WO2010133330A1

WO2010133330A1 - Multi component propulsion systems for road vehicles

Info

Publication number: WO2010133330A1
Application number: PCT/EP2010/003007
Authority: WO
Inventors: Barry Shrier; Ian Hobday
Original assignee: Liberty Electric Cars Ltd
Priority date: 2009-05-18
Filing date: 2010-05-18
Publication date: 2010-11-25
Also published as: GB0908482D0; GB201008264D0; GB2470478A

Abstract

A non-combustion multi component propulsion system for road vehicles comprising electrical supply means such as a battery system (1), electrical energy storage and supply means such as a super capacitor (2), a kinetic energy supply means such as a flywheel (3) operated by a controller (4) which senses the energy needs of the vehicle and the energy capacity of the systems to deliver the required energy and also to employ regenerated energy to replenish the energy sources as required. Additional energy generating systems such as solar panels and wind vanes may be included.

Description

MULTI COMPONENT PROPULSION SYSTEMS FOR ROAD VEHICLES

This invention relates to motive power systems for use in propelling vehicles. The invention particularly relates to motive power systems which include an arrangement of three or more power units coupled to a transmission, commonly termed "hybrid" propulsion systems, for road vehicles.

Road vehicles go through a variety of operating cycles according to the environment in which they are working. For example the energy requirements of the vehicle are different during steady highway motoring from the requirements for urban stop/start motoring. In addition, the energy requirements vary during different stages in any one cycle. For example, for motorway driving there will be a requirement for energy to accelerate up to final speed and there will be surge needs to accelerate, such as to overtake, or to decelerate in traffic congestion. In urban motoring the need for starting from standstill, acceleration, deceleration, stopping, perhaps emergency braking will be required.

Sophisticated energy propulsion systems based on hydrocarbon fuel systems such as gasoline, diesel fuel or gas fired engines have been developed to enable vehicles to function in these various modes.

Hydrocarbon fuel systems however suffer from the disadvantage that they produce emissions that pollute the atmosphere such as carbon dioxide and diesel engine particulate emissions. Furthermore, they have high noise levels and consume finite resources which are subject to dramatic price swings.

There has therefore been a move towards alternate energy forms of vehicle such as electric vehicles or hybrid vehicles which employ two or more forms of energy. Such as hybrid vehicles which employ a combination of electrical energy and hydrocarbon fuels. Electric vehicles are also known however, to have a significant problem with the low energy density of the batteries, along with the relatively high capital cost of suitable power electronic systems for implementing regenerative operations. Furthermore, reduced vehicle performance is experienced as the batteries approach a low state of charge. Traction batteries typically possess an energy density of about 100 kJ/kg at a 3 hour rate of discharge, but only about 50 kJ/kg at a 30 minute rate of discharge. A difficulty with battery powered electric vehicles is that the battery capacity is limited and frequent recharging is required particularly with heavy vehicles such as large saloon cars, four wheel drive vehicles, trucks and busses. This therefore leads to a very short operation span between charging of the battery system. A battery system is also a slow means of supplying electricity creating difficulties when there are needs for energy surges such as during vehicle acceleration and starting from a standing position. Battery powered vehicles can therefore be somewhat sluggish.

Conventionally battery packs in electric vehicles are heavy and can constitute up to 30% of the vehicle mass.

In addition it is difficult to transfer more than 70% of vehicle kinetic energy back into a battery pack of the above mentioned mass. For example, if a vehicle was braked from 60 km/h for 10 to 12 seconds, the electric machine and electronic system would need to deliver 50 W/hr to the battery at an efficiency of perhaps 80% for the electric machine and 85% for the battery, resulting in an overall efficiency of 68%. When braking from higher speeds the efficiencies are worse. Thus an electric drive is not really suited to stop-start operations. Furthermore, the electric machine has to have a sufficiently high power rating in order to be compatible with normal traffic, which requires peak powers of around 15 kW/t of vehicle mass.

Whilst it is apparent from the above discussion that hybrid propulsion systems using a combination of combustion engine and electric machine/battery or a combination of combustion engine and hydraulic machine/accumulator and/or flywheel are known, the combination of electric machine and hydraulic machine/accumulator is much less often employed in practice.

