GB2510302A

GB2510302A - ECU utilising a variable slew rate to modify a PWM signal

Info

Publication number: GB2510302A
Application number: GB201408631A
Authority: GB
Inventors: Gary Oliver
Original assignee: Triumph Designs Ltd
Current assignee: Triumph Motorcycles Coventry Ltd
Priority date: 2014-05-15
Filing date: 2014-05-15
Publication date: 2014-07-30
Anticipated expiration: 2034-05-15
Also published as: GB201408631D0; GB2510302B

Abstract

An electronic control unit configured to provide a pulse-width-modulated signal controlling opening of a valve 14 providing air and fuel vapour from a collector unit 12, used to collect fuel vapour from a fuel tank 10, to an engine 16, the PWM signal being modified by a variable slew rate. Preferably the duty cycle of the PWM signal is increased by the slew rate according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the fuel flow rate and one or more stages of increased slew rates corresponding to a slow increase, or substantially no increase, in flow rate. The ECU may calculate the slew rate using a look-up table or an algorithm. Also claimed is a method of operation. The ECU allows for better management of fuel flow from the collector to the engine.

Description

Electronic Control Unit

Field of the Invention

This invention relates to an electronic control unit. Particularly, the invention relates to improvements in an Electronic Control Unit for an internal combustion engine.

Background to the Invention

Electronic Control Units (ECUs) are embedded systems used in modern vehicles to control many aspects of vehicles, such as the air/fuel mix to the engine, emissions, performance optimization, and the general running of the engine and vehicle subsystems. One of the systems controlled by the ECU is the EVAP (Evaporative emission control) system which deals with fuel that evaporates in the fuel tank. EVAP systems were introduced to adhere to stricter controls on vehicle emissions. The aim of EVAP systems is to store and dispose of fuel vapour so that it does not escape to the atmosphere.

The fuel tank does not vent directly to the atmosphere. The EVAP system captures fuel vapour evaporated from the stored fuel and releases the fuel vapour to the engine at a predetermined time. Fuel vapour is ducted to a collector to store the fuel until it can be released to the engine through a valve and burnt. When the engine is stopped, the fuel tank vapour is collected in the collector. For example, the vapour may be adsorbed by charcoal in the collector. Generally, when the engine is started the vapour stored in the collector is drawn back into the inlet manifold of the engine, by drawing fresh air through the collector, and burnt in the engine.

The purging of the fuel tank emissions, from the EVAP collector, involves opening a valve controlled by the ECU. However, the addition of the fuel vapour from the collector to the main combustion air/fuel mixture can cause problems with the accuracy of the fuelling control system, which is also controlled by the ECU.

The present invention has therefore been devised with the foregoing in mind. The invention seeks to overcome or ameliorate at least one of the disadvantages of the

prior art, or provide a useful alternative.

Summary of the Invention

According to a first aspect of an invention there is provided an electronic control unit (ECU) fol an internal combustion engine, the ECU adapted to control an air/fuel mixture piovided to the engine and to control the opening of a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank.

The ECU is configured to provide a pulse-width-modulated (PWM) control signal controlling opening of the valve, the PWM signal being modified by a variable slew rate.

The advantage of this is that the speed of the opening of the control valve can be controlled so the fine balance of airlfuel mix added to the engine is not substantially affected and the engine can be brought into its ideal air/fuel mix operating range relatively quickly.

The PWM signal has a duty cycle that may be increased by the slew rate, the slew rate may vary according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and may have one or more stages with increased slew rates. This has the advantage of opening the PCV more slowly at the start of each opening event and increasing the speed of opening of the PCV towards the end of each opening event which allows better management of the additional fuel from the collector whilst maximising the speed of emptying the collector. There is a more controlled introduction of fuel throughout the whole % duty cycle and the flow rate (flow over time) can be increased more steadily, which is more manageable for the fuelling control system.

One of the stages with increased slew rate may correspond to an opening range of the valve that produces a slow increase in the flow rate of fuel through the valve. This has the advantage of maximising the speed of emptying the collector.

