EP1040287A1

EP1040287A1 - Continuously variable automatic transmission

Info

Publication number: EP1040287A1
Application number: EP98965268A
Authority: EP
Inventors: Gerald Rowe
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1997-12-19
Filing date: 1998-12-15
Publication date: 2000-10-04
Also published as: DE19756685C2; KR20010024770A; WO1999032806A1; JP2003517540A; DE19756685A1

Abstract

The invention relates to an automatic transmission for a motor vehicle, especially a continuously variable transmission. The transmission has a variator, a primary disk set (12) and a secondary disk set (10) having a pushing linked band, whereby the variator can be adjusted with transmission oil provided from an oil pump (3) via an electrohydraulically controlled pressure supply device. A pressure regulating device (1) is arranged in one of the pressure lines (4) of the pressure supply device leading from the oil pump (3). The pressure regulating device is configured with a control valve (2) which is located in the pressure line (4) and with a bypass line (5) which bypasses the control valve (2). A stepped piston (9) which is arranged in a cylinder housing (6) and which can be displaced between two path limiting devices (7, 8) is arranged in the bypass line (5). The piston borders a first cylinder space (14) with a first front face (13) and borders a second cylinder space (16) with a second front face (15) which faces opposite the direction of the oil pump (3), said second space having a cross-section which is smaller than the first cylinder space (14).

Description

CONTINUOUSLY AUTOMATIC TRANSMISSION

The invention relates to an automatic transmission for a motor vehicle, in particular a CVT transmission, with a varia ^¬ gate, which has a primary disc set and a secondary disc set with a thrust link belt, the variator being adjustable with a transmission oil provided by an oil pump via an electro-hydraulically controlled pressure supply device.

Automatic transmissions of the type mentioned are generally known from practice. One version is e.g. B. in the "ATZ Automobiltechnische Zeitschrift" 96 (1996) p. 378 ff.

In automatic transmissions of this type, hydraulically actuated adjusting devices of the variator are acted upon by an oil pump with the necessary adjusting pressure for setting a gear ratio of the automatic transmission that is matched to the respective operating state of the internal combustion engine or the driving speeds of the motor vehicle. The adjustment pressure is set by the amount of transmission oil delivered by the oil pump to the pressure supply device.

However, these automatic transmissions have the disadvantage that they do not have the necessary adjustment dynamics in certain transmission situations. This means that the oil pump is not able to deliver the required amount of transmission oil into the pressure supply device in particularly short adjustment periods. This disadvantage exists above all in the case of large translation changes, such as those which occur with abrupt changes in the driving speed. This can be a so-called "panic braking" both from high driving speed and when operating in city traffic, the latter representing a particularly critical operating state, since the period until the vehicle comes to a standstill can be very short.

The internal combustion engine is preferably in the partial load range, i.e. H. operated in the optimum speed range for fuel consumption, for which purpose the gear ratio adjusted to this driving state between the primary shaft and the secondary shaft is set in the automatic transmission. In the event of a sudden braking of the motor vehicle from this operating state until the vehicle comes to a standstill, as is often the case in a dangerous situation in road traffic, changing the gear ratio to the maximum gear ratio or the gear ratio intended for a new start is not quick enough within this period feasible. A subsequent comfortable start with the required maximum gear ratio of the automatic transmission is not possible. In addition, in the case of a gear ratio that is too small, an undesirable so-called "stalling" of the engine can occur.

Although this problem could be remedied with oil pumps which are correspondingly larger in terms of the geometric delivery volume, such a solution disadvantageously leads to a greatly deteriorated transmission efficiency. The present invention is therefore based on the object of creating an automatic transmission which, with the smallest possible pump dimensions, has a sufficiently high adjustment dynamic so that a gear ratio which is respectively adapted and required to the driving state is available.

According to the invention, this object is achieved by the features mentioned in the characterizing part of claim 1.

The inventive design of the automatic transmission or the pressure supply with a pressure adjusting device, which according to the invention is equipped with a switching valve and a stepped piston, achieves the advantage of increasing the adjustment dynamics.

