Thermostat for a transmission oil circuit and transmission oil circuit

Abstract

Thermostat for a transmission oil circuit, in particular of a vehicle transmission, comprising a thermostat inlet (20), a thermostat outlet (22), a bypass channel fluidically connecting the thermostat inlet (20) to the thermostat outlet (22), a circuit inlet (26) fluidically connected to the thermostat inlet (20), a circuit outlet (28) fluidically connected to the thermostat outlet (22), a control element (40) defining a valve, and a pressure loss element (60) spaced apart from the control element, wherein the pressure loss element (60) is arranged in the bypass channel and the flow cross-section through the bypass channel is independent of the switching position of the control element (40).

Description

[0001] The invention relates to a thermostat for a transmission oil circuit and a transmission oil circuit, in particular of a vehicle transmission.

[0002] Such thermostats have a thermostat inlet, a thermostat outlet, a bypass channel that fluidically connects the thermostat inlet to the thermostat outlet, as well as a circuit inlet that is fluidically connected to the thermostat inlet, and finally a circuit outlet that is fluidically connected to the thermostat outlet.

[0003] In vehicle transmissions, especially automatic transmissions, it is necessary to cool the transmission fluid, for example, using a transmission oil cooler or a transmission oil-water heat exchanger. When using a transmission oil-water heat exchanger, no change in the flow path of the transmission fluid circuit is necessary, because the heat dissipation from the transmission fluid circuit and the temperature of the transmission fluid are set and regulated by the amount of coolant flowing through the heat exchanger. Furthermore, the pressure loss in the transmission fluid circuit is determined by the change in viscosity as a function of temperature. In contrast, when using a transmission oil cooler to regulate the oil temperature, it is necessary to modify the oil circuit, especially by activating a bypass function during warm-up, thereby bypassing the heat sink.With air-cooled transmission oil, the pressure drop in the oil circuit scales not only with viscosity but also with the shift state of the transmission oil circuit. To use the two different systems—air-cooled transmission oil coolers and water-cooled transmission oil heat exchangers—in a single vehicle would therefore require two different transmissions with different control units. This is costly. It is far more practical to allow the option of using one or the other cooling system with the same transmission, something that was previously impossible, particularly due to the pressures that would subsequently need to be maintained at different temperatures.

[0004] For example, approximately 2500 mbar must be achieved at 1.5 l / min and a transmission oil temperature of -15 °C, as well as a maximum of 1400 mbar at 11 l / min and a transmission oil temperature of 70 °C. Additionally, there is a switching point at 76 °C at which the bypass is activated or deactivated in a transmission oil air cooler. This involves the use of a wax element that switches between two channels within the thermostat. This switching point of the wax element is at 76 °C. If the transmission oil needs to be cooled, the thermostat opens the cooler, allowing the transmission oil to be cooled via the cooler. Conversely, if the transmission oil is too cold, the thermostat switches so that the bypass channel is used, but not the cooler. This, however, makes it even more complex to meet the aforementioned design or pressure loss points.Furthermore, in such a thermostat, the flows in bypass mode are so-called gap flows, because the aforementioned expansion element is typically used as a valve in the thermostat, opening or closing a narrow flow gap in response to temperature changes. However, the pressure losses of gap flows scale very differently with the volume flow rate and oil viscosity and cannot be captured, for example, by simulations on a pipeline. The resulting scaling is detrimental to compliance with the aforementioned design or pressure loss points. A further difficulty arises from the fact that the thermostat is located in a different position in the vehicle depending on the vehicle variant. This, in turn, leads to significant variations in pressure losses when the bypass channel is activated. This can only be addressed by developing different thermostat variants that exhibit different pressure losses in the bypass channel.

[0005] DE 10 2013 021 090 A1 discloses a cooling water control system for a cooling water circuit, wherein the cooling water control system comprises a control roller. The control roller selectively opens and closes the radiator bypass line.

[0006] US Patent 2009 / 0025922A1 discloses a radiator bypass device which has a bypass channel that is closed by a ball valve. The circuit inlet also has a ball valve, which is actuated by an expansion element.

[0007] The object of the invention is to improve a thermostat for a transmission oil circuit, in particular a transmission oil circuit with an attached transmission oil cooler, in such a way that this thermostat is simpler in design and more universally applicable. Furthermore, a transmission oil circuit is to be created in which the adjustment of pressure losses is easier. Finally, the thermostat should make it possible to connect the transmission without requiring any modifications to the connected transmission, so that it can be coupled with a transmission oil cooler without any redesign.

