WO2003086810A1

WO2003086810A1 - Hybrid energy system for traction vehicles

Info

Publication number: WO2003086810A1
Application number: PCT/CA2003/000512
Authority: WO
Inventors: Robert S. Feldstein; Joseph Rait
Original assignee: Powergenix Systems, Inc.
Priority date: 2002-04-05
Filing date: 2003-04-04
Publication date: 2003-10-23
Also published as: CA2380521A1; AU2003218566A1

Abstract

An energy transfer and storage system for traction vehicles which have at least one electric motor/generator (32) and at least one traction wheel (16) is provided, and has a primary energy source (60), a hybrid battery system (62), and a drive/brake control system (52) associated with said at least one traction wheel, which generates electrical power during a braking operation to deliver to the hybrid battery system. The primary energy source may be an internal combustion engine together with an electrical generator, or a fuel cell. The hybrid battery system includes a first high capacity battery (70) having a high electrical energy storage capacity and a high electrical current pass-through capacity; and a second electrical energy storage device (72) having a low energy storage capacity compared to the first high capacity battery, a high electrical current pass-through capacity, a steeply rising output voltage characteristic during charge conditions and a steeply falling output voltage characteristic during discharge conditions.

Description

HYBRID ENERGY SYSTEM FOR TRACTION VEHICLES

FIELD OF THE INVENTION:

[0001] This invention relates to hybrid energy systems for traction vehicles, and particularly to hybrid energy systems that are used in various kinds of traction vehicles such as large and small automobiles, delivery vehicles, bicycles, motorcycles, scooters, and the like. In particular, the present invention provides an energy transfer and storage system which employs a hybrid battery system as an energy buffering system placed between a primary energy source and an at least one traction wheel.

BACKGROUND OF THE INVENTION:

[0002] Electrically driven vehicles of all sorts are well known. Many such vehicles are such as small delivery vehicles, electric golf carts, and more recently there has been the introduction of so-called hybrid vehicles. The hybrid vehicles which are now entering commercial service generally comprise a relatively small internal combustion engine, and a relatively large bank of batteries. Those batteries may be lead acid batteries, nickel-zinc batteries, and other proprietary batteries and battery combinations. Typically, hybrid vehicles require the internal combustion engine to deliver driving energy to the traction wheels of the vehicle, until such time as the vehicle is in a constant speed driving condition, or at least until such time as it is assured that the batteries are fully charged so that reliance upon the internal combustion engine may be foregone. Then, motive power is delivered to the traction wheels from the battery, through electric motors which are associated with each traction wheel. [0003] Indeed, there are a rising number of energy systems which are entering commercial service, the most notable of which is a mixed thermal/electric combination such as that described above. Such systems are typically referred to as "parallel" systems, where an internal engine provides motive power and recharging energy for the on-board batteries. There are also a number of "series" systems, such as a thermal (fuel combustion) power source which provides only charging energy for the on-board batteries. A vehicle which is powered by the fuel cells is an obvious example where all the traction power is electrical.

[0004] However, it is to be noted that in the case of direct fuel cell power being delivered to an electric motor, for delivery of driving power to a traction wheel or wheels, significant constraints are imposed upon the fuel cell performance. Specifically, the peak power requirements that may be necessary to be designed for will compromise the efficiency of the fuel cell, and increase its size. Concomitantly, the weight and cost of such a system also increase. Moreover, without at least some minimal electric storage buffering between the fuel cell and the traction wheels of the vehicle, regenerative braking is not available; meaning that whenever the vehicle is in a braking condition, heat is generated but is wasted.

[0005] The present inventors have unexpectedly discovered that the use of a

"mixed battery system" — such as a hybrid system comprised of a lead acid battery and a nickel-zinc batteiy - may be placed as a buffer between an electrical power source such as a small, constant speed ultra-low emission internal combustion engine, or a fuel cell, and the traction wheel or wheels. Such an electric propulsion system permits optimization of power source efficiency for fixed load operation. Moreover, by providing electrical energy storage capacity in such a system, the power source capacity can be reduced because it needs only to meet average load requirements. Also, of course, the provision of a mixed battery system permits for regenerative braking and thus for energy recovery during a braking operation of the vehicle. [0006] As will be noted hereafter, if a lead acid batteiy is employed, it may itself be of mixed design, so that a high power requirement for a significant period of time, say, twenty seconds under hard acceleration may be satisfied; or alternatively, a moderate power requirement for several minutes, such as during a hill climb condition for the vehicle, may also be satisfied. On the other hand, the other portion the mixed battery system may be such as to provide for maximum peak power with relatively low energy capacity, and may be such that it functions not unlike a "supercapacitor".

