GB2028029A - Traction battery charging system - Google Patents

Abstract

A battery charging system comprises a traction battery (18), thyristors (SCR 1,2) for supplying DC to the battery (18), a section for comparing the battery voltage with a reference voltage varied in accordance with the temperature of the battery electrolyte, a current regulating section for controlling the thyristors, and a timing section for controlling relays during each charging cycle. Each cycle comprises a first phase in which the battery is charged at 30 amps until its voltage exceeds a first predetermined reference value or a predetermined period has elapsed, a second phase in which the battery is charged at 20 amps until its voltage exceeds a second higher voltage or a predetermined period has elapsed, a third phase in which the battery is charged at 10 amps for a predetermined period, and a ready phase in which the battery is charged at 10 amps for a 15 minute period at intervals. The battery includes pressure operated switches (22). If the gas pressure rises above a first predetermined value charging is interrupted until it falls below a second lower value. <IMAGE>

Description

SPECIFICATION Traction battery charging system The present invention relates to a traction battery charging system in which each charging cycle is controlied automatically.

It is known, when charging a fully discharged battery, the first or major part of the charging cycle may be carried out at a relatively high charging rate and that the remainder of the cycle should then be carried out at a lower rate. In one known charging system in which the charging cycle is controlled automatically, in order to achieve this the first phase of the charging cycle is carried out at a relatively high current and is terminated when the battery voltage exceeds a predetermined value, and the second phase is then carried out at a lower current and is terminated when a predetermined period has elapsed. However, if this system is used to charge a battery which is only partially discharged there is a danger that excessive gassing may occur during the second phase.

According to one aspect of the present invention there is provided a traction battery charging system comprising a traction battery, means for supplying current to the traction battery, means for regulating the current supplied to the battery, means for comparing the battery voltage with a reference voltage, means for timing the charging, and means responsive to the comparing means and the timing means for automatically controlling each charging cycle, each charging cycle including a first charging phase in which the battery is charged at a first rate of charging, the first charging phase being terminated when the battery voltage exceeds a first predetermined value, and a second charging phase in which the battery is charged at a second rate of charging, the second phase being terminated when either the battery voltage exceeds a second predetermined value or when a predetermined period has elapsed, whichever occurs first, the second predetermined voltage being equal to or greater than the first predetermined voltage.

The first charging phase may be terminated if a predetermined period elapses before the first predetermined voltage is exceeded.

The charging cycle may include a third charging phase in which the battery is charged at a third rate of charging for a predetermined period.

Afurther problem encountered with the known battery system mentioned above occurs because the internal resistance of the battery and consequently the battery voltage varies with the temperature of the battery electrolyte. Thus if the temperature of the electrolyte rises, there is a danger of overcharging and, if it falls, there is a danger of undercharging.

Both of these conditions should be avoided as they reduce battery life. Also, in the case of overcharging, there is a danger that excessive gassing may occur.

According to a second aspect of the present invention there is provided a traction battery charging system comprising a traction battery, means for supplying current to the traction battery, means for regulating the current supplied to the battery, means for comparing the battery voltage or a fraction of the battery voltage with a reference voltage, eitherthe fraction of the battery voltage or the reference voltage being varied in accordance with the temperature of the battery electrolyte, means for timing the charging, and means responsive to the comparing means and the timing means for automatically controlling each charging cycle, each charging cycle including a phase in which the battery is charged at a first charging rate until the battery voltage exceeds a predetermined value.

In charging systems in which each charging cycle is controlled automatically, it is found that excessive gassing sometimes occurs for an unforeseen reason thereby creating an explosion risk.

According to another aspect of the present invention, there is provided a traction battery charging system comprising a traction battery, means for restricting the flow of gas out of the battery, means responsive to the pressure of gas upstream of the restricting means, means for supplying currentto the battery, means for regulating the current supplied to the battery, means controlled by the pressure responsive means for interrupting the supply of current to the battery if the pressure rises above a first predetermined value until the pressure falls below a second predetermined value, means for comparing the battery voltage with a reference voltage, means for timing the charging, and means responsive to the timing means and the voltage comparing means for automatically controlling each charging cycle.

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which: Figure 1 shows the rectifying section and the connections between the rectifying section and the traction battery of a motor vehicle traction battery charging system embodying the present invention; Figure 2 is a circuit diagram of a set of relays forming part of the charging system of Figure 1; Figures 3 and 4 show a diagram of the voltage comparison section of the charging system of Figure 1; Figure 5 is a circuit diagram of the timing and control section of the charging system of Figure 1; and Figure 6 is a circuit diagram of the current regulating section of the charging system of Figure 1.

The electric motor vehicle traction battery charging system now to be described comprises a leadacid traction battery pack, a rectifying section, a voltage comparison section, a control and timing section and a current regulating section. The battery pack would normally be positioned in an electric vehicle.

Referring now to Figure 1, there are shown the circuit diagrams of the rectifying section 10, and the battery pack 12, together with a plug 14 and a socket 16 for connecting the battery pack 12 to the charging system.

The battery pack 12 comprises a traction battery 18, the positive terminal of which is connected to a terminal S1 of the socket 16 and the negative termi nal of which is connected to a terminal 52 of the socket 16. The battery pack 12 further includes an auxiliary battery 20, a positive terminal of which is connected to a terminal S3 and a negative terminal of which is connected to a terminal S4 of the socket 16. The traction battery 18 also includes four pres sure operated switches 22 which are connected in series between the positive terminal of the auxiliary battery 20 and a terminal 57 of the socket 16.Each of the pressure operated switches 22 is positioned upstream of an orifice which restricts the flow of gas out of the battery 18 and these switches are arranged so that they are normally closed but open if the pressure exceeds a first predetermined value and then close again as the pressure falls below a second predetermined value, the second value being lower than the first value. The battery pack 12 also includes a ventilating fan 24 connected across a pair of terminals S5 and S6 of the socket 16. Finally, the battery pack 12 includes a probe 26 for measuring the temperature of the electrolyte of the traction battery 18.

The probe 26 includes a pair of transistors T1 and T2 housed in a glass tube positioned in the electrolyte and a pair of fixed resistors R1 and R2 and a variable resistor R40 positioned externally of the electrolyte.

