GB1567208A

GB1567208A - Traction instalation for battery-powered electric vehicles

Info

Publication number: GB1567208A
Application number: GB49489/76A
Authority: GB
Original assignee: Fiat SpA
Current assignee: Fiat SpA
Priority date: 1975-12-05
Filing date: 1976-11-26
Publication date: 1980-05-14
Also published as: FR2333662B1; DE2654686B2; FR2333662A1; IT1051340B; JPS5275719A; DE2654686A1; DE2654686C3

Description

(54) TRACTION INSTALLATION FOR BATTERY-POWERED ELECTRIC VEHICLES (71) We, FIAT SOCIETY PER AZIONI, an Italian joint stock company, of Corso Marconi 10, Turin, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a batterypowered electric traction installation, preferably for motor vehicles.

A fundamental requirement for a batterypowered electric traction installation for a motor vehicle is that the autonomy of the vehicle, or its operating range on a fully charged battery, must be the maximum possible.

The duration of the autonomy of an electrically driven battery-powered vehicle can be increased by converting kinetic energy of mechanical inertia, for example the energy of a rotating flywheel, into electrical energy and making the vehicle battery work as much as possible in a regimen of discharge with constant current, without making use of energy dissipative elements such as rheostats in armature circuits of electric traction motors. Apart from being wasteful of energy, such dissipative elements have the disadvantage of producing large quantities of heat which cannot readily be utilized.

According to the present invention there is provided a traction installation for a battery-powered electric vehicle, comprising one or more electric traction motors capable of acting as generators and connected together or separately to a single vehicle wheel or group of wheels, a generator, a flywheel mechanically coupled to the rotor of the generator and an auxiliary electric motor connectible to the battery, the rotors of the generator and the auxiliary motor being mechanic ally interconnected, an electrically operated switch in each of electric circuits between the battery and the armatures of the generator, the auxiliary motor and the one or more traction motors and control means producing electrical signals controlling actuation of said electrically operated switches in such manner that in operation initially and prior to connection of the traction motor(s) to the battery, the auxiliary motor is connected to the battery by operation of a starting switch so that the generator and flywheel are driven, the one or more traction motors being at this time already electrically coupled to the generator, the control means operating to close the electrically operated switch in the circuit between the battery and the traction motor(s) and to open the electrically operated switch between the auxiliary motor and the battery as soon as the output of the generator equals the output of the battery so that the traction motor(s) in this operating condition are supplied with current from the battery and the generator to drive the vehicle and during braking the traction motor(s) are driven by the vehicle wheel to act as generator(s), the control means operating to interrupt the electrical connection between the traction motor(s) and the generator and to close the electrical connection between the traction motor(s) and the auxiliary motor so that the auxiliary motor drives the flywheel to store kinetic energy therein.

The invention will be further described, by way of non-limiting example, with reference to the accompanying drawings, wherein: Figure 1 is a schematic representation of a traction installation according-to one embodiment of the invention; Figure 2 is a block schematic diagram of the control circuit of the installation shown schematically in Figure 1, and Figure 3 represents diagrammatically a detail of Figure 2.

In Figure 1, reference numeral 1 represents a wheel of a vehicle (not shown) upon which the illustrated traction installation is mounted for the purpose of driving the wheel 1. The installation is powered by a battery of accumulators 2 and includes three direct current electric machines with separate excitation comprising a traction motor M1 coupled to the wheel I and capable of acting as a generator when driven by the wheel, an auxiliary motor M2 and a generator M3 which is capable of acting as a motor. A drive transmission unit 3 is interposed between the traction motor M1 and the wheel 1. A rotary mass having the function of a flywheel 4 is mounted on the shaft of the generator M3.

The battery 2 is connected to the rest of the installation through a diode 5 and a switch 6 which connects the battery 2 to the armature of the auxiliary motor Ism2, through the contacts of a normally closed relay switch T3, and to the armatures of the other two machines M1 and M3 through a normally open relay switch T2. The armatures of the latter two machines M1 and M3, which are preferably of the same power, are electrically connected to one another by means of a line 9 and a normally closed relay switch T1 the operation of which is dscribed in detail below.

The auxiliary motor M2 is dimensioned for powers lower than those acceptable by the machines M1 and M3. The generator M3 is connected electrically either to the battery 2 or to the machine M1 by the operation of the relay switches T1 and T2. The rotors of the two machines M2 and M3 are mechanically connected to each other and can be selectively connected to the flywheel 4 by means of an electromagnetic coupling 4a which when disengaged allows the flywheel 4 to rotate freely when a transfer of kinetic energy to and from the flywheel is not required.

