DE3050625A1 - Method of vehicle propulsion - Google Patents

Description

The present invention relates to a vehicle drive and in particular a method for driving a wheel-driven vehicle, in which the operation of a drive motor or engine with the storage of kinetic Energy is coordinated in such a way that the efficiency of the entire propulsion system is maximized.

Hybrid engines or drive line systems for inertial loads, such as those used in the operation of automobiles or others Wheeled vehicles occur are well known. In general, hybrid systems contain a drive motor, such as an internal combustion engine or other device for converting to fuel contained potential energy in mechanical energy or driving force, which e.g. on the drive wheels of a Vehicle can be transmitted to a device for storing kinetic energy, such as a flywheel and a mechanical power transmission, which energy or power or driving force between either the

- the drive motor or the flywheel and the inertial load, represented by the drive wheels of the vehicle. The energy storage device or flywheel is used to reduce excess energy that is generated by optimized operation of the drive motor, or ■ · ■

kinetic energy during vehicle braking or both for a subsequent conversion into usable driving force or Save performance.

The many different hybrid systems used in earlier Patents or other literature described can generally be assigned to one of two classes at least with regard to the intended mode of operation. In a first class, a swing forms. rad relatively high technology or an energy storage facility high capacity is the primary source of mechanical power needed to meet the power needs of the Load or e.g. the drive wheels of a vehicle is used, the generated by the engine or drive motor The power and energy of vehicle deceleration are primarily used to charge the flywheel as required to satisfy the power demand. In theory, you can Hybrid systems of this first class bring with them considerable savings in the amount of fuel required to drive the vehicle is due

(a) the operation of the fuel-consuming drive motor or engine only with optimal special fuel consumption,

(b) the standstill of the engine or drive motor when the stored kinetic energy is sufficient to drive the vehicle to drive, and is greater than the energy required to restart the engine or drive motor is and

(c) the storage and use of braking energy resulting from the braking of the vehicle mass and which otherwise as thermal energy would be lost.

On the other hand, many problems speak against the use of such systems, which are higher with the installation of a flywheel

Technology linked into the drive line system. High speed flywheels contribute to losses Transfer of kinetic energy to and from the flywheel due to the required gear or gear ratio and the clutches and the like. In addition, such flywheels require complicated evacuated ones Housing to avoid air friction losses. High technology flywheel systems and similar energy storage devices large capacity are therefore susceptible to efficiency losses in themselves, whereby the increased efficiency to a considerable extent through the optimized operation of the engine or drive motor is compensated.

* 5 in the second class of hybrid systems satisfies the Drive motor or the engine primarily the power requirement the vehicle mass, with excess energy resulting from either the operation of the drive motor or the vehicle deceleration results in a storage device relative

Of) '■ ■

low capacity is stored, such as. B. an automotive Crankshaft flywheel that is enlarged and operated at speed for increased capacity that is on the order of or slightly greater than the speeds of the crankshafts of conventional internal Internal combustion engines are. Hybrid systems of this second class can be easily applied in an advantageous manner the geometry of existing drive lines can be adapted and can also be related to the known technology Use infinitely variable gears, which for optimization

both classes of hybrid systems are required. This the latter class of hybrid systems is exemplified in published British patent application 2,031,822 and also in an article entitled "The Vadetec Inertial

Drive Line "by S. Shih, E. G. Trackman and Y. Kemper, Society 35

of Automotive Engineers, No. 800101, February 1980.

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Computer simulations of motor vehicles equipped with the second class of hybrid systems results that are comparable to those of the first class of hybrid systems in terms of fuel consumption is significantly reduced compared to conventional automotive driveline. The only change one conventional vehicle drive line, which for the second class of hybrid systems in addition to the substitution a continuously variable transmission for the normal multi-speed transmission and the arrangement of a built-in micro-r ; Processor required for automated control and monitoring is to use a clutch between, the engine crankshaft and the flywheel and a

Increasing the strength of the flywheel. 15th

The operating mode for the second class of hybrid systems, namely an operating mode which differs from the operating mode with vehicle speeds in which the engine crankshaft and the vehicle drive wheels are in direct drive connection, comprises an optimized ^: operation of the drive motor for satisfaction the power requirement on the drive wheels, regardless of how low this power may be. The kinetic energy of vehicle braking is stored in the flywheel and the engine

switched off when the energy stored in the flywheel to satisfy the power requirements of the drive wheel load as well as to restart the drive motor is sufficient.