The resistors R1, R2 and R40 are connected in series between a terminal S8 of the socket 16 and the terminal S2, the common point of resistors R1 and R2 being connected to the base of transistor T1,the collector of which is connected to the terminal S8 and the emitter of which is connected to the base of transistor T2. The collector of transistor T2 is open circuited and the emitter is connected to the terminal S2 so the transistor T2 functions as a diode.

The rectifying section 10 comprises a mains transformerTX1 having a primary winding W1 and a main secondary winding W2 and an additional secondary winding W3. The primary winding W1 is connected to a pair of terminals L, N through a pair of contacts 30a, 30b of a relay 30, one end of the coil of which is connected to the terminal N. One end of the secondary winding W2 is connected to the anode of a thyristor SCR1 and to the cathode of a thyristor SCR2. The cathode of thyristor SCR1 is connected to the cathode of a diode D1 and the anode of the thyristor SCR2 is connected to the anode of a diode D2, the anode of diode D1 and the cathode of diode D2 being connected through the primary winding of a current transformer TX2 to the other end of winding W2.A surge suppressor 32 is also connected across the winding W2 and the primary winding of transformerTX2 and comprises a resistor R3, one end of which is connected to one end of the winding W2 and the other end of which is connected through a pair of series connected capacitors C1 and C2 and the primary winding of transformer TX2 to the other end of winding W2. The cathode of thyristor SCR1 is also connected through a smoothing inductor L1 to a terminal P1 of plug 14 and the anode of thyristor SCR2 is connected to a terminal P2 of the plug 14.

The circuit diagram of Figure 1 also shows a trans formerTX3 having a secondary winding connected to terminals P5 and P6 of plug 14 and a primary winding, one end of which is connected to one end of a relay coil 34 and a resistor R4 is connected in parallel with relay coil 34. A lamp LA2 is connected across the primary winding of the transformer TX3.

The contacts 34a of the relay 34 are connected to a terminal P7 of plug 14. A terminal P4 is connected to earth.

Plug 14 also includes terminals P3 and P8, the connections to which will be described below. When the plug 14 and the socket 15 are joined, terminals P1 to P8 of the plug 14 are connected respectively to the terminals S1 to S8 of the plug 16.

In operation, the terminals Land N are connected to a source of alternating current comprising a mains power supply and the plug 14 and socket 16 are connected together so that charging current is supplied to the traction battery 18. The value of this current is determined by the firing of thyristors SCR1 and SCR2, and as is described below this firing is controlled by the current regulating section of the system.

Referring now to Figure 2, there is shown a set of relays 36,38,40,42,44,46, 48,50, and 52 forming part of the system. The connections of these relays will now be described.

The coil of relay 36 is connected across terminals L and N. One end of the coil of relay 38 is connected to earth and the other end is connected through a contact 48a of relay 48 to terminal P3. A free wheel diode D3 is connected across the winding of relay 38. The relay 38 has a pair of contacts 38a, 38b which connect the terminals Land N to the primary winding of transformer TX3.

One end of the winding of relay 40 is connected through a normally closed contact 46a of relay 46 to one end of contact34a and the other end is connected to the collector of a transistor T3, the emitter of which is connected to earth.

The common point of the winding of relay 40 and contact 46a is connected to the cathode of a zener diode ZD1 the anode of which is connected through a resistor R6 to earth. The common point of zener diode ZD1 and resistor R6 is connected through a resistor R5 to the base of transistor T3. A free wheel diode D4 is connected across the winding of relay 40.

The relay 40 has a normally open contact40a connecting the contact 38a to one end of the coil of relay 30 through an on/offswitch41.

One end of the winding of relay 42 is connected to terminal P3 and the other end is connected to the collector of a transistor T4, the emitter of which is connected to earth. A free wheel diode D5 is connected across the winding of relay 42. The relay 42 has a wiper arm 42a normally connecting a firstter- minal to a second terminal but on energisation of the winding of relay 42 connects the firstterminal to a third terminal, the second terminal being connected through a first phase lamp LA3 to the terminal N and the third terminal being connected through a second phase lamp LA4 to the terminal N.

One end of the winding of relay 44 is connected to the terminal P3 and the other end is connected to the collector of a transistor T5, the emitter of which is connected to earth. A free wheel diode D6 is con nected across the winding of relay 44. The relay 44 has a wiper arm 44a normally connecting a firstter- minal to a second terminal but, on energisation of the winding of relay 44, connects the first terminal to a third terminal, the second terminal being connected to the first terminal of relay 42 and the third terminal being connected through a third phase lamp LA5 to terminal N.

One end of the winding of relay 46 is connected to terminal P3 and the other end is connected to the collector of a transistor T6, the emitter of which is connected to earth. Afree wheel diode D7 is connected across the winding of relay 46. Relay 46 includes a wiper arm 46b normally connecting a first terminal to a second terminal but, on energisation of the winding of relay 46, connects the first terminal to a third terminal, the second terminal being connected to the first terminal of wiper arm 44a and the third terminal being connected through a fourth phase lamp LA6 to terminal N. One end of the winding of relay 48 is connected to terminal P3 and the other end is connected to the collector of a transistor T7, the emitter of which is connected to earth. A free wheel diode D8 is connected across the winding of relay 48.The relay 48 includes a wiper arm 48b normally connecting a first terminal to a second terminal but, on energisation of the winding, connects the first terminal to a third terminal, the first terminal being connected to terminal L and the second terminal being connected to the first terminal of wiper arm 46b. One end of relay 50 is connected to terminal P3 and the other end is connected to the anode of a thyristor SCR3, the cathode of which is connected to earth. A free wheel diode D9 is connected across the winding. The gate of thyristor SCR3 is connected through a pair of resistors R7 and R8 to earth, a capacitor C10 bridging resistor R8. Relay 50 has a pair of normally open contacts 50a, one of which is connected to terminal L.

One end of relay 52 is connected to terminal P3 and the other end is connected to the collector of a transistor T8, the emitter of which is connected to earth. A free wheel diode D10 is connected across the winding. Relay 52 has a pair of normally open contacts 52a, one of which is connected to one of the contacts 50a and the other of which is connected through a ready lamp LA7 to terminal N.

In operation, when the plug 14 and socket 16 are connected together, the winding of relay 38 is energised thereby connecting the fan 24 to the source of alternating current and consequently closing contacts 34a. Then, providing all the contacts 22 are closed, the winding of relay 40 is energised. Thus, by manually closing switch 41, winding 30 may be energised, thereby closing contacts 30a and 30b, and consequently supplying charging current to the traction battery 18.

