Pump with magnetic clutch

Details Pump with magnetic clutch Pump with magnetic clutch

2001-07-13

2003-04-08

Vrablik, John J. (Department: 3748)

Rotary expansible chamber devices

With frangible drive connection or clutch

C418S171000

Reexamination Certificate

active

06544019

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to pumps, in particular to positive-displacement pumps, for oil and other media, preferably liquids. In particular, the invention relates to pumps comprising means of limiting and/or varying delivery. One preferred field of application is in motorized land, air and water vehicles, in particular automobiles and heavy goods vehicles. However, pumps in accordance with the invention are also advantageously applicable in other fields, for example the hydraulic supply of a press.
2. Description of Related Art
In EP 0 994 257 A1 an external gear wheel pump is described, which varies the specific displacement, i.e. displacement/pump speed. This variation is achieved by altering the meshing length of two meshed gear wheels. For this purpose, one of the gear wheels is supported on a piston, receiving on one side the pressure of the pump and on the other side the pressure of a spring, opposing the pump pressure.
A fluid machine in the form of a vane pump including a magnetic clutch is known from EP 0 855 515 A1, for application as a governed motor vehicle coolant pump. The magnetic clutch is adjusted according to the rotational speed, as measured by a sensor, to deliver the coolant according to requirement. Adjustment is achieved by a servomotor and a mechanical gear wheel unit.
In gear wheel pumps, however, for example external and internal gear wheel pumps forming preferred examples of oil pumps in accordance with the invention, two gear wheels mesh and, together with the walls of a surrounding casing, form a displacement space through which the medium to be displaced is delivered, from a low pressure side to a high-pressure side of the pump. The low-pressure side is connected to an inlet port and the high-pressure side to an outlet port of the pump.
In known gear wheel pumps, one of the two gear wheels of a gear wheel set is supported by the casing of the pump. The other gear wheel is rotationally driven by a rotary drive member and is non-rotatably connected to the rotary drive member for this purpose. The rotary drive member supports this gear wheel. In general, the gear wheel is directly connected non-rotatably to the rotary drive member. The rotary drive member is in turn rotatably supported relative to the casing. For reasons of production tolerances, inaccuracies in assembly and loads occurring during operation, the rotary drive member “works” relative to the casing. Accordingly, undesirable movements of the gear wheels of the gear wheel pump relative to each other, for example tilting, also arise.
Positive-displacement pumps, in particular gear wheel pumps, generally comprise a specific delivery [displacement/feed-wheel speed] which is constant according to the system involved, because the geometry of the displacement pockets cannot be altered. They show a proportionality of delivery to speed, as long as the filling ratio of the displacement pockets is 100%. However, in many applications this proportionality is disruptive and undesirable. In a press for example, although a high delivery of the hydraulic fluid is necessary for the rapid motion, only high pressure is required in the end phase of the working stroke, and the oil delivery requirement drops to zero. Since the drive speed of such pumps in presses remains as a rule constant, a high-pressure excess flow of oil arises, which is returned to the fluid reservoir afflicted with a loss of energy. Such an excess flow is particularly disruptive, for example, in automotive engine lube pumps and in automatic transmission fluid pumps. At low engine speeds and thus low pump speeds, these assemblies do require a minimum delivery when idling, and a minimum fluid pressure at high speed, however the flow requirement at high speed is well under the proportionality line, at top speeds mostly under a third of the proportionality flow.
SUMMARY OF THE INVENTION
It is an object of the invention to reduce noise and wear in pumps, preferably in oil pumps and hydrostatic pumps in general, said pumps having means for limiting or varying delivery, or both in combination.
This object is achieved by the subject matters of the independent claims. The sub-claims describe particularly preferred embodiments of pumps.
In accordance with the invention, a pump, preferably a gear wheel pump, is driven via a magnetic clutch. By a rotational drive of the pump being transmitted from a rotary drive member via a magnetic clutch to one of the at least two feed wheels of the pump, the feed wheel nearest to the rotary drive member in the flow of the force, termed the first feed wheel in the following, can be supported independently of the rotary drive member. No mechanical, in particular no positively locking, drive coupling exists between the rotary drive member and the first feed wheel. Possibly occurring, unavoidable friction forces can be assumed to be negligible. In this sense, the first feed wheel is freely rotatable relative to the rotary drive member, aside from the drive coupling produced by the magnetic clutch. In particular, a casing of the pump may form the rotary bearing of the first feed wheel.
The other feed wheel, preferably driven only by the first feed wheel and mating with the first feed wheel to form displacement pockets, is likewise rotatably supported to advantage by the casing. In this way, one and the same rigid body, namely the casing, preferably a single-piece casing part, forms the rotary bearing for the first feed wheel as well as the rotary bearing for the further, second feed wheel. The axes of rotation of the two feed wheels in the pump according to the invention are thus orientated relative to each other more precisely than when the feed wheels are supported on or upon elements moving relative to each other. In particular, the engagement of the two feed wheels with each other can now no longer be disrupted by the change in the loads acting on the rotary drive member, or at least far less than in known pumps. Inaccuracies stemming from assembly are also reduced. The magnetic clutch acts between the rotary drive member and the first feed wheel as a damping member against the transmission of disruptions or irregularities.
The magnetic clutch is preferably configured as a hysteresis or induction-type clutch, or a combination of both. Although less preferred, it is also, however, possible to configure it as a permanently magnetic clutch. The magnetic clutch comprises a magnetic rotating element of a permanently magnetic material in its input half and/or output half. Preferably, the magnetic rotating element is fitted to a soft-iron as a base. A rotating element of the other half of the clutch, producing with the magnetic rotating element the transmission of the magnetic torque, is formed by means of an induction material, or preferably by means of a hysteresis material or a combination of both. An induction material, for example Cu or Al, may form a feedback means and a base for a hysteresis rotating element. However, in such a combined hysteresis/induction clutch, a hysteresis/induction rotating element is preferably likewise fitted to a soft-iron as a base. If the rotating element consists solely of a hysteresis material or solely of an induction material, then a soft-iron likewise advantageously forms the base and the feedback means.
The magnetic clutch may be a face-acting or, more preferably, a centrally-acting rotary clutch. A combination of the two also represents a preferred embodiment.
A gear wheel pump is preferably formed by an internal gear wheel pump or an external gear wheel pump. A gear wheel pump may be formed particularly compactly when the two halves of the magnetic clutch form a central-type rotary clutch, or a combination central/face-type clutch in which the magnetically interacting, concentrically arranged rings encircle the mating feed wheels of the pump, preferably spaced radially from the feed wheels. The combination of an internal gear wheel pump with such a magnetic clutch is of particular advantage.
If the rotary drive member is fo

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