GB1575328A

GB1575328A - Gear pump or motor

Info

Publication number: GB1575328A
Application number: GB2137977A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1976-05-25
Filing date: 1977-05-20
Publication date: 1980-09-17
Also published as: FR2352947A1; FR2352947B3; IT1082090B; DE2623357A1

Description

(54) A GEAR PUMP OR MOTOR (71) We, ROBERT BOSCH GmbH, a German company of Postfach 50, 7000 Stuttgart 1, Germany., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a gear pump or motor, hereafter referred to as a gear machine.

A gear machine has been proposed which has a pilot groove on the high pressure side at the housing wall facing the side surfaces of the gear wheels in the vicinity of the engaging teeth, which groove is so arranged that the single point of contact of a pair of teeth and the reversal point of the sealing tooth engagement coincide with the groove.

With such machines, the pilot groove is so formed that the points referred to above are spaced from one another. That has the result that at the teeth which are in contact considerable change-over forces occur which, among other things, lead to undesirable noise.

According to the present invention there is provided a gear pump, or motor, comprising a housing containing a pair of gear wheels meshing in external engagement, the housing having surfaces facing and adjacent the side surfaces of the gear wheels, which housing surfaces are provided with grooves on the high pressure side of the gear wheels, the grooves being in communication with an outlet, or inlet, bore for the high pressure working fluid and extending towards, but not as far as, a plane containing the axes of rotation of the gear wheels, the nearest approach of the grooves to the said plane being such that, in use, the moment at which the period when the entire torque load transmitted between the gear wheels is transmitted by one tooth on each wheel commences coincides with the moment at which the sealing between the gear wheels returns to the pair of teeth still in contact as the preceding pair of teeth move out of contact.

An embodiment of the invention has the advantage that the impact loading and the sudden unloading of the teeth in a particular region (action region) are avoided. This occurs without any additional outlay, since it is due only to a particular positioning of the pilot groove on the high pressure side.

The noise produced by the gear machine is substantially reduced.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings, wherein: Figure 1 is a longitudinal section through a gear machine; Figure 2 is a section on the line II-II of Figure 1; Figure 3 is an enlarged representation of teeth engagement; and Figure 4 is a diagram of the teeth engagement.

The gear machine shown in the drawings has a central housing portion 10 which is closed at each end by a cover 11, 12. In the central housing portion 10, there is provided a recess 13 passing therethrough, which is formed by two intersecting bores 14, 15 so that the recess has substantially the cross sectional shape of a numeral 8. Two bushlike bearing members 16, 17 are arranged in alignment and opposite one another in the recess 15, in the aligned bores 18, 19 of which are mounted shaft journals 20, 21 of a gear wheel 22.

Two bush-like bearing members 23, 24 are arranged in alignment in the bore 14, in the aligned bores 25, 26 of which are mounted shaft journals 27, 28 of a gear wheel 29 which meshes in external engagement with the gear wheel 22. The shaft journal 28 has an extension 30 which projects beyond the cover 12 through a bore 31 provided in the cover and serves for driving the gear machine when operating as a pump.

A bore 32 which is in communication with the low pressure side, enters into the recess 13 from one side of the housing at the level of the gear wheels, whereas a bore 33 which is arranged on the high pressure side of the machine, enters the recess 13 from the opposite side of the housing and coaxially with respect to the bore 32.

