Pompa a pistoni assiali a circuito chiuso K8V di Kawasaki.

Hydrostatic Transmission System for High Efficiency Mobile Vehicles

Hansa-TMP offers Kawasaki’s hydrostatic transmission consisting of a K8V pump, in combination with the motors of the M7V/M7X series, for use on high-pressure circuits of mobile vehicles that require high efficiency and controllability, such as construction machinery and agricultural equipment.

M7V Kawasaki - Variable displacement axial piston hydraulic motor.
M7V Kawasaki – Variable displacement axial piston hydraulic motor.

For all those vehicles that require high efficiency and controllability Hansa-TMP, a specialist in the production of hydrostatic transmissions and integration of hydraulic system and exclusive distributor for the Italian market of the Kawasaki product range, offers a hydrostatic transmission system consisting of a K8V series pump and motor of the M7V/M7X series for high pressure closed loop. The K8V series consists of variable displacement axial piston pumps for closed loop systems, with superior overall efficiency, stability, and control characteristics. The K8V pumps are applicable for a wide range of applications such as construction machinery and agricultural equipment with hydrostatic drive systems, and other closed loop applications. The K8V series with a range in pump size from 71 to 130 cm3/rev are equipped with electric or hydraulic pilot displacement control. The new pump offers noiselessness, reliability, and a longer life than competing products, thanks to an innovative swash plate system which provides pressurized oil for lubrication and support, unlike other products on the market that mount simple roller bearings. This avoids all the problems due to the imprint of the rollers on the cast iron of the swash plate and to any slippage of the same, always having a gradual response.

The K8V series pumps, having the integrated components required for a closed system, such as a charge pump, high and low pressure relief valves, and a cut-off valve, enable a compact closed loop system. High-pressure relief valves (two valves) are equipped to protect the pump from being overloaded. The allowable setting range of the high-pressure valve is from 300 to 450 bar, while the setting of the integrated low-pressure valve is pre-set at 25 bar at the factory. Pressure cut-off is the function, which adjusts the pump displacement to the neutral position when the pressure reaches its pressure setting. The pressure cut-off is set lower than high-pressure relief valve setting, so that the maximum pump pressure is controlled by the pressure cut-off valve, whereas the high-pressure relief valve acts to the pressure spike. In this way, the Cut-Off valve controls the maximum pressure of the pump, while the safety valves of the pump limit the pressure peaks. The Cut-Off pressure must be set at least 50 bar lower than the setting of the high-pressure relief valves (the cut-off pressure adjustment range is between 300 and 400 bar). Compactness is also achieved thanks to the integrating charging pump which supplies flow to replenish, cool and filtered oil to integrate closed-circuit losses and ensure flow for system control and auxiliary functions. The pressure and flow rate of the charging circuit can be provided by an external auxiliary pump, which can be mounted on the back of main pump using through drive mounting.

The ideal pump/motor combination

The K8V series, featuring high overall efficiency, stability, and excellent reliability, is often used in combination with KAWASAKI M7V/M7X series motor. The M7V/M7X series is a high-speed variable displacement swash plate type axial piston motor, suitable for use in hydrostatic transmissions, drill rigs, crane winch systems and construction machinery. Applicable to an open and closed circuit, these motors have a displacement range from 85 to 160 cm3/rev and the optimized swash plate design enables high-speed performance and excellent low-speed characteristics. This configuration identifies a more compact structure and allows great flexibility in hydraulic system design. The M7V/M7X series allows low noise and longer bearing life compared to competitors, in operating conditions of 200 bar according to a Duty-Cycle, from medium to maximum displacement, operating life is more than 2 times.
These advantages are also due to the particular configuration of the 11-piston rotatory group compared to that normally used with 7 or 9 pistons (depending on the displacements), allowing efficient and smooth rotation. On demand, it is possible to order the speed sensor, allowing extremely precise control in the variation of the displacement, according to the number of revolutions. The M7V/M7X series is available with two types of two-position displacement control, the electric control type and hydraulic pilot control type. The electric control can switch the displacement between minimum and maximum by applying the input current to the solenoid while, the proportional hydraulic control adjusts the motor displacement in response to pilot pressure externally supplied to a regulator. The latter delivers negative or positive displacement controls, which are proportional to an increase in external pilot pressure: negative control type P1X and P3X reduce displacement from maximum to minimum against an increase in pilot pressure, while positive control type P2X and P4X increase displacement from minimum to maximum with an increase in pilot pressure. In both cases, the port with the highest pressure internally supplies control pressure. The M7V/M7X allows a pilot pressure from 20 to 100 bar.

Three different types of pressure controls are available

A M7V/M7X motor equipped with proportional control (electric or hydraulic) can have pressure control function using an optional valve. If the motor has both proportional control (either electric or hydraulic) and pressure control, pressure control overrides proportional displacement control. Under pressure control, the motor maintains minimum displacement until the operating pressure reaches the pressure set point. Upon reaching the pressure set point, the motor increases displacement to maximum to obtain the required output torque, while controlling the operating pressure. If the motor reaches maximum displacement without sufficient output torque, the motor increases pressure until the required output torque is attained.
Three types of pressure control are available, that are constant pressure control (pressure control without pressure increase), pressure control with pressure increase, and pressure control with pressure increase and hydraulic remote control. The constant pressure control (pressure control without pressure increase – H1X) controls the displacement between minimum and maximum in line with the operating pressure. Minimum displacement is maintained until the operating pressure reaches a Set-Point and upon reaching the pressure Set-Point it shifts to maximum displacement until the required output torque is obtained, while maintaining the set pressure. This control can be combined with a two-position electric valve for displacement control. The pressure control with pressure increase – H2X controls the displacement in line with operating pressure and load conditions. In this case, the motor maintains minimum displacement until the operating pressure reaches a Set-Point and, when it exceeds the pressure Set-Point it shifts to maximum displacement. Displacement increases until the required output torque is obtained. If displacement reaches maximum without sufficient output torque, the operating pressure will rise until the required motor output torque is attained. The line with the highest pressure supplies control pressure internally. Finally, the pressure control with pressure increase and hydraulic remote control – H3X allows variations at the start of control pressure and control characteristics by applying the external remote control pressure. The application of external remote control pressure in H3X control reduces the control pressure at the beginning of the constant pressure control, and induces a parallel shift in the control characteristics.