The present invention relates to a shift gearbox, a control unit and at least one electric motor-driven piston-cylinder unit with a piston, which delimits at least one working chamber, which is connected via hydraulic lines to multiple shift gearbox units of the shift gearbox and shifts them, wherein the shift gearbox units comprise at least one gear selector unit and at least one clutch unit.
From DE 10 2006 038 446 A1 a shift gearbox with an electric motor-driven piston-cylinder unit is described, in which one or two piston-cylinder units operate four gear selectors and two clutches. The piston-cylinder unit generates the pressure required to shift the gear selectors and clutches, wherein a pressure sensor measures the pressure generated. DE 10 2006 038 446 A1 describes two possible embodiments for this purpose. In the first embodiment clutches and gear selectors are shifted via so-called multiplex valves for an actuation, by means of the piston-cylinder unit. In this connection the pressure build-up and also the pressure reduction can take place via the piston-cylinder unit. However, it is also possible that additional outlet valves are provided for some or all loads, via which the pressure in the individual loads can be lowered in a regulated manner.
The object of the invention is to further improve the shift gearbox known from DE 10 2006 038 446 A1.
This object is achieved according to the invention with a shift gearbox having the features of claim 1. Advantageous embodiments of this shift gearbox are obtained from the features of the sub-claims.
Through the displacement control of the piston, which corresponds to a volume control, a cost-effective structure is provided in which the number of valves used can be advantageously reduced. On account of the displacement or volume control at least one shift gearbox unit can in a simple manner have more than two switching positions, without a complicated pressure control, since on account of the incompressibility of the hydraulic medium over a predetermined delivered volume the respective shift gearbox unit can be shifted specifically in one of the possible positions. Through the displacement or volume control the shift gearbox units can also be shifted accurately and quickly, and also components (switching valves, seals of piston units of gear selectors or clutch plates) can be diagnosed for leakage, as well as hydraulic flow resistances. Thus, it is advantageously possible that initially a rapid shifting is carried out, and by decelerating, the shift gearbox unit is smoothly shifted to its target position.
By the use of at least one pressure sensor, a pressure regulation for pressure build-up and also alternatively for pressure reduction can be provided for some shift gearbox units in an advantageous further development, so that by means of the same piston-cylinder unit a displacement control and/or a volume control and also a pressure control results. By additionally providing a pressure regulation using a pressure sensor, a precisely adjustable required force can also be applied to loads, such as, for example, the clutch.
Pressure regulation can also be achieved without the use of a pressure sensor via targeted piston displacement control or via targeted electrical energisation of the electric motor. In the pressure control, the non-linear relationship between pressure and piston adjustment path is recorded and stored in a performance map. This map is used in the pressure control in such a way that the piston travels a certain distance, which corresponds to a certain pressure. If the performance map changes due to temperature or air bubbles, it is recalibrated and recorded. Various methods are available for this, such as adjustment via pressure transducer, adjustment via path control, and use of the current of the electric motor.
Alternatively, a torque can be regulated via the current of the electric motor. For an accurate torque determination, the torque constant kt of the electric motor, which represents the relationship between the torque of the electric motor and phase current, can for example be used. The torque constant kt in the case of electric motors can be determined for example during manufacture or initial start-up and is characterised in that kt changes slightly over time and essentially changes linearly only due to temperature influences. As an alternative to the phase current, the supply current of the electric motor can also be used.
If no pressure sensor is available for the calibration, a pressure estimate can be made by means of a model. Such a model can according to the invention consist of a motor with a transmission, which for example presses on or possibly retracts a single-acting or double-acting hydraulic piston. For a sufficiently good pressure estimate for a gearbox unit, the parameters in the subunits (motor torque constant kt, transmission efficiency and hydraulic piston cross-sectional area, friction due to seals) must either be subjected to minor influences or the parameter variations must be adjusted at regular intervals.
An accurate model can be realised in such a way that the aforementioned parameter changes of the model, which interfere in the pressure estimation or pressure control, are detected during operation. For example, pressure sensors that are only active in partial operation or an indirect pressure calculation can be employed.
A method for the indirect measurement of the pressure via the current of the electric motor can be calculated by the position of the clutch piston in the slave cylinder and by the acting cross-sectional area of the piston of the master cylinder, by means of knowledge of the clutch release spring and the diameter of the clutch slave cylinder. Thus, a system based on a pressure transducer can be completely avoided, which leads to significant cost savings since pressure transducers are primary cost drivers of hydraulic systems. In series applications a pressure transducer is about 4 times more expensive than a switching valve and comparably expensive as a proportional valve.