[0008] The invention is solved by a thermostat for a transmission oil circuit, in particular of a vehicle transmission, comprising a thermostat inlet, a thermostat outlet, a bypass channel fluidically connecting the thermostat inlet to the thermostat outlet, a circuit inlet fluidically connected to the thermostat inlet, a circuit outlet fluidically connected to the thermostat outlet, a control element defining a valve, and a pressure loss element. The pressure loss element is arranged at a distance from the control element in the bypass channel. The flow cross-section through the bypass channel is independent of the switching position of the control element; that is, the pressure loss element is not part of the valve defined by the control element.

[0009] The solution according to the invention makes it possible to achieve complete decoupling of the pressure losses that occur when the bypass channel and the cooling circuit are activated. The pressure loss element in the bypass channel allows for precise adjustment of the pressure loss that occurs when the bypass channel is activated. This ensures a suitable pressure loss scaling characteristic with respect to viscosity and volume flow rate at all times. Furthermore, the difficult-to-control or adjust gap flow in the bypass can be replaced by a pipe flow by interposing a suitable pressure loss element. Unlike orifice flow, pipe flow has a pronounced longitudinal extent, in this case at least 2 mm. In orifice flow, the pressure loss scales primarily via the geometry, whereas in pipe flow, the increasingly dominant influence of viscosity is utilized.The invention makes it possible to optimally adjust the ratio of the two effects (viscosity influence and geometry influence).

[0010] The control element is specifically designed to control the volume flow of oil through the circuit inlet and / or the circuit outlet depending on the oil temperature.

[0011] In particular, the control element is an expansion element, as was previously used, so that no new designs are required.

[0012] A spring on the control element provides a return function for the locking element in the switching direction. The spring should, for example, surround the expansion element on the outside.

[0013] Preferably, the pressure loss element is designed as a separate body, i.e., separate from the housing. The replaceability of the pressure loss element thus allows for modifications without major redesigns.

[0014] The pressure loss element, for example, has a body that projects into the bypass channel and narrows it section by section. This means that oil does not need to flow through the pressure loss element; rather, the flow channel in this section is defined by the bypass channel on one side and by the outer surface of the pressure loss element on the other. This allows for a very simple design of the pressure loss element.

[0015] One variant that has proven advantageous in trials involves creating an annular gap between the pressure loss element (or the body) and the wall of the bypass channel, within which a pipe flow develops. The annular gap provides a large wetted surface area, which increases the influence of viscosity.

[0016] The quick changeability and adaptability of the thermostat according to the invention is achieved in particular by a replaceable pressure loss element.

[0017] The body of the pressure loss element can also be spring-mounted to the thermostat housing; in particular, a support for the pressure loss element can be coupled to the body via the spring. This spring also allows, for example, the axial position of the pressure loss element in the bypass to be easily adjusted by pressing the body against a stop.

[0018] The spring preload on the pressure loss element can also be used for other functions. For example, it can be used to implement a pressure relief valve, which, when the bypass is not normally engaged, opens the bypass once a predetermined pressure is reached in the transmission oil circuit.

[0019] If the pressure loss member (or body) has a helical or threaded shape, a spiral channel may form between the body and the inside of the bypass channel. Alternatively, the pressure loss member may have numerous thin channels arranged side by side.

[0020] Another option, which has proven very effective in trials, is to design the pressure loss element with a bundle of parallel pipes, a so-called tube bundle. This tube bundle can either be integrated into the thermostat housing (e.g., formed during the injection molding of the housing), or a separate insert can be used in which the pipes are formed.

[0021] It would also be possible to form the annular gap directly within the thermostat housing without a separate insert. However, this would require connecting the "core" in the center of the ring to the outer wall of the annular gap via bridges.

[0022] The thermostat has a housing with the thermostat inlet and outlet located on one side, the circuit inlet and outlet on the front, and a mounting opening on the top or bottom of the housing for replacing the pressure loss element. This design results in a very compact and easy-to-manufacture housing and its channels, which can be drilled from various sides, usually in a single setup.

[0023] The pressure loss element can be designed as a one-piece section of the housing, which narrows the bypass channel in sections and divides it into two sections, which are connected to each other by several channels in the pressure loss element.

