MXPA98009714A - Electric vehicle with battery regeneration dependant on battery charge state - Google Patents

Abstract

An electric vehicle is controlled to conform its operation to that of a conventional internal-combustion-engine powered vehicle. In some embodiments, the charging of the batteries by the auxiliary source of electricity and from dynamic braking is ramped in magnitude when the batteries lie in a state of charge between partial charge and full charge, with the magnitude of the charging being related to the relative state of charge of the battery. The deficiency between traction motor demand and the energy available from the auxiliary electrical source is provided from the atteries in an amount which depends upon the state of the batteries, so that the full amount of the deficiency is provided when the batteries are near full charge, and little or no energy is provided by the batteries when they are near a discharged condition. At charge states of the batteries between near-full-charge and near-full-discharge, the batteries supply an amount of energy which depends monotonically upon the charge state. Charging of the batteries from the auxiliary source is reduced during dynamic braking when the batteries are near full charge. Control of the amount of energy returned during dynamic braking may be performed by control of the transducing efficiency of the traction motor operated as a generator.

Description

ELECTRIC VEHICLE WITH BATTERY REGENERATION DEPENDENT OF BATTERY CHARGE STATUS This invention relates to an apparatus and method for making the operation and operating characteristics of hybrid electric vehicles simple and effective. Hybrid electric vehicles are widely seen among the most practical of low pollution vehicles. A hybrid electric vehicle includes an electric "pull" battery that provides electrical power for an electric traction motor, which in turn drives the wheels of the vehicle. The "hybrid" aspect of a hybrid electric vehicle is the use of a secondary or complementary source of electric power to recharge the traction battery during vehicle operation. This secondary source of electrical energy can be solar panels, a fuel cell, a generator driven by an internal combustion engine, or in general any other source of electrical energy. When an internal combustion engine is used as the secondary source of electric power, it is commonly a relatively small engine that uses little fuel, and produces little pollution.A concomitant advantage is that this small internal combustion engine that can be operated within a limited scale of revolutions per minute, so that engine pollution controls can be optimized.The terms "primary" "secondary", when used to describe electrical power sources, refer merely to the manner in which s distributed energy during operation, and are not of fundamental importance to the invention.A simple electrically driven vehicle powered only by electric batteries, has the disadvantages that the batteries may become exhausted while the vehicle is away from a station. battery charge, and even when this vehicle returns successfully to your warehouse or after a day's use, the batteries should be recharged then. The hybrid electric vehicle has the significant advantage over a simple electrically energized vehicle, that the hybrid electric vehicle recharges its own batteries during operation, and thus, must not ordinarily require an external battery charge. Accordingly, the hybrid electric vehicle can be used in a manner very similar to an ordinary vehicle powered by internal combustion engines, which require only fuel filling. Another important advantage of the hybrid electric vehicle is its good fuel mileage. The advantage in the kilometraj for fuel is presented by the use of dynamic regenerative braking, which converts the kinetic energy of the movement into electrical energy during at least a portion of braking, and returns the energy to the battery. It has been discovered that braking losses account for almost half of all frictional losses experienced by a vehicle in an urban transit establishment. The recovery of this 50 percent energy, and its return to batteries for later use, allows the use of an electric generator operated by "secondary" fuel much smaller than would be the case if regenerative braking was not used. . In turn, the smaller secondary power source results in less fuel used per unit of time, or per kilometer. Yet, another advantage of a hybrid electric vehicle is that, under many conditions, the energy that is available to accelerate the vehicle is the sum of the maximum energy that can be supplied by the batteries, plus the maximum power that can be generated by the vehicle. secondary electric generator. When the electric generator is a diesel-fueled internal combustion engine, the combination of battery power and diesel energy can result in a total driving force that is very substantial, regardless of good fuel mileage. Although hybrid electric vehicles are economically and environmentally friendly, they should be a bit "foolproof", in that they should be similar to conventional vehicles powered by internal combustion, in their operation and in their responses to operator input. , in order to achieve widespread acceptance.

