1. Field of the Invention
The present invention relates to a valve device, especially a proportional valve and/or a directional control valve.
2. Description of the Related Art
Proportional valves, also referred to as directional control valves, are known in numerous design variations and applied in various applications. Directional control valves are valves whose valve pistons, also referred to as control plungers, can be moved to various fixed shift positions allowing different hydraulic connections to be established for the purpose of controlling operating fluids. As a result, a directional change in fluid flow can be achieved. These valves are characterized by their nominal width, their nominal pressure and their possible distribution options. The main module of a directional control valve is the control unit which houses the valve piston inside the valve body or the control housing, thus bringing about the directional change in the fluid flow. There is an actuator attached to at least one of the two end-faces of the valve piston for the purpose of developing the activation force needed to move the valve piston. A frequently applied design variation is the so-called spool valve whereby the valve closing is initiated by the overlap as a result of the relative movements of the individual valve components, especially the valve piston inside the valve body. Depending upon the design and type of movement, these valves are grouped into rotary spool valves, longitudinal spool valves or a combination of both. The appropriate classification of the control units or valve units is determined by the number of connections or number of possible hydraulic lines that are attached, and by the number of possible shift positions. The control edges of the valve piston and the valve body have an especially significant effect on the precision of the shift events. They impact the throttling of the flow area and, hence, the speed of the consumer, usually a machine. Through appropriate shaping of these control edges in concert with the relative motion of the valve piston with respect to the valve body, different flow characteristics can be achieved. Directional control valves offer a certain number of shift positions.
Proportional directional control valves are defined as continuously variable directional control valves, preferably controlled electrically, whose axial motion of the valve piston is directly controlled in a position control mode or in a force control mode, proportional to a set point value, by pressure sealed actuators. The actuators of electrical, continuously variable directional control valves are designed as control magnets (solenoids) which facilitate an axial movement of the valve piston proportional to an electrical set point value. The valve piston is continuously adjustable in any position within the two stop positions provided by the valve body. This has special advantages when controlling and regulating the speed of hydraulic consumers. Such valves, for example, are known from:
1) Sales literature by Mannesmann Rexrodt:
RD 29 586/09.89
RD 29 175/03.93; and
2) Sales literature by the Herion-Werke KGxe2x80x94Fluidtechnik Nr. 7502263,0503.92.
These types of proportional valves have the disadvantage that the activation force, which, for example, is generated electro-magnetically, hydraulically, mechanically, or through any other devices must be chosen so that the maximum desired pressure that occurs in the consumer downstream of the valve is capable of being maintained on a long-term basis. The size of the effective area exposed to the pressure is determined by this requirement. This, however, has the consequence that lower pressures must be controlled with appropriately lower activation forces. At desired lower pressures, more pressure variability is to be expected during the control process. An increase in the range of activation force usually causes the size of the actuator to increase. For example, if the actuator is designed in form of an electromagnet, a fundamental increase in the magnetic force causes an increase in the size of the magnetizing coil, which requires more room. Furthermore, the costs of the electrical conductors associated with the larger magnetizing coil are higher and the current consumption also increases. As a general rule, and in view of the applications that use these valves, there are limits to the size of the valve and the actuator. Thus, a precise regulation of the pressure in the consumer cannot always be realized.
The present invention provides a proportional-directional control valve without that the stated disadvantages. Especially, the pressure fluctuations at very low target pressure settings are minimized. The valve device is furthermore suitable for applications, for example, automatic transmissions, whose requirements dictate the need to control the relatively low pressures in the hydraulic clutch elements as precisely as possible, combined with the need of high (torque) transmission capability of the clutch elements while operating in the converter range.
Within a first pressure range or the proportional range (this range can also correspond to the total operating range, which is on the order of 1-5 bar), the valve device is capable of exerting control in proportion to an electric current at the highest level of precision and at the highest possible activation force, while fully taking advantage of the maximum allowable activation force. Additionally, the valve is capable of operating as a normal directional control valve in a second, elevated pressure range, ranging from 6 to 20 bar. Thus, it is capable of transmitting the full pressure independently from the available pressure level in the consumer. The valve device is able to provide precise and repeatable shift events with minimum side effects from hydraulically-induced binding moments and mechanical friction. While achieving these requirements, the design complexity and cost is kept to a minimum.
