Hydraulic downshift control method and mechanism

Abstract

The invention discloses a hydraulic downshift control method and a hydraulic downshift control mechanism. When an engine is at a high rotating speed and a gear is at a high gear, a gear shifting piston is kept at the high gear position; if the gear is shifted to the low gear, the engine is still in a high rotating speed state at the moment, so that the pressure given by the engine to the gear shifting piston is greater than the pressure of the working oil, the gear shifting piston is still kept in the high-gear position, and the working oil enters a high-gear oil inlet of the gearbox after sequentially passing through a low-gear oil inlet, the gear shifting piston and a high-gear oil outlet; when the rotating speed of the engine is about to be low, the gear shifting piston moves to the low-gear position, and working oil sequentially passes through the low-gear oil inlet, the gear shifting piston and the low-gear oil outlet and then enters the low-gear oil inlet of the gearbox. By means of the arrangement, the rotating speed of the engine is tightly connected with the gear shifting process of the vehicle, the high-speed locking function is achieved, the defects of an original hydraulic downshift control mechanism are overcome, and interlocking of gears and the rotating speed of the engine is achieved.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic control devices for engineering machinery and agricultural machinery, and in particular to a hydraulic downshift control method and mechanism. Background Art

[0002] The existing hydraulic control valves for agricultural machinery are basically based on the gear shifting function and are mainly used in the gearboxes of agricultural machinery and engineering machinery. They can adjust the working pressure of the gearbox clutch. However, the existing hydraulic control valves do not have the limiting function of controlling the gearbox to directly switch from a high gear to a low gear when the engine is at a high speed.

[0003] The prior art with publication number CN104141780B discloses a method for shifting a transmission device that can be switched between at least two transmission stages, wherein the transmission device is driven by a hydrostatic transmission. In order to switch the gear of the transmission device between the transmission stages, the load of the transmission device is unloaded in a first step, which is achieved by changing the input amount of the hydraulic motor and / or the amount of fluid per revolution of the hydraulic motor until the pressure difference on the hydraulic motor is lower than a preset pressure difference, or by over-adjusting the brake valve device to an open position for closing the brake valve function. In a second step, the transmission device is shifted into neutral. In a third step, the speed of the hydraulic motor is electrically and hydraulically synchronized. In a fourth step, the transmission device is shifted into a new transmission stage. In a fifth step, a load is applied to the transmission device.

[0004] In the prior art, since the engine speed is not constant when the gear is switched, especially when the engine is switched directly to a low gear under a high speed state, it is easy to cause great damage to the machine and there is a great safety hazard. Summary of the invention

[0005] In order to solve the problem in the prior art that the actual engine speed does not match the gear position after shifting, resulting in large impact during the gear shifting process and large structural damage, the purpose of the present invention is to provide a hydraulic downshift control method and mechanism. No matter it is switching from a high gear to a low gear or from a low gear to a high gear, the gearbox will only actually execute the gear shifting action after the engine speed matches the gear shifting requirement, thereby avoiding gear shifting deceleration and mechanical damage.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: hydraulic downshift control method: the shift piston of the hydraulic downshift mechanism is controlled to switch between the high gear position and the low gear position by the engine speed and the working oil pressure; when the pressure given to the shift piston by the engine is greater than the working oil pressure, the shift piston is kept in the high gear position; when the pressure given to the shift piston by the engine is less than the working oil pressure, the shift piston is kept in the low gear position; When the engine is at high speed and the gear is in high gear, the shift piston remains in the high gear position, and the working oil passes through the high gear oil inlet, the shift piston and the high gear oil outlet in sequence and then enters the high gear oil inlet of the gearbox; among them, the oil path from the low gear oil inlet to the high gear oil outlet through the shift piston is blocked; If the gear is shifted to a low gear, at this time, since the engine is still in a high-speed state, the pressure given to the shift piston by the engine is greater than the working oil pressure, and the shift piston remains in the high-speed gear position, and the working oil passes through the low-speed gear oil inlet, the shift piston and the high-speed gear oil outlet in sequence and enters the high-speed gear oil inlet of the transmission; among them, the oil path from the high-speed gear oil inlet to the high-speed gear oil outlet through the shift piston is blocked; when the engine speed is shifted to a low speed, the shift piston moves to the low-speed gear position, and the working oil passes through the low-speed gear oil inlet, the shift piston and the low-speed gear oil outlet in sequence and enters the low-speed gear oil inlet of the transmission.

