GB2420591A

GB2420591A - Assisting start of an internal combustion engine by restricting gas flow through the inlet

Info

Publication number: GB2420591A
Application number: GB0426047A
Authority: GB
Inventors: Edward Timothy Bishop
Original assignee: Connaught Motor Co Ltd
Current assignee: Connaught Motor Co Ltd
Priority date: 2004-11-26
Filing date: 2004-11-26
Publication date: 2006-05-31
Anticipated expiration: 2024-11-26
Also published as: GB0426047D0; GB2420591B

Abstract

A system for initiating starting in an internal combustion engine uses a valve 2 in the inlet passage, such as a butterfly valve, to restrict gas flow through the inlet. The method comprises at least partially closing the valve 2 to restrict flow of gas through the inlet, and accelerating cycling of the piston by means of a motor with the valve remaining closed through at least the downward stroke of the piston. Then on the subsequent downward stroke of the piston, the valve is opened, prior to ignition. The engine may be a diesel engine with a compression ratio of greater than 16:1.

Description

307207.GB

STARTING INTERNAL COMBUSTION ENGINES

This invention relates to the design and control of internal combustion engines, especially for assisting starting.

In order to start a conventional internal combustion engine the engine is cranked to initiate the combustion cycle. This is normally done by means of a motor, and so demands a motor that is sufficiently powerful to spin the engine and overcome resistance from inertia and from compression in the combustion chambers. The issue of compression is especially relevant for conventional diesel engines.

Conventional diesel engines run unthrottled air intake systems and have very high compression ratios. They therefore require powerful starter motors. Such motors are heavy and require a correspondingly powerful electrical system comprising heavy- duty cables and a heavy, high capacity, battery to power them, with a correspondingly large alternator for re-charging in anticipation of the next start. Thus the requirements surrounding the starting of diesel engines involve significant weight and cost penalties.

It is known to provide engines with a decompression valve that can be operated during starting to allow air to escape from the cylinder in the compression stroke.

The valve closes once the inertia of the engine has built to a speed sufficient to rotate it through the next compression event. However, such a valve is usually limited to low-speed or low output engines that do not have the benefit of multiple cylinders for two reasons.

1) The valve itself must find space in the combustion chamber (crowded in high- speed engines), it must exhaust somewhere (requiring additional porting) and yet must not detract from cooling.

2) The more cylinders in the engine the less the cyclic torque variation, and therefore the less the requirement.

There is therefore a need for an improved method of starting such engines, and especially for a less mechanically intrusive method of starting such engines.

In petrol engines throttle valves are installed in the air inlet passages to control the fuel/air mixture and to act as a choke at low temperatures. Whilst such valves can restrict air flow into the cylinders, even at their fully closed position they allow significant air to pass. They are not typically used to assist initial spinning of the engine. In diesel engines excess air in the mixture is advantageous and so diesel engines are not "throttled" for air: they have wide open manifolding, and the amount of diesel fuel injected into that air is the controlling factor.

According to a first aspect of the present invention there is provided a method for initiating ignition in an internal combustion engine having at least one combustion chamber, an inlet for ingress of gas into the combustion chamber, an outlet for egress of combustion products from the combustion chamber, means for supplying fuel to the combustion chamber, piston means movable for cyclically varying the volume of the combustion chamber, a motor for driving the piston to cycle, and a valve for restricting gas flow through the inlet, the method comprising the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.

The engine preferably has a compression ratio greater than 16:1. The engine could suitably be a diesel engine.

The step of opening the valve is preferably performed before ignition takes place; it is preferably performed when the engine has reached a speed suitable for continued operation of the engine under combustion.

The valve could suitably be a butterfly valve, It could suitably be located outside the combustion chamber.

Preferably, at the commencement of the said accelerating step the piston is at rest.

The step of opening the valve is suitably performed in response to the cycling of the piston reaching a preset rate.

During the said accelerating step the valve preferably remains fully closed. During that step, preferably no fuel is introduced into the chamber.

The engine could suitably be part of a hybrid power system in which power generated by the engine can be supplemented by an auxiliary power source.

The engine could have an output shaft coupled to the engine through a clutch and the method could suitably comprise the step of maintaining the clutch in an engaged state during the said accelerating step.

