COMPACT DRIVE UNIT FOR TRACTION VEHICLES
1. A compact drive unit for traction vehicles consisting of an electrical motor supplied by a power electronics converter, a gearbox and a mechanical coupling to a wheelset or a wheel, wherein the electrical motor is a high-speed electrical motor with a speed over 9000 rpm, its rotor is supported by bearings along with pinion gear of an input spur/helical gear of a high-speed gearbox stage and all together create a rotor assembly,wherein an output shaft of the gear is a part of a following bevel gear, an output shaft of the bevel gear is connected either directly or by using the coupling to an axle of the traction vehicle, or to the wheel, wherein at least the electrical motor and the high-speed gearbox stage are embedded in a single compact housing and the electrical motor is a thermal source for preheating of a lubricant of the high-speed gearbox stage before running the gearbox under extremely low ambient temperatures.
A compact drive unit is predominantly intended for traction vehicles, especially for rail vehicles. This invention allows significant reduction of volume and weight of drive units. The drive unit comprises high-speed electrical motor (1) with passive cooling, which is supplied by power electronics converter (2), whose rotor is supported by bearings (3) along with pinion gear (4) of the input spur/helical gear (5). The output shaft (6) of the gear (5) is a part of the next following gear (7). Output shaft of this gear (7) can be connected either directly or by using the coupling (12) to the axle (8) of the traction vehicle, or to the wheel (9). Alternatively, in case the higher transmission ratio is required, it can be connected to another gears (10), where the output shaft of the gears (10) is connected to the wheel (9), or to the axle (8) of the traction vehicle directly or by using the coupling (12). The drive unit can be equipped with brake (13).
- 1. A compact drive unit for traction vehicles consisting of an electrical motor supplied by a power electronics converter, a gearbox and a mechanical coupling to a wheelset or a wheel, wherein the electrical motor is a high-speed electrical motor with a speed over 9000 rpm, its rotor is supported by bearings along with pinion gear of an input spur/helical gear of a high-speed gearbox stage and all together create a rotor assembly,
wherein an output shaft of the gear is a part of a following bevel gear, an output shaft of the bevel gear is connected either directly or by using the coupling to an axle of the traction vehicle, or to the wheel, wherein at least the electrical motor and the high-speed gearbox stage are embedded in a single compact housing and the electrical motor is a thermal source for preheating of a lubricant of the high-speed gearbox stage before running the gearbox under extremely low ambient temperatures.
- 2. A compact drive unit for traction vehicles consisting of an electrical motor supplied by a power electronics converter, a gearbox and a mechanical coupling to a wheelset or a wheel, wherein the electrical motor is a high-speed electrical motor with speed over 9000 rpm, its rotor is supported by bearings along with pinion gear of an input spur/helical gear of a high-speed gearbox stage and all together create a rotor assembly,
wherein an output shaft of the gear is a part of a following bevel gear, an output shaft of the bevel gear is connected to additional gears either directly or by using the coupling connected to an axle of the traction vehicle, or to the wheel, wherein at least the electrical motor and the high-speed gearbox stage are embedded in a single compact housing and the electrical motor is a thermal source for preheating of a lubricant of the high-speed gearbox stage before running the gearbox under extremely low ambient temperatures.
- 8. (canceled)
- 9. (canceled)
This invention concerns a device which is a compact drive unit connected to either a wheel or axle/wheelset of a bogie of a traction vehicle. It is intended especially for drives of rail vehicles such as trams, light rail vehicles, metros, electric units (EMUs) and train sets. The device combines high-speed electric drive with appropriate gearbox and it allows design of drive units with significantly reduced volume and weight.
This invention introduces a compact traction drive unit intended mainly for rail vehicles, which often demand a full low-floor arrangement of the vehicle. Existing solutions of drive units for traction vehicles can be divided into wheel drives and axle/wheelset drives.
Wheel drives are aimed particularly to low-floor design for urban passenger transport. These drives are used with or without a gearbox, i.e. with a low-speed electric motor directly connected to the wheel. Gearless wheel drives typically employ multi-pole electrical motors connected to the wheel directly or by means of a mechanical coupling element which allows mechanical disconnection of the motor shaft from the wheel (specifically under fault conditions). The electric motor usually uses permanent magnets in order to achieve both maximum power density and efficiency. The above mentioned solutions are known e.g. from EP 1 867 543, EP 0 918 676 and they were reported in many non-patent literature publications, e.g. F. Demmelmayr, M. Troyer and M. Schroedl, “Advantages of PM-machines compared to induction machines in terms of efficiency and sensorless control in traction applications,” IECON 2011-37th Annual Conference on IEEE Industrial Electronics Society, Melbourne, VIC, 2011, pp. 2762-2768. doi: 10.1109/IECON.2011.6119749 or Z. Huang, X. Huang, J. Zhang, Y. Fang and Q. Lu, “Design of an interior permanent magnet synchronous traction motor for high speed railway applications,” Power Electronics, Machines and Drives (PEMD 2012), 6th IET International Conference on, Bristol, 2012, pp. 1-6. doi: 10.1049/cp.2012.0253.
