1、STDSAGMA 94FTM5-ENGL 199q m b87575 000457U 153 W 94FTM5 A Special CVT for a New Power Train Concept by: B.-R. Hhn and B. Pinnekamp Technical University of Munich American Gear TECHNICAL PAPER COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSTDmAGNA 94F
2、TN5-ENGL 3774 Ob87575 0004573 07T W A Special CVT for a New Power Train Concept B.-R. Hhn and B. Pinnekamp Technical University of Munich nie statements and opinions contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacture
3、rs Association. ABSTRACT The Autark Hybrid is the power train for auniversai vehicle tha is able to drive in inner city areas with zero emission and is also suited to long distance driving. The combination of two power sources - hybrid transmission with internal combustion engine (IC engine) and sma
4、ll electric engine -enables significant reductions of fuel consumption at constant power as well as at the U.S. city cycle. The fuel saving is accomplished by avoiding the partial load operation areas with high specific fuel consumption and by reducing the engine speed to an optimum value for long d
5、istance driving. This concept requires anew power transmission with wideratio range and continuously variable ratio. Therequirements, the principle function and the progress in development of this so-called i2-CVT is described in this paper as well as the application in the hybrid power train. Copyr
6、ight O 1994 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Virginia, 223 14 October, 1994 ISBN. 1-5 5 5 89-639- 1 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSTD-AGMA 94FTMS-ENGL 1994 = b87575 000572 T2b 1 INTRODUCT
7、ION A Special CVT for a New Power Train Concept B.-R. HOHN, Prof.Dr.-lng. and B. PINNEKAMP, Dr.-lng. Department of Mechanical Engineering Gear Research Center (FZG) Technical University of Munich A steady increase of ic engine driven vehicles can be noticed in all industrial countries. A big part of
8、 the air pollution and fuel consumption is caused thereby. Therefore, the reduction of primary energy consumption and pollutant emission of ic engine driven vehicles is nowadays an important issue. A suitable approach for a solution is a system orientated improvement of the entire power train which
9、is tasked to lower the fuel consumption significantly. Due to the increasing traffic density the demand for zero emission is increasing- i.e. electrically driven vehicles in urban areas and inner cities (noise, smog). A power train concept, that on the one hand enables fuel saving while using the ic
10、 engine and on the other hand enables short distance driving with electric engine (working as motor) would be perfect. The Autark Hybrid aims to meet this requirements. A combination of optimized components of the power train (ic engine, gearbox, electric engine, etc.) leads to an optimum configurat
11、ion. The ic engine (conventional design, low in fuel consumption and emission) is only used in driving modes where it runs with low specific fuel consumption and low pollutant emission and simultaneously provides the electric components with energy when needed (current circuit , charging of the batt
12、ery) . cruising speed Y engine speed Figure 1 - Tractive resistance line of a vehicle and power characteristic of a turbo diesel engine with direct injection 12 The right part of fig. 1 shows the power characteristic of a turbo diesel engine with direct injection and on the left side the required po
13、wer to overcome tractive resistance of an automobile as a function of cruising speed (without acceleration) . The lowest specific fuel consumption of be = 200 g/kWh occurs at an engine power of P, = 40 .65 kW and an engine speed of n, = 2000 min-. The low c,-factor of the vehicles and the powerful e
14、ngines means 1 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services STD-AGHA 74FTMS-ENGL 1774 m Ob87575 O004573 7b2 m that maximum power is only needed for acceleration and for a cruising speed of v 1 150 km/h. At a cruising speed of v I 100 km/h the engin
15、e works in the partial load area with inefficient high specific fuel consumption. This dis- advantageous mode is avoided by including the electric engine into the power train of the Autark Hybrid. The electric engine works as driving motor where the ic engine would run in the mode of high specific f
16、uel consumption (partial load, high emission). That happens especially where the need of power is low (city traffic or stop and go). The electric engine works as generator to charge the battery during the operation periods of the ic engine. The electric engine has significantly lower power than the
17、ic engine. It is also used in inner city areas to avoid pollutant emission and noise. To achieve acceptable acceleration in spite of the low electric power an extremely high starting ratio of the CVT is necessary. For long distance driving a wide overdrive range of the CVT is required to realize min
18、imum fuel consumption and pollutant emission. Therefore, a remarkably enlarged ratio range compared with usual designs is demanded for the Autark Hybrid. 2 AUTARK HYBRID: GOAL AND REQUIREMENTS The goal of the Autark Hybrid is the maximum reduction of primary energy consumption and pollutant emission
19、. Driving in urban areas with limited range should be possible only with the electric engine (motor) with zero emission. The electric energy is stored in the battery during regular operation of the ic engine. There shall be no disadvantage compared to conventional vehicles if the ic engine is used.