The operation of the remaining relays will be described below.

Referring now to Figure 3, there is shown the circuit diagram of the voltage comparison section of the system. As will be described below, two phases of the charging cycle are terminated if the voltage of the traction battery 18 exceeds a predetermined value and the function of the voltage comparison section is to compare the voltage of the traction battery 18 with a reference voltage and to provide an output signal when the former exceeds the latter.

The voltage comparison section comprises a diode D1 the anode of which is connected to a power supply to be described below and the cathode of which is connected to a rail 54, and a rail 56 is connected to the terminal P2 of plug 14. A capacitor C3 is connected between the rails 54 and 56.

The rail 54 is connected to the cathode of a zener diode ZD2, the anode of which is connected through a resistor R9 to the rail 56. The common point of zener diode ZD2 and resistor R9 is connected to the base of a p.n.p. transistor T9, the emitter of which is connected through a resistor R10 to the rail 54 and the collector of which is connected through a resistor R11 to the terminal P8 of plug 14. Zener Diode ZD2, resistor R9, resistor R10, and transistor T9 and resistor R 1 function as a constant current source and, in use, together with probe 26 function to establish a reference voltage at the common point of resistor R1 1 and terminal P8. As may be appreciated, if the temperature of the electrolyte of the traction battery 18 rises, then the value of this reference voltage will fall.

The common point of resistor R11 and P8 is connected through a resistor R12 to the invert input of an operational amplifier Al. The terminal P1 of plug 14, which in use is connected to the positive terminal of the traction battery 18, is connected through a resistor R13, a preset resistor R14, and four further resistors R15, R16, R17 and R18, all connected in series, to rail 56. The common point of resistors R17 and R1 8 is connected through a resistor R1 9 to the non-invert input of the amplifier Al and also through a capacitor C4 to rail 56. A resistor R20 and a capacitor C5 are connected in parallel between the output of amplifier Al and its non-invert input.

Resistors R13 to R18 function as a potential divider and thus, in use, the amplifier Al compares a fraction of the voltage of the traction battery 18 with the reference voltage, the output of amplifier Al going high when this fractional voltage exceeds the reference voltage. Resistor R15 is bridged by contacts 42c of relay 42.

The rail 54 is connected through a resistor R21, a capacitor C6, and a resistor R22, connected in series, to the rail 56, and the common point of capacitor C6 and resistor R22 is connected to the base of an n.p.n.

transistor T1 0. The transistor T10 is connected to a second n.p.n. transistor T1 1 as a Darlington pair, the collector of transistors T10 and T1 1 being connected through a resistor R23 to the common point of resistors R18and R19, and the emitter of T1 1 is connected to the rail 56.

In use, when power is initially supplied to the rails 54 and 56, the transistors T10 and T1 1 function to remove the traction battery voltage from the noninvert input of the amplifier Al thereby providing time for the reference voltage to be established before it is compared with the traction battery voltage.

The reference voltage established at the common point of resistor R11 and terminal P8 of plug 14 is connected through a resistor R41 to the non-invert input of an amplifier A2, the output of which is con nected through a resistor R24 to the non-invert input.

The invert input of amplifier A2 is connected through a resistor R25 to the common pair of a pair of resistors R26 and R27 connected in series between rails 54and56.

The output of amplifier A2 is connected through a resistor R28 and a capacitor C6, connected in series, to the rail 56, and the common point of resistor R28 and capacitor C6 is connected to the emitter of a uni-junction transistor To 2, the first base of which is connected to the rail 56 and the second base of which is connected through a resistor R29 to the rail 54. The common point of resistor R28 and capacitor C is further connected through a resistor R30 to the base of an n.p.n. transistor T13, the collector of which is connected to the rail 54, and the emitter of which is connected through a resistor R31 to the rail 56. The emitter of transistor T13 is further connected to the cathode of a zener diode ZD3, the anode of which is connected through a capacitor C7 to rail 56.

The output of amplifier Al is connected through a pair of resistors R32, R33, connected in series, to rail 56. The common point of zener diode ZD3 and capacitor C7 is connected to the common point of resistors R32 and R33 and also through a resistor R34 to the base of a transistor T14. The emitter of transistor T14 is connected to the anode of a photodiode D12, the cathode of which is connected to the rail 56. The photodiode D12 forms part of a photocoupler as will be described below. The collector of transistorT14 is connected through a resistor R34 to rail 54 and also through a resistor R35 and a capacitor C8, connected in series, to the rail 54.The common point of capacitor C8 and resistor R35 is connected to the base of a p.n.p. transistor To 5, the emitter of which is connected to the rail 54 and the collector of which is connected through a resistor R36 to rail 56. The collector of transistor T15 is also connected through a resistor R37 and a capacitor C9, connected in series, to the rail 56 and the common point of resistor R37 and capacitor C9 is connected to the base of an n.p.n transistor T16, the emitter of which is connected to rail 56 and the collector of which is connected through a resistor R38 to the common point of resistors R23 and R19.

In operation, whilst the fraction of the traction battery voltage applied to the non-invert input of amp lifierAl is lower than the reference voltage, the output of amplifier Al will remain low. However, when the voltage applied to the non-invert input of amp lifier Al exceeds the reference voltage the output of amplifier Al will go high thereby rendering transis torT14conductiveand energising photo diode D12, and also rendering transistors T15 and T1 6 conductive for a short period and thereby removing the traction battery voltage from the non-invert input of amplifier Al.

The output of amplifier A2 will normally be low but if for some reason the connection between resistor R11 and probe 26 is interrupted, the output of amp lifierA2 will go high. When this happens, the capacitor C6 will be repeatedly charged until the intrinsic stand off voltage of unijunction transistor T12 is reached and then rapidly discharged thereby supplying a series of positive pulses, to the base of transistor T13. In consequence, a series of positive pulses will be supplied to the base of transistor T14 and so photodiode D12 will be repeatedly energised and de-energised.

Referring now to Figure 4, there is shown a circuit diagram of the transistor which forms part of the optical-coupler mentioned above together with associated elements.