[0007] Preferably, when the shift piston is in the high gear position, the working oil passing through the low gear oil inlet or the high gear oil inlet flows out from the high gear oil outlet through the conversion check valve; when the shift piston is in the low gear position, the working oil passing through the low gear oil inlet flows out from the low gear oil outlet after passing through the shift piston, and the working oil passing through the high gear oil inlet flows out from the high gear oil outlet through the shift piston and the conversion check valve.

[0008] Preferably, when the shift piston is in the high-speed gear position, the working oil enters the port of the conversion check valve through the control of the conversion check valve to cut off the oil path between the high-speed gear oil inlet and the high-speed gear oil outlet, or the control of the conversion check valve can cut off the oil path between the low-speed gear oil inlet and the high-speed gear oil outlet.

[0009] Preferably, the conversion check valve includes a first oil inlet, a second oil inlet, an oil through hole and a first steel ball that switches between the first oil inlet and the second oil inlet; when the shift piston is in the high-speed gear position: the first oil inlet is connected to the low-speed gear oil inlet through the shift piston, the second oil inlet is connected to the high-speed gear oil inlet through the shift piston, and the oil through hole is connected to the high-speed gear oil outlet; if the working oil enters the low-speed gear oil inlet, then after the working oil enters the first oil inlet of the conversion check valve through the shift piston, the working oil pushes the first steel ball to seal the second oil inlet of the conversion check valve, and the working oil passes through the oil through hole of the conversion check valve and is discharged from the high-speed gear oil outlet; if the working oil enters the high-speed gear oil inlet, the working oil can enter the second oil inlet of the conversion check valve through the shift piston, the working oil pushes the first steel ball to seal the first oil inlet, and the working oil passes through the oil through hole of the conversion check valve and is discharged from the high-speed gear oil outlet.

[0010] Preferably, the working oil enters the low-speed gear oil inlet or the high-speed gear oil inlet through the reversing valve; the reversing valve receives the shift signal and switches according to the shift signal, so that the working oil enters the high-speed gear oil inlet or the low-speed gear oil outlet.

[0011] Preferably, when the shift piston is in the low gear position, the shift piston cuts off the oil path between the low gear oil inlet and the conversion check valve, and connects the oil path between the high gear oil inlet, the conversion check valve and the high gear oil outlet.

[0012] Preferably, the oil pump is transmission-connected to the engine, and the oil pump can draw oil from the oil tank and apply pressure to one end of the shift piston to move the shift piston to the high-speed gear position; the oil passing through the low-speed gear oil inlet can apply pressure to the other end of the shift piston to move the shift piston to the low-speed gear position, and also includes a return spring for driving the shift piston to move to the low-speed gear position.

[0013] A hydraulic downshift control mechanism for implementing the above-mentioned hydraulic downshift control method.

[0014] The beneficial effect of the technical solution of the present invention is that the higher the engine speed, the greater the pressure applied to the shift piston, so that after switching to a low gear at a high engine speed, the engine can still apply a large pressure to the shift piston, so that the shift piston remains in the high gear position, and the oil entering the hydraulic downshift control mechanism through the low gear oil inlet will still flow out from the high gear oil outlet until the engine slows down to a certain value, and the pressure difference at both ends of the shift piston is reversed, so that the vehicle is allowed to switch to a low gear. In this way, the above scheme closely connects the engine speed with the vehicle's shifting process, plays a high-speed locking function, overcomes the shortcomings of the original hydraulic downshift control mechanism, and realizes the interlocking of the gear position and the engine speed; makes the vehicle's shifting process smoother, reduces mechanical damage to components such as the engine, gearbox and drive axle, and reduces the risk of failure damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The structure diagram of the downshift control mechanism Figure 1 ; Figure 2 The structure diagram of the downshift control mechanism Figure 2 ; Figure 3 for Figure 1 Middle AA section view; Figure 4 for Figure 1 Middle BB section view; Figure 5 It is the hydraulic principle diagram of the downshift control mechanism when the engine is at low speed and the gear is at low speed; Figure 6It is the hydraulic principle diagram of the downshift control mechanism when the engine speed is low and the gear is in high gear; Figure 7 It is the hydraulic principle diagram of the downshift control mechanism when the engine is at high speed and the gear is at high gear; Figure 8 It is a hydraulic principle diagram of the downshift control mechanism when the engine is increased from a low speed to a high speed and the gear is a low speed gear; Fig. 9 It is the hydraulic principle diagram of the downshift control mechanism when the engine is at high speed and the gear is switched from a high gear to a low gear.