According to the present invention, a hybrid system is

that from a fuel-consuming drive engine There is a power output which is connected to the vehicle load in series via a clutch, a flywheel and a Gearbox with variable speed ratio connected, operated in such a way that low thermal efficiencies

in the fuel-consuming drive engine. Without loss of efficiency for the rest of the system to be added,

be avoided in a simple manner that the drive motor, if its operation is required, not operated below a minimum level of generated power becomes, creating a relatively narrow range of good thermal Efficiency is created, with the power generated by the drive motor, which is used to drive the vehicle required power goes, is stored in the flywheel during such operation of the drive motor and wherein the power delivered to the vehicle load is controlled by changing the speed ratio of the transmission will. The drive motor is decoupled from the flywheel and switched off to stop fuel consumption, when the flywheel reaches a predetermined speed level. The stored kinetic energy is then used by the Controlled operation of the transmission with variable speed ratio as driving force or power to the load transfer.

The present invention is primarily directed to an improved method of driving a wheel-driven vehicle To create a vehicle using a hybrid system of the identified second class, the fuel- consuming drive motor of the system is only operated as required and, if required, only above Output power levels are operated through which a narrow range of good thermal efficiencies is achieved.

Further features, advantages and possible uses of the The present invention emerges from the following description of exemplary embodiments in conjunction with FIG Drawing. In it show:.

Fig. 1 is a schematic representation of the components of a Hybrid system used in the practice of the present invention

• »Ο» ft β «β« β

2 shows a graphic representation of a family of characteristics the engine power,

FIG. 3 is a graphical representation according to FIG. 2, in which the engine operation according to the present invention is illustrated, and

4 shows a graphical representation of a curve which results from the plot of the values of the specific fuel consumption in the brake test against the generated power (engine horsepower). minimum constant Engine speed results.

In Fig. 1 is a hybrid engine system or drive line shown with a fuel consuming prime mover or engine 10 having an output shaft 12 which releasable via a clutch 14 with a flywheel 16 and the input shaft 18 of a transmission with variable Speed ratio,. Preferably a stepless (adjustable Transmission unit 20 is connected..The output of the continuously variable transmission unit is via an operating mode control unit with a final.? Drive shaft 24 connected to the power transmission with a load, shown

by a drive wheel 26 of a land vehicle. 25th

The prime mover or engine 10 may be any of the various types in which the potential energy is converted into a combustible fuel in ^?

mechanical energy or power converted at the shaft 12

will. This engine is shown schematically in Fig. 1 as a piston engine with a crankshaft ^, whose direct extension the shaft 12, a fuel supply 30 and a metering device 32, preferably a fuel injector, through which a controlled fuel supply from the feeder 3O to the motor 10 is effected. The clutch 14, the continuously variable transmission

Unit 20 and the mode control unit are fully described in the above mentioned published British patent application 2,031,822 and therefore need not be described in detail herein for a complete understanding of the present invention. It is noted, however, that the continuously variable transmission unit can transfer power from the input shaft 18 to the output shaft in a range of continuously variable speed ratios. The operating mode control device can be viewed as a gear ratio through which the system ^{can be shifted between the operating modes "forward '1} ,""neutral" and "reverse", as well as a unit for creating multiple outputs with a fixed speed ratio from the continuously variable transmission unit 20. As shown , the clutch 14 is a friction clutch, which can be adjusted between full engagement and disengagement.

The flywheel 16 is a low-tech flywheel and changes size depending on the size of the

'

Motor 10 as well as the size of the vehicle or one other load to be driven by the system. The flywheel works both as a crankshaft flywheel for the Motor as well as energy storage device and can in practice be of the order of magnitude of conventional crank

Have shaft flywheels that are used with the engine IO would.

In Fig. 1, the direct connection of the flywheel is based

with the input shaft 18 of the continuously variable transmission 30

unit primarily on the ability of the continuously variable transmission unit 20 to achieve a ratio of the output speed to the input speed of 0/1 or infinity. While such relationships are common in known continuously variable transmissions, consideration is given to ■

that a conventional friction clutch (not shown) between

the flywheel and shaft 18 can be used to allow the use of a continuously variable transmission unit with a finite range of speed ratios or a unit in which the. Area does not extend up to a ratio of output speed to input speed of 0/1, _to allow.