The gearless wheel drives (such as EP 1 867 543) are competitive in the drives approximately up to 50 kW. In higher power applications, where this invention is intended for, their weights and volumes make impossible direct mounting to the wheel. Their maximum output power is generally limited by wheel diameter and vehicle speed. The same constraint applies to gearless axle drives (such as EP 0 918 676, WO 2006051046 or J. Germishuizen, A. Jockel, T. Hoffmann, M. Teichmann, L. Lowenstein and F. v. Wangelin, “Syntegra™—next generation traction drive system, total integration of traction, bogie and braking technology,” International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006, Taormina, 2006, pp. 1073-1077), where the limit is given by the wheel gauge. One of the biggest disadvantages of mentioned solutions is a direct coupling between the motor and the wheel or axle resulting in large unsprung masses.
Wheelset drives are dominant in applications where higher power transmission to the axle is required, especially for locomotives, EMUs and metro trainsets. These drive units can be designed directly within bogie or vehicle concepts. In WO9629224, the drive unit for a low-floor vehicle is proposed. It drives two wheels by means of a single longitudinally mounted motor outside the bogie. The gearboxes are connected to both output shafts of the motor. The brake is integrated in the drivetrain between the motor and the wheels. Similar solution of one-sided drive for two single wheels is described in DE 199 45 464. In both cases, the motor is proposed as a low-speed one and therefore its weight and dimensions are treated as disadvantages.
The US 511 97 36 describes a bogie concept which is characterized by the longitudinally placed motor of each wheel which is connected to the associated wheel by interposition of a homokinetic flexible coupling shaft and comprises a reduction gear unit. The motor and reduction units do not create a compact closed unit and the presence of the homokinetic coupling shaft signifies that the motor belongs among low-speed ones and therefore its dimensions are large to achieve the rated power of the proposed drive unit.
The U.S. Pat. No. 8,978,563 introduces a bogie drive concept allowing partly low-floor design of the rail vehicle. Longitudinally placed electric motor inside the bogie has output shafts on both motor ends. The shafts are connected by means of a gearbox to axles suspended in the bogie. The concept allows two possible motor designs as well. However, the full low-floor concept is not possible here and the dimensions of the electric motor are larger due to its low-speed concept. The drive does not include the brake directly but it is placed outside the bogie separately.
The concept of a drive driving two axles of the bogie is presented in U.S. Pat. No. 4,130,065, where the electric motor is placed longitudinally outside the bogie between the two drive axles.
The advantage of this design is that the two ends of the rotor shaft stubs are equipped with the drive pinions. To save the weight, the stator of the electric traction motor is made without housing. For this reason, the stator lamination stack clamped between pressure plates is provided at its back with clamping elements which compress the stator lamination stack. Even if the weight is particularly saved, it is not sufficient in comparison to the solution proposed in presented invention, where the high-speed electric motor concept allows significant reduction of the weight of the whole drive unit by using high speeds to transmit desired power.
Among investigated solutions, patents related directly to drive units exist. These patents deal with various connections of the motor to the driven wheel/axle but in general each of presented solutions incorporates a part or design aspect, which makes the usage of a high-speed motor impossible, therefore they lead to physically larger and significantly heavier solutions than presented invention. This fact applies especially to patents DE 100 50 757, EP 1 386 815 and EP 0 698 540.
In case of DE 10050757, the power transmission from the motor to the axle is ensured through cardan-like element and the alignment imperfections between the gearbox and the axle is performed through inclinable tooth coupling. Such a solution is not suitable for higher speeds because of its dimensions and therefore it makes usage of a high-speed electrical motor impossible. The main advantage of presented invention (which is reduction of weight and volume) cannot be achieved through the solution described in DE 100 50 757.
A very similar disadvantage applies to patent EP 0 698 540. In this case, the power transmission from the gearbox to the axle is performed through hollow cardan coupling, which forms a very heavy and large part. In comparison to presented invention, the EP 0 698 540 forms heavier and larger alternative.
The EP 1 386 815 presumes relatively low output power of the electric motor (approximately 40 kW) and utilizes one stage gearbox. The device is applicable to the wheel drive only, whilst our solution is predominantly intended for the axle drive and allows design of higher power drive. The one stage gearbox in EP 1 386 815 does not allow utilization of high-speed electrical motor. The important benefit of our solution is passive cooling system which uses the whole drive unit housing and all integrated components for motor heat dissipation.
Generally, the bearing and gearing lubrication in the traction drive gearboxes, especially of rail vehicles, is performed by means of gear wading in the oil pool and throwing of oil from the wading gears to bearings by auxiliary collecting and distribution channels. Based on available technical data, the maximum speed of the input shaft of the gearbox is nowadays approximately 5 200 rpm. Protective seal of the inner space of the gearbox against dust, water and oil leakage is performed by labyrinth sealing, or by shaft sealing rings.
Cooling of lubricant is performed by means of passive cooling via the housing of the gearbox.