It has also been proposed to regenerate the kinetic energy generated by the braking of the system by the use of a flywheel. However, to utilise a flywheel over the speed range of a vehicle normally requires a continuously variable transmission. Generally, this is difficult to achieve since there is a large speed mismatch between the flywheel and the vehicle, as the flywheel should be at maximum speed when the vehicle is stationary and vice versa. If electric machines are used to produce a continuously variable transmission (CVT)₁ i.e. if one electric machine is mechanically coupled to the drive shaft and both machines are connected electrically, the motor connected to the drive shaft has to be relatively large to produce the low speed high torque required for a heavy vehicle. An AC machine, such as an induction motor, is typically directly coupled for energising the flywheel. Although the AC machine may be considerably smaller than the main drive motor, induction machines have poor power capability at high speeds. Accordingly a large expensive AC machine is generally required.

Object of the Invention

It is an object of the present invention to provide a hybrid propulsion system for a road vehicle which ameliorates or overcomes at least some of the problems associated with the prior art.

It is a yet another preferred object of the invention to provide a method for controlling a hybrid propulsion system which seeks to maximise the efficiency of operation of each propulsion unit in the system.

Further objects will be evident from the following description.

Disclosure of the Invention

The invention provides a hybrid propulsion system for use in vehicle operations, said propulsion system being free of a combustion energy system and comprising: a) a mechanical transmission for coupling to a final drive of the vehicle; b) a first drive unit coupled to the mechanical transmission; c) a second drive unit and coupled, independently of said first drive unit, to the mechanical transmission; d) a third drive unit arranged in parallel to said mechanical transmission and coupled to the final drive; and e) propulsion control means, for coordinating operation of the drive units in accordance with a plurality of predetermined modes corresponding to a driving cycle of said vehicle; wherein each of the first, second and third drive units includes a different type of energy storage means.

Most preferably, the first drive unit includes an electrical energy storage means and an associated electrical conversion means; the second drive unit includes a kinetic energy storage means and an associated fluid kinetic energy conversion means; and the third drive unit includes an electrical energy supply means with an associated electrical conversion means which can be the same as that associated with the electrical energy storage means. It is preferred that each drive unit is capable of regenerative operation.

In preference the predetermined modes of operation coordinated by the propulsion control means include: i) an acceleration mode, wherein the electrical energy storage means supplies power to the transmission; ii) a cruise mode, wherein the electrical energy supply means supplies the required power; iii) a deceleration mode, wherein one or both of the kinetic energy conversion means and the electrical energy conversion means are operated regeneratively to recover power and supply energy to the kinetic energy storage means and/or the electrical storage means; and/or iv) a stationary mode, when power is supplied for replenishing the electrical energy storage means as required.

Preferably, the electrical energy supply means comprises an electro-chemical storage means, such as a battery pack, and the electrical energy conversion means comprises one or more rotary electric machines, such as a DC motor or an AC machine which drives the transmission. Preferably, the electrical energy storage means includes at least one electrostatic storage means, such as one or more super capacitors.

Preferably, the electrical energy conversion means further includes a solid state power converter, such as a DC-DC motor controller or DC-AC four-quadrant inverter. If required, the electrical energy conversion means may further include an auxiliary electric machine coupled to the combustion engine.

Preferably, the mechanical energy storage means includes a kinetic energy storage means, including at least one flywheel.

Preferably, the propulsion control means comprises a microcontroller interfaced to a series of status transducers and a series of control means associated with respective components of the propulsion system.

Preferably, the microcontroller includes memory means for storing therein signals received from the status transducers associated with each drive unit, which status signals are indicative of the operational state of respective drive units, and which memory means also stores corresponding command signals applied to the control means for the drive units; whereby the stored status signals and command signals are utilised for deterministic or adaptive control of the hybrid propulsion system.

The invention also broadly resides in a method for controlling a hybrid propulsion system for a vehicle, which propulsion system includes at least two drive units preferably arranged for regenerative operation and coupled to a mechanical transmission independently of each other, which mechanical transmission is coupled in parallel with a non-regenerative third drive unit to a final drive of the vehicle, said method including the steps of: determining current state of the propulsion system by monitoring the status of each drive unit, including respective operating speeds and energy storage levels; receiving a demand signal indicative of desired vehicle motion; and if the demand signal indicates that negative wheel power for braking the vehicle is desired: operating any of the regenerative drive units regeneratively in accordance with current system state; or if the demand signal indicates that positive wheel power for cruise or acceleration is desired: operating one or more of the propulsion systems for the drive units; or if the demand signal indicates that no wheel power is desired, the vehicle being stationary: selecting one of the drive units for replenishing energy storage means associated with the regenerative drive units; which steps are repeatedly iterated in order to control the propulsion system consistent with the operating cycle of the vehicle.