The system control or regulation takes place by a microprocessor or computer 34, .der like that in the above published British patent application mentioned above, the system disclosed a plurality of system monitors Entrances ,, a series of driver entrances and a series of outputs or control functions. Monitored

; System functions include engine torque, engine speed, the speed of the flywheel and the input of the continuously variable transmission unit, the speed of the Output of the continuously variable transmission unit, operating mode control status, Load torque and load speed. The driver inputs can be a main switch 36, a direction control element 38, a power controller such as B. have an accelerator pedal 40 and a brake pedal 42. The outputs of the microprocessor 34 'contain a fuel control for adjustment of the fuel injector 32 from one position a complete shutdown of the fuel supply to the

.25 engine 10, a clutch control, through which the clutch 14 between the states of disconnection via partial engagement can be adjusted for full engagement, a control of the speed ratio of the continuously variable transmission unit and a mode controller for the unit 22.

.

The basic. Operation of the drive line or the engine system; illustrated in Fig. 1 in relation to the Power transmission. Between the engine IO or the flywheel 16 and the drive wheel 26, whether such a power transmission is now positive when the wheel 26 is a driven

is, or negative, if the vehicle is braked to return energy from the wheel .26 through the drive line in a reverse direction. to. transmitted, is primarily dependent the state of the clutch 14 and the speed ratio the steplessly adjustable gear unit 20. Da the energy storage flywheel 16 is also the crankshaft flywheel of the motor. It is noted that power generating operation of the engine 10 only occurs can when the clutch 14 is engaged. When the clutch is engaged, the flywheel is right with you the engine crankshaft rotated, and the power transmission from the input shaft 18 of the continuously variable transmission unit, to wheel 26 is solely dependent on the setting the continuously variable transmission unit-20 and the mode control unit 22. Accordingly, the fuel consuming engine .10 operation at all Times when the clutch 14 is disengaged, terminated or discontinued.

From the foregoing it will be clear that the engine 10 can be started initially by turning the main switch 36 can to an electric starter motor (not shown) which is drivingly connected to the flywheel 16. to energize. At this time the flywheel is separated from the wheel 26, either by setting the continuously variable Gear unit to a zero output ratio or through Disengagement of a clutch (not shown) between the Flywheel and the input of the continuously variable transmission unit 20. If the mode control unit 22 so is set so that the drive line is in a forward drive direction works, the power generated by the engine 10 with suitable control of the continuously variable Gear unit 20 and the fuel injector 32 such transferred to the wheel 26, as described in more detail below

^ ° is described.

^ Π Γ Π Ο Λ Γ

¹ Understanding of the manner in which the fuel injector 32 is adjusted to control the power generating operation of the engine 10 when necessary and the adjustment of the speed ratio of the continuously variable transmission unit 20 will be facilitated with reference to FIG. In the engine efficiency characteristic field of Fig. 2, different levels of constant thermal efficiency, represented by lines of constant specific fuel consumption in the brake test, each numbered with numerical values of pound / horsepower / hour units, shown L for: changing values of the engine torque (M- Kg) and the engine speed (RPM). The optimized power generated by the engine is shown in FIG. 2 represented by a curve T. In other words, ideal operation of the engine 10 from the standpoint of obtaining the most cost-effective power generated by the engine itself will require control of the fuel injector 32 to provide torque and speed values on curve T. From the numerical values associated with the constant specific fuel consumption curves in the braking test in FIG. 2, it can be seen that the fuel consumption is above a line at which the constant specific fuel consumption in the braking test is approximately 0.60 pounds / horsepower / hour , is decreasing at a relatively low rate. The specific one

^ However, fuel consumption below ^{1 of} the same line increases rapidly in an exponential manner.

Since each power value supplied to the wheel 26, which requires an acceleration or an increase in the speed of the wheel

acts, .for a constant speed ratio of the stepless adjustable gear unit 20 results in an increased speed of the motor drive shaft 12, requires the power-generating Operation of the motor to precisely match any working line or curve in Fig. 2 is continuous or continuously variable speed ratios in the drive line between the motor and the wheel 26.