Preferably, during normal operation of the engine, the valve could be made to at least partially close in response to detection of a reduction in power demand, and whilst the valve remains partially closed energy from the output shaft could suitably be recovered and stored.

The engine could comprise two or more combustion chambers, and one such valve could be provided for each combustion chamber and all those valves could be closed and opened as aforesaid.

According to a second aspect of the present invention there is provided an internal combustion engine having: at least one combustion chamber; an inlet for ingress of gas into the combustion chamber; an outlet for egress of combustion products from the combustion chamber; means for supplying fuel to the combustion chamber; piston means movable for cyclically varying the volume of the combustion chamber; a motor for driving the piston to cycle; a valve for restricting gas flow through the inlet; and a control unit arranged to initiate ignition of the engine by means of the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.

According to a third aspect of the present invention there is provided a control unit for an internal combustion engine having at least one combustion chamber, an inlet for ingress of gas into the combustion chamber, an outlet for egress of combustion products from the combustion chamber, means for supplying fuel to the combustion chamber, piston means movable for cyclically varying the volume of the combustion chamber, a motor for driving the piston to cycle, and a valve for restricting gas flow through the inlet, the control unit being arranged to initiate ignition in the engine by means of the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: figure 1 is a schematic drawing of a diesel engine and associated control apparatus; figure 2 is an enlarged view of part of the engine of figure 1, showing a valve installation in more detail.

The diesel engine 1 of figure 1 has throttles 2 that can be operated during starting to restrict incoming air flow. When air flow into the engine is restricted, less air is present in the combustion chambers 3 and so the contents of the chambers can more readily be compressed. As a result, in comparison to a conventional diesel engine the engine can be spun more easily up to a starting speed by a starter motor 4. When a suitable speed for starting is reached the throttles 2 are opened, allowing air into the combustion chambers as normal. At that stage the inertia of the rotating components, including the flywheel 5, assist the starter motor in spinning the engine.

As a result, the starter motor 4 can be smaller than would be needed to start a conventional diesel engine and the power supply to it can be scaled down accordingly. This can allow weight and cost savings.

The engine of figures 1 and 2 will now be described in more detail. In figures 1 and 2 like reference numerals denote like components.

The engine of figure 1 comprises an engine block 6 defining a number of cylinders therein. A piston 7 is free to slide axially in each cylinder and has seals 8 that bear against the interior of the respective cylinder. The pistons are connected to a crankshaft 9 so that reciprocating motion of the pistons can drive the crankshaft to rotate. The crankshaft is attached to a flywheel 5 and an output shaft 11. A clutch 26 and a gearbox 27 can couple the output shaft to or decouple it from a final drive shaft 28. The output shaft is normally decoupled from the final drive shaft during starting to reduce the load on the motor 4.

Combustion chambers 3 are defined between the working face of each piston and the top of the respective cylinder. Each combustion chamber has an inlet 12 (see figure 2) for the inflow of air to be combusted, an outlet 13 for the outflow of combustion products and a fuel injector 14 for injecting fuel into the combustion chamber. The inlet 12 and outlet 13 can be closed by valves 15, 16 respectively.

The valves are operated by a camshaft 17 which is mechanically linked and operationally synchronised to the crankshaft by some means so that the engine can follow the normal operational cycle.

A throttle valve 2 is fitted in each inlet 12. In this example the throttles are constituted by butterfly valves and each throttle comprises a throttle butterfly 20 which is pivotally mounted in the respective inlet. Each throttle has an electrically controlled magnetic actuator 21 which can set the position of the butterfly. The magnetic actuators are controlled by an engine management unit 22.

All the throttles could be mounted in-line on a single spindle, or could be individually actuated. They could be operated by many means from hydraulic to electric motor.

The engine management unit controls the operation of the engine. It receives inputs from user controls such as a starter switch 23 and an accelerator 24 and from sensors that monitor the operation of the engine, such as an engine speed sensor 25. It processes those inputs by means of software which it stores, and provides outputs that control the operation of the components of the engine, including the valve actuators 21, the starter motor 4 and the fuel injectors 14.

In operation, with the engine at rest a user can press the starter switch 23 to start the engine. The engine management unit 22 detects that the switch 23 has been pressed and initiates the following starting sequence.