By using a dual-action reciprocating piston, which can convey, via its two working chambers in both stroke directions of the dual-action reciprocating piston, hydraulic medium into or out of one of the shift gearbox units, inter alia a short design of the piston-cylinder unit can advantageously be achieved. Thus, the two piston surfaces can either have the same size, so that the same volume is conveyed with the same displacement of the piston during the forward stroke and the return stroke. It is however also possible that the piston surfaces have different sizes, e.g. in the ratio of 1.5-2:1, so that in the forward stroke 1.5 to 2 times the volume is conveyed as in the return stroke, so that in the forward stroke, volume can be conveyed faster in terms of a rapid pressure build-up and thus rapid actuation of the clutch or a rapid gear operation is promoted. In this way very short switching times of a double-clutch shift gearbox can be achieved, especially if at the same time in another clutch the pressure in the reservoir is reduced via a solenoid valve and the speed-torque characteristic curve of an electric motor can thus be optimally used for a given supply voltage.
Also, the volume ratio 2:1 can be used expediently in such a way that a volume compensation between two working chambers of a dual-action reciprocating piston can be achieved via a switching valve (31) and the axial force load on the shift gearbox is thus reduced, since in the forward stroke and in the return stroke only half the area acts on the shift gearbox unit. This is sensible especially at high pressures, since the axial force reduces the gear load and thus enables the use of a cost-effective plastic trapezoidal spindle drive. The advantage of the dual-action reciprocating piston compared to a continuously operating pump is that the pressure generating unit has to be operated only during a switching operation.
The following advantages can thus be achieved with the shift gearbox according to the invention:
Advantageous possible embodiments of the shift gearbox according to the invention are explained in more detail with reference to the drawings, in which:
The electric motor-driven actuating unit 1, 2 is for reasons of cost and space preferably in the form of a trapezoidal screw drive, alternatively executed by means of a ball screw drive or similar types of gears.
The hydraulic piston-cylinder unit 3 is actuated with the aid of the electric motor-driven actuating unit 1, 2, wherein here a pressure control takes place by using the pressure sensor 5. By adjusting a target pressure by means of the piston 3a (reducing the working chamber 3b) the fluid is displaced from the working chamber 3b via a 2/2-way valve 9 in the direction of the clutch unit 7 and thus opens the unpressurised closed clutch, which is monitored via the centrally arranged pressure sensor 5.
After actuation of the clutch 7, the 2/2-way valve 9 is closed and the clutch 7 is thus held in the open state.
By opening the 2/2-way valve 16 and closing the 2/2-way valve 14 further volume can be displaced via the piston-cylinder unit 3 into the cylinder 10a of the gear selector unit 10, whereby a rotation is exerted on the gear selector mechanism 12, which preferably has three possible switch positions. For this purpose, the 2/2-way valves 15 must be opened and the 2/2-way valve 17 must be closed at the same time. To adjust the gear selector, no pressure control is applied by means of the pressure sensor 5 however, but a volume control is carried out by driving the piston by a predetermined distance Δs, so that a defined amount of fluid is displaced into the cylinder 10a or 10b of the gear selector, whereby the gear selector mechanism 12 is rotated by a certain angle and thus to its desired set position.
In order to complete the switching process further, fluid is displaced via the 2/2-way valve 18 into the gear selector unit 11, whereby the gear selector mechanism 13 is moved to one of preferably three possible switching positions, preferably to one of the two end positions, whereby a spring 14 of the gear selector 11 is tensioned. Here too a volume control is applied, so that separate sensors for detecting the gear selector position could be dispensed with, which however may not be sensible in some cases, so that it is completely within the meaning of the invention to provide such position sensors at one or both gear selectors 10, 11. Only a slight pressure is needed to compensate for the spring forces of the piston-cylinder unit 3. The resetting of the gear selector 11 to its initial position can be carried out by the tensioned spring alone.
After the engagement of the selected gear via the gear selector mechanism 12, 13, the 2/2-way valve 9 is opened and the volume contained therein is moved back via the piston-cylinder unit 3 to its working chamber 3b, whereby the clutch 7 moves back in a controlled manner to its starting position and thus closes. Through the check valve 4 volume can be aspirated from a reservoir 6 into the piston-cylinder unit 3.