The transistor circuit comprises a rail 60 connected to terminal P3 of plug 14 amd a rail 62 connected to earth. Rail 60 is connected to the cathode of a diode D15, the anode of which is connected to rail 62. The rail 60 is also connected through a diode D16 and a resistor R47 to the collector of an n.p.n. transistor T20, the emitter of which is connected to the rail 62 and also to its base through a resistor R48. The transistor T20 forms part of the optical coupler mentioned above and is rendered conductive when the diode D12 is energised. The collector of transistor T20 is connected through a resistor R49 to the base of a transistor T21,the collector of which is connected through a resistor R50 to the junction of diode D16 and resistor R47 and the emitter of which is connected to the rail 62.The collector of transistor T21 is also connected through a resistor R51 and a zener diode ZD6 to the rail 62.

The common point of resistor R51 and zener diode ZD6 is used to provide the output signal for the voltage comparison section, and, in use, when the diode D12 is not energised, the transistor T20 is non-conductive and consequently, the transistor T21 is conductive and the output signal is low. When the photodiode D12 is energised, the transistor T20 is rendered conductive, thereby rendering the transistorT21 non-conductive, and the output signal goes high.

Turning now to Figure 5, there is shown the circuit diagram of the timing and control section of the charging system. This section includes a number of integrated circuits and these integrated circuits have their positive and negative supply terminals connected respectively to the positive and negative supply rails VOD and Vss of a power supply, not shown, fed from the auxiliary battery 20.

The integrated circuits include a clock 70 producing at its output terminal (Q) clock pulses at intervals of 109.2 ms. The integrated circuits further include a divider 72. Three counters 74,76 and 78 are provided and each of these comprises a presettabledown counter. Further included are three monostables 80, 82 and 84. The integrated circuits also include 8 J-K flip-flops, JKA, JKB, JKC, JKD, JKE, JKF, JKG, and JKH. A count data circuit 86 is provided for providing data to the JAM inputs of counters 74 and 76.

The connections of the timing section shown in Figure 5 will now be described.

The output terminal (Q) of the clock 70 is connected to one input of a NAND gate 96. The other input of the NAND gate is connected to the contacts 36a of relay 36 and contacts 36a normally connect this input to the negative supply rail Vss but, on energisation of relay 36, connect this input to the positive supply rail VDD. Thus, the clock pulses only appear at the output of NAND gate 96 when termi nals Land N shown in Figure 2 are connected to a mains power supply. The output of NAND gate 96 is connected to the input terminal (C) of divider 72.

Thus, at the Q14 output terminal (0) of divider 72 there is produced a square wave pulse having a period of 30 minutes. The Q14 output terminal (0) of divider 72 is connected to the CLOCK input terminal (C) of counter 74 and the CARRY OUT terminal (Q) of 74 is connected to the CLOCK input terminal (C) of counter 76.

The JAM input terminals (J 1 to J4) of counters 74 and 76 are connected to the data output terminals of count data circuit 86. The control terminals of count data circuit 86 are connected to the Output termi nals of J-K flip-flop JKA, the Q-output terminal of JK flip-flop JKB, the Q-outputterminal of flip-flop JKC, and the O-output terminal of flip-flop JKD. The input terminals of count data circuit 86, are connected to appropriate BCD data and, by applying signals to the control terminals of the switches, counters 74 and 76 can be made to count a predetermined number of output pulses from divider 72. The signal at the CARRY OUT terminal (0) of counter 76 is normally high but, when the predetermined number of pulses have been counted, goes low.

The common point of resistors R51 and zener diode ZD6 shown in Figure 4 is connected to one input of a NAND gate 98, the other input of which is connected to the 0 output terminal of flip-flop JKF.

The output terminal of NAND gate 98 is connected to one input terminal of a NAND gate 100, the other input of which is connected to the CARRY OUTterminal (Q) of counter 76. The output of NAND gate 100 is connected to the +TR input terminal of monostable 80 and the Q output terminal of monostable 80 is connected to one input terminal of a NAND gate 102 and also to one input terminal of a NAND gate 104. The other input terminal of NAND gate 102 is connected to the Q output terminal of monostable 84 and the output terminal of NAND gate 102 is connected to the +TR input terminal of monostable 82.

The other input terminal of NAND gate 104 is connected to the Q output terminal of flip-flop JKE and the output terminal of NAND gate 104 is connected to the CLOCK input terminal of each one of flip-flops JKA, JKB, JKC, JKD, JKE, JKG, JKH. The Q output terminal of monostable 84 is connected to the SET input terminal of flip-flop JKA and to the RESET input terminal of each one of flip-flops JKB to JKH.

The output terminal of monostable 82 is connected to the RESET inputs (R) of counters 74 and 76 and divider 72. A resistor R46 and capacitor C14 are connected between the positive and negative supply rails VDD and Vss, their junction being connected to the +TR input of monostable 84.

In operation, when the plug 14 and socket 16 are initially connected together, the voltage of the common point of resistor R46 and capacitor C14 will go high thereby providing a positive signal to the +TR input terminal of monostable 84. In consequence, a positive pulse will be produced at the Q outputter- minal of monostable 84 thereby setting flip-flop JKA and resetting flip flops JKB to JKH. Also, a negative going pulse will be produced at the 0 output terminal of monostable 84 thereby providing a positive going pulse to the +TR terminal of monostable 82, and this will result in a positive going pulse at the Q output terminal of monostable 82 thereby resetting counters 74 and 76 and also divider 72.

Subsequently, providing the signal at the Q output terminal of flip-flop JKF is high, if either a positive going pulse appears at the common point of resistor R51 and zener diode ZD6, shown in Figure 4, or if a negative going pulse is produced at the CARRY OUT terminal of counter 76, a positive going pulse will be transmitted to the +TR terminal of monostable 80.

This will result in a negative going pulse being pro duced at the 0 output terminal of monostable 80 which in turn will result in a positive going pulse to the +TR terminal of monostable 82 thereby resetting counter 74 and 76 and also divider 72. Also, provid ing the Q output terminål of flip-flop JKE is high, the negative going pulse at the 0 output terminal of monostable 80 will result in a positive going pulse at the output of NAND gate 104thereby providing a clock pulse to each of the flip-flops JKA, JKB, JKC, JKD, JKE, JKG, and JKH.

The J input terminal of flip-flop JKA is connected to the negative supply rail Vss and the K input termi nal is connected to the positive supply rail VDD. The Q output terminal of flip-flop JKA is connected to the J inputterminal offlip4lop JKB,the K inputterminal of which is connected to the positive supply rail VDD.

