Patent Description:
It is known that some vehicles are provided with a forced induction engine, namely an internal combustion engine that receives precompressed air in the intake manifold.

The intake manifold air can be compressed for example by means of a turbocharger, namely a device comprising a turbine and a compressor fitted on the same shaft, so that the turbine can supply power to the compressor.

The power supplied to the compressor is generated by the turbine by the expansion of at least a portion of the exhaust gases, which is channelled through the turbine.

The remaining portion of the exhaust gases bypasses the turbine and is directly conveyed towards the after-treatment system of the engine.

The bypass is typically regulated by a valve commonly known as wastegate.

<CIT> and <CIT> discloses examples of forced induction devices according to the preamble of claim <NUM>.

In general, although turbochargers are widely used for the forced induction of engines, the need is felt for an improvement in this field.

In particular, forced induction is an important aspect for determining the efficiency and performance of the engine, hence the need is felt to increase or even optimize efficiency and performance.

More specifically, the need is felt to improve the known turbochargers, specifically considering also questions relating to overall dimensions, weights and necessary costs.

An object of the invention is to meet at least one of the above needs, preferably in a simple reliable manner.

The object is achieved by a forced induction device for an internal combustion engine, as defined in claim <NUM>.

The dependent claims define particular embodiments of the invention.

Below, an embodiment of the invention is described for a better understanding thereof by way of non-limiting example and with reference to the attached <FIG>, in which a diagram of an engine of a vehicle is illustrated with a forced induction device according to the invention.

In <FIG>, the reference number <NUM> is used to indicate, overall, a vehicle, specifically a motor vehicle, in particular a sports or racing vehicle.

For example, any one or more of the filter <NUM>, intercooler <NUM>, and even the wastegate <NUM> are entirely optional and can therefore be absent.

The assembly formed by the compressor <NUM>, the hydraulic motor <NUM>, the turbine <NUM> and the hydraulic pump <NUM> is part of a forced induction device for the engine <NUM>.

In greater detail, the hydraulic motor <NUM> and the hydraulic pump <NUM> form part of a hydrostatic transmission configured to drive the compressor <NUM> by means of the power exiting the turbine <NUM>.

More precisely, both or at least one of the hydraulic motor <NUM> and the hydraulic pump <NUM> is of the variable displacement type. In particular, the hydraulic pump <NUM> is a variable displacement pump.

Variable displacement is understood in this technical field as the quantity of fluid pumped or processed respectively for a complete rotation of the input shaft of the pump <NUM> or the output shaft of the motor <NUM>.

In other words, both or at least one of the hydraulic motor <NUM> and the hydraulic pump <NUM> comprises a movable mechanical member (typically called swashplate), the position or movement of which determines the variable displacement.

Therefore, displacement defines a control variable of the pump <NUM> and/or of the motor <NUM>.

Furthermore, the forced induction device comprises a control unit configured to regulate the displacement of the hydraulic pump <NUM> or the hydraulic motor <NUM> or both, namely in particular their respective control variables.

The regulation can be performed for example by means of an actuator controlled by the control unit to move the above-mentioned movable member, thus varying the displacement.

In this way, in other words, the control unit is configured to control the compressor <NUM> or more precisely to regulate at least the speed at the output of the hydraulic motor <NUM>, independently of the turbine <NUM>.

In fact, the speed of the compressor <NUM> and the turbine <NUM> are directly influenced by the displacement of the motor <NUM> and the displacement of the pump <NUM> respectively.

The hydrostatic transmission defines a continuously variable transmission, namely a transmission that allows continuous regulation of the speed at the transmission output starting from any constant speed at the transmission inlet. In other words, the transmission ratio of the hydrostatic transmission, which connects the turbine <NUM> to the compressor <NUM>, is continuously variable.

The hydraulic motor <NUM> is mechanically connected to the compressor <NUM> by means of a mechanical transmission, for example comprising or defined by a drive shaft <NUM>, in particular defining an output shaft for the hydraulic motor <NUM> and an inlet shaft for the compressor <NUM>.