A method of operating a vehicle that derives at least some of its tractive effort or driving power from one or more electric batteries ("batteries"), includes the step of substantially returning all power from a traction motor to the batteries during dynamic braking, during those times when the batteries are in a first charge condition that is less than the full charge. Other steps of the method include returning less than all the energy from the traction motor to the batteries during dynamic braking, when the batteries are at a load level between the first load condition and the full load condition, and not returning substantially No energy from the traction motor to the batteries during braking, when the batteries reach full charge condition. In this mode, the step of returning less than all the energy from the traction motor to the batteries includes the step of returning a quantity of the available dynamic braking energy to the batteries, which is monotonically related to the proportion of the Battery charge in the present time in relation to the full charge condition. In a preferred embodiment of the invention, the steps described above make a smooth transition from one to the other, depending on the state of charge of the batteries. Since the amount of dynamic braking changes gradually as a function of the battery charge, the friction brakes recover any deficiency in the braking, in an automatic way, as a result of the strength of the brake pedal of the operator. Figure 1 is a simplified block diagram of an electric vehicle in accordance with an aspect of the invention, which includes a command controller that performs control according to the invention, and which also includes an energy controller. Figure 2 is a simplified block diagram illustrating some of the functions performed inside the power controller of Figure 1. Figures 3a and 3b are simplified graphs of the regeneration of energy towards the traction battery against the state of charge of the traction battery, and the traction due to the regeneration against the state of charge of the traction battery, respectively. Figure 4 is a simplified flow chart illustrating the logical flow in the command controller of Figures 1 and 2, to provide the operations "illustrated in Figures 3a and 3b." Figure 5 illustrates a simplified graph of the distribution of the traction power supply to the vehicle traction motor of Figure 1, as a function of the traction battery load Figure 6 is a simplified flow chart illustrating a logical flow in the command controller of the Figures 1 and 2, to provide the operations illustrated in Figure 5. Figure 7a is a graph of the motor or generator energy against velocity with the torque as a parameter, and Figure 7b is a representation of the manner in which that the motor / generator energy is controlled Figure 8 is a simplified block diagram that illustrates certain control circuits or configurations to control the amount of electrical energy a generated by the auxiliary power source in response to the state of charge of the traction battery.

In Figure 1, an electric vehicle 10 includes at least one driving wheel 12 connected to an electric voltage-traction motor -alternate 40, which in one embodiment of the invention, is a three-phase alternating current motor. The motor 40 is preferably a motor-generator, as it is known, in such a way that the kinetic energy of the movement can be transduced into electrical energy during dynamic braking. An energy controller 14 is connected by power management lines to the traction motor 40, with a traction battery illustrated in FIG., and with an auxiliary power source illustrated as a block 16. As illustrated in block 16, the auxiliary source may include an internal combustion engine, such as a diesel engine 18, which drives an electric generator 22, or may include a fuel cell 24. A command controller illustrated as a block 50 is connected by way of information lines to the power controller 14, the auxiliary source 16, and the traction motor 40, to control the operation of the controller. energy 14, the auxiliary source 16, and the traction motor 40, in accordance with the appropriate control laws. One of the most common and least expensive battery types, which is capable of storing relatively high energy, includes the common lead / H2S04 battery. This type of battery is suitable for use in an electric vehicle, that some care is taken to prevent the application of a charge current to it when the battery is in full charge, to prevent the gasification of the electrolyte and the generation of unwanted heat , and if you can avoid sulfation. In Figure 1, the visual displays and controls of the vehicle operator 10 are illustrated as a block 30. The block 30 is illustrated connected by a bidirectional data line 31 to the command control block 50, to apply impulse commands to the controller 50, whose command controller 50 can then convert into the appropriate commands for the different energy elements, such as the power controller 14, the auxiliary source 16, and the traction motor 40. The block 30 is also illustrated connected by a line 32 to the friction brakes 36a and 36b, for the direct control of the friction brakes by means of a conventional hydraulic braking system connected to a brake pedal. Figure 2 represents the interconnection of some of the elements of the power controller 14 of Figure 1, with other elements of Figure 1. More particularly, the power controller 14 includes a configuration of rectifier 26 connected to the source auxiliary 16, for (if necessary) converting the alternating current output of the auxiliary source 16 to direct voltage. The power controller 14 also includes a bidirectional propulsion control system, which further includes an alternating current direct current inverter 28 coupled by power connections to the battery 20, the configuration of the rectifier 26, and the traction motor 40. The operations of the inverter 28, the auxiliary source 16, and the traction motor 40 are controlled, as mentioned above, by the command controller 50. It should be noted that, in addition to the direct current to alternating current inverter 28, The propulsion control system includes voltage and current sensors to detect the different operating parameters of the motor / generator, the battery, and the auxiliary power source.