Upon starting of the traction installation the relay,switch -T2 is initially open and the relay switches T1 and T3 are closed. The traction motor M1 is therefore stationary and the generator M3 is devoid of excitation.

At this stage the generator M3 acts simply as a mechanical connection between the flywheel 4 and the auxiliary motor M2, which will be energized from the battery 2 through the relay switch T3 upon closure of the switch 6. Under these conditions the auxiliary motor M2 will absorb from the battery 2 just as much power as is necessary to bring the flywheel 4 to and maintain it at a constant rotational speed.

The vehicle can then be started by operating on the accelerator pedal so as to excite the generator M3, which supplies a voltage to the armature of the traction motor Ml through the relay switch T1. The excitation circuit of the traction motor Ml is at this stage connected to a source of constant voltage, corresponding to the maximum value of the excitation current, hereinafter referred to as the "maximum excitation", which can be, for example, the voltage of the battery 2.

The traction motor M1 then accelerates, rotating the wheel 1. By gradually increasing the excitation of the generator M3 and therefore its output voltage the speed of til motor M1 and wheel 1, and therefore the speed of the vehicle, is increased. When the generator M3 is excited to such a level as to be able to provide a voltage to the traction motor M1 equal to that provided by the battery 2 the relay switch T3 is opened and the relay switch T2 is closed, whereupon the auxiliary motor M2 ceases to be driven because its armature is no longer supplied.

The necessary power to drive the vehicle wheel 1 is then supplied to the traction motor M1 by the supply system in a hybrid way, that is, partly from the battery 2 and partly from the generator M3, the latter being driven in turn by the flywheel 4. If it is now desired to bring the vehicle to the maximum allowed speed it is necessary first to reduce the excitation voltage of the traction motor M1 gradually to the minimum while keeping the output voltage from the generator M3 constant, as the rotating flywheel 4, losing its energy, slows down, effectively imparting its stored energy to the generator M3 and thence to the motor M1. For this purpose it is necessary to act accordingly on the excitation of the generator M3.

During vehicle braking with energy re operation the traction motor M1 acts as a generator driven by the wheel 1, returning its energy to the auxiliary motor M2 which in turn rotates the flywheel 4 to store kinetic energy therein. In this phase, when the accelerator pedal will be released, the excitation of the machine M1 is such as to maintain an output current just sufficient to brake the vehicle.

Figure 2 illustrates schematically a control circuit for the relay switches T1, T2, T3 and for the excitation of the machines Ml, M2 and M3. The control circuit includes a first comparator 101 having a first input on line 103 proportional to the output voltage of the generator M3 and a second input on line 105 proportional to the voltage of the battery 2.

The output of the comparator 101 passes to the "set" input 106 of a bistable multivibrator 108, to the "reset" input 110 of which there is applied the output signal of a second comparator 112. To one input of the second comparator 112 there is applied through a line 114 a signal proportional to the instantaneous current I absorbed by the traction motor M1, while to the other input of the comparator 112 there is applied, through a line 116, a threshold voltage such that the comparator 112 provides an output signal when the current I is negative (braking phase).

The output 118 of the multivibrator 108 is connected to the winding 120 of the normally closed relay switch T3 and to the winding 129 of a remotely controlled change-over switch 130 while the output of the second comparator 112 is connected to the winding 126 of the normally closed relay switch T1.

The outputs of the multivibrator 108 and of the comparator 112 are also connected to the anodes of respective diodes 122, 124 having a common cathode connection to the winding 128 of the normally open relay switch T2.

The change-over switch 130 is shown in detail in Figure 3 and has four fixed input contacts shown as A, B, C, D, five fixed output contacts shown as E, F, G, H, I, and four movable contacts 132, 133, 134, 135.

The first position of the change-over switch 130, corresponding to de-energisation of the winding 129, is shown in Figure 3 with its second, energised, position shown in broken outline, while in Figure 2 the switch 130 is shown in its first position.

The first fixed input contact A of the change-over switch 130 is connected to a line 136 which is fed with the maximum excitation voltage, the second fixed input contact B is connected to a line 138 which is fed with a variable signal voltage from a transducer 100 controlled by the vehicle accelerator pedal 100a, the third fixed input contact C is connected to a line 140 which is fed with the voltage of the cattery 2 and the fourth fixed input contact D is connected to a line 158 which is fed with the output signal of an operational amplifier 152.