SUMMARY OF THE INVENTION:

[0007] Accordingly, the present invention provides an energy transfer and storage system for traction vehicles, where the traction vehicle is one which has at least one electric motor/generator which delivers driving energy to at least one traction wheel, so as to provide motive power for the vehicle.

[0008] The system in keeping with the present invention comprises a primary energy source, and a drive/brake control system associated with at least one traction wheel.

[0009] Moreover, a particular feature of the present invention is that it further comprises a hybrid battery system.

[0010] The at least one motor/generator generates electrical power during a braking operation of the traction wheel, and delivers its generated electrical power to the hybrid battery system.

[0011] The primary energy source is chosen from the group consisting of internal combustion engines together with an electric generator, and fuel cells.

[0012] The hybrid battery system includes a first high capacity battery having a high electrical energy storage capacity. The high capacity battery is such as to have a high electrical current pass-through capacity. The hybrid battery system also includes a second electrical energy storage device having a low energy storage capacity compared to the first high capacity battery. The second electrical on energy storage device also has a high electrical current pass-through capacity, and a steeply rising output voltage characteristic during charge conditions, and a steeply falling output voltage characteristic during discharge conditions. [0013] In keeping with another provision of the present invention, the first high capacity battery may be chosen from the group consisting of lead acid batteries, nickel zinc batteries, and mixtures thereof.

[0014] Moreover, the second electrical energy storage device may be chosen from the group consisting of thin film nickel zinc batteries, thin-plate lead acid batteries, nickel metal hydride batteries, lithium ion batteries, thin film capacitors, thin film electrolytic capacitors, and mixtures thereof.

[0015] Still further, the present invention provides that the output from the primary energy source may be substantially constant, irregardless of the speed and driving or braking condition of the at least one traction wheel of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0016] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example. It is expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. Embodiments of this invention will now be described by way of example in association with the accompanying drawings in which: [0017] Figure 1 is a schematic representation of a typical prior art hybrid vehicle energy delivery system;

[0018] Figure 2 is a schematic representation of a typical prior art fuel cell operating vehicle energy delivery system;

[0019] Figure 3 is a schematic representation of the hybrid energy system for delivering traction power to a traction vehicle in keeping with the present invention; and [0020] Figure 4 is a schematic representation of a hybrid battery system in keeping with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0021] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.

[0022] Turning first Figure 1, a typical motive power system for a prior art hybrid power vehicle is shown. Here, a typical internal combustion engine 12 is shown, and it is typically a low or medium powered four or six cylinder engine of the sort found in low powered, low price vehicles. A control system is shown at 14, and typically that control system includes or comprises an accelerator for the engine 12. Because the engine 12 will deliver traction power directly to the wheels 16, a drive shaft 18 is shown.

[0023] However, also associated with the engine 12 is an alternator 20, whose purpose is to deliver electrical energy to a battery 22, as shown at 24. The traction system for the vehicle is indicated generally at 26, and as well as the wheels 16, it includes a further control 28, a transfer system 30, and at least one electrical motor/generator 32. [0024] It is seen at 34 that electrical energy is delivered from the battery 22 to the traction system 26; and also during a braking condition of the vehicle, recharging energy is delivered from the traction system 26 to the battery 22. [0025] However, the prior art system of Figure 1, while less wasteful of energy than an ordinary vehicle, is still more wasteful than it needs to be, and still requires gasoline or propane as the primary source of energy ~ the fuel for the engine 12. Moreover, while the size of the battery 22 may be very large and heavy, nonetheless the range of such a vehicle is fairly limited. [0026] In a prior art vehicle such as that shown in Figure 2, where similar reference numerals are employed for similar features, the flow of energy is effectively in one direction only, from the fuel cell 40 to the traction system 42, as indicated at 44. As suggested above, there may be some small battery inserted between the fuel cell 40 and the traction system 42, but typically such an item is inconsequential. A control system is shown at 46, and its purpose is primarily to control the flow of fuel to the fuel cell and consequently the delivery of current to the electric motor or motors 32. Of course, driving controls for the vehicle, so as to provide braking, etc., will exist, but they are not necessary to be shown for purposes of the present discussion. [0027] The series operating system of Figure 2 carries with it the disadvantages that the size of the fuel cell 40 must either be very large, or the operating characteristics of the vehicle will be somewhat compromised because of the possibility that only average load requirements can be satisfied. Thus, in acceleration or hill climbing conditions, performance of the vehicle may be less than satisfactory.