The 0 output terminal of flip-flop JKB is connected to the input of an inverter 106, the outputofwhich is connected through a resistor R65 to the base of transistor T4 shown in Figure 2. The Q output termi nal of flip-flop JKB is connected to the J input termi nal of flip-flop JKC, the K input of which is connected to the positive supply rail VDD.

The 0 output terminal of flip-flop JKC is connected to the J input terminals of each of flip-flops JKD and JKG and also to the CLOCK input terminal of JKF. The O output terminal of flip-flop JKC is connected to one input of an exclusive NOR gate 108. The K inputter- minal of flip-flop JKD is connected to the positive supply rail VDD. The 0 output terminal of JKD is connected to the J input terminal of flip-flop JKE and to the J input terminal of JKH.

The K input terminal of flip-flop JKE is connected to the positive supply rail VDD and the Q outputter- minal of flip-flop JKE is connected to one input of an exclusive NOR gate 110.

The J input terminal of flip-flop JKF is connected to the positive supply rail VDD and the K input terminal is connected to the negative supply rail Vss. The K input terminal offlip4lop JKG is connected to the negative supply rail Vss. The 0 output terminal of flip-flop JKG is connected to one input terminal of an exclusive NOR gate 112. The K input terminal of flipflop JKH is connected to the negative supply rail Vss.

The Q output terminal of flip-flop JKH is connected to the input of an inverter 114, the output of which is connected through a resistor R66 to the base of transistor T8 shown in Figure 2. The 0 output terminal of flip-flop JKH is also connected to the PRESET ENABLE terminal of counter 78.

The 0 14 output terminal (Q) of divider 72 is also connected to the CLOCK input terminal (C) of counter 78 and also to one input of a NAND gate 116.

The CARRY OUTterminal (0) of counter 78 is connected to both input terminals of a NAND gate 118, to the other input of exclusive NOR gate 110 and to the other input terminal of exclusive NOR gate 108.

The output terminal of NAND gate 118 is connected to the other input terminal of NAND gate 116 and the output terminal of NAND gate 116 is connected to the other input terminal of exclusive NOR gate 112.

The output of exclusive NOR gate 112 is connected to the input of an inverter 120, the output of which is connected through a resistor R67 to the base of transistor T6 shown in Figure 2. The output of NOR gate 110 is connected to the input of an inverter 122, the output of which is connected through a resistor R68 to the base of transistor T7 shown in Figure 2.

The output of NOR gate 108 is connected to the input of an inverter 124, the output of which is connected through a resistor R69 to the base of transistor T5 shown in Figure 2.

The overall function of the timing and control section shown in Figure 5 will be described below in connection with the overall operation of the system.

Referring nowto Figure 6, there is shown a circuit diagram of the current regulating section of the system.

This section comprises a rectifying bridge having four diodes D21 to D24, the input terminals of this bridge being connected across the secondary winding W3 shown in Figure lithe negative outputter- minal being connected to a negative supply rail 130, and the positive output terminal being connected through a resistor R70 and a zener diode ZD10, connected in series, to the rail 130, through a diode D26 and a capacitor C20, connected in series, to the rail 130 and also through a bleed resistor R42 to the rail 130. The common point of diode D26 and capacitor C20 is connected to a positive supply rail 132.The negative supply rail 139 is connected to terminal P2 of plug 14 so that, in use, this rail is connected to the negative terminal of the traction battery 18, and the positive supply rail 132 is connected to the anode of diode D11 shown in Figure 3, so as to provide power to rail 54.

The current regulating section further includes a resistor R71 connected across the secondary winding of the current sensing transformer TX2 shown in Figure 1. Thus, the voltage appearing across resistor R71 is, in use, proportional to the current supply to the traction battery 18.

One end of resistor R71 is connected to a rail 134 and the other end is connected through a resistor R72, a preset resistor R73, a preset resistor R74 and a resistor R75 to the rail 134. Resistor R73 is bridged by a pair of normally closed contacts 42b of relay 42 and resistor R74 is bridged by a pair of normally closed contacts 44b of relay 44. Thus, resistors R72 to R75 function as a potential divider chain, the potential dividing action being controlled by relays 42 and 44.

The common point of resistors R72 and R73 is connected through a resistor R76 to the base of an n.p.n. transistor T35, the collector of which is con nected to rail 132 and the emitter of which is con nected through a potential dividing resistor R77 to rail 134. A variable point on resistor R77 is connected to the anode of a diode D27 and to the cathode of a diode D28, the cathode of diode D27 being connected to the cathode of a diode D29 and the anode of diode D28 being connected to the anode of a diode D30. The common point of diodes D29 and D30 is connected to rail 134 and the common point of diode D28 and D30 is connected to rail 130.

In use, transistor T25 works as an emitter follower and the signal developed at the common point of diodes D27 and D29 comprises a half rectified alternating voltage, the value of which is proportional to the current drawn by the traction battery 18.

The common point of diodes D27 and D29 is connected through a zener diode ZDl 1, a resistor R78, and a resistor R79, connected in series, to rail 130.

The common point of resistor R70 and zener diode ZD10 is connected to the base of an n.p.n. transistor T26, the collector of which is connected to rail 132 and the emitter of which is connected to a rail 136.

Rail 136 is connected through a resistor R80 to the anode of a diode D31,the cathode of which is connected through a capacitor C21 to rail 130. The common point of diode D31 and capacitor C2l is connected through a resistor R81 to the collector of an n.p.n. transistor T27, the emitter of which is connected to rail 130 and the base of which is connected through a resistor R82 to the common point of resistors R78 and R79.

The rail 136 is also connected through a resistor R38 and a capacitor C22 connected in series to rail 130, the common point of resistor R83 and capacitor C22 being connected to the cathode of a diode D32, the anode of which is connected to the common point of resistor R80 and diode D31. The common point of resistor R83 and capacitor C22 is also connected to the emitter of a unijunction transistor T22, the second base of which is connected through a resistor R84 to rail 136 and the first base of which is connected through a resistor R85 to rail 130. Rail 136 is also connected to the anode of a diode D33, the cathode of which is connected to a rail 138 and also through a smoothing capacitor C23 to rail 130. The cathode of diode D33 is also connected to the cathode of a diode D34, the anode of which is connected to the cathode of diode D31.

