GB2395231A

GB2395231A - Turbocharger with an attached electric motor

Info

Publication number: GB2395231A
Application number: GB0226841A
Authority: GB
Inventors: Timothy Mark Lancefield
Original assignee: Mechadyne PLC
Current assignee: Mechadyne PLC
Priority date: 2002-11-16
Filing date: 2002-11-16
Publication date: 2004-05-19
Also published as: GB0226841D0

Abstract

A turbocharger comprises a turbine and compressor mounted on a common spindle, and an additional electric motor to supplement the action of the turbine when the mass flow rates through it are low. The output shaft 18 of the electric motor is coupled to the spindle 12 of the turbocharger by way of a clutch 20 which can be disengaged when the turbocharger is rotating faster than the electric motor. The clutch may be comprise a friction clutch 20 or an over-running or one way clutch.

Description

239523 1

- 1 TURBOCHARGER

Field of the invention

5 The present invention relates to a turbocharger that is - particularly suitable for use with diesel engines.

Background of the invention

lo It is known that modern light-duty diesel engines use high levels of exhaust gas re-circulation (EGR). A major consequence of this is that the mass flow rates through the compressor and turbine of the turbo-charger are significantly reduced from those that would prevail without 15 EGR.

It is also known that the use of variable geometry turbines "VGT" has allowed the use of compressors with larger mass flow capabilities. AS a result of this, at low so engine speeds, even at full load, the compressor efficiency can be very low and the turbine output can be insufficient to provide rapid increases in boost pressure.

Thus it can be seen that the transient torque rise rate 25 from low speed part load relies on sequentially reducing the EGR flow and accelerating the turbo-charger. To overcome this problem, which manifests itself as poor drivability, it has been proposed that either electrically driven compressors are placed in series with the conventional so compressor, or electric motor torque assistance is provided for the turbine.

The first of these has the draw back that its cost is completely additive to the cost of the conventional turbo 35 charger. This makes the second approach the more attractive.

However, turbo-chargers for light duty diesel engines typically operate over very large speed ranges, from about

20,000 rpm to 200,000 rpm and beyond. Designing and manufacturing electric motors that can operate over this speed range is difficult and expensive. In addition, the windage losses associated with the motor at the higher 5 speeds are substantial.

Summary of the invention

With a view to mitigating at least some of the 10 foregoing disadvantages, the present invention provides a turbocharger for a diesel engine in combination with an electric motor, wherein the output shaft of the electric motor is coupled to the spindle of the turbocharger by way of a clutch which is disengageable to permit the 15 turbocharger to rotate faster than the electric motor.

The invention is predicated on the realization that supplementing the poor low speed torque and improving transient torque rise rate does not require electric motor 20 assistance over the full operating speed range of the turbo-

charger. Assistance to 70,000 or 80,000 rpm would be adequate. By providing a clutch to couple the electric motor to the turbocharger only when its assistance is required, the invention avoids the need for an electric motor that can 25 operate at very high speeds and its attendant windage losses. Different configurations of clutch are possible to allow the motor to be run only to around half maximum turbo so charger speed, above which the turbine can drive the compressor faster than the motor as its power allows. Once above this speed the motor can be idled or stopped.

In a first embodiment of the invention, the clutch 35 comprises a pair of friction plates that are axially displaceable in relation to one another to engage and disengage the clutch selectively.

- 3 - In a second embodiment of the invention, the clutch may comprise an over-running clutch that disengages the turbocharger from the electric motor automatically when the speed of the spindle of the turbocharger speed is greater 5 than the speed of the output shaft of the motor.

In a third embodiment of the invention, an over-running clutch is provided which is axially displaceable relative to the spindle of the turbocharger or the output shaft of the lo motor to disengage the turbocharger from the electric motor in both directions of rotation.

Brief description of the drawings

15 The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic partial section showing a first embodiment of the invention that uses a friction clutch, 20 Figure 2 is a similar view to Figure 1 showing and embodiment that uses an over-running clutch, and Figure 3 is a similar view showing a further embodiment comprising an over-running clutch and also allows the electric motor to be fully disengaged from the turbocharger.

