A transmission having hydraulic components including a hydrostatic unit with a variable displacement component having a hydraulic displacement control with a lubrication circuit for the components and a charge circuit for supplying fluid under pressure. First and second pumps are connected in series, with the first pump having a larger volume than the second pump to provide fluid to the second pump and to a lubricating circuit. A fluid line connects between the charge circuit and the lubrication circuit and has a lubrication priority valve therein which operates to provide fluid flow from the charge circuit to the lubrication circuit when required to maintain pressure in the lubrication circuit. Additionally, the charge circuit has a pair of branch lines, with one branch line having a charge priority valve therein which functions to control the flow through the one branch line leading to the hydraulic displacement control for the hydrostatic unit and to thus provide pressure control in the other branch line. The charge priority valve additionally controls the pressure in said one branch line by modulating flow thereof relative to a drain port and also has provision for increasing pressure in the other branch line when the speed of the hydrostatic unit exceeds the overspeed rating thereof.
The problem of sealing a communication bore (56) in a port plate (40) is solved with a self-sealing transfer tube assembly (52). The transfer tube assembly (52) includes a coupling element (64) which is received in a supply bore (60) which intersects the communication bore (56). A relatively small window (78) is provided in the coupling element to provide hydraulic communication between the transfer tube assembly (52) and the port plate porting area (48), while its solid side wall (68) otherwise seals the outer portion of the communication bore (56).
A prioritizing method and arrangement for a hydraulic system including two independent hydraulic fluid supply units (4, 5) adapted to jointly and severally supply hydraulic fluid to at least two hydraulic components (2, 3). A cross-communication between the at lest two hydraulic components (2, 3) is controlled, with a flow of hydraulic fluid from one of the two hydraulic fluid supply units (5) being diverted to one of the at least two hydraulic components (3) to a substantial exclusion of the other of the at least two hydraulic components (2) in dependence upon an operating condition of the other of the two hydraulic fluid supplying units (5). A biasing force (F) acts upon the prioritizing arrangement so as to define an operating stage at which the respective hydraulic fluid supplying units (4, 5) exclusively supply hydraulic fluid to the respective ones of the at least two hydraulic units (2, 3).
A charge flow distribution valve routes all charge pump flow into a main pump until the main pump has sufficient inlet pressure. The valve opens to a first stage which routes excess charge flow to lubrication circuits. At a slightly higher main pump inlet pressure, it also routes oil to an inlet of the charge pump.
An improved hydraulic apparatus is disclosed having a hydraulic device (14) receiving conditioned hydraulic fluid directly from an inlet port (62) in a case (12) full of hydraulic fluid (16) with the conditioned hydraulic fluid having a characteristic which is better than the characteristic of the fluid within the case. The characteristic may be that the hydraulic fluid is cooled to a temperature below the temperature of the hydraulic fluid within the case, is filtered, or is deaerated. Cooled hydraulic fluid is supplied from a heat exchanger (58) in fluid communication between an outlet port of the case and the inlet port of the case to supply the hydraulic fluid contained within the case. The hydraulic fluid is filtered by a filter (54) external to the case. A deaerator (65) may be located in a fluid circuit external to the case between a scavenge pump (50) and the inlet port (67). Hydraulic fluid is pumped by a charge pump (26) to the input port (72) of the hydraulic device. Fluid line (74) connects the inlet port of the case to an input port of a charge pump so that cooled hydraulic fluid flows directly from the inlet port to the input port of the charge pump. The charge pump has a steady state flow rate of pumping hydraulic fluid to the hydraulic device which is less than a steady state rate at which cooled and filtered hydraulic fluid is supplied to the inlet port of the case which causes excess cooled hydraulic fluid to enter the case from the fluid line through interior case port (80).
A charge pressure priority valve for supplying a flow of sufficient pressure to energize an auxiliary implement while supplying a nearly constant pressure flow to a hydrostatic fluid circuit includes a valve body having an interior bore with a pump inlet passage for communicating a flow from a hydraulic pump thereto. A main flow outlet passage extends from the interior bore for supplying fluid to the hydraulic fluid circuit and has a main flow feedback passage interconnecting the main flow outlet passage and the interior bore. An auxiliary flow outlet passage extends from the interior bore for supplying a flow of sufficient pressure to energize an auxiliary implement. A valve spool is disposed within the interior bore and defines a central chamber intermediate a pair of spaced apart end chambers in the bore, with one of the pair of end chambers being isolated from the other of the pair of end chambers.
