Abstract: A closed cavity piston includes an elongated piston body and a separately formed piston cap having an elongated stem and head thereon. The body includes a closed end and an open end with a cavity having a bottom wall adjacent the closed end and an outer wall terminating in a rim at the open end. The stem of the piston cap is friction inertia welded to the bottom wall of the piston body and the head of the piston cap welds to the rim of the piston body. The stem of the cap is inserted into the cavity of the body until it engages the bottom wall. Then the cap is friction inertia welded to the body at the stem/bottom wall and head/rim interfaces after preheating.

Abstract: A compact vehicle has a frame and an operating position thereon for at least one rider. An engine having a drive shaft is on the frame, as are a plurality of operational wheels. A transmission operatively couples the engine and the wheels. The transmission is a hydrostatic mechanical transmission with at least 2 operational modes.

Abstract: A variable displacement hydraulic power unit has a housing and a rotating piston block with a rotatable axis and a servo piston bore having a reciprocal piston therein with the bore extending in a direction parallel to the rotatable axis of the rotating piston block. The housing and servo piston each have adjacent open ends. A single integral cover is attached to the housing to cover close and close the open ends of both the housing and the piston bore.

Abstract: An electrohydraulic valve pilot stage for controlling differential pressure is disclosed. The electrohydraulic valve pilot stage has a housing for protecting the valve; a first and second inlet capable of connection to fluid supplies; a first nozzle and a second nozzle fluidly connected to the inlets; a baseplate attached to the housing and the nozzles; a restraining member attached to the baseplate at a position between the first nozzle and the second nozzle; a pivot pin; a flapper restrained by the restraining member and having a first end and a second end, the flapper pivotably mounted on the pivot pin; and a null adjust pin mounted in a pivot pin contact capable position for adjusting the position of the ends of the flapper relative to the nozzles.

Abstract: A zeroing mechanism for a hydrostatic piston/cylinder unit (1), has an actuating piston (2) that can be moved from a zero position N into at least one deflected position A and can be returned to its zero position N by a zeroing force, the zeroing force being produced at least in part hydraulically.

Abstract: An improved pilot stage includes a flapper having first and second ends, first and second nozzles in fluid communication with the first and second ends, and a magnetic torque motor having a first coil which is magnetically coupled to the first end of the flapper. An input current to the first coil creates a magnetic torque on the flapper, causing the flapper to pivot. The torque input from the magnetic circuit is reflected through the pivot to create a balancing differential pressure output at the nozzles proportional to the input electrical signal. The flapper does not require a torsion bar (or tube) pivot or a separate armature, as required by functionally similar pilot stages.

Abstract: A loop flushing circuit includes a loop flushing valve that is connected to the low pressure system line in a hydrostatic transmission for selectively bleeding fluid therefrom to the case drain without relying on a shuttle valve to identify the low pressure line. The loop flushing valve is adaptable to electrical or electro-hydraulic actuation by a microcontroller. Thus, the timing of loop flushing can be controlled based upon various system operating conditions or input values. Loop flushing with this circuit avoids adversely impacting control characteristics of the transmission, can be defeated around neutral, and can provide single-sided loop flushing.

Abstract: A hydraulic piston for a cylinder block of a hydrostatic power unit has an elongated cylindrical body with first and second ends. An elongated cavity is formed in the body. A cap is adhered to the body to close the cavity. The cap has an external shape to facilitate the operative engagement thereof with a slipper, which is in subsequent engagement with a swashplate mounted adjacent the cylinder block. The piston has an elongated first conduit formed in the body which is separate from the cavity and extends between the opposite ends thereof. The conduit terminates in registering communication with a second conduit in the cap thereof to permit transmission of oil through the conduit without invading the volume of the cavity. The cap preferably has a tapered surface on the inner end thereof engaging a compatible shaped surface on an adjacent end of the body to center and align the cap with the body.