[0024] Alternatively, the pressure loss element can also be manufactured by injection molding, as explained previously. Manufacturing is simplified if any channels present in the pressure loss element run in the demolding direction. Because the mounting opening is accessible from a different side than the thermostat inlet / outlet and the circuit inlet / outlet, even replacement with the thermostat installed is simplified due to improved accessibility.

[0025] The manufacturability of the thermostat is further simplified by providing two parallel channels inside the thermostat housing. The thermostat inlet opens laterally into one channel, and the thermostat outlet opens laterally from the other channel, so that each channel is divided into two sections, one of which is assigned to the bypass channel and the other to the circuit. This means that the channels can be manufactured, for example, by linear bores, thus eliminating the need for complex molds. The aforementioned problem is also solved by a transmission oil circuit with a transmission and a thermostat, particularly according to the invention, wherein the transmission has a transmission oil outlet that connects directly to the thermostat inlet and / or wherein the transmission has a transmission oil inlet that connects directly to the thermostat outlet.The idea here is that there is no longer a conventional intermediate channel in the form of pipes between the thermostat and the gearbox. Instead, the thermostat is flanged directly to the gearbox. This eliminates the need for lines of varying lengths, which in prior art led to different pressure losses between the gearbox and the thermostat. Consequently, the pressure losses can only be determined via the bypass channel.

[0026] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, to which reference is made. In the drawings: Fig. 1 a side view of the transmission oil circuit according to the invention with thermostat according to the invention, Fig. 2 a sectional view along line II-II through the thermostat in Fig. 1, Fig. 3 a sectional view through a second variant of the thermostat according to the invention along line II-II in Fig. 1, Fig. 4 a sectional view through a third variant of the thermostat according to the invention along line II-II in figure , and Fig. 5 a sectional view through a fourth variant of the thermostat according to the invention along line II-II in Fig. 1.

[0027] In Fig. Figure 1 shows a transmission oil circuit of a transmission of a vehicle, in particular with an automatic transmission. The transmission has a transmission housing 10, to which a thermostat 12 is directly connected and from which lines lead to a transmission oil air cooler 14 (see Fig. 2) lead.

[0028] The thermostat 12 has a housing 16 with a first side 18, on which a thermostat inlet 20, through which transmission oil flows into the thermostat 12, and a thermostat outlet 22, through which transmission oil flows back into the transmission housing 10, are provided. In the present embodiment, the thermostat inlet 20 and thermostat outlet 22 are designed as projecting nozzles fitted with O-ring seals. These nozzles are inserted into corresponding openings in the transmission housing 10. The transmission housing 10 has a transmission oil outlet 11, which is directly connected to and flows into the thermostat inlet 20, and a transmission oil inlet 13, which flows directly into the thermostat outlet 22.

[0029] At one in Fig. A circuit inlet 26 and a circuit outlet 28 are formed on the front side 24 shown in Figure 2, here for example as a widened bore for inserting a corresponding pipe.

[0030] Inside the housing 16, several channels are created by linear drilling and / or during casting of the housing.

[0031] A first channel 30 extends from the front face 24, and a second channel 32, also extending from the front face, runs parallel to the first channel 30. The thermostat input 20 opens into the first channel 30 (in Fig. 2), and the thermostat output 22 flows into the second channel 32 (see Fig. 2) From the opening of the thermostat inlet 20 in the first channel 30, a first section of the channel extends to the circuit inlet 26. Likewise, a first section of the channel 32 extends from the circuit outlet 28 to the opening of the thermostat outlet 22.

[0032] To the right of the two aforementioned first sections of channels 30 and 32, these continue further. In this area, these sections form parts of a so-called bypass channel, which is U-shaped and whose limbs are formed by the sections of channels 30 and 32, and whose central section is formed by a channel 38 originating from a top surface 34 (or possibly from a bottom surface 36).

[0033] Components essential for the thermostat's function are inserted into the channels or channel sections. A control element 40 is inserted into the first channel 30. This control element is received in the seat element 42, which is pressed or screwed into the flared end of the channel 30 and is designed similarly to a sleeve with an intermediate wall. The seat element 42 has several through-channels 44 in its center and circumferentially extending webs between these through-channels 44 towards the center. These webs support or merge into a counter-support 46. A plunger 48 of the control element 40 is received in the counter-support 46. The control element 40 is designed as a thermal expansion element, containing an expansion material that expands when the temperature rises, extending the plunger 48 more or less far out of the housing 50 of the control element.

