Control apparatus for drive transmissions.

摘要

Control apparatus for a drive transmission of a low speed vehicle such as the hydraulic drive transmission of a fork lift truck is provided in which an electrical signal is developed having a frequency representative of the rate of rotation of the drive shaft of the transmission. In order to provide control at very low speeds, instead of utilizing streams of pulses to control changes of gear, the times between successive pulses are sensed. A first switching circuit (SCR1, D5, D6, RL1) remains in one state during each cycle of the said signal which is less than a predetermined duration, and can be set in another state thereof by actuation of a manually operable direction switch (65), serving as a forward-reverse drive selector, when the duration is greater than the said predetermined duration. The direction switch (65) is settable to select an electrical actuator (FWD) for forward drive and settable to select an electrical actuator (REV) for reverse drive. The first switching circuit (SCR1, D5, D6, RL2) is such that the said other state thereof enables setting of the direction switch (65) to effect energization of the electrical actuator (FWD or REV) selected by the setting of the direction switch (65). A second switching circuit (RL2) is set one state thereof whenever the duration of a cycle of the said signal falls below a second predetermined duration, and sets in another state thereof when the duration increases to exceed a third pre-determined duration. The second switching circuit(RL2)effects energisation of a low gear ratio electrical actuator (LO) or a high gear ratio electrical actuator (HI) respectively depending upon which one of the said two states of the second switching means (RL2) prevails.

The said second and third durations differ from one another so that each change from energization of the low gear actuator to energization of the high gear actuator takes place when the said signal represents a higher rate of rotation than it does when each change for energization of the high gear actuator to energization of the low gear actuator takes place.