A hydraulic system is provided to selectively and independently route pressurized fluid to one or more operational systems of a machine. The hydraulic system is capable of switching fluid flow in operation from one of the operational systems to another of the operational systems in the event of hydraulic drive power being required by the latter one of the operational systems. The hydraulic system is also configured to continue supplying a nominal amount of fluid to support one or more auxiliary functions, for example, a lubrication system for bearings associated with the former one of the operational systems while routing the pressurized fluid to the latter one of the operational systems. A recirculation and anti-cavitation arrangement is also provided to allow recirculation of fluid to a hydraulic motor in the former one of the operational systems when pressurized fluid is being routed to the latter one of the operational systems.

A control system that uses an algorithm to control the fan speed in a cooling system for an engine is disclosed. The algorithm is adapted to maintain a cooling medium at a set temperature instead of an operating temperature range of the cooling medium. The algorithm is also adapted to maintain a cooling medium at a set temperature and to build a cooling safety margin in response to an engine output torque percentage that is below an output torque percentage setpoint.

A fan drive device for use with a hydraulic pump featuring a constant displacement volume is disclosed. The fan drive device includes a hydraulic motor configured to be directly coupled to a fan. The hydraulic motor includes a first working connection, a second working connection, and a constant displacement volume. The fan drive device further includes a hydraulic valve having a pump connection and a tank connection. The hydraulic valve includes two fluid connections, each of which can be fluidically connected to the hydraulic motor. The hydraulic valve is designed as a proportional valve including a continuously adjustable control piston proportional to a control current of the hydraulic valve as the sole control mechanism for controlling the fan speed.

A transportation vehicle includes: a cooling fan that is driven by a hydraulic motor; a heat exchanger that is disposed in a front portion of a vehicle body; a fan control valve that controls a flow of a hydraulic operating fluid supplied to the hydraulic motor; a cylinder control valve that controls a flow of the hydraulic operating fluid supplied to a hydraulic cylinder; and a controller. The fan control valve and the cylinder control valve are connected in tandem to a center bypass line. The fan control valve has a neutral position that makes a first hydraulic pump and the cylinder control valve communicate with each other and makes a suction port and a delivery port of the hydraulic motor and a hydraulic operating fluid tank communicate with each other, and a rotation position that makes the first hydraulic pump and the suction port of the hydraulic motor communicate with each other and makes the delivery port of the hydraulic motor and the hydraulic operating fluid tank communicate with each other.