[0034] The housing 50 has shut-off surfaces 52, 54 at its two opposite ends, which can be brought into contact with corresponding valve seats on the seat element 42 or on a shoulder 56 in the channel 30, more precisely in the section which is assigned to the bypass channel.

[0035] A spring 58 surrounding the control element 40 presses the housing 50 in the switching direction towards the seat element 42.

[0036] In the bypass channel, specifically in channel 38, a pressure loss element 60 is inserted via a mounting opening 64 on the upper surface 34. The pressure loss element 60 is a separate and spaced component from the control element 40, and is of very simple design, in this case as a cylinder or slightly conical part. A support 62 closes the channel 38 in the area of ​​the so-called mounting opening 64, which represents the opening of the channel 38. A spring 66 may optionally be provided between the support 62 and the pressure loss element 60, which presses the pressure loss element 60 against a stop 68 on the housing 16. This determines the axial position of the pressure loss element 60 in the channel 38. The pressure loss element 60 projects into the bypass channel and forms an annular gap 72 between the wall of the bypass channel and the so-called body 70 of the pressure loss element 60 (the body forms the outside of the pressure loss element in the area of ​​the bypass), the gap width of which can be precisely adjusted.

[0037] Because the pressure loss element 60 can be replaced very easily and quickly with a pressure loss element with a minimally different geometry, the annular gap 72 can be adjusted so that when the bypass is switched on, the pressure loss in the transmission oil circuit generated via the bypass can be precisely adjusted.

[0038] The pressure loss element 60 can also be designed as a pressure relief valve in the bypass channel. The spring 66 pushes the body 70 in one direction until it stops. However, if a certain overpressure is reached in the bypass channel, the oil pushes the body 70 upward against the spring 66, so that the conicity increases the annular gap and thus the flow cross-section in the bypass channel. The circuit is unthrottled.

[0039] When the transmission oil is still cold, the tappet 48 is still slightly extended from the housing 50, so that it is not supported axially by the support 46. Due to the positioning by the spring 58, the sealing surface 52 presses against the valve seat, so that no flow of transmission oil to the circuit inlet 26 can occur in this area.

[0040] To vent the gearbox during the first engine start, it can be advantageous to provide a small vent hole in the housing that can vent the gearbox oil circuit without opening the control element.

[0041] Since the housing 50 is pressed to the left, the bypass channel is opened, as a sufficiently large gap is created between the shoulder 56 and the sealing surface 54. This gap is significantly larger, e.g., at least twice the size of the annular gap 72 relative to its cross-sectional area, so that the pressure loss in the bypass channel is regulated not by this gap, but by the annular gap 72. Thus, transmission oil flows through the thermostat inlet 20 into the bypass channel, then through the annular gap 72 to the thermostat outlet 22.

[0042] It should be emphasized that the position of thermostat inlet 20 and thermostat outlet 22 can also be reversed. In this case, the flow is in the opposite direction. In the illustrated embodiment, however, the expansion element is directly exposed to warm transmission oil, so it is not influenced by a mixed flow at different temperatures. This solution is therefore more fluidically robust.

[0043] If the transmission oil is hot, the tappet 48 is supported on the support 46 and pushes the housing 50 so far into the bypass channel that it strikes the shoulder 56 and closes the bypass channel, while at the same time the inflow to the cooling circuit is opened in the area of ​​the shut-off surface 52 and transmission oil reaches the circuit inlet 26 via the passage channels 44.

[0044] The embodiment according to Fig. 3 essentially corresponds to the one after Fig. 2, so that in the following only the differences need to be discussed.

[0045] While the body 70 of the pressure loss element 60 after Fig. 2 was designed as a cylindrical or slightly conical body defining the annular gap 72, according to the embodiment according to Fig. 3, the body 70' is designed as a body with a helical or spiral channel 76. On the outside, the channel 76 is closed by the inside of the wall of the bypass channel, i.e., the housing 16. Instead of an annular gap 72, a spiral channel is thus created. The spring 66 is omitted here, but it can also be included optionally.

