The invention relates to a method of operating an electromechanical converter, in particular an electric variable transmission, provided with a primary shaft having a rotor mounted thereon, a secondary shaft having an interrotor mounted thereon, and a stator, fixedly mounted to the housing of the electromechanical converter, wherein, viewed from the primary shaft in radial direction, the rotor, the interrotor and the stator are arranged concentrically relative to each other, and wherein the rotor and the stator are designed with one or more windings, wherein the interrotor forms one whole both mechanically and electromagnetically, and is arranged as a conductor for magnetic flux in an at least tangential direction.
An electric variable transmission (EVT) is an electromechanical converter with two mechanical ports, viz. a primary (driving) shaft and a secondary (driven) shaft, and an electric gate via which energy can be exchanged. If the electric gate is not used, the EVT works as a common infinitely variable transmission, where the transfer ratio has a very wide range. The EVT fulfills a function that is comparable to that of a combination of a clutch and a gearbox of a vehicle. In combination with the EVT, the combustion engine in fact works as a power source, whereby the speed can be set according to an optimum characteristic of the engine. The fuel consumption, the noise level and the emission of noxious gases from the vehicle can thus be reduced. Because the EVT is an infinitely variable transmission, there are no gearshifting shocks during acceleration. It also means that always acceleration with a constant (maximally permissible) power is possible, and not, as in a conventional gearbox, with a more or less sawtooth-shaped course of the power as a function of the time. With the same engine, the acceleration with an EVT therefore proceeds faster than with a conventional gearbox.
The EVT can work as a substantially wear-free starter motor by connecting the electric gate to an on-board battery. As a consequence, city buses equipped with an EVT, can, for instance, switch off their engine at bus stops without any objection, which is more comfortable and moreover leads to a substantial saving of fuel, since frequent starting entails undue wear of the starter motor and the starter ring in conventional starter motors.
Via the electric gate, optionally via a power electronic converter, the on-board network can be supplied and hence the on-board battery can be charged. Thus, a substantially wear-free alternator has been obtained. Since conventional dynamos have a poor efficiency, this also leads to a saving of fuel. In an electric system with a common dynamo, the power is practically limited by the belt drive and the low on-board voltage. In the use of the EVT, optionally via power electronic converters, higher voltage levels can be simply created and the power is limited only by the combustion engine. This means that some auxiliary provisions that are now driven directly by the engine, such as, for instance, the pump for the power steering, or the compressor in buses, can be driven electrically with a high efficiency. They can then be switched on and off at will, so that the no-load losses are less. This also leads to fuel saving.
With the EVT, it is simply possible to brake by way of the motor. The braking power can then be increased by increasing the speed of the engine. However, this is accompanied by an increased noise production. In addition, it is possible to dissipate the brake energy in resistances that are connected to the electric gate. This makes it possible to brake to a halt, this in contrast, for instance, to a conventional retarder in buses. When braking, possibly, the motor can even be switched off, so that the fuel consumption is reduced and the engine does not produce any noise.
To the electric gate, an electrical energy storage system in the form of a battery, supercap and/or a flywheel system can be connected. With these, brake energy can be stored, which can subsequently be used again for acceleration. This relatively costly extension can, particularly with local buses, yield a substantial saving of fuel.
The electric gate makes the converter particularly suitable for use in hybrid vehicles; the mechanical energy for the cardan shaft can be produced both by the IC engine and by an electric source.
An electromechanical converter, as is described in the opening paragraph, is known from the International patent publication WO 03/075437. The two rotor parts of the electromechanical converter described therein have been electromagnetically coupled and have further been integrated into one whole, so that a desired volume and weight saving is rendered possible. In the electromechanical converter, of course, a magnetic flux conduction in radial direction remains present.