20、“ Figure 2 - Autark Hybrid transmission Fig. 2 shows a principle sketch for the function of the Autark Hybrid. The wheel is either driven by the ic engine or by the electric engine connected to a common CVT. The extremely wide gear range of the CVT (imax/iain = 25) enables different driving modes :
21、4 pure electric driving with satisfying acceleration, 4 driving in switch mode at medium power requirements as described below, and optimum specific fuel consumption by using the wide overdrive range at higher cruising speed. 2.1 Electric Power Train For the electric power train the CVT enables on t
22、he one hand the use of a light, fast rotating electric engine (storing of rotation energy, low size, high efficiency) and on the other hand the avoidance of weakening of the field. Furthermore, the electric engine replaces the generator and the starter of conventional vehicles. The wide ratio CVT tr
23、ansforms the power of the small engine to much higher wheel torque than the parallel hybrid with conventional gearbox. The chosen electric engine for the Autark Hybrid provides its nominal power of PE = 8 kW already at v = 4 km/h with a wheel torque of T c: 1600 Nm. This is almost 15 times more than
24、 the torque that could be achieved with a conventional manual transmission. The concept enables the recuperation of braking energy in two ways: First the braking energy is used to charge the battery. Second the braking energy is stored as rotational energy in the electric engine. The kinetic energy
25、may be used for a short time, through adaptive control of the CVT to accelerate the vehicle. The frequent and quick discharging and charging operations are important requirements for the investigation of the battery. The electric engine working as a motor gets the energy out of the battery which is
26、charged by the electric engine working as generator at underload mode of the ic engine or at thrust mode. An additional charging from the mains is usually not necessary but possible if the vehicle stands still for a longer period or if it is used as a pure electric vehicle for a longer time. 2.2 Swi
27、tch Mode To achieve minimum fuel consumption, the ic engine only runs in driving situations, 2 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Serviceswhere high driving power P, is required. The electric engine is used at low driving power, where the ic engin
28、e would work with high specific fuel consumption. The power of the electric engine has to be adapted to the ic engine in such way that in the medium load area (v = 40.70 km/h) also switch mode is possible, i.e. depending on the charging level of the battery the vehicle is powered by electric engine
29、or ic engine. w 50- 40- 30- 20- 10 - 0- wising speed Y engine speed n M Figure 3 - Tractive resistance line of a vehicle and power characteristic at partial load (hatched area of fig. 1) 12 Fig. 3 shows once again as an expanded view of fig. 1 the power characteristic and tractive resistance curves
30、of a vehicle at low driving speed range (hatched area of fig. i). For a driving power of P, at vx = 80 km/h the ic engine runs at a power of P, = Po. Fig. 4 shows that the battery is charged simultaneously. L i Figure 4 - Energy flow for ic engine drive with charging of battery The low driving power
31、 P, at vy = 35 km/h is provided by the battery i.e. the vehicle is moved with zero emission, fig. 5. - Y driving power PF Figure 5 - Energy flow electric drive with discharging of battery the advantages that results out of the ic engine operation with be = 220 g/kWh (P, = Po) instead of be = 440 g/k
32、Wh (P, = PFy) prevail. 2.3 Fuel saving potential For constant power requirement (constant cruising speed, no roadway gradient) there are two possibilities of fuel saving with the Autark Hybrid. Fig. 6 shows the saving potential depending on the cruising speed. overdrive I +- 1 20 4b 60 8 160 lh 140
33、h/h 180 crulslng speed v Flgure 6 - Fuel saving potential of the Autark Hybrid vehicle At cruising speed of v 2 60 km/h the wide overdrive range enables the ic engine to operate with high torque and low speed and therefore with low specific fuel consump- tion. Between v = 70 .160 km/h a theoretical
34、fuel saving of more than 15 % is possible. At v 60 km/h the fuel consumption can be reduced by using the switch mode between ic engine and electric engine described before. The shown graph is valid for a conversion efficiency of q, = 0.8 from mechanical to electrical energy and back (qe+, = 0.8) i.e