[0016] Figure numerals: 1. pressure limiting valve; 2. leakage check valve; 3. conversion check valve; 4. shift piston; 5. control check valve; 6. oil pump inner gear; 7. oil pump outer gear; 8. low-speed gear oil outlet; 9. high-speed gear oil outlet; 10. high-speed gear oil inlet; 11. low-speed gear oil inlet; 12. valve seat; 13. valve cover; 14. oil suction hole; 15. oil filter; 16. lubrication throttle hole; 17. oil pump input shaft; 18. O-ring; 19. reversing valve. DETAILED DESCRIPTION

[0017] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0018] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0019] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more, unless otherwise clearly specified.

[0020] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature. Example

[0022] like Figures 1 to 4 As shown, the hydraulic downshift control mechanism shown includes a valve body, an oil pump and a conversion check valve 3; a shift oil chamber is provided in the valve body, a slidable shift piston 4 is installed in the shift oil chamber, and the moving position of the shift piston 4 includes a low-speed gear position and a high-speed gear position; a low-speed gear oil inlet 11, a low-speed gear oil outlet 8, a high-speed gear oil inlet 10 and a high-speed gear oil outlet 9 are also provided on the valve body, and the low-speed gear oil inlet 11, the low-speed gear oil outlet 8 and are all connected to the shift oil chamber; like Fig. 9 As shown, when the shift piston 4 is in the high-speed gear position, the working oil passing through the low-speed gear oil inlet 11 or the high-speed gear oil inlet flows out from the high-speed gear oil outlet 9 through the conversion check valve 3; when the shift piston 4 is in the low-speed gear position, the working oil passing through the low-speed gear oil inlet 11 flows out from the low-speed gear oil outlet 8 after passing through the shift piston 4, and the working oil passing through the high-speed gear oil inlet flows out from the high-speed gear oil outlet 9 through the shift piston 4 and the conversion check valve 3; like Figures 5 to 9 As shown, the switching check valve 3 includes a first oil inlet, a second oil inlet and an oil through hole; the first oil inlet and the second oil inlet are both connected to the shift oil chamber, and the oil through hole is connected to the high-speed gear oil outlet 9; a first steel ball is arranged in the switching check valve 3, and the first steel ball moves between the first oil inlet and the second oil inlet to seal the first oil inlet or the second oil inlet; When the shift piston is in the low gear position, the working oil passes through the low gear oil inlet 11, the shift piston 4 and the low gear oil outlet 8 in sequence and then enters the low gear oil inlet of the gearbox; When the shift piston 4 is kept in the high-speed gear position, the entry position of the working oil is controlled, and then the first oil inlet or the second oil inlet is blocked, so that the low-speed gear oil inlet 11, the shift piston 4, the high-speed gear oil outlet 9 and the high-speed gearbox oil inlet are connected, or the high-speed gear oil inlet 10, the shift piston 4, the high-speed gear oil outlet 9 and the high-speed gearbox oil inlet are connected; specifically, when the shift piston 4 is in the high-speed gear position: the first oil inlet is connected to the low-speed gear oil inlet 11 through the shift piston, the second oil inlet is connected to the high-speed gear oil inlet 10 through the shift piston, and the oil hole is connected to The high-speed gear oil outlet 9 is connected; if the working oil enters the low-speed gear oil inlet 11, the working oil enters the first oil inlet of the conversion check valve 3 through the shift piston 4, and the working oil pushes the first steel ball to block the second oil inlet of the conversion check valve 3, and the working oil passes through the oil hole of the conversion check valve 3 and is discharged from the high-speed gear oil outlet 9; if the working oil enters the high-speed gear oil inlet 10, the working oil can enter the second oil inlet of the conversion check valve 3 through the shift piston 4, and the working oil pushes the first steel ball to block the first oil inlet, and the working oil passes through the oil hole of the conversion check valve 3 and is discharged from the high-speed gear oil outlet 9; When the shift piston 4 is in the low gear position, the shift piston 4 cuts off the oil path between the low gear oil inlet 11 and the conversion check valve 3, and connects the oil path between the high gear oil inlet 10, the conversion check valve 3 and the high gear oil outlet 9; The working oil passing through the low-speed gear oil inlet 11 can apply pressure to one end of the shift piston 4, and the oil pump can apply pressure to the other end of the shift piston 4; the movement of the shift piston 4 is controlled by the pressure at both ends of the shift piston 4.

