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User-friendly Control of Construction Machines

Speed control of a fan drive by means of the proportional pressure valve

Negative characteristic curve of the proportional pressure relief valve p-I characteristic curve. With increasing value of the control signal, the system pressure in the circuit reduces

Pilot operated pressure relief valve in combination with an electromagnetically actuated unloading function (SR4E-B2).

Transmission control block

Development trends in the construction machine

Performance and security, coupled with an increased operating comfort, define today‘s development trends while simultaneously reducing operating costs. Progressive approaches in the design of new machines require high-tech products and system solutions, adapted to the intended use. The construction machine stands for the transfer of high powers and forces and is therefore predestined for multiple use of hydraulics due to its high power density, especially in the areas of operational functions, the drive, up to the suspension of the chassis. In this context, electrically controlled proportional valves play an essential role. So, in conjunction with an intelligent and sophisticated control, individual functions can be optimally matched to the assignment.
The use of proportional valves makes it possible to divide the control into two basic complexes - in a hydraulic power component, often arranged in the vicinity of a consumer, and an electronic control component in the vicinity of the operator. Both components communicate via electrical control signals. Functional ergonomic joysticks, partly with function display and simulation of a force feedback, enable efficient, precise and convenient operation. For the safety of the machine there are, among others, pressure relief valves with a partly continuous adjustment of the maximum pressures in the hydraulic circuit. In addition, there are proportional pressure reducing valves, which are used for force regulation of the hydraulic cylinders or for regulating the output torque of hydraulic motors.

Proportional control
ARGO-HYTOS offers proportional relief valves which cover a wide range of applications, both in stationary as well as in mobile applications. The valves characterize a pioneering design, high reliability and stability coupled with good dynamics. The two valve series of the pressure relief and pressure reducing valves are pilot operated via a pilot stage. An adequate level of cleanliness of the operating fluid, or which ARGO-HYTOS also offers optimized filter solutions in conjunction with condition monitoring, is a prerequisite for the performance of such controls up to a flow rate of 60 l/min and a maximum pressure of 350 bar.

Modular concept
Both types of valves are controlled by the same pilot stage. This modular design of the valves reduces the number of manufactured parts and thus offers in addition to the cost benefits for the customer also benefits in case of service. In addition, the pilot stage may be used separately as a pressure relief valve up to a flow rate of 1.5 l/min at maximum pressure of 350 bar. Three pressure stages 120 bar, 210 bar and 350 bar provide appropriate pressure ranges for optimizing a pressure regulation, exactly adapted to the respective requirements. The valve control itself is carried out by a proportional pressure magnet. In accordance with the customer requirements, there are three electrical connection types available: DIN or the in mobile applications popular DEUTSCH and APM terminals. The control of the electromagnet is carried out via a PWM signal with a frequency of 250 Hz. The possible supply voltage of 12V or 24V is compatible to the normal mains voltage of construction machines. A built-in suppressor diode protects the control electronics against induced voltage spikes.

For valve control, it is recommended to use the miniature electronics EL6 in the form of a DIN cable socket, which is placed directly onto the valve. The miniature electronics provides a modern compact solution for valve control and enables a simple parameter setting with two knobs and a built-in display, e.g. with ramp functions. In the development of the valves, the operating conditions of construction machines were significantly focused: the operating fluid temperatures from -30° C to + 90° C and kinematic viscosity of the operating fluid from 10 to 500 mm²s-1 are covered as standard. Furthermore, they optimally withstand occurring vibrations.The pressure reducing valve is designed as a 3-way valve. In addition to the retention function at the valve output, the valve provides a protective function of the connected consumer. If there is an overload of the consumer, which may – with construction machines – occur determined by the function, the valve closes the flow and connects the consumer to the tank. This leads to a reduction in order to prevent damage to the consumer by high pressure.

SRN4P1-B2 - A valve with a negative characteristic curve
In some technical applications it is necessary that the function of the pressure valve is reversible due to the functional or safety-related requirements of the system. That means that the maximum pressure is reliably achieved even in case of failure of the control signal. Such requirements correspond to valves with a negative characteristic curve.An example of the use of a proportional pressure valve with a negative characteristic is the speed regulation of a fan drive in agricultural machinery and construction machinery. The proportional control allows continuous observance of an optimum oil and coolant temperature under all working conditions. Thus, sustainable energy saving and extension of the engine and component lifetime is achieved. The specified temperature is maintained by continuous regulation of the fan speed and thus the cooling air flow. In electronics failure respectively failure of the control signal, the motor is protected from overheating by “fail-safe mode”, a characteristic of the curve.

SR4E-B2 - A valve with combined function
SR4E-B2 is a valve which combines the functions of a pilot operated pressure relief valve with a solenoid operated relief valve. Through the pressure relief function, the maximum pressure is secured in the circulation and thus the circuit is protected against overload. With the switching off of the electromagnet, the pressure line is relieved and connected to the tank. With two adjusting screws, the limit values of the solenoid armature can be set and thus also the minimum and maximum pressure in the circuit. There are three pressure stages available with a pressure adjustment range up to 120 bar, 210 bar and 350 bar. The minimum pressure can be adjusted up to 20 bar. The max. flow rate is 60 l/min. Through this combination valve, the system costs are reduced by eliminating a separate relief valve.

Valves for gear and clutch control
An important area, in which hydraulic valves are applied in mobile machines, is the control of gears and couplings. For the coupling circuit, mainly pressure reducing valves are used. For this application, ARGO-HYTOS offers specially tuned valve solutions: Pilot operated proportional pressure reducing valves with a special characteristic curve, designed for mounting in control blocks or directly in the gearbox. The valves are designed as 3-way valves, and thus also include a protective function against overload of the hydraulic circuit. There are two versions available: SP4P1-B4 with thread 7/8-14 UNF and PP4P1-Z3 as “slip-in design“. On request, the input channel can be provided with a filtration screen in order to ensure the functionality even with contaminants. The coils of the electromagnets are available with DEUTSCH and AMP connectors, possible supply voltages are 12V or 24V. An inlet pressure of up to 50 bar, an output pressure up to 25 bar, max. flow rate of up to 40 l/min, are parameters which are adjusted to the use in transmissions for mobile applications. These valves provide high switching speeds at safe and stable function over a long service life.

The 3-way cartridge spool valve PD 2-E in “slip-in” design is often used for transmission controls in mobile applications. The shaped holes of the directly controlled proportional pressure reducing valve PP2P3-W are identical to the s/w switch valve PD2-E, so that for system integrators the number of molds can be minimized.

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