In the basic operation of the configuration of Figures 1 and 2, the control controller (50) controls the individual switches (not shown) of the inverter 28 with commands modulated by pulse amplitude, which results in generation, at the port 28m of the inverter 28 which is coupled with the traction motor 40, of an approximation of an alternating voltage having a selected frequency and magnitude. In a preferred embodiment of the invention, the inverter is a type of field-oriented command (FOC), and the traction motor is similarly a field-oriented command induction motor. The frequency and magnitude of the alternating current pulse commanded to the traction motor 40 are selected to drive the motor with a selected traction current at a selected speed of the motor. In general, the traction motor 40 produces a rearward EMF, which increases with increasing motor speed, and the inverter must produce (under the control of the command controller 50) an alternating voltage that increases in magnitude as the voltage increases. frequency of the alternating voltage, in order to maintain the same impulse current of the traction motor. The motor rotates at a consistent frequency - "with the ordered frequency of the inverter output. Also, in the basic operation of an electric vehicle, such as that of Figures 1 and 2, both dynamic braking and frictional braking can be performed. Dynamic braking is much more preferred, since the (kinetic) energy inherent in the movement of the vehicle is recaptured by operating the traction motor as an electric generator, as the vehicle slows down. During the intervals in which dynamic braking is presented, the alternating current direct current inverter 28 of Figure 2, operating in a second regeneration direction, converts the alternating voltage produced by the traction motor 40, into a direct voltage. charging the traction battery 20. Further, when the electric vehicle is a hybrid electric vehicle, including the auxiliary power source 16, the auxiliary source can be operated during vehicle operation to refill the batteries, and / or provide something of the traction energy, depending on the commands of the command controller 50. It has been observed that, when operating an electric vehicle in a normal mode used dynamic braking, and the batteries are fully charged, dynamic braking tends to push a charging current through the battery already charged. The characteristics of a lead-acid battery are such that, in this situation of applying a charging current to a fully charged battery, the battery voltage tends to rise markedly, as from a fully-charged, no-current value of 13 volts. , in a nominal 12 volt battery, to somewhere near 16 volts, thereby providing an indication to the controller that an overload condition is occurring. If the command controller decouples the energy generated by the dynamic braking from the battery, as it must do in order to protect the battery, the battery voltage immediately drops to its value without fully charged current. In turn, this allows the dynamic braking controller to begin once again to provide power to the battery, until the overvoltage control takes effect. This results in a periodic application of the dynamic braking at an impulse velocity established by the characteristics of the command controller cycle, and produces a perceived braking noise, as well as tends to overload the battery during portions of the pulse interval. Both overload and noise are undesirable. Figures 3a and 3b illustrate together a law of compliance control with an aspect of the invention, which allows the complete regeneration or return to the traction batteries of the energy derived from the dynamic braking, during those intervals in which the traction batteries are in a state of charge less than a particular amount of charge, whose particular amount of charge is less than the full charge, and that, in charge levels of the traction battery that between the particular load and the full charge, the proportion of the regenerated energy derived from the dynamic braking is narrowed in a way that responds to, or is a function of, the then existing state of charge in relation to the difference in charge between the previously determined load and the full load. In one embodiment of the invention, the relationship is monotonic, and the relationship can be linear. In Figure 3a, the graph 310 represents the amount of regeneration as a function of the state of charge of the traction battery according to a control law in accordance with an aspect of the invention. More particularly, the graph 310 defines a portion 312 that is constant at a dynamic braking regeneration value that represents a 100 percent regeneration, or as close to 100 percent as conveniently possible. At full load, the regeneration amount of the energy derived from the dynamic braking is reduced to almost zero, or as close to zero as conveniently possible. The control law represented by the graph by the graph 310 also includes a second portion 314, which ramps monotonically from a 100% regeneration at a predetermined charge level of the traction battery, termed as "first charge" , until zero regeneration in full load of the traction battery. The effect on the regenerative traction or braking of the vehicle as a function of the charging condition of the traction battery is illustrated by a graph 320 in Figure 3b. In Figure 3b, the graph 320 includes a first portion 322, which extends to a constant value representing the maximum regenerative traction from low load levels to the "first" charge level of the traction battery. A second portion 324 of the graph 320 represents the regenerative traction that makes a ramp monotonically from 100 percent to the "first" level of loading, and from 0 percent at full load. Although portions 314 and 324 of graphs 310 and 320, respectively, are illustrated as linear ramps, it is sufficient, for control purposes, that portions 314 and 324 be monotonic. This monotonic reduction in dynamic braking should not be noticeable to the driver of the car, since the state of charge of the traction battery changes slowly, and consequently, the amount of regenerative braking changes slowly. Since regenerative braking changes slowly, the friction brakes gradually recover any deficit between dynamic braking and the desired braking force. In turn, this should reduce the noise that is evident when the control law simply protects the traction battery from overcharging, simply stopping regeneration when the batteries are fully charged. Figure 4 is a simplified flow chart illustrating portion 400 of the control laws, which controls the control processor 50 of Figure 1, which results in the type of operation represented by Figures 3a and 3b. In Figure 4, the logic begins in a block of START 410, and proceeds to a block 412, which represents the supervision of the traction battery pack parameters (20 of Figure 1), such as temperature, voltage , and the current, and also observe the time. Samples of these parameters can be taken at frequent sampling intervals, such as at each iteration of the logic through the cycle of Figure 4. From logic block 412, the logic flows to a block 414, which represents an estimate of the state of charge of the traction battery, by determining the amount of charge that has entered the battery, and the subtraction of the amount of charge left in the battery. The measurement of this load is the amperage / hour. Once an estimate is made of the state of charge of the traction battery, the logic flows to a decision block 416, which compares the current or estimated state in the current charge time of the traction battery, with the previously determined load value represented by the "first load level" of Figures 3a and 3b; As mentioned above, this level of charge is less than the full charge. If the decision block 416 finds that the estimated charge level of the traction battery is less than the first load level, the logic leaves the decision block 416 by the output of SI, and proceeds to an additional block 418, which represents that regenerative braking power or power is allowed to be used. The action taken in block 418 may be, for example, adjusting the field current in the traction motor (operating in its generator mode) during braking, to maximize the electrical output of the traction motor. It should be noted that some types of motors / generators do not have a different field coil, but rather have pluralities of coils, wherein one coil has its desired current induced by the controlled current in another coil; for the purposes of the invention, the way in which the field current is generated is i? -relevant, and it is sufficient that it be generated in the desired amount. From block 418, the logic flows back to block 412 to start another iteration around the cycle. As the hybrid electric vehicle is driven in this state, the traction battery will often become more fully charged, due to the continuous injection of energy (by the action of the auxiliary internal combustion engine / generator) into the system. energy storage, which includes the traction battery and the movement of the vehicle. Eventually, the state of charge of the traction battery will exceed the "first charge level" illustrated in Figures 3a and 3b. At that time, the iterations of the logic of the controller 50 of Figure 1 will change around the portion of its previously programmed logic, represented by the logic cycle 400 of Figure 4, since the flow of the logic will no longer be directed from the output of SI from decision block 416, but instead, it will be directed towards the NO output. From the NO output of the decision block 416, the logic flows to an additional block 420, which represents the reduction of the magnitude of the regenerative power or energy available in the form of the vehicle's kinetic energy, in relation or in inverse proportion to the amount of charge of the present time in relation to the difference between the full charge and the first charge level of Figures 3a and 3b. Accordingly, if the current charge state is at 60 percent of the way between the first charge and the full charge, as illustrated by Cc in Figures 3a and 3b, the amount of movement energy that is allowed to recover and Attach to the battery is 30 percent. When the current charge level reaches 100 percent, the allowable regeneration is 0 percent. As mentioned above, control of the coupling of power or power from the traction motor acting as a generator can be accomplished simply by adjusting the torque of command of the pulse in a field-controlled controlled AC motor. In a real embodiment of the invention, the torque is reduced proportionally to the speed, in order to control the amount of energy produced by the engine acting as a generator, which is returned to the traction battery.