Therefore, the compressor <NUM>, or more precisely an impeller thereof, has an angular velocity directly depending on or corresponding to the speed at the output of the hydraulic motor <NUM>, in turn, in particular, corresponding to the displacement of the motor <NUM>.

Consequently, the control unit is configured to control the angular velocity of the compressor <NUM>, in particular by controlling the displacement of the motor <NUM>.

Furthermore, the control unit is also configured to control the turbine <NUM> or more precisely an output speed thereof.

The hydraulic pump <NUM> is mechanically connected to the turbine <NUM> by means of a mechanical transmission, for example comprising or defined by a drive shaft <NUM>, in particular defining an output shaft for the turbine <NUM> and an inlet shaft for the hydraulic pump <NUM>.

For example, the control unit controls the turbine <NUM> by means of a control of the wastegate <NUM>. This is not limiting, however, since there are many ways of regulating the turbine <NUM> or the output speed thereof, for example by involving mechanical devices such as slip-control clutches, brakes, and the like.

Furthermore, the speed of the turbine <NUM> can also be controlled by controlling the displacement of the pump <NUM>.

In practice, the turbine <NUM> and the compressor <NUM> are controllable independently of each other due to the hydrostatic transmission.

In particular, the control unit is configured to individually control the output speed from the turbine <NUM> and the input speed to the compressor <NUM>, namely the angular velocity of the impeller, more in particular controlling the displacement of the motor <NUM> and the pump <NUM>.

More in particular, the control unit preferably performs an independent control of the compressor <NUM> and the turbine <NUM>, for example in a closed loop, for each of the compressor <NUM> and the turbine <NUM>.

In practice, the control unit controls the compressor <NUM> and the turbine <NUM> according to respective independent control laws.

For example, each control law can be based on an optimization of the efficiency of the compressor <NUM> or the turbine, respectively. More precisely, each control law can be based on the solution to a problem of optimal control, in particular based in turn on maximization of a target function increasing with the performance or efficiency of the compressor <NUM> or the turbine <NUM> respectively.

Alternatively or additionally, the control unit controls the compressor <NUM> or more precisely the input speed to the compressor <NUM> with the sole objective of optimizing intake of the engine <NUM> according to the required performance (namely torque and power to be delivered by the engine <NUM>); in other words, control of the compressor <NUM> is solely aimed at optimizing the combustion in the engine <NUM>, namely its performance. Therefore, the control law with which the control unit controls the compressor <NUM> is based on optimization of the performance of the engine <NUM>.

In practice, the control unit solves in general one or more problems of optimal control, namely by optimizing one or more target functions (maximizing or minimizing, based on the type of target function). The possible target functions can be various: for example, a target function could be a linear or non-linear combination of the efficiencies of the compressor <NUM> and the turbine <NUM>, the overall energy expenditure of the engine <NUM>, the difference between actual torque of the engine <NUM> and a target torque of the engine <NUM>, and similar, in a non-limiting manner.

The target function or functions are a function of the speed of the compressor <NUM> and/or the speed of the turbine <NUM>, so that the result of resolution of the problem of optimal control is a speed target for the compressor <NUM> and a speed target for the turbine <NUM>.

More generally, the control unit is configured to determine or comprise (for example, since they are stored) the speed target for the compressor <NUM> and/or the speed target for the turbine <NUM>.

The speed targets for the compressor <NUM> and for the turbine <NUM> will correspond to target values of the displacement of the motor <NUM> and/or the pump <NUM> respectively.

Therefore, the control unit is configured to control the displacement of the motor <NUM> and/or the pump <NUM>, namely in a corresponding way the speed of the compressor <NUM> and/or the turbine <NUM>, by means of respective control laws configured to minimize or reduce the relative differences between the target values and the actual displacements of the motor <NUM> and/or the pump <NUM>. For example, the control laws can be in open loop, based on the target values, or in closed loop based on feedback signals of the displacements, which can for example be estimated or determined by appropriate transducers. For example, the control laws in closed loop could be PI or PID (proportional-integrative or proportional-integrative-derivative) control laws.