When pressure is reduced in the gear selector 10 via the outlet valves 14, 15, with the valves 16, 17 closed, pressure can be built up at the same time in the clutch 7 and the other gear selector 11.
The electric motor-driven actuating unit 1, 2 is for reasons of cost and space preferably in the form of a trapezoidal screw drive, or alternatively implemented by means of a ball screw drive or similar types of shift gearbox.
The hydraulic piston-cylinder unit 3 is actuated by means of the electric motor-driven actuating unit 1,2. The regulation of the individual hydraulic units in the form of the clutch 7 and gear selector 10, 11 is carried out via the piston movement for conveying the required hydraulic volumes. In this case the displaced volume can be calculated via the piston travel of the actuating unit 3 and therefore need not be measured individually with sensors in the individual hydraulic receivers 10a, 10b, 11, 7. This means that the function of the AMT actuator can only take place with an angle sensor 70 in the motor-shift gear-box-piston unit. Sensors such as for example a pressure transducer 5a or position sensor 71 in the clutch 7 can be used for diagnosis and can guarantee the functionality or evaluate the state of the system. However, they are not absolutely necessary. Assuming that the clutch actuator valve 9 has a leakage and the clutch 7 opens slowly, this can be determined by means of the differential rotational speed of the crankshaft and vehicle gearbox and an additional position or pressure sensor (5a, 71) is therefore not absolutely necessary. In addition, position sensors P1, P2 can also be provided at the gear selectors GS1 and GS2, which can be provided for example for leakage testing. These can however also be used instead of pressure transducers to control the position of the gear selector. In all embodiments which are shown and described in the figures, corresponding sensors Pi can be provided with the gear selectors, which can fulfil the above mentioned functions.
After actuation of the clutch 7, the 2/2-way valve 9 is closed and the clutch 7 is thus held in the open state.
By opening the 2/2-way valve 16 and closing the 2/2-way valve 14, which is closed current-free, further volume can be displaced via the piston-cylinder unit 3 to the cylinder 10a of the gear selector unit 10, whereby a rotation is exerted on the gear selector mechanism 17, which preferably has three switching possibilities. For this purpose, the 2/2-way valves 14 must be opened at the same time and the 2/2-way valve 16 must be closed. However, for adjusting the gear selector, no pressure control by means of a pressure sensor is used, but a volume control is carried out by driving the piston by a predetermined distance Δs, so that a defined amount of fluid is displaced into the cylinder 10a or 10b of the gear selector, whereby the gear selector mechanism 17 is rotated by a certain angle and is thus rotated to its required position.
In order to complete the switching process further fluid is displaced via the 2/2-way valve 18 to the gear selector unit 11, whereby the gear selector mechanism 13 is moved to one of preferably three possible switching positions, preferably to one of the two end positions, whereby a spring 15 of the gear selector 11 is tensioned. In this case as well a volume control is applied, so that separate sensors for detecting the gear selector position could be dispensed with, which however is not expedient in some cases, so it is completely within the meaning of the invention to provide such position sensors with one or both gear selectors 10, 11. Only a slight pressure is required to compensate the spring forces of the piston-cylinder unit 3. The resetting of the gear selector 11 to its initial position can be done by the tensioned spring alone.
After engaging the selected gear via the gear selector mechanism 12, 13, the 2/2-way valve 9 is opened and the volume contained therein is displaced via the piston-cylinder unit 3 back to its working chamber 3b, whereby the clutch 7 moves back in a controlled manner to its starting position and thus closes. Through the check valve implemented as a collar seal on the piston, volume can be aspirated from a reservoir 6 into the piston-cylinder unit 3. An excess of volume can thus be generated in the closed hydraulic system, which restricts the pressure or also the position control in the further course of events. Excessive volume can be drained via the valves 14 and 16 into the reservoir. Alternatively, the hydraulic piston 3 can for this purpose also drive into a position while the clutch 7 is depressed, where a pressure reduction is subsequently executed without any problem.
In the initial state preferably one of the two clutches 7, 19 is closed, whereas the other is in the open state.
