Patent GB-1480052-A (GB)
Title: Electrically driven vehicles
IPC: B60L3/00
Filed: 1973-06-30
Abstract: 1480052 Control of D.C. motors LUCAS INDUSTRIES Ltd 11 June 1974 [30 June 1973 (3)] 31302/73 31304/73 and 31305/73 Heading H2J The motor control system described with reference to Figs. 1 to 4 of Specification 1,480,064 is provided with means to ensure that, when the driver of the vehicle changes from one operating mode to another, the appropriate contactor devices will be energized and de-energized only when the motor current is below a predetermined value. As shown in Fig. 5, the forward, reverse and brake contactor devices F, R, B are energized through contacts 55 responsive to the motor current to be closed or open when it is above or below a predetermined value. The devices F, B, R control auxiliary contacts F2, F3; B2, B3 and R2, the accelerator pedal opens contacts 39 and closes contacts 48, 52 when it is depressed, the brake pedal closes contacts 49 when it is depressed and contacts 34 open when the vehicle speed exceeds a predetermined low value. Thus movement of a selector switch 47 to the forward drive position, with the vehicle at rest, causes transistor 44 to switch on in series with thyristor 43, which is supplied with gate current, together with thyristor 64, because of the closed state of contacts 34, 39. Subsequent depression of the accelerator pedal closes contacts 48 to energize the device F and opens contacts 39, but thyristor 43 continues to conduct. When the motor current exceeds the predetermined value, the contacts 55 close to complete a self-hold circuit for device F through contacts F2. Return of switch 47 to its central "off" position turns off members 43, 44, but device F is not de-energized until contacts 55 open. After this none of the devices F, B, R can be energized until both contacts 34, 39 are closed. If switch 47 is left in its forward position and the accelerator pedal is released and the brake pedal depressed, members 43, 44 remain on although contacts 48 open, but device B cannot be energized until contacts 55 open to de-energize device F and allow contacts F3 to close. A reverse sequence of operations occurs when the brake pedal is released and the accelerator pedal depressed. If switch 47 is moved to its reverse drive position during forward movement of the vehicle, transistor 51 turns on, members 43, 44 turn off and device F or B is subsequently de-energized by the contacts 55. When the speed falls below the predetermined low value thyristor 64 is fired, if the accelerator pedal is not depressed to open co tacts 39, and the device R is energized. If there is a likelihood that the speed will fall below the predetermined value before the motor current falls below its predetermined value, further contacts controlled by devices F, B are inserted in series with transistor 51 to make the energization of device R also dependent on the deenergization of devices F, B. A reverse sequence of operations occurs when switch 47 is moved from the reverse to the forward drive position, further safety being provided, if desired, by connecting extra auxiliary contacts of device R in the collector circuit of transistor 44, to ensure that thyristor 43 cannot be fired until device R is de-energized. The circuit of Fig. 5 may be depicted in logic form, Fig. 6 (not shown) and its operation correspondingly analysed.