CN103026068B - external gear pump - Google Patents

Abstract

This invention relates to an external gear pump having at least two gears meshing with each other in a mating region and a bypass piston. The bypass piston allows for a pressure reduction in the driven external gear pump such that excess delivery volume reaches the suction side of the driven external gear pump via a bypass. A key feature of this invention is that the bypass piston is positioned with a small clearance relative to the gears meshing in the mating region when the bypass is closed.

Description

External gear pump

technical field

The invention relates to an external gear pump having at least two gear wheels meshing with each other in a mating region and having a bypass piston which allows a pressure reduction of the driven external gear pump in such a way that redundant delivery The volume flows from the pressure side of the driven external gear pump to the suction side via a bypass.

Background technique

From the German publication DE 44 36 518 A1 a gear pump is known which has two gears which mesh with each other in a housing, a piston resting against its end face, said piston being mounted axially displaceable in a hollow cylinder. When a defined delivery volume or a predetermined operating pressure is exceeded, the piston moves against the spring force into the hollow cylinder, thereby opening a gap between the bottom of the piston and the end side of the gear for pressure reduction And the excess delivery volume flows directly to the suction side of the pump chamber of the gear pump via this bypass.

Contents of the invention

The object of the invention is to prolong the service life of the external gear pump according to the invention.

This object is solved by an external gear pump having at least two gears that mesh with each other in the mating area and having a bypass piston that can allow the pressure of the driven external gear pump to reduce the excess delivery volume from the pressure side of the driven external gear pump to the suction side via a bypass, the task is solved in that the bypass piston is closed when the bypass is closed relative to the The gears meshing with each other in the mating area are arranged with a small gap. The external gear pump is preferably driven mechanically. For driving the external gear pump, for example, a drive shaft is used which is mechanically coupled to the internal combustion engine. Especially when the delivery medium of the external gear pump is cold and viscous, high backflow pressures and the associated losses can be avoided by the open bypass. This can offer the advantage that the external gear pump does not have to be decoupled from the internal combustion engine when delivery is not required and the internal combustion engine is still running. Undesirable frictional losses, wear and damage to the driven external gear pump can be significantly reduced by the bypass and the small play between the rotating gears.

A preferred embodiment of the external gear pump is characterized in that the outer diameter of the bypass piston is significantly smaller than the outer diameter of the intermeshing gearwheels. This ensures that the axial contact surface for the gear, for example on the housing of the external gear pump, is not reduced as much by the bypass piston as in the gear pump known, for example, from German publication DE 4436518 A1.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston rests on a housing shoulder when the bypass is closed. The housing shoulder can be formed in the bowl-shaped housing base body or in the housing cover. The fact that the bypass piston rests on the housing shoulder makes it possible to arrange the bypass piston with a small amount of play relative to the mating regions of the intermeshing gearwheels in a simple manner.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston is hydraulically preloaded onto the housing shoulder. The hydraulic preloading ensures that the bypass piston rests on the housing shoulder when the bypass is closed. Hydraulic preload can be generated by hydraulic pressure on the bypass piston. When the hydraulic pressure decreases and/or when the delivery pressure of the external gear pump is greater than the hydraulic preload in the mating region of the intermeshing gears, the bypass piston moves away from the housing shoulder and releases the bypass.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston is prestressed against the housing shoulder by means of a spring. This spring is preferably a compression spring, by means of which the bypass piston is held against the housing shoulder when the bypass is closed. The bypass is opened when the delivery pressure in the mating area of the intermeshing gears is greater than the preload of the spring. Hydraulic pressure can additionally be applied to the bypass piston in order to improve the control of the hydraulic piston. A spring can also be used to form a pressure limiting valve with the bypass piston. The bypass piston can then also be used to act as a differential pressure valve if, for example, the delivery pressure of the external gear pump is fed back to the bypass piston as a control force due to the difference in area at the bypass piston. Furthermore, it is also possible for the bypass piston to be produced at least partially from a metal with shape or structure memory, a so-called shape memory alloy. It can thus be achieved that the shape, in particular its dimensions, of the bypass piston change in a temperature-dependent manner. This effect can be used to control the bypass. The bypass piston may also use other temperature dependent components that provide a control force and/or control path. The control force acting on the bypass can also be exerted mechanically, electrically or by means of other technical variables.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston has an axial guide section by means of which the bypass piston is guided reciprocatingly in the housing recess. The housing recess can be arranged in the bowl-shaped housing base body or in the housing cover.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston has an axial bypass section which has a smaller outer diameter than the guide section and is provided with a bypass at its free end. closed surface. The bypass closure surface is, for example, circular and is arranged with a small play relative to the mating regions of the intermeshing gearwheels when the bypass is closed.

