Patent Application
20050164830
The invention concerns a hydraulic gearshift arrangement of an automatic transmission for motor vehicles according to the preamble of patent claim 1.
Automatic transmissions for motor vehicles are equipped with a hydraulic fluid circulation system, the task is to provide the various parts of the automatic transmission, i.e., the converter, the shifting elements and the gear transmission with pressure fluid, cooling fluid and lubricating oil. For these different tasks, a hydraulic fluid (a so-called ATF fluid) is used, which is brought to system or main pressure by a hydraulic pump and is transported in a main pressure line. From the main pressure line individual fluid streams of differing pressure levels are branched off, which is executed by way of pressure reducer valves and distributing valves.
Among other things, a partial stream is branched off from the main pressure line for the various lubricating points of the automatic transmission, e.g., planetary gears and lamella of the shifting elements. In this, the necessary lubricating pressure is controlled by a central lubricating valve. In most cases, there is also a fluid cooler in the partial stream for lubrication, in which the hydraulic fluid is cooled by means of ambient air or by means of a cooling agent from the cooling circuit of the combustion engine of the motor vehicle. Such a hydraulic fluid circulation system is known from DE-A 39 37 976. In this circulation system, the lubricating valve is arranged behind the fluid cooler in direction of the fluid stream, namely, by the in-line arrangement of a control valve.
In other known hydraulic fluid circulation systems of the Applicant, the central lubricating valve is arranged in the supply of the fluid cooler, i.e., upstream, wherein the stream of lubricating oil exiting the fluid cooler provides the lubricating pressure level. The fluid-sided decrease of pressure in the fluid cooler is dependent upon the fluid temperature, i.e., the viscosity of the hydraulic fluid. In this respect, there is a greater decrease in pressure at lower temperatures, which results overall in a lubricating oil stream with a changeable fluid pressure level.
The present invention is based upon the objective of creating a hydraulic gear shift arrangement in the form stated in the beginning, such that a constant lubricating pressure or a constant lubricating oil stream is achieved.
This objective is attained with the characteristics of patent claim 1.
The invention provides that the pressure in the cooler return, the so-called return pressure, is carried back to the lubricating valve, i.e., the lubricating valve is connected to both the supply and the return of the fluid cooler. Depending upon the design of the lubricating valve and the arrangement of the pressure ports, on one hand, a constant lubricating oil pressure and, on the other hand, a constant lubricating oil stream can be achieved.
In an advantageous embodiment of the invention, the lubricating valve has a valve bore in which a gate valve is displaceably arranged and is weighted by a valve spring. Furthermore, the valve bore has individual toroidal chambers;
a control chamber and spring chamber, which serve as pressure ports for the connection to the supply and return or for the system pressure.
A further object of the invention is the cooler return connected via a control line to the frontal side control space, in which the first piston of the spring-weighted gate valve is accommodated. The return pressure is thereby carried back onto the piston surface of the first piston. The pressure in the control space is determined by the valve spring force. This creates the advantage that downstream of the fluid cooler, i.e., in its return, a constant pressure exists, which is available as constant lubricating pressure to the lubricating points of the automatic transmission.
The lubricating pressure is no longer dependent upon the decrease of pressure in the cooler.
Yet another object of the invention is a pressure relief valve arranged parallel to the cooler. This creates the advantage that the cooler is protected against an inadmissibly high supply pressure, since the supply pressure also increases with an increasing decrease in pressure.
In a further advantageous embodiment of the invention is the control line connected to the return of the return pressure with the frontal side spring chamber of the lubricating valve. Thereby, the return pressure is carried back onto the piston surface of the second piston, which is equal to the piston surface of the first piston. This results in a constant decrease in pressure at the cooler, which is adjusted via the rigidity of the spring of the valve spring, and the piston surfaces. By means of this constant decrease in pressure, the advantage of a constant lubricating oil stream is achieved.
A still further object of the invention, the supply pressure of the cooler is carried onto the piston surface of the second piston and via a pressure compensation line onto the piston surface of the first piston, i.e., into the control space. This creates the advantage that the pressure peaks of the supply pressure are dampened for the protection of the fluid cooler.
Exemplary embodiments of the invention are shown in the drawing, and are explained in more detail in the following, whereby is shown in:
A central lubricating valve 1 is connected to a main pressure line 2 with a system pressure Psys via a throttle 3. The lubricating valve 1 consists of a valve bore 4, in which a gate valve 5 is displaceably accommodated with two pistons 6, 7, and is weighted by a pressure spring 8. The lubricating valve 1, the housing of which is only partially illustrated in hatched form, has four ports, namely a frontal side control space 9, as well as a first toroidal chamber 10, a second toroidal chamber 11, and a third toroidal chamber 12. To the toroidal chamber 10, the main pressure line 2 is connected via the throttle 3. The valve bore 4 ends at the front side in a spring chamber 13, which accommodates the pressure spring 8, which is supported on the one hand at the valve body 1, and on the other hand at the piston 7. From the third toroidal chamber 12 a supply line 14 leads to the fluid cooler 16 via a throttle 15. The lubricating valve 1 is thereby arranged in the supply of the fluid cooler 16. The fluid flowing to the cooler 16 via the supply line 14, flows through the fluid cooler 16, and subsequently enters the return line 17, which, via a further throttle 18, leads to lubricating spots of the automatic transmission, which are not illustrated here, and supplies these, e.g., planetary gears, or lamella of gear boxes, with lubricating oil and cooling fluid. The return line 17 is connected to the control space 9 of the lubricating valve 1 via a control line 19, and a further throttle 20. Parallel to the fluid cooler 16 a pressure relief valve 22 is connected via a bypass line 21.
In the supply line 14 the supply pressure PZK exists, in the return line 17 the return pressure PVK. The decrease in pressure at the cooler 16 results from the difference Δp=PZK−PVK. The pressure spring 8 has a spring rigidity C, or a spring force F=C×X resulting therefrom, wherein X is the spring path. In the control space 9, due to the connection via the control line 19, there is the return pressure PVK The piston 6 has a piston surface A1. Therewith the following relationship applies:
PVK=F/A1
The return pressure PVK is therefore determined by the ratio of the spring force F to the piston surface A1, i.e., it is constant. The supply pressure PZK is, however, variable, since the decrease in pressure Δp at the cooler 16 is temperature variable. The greater the decrease in pressure Δp, the greater the supply pressure PZK. To protect the cooler 16 from an increased, inadmissible pressure, the pressure relief valve 22 is thus provided, which opens at an inadmissibly high supply pressure PZK, and relieves the cooler 16.
The piston 7 has a piston surface A2, which is equal to A1. In contrast to the exemplary embodiment according to
Δp=F/A1=F/A2
The decrease in pressure Δp at the cooler 16 is therefore constant, and is adjustable via the spring force F, as well as the piston surfaces A1, A2. This also results in a constant flow of lubricating fluid in the return line 17. By the return of the supply pressure PZK, via the pressure compensation line 25, into the control space 9, pressure peaks of the supply pressure PZK are dampened, and the fluid cooler 16 is protected.
therefore the pressure differential, or decrease in pressure of the fluid cooler 16, is at the lubricating valve 1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 003 692.6 | Jan 2004 | DE | national |