The parts of the electric machine in WO '437 are electromagnetically coupled: flux transfer can take place from the rotor via the interrotor to the stator and vice versa. The machine forms one whole both mechanically and electromagnetically. The parts of the electromagnetic transmission are controlled by a single control device. Owing to the feature that the interrotor forms not only a conductor for the magnetic flux in the radial direction but also in the tangential direction, it is rendered possible, to use flux attenuation in one part of the electromechanical converter, while this is not done in the other part of the converter.
The output torque of the converter is determined by the interrotor frequency, while the machine input torque depends on the angle of the outer and inner field in combination with the interrotor frequency. During operation of the electromechanical converter one or more physical parameters are controlled to obtain a desired power and speed of the interrotor. At relatively high rotational speeds, a voltage differential over the windings of the stator, and thus the stator flux, can be reduced in order to restrict a back electromagnetic force (EMF) so that voltage differential values exceeding system limitations are counteracted. However, the efficiency of the electromechanical converter under stator field weakening conditions might deteriorate.
It is an object of the invention to provide a method of operating an electromechanical converter according to the opening paragraph wherein the efficiency is improved. Thereto, according to the invention, the method comprises the step of variably controlling a magnetic rotor flux such that a magnetic saturation in the interrotor decreases.
The invention is partly based on the insight that under field weakening conditions, the rotor magnetises the interrotor, leading to high rotor copper losses, especially when the interrotor operates in a saturation region. This has some drawbacks as the rotor cannot easily be cooled and the rotor has a lower torque capacity than the stator. Further, the interrotor flux increases leading to iron losses in the interrotor. As a result, the efficiency of the electromechanical converter deteriorates under stator field weakening conditions.
It is noted that the stator under field weakening conditions has a minor contribution to a magnetisation of the interrotor.
By variably controlling a magnetic rotor flux such that a magnetic saturation in the interrotor decreases, a work point on the interrotor magnetisation curve can be modified such that the interrotor is less saturated, so that copper losses in the rotor, as well as iron losses in the interrotor can be reduced, thereby improving the efficiency of the electromechanical converter.
In this context, it is noted that the magnetic rotor flux can comprise different components, i.e. a magnetic flux that extends merely in the rotor, a magnetic flux that extends into the gap between the rotor and interrotor and a flux linking the inner squirrel cage in the interrotor. The above-mentioned components are mutually related, so that controlling one or more of said rotor flux components can in principle lead to a desired modification of the work point on the interrotor magnetisation curve.
Advantageously, the magnetic rotor flux can be reduced under stator field weakening conditions, thereby reducing copper losses in the rotor, as well as iron losses in the interrotor, as the interrotor is thus less saturated. The reduction of losses is obtained by overruling the commonly applied idea of generating a maximum field.
The invention not only relates to an electromechanical converter, but also to an apparatus provided with an electromechanical converter as described above for starting a driving combustion engine or for supplying electrical equipment, and to an apparatus provided with an electromechanical converter as described above and provided with a system for the storage of energy.
The invention also relates to a controller.
Further, the invention relates to a computer program product.
Other advantageous embodiments according to the invention are described in the following claims.
By way of example only, embodiments of the present invention will now be described with reference to the accompanying figures in which
It is noted that the figures shows merely preferred embodiments according to the invention. In the figures, the same reference numbers refer to equal or corresponding parts.
The electric variable transmission (EVT) is an electromechanical converter with two mechanical gates and one electric gate. The EVT is primarily an infinitely variable transmission, while moreover via the electric gate energy can be exchanged.
The basic structure of an electric variable transmission (EVT) is schematically represented in
The interrotor comprises one more electric circuits and a magnetic circuit. In a first embodiment according to the invention, the magnetic circuit is formed by a cylindrical yoke which is provided on the radial inner and outer side with teeth between which longitudinally extending grooves are situated in which extend shortcircuit windings forming the electric circuit. In a second embodiment, the interrotor is formed by a magnetic flux conducting cylindrical yoke, while on the radial inner and outer side permanently magnetic material, for instance in the form of blocks, is arranged. In a third embodiment, the interrotor is formed by a magnetic flux conducting cylindrical yoke, while on the one side permanently magnetic material is provided and on the other side longitudinally extending grooves are arranged in which an electrically accessible winding is provided. In the latter case, however, it is to be ensured that a current supply point be present on the interrotor or on the secondary shaft; on the secondary shaft, slip rings can be easily mounted, via which current can be supplied or removed.