In addition to a valve body, which includes at least one supply channel and one return channel, the valve device also includes an axially-moveable valve piston residing inside the valve body. This valve piston includes control edges to open and block the connections of the cross-sectional areas of the supply and return channels, as well as an actuator for providing an activation force onto the valve piston. Devices are provided for the generation of a force, opposing the activation force, at least over a part of the total operating range of the valve device. This force is dependent upon the pressure in the return channel. Inside a pressure range, which determines a first part of the total operating range of the valve device (this first part can also correspond to the total operating range), the possible range in activation force is increased relative to the pressure range at the consumer, promoting a more sensitive modulation of the activation forces and the final pressure at the consumer. Thus, a given pressure range at the consumer or return channel requires a larger range in activation force as compared to a conventionally-designed proportional valve. This is achieved after the valve piston has reached a control position by reaching an equilibrium between the activation force and a pressure force. The pressure force imposes a load on a certain area as a function of the pressure in the consumer, directionally opposing the activation force.
An interior opening inside the valve piston extends all the way to the far end of the valve piston relative to the actuator. A plunger resides inside the interior opening, whereby the plunger and the valve piston are moveable relative to one another. A limit stop provides support for the plunger. A connecting hole is between the interior opening of the valve piston and the outer periphery of the valve piston. The mouth of the connecting hole at the outer periphery of the valve piston is arranged so that the connecting hole is in communication with the return channel while operating in the stated portion of the total operating range, the proportional range.
The present invention makes it possible to achieve the highest possible ratio between activation forces and friction forces. The friction forces are determined primarily by the pressure differences at the valve, the contamination level of the operating fluid, the valve diameter or other design-related features. The activation forces are limited primarily by the size of the actuators. In the case of electromagnetic devices, the size of the magnet is the limiting factor. Even at lower activation force ranges, it is possible to adjust lower pressure levels in the consumer or in the return channel connected to the consumer.
In a preferred embodiment, the valve is designed as a combination of a proportional-directional control valve. In addition to offering the function of distributing the fluid, the valve device further includes a device which limits and compensates the magnitude of the force opposing the activation force. This device is designed in the form of an energy storage unit which is associated with the limit stop for the plunger and limits the force upon the plunger. In the event the pressure force, which is determined by the pressure in the return channel and the plunger area, exceeds the opposing force supporting the plunger, developed by the energy storage unit, the limit stop no longer functions as a solid stop. Instead, the limit stop is forcibly moved by the plunger. This movement is limited by an additional limit stop located between the plunger and the valve piston. Once the plunger has reached this limit stop, the plunger is no longer moveable in the direction of the pressure force, and the valve piston then moves solely in response to the activation force.
The valve device facilitates the control of at least a first lower pressure range at the consumer, which determines a first part of the total operating range of the valve device, at nearly the maximum possible activation forces. In an upper pressure range, which determines a second part of the total operating range of the valve device, the valve functions solely as a directional control valve. This means that for the second part of the total operating range, the pressure present in the return channel, which is directly coupled to the consumer, no longer has any impact whatsoever on the function of the valve device. Thereby, precise control performance can be obtained in the first part of the total operating range of the valve device, which is the lower pressure range, in spite of small command values. The transition of the valve device from the proportional function to the directional control function occurs automatically as a function of the pressure in the consumer. The point of transition can be determined through appropriate geometric and dynamic design considerations of the valve device.
In terms of the design arrangement, the valve device includes at least one valve body with a center bore, containing a valve piston which is moveable in axial direction. The center bore, in combination with associated chambers, form so-called pressure compartments, which, corresponding to the position of the valve piston in the center bore, allow a connection between a supply line and a return line, preferably a return line that is connected to a consumer. In addition, the valve piston includes an interior opening containing a plunger which is moveable in axial direction. The plunger is axially limited by a limit stop, which is supported by an energy storage unit. The plunger, or more precisely, the end-face of the plunger facing away from the limit stop and extending into the interior opening of the valve piston, is exposed to the pressure present in the return line or the connecting line to the consumer via a connecting hole (preferably in the form of a connecting orifice). The purpose of the orifice is to provide a path linking the interior opening to the outer periphery of the valve piston, which is positioned in the proportional range in the area of the return flow. The valve is conceptually designed so that in a first end position, the connection between the supply and the return, the connection to the consumer, is blocked.