This requirement can be understood by considering the curve or line segment ^p _o ~ ^p _a ^of curve T ₁ , which represents engine operation with the essential constant minimum speed. In the illustrated embodiment

5 it is assumed that 1.00.0 RPM is the minimum speed at which the engine 10 remains in an operational state. It can therefore be assumed that the fuel injector 32 is idling / when the engine is running at a point P is / which is a torque zero and corresponds to a generated power of zero. The motor operation on the line segment up to point P results in an increased

generated power up to a torque value of 10 M-Kg or about 14 H.P. with very little increase in engine speed as a result of the increase in the fuel supplied to the engine. The engine speed is in this status of the Engine operation without substantial increases by increasing the load to which the drive shaft 12 is connected, held. The change in the load to maintain the speed of the engine 10 is made by changing the speed ratio the continuously variable transmission unit 20 achieved in order to keep the engine speed relatively constant regardless of the speed at which the wheel 26 is driven.

A consequence of the operation of the engine 10 with changing Performance levels without corresponding changes in the speed at which the. Motor is operated which for a full Understanding the present invention is important is that when the power generated by the engine is greater than is the power required at wheel 26 regardless of wheel speed (provided that the speed ratio range of the unit 20 is not exceeded), the speed of the motor and the motor drive shaft 12 with a the rate determined by the excess power is increased.

any such increase in engine speed due to the dated Motor generated power that was used on wheel 26 Exceeding power results in an acceleration or an increase in the speed of the flywheel 16. In this way

can the power generated by the engine 10, which is for the Vehicle drive required power exceeds, are stored as kinetic energy in the flywheel 16.

., ^, "■■ 3 5 In FIG. 3 the efficiency characteristic field of FIG. 2 is reproduced in part to the method of operation of the drive line or powerplant system of Fig. 1 according to the present To illustrate invention. The ideal engine working curve T. is again for the same values of the engine torque and the engine speed according to the points

'P. and P __, - shown which exemplary values of the generated : a max. . ■ ■

best performance. In addition, however, there is a point P in FIG. minimum acceptable generated power is shown as the intersection of the curve T. and a line T of constant torque, which is selected in the illustrated embodiment such that it approximately coincides with the line which has a constant specific fuel consumption in the brake test of 0.60 Lb / HP / Hr represents.
20th

ν-- -.- Λ: {- i In connection with FIG. 3, the engine "10" is therefore switched off in an operating mode that does not consume any fuel

^ V.ΐ 'or operated in a power generating mode and, when operated in this latter mode, only

"# - *> 25 at or above a selected minimum amount of the thermal efficiency, e.g. a specific fuel consumption in the brake test of 0.60 Lb / H.P. / Hr, or only in a way that a minimum constant torque, represented by the line T is generated. at

on ^C

^Ou this power-generating operating mode, the power requirement on wheel 26, determined by the driving conditions and the driver's actuation of the accelerator pedal 40, often becomes smaller

than the minimum power P. be which legally ......-_ min

2äSi t may be generated by the motor 10. In this case it will Speed ratio of the continuously variable transmission unit 20 and the fuel injector 32 by the microprocessor 34 controlled so that the engine with minimal acceptablera

thermal efficiency is operated, with the result, that the power generated beyond the power required at the wheel 26 increases the speed of the motor 10 causes. The increased engine speed will in turn increase the speed of the flywheel 16, so that the over Power requirement of the wheel 26 'beyond the generated power is stored as kinetic energy in the flywheel 16.

The power-generating operation of the engine 10 can be continued with constant torque or on the line T in FIG. 3 and, in the absence of an increased power requirement at the wheel 26, results in engine and flywheel speeds which increase up to a preprogrammed cut-out speed, e.g. 3,000 RPM. If no major power requirement during operation of the engine on the line T between the point P-. and the shutdown speed is present ,

min

the engine is stopped, the clutch 14 is disengaged and the speed ratio of the continuously variable Gear unit 20 so set / to kinetic energy stored in the flywheel 16 as power to the drive wheel 26 to transfer. If the flywheel speed drops to a minimum engine starting speed of e.g. 1,000 RPM, the engine is restarted by engaging clutch 14 and the fuel injector 32 is set to to produce a power which is not below one through the point P. is the value shown in Figure 3.