There is a major translation change such as In the case of panic braking described at the beginning, the connection between the oil pump and the variator with the primary disk set and secondary disk set is interrupted by means of the switching valve, and the oil pump delivers the transmission oil via the bypass line into the second cylinder chamber, which communicates with the variator via the step piston Active connection is established.

Due to the amount of transmission oil introduced by the oil pump, pressure advantageously builds up in the second cylinder space, which axially displaces the stepped piston in the direction of the first end face. The volume of the second cylinder chamber increases steadily by the amount of transmission oil introduced, while the volume of the first Cylinder space is reduced in proportion to the displacement of the stepped piston.

In this way, a pressure increase is achieved in the pressure setting device according to the invention, which corresponds to a fictitiously introduced amount of transmission oil, which advantageously does not have to be applied by the oil pump. The fictitious amount of gear oil results from the product of the amount of gear oil actually delivered and the value of the diameter ratio between the first

End face and the second end face of the stepped piston.

The present invention thus advantageously ensures that a greater change in the gear ratio can be set in a certain time interval than in the automatic transmissions known from the prior art. In addition, if the stepped piston is designed as required, the required amount of transmission oil can also be achieved with an oil pump that is smaller, less expensive and takes up less space.

Advantageous refinements and developments of the invention result from the subclaims and from the exemplary embodiment described in principle below with reference to the drawing. Show it:

Fig. 1 is a schematic representation of a pressure adjusting device in an automatic transmission; 2 shows a course of the driving speed of a motor vehicle and the speed of the internal combustion engine during a braking operation over time;

3 shows the course of the transmission ratio of an automatic transmission and the corresponding adjustment path of the disk set of the secondary shaft over time as a function of the change in driving state according to FIG. 1 and

4 shows the course of the required and the actual amount of transmission oil over time for the adjustment path of the secondary disc set according to FIG. 3.

1 shows a schematic representation of a pressure setting device 1 in a pressure supply (not shown) of an automatic transmission, the

Pressure setting device 1 has a switching valve 2 in a pressure line 4 leading away from an oil pump 3 and a bypass line 5 bypassing the switching valve 2. In the bypass line 5, a stepped piston 9 is arranged in a cylinder housing 6 and can be displaced between two path limiting devices 7, 8.

Oil is transferred from the oil pump 3 via the pressure setting device 1 to a secondary disk set 10, which is only symbolically indicated in FIG. 1, and after an upstream one

Control unit 11 is conveyed to a primary disc set 12, likewise only indicated, of a variator of the automatic transmission, the disc sets 10, 12 being affected by the oil pressure a primary shaft or secondary shaft, not shown, can be axially displaced to set a specific transmission ratio.

The stepped piston 3 is arranged in the pressure setting device 1 or the bypass line 5 such that it has a first cylinder space 14 with a first end face 13 and a second cylinder space 16 with a second, opposite end face 15 in the direction of the oil pump 3, rather a smaller one Cross-section than the first cylinder chamber 14 has limited. The first cylinder chamber 14 forms a spatial unit with the pressure line 4 in its section downstream of the switching valve 2.

The switching valve 2 can be switched into a blocking position by a solenoid valve 17, so that the pressure line 4 for the oil supply from the oil pump 3 to the variator is interrupted.

The bypass line 5 branches off from the pressure line 4 in an area between the oil pump 3 and the switching valve 2 and opens into the second cylinder space 16 of the stepped piston 9.

In the present exemplary embodiment, the stepped piston 9 is designed as a rotationally symmetrical body which has a first section 18 and a second section 19 stepped therefrom, the diameter of the first section 18 being the diameter of the first end face 13 and the diameter of the second section 19 being the diameter corresponds to the second end face 15. The stepped piston 9 can be displaced in the axial direction over a maximum adjustment path between the path limiting device 7, which represents a cylinder bottom of the first cylinder chamber 14, and a shoulder 8 serving as a path limiting device, a connection being provided in the area between the first cylinder chamber 14 and the second cylinder chamber 16 an end position of the stepped piston 9 on the cylinder bottom 7 of the first cylinder chamber 14 is opened and is closed in a position of the stepped piston 9 which deviates therefrom.