The capability of activating the valve piston in the valve body is provided by use of an actuator. A preferred actuator is an electromagnetic actuator. Other possibilities are also possible, such as, for example, an electro-hydraulic actuator. When desiring continuous control, the valve piston is activated by the actuator by applying a force Fapplication. This causes a connection to be established between the pressure compartments, which are formed by the chamber connected to the inlet by the center bore, as well as the center bore and a chamber at the outlet. As a result, the operating fluid can flow from the supply to the consumer. At the same time, a pressure level is reached across the connecting orifice between the interior opening and the outer periphery of the valve piston in the area of the return, which is acting upon the end-face of the plunger, which in turn, is supported by the limit stop in the valve body. Thereby, an equilibrium condition is created, i.e., the activation force equals the pressure force, which is the result of the consumer pressure acting on the plunger area. Through provisions of a further energy storage unit between the valve piston and the plunger in the interior opening of the valve piston, the resultant force is added to the pressure force.
The plunger is supported by the limit stop, which is part of the energy storage unit. The force generated by the energy storage unit corresponds to the force of the plunger at maximum desired proportional pressure, so that in the entire proportional range, no changes take place to the force exerted by the energy storage unit, or to the position of the limit stop. The pre-load of the energy storage unit serves as a direct set value for the targeted maximum, desired proportional pressure.
Only when the regulated pressure in the consumer, that is, the return, generates a force on the plunger inside the interior opening greater than the force generated by the energy storage unit associated with the limit stop, does the plunger compress the energy storage unit and come to rest on at least one limit stop shaped as an overhang and integrated into the valve piston. As soon as this condition is reached, the pressure in the consumer can no longer act upon the valve. The position of the valve piston is then determined solely by the external forces of the actuator and the energy storage unit, in the same way as in the case with a directional control valve.
For applications of a valve device, with the two functions, proportional function and directional control function, on automatic transmissions, the shift pressure can be arranged such that all shift events lie within the proportional range, and the upper pressure range solely serves to transmit torque.
In addition to the valve""s more sensitive capability to adjust pressure, there are other substantial advantages such as universal application potential, whereby several design requirements can be satisfied by only one valve device. These advantages include a more sensitive modulation of the activation forces and the final pressure at the consumer, especially at low pressure levels, as well as the ability to provide high pressures to the consumer and reliably maintain these pressures.
It is advantageous to design these energy storage units in the form of pressure storage units such as, for example, individual compression springs or spring packs. It is also possible to use elastic membranes.
The valve device can be operated as a pure proportional valve by dispensing with the energy storage unit at the limit stop, or it can be operated as a pure directional control valve by designing the energy storage unit so that the activation force immediately leads to the movement of the valve piston to the end position. This can be accomplished by selecting a very low pre-load in the energy storage unit. A low pre-load of the energy storage unit results in a small proportional range. A large pre-load of the energy storage unit results in a large proportional range. This makes it possible to create a compact base valve unit which can be adapted with little effort, through only minor modifications, to different requirements. The individual components can be designed utilizing the modular concept.
The valve device described by this invention can include any type of actuator. The use of electromagnetic, mechanical, hydraulic, or any other type of actuator is possible.
Electro-magnetic actuators include at least an electromagnet including a coil and an armature.
For valves whose activation force is generated electro-magnetically, different displacement limits of the valve piston or the armature can be assigned to the individual functional states xe2x80x9cproportional valvexe2x80x9d and xe2x80x9cdirectional control valve.xe2x80x9d This has the advantage of lower current consumption of the magnetizing coil in state xe2x80x9cdirectional control valve,xe2x80x9d which is especially advantageous since this state occupies the majority of time and, therefore, is most significant in terms of the heating and the resultant durability of the coil, as well as the hardware responsible for controlling the valve. The maximum possible displacement within the proportional range is approximately 80 percent in relation to the total displacement. Minor deviations from this value are possible.