Rail 138 is connected through a resistor R86 to the collector of an n.p.n. transistor T23, the emitter of which is connected to rail 130 and the base of which is connected through a resistor R87 to the first base of transistor T22. The collector of transistor T23 is connected through a capacitor C24 and a resistor R88, connected in series, to rail 130, and the common point of capacitor C24 and resistor R88 is connected to the cathode of a diode D35.

Rail 138 is connected through a resistor R89, to the anode of a diode D36, the cathode of which is con nected through a resistor R90 to rail 130. The cathode of D36 is also connected to the base of an n.p.n. transistor T24, the emitter of which is con nected to rail 130 and the collector of which is con nected through a resistor R91 to rail 138. The collector of transistor T24 is also connected through a resistor R92 to the base of an n.p.n. transistor T28, the emitter of which is connected to rail 130 and the collector of which is connected through a resistor R93 to rail 138. The collector of transistor T25 is also connected through a capacitor C25 to the anode of diode D36.

In use, resistor R89, diode D36 resistor R90, resistor R91, transistor T24, resistor R92 resistor R93, transistor T28, and capacitor C25 function as a monostable 140, the input to the monostable comprising the anode of diode D36 and being connected to the anode of diode 35 and the output comprising the collector of transistor T24.

The output of monostable 140 is connected through a resistor R94 to the base of an n.p.n. transistor T26, the emitter of which is connected to rail 130 and the collector of which is connected through a resistor R95, and the primary winding of the transformer TX5, connected in series, to rail 138. The primary winding is bridged by a freewheel diode D37. The transformer TX5 has a pair of secondary windings, one of which is bridged by a resistor R96 and the other of which is bridged by a resistor R97. One end of resistor R96 is connected to the anode of a diode D38, the cathode of which is connected through a resistor R98 to the gate of thyristor SCR2 shown in Figure 1, and the other end of resistor R96 is connected to the cathode of thyristor SCR2.One end of resistor R97 is connected to the anode of a diode D39, the cathode of which is connected through a resistor R99 to the gate of thyristor SCR1, and the other end of resistor R97 is connected to the cathode of thyristor SCR1.

The operation of the current regulating system will now be described.

During each half cycle of the mains power supply, the capacitor C22 is charged through resistor R83 until the intrinsic stand off voltage of uni-junction transistor T22 is reached, at which stage capacitor C22 discharges through resistor R85 and thereby applied a pulse to the base oftransistor T23. Transistor T23 is thereby rendered conductive and conse quentlytriggers monostable 140 and the output of monostable 140 is amplified by transistor T26 thereby energising the primary winding of transformer TX5.

This results in a pulse being developed in each of the two secondary windings of transformer TX5 and these pulses are transmitted to thyristors SCR1 and SCR2, with the result that the forward biassed thyristor conducts and permits charging current to be supplied to the traction battery 18. During the remainder of the half cycle, the transistor T22 will continue to fire periodically but as the forward biassed thyristor is now conducting, this will be of no consequence.

At the end of each half cycle, the capacitor C22 will be set to the voltage of capacitor C21, and this voltage will determine the delay which occurs before one of the thyristors is fired, and consequently the value of the current charging the traction battery 18.

As explained above, the value of the charging current is sensed by the transformerTX2 and, by way of a feedback loop consisting of resistor R71, the potential dividing chain comprising resistors R72 to R75, transistor T25, and transistor T21 controls the voltage of capacitor C21. The value of the charging cur rent may be set to a predetermined value by the potential dividing chain. If the charging current rises above the predetermined value, then the voltage across capacitor C21 will fall and consequently the delay period before firing occurs in each half cycle will be increased and if the current falls below the predetermined value, then the voltage across capacitor C21 will rise and consequently the delay period in each half cycle before firing occurs will be decreased.

In the present example, when both relays 42 and 44 are not energised, the predetermined value is 30 amps, when relay 42 only is energised, the charging current is 20 amps, and when relay 44 is energised, the charging current is 10 amps.

The overall operation of the system will now be described.

The operation of the system during each charging cycle is summarised in the table given below. Each charging cycle consists of five phases. During phase 1, the traction battery is charged at 30 amps and this phase is terminated when the traction battery reaches a predetermined voltage or when a predetermined period of time has elapsed. During phase 2, the traction battery 18 is charged at a current of 20 amps and this phase is terminated when the traction battery 18 reaches a predetermined voltage or when a predetermined period of time has elapsed. During phase 3, traction battery 18 is charged at 1 q amps and this phase is terminated after a predetermined period of time. In phase 4, there is no charging but fan 24 is energised for a predetermined period of time.At the commencement of phase 5, fan 24 is de-energised and the traction battery 18 should then be fully charged and ready for use. During phase 5, in order to maintain the battery 18 in its fully charged state, at periodic intervals it is charged for a 15 minute period at a current of 10 amps. The fan 24 is also maintained energised at the end of each 15 minute charging period for a further period of 15 minutes. The detailed operation of the system during these 5 phases will now be described.

The first phase commences when plug 14 is connected to socket 16 thereby energising fan 24 and also closing contacts 30a, 30b so that the rectifying section 10 is energised. Also, when the plug 14 is connected to the socket 16, capacitor C14 shown in Figure 5 is charged thereby applying a positive going signal to the +TR terminal of monostable 84. This produces a positive going pulse at the Q outputter- minal and a negative going pulse at the Terminal of monostable 84. The positive going pulse causes flip-flop JKA to be set and flip-flops JKB to JKH to be reset and the negative going pulse causes divider 72 and counters 74 and 76 to be reset. Flip-flop JKA applied a positive signal to count data circuit so that counters 74 and 76 will count 14 pulses from divider 72 before a negative going pulse is produced at the CARRY OUT terminal (Q) of counter 76. During phase 1 the first phase lamp LA3 is energised and, as both contacts 42b and 44b in Figure 6 are closed, the traction battery 18 is charged at 30 amps.

Phase 1 terminates when either the fraction of the voltage of traction battery 18 applied to the non invert terminal of amplifier Al exceeds the reference voltage applied to the non-invert terminal, or when counters 74 and 76 have counted 14 pulses from divider 72. If the voltage applied to the invert termi nal of amplifier Al exceeds the voltage supplied to the invertterminal, then the output will go high, thereby energising photodiode D12, rendering trans istor T20 conductive and consequently transistor T21 non-conductive, thereby producing a positive signal at the common point of resistor R51 and zener diode ZD6 which is applied to one of the inputs of NAND gate 98, and thereby applying a positive going pulse to the +TRIGGER input terminal of monostable 80.