[0028] Referring now to Figure 3, a system in keeping with the present invention is shown. Here, the traction system for the vehicle, shown generally at 50, comprises at least one electrical motor/generator 32, and a control module 52. The vehicle may, indeed, only have one traction wheel, such as a bicycle, motorcycle, or scooter. [0029] In any event, the control module 52 will be such as to control the electrical operation of the electrical motor or motors 32, as well as the physical braking requirements that may be placed on the wheels 16 from time to time. [0030] A primary energy source 60 may be an internal combustion engine, or it may be a fuel cell. If it is an internal combustion engine, it may be such as to be a low emission engine, because as seen hereafter it will be one that operates substantially at constant speed. A hybrid battery system 62 is interposed between the primary energy source 60 and the traction system 50. It will be seen at 64 that energy is delivered from the primary energy source 60 to and through the hybrid battery system 62, to the traction system 50.

[0031] Referring briefly to Figure 4, a hybrid battery system 62 is shown in more detail, and comprises a first high capacity battery 70 and a second electrical energy storage device 72 which has a low energy storage capacity compared to that of the first high capacity battery 60.

[0032] As seen at 66 in Figure 3, energy is delivered from the hybrid battery system 62 to the traction system 50; and in braking conditions, energy is delivered back from the traction system 50 and the electrical motor/generators 32 therein, to the hybrid battery system 62. It will also be understood that under normal driving conditions, the capacities of the electrical storage devices 70 and 72 in the hybrid battery system 62 may be such that they will be fully charged, so that energy delivered from the primary energy source 60 is delivered in a pass-through condition to the traction system 50. However, in coasting or braking conditions, acceleration, or hill climbing conditions, the capacities of the hybrid battery system 62 may be called into play in different manners.

[0033] For example, if the vehicle is required to accelerate, or is in a hill climbing condition, then it may draw power from the battery 70. Indeed, in rapid acceleration conditions, power may be drawn from the second device 72. [0034] It will be understood that the characteristics of the first high capacity battery 70 are such that it has a high electrical energy storage capacity. Moreover, the high capacity battery 70 will have a high electrical current pass-through capacity. As energy is withdrawn from the high capacity battery 70, its output voltage will gradually decrease. However, the output voltage of the other device 72 — which has a characteristic such that its output voltage will remain relatively constant and then drop off sharply ~ may assist in maintaining a relatively constant output voltage of the high capacity battery 70. [0035] Of course, during braking conditions, regenerative electric power will be delivered from the motor/generators 32 to the high capacity battery 70.

[0036] As noted, the characteristics of the second electrical energy storage device 72 are such that it has a low energy storage capacity compared to the high capacity battery

70, but it will also have a high electrical current pass-through capacity so as to deliver motive electric power to the traction system 50. However, as noted above, the second electrical energy storage device 72 is such that it has a steeply rising output voltage characteristic during charge conditions, and a steeply falling output voltage characteristic during discharge conditions.

[0037] Typically, the first high capacity battery 70 may be a nickel zinc battery, a nickel metal hybrid battery, or in some conditions it may be a mixture of both kinds of batteries. It might also be a lead acid batteiy.

[0038] Also, the second electrical energy storage device 72 may be such as a thin plate lead acid battery, a thin film nickel zinc battery, a lithium ion battery, a thin film capacitor, a thin film electrolytic capacitor, or mixtures thereof.

[0039] Because of the presence of the hybrid battery system 62, the energy output from the primary energy source 60 may be substantially constant, irregardless of the speed of the vehicle, and whether or not the traction wheel or wheels 16 are in a driving or braking operation.

[0040] Some basic discussion concerning hybrid batteries as they may be employed in the present invention, now follows.

[0041] Essentially, a hybrid battery will comprise the combination of two different types of batteries. The first type is, as noted above, a high energy, high capacity battery; the second type of battery, although it may be in some instances a supercapacitor, will generally be a high power battery. The main storage or high energy battery or device will typically have high energy density - meaning that it will have significant energy storage per unit volume or per unit weight; and the high power or peak power battery or other device is such that it will provide both energy density and power density in a manner which is superior to any single battery system.

[0042] Both functions can conceivably be provided by the same chemistry, for example lead acid, where the high power battery is one which is spiral round thin plate design, and the high energy battery is a more typical cored plate battery - which might also be bi-polar. A low cost compromise to provide a hybrid battery in keeping with the present invention may be a single battery construction which provides both functions, high energy and high power. However, such low cost compromise will not be optimized for performance results for either high power or high energy requirements. [0043] Moreover, other chemistries such as, in particular, nickel zinc batteries, can be modified to provide both high energy, high capacity batteries, and high power batteries, and maximum energy design batteries and maximum power density design batteries can be combined, as discussed above.