1. The actuators 21 are signalled to close the throttles 2, restricting flow of air into the combustion chambers. The throttles are preferably closed fully, but they could be closed only partially to reduce the load on the engine during the induction stroke.

2. The motor 4 is signalled to start spinning the crankshaft 9. Due to the action of the throttles 2 air flow into the combustion chambers is limited. As a result, there is little air to be compressed during the compression stroke of each piston, and so there is reduced and more evenly distributed resistance to rotation due to compression. At this point in the sequence the fuel injectors can optionally be controlled to prevent injection of fuel since due to the action of the throttles 2 there will be insufficient air in the combustion chambers to allow useful combustion.

3. When the management unit 22 detects that a suitable starting speed has been reached it signals the actuators 21 to open the throttles 2. This allows air freely into the combustion chambers. As a result the resistance due to compression increases, but this is mostly counteracted by the inertia of the rotating parts of the engine, and especially the flywheel 10. At this point the injectors 14 can be controlled to inject fuel into the combustion chambers as normal to allow the combustion cycle to start.

4. When the management unit detects that the engine has fired the motor 4 is deactivated, and the engine can run as normal. The motor can be physically decoupled from the crankshaft by means of a solenoid-operated gear.

Due to the action of the valves 2 in restricting the flow of air into the combustion chambers the force required during each compression stroke is reduced, and the load on the motor is less. In a normal engine a full intake of air would be inducted and then squeezed into a space about 1120th of its size, i.e. to 20 bar (300psi). In comparison, during the induction stroke of the present engine, when inflow is restricted, the pressure imposed on the underneath of the piston by causing a suction on top, atmospheric pressure is I bar or (14.7 psi), which is the maximum that can be achieved. If the piston has a surface area of 6 in2 (3900 mm2) the maximum suction would be 6 bar (90 psi). In that example the peak force required during cranking can be reduced to about 113rd of the normal.

As the engine continues to run, two classes of control regime are available. The throttles 2 could be left fully open during normal operation. Alternatively, the throttles could be adjusted by the engine management unit 22 based on the programming stored in it and the inputs received by it in order to affect the performance of the engine. One example of such a method is described in more detail below.

The engine speed at which the throttles are closed during the starting sequence is preferably in the range from zero to 200 rpm. For a hybrid type "starter", however, it might be advantageous to spin the engine up to 1200rpm. The valves 2 could be opened gradually at step 3 of the starting sequence so as to avoid suddenly increasing the load on the starter motor. The valves 2 could be opened gradually as the engine speed increases even from a very low level.

It is preferred that the throttles 2 are located as close as possible to the combustion chambers. This minimises the amount of air that can be drawn into the combustion chambers during the starting sequence and reduces the need to reinforce the downstream portions of the inlet pathways against any effects of negative pressure that might be experienced when the throttles are closed during the starting sequence.

However, it would be possible to locate the throttles downstream or even to have a single throttle in a part of the inlet pathway that is common to all the combustion chambers. It will also be appreciated that advantages can be obtained even if inflow to fewer than all of the cylinders is restricted. To restrict the amount of air in the cylinders, it is highly advantageous that the throttle plates of the valves be mounted with the minimum port volume between them and the combustion chamber.

Preferably the valves are located adjacent to the combustion chambers.

Whilst butterfly valves are one suitable type of valve, other types could be used. If the normal inlet valves 15 are individually controllable or separately controllable to that of the exhaust valves then they can be used to limit flow during the starting sequence, avoiding the need for additional valves. However, this requires complex control mechanisms.

The techniques described above provide particular advantages in diesel engines. In the engine of figure 1 ignition is initiated by compression of the fuel/air mixture, possibly with the assistance of a glow plug (not shown in the figures).

The techniques described above have particular advantages when applied to diesel/electric hybrid powertrains, especially those of the types proposed for automotive use. Since the motor 4 can drive the output shaft 11, in a hybrid application the motor could provide output power to supplement or replace that from the engine during certain circumstances. The use of valves 2 as described above means that the rotation of the engine during starting will be smoother than in engines in which full compression is experienced during starting. As a result, the motor can drive the output shaft relatively smoothly whilst cranking the engine during starting.