If counters 74 and 76 count 14 pulses from divider 72, then a negative going pulse is produced atthe CARRY OUT terminal of counter 76, thereby causing NAND gate 100 to apply a positive going pulse to the +TRIGGER input terminal of monostable 80. Monostable 80 then produces a negative going pulse at its Q output terminal thereby causing divider 72 and counters 74 and 76 to be reset and causing NAND gate 104 to apply a positive going pulse to the CLOCK input terminal of flip-flops JKA to JKE JKG and JKH. Phase two then commences.

At the beginning of phase 2, flip-flop JKB is set thereby supplying a positive signal to the count data circuit 86 and it also supplied a positive signal to the base of transistor T4 so that relay 42 is energised.

Count data circuit 86 is supplied with data at its input terminals so that counters 74 and 76 now count 4 pulses from divider 72 before the output of counter 76 goes low. As relay 42 is energised, wiper arm 42a is displaced so that the second phase lamp LA4 is energised, contacts 42b in the current regulating section are opened so that the battery 18 is charged at 20 amps, and contacts 42c in the voltage comparison section are opened thereby reducing the fraction of the voltage of traction battery 18 which is supplied to the non-invert terminal of amplifier Al.As in phase 1, phase 2 terminates when eitherthe output of amplifier Al goes high or when the output of counter 76 goes low, thereby resetting divider 72 and counters 74 and 76 and also supplying a positive pulse to the CLOCK inputterminal of flip-flops JKA to JKE, JKG, and JKH.

If the output of amplifier A1 goes high during either phase 1 or phase 2, then a positive pulse will be supplied to the gate of thyristor SCR3, thereby energising relay 50 and closing contacts 50a, and consequently supplying current to one of the terminals of contacts 52a.

At the beginning of phase 3, flip-flops JKC and JKF are set. As JKC is set, it supplied a positive signal to the count data circuit 86 and relay 44 is energised.

Count data circuit is supplied with data at its input terminals so that counters 74 and 76 now count 9 pulses from divider 72 before the output of counter 76 goes low. As relay 44 is energised, wiper arm 44a is displaced so that the third phase lamp LA5 is energised, and contacts 44b of the current regulating section are opened so that the battery 18 is charges at a current of lamps. As flip-flop JKF is set, the signal at its 0 output terminal goes low thereby disenabling NAND.gate 98 and so rendering the control and timing section non-responsive to the output of the voltage comparison section.The third phase terminates when the output from counter 76 goes low thereby resetting divider 72 and counter 74 and 76 and supplying a positive pulse to the CLOCK input terminal ofJKflip-flops JKAto JKE and JKG and JKH.

At the beginning of phase 4, flip-flops JKD and JKG are set. As flip-flop JKD is set, it supplies a positive signal to the count data circuit 86 which is supplies with data at its input terminals so the counters 74 and 76 now count only one pulse from divider 72 before the output of counter 76 goes low. As flip-flop JKG is set, relay 46 is energised, with the result that contacts 46a are opened thereby disconnecting the main supply power from the rectifying section 10 and preventing the battery 18 from being charged, and wiper arm 46b is displaced so that the fourth phase lamp LA6 is energised.

Phase 4 terminates when the output of counter76 goes low thereby applying a positive pulse to the CLOCK input terminals of flip-flops JKA to JKE, JKG and JKH.

At the beginning of phase 5, flip-flops JKE and JKH are set. As flip-flop JKE is set, the signal at its 0 output terminal will be low with the result that a low signal will be supplied to one input of NAND gate 104, thereby preventing further pulses being supplied to the CLOCK input terminals of the flip-flops, and with the result that relay 48 will be energised, contacts 48a, will be opened, and consequently fan 24 will be de-energised. As flip-flop JKH is set, relay 52 will be energised, with the resu It that contacts 52a will be closed, thereby energising the ready lamp LA7 providing contacts 50a are closed. Also, as JKH is set, the signal supplied to the PRESET ENABLE terminal (PE) of counter 78 will be low with the result that counter 78 will be enabled.

As counter 78 is a decade counter, at every tenth pulse produced by divider 72 the signal produced at the CARY OUTterminal (Q) of counter 78 will go low and will stay low until the next pulse is received 30 minutes later. Also, for the first half of this 30 minute period, the output signal produced at the output terminal (Q) of divider 72 will be high and forth second half of this 30 minute period it will be low.

Consequently, during the first 15 minute period, relay 44 will be energised and relay 46 and 48 will be de-energised with the resu It that the traction battery 18 will be charged at a current of 10 amps, fan 24 will be energised, and the third phase lamp LA5 will be energised, and during the second 15 minute period relay 44 and 46 will be energised, with the result that fan 24 will be energised, the fourth phase lamp LA6 will be energised, and the mains power supply will be disconnected from the rectifying section 10.

Afully discharged traction battery may be charged at a relatively high currentforthe first part of its recharging but this current must be reduced as charging is continued as otherwise there is danger that excessive gassing may occur. As outlined above, in the present system, the battery is charged at 30 amps for the first phase, 20 amps for the second phase and 10 amps for the third phase. By providing that the first phase is terminated if the battery voltage exceeds a first predetermined value, and that the second phase is also terminated if the bat tery voltage exceeds a second and higher predetermined value, it is ensured that if an only partially discharged battery is being recharged the charging system will move quickly into the second or even the third phase as may be appropriate.

Also when charging a traction battery, if the temperature of the electrolyte varies, the internal resistance of the battery and consequently the battery voltage also varies. In order to compensate for this in the present system, the reference voltage is varied with the temperature of the electrolyte and thereby avoiding overcharging or undercharging the battery.

For maximum battery life it is important that the battery should be correctly charged and it is also importans to avoid overcharging as this leads to excessive gassing.

Although in the system herein described the probe 26 causes the reference voltage which is supplied to the invert input of amplifier Al to vary, it could alternatively be arranged for the fraction of the battery voltage which is supplied to the non-invert input of amplifier Al to vary.

The present system includes a number of safety features as will now be described.

If a charging system is connected to a source of mains electricity, and the plug 14 and socket 16 are not connected, then relay 30 will not be energised and consequently none of the pins of plug 14 will be live.

If plug 14 and socket 16 are connected, but the mains electricity is not connected, the relay 36 will not be energised, and consequently the output pulses produced by clock 70 will not be delivered to divider 72.