[0046] In the embodiment according to Fig. 4, the pressure loss element 60, designed as a separate body 70, has several thin, long channels 76, the length of which corresponds to a multiple of their diameter and which divides the flow into many partial flows.

[0047] The pressure loss element 60 is formed integrally with the support 62 and can therefore be easily removed from the outside.

[0048] A seal 80 seals the outer circumference of the pressure loss element against the inside of the channel wall.

[0049] The embodiment according to Fig. 5 largely corresponds to the one after Fig. 4, wherein the pressure loss element 60 is formed as a one-piece section of the housing 16, which narrows the bypass channel section by section and divides it into two sections, here the channels 30, 32, which are connected to each other by several channels 76, the length of which corresponds to a multiple of their diameter.

[0050] The channels 76 can be created by drilling or already during the injection molding of the housing 16.

Claims

[1] Thermostat for a transmission oil circuit, in particular of a vehicle transmission, with a thermostat inlet (20), a thermostat outlet (22), a bypass channel which fluidically connects the thermostat inlet (20) to the thermostat outlet (22), a circuit inlet (26) which is fluidically connected to the thermostat inlet (20), a circuit outlet (28) which is fluidically connected to the thermostat outlet (22), a control element (40) which defines a valve, and a pressure loss element (60) spaced apart from the control element, wherein the pressure loss element (60) is arranged in the bypass channel and the flow cross-section through the bypass channel is independent of the switching position of the control element (40). [2] Thermostat according to claim 1, characterized by that the control element (40) is designed such that it can control the volume flow of the oil through the circuit inlet (26) and / or the circuit outlet (28) as a function of the oil temperature. [3] Thermostat according to claim 1 or 2, characterized by that the control element (40) has an expansion element. [4] Thermostat according to one of the preceding claims, characterized by that the control element (40) has a spring (58) for biasing a closure member in the switching direction. [5] Thermostat according to one of the preceding claims, characterized by that the pressure loss member (60) is formed separately from the control element (40) and has a body (70, 70') which projects into the bypass channel and narrows it in sections. [6] Thermostat according to one of the preceding claims, characterized bythat the pressure loss element is arranged in the bypass channel in such a way that an annular gap (72) is formed between the pressure loss element (60) and the wall of the bypass channel, wherein the annular gap (72) preferably has a length in the flow direction which corresponds to at least half, in particular at least the entire inner diameter of the annular gap. [7] Thermostat according to claim 5 or 6, characterized by that the pressure loss element (60) is provided in the thermostat (12) in an exchangeable manner. [8] Thermostat according to one of claims 5-7, characterized by that the body (70) is spring-mounted on the thermostat. [9] Thermostat according to one of claims 5-8, characterized by that the pressure loss element (60) is designed as a pressure relief valve in the bypass channel, which increases the flow cross-section in the bypass channel when a certain pressure is reached. [10] Thermostat according to one of the preceding claims, characterized bythat the thermostat (12) has a housing (16), wherein the thermostat inlet (20) and the thermostat outlet (22) are provided on one side of the housing (16), wherein the circuit inlet (26) and the circuit outlet (28) are provided on an end face (24) of the housing (16), and wherein an assembly opening (64) for replacing the pressure loss element (60) is provided on an upper or lower side (34, 36) of the housing (16). [11] Thermostat according to one of claims 1-4, characterized by that the pressure loss member (60) is designed as a one-piece section of the housing (16) which narrows the bypass channel in sections and divides it into two sections which are connected to one another by a plurality of channels (76) in the pressure loss member (60). [12] Thermostat according to one of the preceding claims, characterized bythat the pressure loss member comprises a spiral channel (76) or several channels (76) arranged next to one another, the length of which corresponds to a multiple of their diameter. [13] Thermostat according to one of the preceding claims, characterized by that two parallel channels (30, 32) are provided inside the housing (16) of the thermostat (12), the thermostat inlet (20) opening laterally into one channel (30) and the thermostat outlet (22) extending laterally from the other channel (32), so that the channels (30, 32) are each divided into two sections, one of which is assigned to the bypass channel and one to the circuit. [14] Transmission oil circuit with a transmission and a thermostat (12) according to one of the preceding claims, wherein the transmission has a transmission oil outlet (11) which merges directly into the thermostat inlet (20) and / or wherein the transmission has a transmission oil inlet (13) which merges directly into the thermostat outlet (22).

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