The present invention relates to an articulated vehicle with hydraulic steering comprising a hydraulic control unit and a hydraulic steering motor connected to the control unit by two conduits.
In the control of articulated vehicles with hydraulic steering, situations can arise in which the driver and certain parts of the vehicle are subjected to uncomfortable side acceleration. A side acceleration exists at the start and end of every steering movement. The acceleration upon commencement of the steering movement is limited by the reaction period for the build up of pressure in the hydraulic system and by the inertia of the mechanical system. However, the position is different if a rapid steering movement is interrupted abruptly, say because the supply and withdrawal apertures of the cylinder are blocked or the steering is reversed. In this case, the front portion and the rear portion which are often of considerable mass are suddenly halted. Their momentum must, however, be somehow eliminated. Apart from the elasticity of the hydraulic elements, particularly the connecting conduits, and the relatively low compressibility of the hydraulic fluid, there is no energy store or eliminator available for taking up the energy and braking the movement. The moved masses and the elasticity of the hydraulic system now form an oscillating system in which the energy appears alternately as pressure and momentum. After a certain time, the oscillation dies down on account of friction and internal damping.
The driver, who is generally located near the pivot point, finds the oscillation to be uncomfortable. In addition, all mechanical connections and bearings suffer under the impact following oscillation.
It is therefore the problem of the present invention to provide an articulated vehicle with hydraulic steering offering improved driving and steering comfort.
This problem is solved in an articulated vehicle of the aforementioned kind in that parallel to the steering motor there is a double acting hydraulic shock absorber with a closed tubular housing connected at both ends to the two conduits by way of a respective passage and a piston which is movable longitudinally of the housing, disposed in the region of the middle of the housing and on both sides of which there is a respective spring pre-stressed by prestressing means which are connected to the piston and, on movement of the piston, permit only compression of the spring between the housing end and the piston but no expansion of the spring, the response pressure of the shock absorber having a predetermined value as a result of pre-stressing the springs.
In connection with an excavator boom, US-PS 28 01 013 discloses a double acting hydraulic shock absorber comprising a closed tubular housing which is connected at both ends by way of a respective passage to two hydraulic pressure conduits and a piston which is movable longitudinally of the housing and disposed in the region of the middle of the housing between two springs supported by the ends of the housing. In this shock absorber, the springs are clamped between the piston and the ends of the housing. When steering in one direction, the piston compresses one of the springs but allows the other spring to expand so that the available damping force is only the small difference between the two spring forces. Accordingly, the incorporation of this shock absorber in the steering system of an articulated vehicle with hydraulic steering fails in that the shock absorber would respond upon each steering movement. The result of this would be that even normal steering is made more difficult and a higher application of force would become necessary.