Detailed description of the preferred embodiments.

In the drawings, like reference numerals have been used to designate like components and they will only be described so once with reference to the embodiment of Figure 1.

A turbocharger for a diesel engine has a spindle 12 rotatably supported in a housing 10 by means of a bearing 14, which is preferably constructed as a combined bearing 35 and seal. The remainder of the turbocharger, is not shown as it is known per se.

- 4 An electric motor is provided to assist in driving the spindle 12 when the mass flow over the turbine of the compressor is low. The motor, which has a rotor 18 supported in a housing 16 by means of a bearing 17, needs to be 5 coupled to the turbocharger only over a narrow range of speeds when its assistance is required.

The selective coupling of the motor to the turbocharger is achieved in the embodiment of Figure 1 by means of a 10 friction clutch. The clutch comprises a plate fixedly mounted on the spindle and a friction plate 20 that is rotatable with the rotor 18. The connection between the friction plate 20 and the rotor 18 is effected by means of splines 22 which permit the friction plate 20 to move into 15 and out of frictional contact with the fixed plate on the spindle, so as to engage and disengage the clutch. The axial movement of the friction plate is brought about by a pivoted clutch release arm 24 that engages in a groove in the friction plate 20.

A control system is provided to act on the clutch release arm 24. The clutch is engaged whenever the torque output of the turbine is not sufficient to meet the needs of the compressor. Above a certain speed, when the assistance 25 of the motor is no longer required, it is disconnected from the turbocharger by moving the friction plate 20 to disengage the clutch.

In the embodiment of Figure 2, the end of the rotor 18 30 is supported in the housing 10 of the turbocharger by means of a bearing 30 and is connected to the spindle 12 by means of an over-running or one-way clutch. Over-running clutches are well known and are used for example in automatic transmissions to couple one shaft for rotation with another 35 in only one direction. In this embodiment of the invention, the over- running clutch 32 permits the spindle 12 to rotate

- 5 - faster the rotor 18 of the motor but will not allow it to rotate any slower than the rotor 18.

The embodiment of Figure 2 has the advantage of not s requiring a control system and no axial movement is required to disengage the drive between the motor and the turbocharger. However, at higher speeds, the one-way clutch can result in frictional losses.

lo The embodiment of Figure 3 may be considered as a combination of the features of both of the previously described embodiments. The one-way clutch 32 is carried on the rotor 18 of the motor, and the latter is mounted on bearings 30 and 34 which allow it to be moved axially so 5 that the inner race of the one-way clutch 32 is totally disengaged from the spindle 12 to avoid frictional losses when the turbocharger is operating at high speed.

Though a motor assisted turbocharger is particularly 20 suitable for use with a diesel engine for the reasons previously described, it will be appreciated that it may find application with other types of engine, to help improve drivability.

Claims

t CLAIMS

1. A turbocharger in combination with an electric motor, wherein the output shaft of the electric motor is 5 coupled to the spindle of the turbocharger by way of a clutch which is disengageable to permit the turbocharger to rotate faster than the electric motor.

2. A turbocharger as claimed in claim 1, wherein the lo clutch comprises a pair of friction plates that are axially displaceable in relation to one another to engage and disengage the clutch selectively.

3. A turbocharger as claimed in claim 1, wherein the 15 clutch comprises an over-running clutch that disengages the turbocharger from the electric motor automatically when the speed of the spindle of the turbocharger speed is greater than the speed of the output shaft of the motor.

20

4. A turbocharger as claimed in claim 3, wherein over-running clutch is axially displaceable relative to the spindle of the turbocharger or the output shaft of the motor to disengage the turbocharger from the electric motor in both directions of rotation.

5. A turbocharger for a diesel engine in combination with an electric motor, substantially as herein described with reference to and as illustrated in the accompanying drawings.