Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1998-09-14
2001-04-10
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C180S442000, C137S625240, C060S384000
Reexamination Certificate
active
06213247
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic steering device, in particular for vehicles, having a housing in which two sliders are arranged to move relative to one another and together form at least one adjustable throttle, a restoring device for restoring the two sliders to their neutral position being provided, one of the two sliders being driveable and the other of the two sliders being in operative connection with a measuring device. Furthermore, the invention relates to a method for steering a vehicle, in which hydraulic fluid is supplied to steering motor, is passed by way of a steering device and back again, two sliders being mutually displaced in the steering device.
Such a steering device and such a method are known from U.S. Pat. No. 4,759,182. The two sliders are in that case arranged concentrically with respect to one another in the housing. They are mutually rotated during steering, in which case the inner slider can be acted upon by a steering handwheel whilst the outer slider is connected by way of a spring arrangement, which serves as the restoring arrangement, to the inner slider. In this manner a certain relative movement is possible between the two sliders. The neutral position can be achieved, however, only if hydraulic fluid has flowed through the measuring motor and has driven it so that the outer slider is able to track the inner slider. With the known steering device, it is intended to achieve amplification of the hydraulic fluid so that not all of the hydraulic fluid is able to flow through the measuring motor. For that purpose an adjustable throttle is provided parallel to the measuring motor.
Nevertheless, it should also be possible to operate such steering devices even when the pressure source fails. In that case the measuring motor has to be used as an auxiliary pump, which generates the pressure required to control the steering motor. For that reason the adjustable throttle in the flow path that is arranged parallel to the measuring motor has to close at the upper end of the control range. The in itself intended amplification of the hydraulic flow thus disappears just as a large and rapid angle of lock is being effected. It is precisely in critical situations, however, that such an angle of lock is often desirable. If the desired amplification is not forthcoming, this can lead to dangerous situations.
SUMMARY OF THE INVENTION
The problem underlying the invention is to improve the co-operation between the steering torque and the amplification of the flow, in particular to linearize the relationship between steering torque and amplification of the flow in a better manner and to improve the stability of the steering device.
In a steering device of the kind mentioned in the introduction, that problem is solved in that the measuring device is arranged in a flow path closed in itself, and operates as a pump, and an open flow path runs past the closed flow path from an inlet connection arrangement to an outlet connection arrangement.
The outlet connection arrangement in this case contains two working connections that are connected to a steering motor. Depending on which one of the two working connections is being pressurized, the steering motor steers to the left or to the right. The inlet connection arrangement comprises a pump connection, which is connected to a pump or to another source of pressure, and a tank connection, which feeds hydraulic fluid flowing back from the steering motor back into the tank. The construction according to the invention provides two circulations, which can be isolated from one another hydraulically. These circulations are the closed flow path, in which the measuring device is arranged and which is designed merely to control the relative movement of the two sliders, and the open flow path, through which the “working fluid” flows from the pressure side to the steering motor and back again. At least the open flow path is controlled by the movement of the two sliders relative to one another. After actuation of the one slider, the adjustable throttle in the open flow path is opened and the hydraulic fluid is able to flow from the pump to the working connections. By means of the restoring device, the driven slider now attempts to take the non-driven slider with it, that is, the restoring device tracks the other slider onto the driven slider. In this connection, however, the guided slider has to operate the measuring device in the form of a pump and convey a fluid through the closed circulation so that because of this work to be performed, restoring of the non-driven slider into the neutral position is delayed. With an appropriate configuration of the adjustable throttle and of the two sliders, it is possible to ensure that on movement of the one slider effected by the external drive means, the throttle in the open flow path remains open just long enough for the desired amount of hydraulic fluid to flow to the steering motor. The desired amount of hydraulic fluid is the amount that is necessary to move the steering motor by a desired distance. Because the closed flow path is kept clear of the hydraulic fluid in the open flow path, the measuring device can be made relatively small. Good accuracy is achieved even when the vehicle requires a relatively large amount of hydraulic fluid for steering, which is the case, for example, with large vehicles or driven machines. Both flow paths can be dimensioned independently of one another. Isolating the two flow paths from one another prevents hydraulic fluid being forced out of the open flow path into the closed flow path. In addition, the steering device is more stable than known steering devices, in particular in respect of a tendency to oscillate.
In a preferred construction, the closed flow path has at least one throttle that is adjustable through movement of the two sliders relative to one another. In this manner the control behaviour of the steering device can be yet further improved. The response behaviour of the steering device can, in fact, be changed by the adjustable throttle in the closed flow path. When the throttle is opened wide, the non-driven slider is able to track onto the driven slider more quickly than when this throttle is closed or almost closed. The adjustable throttle in the closed flow path accordingly also remains open for a longer or for a shorter period. The adjustable throttle in the closed flow path therefore provides a further opportunity for the amplification factor of the steering device to be influenced.
In the closed flow path there is preferably at least one adjustable throttle which increases the flow resistance through the closed flow path from a predetermined relative movement of the two sliders onwards. In this manner, particularly when using a steering handwheel to drive the one slider, a counter-torque can be generated, because it is more difficult for the restoring device to guide the non-driven slider on account of the greater hydraulic resistance in the closed flow path. The counterforce that is acting on the driven slider through the restoring device is accordingly the force then acting on the steering handwheel.
The open flow path preferably has at least one adjustable throttle, both between the inlet connection arrangement and the outlet connection arrangement and between the outlet connection arrangement and the inlet connection arrangement. A more uniform distribution of the forces acting on the two sliders can thus be achieved. The risk that the two sliders will become jammed against one another or in the housing is less. By using two throttles matched to one another, the load on an individual throttle is additionally kept lower.
In the open flow path there is preferably arranged an adjustable measuring throttle, which serves as signal generator for an LS-signal. An LS-signal, which is also called a loadsensing-signal, provides information about the pressure load in the steering device. This information can be used, for example, for controlling, as required, the pump providing the necessary hydraulic pressure.
Prefer
Arbjerg Niels
Rom Holger Krogsgård
Danfoss A/S
Johnson Brian L.
Lee Mann Smith McWilliams Sweeney & Ohlson
Lerner Avraham H.
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