With a gear change from first to second gear, volume is displaced via the hydraulic piston-cylinder unit to the hydraulically open gear selector system. The inlet valves of all gear selectors and the currently not activated clutch 19 are closed. By opening the 2/2-way valve 23b and simultaneously opening the outlet valve 26, the second gear is engaged by displacement of the piston in the gear selector 27b, following which the valve 23b is closed. A displacement or pressure control of the piston can be carried out here. For the change from first to second gear, volume is now displaced from the piston-cylinder unit 3 to the preferably hydraulically closed clutch unit system. The clutch C17 is closed and thus the first gear of the gear selector 27a is in the power train. The clutch C219 is in the open state in the starting position. By means of two 2/2-way valves 9, 20 the pressure reduction in clutch 7 and sequentially the pressure build-up in clutch 19 is carried out in the so-called multiplex operation. The pressure sensor 5 serves in this case for the pressure-volume control. For a gear change from second to third gear again all the inlet valves of the clutches and gear selectors as well as the outlet valve 26 are closed and the inlet valve 24a and the outlet valve 25 are opened. Via the control of the electric motor-driven actuating unit, the hydraulic fluid is displaced via the piston-cylinder unit to the piston chamber of the piston-cylinder unit 29a and third gear is thus engaged. The completion of the gear change operation is accomplished by opening or closing the clutches 7, 19 in multiplex mode.
A simplification of the hydraulic circuit diagram and a reduction in the number of valves is achieved by the use of one check valve per gear selector-piston chamber. In this connection for example the piston chambers of the gears 3, 4, 7, R can be hydraulically combined. A connection to the reservoir 6 is formed via an outlet valve 26.
In contrast to
The pressure build-up can also take place without a pressure transducer via a path control, in which the pressure-volume characteristic curve should then be taken into account and a pressure estimate is made by measuring the phase current of the electric motor. However, for safety reasons it is expedient to provide at least one pressure transducer also for adjusting the model.
The dual-action reciprocating piston can be implemented as a continuous pressure supply unit, which is used only as required, in which the check valves 4, 4a and 36 are employed. With an area ratio of the two piston surfaces or piston ring surfaces of 2:1, the same volume is conveyed to the system both in the forward stroke and the return stroke. In the forward movement of the dual-action reciprocating piston the volume is conveyed from the forward stroke piston 34b via the check valve 36 on the one hand to the return stroke chamber 34c, and on the other hand the other half of the volume is made available to the system. In a reverse movement of the dual-action reciprocating piston, volume is made available via the check valve 4 in the forward stroke chamber 34b and the volume is fed from the return stroke chamber 34c to the system.
On account of the hydraulic connection of the forward and return stroke chambers 34b, 34c, the effective piston area is the difference between the piston forward stroke surface and piston return stroke surface, or only the return stroke surface. This area must be taken into consideration for the design of the engine torque and/or the shift gearbox. The unit can be designed so that axial forces are reduced as much as possible, which can allow the use of a plastic transmission.
In contrast to
In contrast to
The volume from the forward stroke chamber 34b can conveyed via the 2/2-way valve 20 to the clutch 7. At the same time the volume can be displaced from clutch 19 to the return stroke chamber 34c. For a change of the pressure gradient the outlet valve 50 can in addition be electrically energized in PWM control. The closing or opening operation of the individual clutches can thus be influenced. On actuation of a gear selector the volume of the forward stroke chamber is used for example for the pressure build-up in a gear selector, and at the same time the volume is displaced from the second chamber of the gear selector to the return stroke chamber of the double-acting piston unit 34.
Preferably the piston 34e is in a middle position before the start of its travel, since it cannot be predicted whether first gear or reverse gear is engaged when the vehicle is started. Thus, for both manoeuvres a corresponding volume is present in the chambers 34b and 34c for actuating a gear selector and a clutch. Alternatively, the piston 34e would have to be moved to the correct position with the valves 50 and 51 open.
Contrary to the embodiment shown in
The spindle 62 is connected to the rotor 66 and drives the axially displaceably mounted spindle nut 63, which is arranged in a torque-proof manner with its collar in the second housing part 60. The spindle nut 63 forms as it were with its front end 64 the piston of the piston-cylinder unit. The working chamber 3b is delimited by the first housing part 60 and the piston 64. Seals 69 ensure that no fluid can move in the direction of the electric motor 65, 66. A trapezoidal spindle 63 made of plastic is preferably used, since only low pressures have to be built up for a shift gearbox and thus only small forces are exerted. The working chamber 3b is connected to the hydraulic line HL, not shown, via the channel 68.
The spindle nut 63 of the pressure supply unit according to
Number | Date | Country | Kind |
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10 2016 116 778.9 | Sep 2016 | DE | national |
10 2016 118 423.3 | Sep 2016 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2017/054643 | 2/28/2017 | WO | 00 |