One of the stages with increased slew rate may correspond to an opening range of the valve that produces substantially no increase in the flow rate of fuel through the valve.

The ECU may be configured to calculate the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table. This has the advantage of using the ECU to set, and modify if required, the step sizes at predetermined % duty cycle which controls the speed of opening of the control valve.

The ECU may be configured to calculate the slew rate corresponding to the current % duty cycle at that time using an algorithm. This has the advantage of using the ECU to set, and modify if required, the step sizes at any predetermined % duty cycle which controls the speed of opening of the control valve.

According to a second aspect of the present invention, there is provided an internal combustion engine having a fuel inlet for receiving a fuel and air mixture, the fuel inlet comprising an auxiliary fuel inlet for receiving fuel from a collector unit used to collect fuel vapour from a fuel tank. The auxiliary inlet comprises a control valve responsive to a pulse-width-modulated (PWM) control signal controlling opening of the valve, and an electronic control unit (ECU) configured to provide said FWM signal to said valve. The PWM signal is modified by a variable slew rate. This has the advantage of avoiding the fuel from the auxiliary inlet overly affecting the optimum fuel/air mix added to the engine.

The PWM signal has a duty cycle that may be increased by said slew rate, the slew rate may vary according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and may have one or more stages with increased slew rates.

According to a third aspect of the present invention, there is provided a method of opening a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank using an electronic control unit (ECU) for an internal combustion engine comprising: providing a pulse-width-modulated (PWM) signal and modifying the PWM control signal by a variable slew rate. This has the advantage of allowing the opening of the control valve to be controlled depending on the flow rate of fuel required to not overly affect the air/fuel mix calibration set by the fuelling control system.

The method of opening a control valve may further comprise increasing a duty cycle of the PWM signal by said slew rate, and varying the slew rate according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates. This has the advantage of avoiding the large flow of fuel which would upset the calibration of the air/fuel mix to the engine and introduces the fuel more slowly.

The method of opening a control valve may further comprise calculating the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table.

The method of opening a control valve may further comprise calculating the slew rate corresponding to the current % duty cycle at that time using an algorithm.

Brief Description of the invention

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a view of a simple EVAP system in accordance with an embodiment of the present invention; Figure 2 shows a graph of % duty cycle against flow for a PWM control in accordance with the embodiment of Figure 1.

Figure 3 shows a graph of the increase over time of % duty cycle of the PCV with a modified slew rate in accordance with an embodiment of the present invention.

Figure 4 shows a graph of the increase over time of % duty cycle of the PCV with a modified slew rate in accordance with an embodiment of the present invention.

Description of the embodiments of the invention

With reference to Figure 1, there is shown an EVAP system 1 comprising a fuel tank 10, a collector 12, a purge control valve (PCV) 14, an engine 16, inlet manifold 17, an oxygen sensor 18 in an exhaust pipe 20, a first EVAP pipe 21 and a second EVAP pipe 22. The collector also comprises a collector vent 24.

When the engine 16 is stopped, the vapour which evaporates in the fuel tank 10 passes through the first EVAP pipe 21 and is collected in the collector 12. When the engine 16 is started the vapour stored in the collector 12 is drawn through the second EVAP pipe 22 and into the inlet manifold 17 of the engine 16 and burnt in the engine 16. In order to run the engine 16, while the vapour from the collector 12 is being added to the inlet manifold 17, fuel from the fuel tank 10 and air from the atmosphere is added to the inlet manifold 17 through a main fuel pipe and an air pipe (not shown) respectively. The additional fuel from the collector 12 that is added at the same time as the air/fuel mix can cause problems with the accuracy of the fuelling control system. A part of an ECU (Electronic Control Unit), which controls many features of a vehicle, is the fuelling control system. This uses readings from the oxygen sensor 18, in a closed loop feedback system, to keep the air/fuel mix in the engine 16 operating within an ideal operating range in real time. The fuel from the collector 12, when added, can affect this fine balance and means it can take longer to bring the engine 16 into its ideal operating range.