Grooves or recesses in communication with the high pressure side are formed on the ends of the bearing members facing the side surfaces of the gear wheels, of which the visible recesses in the bearings 17, 24 are referenced 34 and 37. The recess 34 is made up of two symmetrical halves 35, 36, wherein the portion 35 is arranged in the bearing member 17, the portion 36 is arranged in the bearing member 24. The depth of these recesses amounts to a few millimetres. The recess 34 extends towards the plane A-A containing the axes of rotation of the gear wheels but does not, however, extend up to the plane. The extent to which the summits 35', 36' of the recess 34 approach the plane A-A is shown in Figure 3, wherein the line of action of the gear wheels 22, 29 is referenced e. The same references are also to be found in Figure 4.Therein, the axes of the gear wheels 22, 29 are referenced 0i and 0, respectively. The points of contact of the base circle-radii of the gear wheels with the line of action, are referenced Nl and N2; this is also the usable portion of the line of action. The adjacent points K, and K2 are points of intersection of the addendum circle radii dk, and dk2 of the gear wheels 22, 29 with the line of action. D1 and D2 are the sealing points of the teeth to which further reference will be made below. The point E, illustrates where a tooth of the wheel 22 comes out of contact with a tooth of the wheel 29.A further tooth of the wheel 29 comes into contact with a tooth of the wheel 22 at point E. At the point K2, the addendum circle of the wheel 29 touches the flank of a tooth of the wheel 22 for the first time (= beginning of contact). The teeth of the wheels come out of contact at the point K1. Thus, point El for one pair of teeth is reached at the moment when the preceding pair of teeth reach point K1, whilst point E, for one pair of teeth is reached at the moment when the succeeding pair of teeth reach point K2. In the region E,-E2 only one tooth of each wheel is continually in contact with a tooth of the other wheel, but outside this region two teeth of each wheel are in contact with two teeth of the other wheel.The teeth which are in contact in the region between D1 and D2 seal the high pressure side with respect to the low pressure side. The point of sealing travels from D1 towards D2. At point D2, the sealing point changes back from the point D2 to the point D1 brought about by the presence of the recess 34. The distance the sealing point is moved is the extent of a tooth thickness + tooth spaces measured on the pitch circle. In so doing, the torque and the tooth force is reduced. When a tooth of the gear wheel 29 comes out of contact at the point El, the tooth force is doubled.

When, at the point D2, the sealing point returns to D1, the tooth force is reduced. If the point D1 is spaced from the point El as shown in Figure 4 strongly changing tooth forces are encountered. Undesirable noise is stimulated due to these strongly changing tooth forces.

It has now been established, that if the points El and D1 are made to coincide, these forces can be reduced. This coincidence is achieved by making the recess 34 extend up to a point at which the leading flank F of the tooth 22' of the gear wheel 22 is tangential to the recess 34, (as shown in Figure 3) when the crest of the tooth 22" arrives at the point K1, that is to say comes out of contact with the tooth 29". Then, of course, the points El and Dl coincide. The unloading of the tooth at the point D1 and the impact loading at the point El coincide and tend to cancel each other out.

The form of the pilot grooves can, of course, be of any other form provided they fulfill the above requirement. Pilot grooves can be entirely omitted from the low pressure side, but they can however be provided as is shown in Figure 2. This recess is referenced 37. A similar recess is located on the opposite side of the bearing member.

Both recesses are in communication with the bore 32. The distance between the sealing points D1 and D2 is referenced te in Figure 4 and represents the base pitch contact.

In the embodiment described above, bearing members are provided in which the recesses referred to are arranged. With pumps not having such bearing members, thus those in which the shaft journals are mounted directly in the housing, the recesses are then formed in the side surfaces of the housing, for example in the covers.

WHAT WE CLAIM IS: 1. A gear pump, or motor, comprising a housing containing a pair of gear wheels meshing in external engagement, the housing having surfaces facing and adjacent the side surfaces of the gear wheels, which housing surfaces are provided with grooves on the high pressure side of the gear wheels, the grooves being in communication with an outlet, or inlet, bore for the high pressure working fluid and extending towards, but

