GB2211245A

GB2211245A - Forced induction I.C. engine control system

Info

Publication number: GB2211245A
Application number: GB8724473A
Authority: GB
Inventors: Mark Jonathan Kingscott
Original assignee: STAG ELECTRONIC DESIGNS
Current assignee: STAG ELECTRONIC DESIGNS
Priority date: 1987-10-19
Filing date: 1987-10-19
Publication date: 1989-06-28
Also published as: GB8724473D0

Abstract

A waste gate control valve 6 is operated in response to the pulse width of the pulses from a pulse generator7 to switch between air at atmospheric pressure and compressed air. The pulse width may be controlled by a manually operable potentiometer 8 to provide a desired boost pressure and/or in response to signals from an engine ignition and fuel injection control 10 and maximum speed or boost or boost range signals. <IMAGE>

Description

CONTROL SYSTEM FOR FORCED INDUCTION INTERNAL COMBUSTION ENGINE The present invention relates to a control system for a forced induction internal combustion engine.

It is known to provide an internal combustion engine with a forced induction arrangement comprising a turbine driven by exhaust gases from the engine and driving an air compressor which supplies pressurised air to the inlet manifold of the engine. It is also known to provide a waste gate for varying the exhaust gases supplied to the turbine in order to control or limit the boost pressure of air in the inlet manifold. It is further known to provide a servo for controlling the waste gate permitting a degree of manual control of the boost pressure by means of a control device which is operable by a driver of the vehicle. The control device comprises a bleed off valve controlled from the passenger compartment by a tap which can be turned from a fully opened position corresponding to maximum boost to a fully closed position corresponding to minimum or zero boost.However, this is inconvenient because the tap requires many turns to change from minimum to maximum boost and provides no indication of the degree of boost. Also, the contol law of the system is somewhat unpredictable, and the presence of a boost gauge gives only little information about the actual setting of the boost pressure.

According to one aspect of the invention, there is provided a control system for a forced induction internal combustion engine, in which boost pressure is controlled or limited by pulse width modulation.

According to another aspect of the invention, there is provided a control system for a forced induction internal combustion engine having a waste gate controlling supply of exhaust gases to a turbo charger.

the control system comprising a user-operable control for controlling boost pressure. a pulse generator for generating pulses whose width is controlled by the useroperable control, a control valve for switching between air at atmospheric pressure and compressed air in response to the pulse width of the pulses from the pulse generator, and a servo for controlling the waste gate in response to air from the control valve.

The user-operable control may be a potentiometer or variable resistor, for instance having a rotary travel of 270 and a graduated or calibrated scale giving a clear indication of the boost pressure or degree of control and allowing easy adjustment between minimum and maximum boost. Thus, boost can be easily and accurately set and re-set and is convenient for use by a driver of a vehicle. By pulse width modulating the control valve between atmospheric pressure and inlet manifold pressure. the waste gate control servo effectively receives a variable pressure which depends on the pulse width modulation.

Connection between the control valve and the pulse generator, or between the pulse generator and the control, may conveniently be by means of electrical conductors so that there is no need for any complex mechanical linkage or plumbing in order to control the boost pressure.

The invention will be further described, by way of example, with reference to the accompanying drawing which is a block schematic diagram of a preferred control system.

An internal combustion engine 1, which may be a spark-ignition engine or a compression-ignition (diesel) engine, receives a fuel/air mixture from an inlet manifold 2. Exhaust gases from the engine 1 are supplied to the turbine of a turbo charger forming part of a turbo charging arrangement 3. from which the gases are vented to the atmosphere via a conventional exhaust system. The turbo charging arrangement includes a waste gate which controls the proportion of exhaust gases fed to the turbine, the remainder by-passing the turbine and flowing directly to the exhaust system, so as to control, for instance limit, the speed of the turbine.

The turbine drives an air compressor or "booster" which receives air at atmospheric pressure from an air intake 4 and supplies compressed air to the inlet manifold 2.

In the embodiment shown, the waste gate is aircontrolled by means of a waste gate control servo shown diagrammatically at 5. The control servo 5 receives air from a waste gate control valve 6 at a (mean) pressure which determines the opening and closing-of the waste gate by the control servo 5. The control valve 6 is electronically controlled and comprises a two-way valve for switching between air at atmospheric pressure from the intake 4 and compressed air whose pressure has been boosted by the turbo charger from the inlet manifold '2.

