Closed loop drive circuit with external brake assist

摘要

A hydrostatic drive system for a vehicle (10) comprises an open circuit (100), a closed travel circuit (120), an electronic controller (320), and a main variable displacement hydraulic pump (102) driven by an internal combustion engine (12) equipped with a speed sensor (350). The main variable displacement hydraulic pump may be configured to supply hydraulic fluid to a hydraulic consumer (34, 44, 50) via a hydraulic supply line (106). A pressure relief valve (118) may be connected to a reservoir (300) and may be permanently connected to the hydraulic supply line of the open circuit. The electronic controller may be configured to run a strong braking mode in which the electronic controller at least partially increases the displacement of the main variable displacement hydraulic pump such that hydraulic fluid is discharged via the permanently connected pressure relief valve into the reservoir if the sensed engine speed is higher than a predetermined maximum engine speed.

主权项

1. A hydrostatic drive system for a vehicle, comprising:
an open circuit including:
a main variable displacement hydraulic pump configured to be driven by an internal combustion engine equipped with a speed sensor, the main variable displacement hydraulic pump being configured to supply hydraulic fluid to at least one hydraulic consumer via a hydraulic supply line, anda pressure relief valve connected to a reservoir, the pressure relief valve being connected to the hydraulic supply line such that hydraulic fluid in the hydraulic supply line is discharged into the reservoir if a preset maximum operation pressure is reached in the open circuit; a closed circuit configured to propel the vehicle including:
an auxiliary variable displacement hydraulic pump configured to be driven by the internal combustion engine and to propel the vehicle, anda hydraulic motor connected to the auxiliary variable displacement hydraulic pump; and an electronic controller connected to the speed sensor and the main variable displacement hydraulic pump, the electronic controller being configured to run a strong braking mode in which the electronic controller at least partially increases the displacement of the main variable displacement hydraulic pump such that hydraulic fluid is discharged via the pressure relief valve into the reservoir if an engine speed is determined, based on a signal received from the speed sensor, which is higher than a predetermined maximum engine speed, wherein the electronic controller is configured to control the displacement of the main variable displacement hydraulic pump by increasing and decreasing the displacement during the strong braking mode such that the engine speed varies within a predetermined engine speed range including the predetermined maximum engine speed, and wherein the electronic controller is additionally configured to control at least one of the displacement of the auxiliary variable displacement hydraulic pump and a displacement of the hydraulic motor by increasing and decreasing the displacements during the strong braking mode such that the engine speed varies within a predetermined engine speed range including the predetermined maximum engine speed.