The PCV 14 is disposed in the second EVAP pipe 22, between the collector 12 and the manifold 17, and comprises a pulse-width-modulated (PWM) controlled solenoid which controls the rate of opening of the FCV 14 for drawing fuel into the engine 16 from the collector 12. The PWM control signal has a % duty cycle which measures the proportion of "on" time for the signal to the period of time. The % duty cycle determines how far the PCV 14 has opened, e.g. a % duty cycle of 30% means that the valve is 30% open. As shown in Figure 2, a graph of % duty cycle against flow, PWM signal for the PCV 14 has a very non-linear relationship. At idle there is no flow so the % duty cycle is set to 0% and then, as the throttle (not shown) is opened the % duty cycle increases with a corresponding increase in flow rate. As mentioned, the % duty cycle and flow have a very non-linear relationship so, in an initial section, at a low % duty cycle, there is a relatively low and constant flow, shown by a flat line; in a mid section, as the % duty cycle is increased the flow increases rapidly, shown by a steep gradient; and in an end section the % duty cycle is increased further the flow increases more slowly, shown by a slowly reducing gradient, before flattening off once more to constant level. This means that as the % duty cycle is increased, there would be a, relatively, very rapid increase in flow of fuel in the mid % duty cycle section. This rapid increase could affect the fuelling control system as the fuel needs to be introduced slowly to avoid affecting the fine balance of the air/fuel mix in the engine.

To overcome the problem of the fuel from the collector 12 affecting the fuelling control system, embodiments of the present invention make use of a variable slew rate. The % duty cycle of the PWM signal is increased at the slew rate. With a linear, or non-varying, slew rate the PWM signal % duty cycle is increased by a small step value each event time, e.g. moving from 0% duty cycle to 100% duty cycle by 1% every 1 second.

Such a linear slew rate, if set to a small enough step size, would result in a slow and manageable introduction of fuel, and so would avoid a rapid increase in fuel flow in the mid % duty cycle. However it would take longer, e.g. 100 seconds, before full flow was achieved which is not ideal for emptying the EVAP collector 12. On the other hand, if the speed of the linear slew rate was increased, i.e. to a larger step size per event time, to reduce the collector 12 overall emptying time, then there would be a higher risk of the emission problems referred to above recurring.

Therefore, in embodiments of the invention the step size of the slew rate is varied so that, at lower PWM signal % duty cycle the step size is small, which results in a slower opening of the PCV 14, and at higher PWM signal % duty cycle the step size is large, which results in a faster opening of the PCV 14. This modified slew rate is advantageous over the linear slew rate as it means that, at lower FWM signal % duty cycle there is a slower opening of the PCV 14 whereas at higher PWM signal % duty cycle there is a faster opening of the PCV 14. Hence, a more controlled introduction of fuel throughout the whole % duty cycle can be achieved, i.e. the flow rate (flow over time) can be increased more steadily, which is more manageable for the fuelling control system. Therefore, in embodiments of the present invention, instability in the air/fuel mix to the engine 16 can be avoided and flow rate of the fuel from the collector 12 can be maximised.

In some embodiments a look-up table in the ECU is used to produce the modified slew rate and relies on modifying the step value of the slew rate depending on the current % duty cycle -see Table 1 for example values and rates.

PCV%DUTY 0 8 20 50 100 MPCV DUTY 0.1 0.5 1 1 Table 1: Example values for Modifier PCV DUTY and PCV % Duty cycle.

The modified slew rate is calculated by multiplying the step size of the slew rate by the number (modifier) in the "MPCV DUTY" row corresponding to the current % duty cycle cross-referenced in the PCV % DUTY row. So in the example of Table 1, if the step size of the slew rate is calibrated to be an increase of 10% duty cycle every 1 second, then: When % duty cycle is low (0 to 20%) the step size would be 1% duty cycle every 1 second as 0.lxlO% = 1%. When % duty cycle is medium (20% to 50%) the step size would be 5% duty cycle every 1 second 0.5x10% = 5%. When % duty cycle is high (50 to 100%) the step size would be 10% duty cycle every 1 second as 1 xlO% = 10%.