Preferably, the magnetic flux conducting circuit of the interrotor, in particular the yoke with teeth between which grooves are located, has a substantially smooth surface on the radial inner side and/or the radial outer side of the interrotor. In particular, the radial inner and/or outer side of the magnetic flux conducting material of the circuit are parts reaching outwards freely with respect to the contour of the circuit. What is thus achieved is that salient poles are absent which impose a predetermined fixed pattern of magnetic poles on the magnetic flux conducting material of the interrotor, so that the pattern of magnetic poles in the magnetic flux conducting material of the interrotor is free and can be varied during operation. It is noted that in this context a substantially smooth surface is understood to mean not only a completely smooth surface, but can also comprise a surface having, with respect to a smooth, for instance circular cylindrical contour, grooves (slots) directed radially inwards with respect to the circuit. Such recesses then comprise less than half of the total circumference of, respectively, the radial inner or outer side of the circuit, preferably less than about 20-30% of the circumference.
In an embodiment according to an aspect of the invention, the interrotor comprises a magnetic and an electric circuit, the magnetic circuit including a magnetic flux conducting cylinder and the electric circuit including a number of electric circuit-forming windings extending in the flux conducting cylinder, and wherein the interrotor is arranged as a conductor for the magnetic flux in a tangential and radial direction so that exertion of a direct torque between the rotor and the stator can occur upon magnetic saturation of the interrotor.
During operation of the electric variable transmission, magnetic fluxes 29 are induced. A magnetic rotor flux can comprise different components, i.e. a magnetic flux 30 that extends merely in the rotor, a magnetic flux 31 that extends into the rotor-interrotor gap 27, and a flux 32 linking the inner squirrel cage 9 in the interrotor. The above-mentioned components are mutually dependent.
In this context, field weakening conditions denote states of the electric variable transmission wherein the flux of the stator is reduced at relatively high rotational speeds to counteract that a back electromagnetic force exceeds pre-specified system requirements.
At relatively high rotational speeds, a direct axis current in the stator generating the stator flux is reduced to restrict voltage differential values. As a consequence, also the stator flux reduces. However, a magnetic flux occurring in the interrotor increases under such stator field weakening conditions if magnetic rotor flux values are maintained.
In prior art systems, the rotor flux is generated in full in order to create a maximum torque. However, according to the invention, the magnetic flux Φ of the interrotor 15 is indirectly controlled by variably controlling the magnetic rotor flux to obtain a pre-specified performance of the electric variable transmission. More specifically, the magnetic rotor flux control is such that a magnetic saturation in the interrotor decreases.
By reducing the interrotor magnetic flux Φ the work point 36 is moved to another work point 37 that is more in the linear region of the flux curve 35, so that interrotor is less magnetized and copper losses in the rotor windings are reduced.
Referring again to
Similarly,
Advantageously, the magnetic flux is reduced by reducing the direct-axis current in the rotor, e.g. by implementing a vector control scheme.
It is noted that the reaction time of the electromechanical converter remains acceptable since the stator can run at a maximum allowable flux level. In a hybrid vehicle, additional torque is available in the millisecond range by increasing a quadrature current to increase a torque. Further, increasing input torque by increasing rotor flux is of the order of hundreds of milliseconds due to the machine time constant which is acceptable as this rate of change is similar to that of a combustion engine driving the converter.