[0023] With such arrangement, the higher the engine speed, the greater the pressure applied by the oil pump to the shift piston 4. In this way, after the engine switches to a low gear at a high speed, the oil pump can still apply a large pressure to the shift piston 4, so that the shift piston 4 remains in the high gear position, and the oil entering the hydraulic downshift control mechanism through the low gear oil inlet 11 will still flow out from the high gear oil outlet 9 until the engine slows down to a certain value and the pressure difference at both ends of the shift piston 4 is reversed, so that the vehicle is allowed to switch to a low gear. In this way, the above scheme closely connects the engine speed with the vehicle's shifting process, plays a high-speed locking function, overcomes the shortcomings of the original hydraulic downshift control mechanism, and realizes the interlocking of the gear position and the engine speed. It makes the vehicle's shifting process smoother, reduces mechanical damage to components such as the engine, gearbox and drive axle, and reduces the risk of failure damage.

[0024] In this embodiment, Figure 2As shown, a leakage check valve 2 is installed on the valve body, one end of the oil passage on which the leakage check valve 2 is installed is communicated with the oil passage between the second oil inlet and the shift oil chamber, and the other end of the oil passage on which the leakage check valve 2 is installed is communicated with the oil passage between the shift oil chamber and the low-speed gear oil outlet 8. Furthermore, a second steel ball is installed in the leakage check valve 2, and the second steel ball can block any port of the leakage check valve 2.

[0025] In this embodiment, the shift piston 4 is provided with a first force-bearing portion and a second force-bearing portion which are relatively arranged, and the valve body is provided with an internal oil channel, and the ports of the internal oil channel are all connected with the reversing oil chamber. The oil flowing through the low-speed gear oil inlet 11 or the low-speed gear oil outlet 8 passes through the shift piston 4 and then acts on the first force-bearing portion of the shift piston 4 through the internal oil channel; the oil entering the valve body through the oil pump acts on the second force-bearing portion.

[0026] In this embodiment, a control check valve 5 is also installed on the valve body. The oil passage on which the control check valve 5 is installed is connected with the low-speed gear oil inlet 11 and the oil passage of the shift oil chamber, and the oil passage on which the control check valve 5 is installed is connected with the internal oil passage on the valve body at the other end. The control check valve 5 can limit the oil at the low-speed gear oil inlet 11 from directly entering the internal oil passage.

[0027] In this embodiment, a return spring is also installed in the shift oil chamber, and the return spring is arranged between the shift piston and the valve body; the return spring is used to drive the shift piston to move to the low gear position.

[0028] In this embodiment, Figure 1 As shown, the valve body includes a valve seat 12 and a valve cover 13 that are fixedly connected, the shift oil chamber is arranged in the valve seat 12, and the low-speed gear oil inlet 11, the low-speed gear oil outlet 8, the high-speed gear oil inlet 10 and the high-speed gear oil outlet 9 are arranged on the valve cover 13.

[0029] In this embodiment, Figure 1 and Figure 4 As shown, a connection portion is raised on the valve seat 12, and two axially arranged O-rings 18 are sleeved on the outside of the connection portion; the hydraulic downshift control mechanism is fixed to the tank body of the oil tank through the connection portion. Further preferably, a lubrication area is provided in the valve seat 12, and an oil suction hole 14 connected to the lubrication area is provided on the valve seat 12, and one end of the oil pump input shaft extends into the lubrication area; when the oil pump is working, the oil in the lubrication area can be sent to the end of the shift piston 4. Further preferably, the oil pump input shaft has an inner hole, and the oil in the lubrication area is sent to the end of the shift piston 4 through the inner hole of the oil pump input shaft; specifically, the oil pump can extract the oil in the oil tank through the oil suction hole 14, and the end of the oil pump input shaft extending into the lubrication area is provided with a throttle hole 16 connected to the inner hole.