As described so far, the logic of Figure 4 controls the regeneration according to the state of charge of the traction battery. This means that the retarding force acting on the vehicle by means of the traction motor acting as a generator is reduced during braking. One of the advantages of an electric vehicle that uses regenerative braking, is that the brakes by friction are not required to do all the braking, and in this way, its design and construction can be such as to take advantage of less use, such as , making them a lighter construction. As described so far, in conjunction with the logic of Figure 4, dynamic braking is reduced under certain load conditions of the traction battery. In order to provide additional braking during the times when regenerative braking is reduced, in accordance with another aspect of the invention, logic flows from block 420 of Figure 4 to an additional block 422, which represents the reduction of the efficiency of the traction motor that acts as a generator. This reduction in the efficiency of the traction motor acting as a generator can be realized by adjusting the slip or the current in the field coil, or preferably both. From block 422 of Figure 4, the logic returns to block 412, to start another iteration "around the cycle", or through logic 400.

As described so far, noise or irregular operation resulted from the protection of the fully charged battery, from the additional charge. There is a similar effect on acceleration with a battery almost discharged. During the acceleration of the vehicle 10 of Figure 1, both the traction battery 20 and the auxiliary or secondary power source 16 (of the internal combustion engine / generator) are available as sources of electrical energy for the traction motor 40. Accordingly , the traction motor 40 can provide power at a speed which is the sum of the maximum energy that can be drawn from the traction battery 20, together with the maximum energy that the auxiliary source 16 can provide. This is convenient for operating on a city, where acceleration bursts may require significant power. However, under some conditions, the traction battery protection controls, if they simply stop drawing power from the traction battery when the battery reaches a state of charge that is considered a discharged state, will also cause a form of noise. This form of noise is presented < if the vehicle is working uphill for a long period of time, such as at the crossing of the Continental Divide. If the speed of energy utilization when lifting the vehicle along the road exceeds the speed of delivery of energy by the auxiliary source 16, the batteries will discharge continuously, and eventually reach the level of charge considered as the level " Discharged" . If at that time the traction battery controller were simply to cut the traction battery from the traction motor circuit, the amount of current available to the traction motor would suddenly decrease to the level provided by the auxiliary source 16, with a Sudden abrupt change in traction power, and the vehicle would experience a sudden reduction in speed. The removal of the traction battery discharge to the traction motor, however, allows the battery voltage to rise abruptly to its no-load voltage. If the controller interprets this elevation in voltage as an indication that the traction battery has useless charge, it can reconnect the traction battery to the traction motor, thus providing once again additional traction power from the traction battery, but causing the voltage of the traction battery to drop. Those skilled in the art will recognize this as an oscillatory condition, which can cause the vehicle to "cough" or jerk repeatedly during the climb. At this point, it should be noted that a "fully" discharged battery, in the context of a traction battery where a long life is desired, still contains a substantial charge, because the life of these batteries is dramatically reduced if the Depth of discharge is too large; accordingly, a battery discharged for the purposes of the discussion of electrically driven vehicles, is one in which the batteries are in a state of charge which is considered to be the condition completely discharged, but which still contains a substantial charge. In a hybrid electric vehicle, the auxiliary power source provides power continuously, which can be used to charge the traction batteries if the demand for traction is less than the output of the auxiliary power source. The control laws allow both the auxiliary power source and the traction batteries to provide power to the traction motor. When the demand of the traction motor exceeds the output of the auxiliary source, the current is drawn from the traction battery, which lowers its voltage. If the traction battery is near a full discharge condition, the voltage drop due to this current draw may be such as to trip the battery protection, stopping the current drain from the battery. The removal of the current drain by the control laws, in turn, causes the vehicle to be energized exclusively by the auxiliary source, and allows the voltage of the traction battery to rise. When the traction battery is raised, the control laws no longer recognize the battery as discharged, and again the drainage of current from the traction battery is allowed.

