The problems with the use of the turbocharger with the internal combustion engine are well documented. One is known as"throttle lag"and is caused by the low speed of the turbocharger rotor when the engine is operated at part load, combined with the energy required to overcome its inertia and accelerate the rotor to a speed where sufficient boost is created when increased power is required. If the rotor can be made to rotate at a greater speed at engine part load requirement by a reduction in compressor work and/or some additional work input, this problem could be alleviated very substantially.

A second significant problem is the difficulty in matching a turbocharger to an engines operating parameters, particularly its speed range. An additional work input to the turbocharger could significantly increase an engines torque where a deficit currently exists.

Other benefits can accrue from this course of action, including a reduced tendency to turbocharger surge, an increase in engine thermal efficiency due to an increase in pressure in the induction pumping loop if the additional work input is sourced from an energy stream which would otherwise be wasted, and a reduction of losses due to throttling in the spark ignition engine.

According to the present invention the induction system of an internal combustion engine is provided with valve means to recirculate some portion of the compressed charge to the low pressure side of the compressor with some recovery of the energy expended in its compression by means of one or more nozzles or directing devices arranged so that the stream of this charge should impinge on the blades of the impeller so as to impart energy on them in their direction of rotation or cause the charge entering the compressor to rotate in the aforementioned direction.

This devised approach will have the effect of increasing the rotational speed of the rotor. A heat source, possibly a heat exchanger using waste heat from exhaust gases, can be provided to heat the recirculating charge between the two pressure regimes, the increase in the energy of this recirculating charge causing a further increase in the rotational speed of the rotor, and in most cases an increase in the pressure ratio of the turbocharger.

There will also be an additional effect due to the heating of the charge being delivered to the compressor and engine with further advantages accruing. Heated air, though requiring greater energy per unit mass for compression through a given ratio, has a lower energy requirement per unit volume for a similar compression, due to its lower density. It logically follows from this that for a given charge air density requirement at the engine, operating at some part of its rating, less throttling of the charge is required, reducing pumping losses at the engine and increasing turbocharger speed.

With use with engines using variable valve timing as a load control means, the deficiency in charge temperature prior to ignition, which can have adverse effects on ignition and combustion, can be reduced.

Occurrence of surge in the compressor can be reduced, due to the increase in mass flowrate through the compressor when this type of charge recirculation is operated, and a reduction in turbocharger pressure ratio is also anticipated within embodiments of this invention, though an increase in pressure ratio would be more usual with additional work input.

By means of a shunt and distributor valve to bypass the heat source of the recirculatory system and/or a shunt and distributor valve to bypass any chargecooler, the optimum temperature and density of charge reaching the cylinders can be provided.

A circumferentially split volute with more than one chamber where one chamber is arranged to be able to cause the charge to be compressed to a greater pressure-to be recirculated in any of the manners described in the above paragraphs-could be used within the context of this invention to achieve greater efficiency of operation.

Valve means can be provided to allow inflow of charge from the substantially atmospheric side of the induction system to the nozzle (s) or directing device (s) to increase the flow capacity of the compressor and decrease the incidence of compressor choke. The valve means shall be arranged to prevent compressed charge from venting through the recirculatory system to the substantially atmospheric side of the induction system.

In the context of the description of this invention, the phrase"valve means"implies valve means with a variable action with control from the engine operator and/or engine management system.

There are three general manners in which this device can be operated, each manner being able to be used separately or in any combination with the other two.

The first is a turbo-lag reduction device where the purpose of the device is to keep the impeller of the turbocharger revolving at a speed where immediate boost is available when increased power is required.

The second is as a torque enhancement device whereby an increase in the pressure ratio of the turbocharger is provided by the increased energy input from the heat source, and the inlet charge density is optimised by the use of a chargecooler.

The third is as a device to increase engine thermal efficiency at engine part load. The heat source would provide an increase in energy input and consequently turbocharger pressure ratio, though this heat would not be removed before passage of the charge to the engine. If a chargecooler is fitted, a distributor valve and shunt would be operated as described previously.

A reduction in charge density can then be provided by the device, so reducing engine torque whilst providing the engine with an induction charge of higher pressure and enthalpy than would normally be the case at this torque value. The increased heat of charge would enable a more lean homogenous cylinder charge to be ignited and would also reduce the problems inherent in the use of variable valve timing as load control means as described previously.

It is obvious that the effects of this device and its peripheral devices are interlinked and that though certain simpler of its functions could be controlled by relatively simple control means, it is likely that to achieve the devices full potential, control by a computer engine management system is desirable, with"fly by wire"control an option.

One embodiment of the turbocharger system according to the invention is shown in figures 1,2 and 3. Figure I shows a section through a turbocharger compressor 8 with impeller 9 and nozzles 3. Figure 2 shows another section through a similarly equipped compressor. Figure 3 shows the turbocharger system diagramatically with reference numeral 1 indicating a turbocharger and 7 an internal combustion engine. The engine feed charge passes into the centrifugal compressor 8 from which it passes into inlet manifold 11. From here it passes to distributor valve 2 where some portion can be diverted to the charge recycling apparatus. The remainder of the charge passes to the engine. The charge in the recycling apparatus then encounters distributor valve 6 where it can be directed in variable proportions to exhaust gas heat exchanger 4 and shunt 5. The charge then passes to nozzles 3 where it re- enters compressor 8, impinging on the blades of the impeller, causing the impeller to rotate at greater speed. Numeral 10 indicates a chargecooler.