The values in the table and therefore the step sizes may be set to any suitable number that may produce the required modified slew rate. Also, interpolation could be used to estimate the values of the step size (% duty cycle increase per second) between the step size values with specific predetermined multipliers, e.g. a value for the step size at 15% duty cycle may be interpolated from the step size at 8% duty cycle and 20% duty cycle which have been calculated from multiplying the predetermined modifier and the calibrated slew rate. However, preferably, interpolation is not used so as to reduce processing load.

The slew rate is modified according to the factor in the table corresponding to the current % duty cycle. The PCV 14 would be opened more slowly at the start of each opening event which allows better management of the additional fuel from the collector 12 by the fuelling control system. Also, it allows the % duty cycle to be increased quickly towards the end of each opening event, which increases the speed of opening of the PCV 14, and allows the flow of the fuel and the speed of emptying the collector 12 to be maximised. -See Figure 3 for a graph of the increase in % duty cycle of the PCV 14 when the slew rate has been modified by Table 1. Figure 3 shows that the opening of the PCV 14 follows a non-linear response with an increasingly steep gradient as time progresses.

Table 2 shows another example of possible values for modifying the slew rate.

PCV%DUTY 0 8 20 50 100 MPCVDUTY 0.5 0.5 0.75 1 1 Table 2: Example values for MPCVDUTY and PCV % Duty cycle.

In the example of Table 2, if, again, the step size of the slew rate is calibrated to be an increase of 10% duty cycle every 1 second, then: When % duty cycle is low (0 to 8%) the step size would be 5% duty cycle every 1 second as 0.5x10% = 5%. When % duty cycle is medium (20%) the step size would be 7.5% duty cycle every 1 second as 0.75x10% = 7.5%. When % duty cycle is high (50 to 100%) the step size would be 10% duty cycle every 1 second as lxlO% = 10%. Figure 4 shows a graph of the increase in % duty cycle of the PCV when the slew rate has been modified by Table 2.

At the mid section of the % duty cycle, which produces a rapid increase in fuel flow rate in the graph of Figure 2, the step size is kept smaller due to the large increase in flow for a relatively small increase in % duty cycle; and then at the end section of the % duty cycle, the step size is increased as the flow increases at a steadily decreasing rate when compared with % duty cycle.

In alternative embodiments other ways of varying the slew rate may be used. For example an algorithm may be employed by the ECU to calculate the slew rate depending on the current % duty cycle signal.

It will be appreciated by persons skilled in the art that various modifications may be made to the above embodiment without departing from the scope of the present invention as defined by the claims. For example, whilst the above discussion has been concerned with controlling the opening of a FCV, the invention is equally applicable to other types of valves.