[0030] In this embodiment, Figure 2As shown, a pressure limiting valve 5 is installed at the oil pump to ensure that the maximum pressure of the lubricating oil does not exceed the limit. The pressure limiting valve 5 is installed in the lubrication area of ​​the valve seat 12.

[0031] In this embodiment, Figures 1 to 4 As shown, the oil pump is integratedly installed on the valve body; specifically, the oil pump includes an oil pump input shaft 17, an oil pump external gear 7 and an oil pump internal gear 6 which are rotatably installed on the valve seat 12, the oil pump external gear 7 is located on the inner side of the oil pump external gear 7 and is meshed for transmission, and the oil pump input shaft 17 is fixedly connected to the oil pump internal gear 6; one end of the oil pump input shaft 17 extends from the valve seat 12 and is provided with an internal spline, and the internal spline of the oil pump input shaft 17 is spline-connected to the output shaft installed on the oil tank body.

[0032] In this embodiment, the oil pump is a bidirectional oil pump; Figure 4 As shown, part of the oil in the lubrication area passes through the throttle hole 16 at the top of the oil pump input shaft 17 and the inner hole of the oil pump input shaft 17 to lubricate the parts, and the other part reaches the end of the shift piston 4 through the flow channel inside the valve body, providing the shift piston 4 with a downshift interlock signal.

[0033] In this embodiment, an oil filter 15 is installed at the oil suction hole 14 of the valve body.

[0034] In this embodiment, the working oil enters the low-speed gear oil inlet 11 or the high-speed gear oil inlet 10 through the reversing valve 19; the reversing valve 19 receives the shift signal and switches according to the shift signal, so that the working oil enters the high-speed gear oil inlet 10 or the low-speed gear oil outlet 8; further, the reversing valve 19 is a solenoid valve. Example

[0035] A method for controlling vehicle lowering by using the hydraulic downshift control mechanism described in the above embodiment 1: Among them, if the gear is changed to a low gear, at this time, since the engine is still in a high speed state, the pressure given by the engine to the shift piston 4 is greater than the working oil pressure, the shift piston 4 remains in a high speed position, and the working oil passes through the low speed oil inlet 11, the shift piston 4 and the high speed oil outlet 9 in sequence and enters the high speed oil inlet of the transmission; among them, the oil path of the high speed oil inlet 10 entering the high speed oil outlet 9 through the shift piston 4 is blocked; when the engine speed is about to reach a low speed, the shift piston 4 moves to the low speed gear position, and the working oil passes through the low speed oil inlet 11, the shift piston 4 and the low speed oil outlet 8 in sequence and enters the low gear oil inlet of the transmission. Among them, when the shift piston 4 is in the high-speed gear position, the working oil enters the port of the conversion check valve 3 through the working oil, and the steel ball blocks the first oil inlet or the second oil inlet, thereby controlling the conversion check valve 3 to cut off the high-speed gear oil inlet 10 and the high-speed gear oil outlet 9, or controlling the conversion check valve 3 to cut off the oil path between the low-speed gear oil inlet 11 and the high-speed gear oil outlet 9.

[0036] Specifically, Figure 5 As shown, when the vehicle engine is at a low speed and the vehicle is in the low gear: the pressure oil enters the low gear oil inlet 11 through the reversing valve 19, and the oil in the low gear oil inlet 11 is divided into two paths; one path acts on the first force-bearing part through the shift piston 4 and the internal oil channel on the valve body, so that the shift piston 4 is kept in the low gear position under the action of the return spring and the pressure oil; the other path of oil pressure oil flows directly out of the low gear oil outlet 8 after passing through the shift piston 4, and then the oil enters the low gear oil inlet 11 of the gearbox. The high gear return oil passes through the high gear oil outlet 9, the conversion check valve 3, the shift piston 4 and the high gear oil inlet 10, and then flows back to the oil tank from the reversing valve 19.