In an embodiment according to the invention, a magnetic rotor flux is determined from desired parameters associated with the interrotor, such as a requested power and output speed of the EVT, a desired engine torque, speed and EVT output torque. In practice, such a magnetic rotor flux can be determined by retrieving a value from a look-up table and/or by numerically modelling the physical behaviour of the electromechanical converter. To that end, according to an aspect of the invention, a controller is provided comprising a processor arranged for operating an electromechanical converter as described above, wherein the processor is arranged for controlling a magnetic rotor flux such that a magnetic saturation in the interrotor decreases.
The method according to the invention can be performed using dedicated hardware components or standard components on which a computer program product is loaded.
The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.
It is noted that the method according to the invention of operating an electromechanical converter can be applied in a condition wherein a combustion engine drives the converter, or in other drive conditions, such as electric driving conditions wherein the rotor torque is substantially zero. In the latter case, the rotor flux can be set to a value to avoid high magnetization losses and copper losses in the interrotor by balancing the rotor flux and the interrotor flux according to the machine configuration and/or work point. As such, the rotor flux can be set to said value from an initial state wherein the rotor flux is e.g. zero or maximal. Starting from the full flux situation, the rotor flux can be reduced to obtain said value. On the other hand, when starting from the initially zero flux situation, the rotor flux can be increased to arrive at the desired situation wherein the rotor flux has the desired value.
Number | Date | Country | Kind |
---|---|---|---|
07076103 | Dec 2007 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/NL2008/050815 | 12/18/2008 | WO | 00 | 9/16/2010 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2009/078720 | 6/25/2009 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4442730 | Snoy | Apr 1984 | A |
4643040 | Adam et al. | Feb 1987 | A |
4722248 | Braun | Feb 1988 | A |
5021724 | Hirano et al. | Jun 1991 | A |
5027670 | Adam | Jul 1991 | A |
5040430 | Adam et al. | Aug 1991 | A |
5117710 | Asano et al. | Jun 1992 | A |
5172784 | Varela, Jr. | Dec 1992 | A |
5233525 | Overmann et al. | Aug 1993 | A |
5264764 | Kuang | Nov 1993 | A |
5318142 | Bates et al. | Jun 1994 | A |
5335568 | Kammerl et al. | Aug 1994 | A |
5351776 | Keller et al. | Oct 1994 | A |
5418437 | Couture et al. | May 1995 | A |
5427196 | Yamaguchi et al. | Jun 1995 | A |
5436834 | Graf et al. | Jul 1995 | A |
5468198 | Holbrook et al. | Nov 1995 | A |
5558589 | Schmidt | Sep 1996 | A |
5637987 | Fattic et al. | Jun 1997 | A |
5650713 | Takeuchi et al. | Jul 1997 | A |
5722502 | Kubo | Mar 1998 | A |
5761628 | Steeby et al. | Jun 1998 | A |
5771478 | Tsukamoto et al. | Jun 1998 | A |
5775449 | Moroto et al. | Jul 1998 | A |
5845224 | McKee | Dec 1998 | A |
