Fluid handling – Self-proportioning or correlating systems – Self-controlled branched flow systems
Patent
1994-01-14
1995-02-21
Nilson, Robert G.
Fluid handling
Self-proportioning or correlating systems
Self-controlled branched flow systems
60384, B62D 509
Patent
active
053906934
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a flow amplifier with an inlet and an outlet, between which a first branch, through which a flow of a fluid to be amplified is flowing, with a first throttling device, the throttle resistance of which is adjusted in dependence on the pressure across and by the flow rate through the first throttling device, and a second branch with a second throttling device, the throttle resistance of which is adjusted in dependence on the throttle resistance of the first throttling device, are arranged parallel to one another.
A flow amplifier of that kind is known from U.S. Pat. No. 4,914,913. Such a flow amplifier is used in a hydraulic standard control system for heavy vehicles in which a control unit, which controls the flow amplifier, supplies a control cylinder with oil. The amplification factor of the flow amplifier can be varied in dependence on the speed of rotation of the steering handwheel, so that the amplification factor increases as the steering handwheel speed increases. This is achieved in that the second throttling device is opened more at a higher steering handwheel speed than at a lower steering handwheel speed, with the result that the throttle resistance of the second throttling device is reduced. At any rate, in the case of the known flow amplifier the amplification factor is additionally dependent on the pressure drop and the friction around the measuring motor, so that precision adjustment elements have to be provided here.
The invention is based on the problem of producing a flow amplifier which can be kept substantially unaffected by detrimental influences.
This problem is solved in a flow amplifier of the kind mentioned in the introduction by providing at least one pressure-divider with a central take-off point, which is supplied by a pressure difference between inlet and outlet or a pressure difference depending thereon, the pressure at the central take-off point controlling the flow rate through the second throttling device.
The pressure controlling the flow rate through the second throttling device can then be controlled without being influenced by the pressure drop at the measuring motor or by other variables. It is solely dependent on a fixedly predeterminable or adjustable pressure which moves between the pressure at the inlet and the pressure at the outlet of the flow amplifier. The flow rate through the second throttling device is therefore influenced firstly by the flow rate through the first throttling device. Secondly, it is influenced by the pressure at the central take-off point of the pressure-divider. Both variables are combined by multiplication with one another, so that by superimposing the two flows through the first and through the second throttling device the flow through the first throttling device is amplified. The amplification can be proportional, the proportionality factor being determined substantially by the throttle resistance of the second throttling device. A progressive or degressive amplification is also possible.
In a preferred construction, the division ratio of the pressure-divider is adjustable. Because the pressure at the central take-off point controls the flow rate through the second throttling device, a change in the division ratio also generates a change in the flow rate through the second throttling device. A flow amplifier with a variable or adjustable amplification factor is obtained in this way. The amplification factor, that is, the proportionality factor between the flow to be amplified and the sum of the two flows through the first and the second throttling device, can be changed by a simple change in the division ratio.
For that purpose, the pressure-divider has a divider-throttling device between the central take-off point and each of its ends, at least one of which devices has an adjustable throttle resistance. By adjusting the throttle resistance the division ratio of the pressure-divider can be varied.
It is preferable for at least one divider-throttling device to have an electromagnetic valve. The throttle resistance
REFERENCES:
patent: 4759182 (1988-07-01), Haarstad
patent: 4914913 (1990-04-01), Germain
patent: 4947894 (1990-08-01), Obidin
Danfoss A/S
Nilson Robert G.
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