A line 142 leads from the first fixed output contact E to an amplifier 143 which feeds a direct current converter or chopper 143a the output voltage d which is applied across the excitation winding 144 of the traction motor M1. The second fixed output contact F is connected by a line 146 to a first input 148 of an operational amplifier 150 acting as a summation circuit. The output of the operational amplifier 150 is amplified by an amplifier 165 and drives a chopper 165m which provides a voltage across the excitation winding 166 of the generator M3. The third fixed output contact G of the changeover switch 130 is left free or is not connected.The fourth fixed output contact H is oonnected through a line 159 to a second input 164 of the operational amplifier 150; finally, the fifth fixed output contact I is connected through a line 171 to a first input 170 of an operational amplifier 160 acting as a first subtraction circuit.

At the inputs of the operational amplifier 152, which acts as a second subtraction circuit, there are connected respectively a line 154 fed with a current signal proportional to the actual value of the current provided by the battery 2 and a line 156 fed with a signal proportional to the value of a reference current Im. The reference current Im is equal to the prefixed value desired for the constant discharge current of the battery 2 from starting to stopping. The output of the operational amplifier 152 will therefore be an error signal representing the difference between the actual battery current and the reference current Im.

The opeation amplifier 160, also acting as a comparator, has a second input 172 to which is applied, through a line 162, the abovementioned current value signal from the line 156. The output signal of the operational amplifier 160 is amplified by an amplifier 167 and drives a chopper 167a which provides a voltage across the excitation winding 168 of the auxiliary motor M2.

The choppers 143a, 165a, 167a are supplied through a line 200 connected directly to the vehicle battery 2.

The output signal of the operational amplifier 152 is also supplied, through the line 158, the output contact H of the change-over switch 130 and the line 159, to the second input 164 of the operational amplifier 150 when the movable contact 135 of the changeover switch 130 is in the energised position shown in broken outline in Figure 3. In this position the movable contact 134 puts the line 140 in communication with the line 146; the movable contact 133 puts the line 138 in communication with the line 142 and the movable contact 132, by opening the electric circuit, will prevent the passage of the signal from the line 136 to the line 142.

The operation of the control circuit will now to be described with reference to the drawings.

When it is desired to start the traction installation the switch 6 (Figure 1) is closed so that current is supplied from the battery 2 to the auxiliary motor M2 through the relay switch T3, causing the rotor of the generator M3 and the flywheel 4 to be driven, as described earlier. When the flywheel 4 reaches a predetermined rotational speed it is possible to start the vehicle. Initially, the voltage generated by the generator M3 on the line 103 (Figure 2) will be lower than the battery voltage applied to the line 105, so that the output signal from the multivibrator 108 will be zero and the windings 126, 128, 120 of the relay switches T1, T2, T3 and the winding 129 of the change-over switch 130 are not excited.The relay switches T1 and T3 therefore remain closed and the relay switch T2 remains open, so that battery 2 maintains the auxiliary motor M2 in rotation, while the generator M3 generates a voltage which drives the traction motor M1.

In the meantime the auxiliary motor M2, continues to drive the rotor of the generator M3 and the flywheel 4, being supplied with armature current direct from the battery 2 through the relay switch T3. The field excitation winding 168 of the auxiliary motor M2 is supplied with voltage sufficient to maintain a substantially constant current discharge from the battery 2 by means of the two amplifiers 160 and 152 -which together form first and second subtraction circuits which provide a signal for effecting variation of the excitation of the motor M2 as long as the output of the amplifier 152, comprising the error signal representing the difference between the actual current and the reference current Im, is not annulled.

When the voltage applied to the armature of the traction motor M.1 by the generator M3 equals the battery voltage the comparator 101 provides an output signal which 'sets' the bistable multivibrator 108. The output of the multivibrator 108 then comprises a voltage which excites the winding 129 of the change-over switch 130 causing the moveable contacts of the latter to be moved into the energised positions represented by broken lines in Figure 3, in which the contacts 133 and 134 are connected respectively with the fixed contacts "E", "F" allowing the signal proportional to the battery voltage to pass from the line 140 to the line 146 and the signal proportional to the position of the accelerator pedal 100at given by the signal transducer 100 to pass from the line 138 to the line 142.The output signals from the contact E of the change-over switch 130 are passed on line 142, through the amplifier 143 to the chopper 143a which supplies the excitation winding 144 of the traction motor M1.

The output signals from the contact F of the change-over switch 130 are passed through the line 146, the operational amplifier 150, the amplifier 165 to the chopper 165a which supplies the excitation winding 166 of the generator M3. Furthermore, the movable contact 135, upon moving into the position shown with a broken line in Figure 3 allows the signal proportional to the discrepancy between the battery current and the reference current to pass from the line 158 to the line 159.