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. journal 28 has an extension 30 which projects beyond the cover 12 through a bore 31 provided in the cover and serves for driving the gear machine when operating as a pump. A bore 32 which is in communication with the low pressure side, enters into the recess 13 from one side of the housing at the level of the gear wheels, whereas a bore 33 which is arranged on the high pressure side of the machine, enters the recess 13 from the opposite side of the housing and coaxially with respect to the bore 32. Grooves or recesses in communication with the high pressure side are formed on the ends of the bearing members facing the side surfaces of the gear wheels, of which the visible recesses in the bearings 17, 24 are referenced 34 and 37. The recess 34 is made up of two symmetrical halves 35, 36, wherein the portion 35 is arranged in the bearing member 17, the portion 36 is arranged in the bearing member 24. The depth of these recesses amounts to a few millimetres. The recess 34 extends towards the plane A-A containing the axes of rotation of the gear wheels but does not, however, extend up to the plane. The extent to which the summits 35', 36' of the recess 34 approach the plane A-A is shown in Figure 3, wherein the line of action of the gear wheels 22, 29 is referenced e. The same references are also to be found in Figure 4.Therein, the axes of the gear wheels 22, 29 are referenced 0i and 0, respectively. The points of contact of the base circle-radii of the gear wheels with the line of action, are referenced Nl and N2; this is also the usable portion of the line of action. The adjacent points K, and K2 are points of intersection of the addendum circle radii dk, and dk2 of the gear wheels 22, 29 with the line of action. D1 and D2 are the sealing points of the teeth to which further reference will be made below. The point E, illustrates where a tooth of the wheel 22 comes out of contact with a tooth of the wheel 29.A further tooth of the wheel 29 comes into contact with a tooth of the wheel 22 at point E. At the point K2, the addendum circle of the wheel 29 touches the flank of a tooth of the wheel 22 for the first time (= beginning of contact). The teeth of the wheels come out of contact at the point K1. Thus, point El for one pair of teeth is reached at the moment when the preceding pair of teeth reach point K1, whilst point E, for one pair of teeth is reached at the moment when the succeeding pair of teeth reach point K2. In the region E,-E2 only one tooth of each wheel is continually in contact with a tooth of the other wheel, but outside this region two teeth of each wheel are in contact with two teeth of the other wheel.The teeth which are in contact in the region between D1 and D2 seal the high pressure side with respect to the low pressure side. The point of sealing travels from D1 towards D2. At point D2, the sealing point changes back from the point D2 to the point D1 brought about by the presence of the recess 34. The distance the sealing point is moved is the extent of a tooth thickness + tooth spaces measured on the pitch circle. In so doing, the torque and the tooth force is reduced. When a tooth of the gear wheel 29 comes out of contact at the point El, the tooth force is doubled. When, at the point D2, the sealing point returns to D1, the tooth force is reduced. If the point D1 is spaced from the point El as shown in Figure 4 strongly changing tooth forces are encountered. Undesirable noise is stimulated due to these strongly changing tooth forces. It has now been established, that if the points El and D1 are made to coincide, these forces can be reduced. This coincidence is achieved by making the recess 34 extend up to a point at which the leading flank F of the tooth 22' of the gear wheel 22 is tangential to the recess 34, (as shown in Figure 3) when the crest of the tooth 22" arrives at the point K1, that is to say comes out of contact with the tooth 29". Then, of course, the points El and Dl coincide. The unloading of the tooth at the point D1 and the impact loading at the point El coincide and tend to cancel each other out. The form of the pilot grooves can, of course, be of any other form provided they fulfill the above requirement. Pilot grooves can be entirely omitted from the low pressure side, but they can however be provided as is shown in Figure 2. This recess is referenced 37. A similar recess is located on the opposite side of the bearing member. Both recesses are in communication with the bore 32. The distance between the sealing points D1 and D2 is referenced te in Figure 4 and represents the base pitch contact. In the embodiment described above, bearing members are provided in which the recesses referred to are arranged. With pumps not having such bearing members, thus those in which the shaft journals are mounted directly in the housing, the recesses are then formed in the side surfaces of the housing, for example in the covers. WHAT WE CLAIM IS:

1. A gear pump, or motor, comprising a housing containing a pair of gear wheels meshing in external engagement, the housing having surfaces facing and adjacent the side surfaces of the gear wheels, which housing surfaces are provided with grooves on the high pressure side of the gear wheels, the grooves being in communication with an outlet, or inlet, bore for the high pressure working fluid and extending towards, but

not as far as, a plane containing the axes of rotation of the gear wheels, the nearest approach of the grooves to the said plane being such that, in use, the moment at which the period when the entire torque load transmitted between the gear wheels is transmitted by one tooth on each wheel commences coincides with the moment at which the sealing between the gear wheels returns to the pair of teeth still in contact as the preceding pair of teeth move out of contact.

2. A gear pump, or motor, according to claim 1 wherein the grooves each include two projections which extend towards the said plane.

3. A gear pump, or motor, according to claim 1 or claim 2 wherein the housing surfaces are provided with corresponding grooves on the low pressure side of the gear wheels.

4. A gear pump, or motor, substantially as hereinbefore described with reference to and as shown in the accompanying draw ings.