This reduces the need to disconnect the output shaft from the final drive and the driven equipment during starting. For example, in the case where the output shaft is connected to the wheels of a vehicle the motor could drive both the wheels and the engine from rest as the starting sequence is conducted. When the engine fires it could take over drive from the motor. The relative smoothness of the engine during start-up means that the final drive shaft turns relatively smoothly throughout this procedure.

In hybrid vehicles energy can be regenerated as the vehicle is decelerating by driving a generator (which could be motor 4) from the output shaft 11. Such regeneration is hampered by the fact that compression in the combustion chambers of the engine causes engine braking which also absorbs energy. The valves 2 can be used to reduce engine braking by reducing compression in an analogous way to that which is employed during starting. During regeneration the valves 2 can be fully or partially closed by the engine management unit.

The techniques described above are applicable to engines of other physical designs, for example rotary engines. They are also suitable for engines in which the fuel is introduced into the cylinder with the incoming gas (e.g. engines having a carburettor or fuel injectors in the inlet path) since the gas is allowed to flow into the cylinder when ignition is desired to commence.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A method for initiating ignition in an internal combustion engine having at least one combustion chamber, an inlet for ingress of gas into the combustion chamber, an outlet for egress of combustion products from the combustion chamber, means for supplying fuel to the combustion chamber, piston means movable for cyclically varying the volume of the combustion chamber, a motor for driving the piston to cycle, and a valve for restricting gas flow through the inlet, the method comprising the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.

2. A method as claimed in claim 1, wherein the engine has a compression ratio greater than 16:1.

3. A method as claimed in any preceding claim, wherein the engine is a diesel engine.

4. A method as claimed in any preceding claim, wherein the step of opening the valve is performed before ignition takes place.

5. A method as claimed in any preceding claim, wherein the step of opening the valve is performed when the engine has reached a speed suitable for continued operation of the engine under combustion.

6. A method as claimed in any preceding claim, wherein the valve is a butterfly valve.

7. A method as claimed in any preceding claim, wherein the valve is located outside the combustion chamber.

8. A method as claimed in any preceding claim, wherein at the commencement of the said accelerating step the piston is at rest.

9. A method as claimed in any preceding claim, wherein the step of opening the valve is performed in response to the cycling of the piston reaching a preset rate.

10. A method as claimed in any preceding claim, wherein during the said accelerating step the valve remains fully closed.

11. A method as claimed in any preceding claim, wherein during the said accelerating step no fuel is introduced into the chamber.

12. A method as claimed in any preceding claim, wherein the engine is part of a hybrid power system in which power generated by the engine can be supplemented by an auxiliary power source.

13. A method as claimed in claim 12, wherein the engine has an output shaft coupled to the engine through a clutch and the method comprises the step of maintaining the clutch in an engaged state during the said accelerating step.

14. A method as claimed in claim 12 or 13, comprising during normal operation of the engine at least partially closing the said valve in response to detection of a reduction in power demand, and whilst the valve remains partially closed recovering and storing energy from the output shaft.

15. A method as claimed in any preceding claim, wherein the engine comprises two or more combustion chambers and one such valve is provided for each combustion chamber and all those valves are closed and opened as aforesaid.

16. An internal combustion engine having: at least one combustion chamber; an inlet for ingress of gas into the combustion chamber; an outlet for egress of combustion products from the combustion chamber; means for supplying fuel to the combustion chamber; piston means movable for cyclically varying the volume of the combustion chamber; a motor for driving the piston to cycle; a valve for restricting gas flow through the inlet; and a control unit arranged to initiate ignition of the engine by means of the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.

17. A control unit for an internal combustion engine having at least one combustion chamber, an inlet for ingress of gas into the combustion chamber, an outlet for egress of combustion products from the combustion chamber, means for supplying fuel to the combustion chamber, piston means movable for cyclically varying the volume of the combustion chamber, a motor for driving the piston to cycle, and a valve for restricting gas flow through the inlet, the control unit being arranged to initiate ignition in the engine by means of the following steps: at least partially closing the valve to restrict flow of gas through the inlet; accelerating cycling of the piston by means of the motor with the valve remaining at least partially closed during at least a part of the piston's cycle in which it would otherwise draw gas through the inlet into the combustion chamber; and subsequently opening the valve to enable the piston to draw gas freely past the valve during the said part of the piston's cycle.