A further preferred embodiment of the external gear pump is characterized in that the guide section has a larger axial groove than the bypass section. This improves the guidance of the bypass piston in the housing recess.

A further preferred embodiment of the external gear pump is characterized in that the bypass piston has a step between the guide section and the bypass section, with which step the bypass piston rests against the housing shoulder when the bypass is closed. superior. Through the axial extension of the bypass section, the play between the bypass closing surface and the gear wheels meshing with each other in the mating region can be adjusted.

The invention furthermore relates to the use of the aforementioned external gear pump for supplying a hydraulic control system, in particular a hydraulic control system of an automatic transmission of a motor vehicle. Hydraulic control systems in automatic transmissions supply the transmission actuators on the one hand and are often also necessary for cooling and lubrication functions on the other hand. The use of the inventive external gear pump can provide an advantageous alternative to the mechanical decoupling of the pump from its mechanical drive. Via the bypass released by the bypass piston, the external gear pump can optionally be short-circuited in order to reduce the pressure loss of the driven pump. The delivery of the external gear pump is thereby interrupted.

Description of drawings

Further advantages, features and details of the invention emerge from the following description, in which various exemplary embodiments are described in detail with reference to the drawings. In the attached picture:

Figure 1 is a longitudinal section of an external gear pump according to the invention when the bypass is closed;

Figure 2 is the external gear pump in Figure 1 when the bypass is open;

Figure 3 is an embodiment similar to Figures 1 and 2, with a bypass piston preloaded by a spring in the closed position.

detailed description

1 and 2 show a longitudinal section through an external gear pump 1 with a pump housing 2 , the bypasses being respectively opened and closed here. The pump housing 2 consists of a bowl-shaped housing base body, the bottom of which is reinforced by a plate 3 . The bowl-shaped base body of the pump housing 2 is closed by a pump cover 4 .

In the pump housing 2 two gear wheels 11 , 12 mesh with each other. The gear 11 is driven by a (not shown) drive shaft 14 via a driver 15 . The gear wheel 12 is mounted rotatably on a bearing seat 18 in the pump housing 2 . The two gears 11 , 12 mesh with each other in the mating region 20 in such a way that as soon as the gear 11 is driven via the drive shaft 14 , the conveyed medium is conveyed by means of the two gears 11 , 12 from the suction side of the external gear pump 1 to the pressure. side.

In the mating region 20 of the two gearwheels 11 , 12 , the pump housing 2 has a housing recess 24 , in which recess a bypass piston 25 is guided so as to be reciprocable. Bypass piston 25 delimits with its end side facing away from counter region 20 a control pressure chamber 26 which can be acted upon with hydraulic pressure. The bypass piston 25 is hydraulically biased via the control pressure chamber 26 against a housing shoulder 30 which is formed in the housing recess 24 .