The process of repeatedly coupling and uncoupling the traction battery towards the traction motor constitutes an oscillation of the control system. This oscillation results in a pulling force that varies at the oscillation speed of the control system, and which may be perceptible to the operator of the vehicle. In accordance with another aspect of the invention, the controller 50 controls the amount of energy that can be drawn from the traction battery in response to the state of charge of the traction battery. This avoids the "cough" situation described above, and allows for a smooth decrease in the speed with which the vehicle can climb a mountain, as the battery charge decreases. Figure 5 illustrates a graph 500 representing the result of the control in accordance with this aspect of the invention. In Figure 5, the traction energy available to the vehicle is plotted against the state or level of charge of the traction battery. The graph 50 includes a portion 510, which represents the continuous output of the auxiliary power source or electrical power, which is a relatively low level. The portion 510 of the graph extends from a level less than the nominal discharge condition, up to a load level designated as "low load point", which is the nominal discharged condition of the traction battery. In an operating region represented by portion 512 of the graph, the available traction energy for the vehicle is at a relatively high level, which represents the sum of the battery and auxiliary energy. This maximum energy level represented by the portion 512 of the graph extends from a load condition referred to as "first load" to the fully loaded condition. In the "low load" condition of the traction battery, and the "first load" condition, the amount of traction energy depends on the state of charge of the traction battery, as suggested by the portion 514 of the graph . The effect of this type of control is to allow operation in full traction power for a period of time, until the traction battery is partially discharged to the "first" level. When the traction battery drops just below the first level, the amount of battery power that is available to the traction motor decreases slightly, in an amount that is not expected to be noticeable. This slight decrease in energy at the point just below the first load level in Figure 5, reduces a little the discharge speed of the traction battery. If the rise is long, the traction battery can be additionally discharged. When the traction battery becomes additionally discharged in the region between the "low" and "first" charge condition of Figure 5, there is relatively less of the battery power available for the traction motor, resulting in slow down the vehicle. For longer rises, the traction battery will eventually reach the "low" load condition, which is considered to be nominally discharged. When this level is reached, no more power is drawn from the traction battery, and in general, the charge state of the traction battery can not extend below the "low" charge level, in the 510 portion of the graph, Unless there is some other drainage on the traction battery, such as an emergency cancellation of the battery protection under conditions of imminent danger to the vehicle or its occupants. With the control as shown in Figure 5, there is no abrupt transition in tensile energy at any point along the control curve. When the battery charge is just above the "low" charging point, and is transitioning to full operation from the auxiliary power source, the amount of traction power provided by the traction battery is already very small, and the transition must be imperceptible to the driver of the vehicle. Figure 6 is a simplified flow chart illustrating portion 600 of the logic of the controller 50 of Figure 1, which provides control according to the graph 500 of Figure 5. In Figure 6, the logic begins at the block 610, and proceeds to a block 612, which represents the reading of the characteristics of the battery, in a manner very similar to block 412 of Figure 4. From block 512 of Figure 5, the logic flows to a block 614, which represents the estimate of the state of charge, also generally described in Figure 4. Decision block 616 of Figure 6 determines whether the current state of charge is above the "first" load point of Figure 5. , and directs the logic by means of the SI output of the decision block 616, if the state of charge is greater than the point of "first" load. From the SI output of the decision block 616, the logic flows to a block 618, which represents that the full traction energy for the traction motor is made available. This is done by removing the energy limits, as described in conjunction with Figures 7a and 7b, in the software that controls the inverter, noting that the auxiliary source is only one source, while the battery and the motor / generator can be sources or subsidence, depending on the operation of the investor. From block 618, the logic flows back to block 612, to start another iteration through the logic of Figure 6. In general, when starting with a traction battery almost fully charged, the logic will iterate around the cycle which includes blocks 612, 614, 616, and 618 of Figure 6, for as long as the load of the traction battery exceeds the load represented by the "first" load level in Figure 5.