In Figure 4, the curve S. the result of the recording the values of the thermal efficiency in the form of the specific fuel consumption in the brake test against the Engine power (in horse power), where the engine speed is kept at a constant minimum speed of e.g. 1,000 RPM. In this figure lies the point P, which represents the minimum power with which the engine 10

may be operated in a power-generating company on Intersection of a line F constant specific fuel consumption in the brake test (o, 60 Lb / H.P. / Hr) and the Curve S. As can be seen from Figure 4, by loading

Restriction of engine operation in the power-generating mode of operation to a relatively small amount of power (in Horse power) that is available at the speed shown, the greater part of the relatively low thermal Avoided efficiencies at this speed.

The previous discussion of system operation for practicing the invention is primarily related to the operation of the engine directed at minimum acceptable thermal efficiency / which is either indicated by the line T in Figure 3 or is shown by the line F in FIG. It will taking into account 'that in practice the exact value of the minimum thermal efficiency for a motor in is calculated for a given vehicle to accommodate operation of the engine 10 with relatively low power, as it occurs e.g. under city driving conditions in which the vehicle driver depends more on the traffic conditions than is directed by conditions requiring high engine power. When the power requirement on wheel 26 is greater than that obtained by operating the engine 10 at the minimum previously described amount of thermal Efficiency is represented, the engine is preferably on the ideal performance line or by the Curve T. in Fig. 3 line shown operated. If the engine speed is between 1,000 and 3,000 RPM, e.g. is at 2,500 RPM, the engine operation is started on the curve T. by terminating the power generating operation of the engine 10, disengaging the clutch 14 and applying kinetic energy from the flywheel 16 for an initial acceleration through a suitable setting of the continuously variable transmission unit 20. When the flywheel slows down to approximately 1000 RPM., the engine is restarted and the fuel injector 32 adjusted to run for minimum power

by P. to care. Then the fuel inmm

spritzer 32 and the continuously variable transmission unit 20 controlled in such a way as to keep the engine operation on the ideal curve T.

The aforementioned transition from operation on line T with minimal accepted thermal efficiencies to the ideal performance line T. is preferred if there is no significantly increased power requirement on wheel 26 due to extreme movement of accelerator pedal 40. It is noted that the microprocessor 34 is programmed / again to accommodate such rapid increases in power demand by restarting the motor 10. suitable setting of the fuel injector 32 and ¹ ^ of the continuously variable transmission unit 20 / at whatever speed the flywheel may turn. Under these conditions and in connection with FIG. 3, the engine operation follows a curve from the line T rising sharply to and along or above the ideal curve T. possibly to an absolute maximum power-generating capacity of the engine 10. In a situation in which the driver has more engine power as operating economy demands or chooses, the system operation can correspond to the conventional operation of a motor vehicle engine. In this latter

Relationship is noted that since the flywheel is nearly may be the size of a conventional crankshaft flywheel, the speed response of the engine to a fully depressing the accelerator pedal 40 does not change significantly

differs from a conventional automobile engine. 25th

In addition, the flywheel 16 is used to store kinetic energy when the vehicle is braked. Around to achieve this use of the flywheel 16 when

the load on wheel 26 becomes zero or becomes negative, either 30th

controlled by the accelerator pedal 40 or the brake 42 is the clutch 14 disengaged. When the brake 42 is depressed, the energy of vehicle motion is in the flywheel with suitable downshifting the continuously variable transmission unit 20 is absorbed by the flywheel speed to increase. When there is a subsequent need for acceleration, the energy previously stored in the flywheel 16 is used as Power delivered to wheel 26 until the speed of the swing

9 * m

rades 16 to a minimum starting speed in the absence of a sudden need for more power, as described, is decreased. At this time, the clutch 14 is re-engaged and the engine 10 is started under control ^ Turn the remaining stored in the flywheel 16 Energy.

It is therefore clear that the method of the present invention low thermal efficiencies or high fuel consumption rates during operation of the engine 10 as a result of the ability of the flywheel to avoid To store energy that is generated by the engine when the power generated by the engine meets the power requirement Wheel exceeds 26. Moreover, it is clear that changes and / or modifications in the exemplary embodiment described can be made without departing from the present invention. It is therefore expressly intended that the preceding description, for example, a preferred, in no way restrictive embodiment

Example illustrated and that the true spirit and scope of the present invention is determined by the claims is.