35、. an entire conversion loss of 36 %. In spite of this loss there is a remarkable saving potent ia1 especially for v 40 km/h. In spite of the unavoidable conversion losses in the transformation from mechanical to electrical energy and back 3 COPYRIGHT American Gear Manufacturers Association, Inc.Lice
36、nsed by Information Handling ServicesSTD-AGHA 94FTHS-ENGL 1994 m 3 iZ -CVT 3.1 Principle of Function For the Autark Hybrid a CVT with wide ratio range is developed: the i-CVT. In this unit the complete ratio range of a chain CVT is used twice by switching the torque direction at the maximum ratio of
37、 the low speed range (Vi) to the minimum ratio of the high speed range (Va) without changing the actual ratio and chain position. During the shifting operation power transmission is not interrupted. This is achieved by use of two multiple disc clutches and two tooth clutches with serial synchronizer
38、 units. The change of ratio and the shift of speed ranges is described in detail as follows: For starting tooth clutch K1 has to be engaged, the torque flow is enabled by actuating multiple disc clutch L1, fig. 7a. The CVT is in its extreme starting ratio position. By shifting the CVT all ratio valu
39、es of speed range lllowll (Vl) can be adjusted, fig. 7b shows the minimum ratio of VI. The CVT is in its lowest ratio position. Regarding to the adequate choice of the spur gear stages there is no differential speed in tooth clutch K2 and multiple disc clutch L2 in this position. Therefore, the torq
40、ue can be transmitted by multiple disc clutch L2 directly through shaft W1 to the output shaft without use of the CVT. This is the socalled synchro point (SP), fig. 7c. Without load tooth clutch K1 can be opened and K2 can easily be engaged, fig. 7c. By opening multiple disc clutch L1 the power is t
41、ransmitted via K2, shaft W2 and CVT to shaft W1 and via L2 to the output shaft. The power flow passes the CVT in the opposite direction. It is therefore again in its highest ratio position, fig. 7d. The complete ratio range of the CVT can be used another time until the maximum overdrive ration is re
42、ached, fig. 7e. The total ratio range between starting ratio (fig. 7a) and overdrive (fig. 7e) is the square of the gear of the CVTs gear range itself: b87575 0004575 735 m Vl = 1 O (without final drive) input “output i- inp a) i- 2 i- 2 - SP i- 2 v2 3.2 Gear arrangement Besides suitable efficiency
43、and acceptable effort for manufacturing especially the Figure 7 - Function of the i2-CVT 4 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Servicesa STD-AGMA 94FTM5-ENGL 1994 Ob87575 000457b b7L available space for the i*-CVT for transaxle transmission has to
44、be considered carefully for the decision about the gear arrangement. For backward driving no mechanical gear stage is necessary because the electric engine is used. The appropriate gear arrangement or the application at the Autark Hybrid was determined by means of a thorough variation and analysis o
45、f different gear structures meeting the requirements in an more or less suitable way. By means of three examples the criteria are introduced, by which the most suitable arrangement is found. A t 1 Figure 8 - Gear structure, example 1 The gear structure shown in fig. 8 works with good efficiency in r
46、ation range V2 because there are only two gear meshes active besides the CVT. Another advantage is the use of a complete synchronizer unit for both, K1 and K2 with one common sliding sleeve which enables simplified electronic control. The main disadvantage of this example is the shape of the CVT its
47、elf: Because the torque is transmitted to both sheave sets by a hydromechanical torque sensor it would be necessary to design the sheaves on shaft A as hollow shaft to lead the torque from the left side to the torque sensor. This would require higher design and manu- facturing effort, already existi
48、ng CVTs could not be applied. Therefore, solutions with this restriction are put aside first. Another disadvantage of example 1 is a high differential speed in multiple disc clutch L1 at high cruising speed in range V2. -+-IB T I Figure 9 - Gear structure, example 2 Main advantage of example 2, fig.
49、 9, is the less required axial space and the opportunity to use an already designed CVT. The differential speed in multiple disc clutch L1 is as high as in example 1. Four gear meshes as well in Vi as in V2 cause loss of efficiency. T Figure 10 - Gear structure, example 3 Example 3, fig. 10, works with few gear meshes and can be realize with relatively small axial and radial dimension. A common CVT design can be applied. The occurring differential speed in K1 and L1 are relatively low (max. E 4.500 rpm) . In spite of this advantages example 2 may be more appropri