In a long climb, the charge of the traction battery may eventually drop to equal or less than the "first" load point of Figure 5, and in the next iteration, through the logic of Figure 6, the logic 6 will exit the decision block 616 through the NO output, and will proceed to a block 620. The block 620 represents the reduction in the amount of energy available to the traction motor from the traction battery, by an amount that depends of the magnitude of the load of the current traction battery in relation to the difference in charge between the "first" load and "low" load states of Figure 5. For example, if the load level of the present time of the traction battery falls under the condition of "first" load of Figure 5, up to a level represented in Figure 5 as "current load", which is 9/10 of the way between the load levels represented by the "low" and "first" load levels charging, the controller 50 controls the amount of energy available to the traction motor from the traction battery to be 90 percent of the component supplied by the battery of the full power represented by the portion 512 of the graph. Put another way, since the current state of charge indicated in Figure 5 as "current load" is 90 percent of the component of the total traction energy designated as attributable to the battery, the battery power provided to the motor of traction is reduced to 90 percent of the battery's energy. Naturally, there is no requirement that portion 514 of the graph of Figure 5 be a linear ramp, as illustrated, but the control system is simplified if portion 514 of the graph is at least monotonic. From block 620 of Figure 6, the logic flows to a decision block 622, which compares the energy demand of the traction motor with the energy from the auxiliary power source. If the demand for traction energy exceeds the power from the auxiliary source of electricity, the batteries are being discharged, and the logic leaves the decision block 622 by the output of SI. From the SI output of the decision block 622, the logic flows to a block 624, which represents the increase of the available energy from the auxiliary source to its maximum value. From block 624, the logic flows to a decision block 626. Decision block 626 compares the current charge state of the traction battery, with the "low" charge point of Figure 5. If the state of charge is below the "low" load point, indicating that the traction battery should not be additionally discharged in order to prevent damage to the traction battery, the logic exits the decision block 626 through the SI output, and proceeds to a block 628. Block 628 represents the limitation of the power of the traction motor, by means of the FOC control, to the known amount of energy available from the auxiliary power source, easily determined as the product of the voltage multiplied by the current. From block 628, the logic flows by means of a logical line 630 back to block 612 by means of a logical line 630, to start another iteration through the logic of Figure 6. Yes, when decision block 626 examines the state of charge of the traction battery, the current state of charge is greater than the "low" load point of Figure 5, the logic exits the decision block 626 by the NO output, and proceeds on the line logic 630 back to block 612, without passing through block 628. Accordingly, when there is a significant waste load on the traction battery, the logic of Figure 6 allows its use. If, during the transit of the logic through Figure 6, the decision block 622 finds that the traction energy is not greater than the energy produced by the auxiliary source 16, the logic leaves the decision block 622 through the output of NO, and proceed by means of logical line 630 to block 612, to start another iteration; this line derives the increase of the energy of the auxiliary source 16 up to the maximum. Figure 7a illustrates a simplified parametric graph 710a, 710b, 710c, ..., 710N, of the motor (or generator) energy versus speed. In Figure 7a, graphs 710, 710b, 710c, ..., 710N have an inclined portion 712 in common. The energy for a motor or generator is the product of the torque multiplied by the speed. Consequently, at zero speed, the energy is zero, regardless of the torque. As the speed is increased to a constant torque, the energy is increased, as suggested by the portion 712 of the graphs of Figure 7a, to a base velocity. Above the base frequencies, the motor / generator design is such that no more energy can be handled, for thermal or other reasons. Consequently, in the maximum torque, the motor / generator energy is limited by the laws of control of the inverter to be in the graph 710a. If the torque is a little less than the maximum torque, the maximum energy is reached at a slightly lower speed of the motor than the base, represented by the graph 710b. The graph 710c represents an even lower magnitude of the torque, and the lower graph, 710N, represents the lowest torque that the quantized control system can hold. The control system will limit the torque produced by the engine to a limiting value, depending on the speed, to prevent the engine from operating above the maximum energy limits desired. The limiting torque limit is determined by simply dividing the maximum energy between the current motor speed: torque limit = Pmax / speed and the resulting limit on the torque causes the power graph to be limited by a value not greater than the one represented in Figure 7a by the graph 710a and the portion 712 of the graph. If the energy is to be limited to a value less than Pma? / - the energy graph that follows the motor will correspond to one of the graphs 710b, 710c, ..., 710N of Figure 7a. Figure 7b is a simplified block diagram illustrating the relationship of the torque command and the energy limiter. In Figure 7b, the torque command is applied to a limiting block 714, which adjusts the magnitude of the torque command (Limited Torque Torque Command), which reaches the Field Oriented Control Inverter (FOC) 28, in a manner that limits the energy to fall below a curve 716. Curve 716 is a plot of the torque versus speed, determined by dividing the selected or set energy P by the engine speed. Accordingly, the field-oriented control inverter can control the motor power by controlling the ordered torque in view of the motor speed. The torque in question can be a traction or impulse torque, or it can be a retarding or braking torque. When control of the energy flowing to the batteries from the motor is desired, acting as a generator, the appropriate FOC commands result in the application of the limit.

