Abstract: An electrical steering system for a vehicle includes an electrically supplied steering motor arrangement which is connected with an inverter arrangement, whose output voltage is influenced by a computer arrangement, and a sensor arrangement. To reduce the cost of the steering system while also allowing the steering system to be steerable during braking in the case of a fault, the steering motor arrangement has a redundant steering motor which is connected with the computer arrangement via two separately run control circuits. The control circuits have separate electric supplies and the computer arrangement is redundant.

Abstract: A hydrostatic steering arrangement with two control systems, each of which has a control unit with an inner and an outer rotary slide and a steering motor, one steering handwheel being common for both control units, and the control units being arranged in series in the axial direction of the rotary slides. On a failure of one control unit it is desired that the steering can be continued with a relatively high accuracy. For this purpose, a common inner rotary slide is provided for both control units.

Abstract: A hydraulic steering arrangement, having a steering value, which connects a steering motor with a pump, and which has a slide with two front sides, the slide being adjustable by means of a pressure fluid both through a hydraulic steering unit with a steering hand wheel and through an electro hydraulic steering unit with a control pressure generator. The two steering units have working connections and the front sides of the slide are connected with shuttle valves, each of which is connected with hydraulic steering unit on the one side and with the electro hydraulic steering unit on the other side. A valve arrangement connects the working connection of both steering units, which has the highest pressure, with one front side of the slide, and the working connection of both steering units, which has the lowest pressure, with the other front side of the slide.

Abstract: The invention relates to a method for hydraulic steering, particularly of vehicles, according to which a steering unit (5) is supplied, in dependence of a load signal, with a controlled working pressure from a load signal line (20), the load signal being generated via a load signal fluid with a fluid flow, and to a hydraulic steering arrangement (1) for carrying through this method.

Abstract: The invention concerns a hydraulic line connection with a supply connection (2) having a pressure line and a return line, each ending at a connection valve (4,5), and with a safety valve (8) in a line between the pressure line and a consumer (1), said safety valve having a valve element (9), whose one side is acted upon by the pressure at the pressure connection (P) with the purpose of opening. The aim is to safely provide a connection of this kind in a simple way. For this purpose the other side of the valve element (9) is directly connected with the return line.

Abstract: In a hydraulic vehicle drive which has a hydraulic circuit consisting of a variable displacement pump (2) and a hydraulic motor (10), the variable displacement pump (2) is driven by a diesel engine (1). During the braking or overrunning operation of the vehicle, the hydraulic motor becomes the pump and drives the variable displacement pump (2) which acts as a motor on the diesel engine (1) and attempts to accelerate the latter. The braking effect which is intended and obtained thereby involves the risk of the diesel engine (1) reaching impermissibly high rotational speeds. The braking therefore takes place in a controlled manner by a sequence valve (16) being arranged in the line (12) between the hydraulic motor (10) and the variable displacement pump (2). The sequence valve acts on the pivot angle of the variable displacement pump (2) via the pump bypass line (12B).

Abstract: The invention concerns a hydraulic valve arrangement with a control valve (3), which, in a first operating position (5), connects a motor connection (21) with a pump connection, in a second operating position (6), connects a motor connection with a tank connection, and, in a locking position (4), disconnects the motor connection (21) from the pump and tank connection. A locking valve (19) is coupled between the control valve (3) and the motor connection (21), dividing the motor line (22) into a first section (23) allocated to the control valve (3) and a second section (24) allocated to the motor connection (21). For the locking valve (19), a pressure release valve (20) in the shape of a seated valve is provided. The operating element (32) of said pressure release valve (20) is loaded in the closing direction by the pressure in the first section (23) and a spring (36) and in the opening direction by a constant control pressure (V) acting in dependence of the position of the control valve (3).

Abstract: A fluid pump has a housing (4), a main output port (10), an auxiliary output port (14) and a priority pressure regulating valve contained with the housing (4). The priority pressure regulating valve has a spool (20) to direct fluid to one or both of the of the output ports (10,14), a force means (34,36) associated with the spool to bias the spool (20) to a position where it causes fluid to flow to the main output port (10) exclusively, and a pressure release means (40) which enables the spool (20) to move to a position where it permits fluid to flow to the auxiliary output port (14) when the pressure at the main output port (10) is at or greater than a predetermined pressure.

Abstract: A loop flushing arrangement for controlling a closed circuit hydraulic propulsion drive. The variable displacement pump 12 is driven by a combustion engine 11. A flush valve 21 is used to clean and cool the hydraulic fluid in the closed hydraulic circuit. The flush valve is electrically operated and, as a result, permits novel and varied control options. The flush valve is controlled automatically, for example by a digital computer 1 as a function of the vehicle speed, the rotational speed of the combustion engine 11, or the temperature of the hydraulic fluid in the variable displacement pump 12. This results in the flushing procedure only being triggered and carried out if the operating state of the vehicle requires and permits it, i.e. when traveling at high speeds, for example.

Abstract: A hydromechanical transmission includes a hydrostatic transmission driven by an engine and drivingly connected to a planetary gear set. A plurality of clutches are associatable with the ring gear or elements of the planetary gear set for establishing a corresponding plurality of operating modes in which additional overall transmission speed can be achieved while reducing the power transmitted by the hydrostatic transmission. The gears of the planetary gear set can be removed and replaced with gears having a different number of teeth so as to change the overall ratio of the hydromechanical transmission without changing the power rating of the hydrostatic transmission or the size of the housing. Thus, multiple overall corner horsepower capabilities can be provided with the same hydrostatic transmission and housing package size.