To form this connection, the stepped piston 9 has a channel 21 which starts from its first end face 13 and is arranged coaxially to its central axis 20 and extends into the second section 19 of the stepped piston 9 with a smaller diameter. In the area of this section 19 of the stepped piston 9, the channel 21 is connected to four boreholes 22, which extend radially outward into the peripheral region of the stepped piston 9.

Corresponding to the position of the bore 22 in the stepped piston 9 in its end position on the cylinder bottom 7 of the first cylinder chamber 14, an annular groove is formed in the cylinder housing 6 to form the connection between the cylinder chambers 14, 16

Connection 23 is provided with a connecting line 24 opening into the bypass line 5. Thus, in this end position of the stepped piston 9, an oil flow from the oil pump 3 via the bypass line 5 and the stepped piston 9 into the pressure line 4 is possible, bypassing the switching valve 2.

In the bypass line 5 is in the area between its branch from the pressure line 4 and the junction Connection line 24 arranged a pump-effective aperture 25 as a throttle device.

The mode of operation of the pressure setting device 1 is illustrated by means of a driving course shown by way of example in FIGS. 2 to 4.

2 shows the course of a driving speed v_F of the motor vehicle and the corresponding speed n_M of an internal combustion engine during a braking operation over time t. If the vehicle speed v_F is continuously reduced due to a specific traffic situation, the engine speed n_M has a constant value up to a point in time t_WK. At time t_WK, i.e. H. from a fixed vehicle speed, a converter lock-up clutch of known design is opened to prevent the engine from being "stalled" when the speed is reduced further. The engine speed n_M then falls within a short time interval, which at Time t_L has ended, down to the idling speed.

3, the course of a gear ratio i of the automatic transmission and a corresponding adjustment path x of the disk set of the secondary shaft as a function of the course of the driving speed is shown in FIG. 1 over time t. The translation i should be set as the optimal translation i_opt according to a control characteristic for the respective operating point, which is optimized with regard to driver behavior and / or consumption. At t_0 there is a minimally adjustable translation i_min with a so-called ter "Overdrive", ie the transmission output speed is greater than the transmission input speed. With increasing time, the ratio 1 is adjusted by a controller according to an optimal size stored in a map of the transmission control m as a function of several parameters such as driving speed v_F, engine speed n_M and throttle valve position .

The present example is based on a partial load operation as the operating situation of the internal combustion engine and the automatic transmission, in which the internal combustion engine is operated in a low-speed range that is optimal for consumption and in which the largest driving stage is present, i. H. that the automatic transmission has a minimal translation ι_Mm. An adjustment path of the secondary disc set of x corresponds to this minimum translation ι_Mm. As the vehicle speed v_F decreases, as shown in FIG. 2, the transmission ratio I steadily increases up to a maximum transmission ratio ι_max at the time t_3, the adjustment path x likewise increases up to the maximum adjustment path x_max.

FIG. 4 shows the course of the required as well as the actual amount of oil required by the oil pump 3, which is required for the adjustment path x of the secondary disk set according to FIG. 3. It can be seen that the actual demand quantity V_real has a constant value in the range from t_0 to time t_WK. At time t_WK, the actual transmission oil requirement quantity V_real abruptly drops to a smaller value. This course of the required quantity of gear oil results from the fact that the oil pump 3 is driven by the internal combustion engine w rα, the speed of the oil pump 3 being the speed of the engine Internal combustion engine corresponds. From the decrease in engine speed n_M at the time the converter lock-up clutch t_WK opens, the drop in the actual amount of transmission oil V_real follows.

The course of the required amount of transmission oil V_erf, which is also shown in FIG. 4, which results from leaks in the pressure feeds, the amount of lubricating oil, the basic transmission supply, i.e. H. the oil supply to the pressure regulator and control unit leakage, as well as the required adjustment dynamics of the disc sets, on the other hand, shows that in the time interval between t_0 and t_WK the amount of required transmission oil increases from a basic transmission supply to a value that is always far below the value of the actually promoted Transmission oil quantity V_real is. From the time t_L, the value of the required transmission oil quantity V_erf rises above the value of the transmission oil quantity V_real that is actually delivered.

