Rotary expansible chamber devices – Working chamber surface expressed mathematically
Reexamination Certificate
2002-10-29
2004-03-02
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Working chamber surface expressed mathematically
C418S225000
Reexamination Certificate
active
06699025
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a roller vane pump, in particular suited for pumping fluid in a continuously variable automatic transmission (CVT) for motor vehicles. Such a roller vane pump is known from the European patent 0.921.314 and is intended for pumping automatic transmission fluid in hydraulically controlled and/or operated continuously variable transmissions for motor vehicles. Particularly in a belt-and-pulley type CVT, a large flow of fluid at a high pressure may be required for control of the transmission. Since the pump is usually drivingly connected to a main drive shaft of the vehicle, it is designed to be able to provide a desired pump yield, i.e. a desired flow of fluid, even at a lower most rotational speed of the vehicle engine, i.e. idle engine speed. At the same time, the pump is designed to reliably withstand prolonged operation at an upper most rotational speed of the vehicle engine.
The pump is provided with a pump housing accommodating a substantially cylindrically shaped carrier, which is rotatable about a central axis extending in a axial direction by means of a pump shaft, and with a ring shaped cam ring radially encompassing the carrier. The carrier is provided with a slot extending inward from its radially outer surface in an essentially radially direction, which slot slidably accommodates an essentially cylindrically shaped roller element having a roller diameter. The carrier, the roller element and the cam ring have virtually the same axial dimension and are enclosed by the pump housing on either axial side. During operation of the pump, the carrier is rotated, whereby the roller element contacts a radially inner surface of the cam ring, i.e. the cam surface, under influence of a centripetal force. The housing, the carrier, the cam ring and the roller element then enclose a rotating pump chamber.
The cam surface is located at a radial distance from the central axis, which varies in dependence on an angular rotation in the direction of rotation of the carrier along the circumference of the cam ring according to a so-called cam curve. Said radial distance varies such, that the volume of a pump chamber cyclically increases and decreases during operation of the pump, due to said radial distance increasing respectively decreasing. The pump operates in that fluid is allowed to flow into the pump chamber at a location where its volume increases, i.e. at a low pressure pump section, and out of the pump chamber at a location where its volume decreases, i.e. at a high pressure pump section. For effecting smooth operation of the pump, it is known in the art to adopt a smoothly changing cam curve, i.e. to provide the pump with a cam ring having a cam surface that is curved such that said radial distance varies smoothly in dependence on the angular rotation.
Although the known pump functions satisfactory per se, the noise generated by the pump designed according to the known art is at a surprisingly high level, particularly when applied in a CVT. Furthermore, it is found that the efficiency of the known pump applied in a CVT is considerably lower than what might be expected beforehand. These disadvantages are particularly a problem for automotive application of the CVT, where high efficiency and low noise levels are generally considered to be a prerequisite.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems associated with the application of the known roller vane pump to a large extend and, more in particular, to provide for a roller vane pump having an improved design with regard to pump efficiency and pump noise.
According to the invention these objects are achieved with the roller vane pump defined by the characterising features of claim
1
. With the pump according to the invention the said contact between the roller element and the cam surface is ameliorated, thereby realising an improved pump efficiency and acceptable pump noise levels. The measure according to the invention effects that a radially outwardly oriented acceleration of the roller element required for maintaining said contact when said radial distance increases, which acceleration is substantially proportional to the second mathematical derivative of the cam curve, is smaller than a radially outward, or centrifugal, acceleration experienced by the roller element during operation of the pump, which centrifugal acceleration is proportional to the radial position of a mass centre point the roller element. According to the invention said radial position is determined by said radial distance according to the cam curve minus halve the value of the roller diameter or may be approximated by said radial distance only, which usually results in an approximation of the actual centrifugal acceleration within about 10%.
With the measure according to the invention, the so-called phenomenon of bouncing rollers, i.e. the breaking and making of the contact between the roller element and cam surface, which has an adverse effect on pump efficiency because it enables leakage of fluid between the roller element and the cam ring, is advantageously avoided, simultaneously with irritating noise peaks caused by said bouncing. Put alternatively, the invention provides a tool for determining the optimum, i.e. minimum, radial dimension of the roller vane pump for a given cam curve, which is determined by the desired pump yield.
It is remarked, that when taking a minimum value of the cam curve for said radial distance, the actual value of said radial distance at the value of the angular rotation where the maximum value of the second derivative of the cam curve occurs is approximated fairly accurately, as well as on the safe side. This is, because in the usually adopted pump designs, said maximum value occurs in the direct vicinity in terms of angular rotation of said minimum value.
The measure defined in the characterising portion of claim
1
is particularly suited and intended for a roller vane pump of the present type, rather than e.g. for a pump having slots that are oriented at a substantial angle with respect to the radial direction, since in such a pump a variable driving force exerted on the roller element by the carrier during rotation thereof has a radially oriented component which acts on the roller element. According to the invention such radially oriented component is highly undesirable, since it is variable, for instance in dependence on the rotational speed of carrier, and since it either decreases the radially outward oriented acting on the roller element or increases friction between the roller element and the cam surface, or for a blade vane pump where the present measure would not be suited, since in such a pump not only a centrifugal force acts on the blades, but also a variable force resulting from a pressure gradient prevailing in radial direction over the vane and often also from a resilient element located between the carrier and the vane.
The pump according to the invention is in particular suited for automotive application. According to the invention, it is for such application highly advantageous, if not only the cam curve itself is a continuous curve, i.e. a curve of which at least the first order mathematical derivative does not show any step changes, but also the first and the second, or even higher, order mathematical derivatives thereof. In this manner a smooth operation of the pump is obtained between said lower most and said upper most rotational speed of the vehicle engine. As a consequence, variations in said radial distance associated with a changing volume of the pump chamber at the high pressure and the low pressure pump sections require a considerable part of the circumference of the cam ring for their accommodation. To still be able to accommodate said variations along the circumference of the cam ring, the rate of change of said radial distance in dependence on the angular rotation must be increased, in which case the phenomenon of bouncing rollers may then unwittingly become a problem. However, in the pump accord
Denion Thomas
Trieu Theresa
Van Doorne's Transmissie B.V.
Young & Thompson
LandOfFree
Roller vane pump does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Roller vane pump, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Roller vane pump will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3231344