Abstract: A hydraulic vehicle drive, having a closed hydraulic circuit consists of a variable displacement pump and one or several hydraulic motors. The variable displacement pump is driven by a diesel engine. During the braking or pushing operation of the vehicle, the hydraulic motor becomes a pump and drives the variable displacement pump which, in turn, acts as a motor upon the diesel engine and acts to accelerate the latter. Thus, the intended braking effect prevents the danger that the diesel engine will reach non-permissible high revolutions per unit time, which is particularly dangerous for diesel engines with turbochargers. In order to prevent non-permissible high revolutions per unit time, a pressure regulator acting as a throttle is placed in the return line between the hydraulic motor and the variable displacement pump. The valve throttles the rate of flow when the pressure of the hydraulic fluid in the line exceeds a certain desired value during the braking operation.

Abstract: A reduced oil volume piston assembly for a hydrostatic unit includes a piston assembly having a piston body and a stem formed separately from the piston body. A cavity is formed in one end of the piston body. The stem includes an enlarged head and an elongated neck extending upwardly from the head. The neck lossely inserts into the cavity of the piston body so as to at least partially fill the cavity. The head is unattached to the piston body and cannot enter the cavity, but its shape allows fluid flow into the cavity around the stem. These components can be incorporated into the cylinder block assembly as separate components or the stems can be integrally cast with the cylinder block or attached thereto as a stem ring assembly.

Abstract: A hydrostatic loop dump valve for reducing the starting torque required for a hydrostatic unit includes a normally biased open dump valve connecting one or more of the system pressure lines to the reservoir. The dump valve(s) will automatically open and oil will drain out by gravity when the engine is not running. When the engine turns the hydrostatic unit at sufficient speeds to generate significant charge pressure, the dump valves will close and the unit will operate as normal. Thus, the input torque required to start the engine and the hydrostatic unit is minimized without damaging the hydrostatic unit.

Abstract: A method for determining system parameters, such as the operating speed, working pressure and pivot angle of an axial piston unit in which the operating speed, working pressure and pivot angle are determined by means of a frequency analysis of a detected solid-borne sound signal from an axial piston unit of a hydrostatic drive mechanism. A liquid-borne sound signal of airborne sound signal can be used, in which case a respective system parameter is determined by means of a frequency analysis of a detected liquid-borne sound signal or airborne sound signal from the axial piston unit.

Abstract: A piston for use in the cylinder block of a hydraulic power unit. The piston has an elongated cylindrical body and one end terminating in a spherical surface. The piston is composed of a body and insert which are made from different materials, preferably metallic materials, and joined together. The piston body takes the form of a solid cylinder or a hollow cylindrical tube. The spherical surface takes the form of an internal spherical socket or an external spherical ball. The insert takes an elongated or abbreviated form providing for both open cavity and closed cavity piston configurations. The piston includes a conduit which traverses the body and insert, providing a path for pressurized fluid. The body and the insert are preferably formed by a metal injecting molding process utilizing a molding material comprised at the time of molding of a mixture of metallic grains and a binder.

Abstract: The present invention relates to a filled piston assembly for a hydraulic pump or motor. The filled hydraulic piston assembly includes a blank piston body having first and second ends and a cavity or compartment in the piston body extending inwardly from one of the ends. The piston is filled with a lightweight solid insert element which is placed into the compartment of the piston. The material of the blank piston body is then cold formed around the insert element to encapsulate the element. The piston body is then further cold rolled to receive a spherical ball in one end. It is then cut to length, machine finished, and a longitudinal center bore is drilled therein.

Abstract: A specific type of hydraulic fan drive system is provided for engine drive machines, such as on road and off road machines, such as buses, construction equipment, agricultural equipment, and so on. The hydraulic fan drive systems turn a cooling fan (39) which provides airflow to cool the engine on such machines. This system uses a proportional pressure reducing valve (34) (or combination of valves providing a pressure reducing function) between the pump (12) and the fan motor (38). This valve (34) or (combination of valves) controls the pressure drop across the fan motor (38) based on a control signal from an electronic controller (50). The valve allows as little or as much flow to pass as is required to maintain this pressure drop at the load (the fan motor (38)).

Abstract: A closed cavity piston assembly includes a piston body, a separately formed piston cap sealingly joined to the body, and an elongated stem integrally formed with one of the piston body or the cap. In one embodiment, the stem is integrally formed with the piston body. In another embodiment, the stem is integrally formed with the piston cap and slidably journaled in and sealed to a hole in the bottom of the piston body. The cap of the piston assembly also has a surface for engaging a slipper. In either case, a fluid passageway extends through the stem, body, and cap of the piston assembly. The passageway is remote from the side wall of the piston body and fluidly isolated from the main interior cavity of the hollow piston body once the cap and body are sealingly joined together. The piston assembly can be pivotally attached to a slipper that has its own fluid passageway, which registers with the passageway in the cap, to provide fluid for slipper lubrication and balance.

Abstract: A piston for use in the cylinder block of a hydraulic power unit. The piston has an elongated cylindrical body and one end terminating in a spherical surface. The piston is composed of a body and insert which are made from different materials, preferably metallic materials, and joined together. The piston body takes the form of a solid cylinder or a hollow cylindrical tube. The spherical surface takes the form of an internal spherical socket or an external spherical ball. The insert takes an elongated or abbreviated form providing for both open cavity and closed cavity piston configurations. The piston includes a conduit which traverses the body and insert, providing a path for pressurized fluid.

Abstract: A tandem fixed displacement pump circuit with torque control includes first and second pumps that draw fluid from a reservoir to supply respective load circuits, pressure relief valves for each of the load circuits, and a pilot operated sequence valve that monitors the pressure for each of the circuits and reduces the pressure of one of the circuits as the pressure in the other circuit rises. The sequence valve modulates to control the pressure in the secondary priority circuit so that a predetermined input torque value is not exceeded.