Transmission shift control. In order to provide as nearly as possible an automatically shifting transmission with the well-known advantages thereof, and yet to maintain basic operator control over same, with equally well-known advantages thereof, there is provided a transmission control which, when in an operator determined upshift mode, will automatically upshift to a ratio preselected by the operator but not beyond same nor will it while in such mode downshift regardless of load change, and which will when in an operator determined downshift mode, automatically downshift to a lower gear preselected by the operator but will not go beyond same nor will it while in such mode upshift regardless of load change. Thus, for example, in a road speed gear as load comes onto the vehicle such as by a minor grade or the appearance of a head wind, the vehicle speed may lug down but the transmission will not shift unless and until the operator permits same to happen by moving a gear selector to a lower speed position. Thus, the operator can determine by the nature of a load change whether or not a shift change should be permitted to take place and thereby minimize or eliminate unnecessary shifting in response to only minor changes in load.
An apparatus is provided for use in a vehicle having an engine driven transmission which includes a plurality of gear ratios. The apparatus includes a sensor adapted to sense a parameter indicative of vehicle speed and responsively produce a vehicle speed signal. A downshift switch is provided to controllably produce a downshift signal. An engine speed sensor senses engine speed and responsively produces an engine speed signal. A controller is adapted to receive the vehicle speed, engine speed, and downshift signals, process the vehicle speed signal to produce a transmission control signal, produce a down shift enable value as a function of the engine speed signal, and modify the transmission control signal to correspond to a lower gear ratio in all but the lowest gear ratio when the downshift signal is received and a value responsive to the vehicle speed signal is less than the down shift enable value signal. An actuator is adapted to receive the transmission control signal and responsively control the transmission gear ratio.
An automatic transmission control system couples frictional coupling element, such as a low reverse brake, so that the frictional coupling element provides different torque transmissive capacities in a reverse gear and a first gear in which engine braking is available. The system includes a pressure regulator which regulates a coupling pressure, by which the frictional coupling element is coupled and which is controlled and gradually supplied to the frictional coupling element, during a shifting of the automatic transmission to a reverse gear. The pressure regulator is disabled from regulating the coupling pressure in the reverse gear.
Control apparatus for a drive transmission 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. A first switching circuit is controlled in response to the said signal so as to remain in one state thereof during each cycle of the said signal when the duration of the cycle is less than a predetermined duration, and to be settable in another state thereof by actuation of a manually operable direction switch, serving as a forward-reverse drive selector lever, when the duration of the said cycle is greater than the said predetermined duration. A second switching circuit is so controlled in response to the said signal as to be set into one state thereof in response to a cycle of the said signal when the duration of the said cycle falls below a second predetermined duration, and to be set into another state thereof when the duration of the said cycle increases to exceed a third predetermined duration. The second switching circuit effects energization of a low gear ratio electrical actuator or a high gear ratio electrical actuator respectively depending upon which one of the said two states of the second switching means prevails.
A control system for automatic transmissions having a multiple stage transmission gear mechanism in which shift control is accomplished based on an automatic shift control mode or a holding mode wherein a higher gear stage is selected under the holding mode and when a predetermined driving condition is detected, a shift down control is carried out so as to obtain a desirable feeling in a reacceleration operation.
