The invention relates to a method for hydraulic steering, particularly of vehicles, according to which a steering unit is supplied with a controlled working pressure in dependence of a load signal from a load signal line, the load signal being generated via a load signal fluid with a fluid flow, and to a hydraulic steering arrangement with a steering unit, which can be supplied, in dependence of a load signal, with a fluid flow in a load signal line with a controlled working pressure.
A steering arrangement of this kind is known from DE 43 42 933. In this embodiment, the pressure of the controlled steering fluid can be taken from an outlet of the priority valve. The slide of the priority valve, which limits the outlet towards the inside of the priority valve, is penetrated by two pressure paths, each provided with a throttle, through which the pressure on the outlet is passed on to pressure chambers, arranged on both front sides of the slide. One of the two pressure chambers has a spring, which additionally acts upon the corresponding front side of the slide with a spring force. Further, this pressure chamber is connected with a steering throttle via a load signal line. On the outlet, a load signal fluid is branched off from the steering fluid, and flows via the pressure path inside the slide, which is connected with the pressure chamber with the spring, into this pressure chamber and on to the steering throttle via the load signal line. The flow of the load signal fluid is thus regulated in the slide via the pressure difference of the throttle of this pressure path, which corresponds to the pressure of the spring. This means that changes of the flow of the load signal fluid can be effected by displacing the slide.
The invention is based on the task of improving the operating comfort with a method and an arrangement of the kind described in the introduction.
With regard to method, this task is solved according to the invention in that the fluid flow is adjusted to assume an at least approximately constant value.
This ensures a stable flow of the fluid and thus stable conditions for the generation of the load signal in the load signal line. This permits a more accurate control of the working pressure, which increases the operating comfort of the steering arrangement.
It is advantageous that the adjustment of the fluid flow is merely effected by means of parameters of the load signal fluid. This procedure ensures that the fluid flow is adjusted independently of other parameters, which occur during the steering. For example, the influence of the working pressure of the steering fluid on the load signal fluid can be prevented, which could otherwise cause an interference with the load signal.
It is particularly advantageous that a load signal pressure in the load signal line adjusts the fluid flow. The use of the load signal pressure in the load signal line provides a wide spectre of useful, known and reliable adjustment functions. In most cases it will thus be possible to adapt the method to the anticipated operating conditions by means of already tested adjustment functions.
With regard to the arrangement, the task is solved according to the invention in that a load signal adjustment device is provided, through which the fluid flow can be adjusted to an at least approximately constant value.
Through the at least approximately constant fluid flow, the load signal adjustment device ensures stable conditions in the load signal line. This enables the generation of a relatively accurate load signal, which again causes a more accurate control of the working pressure and thus an improvement of the operating comfort.
In this connection, it is advantageous that the load signal adjustment device is merely adjustable by parameters of the load signal fluid. Thus, other parameters occurring in the hydraulic steering arrangement have no influence on the function of the load signal adjustment device. This prevents the occurrence of possible interferences when generating the load signal in the load signal line.
Further, it is advantageous that the load signal adjustment device is adjustable by means of a load signal pressure in the load signal line. This enables several variants when operating the adjustment device, and thus a good adaptation of the hydraulic steering arrangement to the operating conditions in question.
In a preferred embodiment it is ensured that the load signal adjustment device is arranged in the load signal line and has a direct connection only with this line. Thus, the load signal line has an independent load signal adjustment device, which works independently of other devices or parameters than the load signal devices and their parameters. In this way, interfering influences on the adjustment of the fluid flow can be avoided.
In a further favourable embodiment it is ensured that the load signal adjustment device is connected with a control throttle in the steering unit via the load signal line, the load signal pressure being adjustable via said throttle. This causes that the control throttle, which controls the load signal pressure, can be acted upon with a relatively constant fluid flow of the load signal fluid. This gives stable conditions for building up the load signal pressure or the generation of the load signal, respectively.
It is advantageous that the load signal adjustment device has a flow control valve, which keeps a fluid flow at an at least approximately constant value. This substantially constant fluid flow ensures stable flow conditions, also at the adjustable control throttle. Accordingly, during operation of the steering arrangement, a stable relation may be anticipated between an opening width of the adjustable control throttle and the load signal pressure in the load signal line depending on this opening width, said pressure acting upon the slide of the priority valve. This ensures a stable control function of the steering arrangement.
It is favourable that the load signal adjustment device has an adjustment throttle, taps being arranged before and after the adjustment throttle, said taps being connected with the flow control valve via adjustment connections. This gives a simple control of the fluid flow within the load signal line. As the control of the fluid flow is exclusively based on pressures available in the load signal line, the priority valve and the pressures of the steering fluid have no essential influence on the load signal adjustment device. This increases the stability of the steering arrangement, as potential interference sources are avoided.
It is particularly advantageous that the flow control valve is a 2/2-way valve, which is adjustable by means of a valve spring. In this way, the flow control valve can be adapted to the adjustment and/or control throttle. Further, it permits the adaptation of the load signal adjustment device to various operating conditions through the use of different valve springs.
It is also advantageous that a connecting branch to a priority valve is provided between the load signal adjustment device and the control throttle, which branch controls the working pressure supplying the steering unit. The load signal pressure, which is generated by means of the very uniform fluid flow can be supplied to the priority valve through the connecting branch. Thus, a very stable control of the working pressure of the hydraulic steering arrangement can be performed.
It is also favourable that the load signal adjustment device is connected between the priority valve and a pressure source. With such an arrangement, the admission of the load signal fluid to the priority valve takes place via its own line from the pressure source via the load signal adjustment device to the priority valve. In this way interfering influences from other devices of the hydraulic steering arrangement can be avoided.
It is particularly advantageous that the pressure source is controlled by the load signal pressure. Thus, a relatively uniform fluid flow can already be ensured by the pressure source.
Further it is favourable that the load signal line connects a pump connection of the pressure source with a tank connection of a pressure sink in parallel with a working path, the priority valve, the steering unit and a steering motor being arranged in the working path. In this way, both the priority valve and the steering fluid are, at least to a great extent, separated from the load signal line, thus having no substantial influence on the load signal pressure. This reduces the risk of possible interferences with the fluid flow, which increases the function stability of the steering arrangement.