[0044] However, most hybrid battery designs of the sort particularly contemplated by the present invention will comprise mixed types of batteries or other electrochemical systems. For example, excellent energy storage systems with moderate energy rate or power delivery capabilities are nickel zinc batteries. Lithium ion systems have even larger energy capacity, but lower rate capabilities. Thus, a high peak power capacity may be required for a given demand profile, if such systems as nickel zinc or lithium ion were to be used on there own.

[0045] However, other systems such as lead acid have very high power capabilities ; and that capability may be even further enhanced by the cell design; for example, by designing a battery in a manner so as to function as a supercapacitor, for a specific application.

[0046] Typically, the charge/discharge voltage characteristics of the two parts of a hybrid system are not generally well matched. Thus, the specific design of any hybrid battery, as to the combination of energy and power storage, will be determined by the specific application, as will be well understood by those skilled in the art. This is especially true in bi-directional applications, such as those where regenerative braking will be employed.

[0047] Thus, a traction vehicle such as that which has been discussed above may employ a small gasoline engine associated with a thin plate lead acid, high power battery combined with a nickel zinc high capacity batteiy. They, in turn, are connected in series with a traction motor which will also operate as a generator in a regenerative braking condition. However, this may require that the battery system should have sufficient unfilled capacity so as to absorb full regenerative braking energy; while at the same time, it cannot be run at a low state of charge. Typically, the high energy portion of a hybrid system of the sort described herein will generally have only a moderate charge rate capability; and therefore, a substantial portion of the regenerative braking charge current may be required to be absorbed by the power portion of the hybrid batteiy. That portion must therefore be sufficiently large to absorb the regenerative braking energy; but it must be designed so as not to be required to spend long operating periods at excess capacity, which materially effects the operating life of such a high power battery.

[0048] Various battery systems have varying power densities, measured in either energy per unit volume or energy per unit weight. It is considered that the following is a list of varying power densities, in decreasing order with respect to the systems that are designated: lead acid; nickel cadmium; nickel zinc; nickel metal hydride; lithium sulphide; lithium ion; solid electrolyte lithium ion - referred to generally as lithium polymer batteries.

[0049] Energy density ratings of the various electrochemical systems referred to immediately above will essentially be in the reverse order, although nickel cadmium and nickel zinc systems may be exchanged in the order listed. [0050] Thus, a typical hybrid battery system in keeping with the present invention, and one which finds particular utility in traction vehicles in the manner described above, is a battery system which employs either nickel zinc or nickel metal hydride as the high energy, high capacity portion of the hybrid system, and lead acid as the high power, smaller capacity portion of the hybrid battery system.

[0051] There has been described an energy transference storage system for traction vehicles, which effectively is a compound series/parallel operating system in the sense of the definitions of those terms as they have been applied to the prior art. An internal combustion engine may or may not be employed; a fuel cell may or may not be employed; a parallel operating hybrid battery system is used; and the traction power delivered to the driving wheel or wheels for the vehicle is electrical power.

Claims

WHAT IS CLAIMED IS:

1. An energy transfer and storage system for traction vehicles, where the traction vehicle is one which has at least one electric motor/generator (32) which delivers driving energy to at least one traction wheel (16) so as to provide motive power for the vehicle, said system comprising: a primary energy source (60);and a drive/brake control system (52) associated with said at least one traction wheel; said energy transfer and storage system being c h a r a c t e r i z e d by a hybrid battery system (62); wherein said at least one electric motor/generator generates electrical power during a braking operation of said traction wheel and delivers its generated electrical power to said hybrid battery system; wherein said primary energy source is chosen from the group consisting of internal combustion engines together with an electrical generator, and fuel cells; and wherein said hybrid battery system includes a first high capacity batteiy (70) having a high electrical energy storage capacity and a high electrical current pass- through capacity; and a second electrical energy storage device (72) having a low energy storage capacity compared to said first high capacity battery, a high electrical current pass-through capacity, and a steeply rising output voltage characteristic during charge conditions and a steeply falling output voltage characteristic during discharge conditions.

2. The energy transfer and storage system of claim 1, wherein said first high capacity battery is chosen from the group consisting of nickel zinc batteries, nickel metal hybrid batteries, lead acid batteries, and mixtures thereof; and wherein said second electrical energy storage device is chosen from the group consisting of thin plate lead acid batteries, thin film nickel zinc batteries, lithium ion batteries, thin film capacitors, electrolytic capacitors, and mixtures thereof.

3. The energy transfer and storage system of claim 1 , wherein the output from said primary energy source is substantially constant, irregardless of the speed and driving or braking condition of said at least one traction wheel.