If at any stage during charging, the voltage of the auxiliary battery 20 falls below a certain predetermined voltage, then zener diode ZD1, shown in Figure 2, will cease to conduct, and consequently relay 40 will be de-energised, and so contacts 30a and 30b will open thereby preventing further charging from taking place. It is arranged that zener diode ZD1 ceases to conduct before the voltage of auxiliary battery 20 has fallen below a value at which the integrated circuits cease to operate.

If for some reason fan 24 does not work, for example due to a fuse failure, then relay 34 will not be energised, and consequently contacts 34a will not close, relay 40 will not be energised, and consequently charging will not take place. Therefore, there is no danger of charging taking place when the traction battery 18 is not being ventilated by the fan 24.

If, during phases 1 and 2, an open circuit occurs between probe 26 and the voltage comparison section, then the output of amplifier A2 will go high, unijunction transistor T1 2 will be repeatedly charged and discharged, and consequently the charging cycle will proceed to phase 3. Thus, there is no danger of the charging cycle proceeding in either phase 1 or phase 2 after such a failure.

Finally, if at any stage of the charging cycle, excessive gassing occurs, then one of the pressure switches 22 will open, thereby de-energising relay 40, and preventing further charging from taking place until the excessive gassing has ceased.

TABLE OF OPERATION CYCLE PHASE 1 2 3 4 5 FUNCTION 30ACHARGE 20ACHARGE 10CHARGE FAN NONE 10ACHARGE FAN TERMINATION CONDITION VOLTS OR TIME VOLTSORTIME TIME TIME TIME TIME TIME QA 1 0 0 0 0 0 0 Os O 1 0 0 0 0 0 Os 1 0 1 1 1 1 1 OC 0 0 1 0 0 0 0 OC 1 1 o 1 1 1 1 OD 0 0 0 1 0 0 0 Os 1 1 1 1 0 0 0 OF 1 1 0 0 0 0 0 DO 1 1 1 0 0 0 0 OH 1 1 1 1 0 0 0 42 (20A) OFF ON OFF OFF OFF OFF OFF 44(10A) OFF OFF ON OFF OFF ON ON 46 (Charge) OFF OFF OFF ON ON OFF ON 48 (Fan) OFF OFF OFF OFF ON OFF OFF 52 (Ready Lamp) OFF OFF OFF OFF ON ON ON LA3 (Phase 1) ON OFF OFF OFF OFF OFF OFF LA4 (Phase 2) OFF ON OFF OFF OFF OFF OFF LA5 (Phase 3) OFF OFF ON OFF OFF ON OFF LA6 (Phase 4) OFF OFF OFF ON OFF OFF ON

Claims (15)

1. A traction battery charging system comprising a traction battery, means for supplying current to the traction battery, means for regulating the current supplied to the battery, means for comparing the battery voltage with a reference voltage, means for timing the charging, and means responsive to the comparing means and the timing means for automatically controlling each charging cycle, each charging cycle including a first charging phase in which the battery is charged at a first rate of charging, the first charging phase being terminated when the battery voltage exceeds a first predetermined value, a second charging phase in which the battery is charged at a second rate of charging, the second phase being terminated when either the battery voltage exceeds a second predetermined value or when a predetermined period has elapsed, whichever occurs first, the second predetermined voltage being equal to or greater than the first mentioned voltage.

2. A system as claimed in claim 1 in which the first charging phase is terminated if a predetermined period elapses before the first predetermined voltage is exceeded.

3. A system as claimed in claim 1 or claim 2 in which the charging cycle includes a third charging phase in which the battery is charged at a third rate of charging for a predetermined period.

4. A system according to any one of the preceding claims in which during each phase the battery is charged at a current which is constantforthe whole of the phase, the constant current value during the second phase being less than or equal to the value for the first phase.

5. A system according to any one of the preceding claims in which the charging cycle includes a ready phase in which the battery is charged for a predetermined period at predetermined intervals.

6. Atraction battery charging system comprising a traction battery, means for supplying current to the traction battery, means for regulating the current supplied to the battery, means for comparing the battery voltage or a fraction of the battery voltage with a reference voltage, either the fraction of the battery voltage or the reference voltage being varied in accordance with the temperature of the battery electrolyte, means for timing the charging, and means responsive to the comparing means and the timing means for automatically controlling each charging cycle, each charging cycle including a phase in which the battery is charged at a first charging rate until the battery voltage exceeds a predetermined value.

7. A system according to claim 6 in which the reference voltage is reduced as the temperature of the battery electrolyte rises and is increased at the temperature of the battery electrolyte falls.

8. A system according to claim 7 in which the reference voltage is established by a probe positioned in the battery electrolyte.

9. A system according to claim 8 in which the charging system includes at least one phase which is terminated when the battery voltage exceeds a predetermined value followed by at least one phase terminated after a predetermined period has elapsed, and which further includes means for detecting an open circuit between the probe and the comparing means, the charging cycle jumping to said phase terminated after a predetermined period upon detection of such as open circuit.

10. Atraction battery charging comprising a traction battery, means for restricting the flow of gas out of the battery, means responsive to the pressure of gas upstream of the restricting means, means for supplying current to the battery, means for regulating the current supplied to the battery, means controlled by the pressure responsive means for interrupting the supply of current to the battery if the pressure rises above a first predetermined value until the pressure falls below a second predetermined value, means for comparing the battery voltage with a reference voltage, means for timing the charging and means responsive to the timing means and the voltage comparing means for automatically controlling each charging cycle.

11. A system according to any one of the preced ing claims in which the supplying means includes a plug which is connectable with a socket connected to the battery for supplying current to the battery, and in which the system includes means for sensing when the plug and socket are connected, the plug being supplied with current only when the plug and socket are connected.

12. A system according to to any one of the pre ceding claims including means for sensing when mains power is being supplied to the system, the timing means being disenabled in the absence of mains power supply.

13. A system according to any of the preceding claims in which the timing means and controlling means have their own power supply and including means for detecting when the voltage of said power supply falls below a predetermined value, the current supply to the battery being interrupted upon detection of such a voltage fall.

14. A system according to any of the preceding claims including fan means for ventilating the battery, and means for detecting failure of the fans means, the current supply to the battery being interrupted upon detecting such a failure.

15. A battery charging system substantially as hereinbefore described with reference to and as described in the accompanying drawings.