[0037] like Figure 8 As shown, when the vehicle engine is at a low speed and the vehicle gear is in a low gear, if the engine speed rises to a high speed, the pressure of the oil pump on the shift piston 4 reaches 2.8 bar, which is the pressure that pushes the shift piston 4. Since the working oil pressure in the low gear of the vehicle is much greater than 2.8 bar at this time, the shift piston 4 can be kept in a low speed position, and the pressure oil still flows out from the low gear oil outlet 8.

[0038] like Figure 6 As shown, when the vehicle engine is at a low speed and the vehicle is in a high gear: at this time, since the speed of the oil pump driven by the engine is low, the pressure given by the oil pump to the shift piston 4 is not enough to drive the shift piston 4 to move, so the shift piston 4 remains at a low speed position; the pressure oil enters the high-speed oil inlet 10 of the hydraulic downshift control mechanism through the reversing valve 19, and then the pressure oil enters the conversion check valve 3 from the second oil inlet through the shift piston 4 in turn, and the oil entering the conversion check valve 3 pushes the first steel ball to block the first oil inlet, and then the pressure oil enters the high-speed oil inlet of the gearbox through the oil hole and the high-speed oil outlet 9. The oil that needs to perform the oil return action flows back to the oil tank through the low-speed oil return, the shift piston 4, and the reversing valve 19.

[0039] like Figure 7As shown, when the vehicle engine is at high speed and the vehicle is in high gear, the low speed oil inlet and low speed oil outlet are both in a pressure relief state. When the engine is at high speed, the oil pump applies greater pressure to the shift piston 4 to keep the shift piston 4 at a high speed position; wherein, the pressure oil entering the hydraulic downshift control mechanism through the reversing valve 19 enters the second oil inlet of the conversion check valve 3 after passing through the shift piston 4, thereby sealing the first oil inlet of the conversion check valve 3, and the pressure oil enters the high speed oil inlet of the gearbox after passing through the oil hole of the conversion check valve 3 and the high speed oil outlet 9 on the valve body; wherein, the oil that needs to be returned passes through the low speed oil return port and the shift piston 4 and then through the internal oil channel on the valve body to act on the first force-bearing part of the shift piston 4 and the control check valve 5 in the valve body, and the oil flowing out of the control check valve 5 flows back to the oil tank through the low speed oil inlet 11 and the reversing valve 19.

[0040] like Fig. 9 As shown, when the vehicle engine is at high speed and the vehicle gear is at high speed, if the gear is reduced from high speed to low speed, the pressure oil enters the hydraulic downshift control mechanism from the low speed oil inlet 11 of the reversing valve 19, but due to the action of the control check valve 5, the pressure oil cannot directly act on the first force-bearing part of the shift piston 4, and the engine is still in a high speed state at this time. At this time, the pressure applied by the oil pump on the second force-bearing part is greater than the pressure of the first receiving part, thereby keeping the shift piston 4 in the high speed position; the pressure oil passes through the low speed oil inlet 11 and the shift piston 4 and then enters the conversion check valve 3 from the second oil inlet. The first steel ball inside the conversion check valve 3 blocks the first oil inlet, and the pressure oil enters the high speed oil inlet of the gearbox through the oil hole and the high speed oil outlet 9. Only when the engine speed drops to a low speed state, the shift piston 4 returns to the low speed position, and the pressure oil flows out directly from the low speed oil outlet 8 through the shift piston 4.

[0041] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0042] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A hydraulic downshift control method, Features: The shift piston (4) of the hydraulic downshift mechanism is controlled to switch between a high gear position and a low gear position by the engine speed and the working oil pressure; when the pressure applied by the engine to the shift piston (4) is greater than the working oil pressure, the shift piston (4) is maintained at the high gear position; when the pressure applied by the engine to the shift piston (4) is less than the working oil pressure, the shift piston (4) is maintained at the low gear position; When the engine is at a high speed and the gear is in a high gear, the shift piston (4) remains in the high gear position, and the working oil passes through the high gear oil inlet (10), the shift piston (4) and the high gear oil outlet (9) in sequence and then enters the high gear oil inlet of the transmission; wherein the oil path from the low gear oil inlet (11) to the high gear oil outlet (9) through the shift piston (4) is blocked; If the gear is changed to a low gear, at this time, because the engine is still in a high speed state, the pressure applied by the engine to the shift piston (4) is greater than the working oil pressure, the shift piston (4) remains in the high gear position, and the working oil passes through the low gear oil inlet (11), the shift piston (4) and the high gear oil outlet (9) in sequence and then enters the high gear oil inlet of the transmission; wherein the oil path from the high gear oil inlet (10) to the high gear oil outlet (9) through the shift piston (4) is blocked; when the engine speed is changed to a low speed, the shift piston (4) moves to the low gear position, and the working oil passes through the low gear oil inlet (11), the shift piston (4) and the low gear oil outlet (8) in sequence and then enters the low gear oil inlet of the transmission.