In modern traction drives, the manufacturers use ac electrical motors, most popular are induction and permanent magnet motors which are generally known and they were reported in many non-patent literature publications as described above.
These electrical motors have maximum speeds up to 5 200 rpm (extremely up to 6 000 rpm). They are usually cooled by an independent fan or by a fan placed on the shaft of the motor. The liquid cooling is often used as well.
Existing solutions of traction drive units are designed for lower speeds of electrical motors (approx. up to 5 200 rpm). To assure the transmission of the power from such motor to the axle or wheel, the corresponding design leads from transmitted torque point of view to relatively robust solutions characterized by large volumes of drive units and their considerable weight. The idea of high-speed drive (i.e. with the electrical motor speed over 6 000 rpm), which could enable essential reduction of dimensions and weight of the drive unit, is generally known in the theory. It comes from the equation for mechanical power Pm=Tω, where Pm is a mechanical power at the rotor output, T is a torque and ω is a mechanical rotor speed. Therefore, if the rotor speed is significantly increased and the output power is kept constant, then the output torque substantially decreases. Thus, all mechanical components result smaller in volume and weight. However, there is no existing reliable design solution available for traction applications up to now. This invention describes a robust design solution of the compact drive unit, which allows significant reduction of the volume and the weight of the traction unit due to significant increase of the traction motor speed (typically over 9 000 rpm) while keeping the same traction vehicle characteristics. Although, higher speeds of traction motor require usage of high-speed stages of the gearbox to reduce the speed to rated output speeds of the axle/wheel, the torques transmitted by high-speed stages of the gearbox are significantly lower, which principally decreases demands on gear train dimensions. Moreover, the proposed compact unit, due to significant reduction of dimensions of particular parts of the drive, enables the integration of the drive into a single compact housing. This integration into the one housing together with unique construction design of high-speed electrical motor makes possible to improve the heat transfer from particular components and to use passive cooling of the electrical motor, which is a significant advantage compared to the existing solutions. As explained above, the proposed invention significantly overcomes currently known designs and arrangements of drives for traction vehicles. It allows significant reduction of weight and volume of the drive unit and, based on that, integration of the drive unit into the single compact housing, which further enables the use of passively cooled electrical motor and significantly simplifies and reduces the cost of drive assembling.
The proposed solution requires preheating of the lubricant of high-speed stage of the gearbox during extremely low ambient temperatures, which can typically go down to −40° C. This is, as described in detail below, solved by design arrangement of the drive and by the usage of thermal sources available in the integrated body of the drive unit, i.e. without any further external equipment. In comparison with existing designs of traction drives employing low-speed gearboxes having no extreme demands on gearing and bearing lubrication or pre-heating of lubricant, the required preheating in this invention is not any significant disadvantage.
The invention is further explained by means of the drawings.
The electrical motor 1 is supplied by a power electronics converter 2. Typically, it is a voltage-source inverter. The power electronics converter 2 can also be a current-source inverter.
Output shaft of the gear 7 can be connected either directly or by using the coupling 12 to the axle 8 of the traction vehicle, or to the wheel 9. In case the higher transmission ratio is required, the output shaft of the gear 7 can be connected to another gears 10 (as shown in
Due to significant reduction of both dimensions and weight of particular components of invented drive unit, all the drive unit components can be embedded into one compact housing. This solution significantly decreases the assembly cost and time. However, it is important that at least electrical motor 1 and high-speed gearbox stage 11 are embedded into common compact housing. The integration of the drive unit components into the single housing together with unique construction design of the high-speed motor 1 result in better heat dissipation from all components and it allows a passive cooling of the electrical motor 1 and the whole drive unit. This is very important advantage of the presented invention in comparison to existing traction drive technologies.
The proposed two-stage solution of the gearbox requires preheating of the lubricant of the high-speed gearbox stage 11 under extremely low ambient temperatures (typically down to −40° C.) before running the gearbox. Due to integration of the drive unit components into one housing, the proposed invention uses preheating of the lubricant of the gearbox 11 by means of the losses of the electrical motor 1. Thus, the power electronics converter 2 feeds the current into the stator winding of the motor 1 which causes production of the heat due to existing losses in the motor 1 (the resistive losses play the major role in this phenomenon). The produced losses, respectively resulting heat is distributed inside the drive unit using the conduction via both drive components and the housing and it preheats in this way the lubricant of the gearbox 11 before its running. Thus, the invented concept does not require any additional device (external thermal source, etc.) and it is very robust and reliable.
This invention allows significant reduction of drive units volume and weight while demanded traction power/tractive effort is kept. If the electrical motor 1 has the rated speed around 9 000 rpm and the rated power close to 100 kW (typical application for light traction vehicles), our conservative calculation shows that the drive unit volume and weight will decrease at least by 25% while keeping the same traction vehicle characteristics. This invention allows manufacturing of the traction drive unit in a single compact housing. It results in better heat dissipation from the drive components, it is not necessary to use a fan for the drive cooling (passive cooling of the whole drive forms the important advantage in comparison to competitive solutions) and the single drive housing also cuts the assembly cost and time.