The bypass piston 25 is divided axially into an axial guide section 31 and an axial bypass section 32 . The axial guide section 31 has a larger outer diameter than the axial bypass section 32 . A step 33 is formed between the guide section 31 and the bypass section 32 , with which the bypass piston 25 rests or rests against the housing shoulder 30 in its closed position shown in FIG. 1 . On its end side facing the mating area 20 , the bypass piston 25 has a bypass closing surface 35 which, in the closed position of the bypass piston 25 , is opposite to the gearwheels 11 and 12 in the mating area 20 at a A small gap (not visible in Figure 1) is set.

In the open position shown in FIG. 2, the bypass piston 25 is spaced with its bypass closure surface 35 from the gear wheels 11 and 12 in the mating area 20 to such an extent that a sufficiently large bypass 40 is released, which The pressure side and the suction side of the external gear pump 1 are shorted. The bypass piston 25 is opened, for example, by reducing the hydraulic pressure in the control pressure chamber 26 . The bypass piston 25 can be closed again as required by a corresponding increase in the pressure in the control pressure chamber 26 .

In FIG. 3 there is shown an external gear pump 41 which is very similar to the external gear pump 1 of FIGS. 1 and 2 . The same components are denoted with the same symbols. In order to avoid repetition, only the differences between the two external gear pumps 1 and 41 will be described below.

In the external gear pump 41 shown in FIG. 3 , the bypass piston 45 is prestressed in its closed position by a spring 46 . The spring 46 is configured as a helical compression spring and is partially received in a corresponding groove of the bypass piston 45 . The bypass piston 45 can additionally be controlled hydraulically via the control pressure chamber 26 .

Table of reference signs

1 external gear pump

2 pump housing

3 plates

4 pump covers

11 gears

12 gears

14 drive shaft

15 moving parts

18 bearing seat

20 fit areas

24 housing groove

25 bypass piston

26 control pressure chamber

30 shell shoulder

31 Axial guide section

32 axial bypass sections

33 steps

35 bypass closed surface

40 bypass

41 external gear pump

45 bypass piston

46 springs

Claims (10)

1. an external gear pump, it has at least two intermeshing gears (11,12) and have a pass piston (25) in mating area (20), and described pass piston can allow driven external gear pump (1 as follows; 41) pressure reduces, make unnecessary quantity delivered via the on the pressure side arrival suction side of a bypass (40) from described driven external gear pump (1,41), it is characterized in that, described pass piston (25) is arranged with small―gap suture relative to intermeshing gear (11,12) in described mating area (20) when described bypass (40) is closed, and described pass piston (25) is close to when described bypass is closed and is supported on a housing shoulder (30).

2. external gear pump according to claim 1, is characterized in that, the outer diameter of described pass piston (25) is significantly less than the outer diameter of intermeshing gear (11,12).

3. external gear pump according to claim 1, is characterized in that, described pass piston (25) is tightened on described housing shoulder (30) in advance by with hydraulic way.

4. according to the external gear pump of one of claim 1-3, it is characterized in that, described pass piston (25) is tightened on described housing shoulder (30) in advance by spring (46).

5. according to the external gear pump of one of claims 1 to 3, it is characterized in that, described pass piston (25) has the guide section (31) of an axis, and described pass piston (25) can utilize described guide section to be reciprocally directed in a housing groove (24).

6. external gear pump according to claim 5, it is characterized in that, described pass piston (25) has the bypass section (32) of an axis, and described bypass section has the outer diameter less than described guide section (31) and on its free end, constructs a bypass closing face (35).

7. external gear pump according to claim 6, is characterized in that, the axis of described guide section (31) stretches and stretches large than the axis of described bypass section (32).

8. according to the external gear pump of claim 6 or 7, it is characterized in that, described pass piston (25) has a ladder (33) between described guide section (31) and described bypass section (32), and described pass piston (25) utilizes described ladder backstop on described housing shoulder (30) when described bypass (40) is closed.

9. according to the external gear pump (1 one of the claims Suo Shu; 41) application, for sap pressure supply control gear.

10. application according to claim 9, is characterized in that, described hydraulic control device is the hydraulic control device of the automatic transmission of Motor Vehicle.