5865263 | Yamaguchi et al. | Feb 1999 | A |
5875410 | Fowler et al. | Feb 1999 | A |
5917248 | Seguchi et al. | Jun 1999 | A |
5941137 | Beer et al. | Aug 1999 | A |
5994870 | Kaneko et al. | Nov 1999 | A |
6019183 | Shimasaki et al. | Feb 2000 | A |
6048288 | Tsujii et al. | Apr 2000 | A |
6054776 | Sumi | Apr 2000 | A |
6054786 | Springer | Apr 2000 | A |
6083139 | Deguchi et al. | Jul 2000 | A |
6089512 | Ansorge et al. | Jul 2000 | A |
6104159 | Seok | Aug 2000 | A |
6148855 | Rauner et al. | Nov 2000 | A |
6176807 | Oba et al. | Jan 2001 | B1 |
6287237 | Graf et al. | Sep 2001 | B1 |
6320349 | Kaneko et al. | Nov 2001 | B1 |
6383114 | Hoshiya et al. | May 2002 | B1 |
6409623 | Hoshiya et al. | Jun 2002 | B1 |
6442080 | Tanzawa et al. | Aug 2002 | B2 |
6469402 | Morimoto et al. | Oct 2002 | B2 |
6488609 | Morimoto et al. | Dec 2002 | B1 |
6494809 | Suzuki et al. | Dec 2002 | B1 |
6533703 | Michau et al. | Mar 2003 | B2 |
6541876 | Shimizu et al. | Apr 2003 | B2 |
6558287 | Hayabuchi et al. | May 2003 | B2 |
6612386 | Tamai et al. | Sep 2003 | B2 |
6616569 | Hoang et al. | Sep 2003 | B2 |
6626056 | Albert et al. | Sep 2003 | B2 |
6713889 | Dietz et al. | Mar 2004 | B2 |
6739418 | Ogata et al. | May 2004 | B2 |
6752036 | Kropp et al. | Jun 2004 | B2 |
6768215 | Souki et al. | Jul 2004 | B2 |
6920383 | Graf et al. | Jul 2005 | B2 |
6952057 | Tajima et al. | Oct 2005 | B2 |
6997831 | Kanda et al. | Feb 2006 | B2 |
6998727 | Gray, Jr. | Feb 2006 | B2 |
7164219 | Hoeijmakers | Jan 2007 | B2 |
7469612 | Rouphael et al. | Dec 2008 | B2 |
20030057796 | Fan et al. | Mar 2003 | A1 |
20040119373 | Akatsu | Jun 2004 | A1 |
20050077800 | Hoeijmakers | Apr 2005 | A1 |
20050082992 | Aizawa et al. | Apr 2005 | A1 |
20050084191 | Fees et al. | Apr 2005 | A1 |
20050285556 | Chen et al. | Dec 2005 | A1 |
20060035736 | Umeda et al. | Feb 2006 | A1 |
20060055363 | Patel et al. | Mar 2006 | A1 |
20070129198 | Atarashi | Jun 2007 | A1 |
Number | Date | Country |
---|---|---|
1572052 | Jan 2005 | CN |
0872396 | Oct 1998 | EP |
1146257 | Oct 2001 | EP |
1 154 551 | Nov 2001 | EP |
1330013 | Jul 2003 | EP |
1389825 | Feb 2004 | EP |
1526308 | Apr 2005 | EP |
1625991 | Feb 2006 | EP |
1832466 | Sep 2007 | EP |
05-284611 | Oct 1993 | JP |
8-214475 | Aug 1996 | JP |
10-243679 | Sep 1998 | JP |
2000-253635 | Sep 2000 | JP |
2003-111318 | Apr 2003 | JP |
2004-135375 | Apr 2004 | JP |
2005-119584 | May 2005 | JP |
2005-124346 | May 2005 | JP |
2005-519571 | Jun 2005 | JP |
2005-214105 | Aug 2005 | JP |
2005-341696 | Dec 2005 | JP |
2005-348472 | Dec 2005 | JP |
2007-195387 | Aug 2007 | JP |
2007-237782 | Sep 2007 | JP |
WO 0034066 | Jun 2000 | WO |
WO 0156826 | Aug 2001 | WO |
WO 02057659 | Jul 2002 | WO |
WO 03019046 | Mar 2003 | WO |
WO 03052538 | Jun 2003 | WO |
WO 03075437 | Sep 2003 | WO |
WO 2004069573 | Aug 2004 | WO |
WO 2005038307 | Apr 2005 | WO |
WO 2009078720 | Jun 2009 | WO |
Entry |
---|
Okamura et al., “Development of Hybrid Electric Drive System Using a Boost Converter,” Toyota Motor Corporation, Toyota Hybrid System THSII, Press Release Apr. 17, 2003. |
Number | Date | Country | |
---|---|---|---|
20120025747 A1 | Feb 2012 | US |