Claims

CLAIMS: 1. An electronic control unit (ECU) for an internal combustion engine, the ECU adapted to control an air/fuel mixture provided to the engine and to control the opening of a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank, wherein the ECU is configured to provide a pulse-width-modulated (PWM) control signal controlling opening of the valve, the PWM signal being modified by a variable slew rate.
2. The ECU of claim 1, wherein the PWM signal has a duty cycle that is increased by said slew rate, the slew rate varying according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates.
3. The ECU of claim 2, wherein one of the stages with increased slew rate corresponds to an opening range of the valve that produces a slow increase in the flow rate of fuel through the valve.
4. The ECU of either of claims 2 or 3, wherein one of the stages with increased slew rate corresponds to an opening range of the valve that produces substantially no increase in the flow rate of fuel through the valve.
5. The ECU of any of claims 2 to 4, wherein the ECU is configured to calculate the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table.
6. The ECU of any of claims 2 to 4, wherein the ECU is configured to calculate the slew rate corresponding to the current % duty cycle at that time using an algorithm.
7. An internal combustion engine having a fuel inlet for receiving a fuel and air mixture, the fuel inlet comprising an auxiliary fuel inlet for receiving fuel from a collector unit used to collect fuel vapour from a fuel tank, wherein the auxiliary inlet comprises a control valve responsive to a pulse-width-modulated (PWM) control signal controlling opening of the valve, and an electronic control unit (ECU) configured to provide said PWM signal to said valve, wherein the PWM signal is modified by a variable slew rate.
8. The internal combustion engine of claim 7, wherein the PWM signal has a duty cycle that is increased by said slew rate, the slew rate varying according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates.
9. A method of opening a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank using an electronic control unit (ECU) for an internal combustion engine comprising: providing a pulse-width-modulated (PWM) signal; modifying the PWM control signal by a variable slew rate.
10. The method of claim 9, further comprising: increasing a duty cycle of the PWM signal by said slew rate; and varying the slew rate according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates.
11. The method of claim 10, further comprising: calculating the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table.
12. The method of claim 10, further comprising: calculating the slew rate coriesponding to the current % duty cycle at that time using an algorithm.
13. An ECU substantially as hereinbefore described with reference to the accompanying drawings.
14. An internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings
15. A method of opening a control valve substantially as hereinbefore described with reference to the accompanying drawings.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS: 1. An electronic control unit (ECU) for an internal combustion engine, the ECU adapted to control an air/fuel mixture provided to the engine and to control the opening of a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank, wherein the ECU is configured to provide a pulse-width-moduiated (PWM) control signal controlling opening of the valve, the PWM signal being modified by a variable slew rate, and wherein the PWM signal has a duty cycle that is increased by said slew rate, the slew rate varying according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates. n.e2. The ECU of claim 1, wherein one of the stages with increased slew rate * corresponds to an opening range of the valve that produces a slow increase in the : *". flow rate of fuel through the valve. 0*e*3. The ECU of claim 2, wherein one of the stages with increased slew rate corresponds to an opening range of the valve that produces substantially no * :e: increase in the flow rate of fuel through the valve.4. The ECU of either of claims 2 or 3, wherein the ECU is configured to calculate the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table.5. The ECU of either of claims 2 or 3, wherein the ECU is configured to calculate the slew rate corresponding to the current % duty cycle at that time using an algorithm.6. An internal combustion engine having a fuel inlet for receiving a fuel and air mixture, the fuel inlet comprising an auxiliary fuel inlet for receiving fuel from a collector unifr used to collect fuel vapour from a fuel tank, wherein the auxiliary inlet comprises: a control valve responsive to a pulse-width-modulated (PWM) control signal controlling opening of the valve, and an electronic control unit (ECU) configured to provide said PWM signal to said valve, wherein the PWM signal is modified by a variable slew rate, wherein the PWM signal has a duty cycle that is increased by said slew rate, the slew rate varying according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates.7. A method of opening a control valve providing air and fuel vapour from a collector unit used to collect fuel vapour from a fuel tank using an electronic control unit (ECU) for an internal combustion engine comprising: providing a pulse-width-modulated (PWM) signal; modifying the PWM control signal by a variable slew rate: * increasing a duty cycle of the PWM signal by said slew rate; and varying the slew rate according to a predetermined pattern having a stage with a low slew rate corresponding to an opening range of the valve that produces a rapid increase in the flow rate of fuel through the valve and one or more stages with increased slew rates.**** - 8. The method of claim 7, further comprising: calculating the slew rate by multiplying a predetermined value, corresponding to the current % duty cycle at that time, by a calibrated slew rate using a look-up table.9. The method of claim 8, further comprising: calculating the slew rate corresponding to the current % duty cycle at that time using an algorithm.10. An ECU substantially as hereinbefore described with reference to the accompanying drawings.11. An internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings 12. A method of opening a control valve substantially as hereinbefore described with reference to the accompanying drawings. oeG*S * * .. o * * S... 00*. *0 * 0 * * *0