The vehicle may be provided with a plurality of drive units such as motors, for example each wheel may have a motor. In this embodiment each motor can be a source of regenerative braking energy. For example a two wheel vehicle may have two motors, a three wheel vehicle three motors a four wheel vehicle four motors. Although for multi wheeled vehicles not every wheel may have a motor.

It is preferred that the second electrical energy storage system comprise a capacitor system which can be one or more capacitors and which can be used to provide surges in electrical energy such as those required for acceleration or starting from a stationary position. The capacitor system may be replenished by the regenerative action of the energy systems such as during braking where the reverse action of the main motor can put energy back into the kinetic energy system, such as a flywheel and can also become a generator of electrical energy for replenishing the capacitor system and optionally for recharging the battery system. It is preferred that the energy management system balance the energy sources to retain space for the introduction of energy into the capacitor system and yet maintain the energy level within the capacitor system sufficient for the surge requirements upon acceleration or starting from a standing position. It is preferred that the energy level of the capacitor system be maintained at from 20 to 80% of its maximum capacity. The drive mechanisms associated with the various energy sources are preferably a continuous variable transmission associated with the kinetic energy source which can be used to transmit the kinetic energy to the vehicle drive mechanism such as the rear axel of the vehicle. The drive mechanism associated with the electrical energy sources (the battery system and the capacitor system) will be one or more electric motors again coupled to the drive mechanism of the vehicle which may be a motor for each or several of the wheels of the vehicle.. One benefit of the energy system of the present invention is that the use of the kinetic energy and the capacitor system allows use of a smaller, and therefore a lighter, electric motor.

In addition the hybrid energy supply system allows the use of smaller, and therefore lighter battery systems. The hybrid energy system of the present invention satisfies different energy requirements and also provides energy supplies that have varying energy lifetimes. The kinetic energy supply tends to be short term lasting a matter of minutes, the capacitor system can provide energy on and off over a matter of days and the battery system can provide continuous low level electrical energy. The kinetic energy can be employed directly as mechanical energy to the vehicle drive shaft or alternatively it can be converted to electrical energy for recharging the battery system or storage in the capacitor system.

The energy management system is preferably an intelligent system which is aware of the energy stored in the various energy sources and, furthermore, can predict the energy requirements of the vehicle, perhaps through linkage to a navigational system. In this way the energy requirements for operation of the vehicle at different stages of the driving cycle can be satisfied and the regenerative energy can be directed to the sources that require replenishment.

Although the invention has been described within reference to a three component energy supply system additional energy supply systems may also be included. For example, solar panels may be provided to capture solar energy and/or wind vanes may be provided to capture energy from the wind or by virtue of movement of the vehicle. In situations where such additional energy sources are employed the energy management system may be such that it can direct the energy created to the drive systems or the energy storage systems as required.

We have found that the provision of the three (or more) component energy systems of the present invention together with the energy management system enables a heavy vehicle to perform an operating cycle comparable to the same vehicle powered by the traditional gasoline or diesel engines. We have found that a large passenger vehicle weighing about 2.7 tons can operate with normal acceleration such as 0 to 60 miles per hour in about 7 seconds and similarly 60-0 miles per hour deceleration in about 7 seconds and a top speed of 100 miles per hour over a period of several hours without the need for battery recharging.

The present invention is illustrated but in no way limited by the accompanying drawings in which

Figure 1 is a schematic illustration of a hybrid propulsion system of the present invention and Figure 2 is a chart showing the power mode phasing during a typical vehicle driving cycle.

Figure 1 shows how three power supply sources, a battery system (1); a capacitor system (2) and a kinetic energy system (3) can be controlled by a controller (4) to supply energy to the motor drive (5) and/or the mechanical drive (6). The dotted lines (7), (8), (9), (10), (11), (12) and (13) show how signals from the controller can open and close the energy supply channels by means of switches (14), (15), (16), (17), (18), (19), (20) and (21) to supply power to the drives or to pass regenerated energy back to the energy systems. (22) is a converter that converts regenerated mechanical energy to electrical energy and (23) is a switch which can be used to provide the electrical energy so produced to charge the battery system or for storage in the capacitor system.

