Downshift arrest device e.g. for dredging machine transmission

摘要

The transmission has a manual selector valve (30) to switch the transmission to one of two settings. A solenoid valve (34) between the manual control valve and the transmission is set in either the open position or the protected position, with the latter only permitting gear setting into the higher ratio. This higher ratio is maintained irrespective of the setting of the manual control if the engine speed is above a preset level. The control system has monitors for the vehicle speed, engine speed and gear settings. The engine speed is converted into a signal level which is compared with a reference signal level to generate high and low control signals. A simple logic control system operates the solenoid valve to prevent transmission damage by premature downshift.