Control system for an internal combustion engine boosted...

Internal-combustion engines – Charge forming device – Supercharger

Reexamination Certificate

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Details

C123S559100

Reexamination Certificate

active

06684863

ABSTRACT:

BACKGROUND
a. Field of the Invention
The present invention relates to an electronically driven pressure boosting system that is used to boost the torque output of an internal combustion engine.
b. Related Art
One way to boost the torque and peak power provided by a reciprocating piston internal combustion engine, is to use a pressure boosting device to increase the mass airflow into the engine. The increased air supply then permits a greater amount of fuel to be combusted in each ignition event.
Examples of pressure boosting devices include turbochargers and superchargers, referred to herein collectively as “compressors”. A turbocharger is driven entirely or partly by energy in the exhaust stream. This is an efficient use of otherwise mostly wasted energy, but such devices suffer from the limitation that the boost is not available or significant at low engine speeds (rpms). The time taken for the boosted torque to become apparent to the driver is called “turbo lag”. Often, a driver may demand high torque from an engine at low rpms, for example at the start of an overtaking manoeuvre. If the pressure boost device is driven only by exhaust gasses, then boosted torque will not be available at low rpms.
One way of dealing with the limitation is to provide an electrical motor connected to the turbocharger, which is energised when the turbo boost is insufficient. This type of electrically driven pressure boosting device is, however, expensive in terms of hardware cost. Another solution is to use a supercharger, that is, a compressor device that is driven by means other than an exhaust gas turbine, for example via a mechanical linkage to the engine, or by an electrical motor driven from the vehicle battery and/or battery charging system. Mechanical supercharger systems can however, be mechanically bulky and expensive, and do not reduce “turbo lag”. Electrically driven supercharger systems provide a lower cost and compact solution, but can require a significant amount of electrical energy when driven, for example, up to three times the current which can normally be supplied by a typical motor vehicle 12 volt battery. A typical electrical motor for a supercharger driven from a conventional motor vehicle electrical power supply system, can take up to 0.5 seconds to reach operating speed. Although this is a considerable reduction in lag compared with an exhaust gas driven turbocharger, this is still a noticeable lag for the vehicle driver.
Motor vehicle alternators are typically specified to provide either all or most of the power requirement for the entire vehicle, the battery only being used to store sufficient electrical power to start the vehicle engine and occasionally deliver power when the accessory load exceeds the alternator output. Typical European vehicle alternators are specified to provide about 130 A of current, while an electrically powered supercharger can require in excess of 300 A. An alternator able to supply this much current is significantly more expensive, heavy and bulky than a conventional alternator.
Because the pressure-boosting device cannot be 100% efficient, there will also be inevitable electrical and mechanical losses associated with the device, that can place significant mechanical and thermal stress on components within the device.
The expense of increasing the capacity of the vehicle battery and charging system, or the dealing with inherent thermal and mechanical limits of components within the pressure boosting device, to meet any level of driver demand can easily outweigh the benefits of using an electrically driven compressor. Therefore it is important to drive such a device in an efficient manner, and within the limits of the vehicle electrical power supply, and thermal and mechanical limits of the device itself. At the same time, it is important to minimise lag and to maximise the torque boost benefit perceived by the driver over as wide a range of driving conditions as possible. Because the level at which an electrically driven pressure boosting device is driven, is essentially independent from the engine operating speed, it is therefore necessary to devise an appropriate control system for operating the pressure boosting device that takes account of the system's limitations.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a convenient and economical electrical pressure boosting device and method for increasing the torque available from an internal combustion engine.
According to the invention, there is provided a torque boosting system for boosting the torque of an internal combustion engine, said system comprising means for generating one or more engine operating parameters, an electrically driven rotary compressor for assisting aspiration of the engine to boost engine torque, an electrical supply system for providing electrical power to drive the compressor, and an electronic control system responsive to the engine operating parameter(s) to control the operation of the engine and the compressor such that in an idle mode of operation of the compressor said device does not assist the aspiration of the engine, and in a boost mode of operation of the compressor said device does assist the aspiration of the engine, wherein:
a) the compressor in the idle mode of operation operates within a first range of speeds and in the boost mode of operation operates within a second range of speeds, the second range of speeds being greater than the first range of speeds;
b) when activated by the electronic control system, the compressor requires a lag time to accelerate from an idle speed within the first range of speeds to a boost speed within the second range of speeds;
c) the electronic control system monitors the engine operating parameter(s) and calculates therefrom a likelihood that the engine torque will need to be boosted by the compressor; and
d) when the compressor is operating at an idle speed, the electronic control system controls said idle speed so that the lag time varies inversely with the calculated likelihood that the compressor will be needed to boost engine torque.
Also according to the invention, there is provided a method of using a torque boosting system to boost the torque of an internal combustion engine, said system comprising means for generating one or more engine operating parameters, an electrically driven rotary compressor for assisting aspiration of the engine to boost engine torque, an electrical supply system for providing electrical power to drive the compressor, and an electronic control system responsive to the engine operating parameter(s) to control the operation of the engine and the compressor, wherein the method comprises the steps of:
i) operating the compressor in an idle mode of operation within a range of idle speeds in which the compressor does not assist engine aspiration;
ii) after step i), operating the compressor in a boost mode of operation within a range of boost speeds in which the compressor does assist engine operation, the compressor requiring a lag time in order to accelerate from an idle speed to a boost speed;
iii) prior to step ii), using the electronic control system to monitor one or more engine operating parameters, and to calculate therefrom a likelihood that the engine torque will need to be boosted by the compressor to meet future driver demand; and then
iv) using the electronic control system to vary the idle speeds so that the lag time varies inversely with the calculated likelihood that the compressor will be needed to boost engine torque.
The inverse relationship between the calculated likelihood and the lag time may be a simple 1/x inverse relationship, or any other suitable function in which the lag time decreases with increasing likelihood, or vice versa.
Several benefits flow from this approach. First of all, the higher the idle speed, the greater the reduction in lag time. The lag time is therefore reduced most in situations where it is judged most likely that compressor boost will be required.
Second, because the idle speed of the compressor is variable,

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