Abstract: A hydrostatic vehicle drive has a control (5) for controlling an output torque of the drive and another control device (5) for controlling the output torque of a hydrostatic drive, the control device (5) having a controllable pressure-limiting valve (6) by means of which the working pressure can be adjusted and which is used for sensitive control of the output torque of a hydraulic motor (3). The pressure-limiting valve (6) can be controlled by a proportionally adjustable pressure-reducing valve (7).

Abstract: A system and method for connectionless sensing of the physical parameters of a shaft that is capable of continuous rotation. The system involving placing a circuit assembly on the rotating shaft, powering the circuit assembly through energy transferred from a stator coil across a gap to a rotor coil, sensing physical parameter data on the shaft and communicating this data across the gap from the rotor coil to a stator coil.

Abstract: A hydraulic neutral cold start control valve for a variable displacement hydraulic unit includes a housing with a spool bore and an intersecting signal pressure passage therein. A spool is disposed in the bore and is mechanically biased to a closed or neutral position of the valve by a pair of opposing springs. A plunger is associated with one of the springs and has a surface that usually sealingly contacts one end of the spool but extends radially therebeyond such that it is in fluid communication with the signal pressure passage. When the signal pressure exceeds a threshold value, the pressure forces the plunger to separate from the end of the spool. Then the movement of the spool becomes proportional to the signal pressure, which is desirable for normal operation and control of the hydraulic unit.

Abstract: A method to provide a smooth shift during mode changes of an HMT when using mechanical clutches by reducing the power into the transmission momentarily when a shift is initiated by cutting fuel to the engine, and also reducing power in the hydrostatic transmission by crossporting the fluid circuit, and then reapplying power to both the engine and the transmission after the clutch has been shifted.

Abstract: A swashplate assist mechanism for dynamically varying swashplate moments in a multiple piston hydraulic unit includes a valve means disposed in the swashplate and defining a variable orifice for metering fluid from at least one of the pistons; and means for generating a control error signal to the valve means so as to adjust the size of the variable orifice based upon the control error signal. When fluid is metered from a leading piston to a trailing piston near one or more of the pressure transition zones, or when fluid is metered from a trailing piston to a leading piston near the opposite transition zones, the swashplate moments can be reduced.

Abstract: A hydraulic motor (2) with a braking device (8), is acted upon by means of a control fluid via a brake release line (6). The brake release line (6) is used to allow a continuous flushing flow of control fluid through the hydraulic motor at the same time as the release of the brake. The braking device (8) is connected to the casing of the hydraulic motor (2). An outlet opening (12) of the hydraulic motor (2) leads via a leakage-oil line (13) to the tank for the control fluid. In a hydraulic travel drive with a closed hydraulic circuit, the brake release line (6) can be connected to the shut-off device (4) for the servo adjustment system of the variable-displacement pump (1), and the leakage-oil line (13) of the hydraulic motor (2) can lead to the tank for the entire hydraulic fluid in the system.

Abstract: An electronic traction control system for a vehicle having multiple hydraulically driven wheels includes a pump, a plurality of hydraulic drive motors each fluidly connected to the pump for driving one of the wheels, a corresponding plurality of speed sensors for generating a motor speed signal for each of the motors, and an electronic flow control valve. The electronic flow control valve includes a microcontroller electrically connected to the speed sensors for receiving and comparing the motor speed signals and a plurality of normally open anti-slip valves each electrically connected to the microcontroller for receiving a flow command signal therefrom based upon comparison of the motor speed signals. Each anti-slip valve fluidly connects to a drive motor between the drive motor and the pump. This electronic traction control system provides a method of controlling motor speed without changing the displacement of the motor.

Abstract: A hydraulic circuit includes a pump controlled by a two-stage non-feedback proportional control assembly. The first stage of the control assembly includes a single non-feedback proportional control valve that generates a displacement magnitude hydraulic signal that is proportional to an input signal. The second stage of the control assembly includes a directional control valve located downstream of the proportional control valve for conditioning and routing the displacement magnitude signal to the pump with an appropriate directional indicator.

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: 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 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.