Motor vehicles – Steering gear – With fluid power assist
Patent
1996-06-05
1997-12-30
Sotelo, Jesus D.
Motor vehicles
Steering gear
With fluid power assist
60384, 180441, B62D 509
Patent
active
057019703
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for controlling the pressure to be supplied to a hydrostatic steering unit by means of a control signal, having a pressure control device and a rotary slide valve arrangement, one slide valve element of which is rotatable by means of a steering means, the other slide valve element of which is corrected by means of a measuring motor through which the flow passes, and both slide valve elements of which are rotatable relative to one another through a limited angle of rotation on either side of a neutral setting, and both slide valve elements have control openings which form at least one first throttle, which is closed in the neutral setting, in the intake path to a steering motor, at least one second throttle, which is closed in the neutral setting, in the return of the steering motor, and at least one control throttle which is open in the neutral setting and is connected between a tap for the control signal and the tank.
In known devices of that kind (DE-PS 36 35 162, U.S. Pat. No. 4,620,416) the control signal is tapped at a point lying between two throttles arranged in the intake path, namely, a measuring throttle and a further throttle; the tap point is connected by way of a control throttle to the tank side. When the steering means is operated, the control throttle must close after the smallest possible angle of rotation, because otherwise, as the throttles lying in the intake path open, a part of the fluid under pressure intended for the steering motor escapes by way of the control throttle. With relatively large angles of rotation, a control signal of such magnitude is produced that the pressure drop at the measuring throttle in the intake path is held constant. The transition from the first type of determination of the control signal by the control throttle to the second type of determination of the control signal by the measuring throttle causes an undesirable increase in the control signal during operation, that is to say, an undesirable increase in the so-called LS pressure, and consequently an undesirable change in pressure in the motor lines.
The load acting on the steering motor additionally influences the control signal. If, if fact, negative control forces are acting on the steering motor, a negative pressure occurs in the steering motor. This is the case, for example, when the speed of the piston of the steering motor exceeds a maximum value predetermined by the construction of the steering unit. The negative pressure causes fluid under pressure to be sucked by way of the intake path, which leads to a corresponding drop in pressure at the measuring throttle. As a result, the control signal changes, so that the pressure control device generates a reduced pressure.
The invention is based on the problem of providing a device of the kind mentioned in the introduction, with which the needs of practice can be fulfilled even better than before.
This problem is solved according to the invention in that the control throttle, together with a series throttle, forms a series circuit independent of the intake path of the steering motor, which circuit is supplied from a pressure source and has a closing characteristic that extends substantially across the entire working range of the angle of rotation of the slide valve elements.
In this construction, there is no dependency on the load of the steering motor. On the contrary, the control signal is matched by the choice of the closing characteristic to the actual steering requirement, as preset by the relative rotation of the two slide valve elements with respect to one another. For that purpose, the control throttle is effective over the entire working range of the angle of rotation. This is possible because the control throttle is not connected to the intake path. For that reason, there is also no change from a first to a second kind of determination of the control signal. The amount flowing of by way of the series circuit can be small. In practice, it is determined by supplying sufficient fluid under pressure to the steeri
REFERENCES:
patent: 4620416 (1986-11-01), Yip et al.
patent: 4696161 (1987-09-01), Rasmussen et al.
patent: 4730544 (1988-03-01), Jorgensen
Danfoss A/S
Sotelo Jesus D.
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