Figure 2 is not to scale but illustrates how the different power supplies shown in Figure 1 may be used during a driving cycle. The positive acceleration showing how the different power supplies can be employed according to the driving mode and the negative acceleration showing how the regenerated energy can be captured and fed to the various power sources as indicated.

Claims

1. A hybrid propulsion system for use in vehicle operations, said propulsion system being free of a combustion energy system and comprising: a) a mechanical transmission for coupling to a final drive of the vehicle; b) a first drive unit coupled to the mechanical transmission; c) a second drive unit and coupled, independently of said first drive unit, to the mechanical transmission; d) a third drive unit arranged in parallel to said mechanical transmission and coupled to the final drive; and e) propulsion control means, for coordinating operation of the drive units in accordance with a plurality of predetermined modes corresponding to a driving cycle of said vehicle; wherein each of the first, second and third drive units includes a different type of energy storage means.

2. A propulsion system according to Claim 1 in which the first drive unit includes an electrical energy storage means and an associated electrical conversion means.

3. A propulsion system according to Claim 1 or Claim 2 in which the second drive unit includes a kinetic energy storage means and an associated fluid kinetic energy conversion means.

4. A propulsion system according to any of the preceding claims in which the third drive unit includes an electrical energy supply means.

5. A propulsion system according to any of the preceding claims in which the predetermined modes of operation coordinated by the propulsion control means include: i) an acceleration mode, wherein the electrical energy conversion means supplies power to the transmission; ii) a cruise mode, wherein the electrical energy supply means supplies the required power; iii) a deceleration mode, wherein each of the kinetic energy conversion means and the electrical energy conversion means are operated regeneratively to recover power and supply energy to the kinetic energy storage means and/or the electrical storage means; and/or iv) a stationary mode, power is supplied for replenishing the electrical energy storage means as required.

6. A propulsion system according to any of the preceding claims in which the electrical energy supply means comprises a battery pack.

7. A propulsion system according to any of the preceding claims in which the electrical energy conversion means comprises a rotary electric machine.

8. A propulsion system according to Claim 7 comprising several electric motors associated with wheels of the vehicle.

9. A propulsion system according to any of the preceding claims in which the electrical energy storage means includes one or more super capacitors.

10. A propulsion system according to any of the preceding claims in which the mechanical energy storage means includes a kinetic energy storage means.

11. A propulsion system according to Claim 10 in which the kinetic energy storage means includes at least one flywheel.

12. A propulsion system according to Claim 11 in which the propulsion control means comprises a microcontroller interfaced to a series of status transducers and a series of control means associated with the components of the propulsion system.

13. A propulsion system according to Claim 12 wherein the microcontroller includes memory means for storing signals received from the status transducers associated with each drive unit, which status signals are indicative of the operational state of respective drive units, and which memory means also stores corresponding command signals applied to the control means for the drive units.

14. A propulsion system according to any of the preceding claims in which the energy level of the capacitor system is maintained at from 20 to 80% of its maximum capacity.

15. A propulsion system according to any of the preceding claims in which the energy management system is an intelligent system which is aware of the energy stored in the various energy sources and can predict the energy requirements of the vehicle.

16. A propulsion system according to any of the preceding claims in which the energy management system is linked to a navigational system.

17. A propulsion system according to any of the preceding claims including an additional energy supply systems.

18. A propulsion system according to Claim 16 in which the additional energy supply systems comprises one or more solar panels.

19. A propulsion system according to any of the preceding claims in which the additional energy supply system comprises one or more wind vanes.

20. A propulsion system according to any of Claims 17 to 19 in which the additional energy supply means is linked to the energy management system so the energy created can be directed to the drive systems or the energy storage systems as required.

21. A method for controlling a hybrid propulsion system for a vehicle, which propulsion system includes at least two non-combustion drive units optionally arranged for regenerative operation and coupled to a mechanical transmission, which mechanical transmission is coupled in parallel with a non- combustion third drive unit to a final drive of the vehicle, said method including the steps of: determining current state of the propulsion system by monitoring status of each drive unit, including respective operating speeds and energy storage levels; receiving a demand signal indicative of desired vehicle motion; and if the demand signal indicates that negative wheel power for braking the vehicle is desired: operating any of the regenerative drive units regeneratively; or if the demand signal indicates that positive wheel power for cruise or acceleration is desired: operating one or more of the propulsion systems for the drive units; or if the demand signal indicates that no wheel power is desired, the vehicle being stationary: selecting one of the drive units for replenishing energy storage means.