Correspondingly and implicitly, the control laws are configured to minimize or reduce the differences between the actual speeds of the compressor <NUM> and turbine <NUM> and the relative speed targets.

With greater reference to <FIG>, the hydraulic motor <NUM> is hydraulically connected to the hydraulic pump <NUM> to receive the liquid provided by the latter. In particular, the connection is made through a duct or hydraulic circuit <NUM> of the forced induction device.

Furthermore, the forced induction device comprises an intake line <NUM> that connects an outlet for the compressed air of the compressor <NUM> to an intake manifold of the engine <NUM>, in particular passing through the intercooler <NUM>.

In practice, the intake line <NUM> is configured to supply the intake manifold with the compressed air emitted by the compressor <NUM>.

In addition, the forced induction device comprises an exhaust line <NUM> that connects an exhaust manifold of the engine <NUM> to an inlet of the turbine <NUM>.

Preferably, the forced induction device further comprises a bypass line <NUM> connected to the exhaust line <NUM> upstream of the turbine <NUM> and having an exhaust termination downstream of the turbine <NUM>.

The bypass line <NUM> comprises for example the wastegate <NUM>. The wastegate <NUM> is configured to split the exhaust gas flow through the bypass line <NUM>, thus forcing a portion of the exhaust gases coming from the exhaust manifold of the engine <NUM> to pass through the turbine <NUM>.

The control unit is configured to regulate splitting of the flow by means of the wastegate <NUM>.

From the above, the advantages of the forced induction device according to the invention are evident.

The mechanical separation between the turbine <NUM> and the compressor <NUM> offers a considerable advantage, in particular due to a clearly increased controllability of the forced induction device compared to a traditional turbocharger.

In fact, since they are uncoupled, the turbine <NUM> and the compressor <NUM> can operate in respective independent regimes, thereby maximizing efficiency.

Furthermore, the use of a hydrostatic transmission is particularly advantageous, especially with respect to the use of electric components. The forced induction device is without electric machines like electric motors or alternators. This results in a significant advantage in terms of weight, overall dimensions and cost.

Lastly it is clear that modifications and variations that do not depart from the protective scope defined by the claims can be made to the forced induction device according to the invention.

Claim 1:
A forced induction device for an internal combustion engine (<NUM>), the device comprising
- a compressor (<NUM>) operable to provide compressed air,
- an intake line (<NUM>) configured to supply an intake manifold of the internal combustion engine (<NUM>) with the compressed air provided by the compressor (<NUM>),
- a turbine (<NUM>) configured to generate mechanical power through expansion of at least a portion of exhaust gases of the internal combustion engine (<NUM>),
- an exhaust line (<NUM>) configured to supply the turbine (<NUM>) with the exhaust gas portion coming from an exhaust manifold of the internal combustion engine (<NUM>), and
- a hydrostatic transmission (<NUM>, <NUM>, <NUM>) configured to drive the compressor (<NUM>) by means of the mechanical power generated by the turbine (<NUM>),
wherein the hydrostatic transmission comprises
- a hydraulic pump (<NUM>) coupled to the turbine (<NUM>), so that the mechanical power generated by the turbine (<NUM>) drives the hydraulic pump (<NUM>), and configured to provide a liquid under pressure, and
- a hydraulic motor (<NUM>) hydraulically connected to the hydraulic pump (<NUM>) to receive the liquid under pressure provided by the hydraulic pump (<NUM>) and coupled to the compressor (<NUM>) to drive the compressor (<NUM>) by means of the liquid under pressure received from the hydraulic pump (<NUM>),
characterized in that both or at least one of the hydraulic pump (<NUM>) and the hydraulic motor (<NUM>) is of the variable displacement type.