In Figure 8, the desired torque or torque command is derived from an electric accelerator (not shown), and is applied via a line 810 to a first input port of a multiplier 812, which receives the detected vehicle speed (or the speed of the traction motor if the vehicle is equipped with interchangeable gears) from the sensors (not shown), at its second input port 814. The multiplier 812 outputs the product from the motor speed and the ordered torque, to produce a signal representing the energy ordered to be applied to the traction motor. A block 816 scales the ordered energy by a constant k, if necessary, to convert the signal into a Pc representation of the traction motor energy in watts. The signal Pc representing the energy ordered in watts, is applied from block 816 to an additional block 818, which represents the division of the energy ordered in watts by the voltage of the traction battery, to obtain a signal representing the Rated traction motor current (IC = P / E). The voltage of the traction battery is an acceptable indicator of the voltage of the traction motor, because all the voltages of the system tend towards the voltage of the battery. The signal representing the ordered current Ic is carried by a signal line 819 to a portion of the command controller 50 of FIG. 1, to control the FOC inverter 28 and the traction motor 40 in a manner that produces the desired current. the motor. The signal representing the ordered current Ic, is also applied from the output of block 818 by means of a scaler circuit illustrated as a block 820, to an error signal generator 822. The purpose of the scaler circuit 820 is explained below, but its action results in the conversion of the ordered current of the motor Ic into the ordered current of the generator Ic. The error signal generator 822 generates an error signal by subtracting a feedback signal from a signal line 824, which represents the detected output current of the internal combustion engine / generator (generator), of the ordered current of generator Ic. The error signal produced by the error signal generator 822 is applied to a cycle compensating filter, which may be a simple integrator, to produce a signal representative of the ordered speed of the auxiliary power source 16, more specifically the diesel engine 18. The diesel engine 18 drives the electric generator 22, to produce an alternating output voltage to be applied by means of the power conductors 832 to the inverter 28 of Figure 1. A current sensor configuration illustrated as a Circle 834 is coupled to the output conductors 832 to detect the generator current. Blocks 822, 826, 18, 22, and 824 of Figure 8 together constitute a closed feedback loop which tends to make the output current of the generator 22 equal to the amount commanded by the control signal Ic applied to the error generator. The cycle compensator 826 is selected to prevent the speed of the diesel engine from changing too rapidly, which could undesirably result in an increase in the emission of contaminants. As described so far, the configuration of Figure 8 produces an Ic signal to command the current of the traction motor, to control the movement of the vehicle, and also produces an I_ signal which orders the current of the auxiliary generator 22. In the Figure 8, a signal representing a desired state of charge (SOC) of the traction battery is received at the non-inverting input port of a summing circuit 850. The signal representing the current state of charge is received at the inverting input port of the summing circuit 850 from a load state determining block (SOC) of the battery 852. The load state determining block 852 receives signals representing the battery voltage, the temperature of the battery, and the battery currents. In general, the state of charge of a battery is simply the time integral of the network of the input and output currents. The load state determining block 852 integrates the current amperes of the network, to produce ampere-hours of charge. The summing circuit 850 produces, on a signal line 854, an error signal representing the difference between the desired or ordered charge state of the traction battery, and its actual charge state, to thereby identify an excess or instantaneous charge deficiency. The error signal is applied to a cycle compensator filter 856, which integrates the error signal, to produce an integrated error signal. The integrated error signal changes slowly as a function of time. The integrated error signal acts on the block 820 by means of a limiter 858. More particularly, the integrated error signal, when applied to the scaler block 820, selects the scale factor by which the ordered current is scaled of the Ic motor, to convert it into the ordered current of the generator. The limiter 858 merely limits the integrated error signal from block 856, such that the scale factor range of the scaler block 820 is limited to the range between zero and one (the unit). Accordingly, the ordered current of the generator IG can never be greater than the ordered current of the traction motor Ic, but can be smaller according to the scale factor ordered by the integrated signal limited from the limiter 858, and the ordered current of the IG generator can be as low as zero current. The desired state of charge of the traction battery is its charge level which is less than the full charge, so that regenerative braking can be applied without the danger of damaging the traction battery due to an overload. Therefore, the set point of the desired charge state is a load less than the full charge. The operation of the configuration of Figure 8 can be understood assuming that the normal state of the integrator output in the 856 cycle compensating filter is 0.5"volts", half way between the maximum of 1.0 volts and the minimum of 0.0 volts allowed by the limiter 858. The value of the integrated error signal (as limited by the limiter 858), can be seen as a multiplication factor by which the scaling circuit 820 scales the ordered current of the traction motor , so that an integrated error signal having a value of 1.0 causes the ordered current of the traction motor Ic to be transmitted to a full amplitude by the • error signal generator 822, while a value of 0.5 would result in the magnitude of the ordinate current of the generator IG being exactly half the magnitude of the ordered current of the traction motor Ic. In operation the vehicle under the control of the configuration of Figure 8, when the traction battery exceeds the desired state of charge, the error signal generator 850 subtracts a large signal value representing a state of high load, value of the set point, thus producing a difference or error signal that has a negative polarity.

