

dependent on the rate of fuel flow. The solenoid valve used is, as mentioned, a conventional fuel injector type in this embodiment. While the valve is energised (ie. delivering) it has a substantially fixed flow rate. Thus, the actual flow over a given time is a product of the energised/de-energised duty cycle as is the case in an EFI system. As a point on each pulse from the sensor 10A represents a certain volume of fuel that has flowed since the equivalent on the last pulse, it is possible to energise the injector 16A for a fixed time on each pulse commensurate with the amount of additive required for that volume of fuel per cycle in the pulse train. To set the amount of additive per unit volume, it is simply a matter of adjusting the time constant of the monostable pulse output to command delivery for a greater or shorter duration by varying values of the resistor R6 and/or the capacitor C2.

The regulating and delivery apparatus according to the invention does not make a calculation based partially on a count of the pulses to produce a theoretical required rate of injection of additive to maintain a desired ratio. More simply and accurately the present invention actually drives directly the additive delivery valve, possibly through a conditioning circuit such as monostable multivibrator type pulse generating circuit. This results in a very simple circuit that is able to control the rate of injection more immediately based on the actual rate of fluid flow sensed directly by the sensor.

It will be appreciated that the invention is applicable to many different situations in which it is necessary to regulate accurately the rate of additive delivered to a fluid, for example liquid, line. The invention is also particularly suited to chemical processes involving the incorporation of additives to a fluid flow in specified ratios.