A pump operation piston biased by a neutral spring mechanism and a larger volume operation spring biased by a larger volume operation spring in a larger volume direction operatively move pump and motor volume adjusting members, respectively, is provided. A first pressure control valve commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction and the motor operation piston in a smaller volume direction. A second pressure control valve controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction. Biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after the pump operation piston is moved in the first slide direction by a predetermined distance, the motor operation piston starts moving.

In ore aspect, a method is provided or braking a work vehicle including an engine and a hydrostatic drive system including a hydraulic pump configured to be rotationally driven by the engine and a hydraulic motor fluidly coupled with the hydraulic pump through a closed hydraulic loop of the hydrostatic drive system. The hydraulic pump may be configured to fluidly drive the hydraulic motor. The method may include receiving an operator request to reduce a ground speed of the work vehicle. The method may include monitoring a fluid temperature of a hydraulic fluid associated with the closed hydraulic loop and automatically controlling at least one of a pump displacement of the hydraulic pump or a motor displacement of the hydraulic motor based on the operator request and the monitored fluid temperature to adjust hydrostatic braking of the work vehicle and thereby reduce the ground speed of the work vehicle.

In ore aspect, a method is provided or braking a work vehicle including an engine and a hydrostatic drive system including a hydraulic pump configured to be rotationally driven by the engine and a hydraulic motor fluidly coupled with the hydraulic pump through a closed hydraulic loop of the hydrostatic drive system. The hydraulic pump may be configured to fluidly drive the hydraulic motor. The method may include receiving an operator request to reduce a ground speed of the work vehicle. The method may include monitoring a fluid temperature of a hydraulic fluid associated with the closed hydraulic loop and automatically controlling at least one of a pump displacement of the hydraulic pump or a motor displacement of the hydraulic motor based on the operator request and the monitored fluid temperature to adjust hydrostatic braking of the work vehicle and thereby reduce the ground speed of the work vehicle.

A HST system for use in traveling of a vehicle includes a controller that controls a pump regulator that changes a displacement of a pump and a motor regulator that changes a displacement of a motor. The controller determines whether or not a particular downhill travel condition is satisfied based on a result of detection by a vehicle speed detector that detects a vehicle speed of the vehicle and a result of detection by a rotation number detector that detects a number of rotations of an engine per unit time. In a case where a depression amount of an accelerator pedal, which is detected by a depression amount detector, is zero and the particular downhill travel condition is satisfied, the controller controls the motor regulator to increase the displacement of the motor.

A transmission structure of the present invention causes, during a period from a time point when a rotational speed of a drive rotational power reaches a predetermined first/second speed stage shift-up start speed until a first/second speed stage shift-up end time point, one of an input-side clutch mechanism pair and an output-side clutch mechanism pair to be in a double transmitting state, and causes, in the double transmitting state, a first clutch mechanism and a second clutch mechanism of the other one of the input-side clutch mechanism pair and the output-side clutch mechanism pair to be shifted to a disengagement sate and an engagement state, respectively, while having frictional plate slid.

A hydrostatic traction drive includes a hydrostatic pump and a hydrostatic motor connected to each other in an open circuit. One of the pump and motor is pressure-regulated while the other is torque-controlled or regulated in terms of pivot angle. A braking mode is therefore possible in which the secondary-side braking torque can be adapted to the permissible primary-side supporting torque of a primary machine coupled to the pump. To further increase the braking power, even in a high rotational phase of the primary machine, the permissible drag torque thereof can be temporarily exceeded. To further increase the braking power and therefore to have high-performance braking during operation, further means for converting energy can be provided in order to adjust a secondary-side braking torque and a primary-side supporting torque independently of each other.

A closed-loop hydraulic circuit associated with a swing mechanism of a machine is controlled to obtain both a pressure control during acceleration and deceleration of the swing mechanism and a velocity control during coasting. In this manner, a system pressure in closed-loop hydraulic circuit is maintained below a maximum allowable pressure during acceleration and deceleration, and the swing mechanism can be rotated at a desired constant speed during coasting. This is achieved by controlling a hydraulic actuator adjusting the displacement of a variable displacement pump in different control modes, depending on a comparison between a desired displacement of the pump and an actual displacement of the same.

A closed-loop hydraulic circuit associated with a swing mechanism of a machine is controlled to obtain both a pressure control during acceleration and deceleration of the swing mechanism and a velocity control during coasting. In this manner, a system pressure in closed-loop hydraulic circuit is maintained below a maximum allowable pressure during acceleration and deceleration, and the swing mechanism can be rotated at a desired constant speed during coasting. This is achieved by controlling a hydraulic actuator adjusting the displacement of a variable displacement pump in different control modes, depending on a comparison between a desired displacement of the pump and an actual displacement of the same.

The invention relates to a self-propelled construction machine, in particular a road milling machine, stabiliser, recycler or surface miner, which has a machine frame 2 supported by at least three running gears 10A, 10B, 11A, 11B, a drive device 14 for driving at least two running gears, and a work roller 4 arranged on the machine frame. The invention also relates to a method for controlling a construction machine of this kind. The drive device 14 comprises adjustable hydraulic motors 15, 16, 17, 18 associated with the drivable running gears, which hydraulic motors have a displacement volume Vg that can be varied by an adjusting device 15A, 16A, 17A, 18A, and comprises at least one adjustable travel drive-hydraulic pump 19 driven by at least one drive motor to supply the hydraulic motors with a variable total volume flow Q of hydraulic fluid. In addition, a controller 28 is provided which is configured in such a way that a partial volume flow Q.sub.1, Q.sub.2, Q.sub.3, Q.sub.4 is determined for each adjustable hydraulic motor 15, 16, 17, 18 from the total volume flow Q provided by the at least one travel drive-hydraulic pump 19, by means of which partial volume flow the particular hydraulic motor is to be operated, and when the speed n of an adjustable hydraulic motor increases as a result of slippage of the running gear associated with the adjustable hydraulic motor, the adjusting device of the adjustable hydraulic motor is controlled in such a way that a displacement volume Vg is set for the adjustable hydraulic motor, at which displacement volume the partial volume flow determined for the adjustable hydraulic motor is maintained. The self-propelled construction machine according to the invention is characterised in that a hydraulic flow divider is not required.

When an inclination angle is greater than or equal to a first threshold, a controller determines a displacement of a hydraulic pump from a command vehicle speed based on second pump data and determines a displacement of a hydraulic motor from the command vehicle speed based on second motor data. The second pump data defines the displacement of the hydraulic pump that is smaller than that of first pump data with respect to the command vehicle speed. The second motor data defines the displacement of the hydraulic motor that is smaller than that of first motor data with respect to the command vehicle speed.