Claims (6)

mi U.IN ι "uiNu rii-onioni ^» vnn Cl ·· · »·· PAGENBERG, DOST, ALTENBURG & PAR? ri <lEj? · ♦ · j .. ^." -. '"ν RECHTSANWÄLTE JOCHEN PAGENBERG or. jur .. ll. m. hahvaro- · A $ patent attorneys - european patent attorneys BERNHARD FROHWITTER DiPL.-iNG- *" * "" ^ WOLFGANG A. DOST dr .. dipl.-chem. GÜNTER FHR. v. GRAVENREUTH oipl.-ing. (fh> UDO W. ALTENBURG dipl.-phys. POSTFACH 860620. 80OO MUNICH TELEPHONE (089) 980361 TELEX 522791 padd CABLE: PADBDRO MUNICH OFFICE: GALILEIPLATZ 1, 8 MUNICH date June 29, 1982 Z 2473 Al / Iu a η s ρ rü che 1. procedure for driving a wheel-driven vehicle with ^ - your drive line with a fuel consuming one Drive motor with variable amounts of thermal efficiency to generate drive force or power works, an energy storage device, which is used to transfer energy to the drive motor at all times during the power-generating operation of the drive motor can be connected and disconnected from this when the Drive motor does not work and does not consume fuel, and with a gear with variable speed ratio for the transmission of power between the Energy storage device and the drive wheels of the vehicle, characterized by the following steps: Operation of the drive motor only with thermal efficiencies above a minimum amount of the thermal Efficiency when the operation of the drive motor to Propulsion of the vehicle is required. Increase the energy in the storage device with the .Power generated by such operation of the drive motor when the at the minimum amount of thermal Efficiency generated power is greater than the power required to drive the vehicle, whereby this excess power is stored as kinetic energy in the storage device, Ending the fuel-consuming operation of the drive engine, if the power stored as kinetic energy in the storage device is necessary for the drive the vehicle's required power, ■ disconnect the storage device from the drive motor and Changing the gear ratio of the transmission to transfer kinetic energy from the storage device as power to drive the vehicle and Reconnecting the storage device and the drive motor to restart the power-generating operation of the drive motor at the predetermined minimum amount of thermal efficiency when in the Storage device stored energy reaches a predetermined lower limit value. 2. The method of claim 1, wherein the energy storage device a flywheel is that in direct Drive relationship can be connected to the power output of the drive motor, characterized by the following steps:. Regulate the fuel supply to the drive engine Generation of power with thermal efficiencies above the predetermined minimum amount, Setting the speed ratio of the gearbox to Transmission of power generated by the drive motor via the flywheel to the vehicle drive wheel and Increase the operating speed of the drive motor and the flywheel to convert that from the drive motor generated power or energy that exceeds the power required to drive the vehicle ,, in kinetic energy, which results in increased flywheel speeds. 3. The method according to claim 2, characterized by terminating the operation of the drive motor when the speed of the flywheel is above the output speed of the drive motor at which the required for the drive Power level is most effectively generated by the drive motor, and restarting the drive motor to generate power at optimal thermal 2Q efficiencies. 4. Method of driving a wheel-driven vehicle with a drive line with a fuel-consuming one Drive motor with variable amounts thermal efficiency for generating driving force or power with variable torque and variable speed works on an output shaft, a flywheel, which works directly with the output width At all times during the power-generating operation, the drive motor can be connected and disconnected from it is when the drive motor is not working and. does not consume fuel, and with a gearbox with continuously variable adjustable speed ratio for the transmission of the Power between the flywheel and the drive wheels 35 of the vehicle, characterized by the following steps: Operating the drive motor with a predetermined minimum amount of thermal efficiency to generation of power on the output shaft when the drive motor is operating to propel the vehicle is required, Transferring the power from this output shaft to Need to drive the vehicle, Storing the power generated by the drive motor as kinetic energy in the flywheel while operating at the predetermined minimum amount of thermal efficiency, if so produced Power is greater than the power transmitted to propel the vehicle,, and Operating the drive motor with thermal efficiencies above the predetermined minimum amount to generate only the power required to drive the vehicle. 5. The method according to claim 4, characterized by terminating the operation of the drive motor and decoupling of the flywheel from the output shaft when the vehicle is driving Power is negative and when the flywheel reaches a predetermined speed, which is adequate to propel the vehicle. 6. The method according to claim 5, characterized by restarting of the drive motor when the speed of the flywheel reaches a predetermined minimum speed, which is representative of the energy required to restart the drive motor.