In this way the two operational amplifiers 150 and 152 form a feed-back circuit which varies the excitation of the generator M3 until the requisite current is provided by the batery 2. The signal at the output 118 of the bistable multivibrator 108, in addition to exciting the winding 129 of said change-over switch 130 causes excitation of the windings 128 and 120 of the relay switches T2 and T3, closing the former and opening the latter. As a result the battery 2 is connected to, and in parallel with, the generator M3 which generates a voltage derived from the energy stored by the rotating flywheel 4, so that the battery 2 and the generator 3 together provide current to the traction motor M1. The relay switch T1 remains closed because its winding 126 is not excited by virtue of the rectification effected by the diodes 122 and 124.In this way the traction motor M1 is driven by energy derived from the hybrid battery/flywheel,system as previously described.

In the braking phase the comparator 112 emits a signal which resets the bistable multivibrator 108, so that the signal at the output of the multivibrator disappears. In this situation the winding 128 of the relay switch T2 will continue to be excited by the output signal from the comparator 112, de-exciting the windings 120 and 129 will cause the relay switch T3 to be reclosed and the change-over switch 130 to revert to the position shown in Figure 2 and exciting the winding 126 will cause the relay switch T1 to open.This brings about the braking phase with energy recovery because, as shown diagrammatically in Figure 1, the traction motor M1, acting now as a generator, supplies power to the auxiliary motor M2 through the relay switches T2 and T3, rotating the flywheel 4 to which the motor M2 is mechanically connected through the rotor of the generator M3, so that the flywheel 4 stores kinetic energy as previously described, effectively absorbing kinetic energy of the vehicle.

In this case the excitation of the traction motor M1 is such that it generates a voltage equal to that of the battery 2, because the line 136 is connected, through the movable contact 132 of the change-over switch 130, with the line 142, while the excitation winding 168 of the- auxiliary motor M2 is controlled by the feed-back circuit formed by the two amplifiers 160 and 152.

According to the arrangement shown in Figure 2 braking always takes place with a constant current Im. A transducer may be provided to vary this current, as a function of, for example, the position of the vehicle brake pedal to obtain a progressively variable braking effect.

WHAT WE CLAIM IS: 1. A traction installation for a battery powered electric vehicle, comprising one or more electric traction motors capable of acting as generators and connected together or separately to a single vehicle wheel or group of wheels, a generator, a flywheel mechanically coupled to the rotor of the generator and an auxiliary electric motor connectible to the battery, the rotors of the generator and the auxiliary motor being mechanically interconnected, an electrically operated switch in each of electric circuits between the battery and the armatures of the generator, the auxiliary motor and the one or more traction motors and control means producing electrical signals controlling actuation of said electrically operated switches in such manner that in operation

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. armature current direct from the battery 2 through the relay switch T3. The field excitation winding 168 of the auxiliary motor M2 is supplied with voltage sufficient to maintain a substantially constant current discharge from the battery 2 by means of the two amplifiers 160 and 152 -which together form first and second subtraction circuits which provide a signal for effecting variation of the excitation of the motor M2 as long as the output of the amplifier 152, comprising the error signal representing the difference between the actual current and the reference current Im, is not annulled. When the voltage applied to the armature of the traction motor M.1 by the generator M3 equals the battery voltage the comparator 101 provides an output signal which 'sets' the bistable multivibrator 108. The output of the multivibrator 108 then comprises a voltage which excites the winding 129 of the change-over switch 130 causing the moveable contacts of the latter to be moved into the energised positions represented by broken lines in Figure 3, in which the contacts 133 and 134 are connected respectively with the fixed contacts "E", "F" allowing the signal proportional to the battery voltage to pass from the line 140 to the line 146 and the signal proportional to the position of the accelerator pedal 100at given by the signal transducer 100 to pass from the line 138 to the line 142.The output signals from the contact E of the change-over switch 130 are passed on line 142, through the amplifier 143 to the chopper 143a which supplies the excitation winding 144 of the traction motor M1. The output signals from the contact F of the change-over switch 130 are passed through the line 146, the operational amplifier 150, the amplifier 165 to the chopper 165a which supplies the excitation winding 166 of the generator M3. Furthermore, the movable contact 135, upon moving into the position shown with a broken line in Figure 3 allows the signal proportional to the discrepancy between the battery current and the reference current to pass from the line 158 to the line 159. In this way the two operational amplifiers 150 and 152 form a feed-back circuit which varies the excitation of the generator M3 until the requisite current is provided by the batery 2. The signal at the output 118 of the bistable multivibrator 108, in addition to exciting the winding 129 of said change-over switch 130 causes excitation of the windings 128 and 120 of the relay switches T2 and T3, closing the former and opening the latter. As a result the battery 2 is connected to, and in parallel with, the generator M3 which generates a voltage derived from the energy stored by the rotating flywheel 4, so that the battery 2 and the generator 3 together provide current to the traction motor M1. The relay switch T1 remains closed because its winding 126 is not excited by virtue of the rectification effected by the diodes 122 and 124.In this way the traction motor M1 is driven by energy derived from the hybrid battery/flywheel,system as previously described. In the braking phase the comparator 112 emits a signal which resets the bistable multivibrator 108, so that the signal at the output of the multivibrator disappears. In this situation the winding 128 of the relay switch T2 will continue to be excited by the output signal from the comparator 112, de-exciting the windings 120 and 129 will cause the relay switch T3 to be reclosed and the change-over switch 130 to revert to the position shown in Figure 2 and exciting the winding 126 will cause the relay switch T1 to open.This brings about the braking phase with energy recovery because, as shown diagrammatically in Figure 1, the traction motor M1, acting now as a generator, supplies power to the auxiliary motor M2 through the relay switches T2 and T3, rotating the flywheel 4 to which the motor M2 is mechanically connected through the rotor of the generator M3, so that the flywheel 4 stores kinetic energy as previously described, effectively absorbing kinetic energy of the vehicle. In this case the excitation of the traction motor M1 is such that it generates a voltage equal to that of the battery 2, because the line 136 is connected, through the movable contact 132 of the change-over switch 130, with the line 142, while the excitation winding 168 of the- auxiliary motor M2 is controlled by the feed-back circuit formed by the two amplifiers 160 and 152. According to the arrangement shown in Figure 2 braking always takes place with a constant current Im. A transducer may be provided to vary this current, as a function of, for example, the position of the vehicle brake pedal to obtain a progressively variable braking effect. WHAT WE CLAIM IS:

1. A traction installation for a battery powered electric vehicle, comprising one or more electric traction motors capable of acting as generators and connected together or separately to a single vehicle wheel or group of wheels, a generator, a flywheel mechanically coupled to the rotor of the generator and an auxiliary electric motor connectible to the battery, the rotors of the generator and the auxiliary motor being mechanically interconnected, an electrically operated switch in each of electric circuits between the battery and the armatures of the generator, the auxiliary motor and the one or more traction motors and control means producing electrical signals controlling actuation of said electrically operated switches in such manner that in operation

initially and prior to connection of the traction motor(s) to the battery, the auxiliary motor is connected to the battery by operation of a starting switch so that the generator and flywheel are driven, the one or more traction motors being at this time already electrically coupled to the generator, the control means operating to close the electrically operated switch in the circuit between the battery and the traction motor(s) and to open the electrically operated switch between the auxiliary motor and the battery as soon as the output of the generator equals the output of the battery so that the traction motor(s) in this operating condition are supplied with curent from the battery and the generator to drive the vehicle and during braking the traction motor(s) are driven by the vehicle wheel to act as generator(s), the control means operating to interrupt the electrical connection between the traction motor(s) and the generator and to close the electrical connection between the traction motor(s) and the auxiliary motor so that the auxiliary motor drives the flywheel to store kinetic energy therein.

2. A traction installation according to Claim 1 in which a change-over switch is connected to the excitation circuits of the generator and of the auxiliary motor through a summation circuit and a first subtraction circuit respectively, the change-over switch having a first position in which it connects (a) a constant voltage signal to control the excitation circuit of the or each traction motor, (b) a vehicle accelerator control signal to the first input of said summation circuit to control the excitation circuit of said generator, and (c) the output of a second subtraction circuit, comprising a signal representing the difference between a signal proportional to the value of instantaneous current provided by the battery and a signal proportional to the desired value of the battery current from starting to stopping, to a first input of said first subtraction circuit to control the excitation circuit of said auxiliary motor, the change-over switch having a second position in which it connects (d) said vehicle accelerator control signal to control the excitation circuit of the or each said traction motor, (e) a source of constant voltage to said first input of said summation circuit, and (f) the output signal of said second subtraction circuit to the second input of said summation circuit, the signal proportional to the prefixed value for the discharge current of the battery from starting to stopping, being applied to a second input of said first subtraction circuit in both said positions of said change-over switch.

3. A traction installation according to Claim 2 in which the or each traction motor, the generator and the auxiliary motor are all direct current electric machines with separate excitation circuits supplied by respective chopper circuits which are, respectively, controlled by signals from said change-over switch directly, controlled by signals from the summation circuit, and controlled by signals from the first subtraction circuit.

4. A traction installation for a batterypowered electric vehicle, substantially as herein described with reference to and as shown in the accompanying drawings.