The control valve 6 is controlled by a pulse width modulation electronic circuit 7 provided with a variable boost control in the form of a potentiometer 8 and an override switch 9. The pulse width modulation electronic circuit 7 also receives control signals from an engine control unit 10, for instance forming at least part of an engine management system for controlling ignition timing and injection of fuel. The pulse width modulation electronic circuit 7 further receives input parameters indicated at 11 such as signals or stored values representing preset maximum engine speed, preset turbo charger boost range, and preset turbo charger boost limit.

The circuit 7 processes the various input signals and supplies to the control valve 6 a pulse width modulated signal. The pulse width modulation or mark/space ratio of this signal provides the desired control of the turbo charger waste gate. For instance.

during the mark periods, the control valve 6 supplies air at atmospheric pressure from the intake 4 to the control servo 5 whereas, during the space periods, the valve supplies air at boosted pressure from the inlet manifold 2 to the control servo 5. The repetition rate of this pulse signal is sufficiently high for the air supplied to the control servo 5 and/or to the waste gate to have a mean pressure in the range limited by atmospheric pressure and boost pressure from the inlet manifold 2 with superimposed ripple or fluctuations of a level sufficiently low to avoid any undesirable effects on control of the engine.

The variable boost control 8 is mounted, for instance, on the dashboard of a vehicle, such as a car.

The control is provided with a scale which is calibrated in terms of boost pressure and has a rotary range of, for instance, 270". This control may therefore be readily operated by a driver while the vehicle is in motion and can be accurately reset to any desired setting. The override switch 9 may be used to override the effect of the variable boost control 8 and/or other parameters normally used by the electronic circuit 7 for setting the pulse width of the output signal. For instance, the override switch 9 may be used to switch off turbo charging, to switch to a predetermined control schedule or boost limit for turbo charging, or to switch to automatic control by means of the engine control unit 10.

This system allows the control pressure supplied by the control valve 6 to the control servo 5 to be accurately set to any desired pressure between atmospheric pressure and the boost pressure at the inlet manifold 2. The control law between the variable boost control 8 and control of the turbo charging arrangement 3 can follow any desired function, according to processing performed by the electronic circuit 7 and, for instance, can easily be made a logarithmic or linear function of the rotary position of the boost control 8.

Depending on requirements, the control 8 and the switch 9 may be mounted on the dashboard with the circuit 7 within the engine compartment, or the control and switch and the circuit can be mounted at the dashboard. In either case, it is merely necessary to provide electrical connections between the dashboard, or indeed elsewhere in the passenger compartment, and the engine compartment, thus avoiding the need for plumbing or pipework between the engine compartment and the passenger compartment.

It is also possible to provide an embodiment in which no manually operable controls are provided.

Instead, control of the waste gate control valve 6 is performed by means of a pulse width modulated signal, for instance in response to parameters supplied by the engine control unit 10 and/or the preset parameters indicated at 11. Such an embodiment has the advantage that accurate control of the waste gate is provided because the pressure of air supplied by the control valve is easily and accurately controlled. This avoids the need for a control valve for mixing air at different pressures to produce an intermediate pressure, such a system being notoriously difficult to implement with any degree of accuracy and controllability.

Claims

1. A control system for a forced induction internal combustion engine, in which boost pressure is controlled or limited by pulse width modulation.

2. A control system for a forced induction internal combustion engine having a waste gate controlling supply of exhaust gases to a turbo charger, the control system comprising a user-operable control for controlling boost pressure, a pulse generator for generating pulses whose width is controlled by the user-operable control, a control valves for switching between air at atmospheric pressure and compressed air in response to the pulse width of the pulses from the pulse generator, and a servo for controlling the waste gate in response to air from the control valves.

3. A control system according to claim 2, wherein the user-operable control is in the form of a potentiometer or variable resistor.

4. A control system according to claim 3, wherein the potentiometer or variable resistor has a rotary travel of substantially 2700 and a graduated or calibrated scale giving a clear indication of the boost pressure or degree of control thereby allowing easy adjustment between minimum and maximum boost.

5. A control system according to any one of claims 2 to 4, wherein connection is established between the control valve and the pulse generator by means of electrical conductors.

6. A control system substantially as hereinbefore described with reference to the accompanying drawing.