GB2214979A

GB2214979A - Mechanically driven diesel engine supercharger

Info

Publication number: GB2214979A
Application number: GB8802305A
Authority: GB
Inventors: Alan B Riach
Original assignee: FLEMING THERMODYNAMICS Ltd
Current assignee: FLEMING THERMODYNAMICS Ltd
Priority date: 1988-02-03
Filing date: 1988-02-03
Publication date: 1989-09-13
Also published as: GB8802305D0

Abstract

To reduce the power absorbed by the supercharger 3 when the engine 8 is operating at low power a valve 13 at the supercharger outlet is closed and an inlet valve 14 is at least substantially closed and the supercharger working chamber is evacuated by connection to a vacuum source 18, 20. Under this condition air is supplied to the engine 8 through a by-pass 10, 11 containing a non-return valve 12. The valves 13, 14, 15 may be actuated with the engine electronic fuel control system. The vacuum pump 20 may be engine or electrically driven. <IMAGE>

Description

OFFLOADING SYSTEM FOR A MECHANICALLY DRIVEN SUPERCHARGER ON A DIESEL ENGINE This invention relates to an offloading system for a mechanically driven supercharger on a diesel engine.

The use of mechanically driven superchargers on diesel internal combustion engines is well known. The mechanical drive means is usually from the engine crankshaft via a belt, chain or gear train.

By virtue of their mode of operation, diesel engines must operate at all load conditions with a fully open air inlet duct, the power output of the engine being controlled by varying the amount of fuel fed into the engine combustion chamber.

When a mechanically driven supercharger is applied to a diesel engine the above open air inlet duct condition will result in the supercharger operating continuously at its full pressure ratio.

It is a well known characteristic of superchargers that the absorbed driving power is proportional to the mass flow of gas through the supercharger and the pressure ratio between its outlet and inlet ducts.

The supercharger will thus absorb a significant amount of power at all engine operating conditions.

When the engine is operating at low power, supercharging may not be a requirement and it would be advantageous during this condition to switch off or offload the supercharger and thus reduce or eliminate the power required to drive it.

Switching off can be achieved by fitting a declutching mechanism in the supercharger drive line.

However, switching off the drive to the supercharger and allowing it to stop when the engine is operating at low power can cause certain problems. For example, when increased power is required from the engine and this requires the supercharger drive to be engaged, it takes some time to bring the supercharger up to speed. This causes a time lag between the time when higher power is demanded by the load and the time when higher power is made available from the engine. Moreover the drive declutching mechanism is costly and may require maintenance.

To overcome these problems it is preferable to offload the supercharger without declutching its drive from the engine.

According to the present invention there is provided an offloading system for a mechanically driven supercharger on a diesel engine having a duct from the engine inlet air filter or orifice to the inlet of the mechanically driven supercharger, a duct from the outlet of the supercharger to the engine air inlet manifold, a bypass duct from the engine inlet air filter to the engine air inlet manifold containing a non-return valve upstream of the point at which this bypass duct joins the duct from the supercharger outlet to the engine air inlet manifold, air flow control valves at the inlet and outlet of the supercharger and a means for evacuating the working chamber of the supercharger when the air flow control valves are closed.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing (Figure 1) which shows in diagrammatic form the layout of the system.

Referring ~to the drawing, the control system for the offloading of mechanically driven superchargers on diesel engines comprises a duct 1 conducting air from engine inlet air filter 2 to mechanically driven supercharger 3 which feeds compressed air via ducts 4 and 5 to engine air inlet manifold 7 of diesel engine 8.

Supercharger 3 is driven mechanically from engine 8 by drive 9.

Engine inlet air filter 2 is also connected to engine air inlet manifold 7 by ducts 10, 11 and 5 via non-return valve 12.

When the engine is operating at a load high enough to require supercharging then flow control valves 13 and 14 will be open and the supercharger will be delivering compressed air to the engine. This will cause non-return valve 12 to close thus preventing escape of the compressed or supercharged air back to the supercharger inlet.

When the demand for power from the engine is low and supercharging is not required then control valves 13 and 14 will be closed by a linkage from the engine fuel control system and simultaneously control valve 15 shall be opened, exposing ducts 16 and 17 to chamber 18 which in turn is connected via duct 19 to the inlet port of a vacuum pump 20.

By these means the working chamber of supercharger 3 is evacuated of air and the supercharger then rotates in a partial vacuum which substantially reduces the required driving power.

When valves 13 and 14 are closed the engine can draw its inlet air along ducts 1, 10, 11 and 5 via valve 12, which valve immediately opens upon the reduction in pressure which occurs in duct 11 due to engine suction.

Valves 13 and 14 may be connected to the engine fuel control (ie. load control) system by mechanical or electro-mechanical means.

Claims

1. An offloading system for a mechanically driven supercharger on a diesel engine having a duct from the engine inlet air filter or orifice to the inlet of the mechanically driven supercharger, a duct from the outlet of the supercharger to the engine air inlet manifold, a bypass duct from the engine inlet air filter to the engine air inlet manifold containing a non-return valve upstream of the point at which this bypass duct joins the duct from the supercharger outlet to the engine air inlet manifold, air flow control valves at the inlet and outlet of the supercharger and a means for evacuating the working chamber of the supercharger when the air flow control valves are closed.

2. An offloading system for a mechanically driven supercharger on a diesel engine as described in claim 1 whereby the non-return valve positioned between the engine inlet air filter and the engine air intake manifold is actuated by the engine fuel control system.

3. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1 or 2 whereby the air flow control valves at the inlet and outlet of the supercharger are connected so as to operate synchronously.

4. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2 or 3 whereby the air flow control valves at the inlet and outlet of the supercharger are connected to the engine fuel control system.

5. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2 or 3 whereby the air flow control valves at the inlet and outlet of the supercharger are controlled by an electronic engine management system.

6. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2, 3, 4 or 5 whereby the air flow control valves are connected so that one valve closes before the other.

7. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2, 3, 4, 5 or 6 whereby the air flow control valve at the inlet end of the supercharger is never fully closed thus allowing a small amount of air to pass through the supercharger for cooling purposes.

8. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2, 3, 4, 5, 6 or 7 whereby the working chamber of the supercharger is evacuated in the offloaded mode by an engine driven vacuum pump.

9. An offloading system for a mechanically driven supercharger on a diesel engine as described in claim 8 whereby the vacuum pump is the vacuum pump normally provided on the diesel engine of a car or light truck for vacuum assisted operation of the vehicle brake system.

10. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2, 3, 4, 5, 6 or 7 whereby the working chamber of the supercharger is evacuated in the offloaded mode by an electrically driven vacuum pump.

11. An offloading system for a mechanically driven supercharger on a diesel engine as described in claims 1, 2, 3, 4, 5, 6 or 7 whereby the working chamber of the supercharger is evacuated by a section of the engine which is temporarily configured to operate as a vacuum pump.