The integrator of the 856 cycle compensating filter integrates the negative polarity signal, which tends to "reduce" or boost the integrated signal of the network to the output of the 856 cycle compensating filter, moving away from its "normal" value of 0.5. volts, possibly going down to 0.3 volts, as an example. Since a value of 0.3 volts of the integrated error signal is within the allowed range of the limiter 858, the integrated error signal simply flows through the limiter 858, to control the scaling circuit 820 in a manner that causes the ordered current of the traction motor Ic is multiplied by 0.3, instead of 0.5"normal", to produce the ordered current of the IG generator. Accordingly, a state of battery charge greater than the desired set point results in the reduction of the average output of the generator. In the same way, if the state of charge of the traction battery is lower than the set point desired, the signal applied from block 852 of Figure 8 to the inverting input port of the error signal generator 850, arrives to be of a magnitude smaller than the signal representing the desired state of charge, which results in a positive value of the error signal at the output of the error signal generator 850. The integrator associated with the cycle filter 856 integrates its positive input signal to produce an integrated output signal that tends to increase above its "normal" value of 0.5 volts, up to a value, for example, of 0.8 volts. Since this value is within acceptable values for limiter 858, the integrated 0.8 volt error signal is applied to scaler circuit 820 unchanged. The integrated error voltage of 0.8 volts causes the scaler circuit 820 to multiply the signal representing the ordered current of the traction motor Ic by 0.8, such that the ordered current of the generator IG is greater than before. The net effect of the decrease in the charge of the traction battery to a value below the set point is to increase the average output power from the generator 22, which would tend to increase the charge level of the traction battery. Those skilled in the art will understand that the "normal" value of the integrated error signal referred to above, does not really exist, and is used only to help understand the operation of the control system. Accordingly, a method (Figures 3a, 3b, and 4) for operating a vehicle (10) that derives at least some of its tractive effort or driving power from one or more electric batteries ("batteries") (20) , includes the step (312; 418) of substantially returning all the energy from a traction motor (40) to the batteries (20) during dynamic braking, during those times when the batteries (20) are in a first condition of load (below the first load level), which is less than the full load condition. Other steps (420, 422) of the method include returning less than all the energy (314) from the traction motor (40) to the batteries (20) during dynamic braking, when the batteries are at a load level between the first load condition (first load condition of Figures 3a and 3b) and full load condition, and substantially no energy returned (graph 314 at the full load point of Figure 3a) from the traction motor (40 ) to the batteries (20) during braking, when the batteries (20) reach the condition of full charge. In this embodiment, the step (420, 422) of returning less than all the energy from the traction motor (40) to the batteries (20) includes the step of returning an amount of the available dynamic braking energy to the batteries ( 20), which is monotonically related (ramp 314) in the proportion of the battery charge in the present time (Cc) in relation to the 'full charge condition. In the preferred embodiment of the invention, the steps described above make a smooth transition from one to the other, depending on the state of charge of the batteries. Since the amount of dynamic braking changes gradually as a function of the battery charge, the friction brakes (36a, 36b) recover any deficiency in the braking, in an automatic way, as a result of the force of the brake pedal of the operator (30a).

Claims (3)

1. A method for operating a vehicle that derives at least some of its traction effort from electric batteries, which comprises the steps of: substantially returning all the energy from a traction motor to the batteries during dynamic braking, when the batteries they are in a first load condition, which is less than the full load; return less than all the power from the traction motor to the batteries during dynamic braking, when the batteries are at a load level between the first charge condition and the full charge condition; and not substantially returning any energy from the traction motor to the batteries during braking, when the batteries reach full load condition.

A method according to claim 1, wherein the step of returning less than all the energy from the traction motor to the batteries includes the step of returning an amount of the available dynamic braking energy to the batteries, which is monotonically related to the proportion of this charge in relation to the full charge.

3. A method according to claim 1, which further comprises the step of making a smooth transition between the steps of returning substantially all the energy and returning less than all this energy, and between the steps of returning less than all the energy and not return substantially no energy.