2. A hydraulic downshift control method according to claim 1, Features: When the shift piston (4) is in the high-speed gear position, the working oil passing through the low-speed gear oil inlet (11) or the high-speed gear oil inlet flows out from the high-speed gear oil outlet (9) through the conversion check valve (3); when the shift piston (4) is in the low-speed gear position, the working oil passing through the low-speed gear oil inlet (11) flows out from the low-speed gear oil outlet (8) after passing through the shift piston (4), and the working oil passing through the high-speed gear oil inlet flows out from the high-speed gear oil outlet (9) through the shift piston (4) and the conversion check valve (3).

3. A hydraulic downshift control method according to claim 2, Features: When the shift piston (4) is in the high-speed gear position, the working oil enters the port of the conversion check valve (3), and the conversion check valve (3) is controlled to cut off the oil path between the high-speed gear oil inlet (10) and the high-speed gear oil outlet (9), or the conversion check valve (3) is controlled to cut off the oil path between the low-speed gear oil inlet (11) and the high-speed gear oil outlet (9).

4. A hydraulic downshift control method according to claim 3, Features: The switching check valve (3) comprises a first oil inlet, a second oil inlet, an oil through hole, and a first steel ball that switches between the first oil inlet and the second oil inlet; When the shift piston (4) is in the high-speed gear position: the first oil inlet is connected to the low-speed gear oil inlet (11) through the shift piston (4), the second oil inlet is connected to the high-speed gear oil inlet (10) through the shift piston (4), and the oil through hole is connected to the high-speed gear oil outlet (9); if the working oil enters the low-speed gear oil inlet (11), the working oil enters the first oil inlet of the conversion check valve (3) through the shift piston (4), and the working oil pushes the first steel ball to block the second oil inlet of the conversion check valve (3), and the working oil passes through the oil through hole of the conversion check valve (3) and is discharged from the high-speed gear oil outlet (9); if the working oil enters the high-speed gear oil inlet (10), the working oil can enter the second oil inlet of the conversion check valve (3) through the shift piston (4), and the working oil pushes the first steel ball to block the first oil inlet, and the working oil passes through the oil through hole of the conversion check valve (3) and is discharged from the high-speed gear oil outlet (9).

5. A hydraulic downshift control method according to claim 4, Features: The working oil enters the low-speed gear oil inlet (11) or the high-speed gear oil inlet (10) through the reversing valve (19); the reversing valve (19) receives a gear shift signal and performs reversal according to the gear shift signal, so that the working oil enters the high-speed gear oil inlet (10) or the low-speed gear oil outlet (8).

6. A hydraulic downshift control method according to claim 2, Features: When the shift piston (4) is in the low-speed gear position, the shift piston (4) cuts off the oil path between the low-speed gear oil inlet (11) and the conversion check valve (3), and connects the oil path between the high-speed gear oil inlet (10), the conversion check valve (3) and the high-speed gear oil outlet (9).

7. A hydraulic downshift control method according to claim 1, Features: The oil pump is in driving connection with the engine, and can draw oil from the oil tank and apply pressure to one end of the shift piston (4), so that the shift piston (4) moves to the high-speed gear position; the oil passing through the low-speed gear oil inlet (11) can apply pressure to the other end of the shift piston (4), so that the shift piston (4) moves to the low-speed gear position, and also includes a return spring for driving the shift piston (4) to move to the low-speed gear position.

8. A hydraulic downshift control mechanism for implementing a hydraulic downshift control method according to any one of claims 1 to 7.

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