From this it can be seen that with an embodiment of an automatic transmission known from the prior art, setting an optimal transmission ratio i_opt is no longer possible from the time t_L. The curve difference in the area of the hatched area in FIG. 4 shows the integral of the required oil quantity, which is required to set the optimal transmission ratio i_opt or to ensure a maximum transmission ratio for a subsequent starting process.

The transmission control recognizes the case described above, e.g. B. by the ratio change exceeding a predefined limit value, then the pressure line 4 of the pressure setting device 1 by means of the switching valve 2 blocked. The oil pump 5 then conveys the transmission oil via the bypass line 10 with the orifice 25 into the second cylinder space 16. Due to the quantity of transmission oil supplied, the pressure in the second cylinder space 16 rises such that the stepped piston 9 is axially displaced in the direction of the first end face 13. The displacement of the stepped piston 9 in turn has the consequence that the volume of the first cylinder space 14 is reduced in proportion to the adjustment path of the stepped piston 9. Since the first end face 13 of the stepped piston 9 is dimensioned larger than the second end face 15, a larger amount of oil is pushed out of the first cylinder chamber 14 with the same adjustment path than is conveyed into the second, smaller cylinder chamber 16 by the oil pump 3.

In this way, a fictitious introduced amount of gear oil is generated in the pressure setting device 1, which reproduces the course of the required amount of gear oil V_erf in the time interval between t_L and t_3. With this fictitious amount of transmission oil, a higher adjustment dynamic of the automatic transmission is now achieved, so that the optimal transmission ratio i_opt can be set between the primary and the secondary pulley set.

When the stepped piston 9 with its first end face 13 reaches an end position on the cylinder base 7, the bores 22 of the stepped piston 9 are arranged congruently with the connection 23 of the housing 4, whereby - as already described above - a connection between the oil pump 3 and the first Cylinder chamber 14 is made. This means that the oil pump 3 now pumps the transmission oil into the first cylinder space 14 or into the pressure line 4. This ensures that the variator also after Reaching the end position of the stepped piston 9 is pressurized.

In addition, the connection prevents the oil pressure from rising to a critical range, as a result of which the

Stepped piston 9 is protected from damage and an additional pressure relief valve is unnecessary.

If the switching valve 2 is switched back to the open position, the oil pump 3 delivers the transmission oil again via the pressure line 4 into the first cylinder chamber 14 and to the variator. Due to the diameter ratio between the first end face 13 and the second end face 15, the stepped piston 9 is displaced towards the shoulder 8 in the direction of the second end face 15.

The unidirectional aperture 25 prevents the displacement from exceeding a permissible displacement speed and the adjustment dynamics from the maximum transmission ratio i_max being reduced.

The volume of the first cylinder chamber 14 is dimensioned such that the oil volume is sufficient for adjustment and the first cylinder chamber 14 serves as an absorber in the end position of the stepped piston 9 on the shoulder 8. Reference numerals

1 pressure setting device 2 switching valve

3 oil pump

4 pressure line

5 bypass line

6 cylinder housing 7 travel limitation device, cylinder base

8 path limiting device, paragraph

9 step pistons

10 secondary disc set

11 Control unit 12 consumers, primary disc set

13 first face

14 first cylinder chamber

15 second end face

16 second cylinder chamber 17 solenoid valve

18 first section of the stepped piston

19 second section of the stepped piston

20 central axis of the stepped piston

21 channel of the stepped piston 22 holes of the stepped piston

23 connection, annular groove

24 connecting line

25 throttle device, orifice

Claims

Patent claims

1. Automatic transmission for a motor vehicle, in particular C / T transmission, with a variator, which has a primary disc set and a secondary disc set with a thrust link belt, the variator being adjustable with transmission oil provided by an oil pump via an electrohydraulically controlled pressure supply device that in a pressure line (4) leading away from the oil pump (3) of the pressure supply device a pressure setting device (1) is arranged, which has a switching valve (2) in the pressure line (4) and a bypass line (5) bypassing the switching valve (2) In the bypass line (5), a step piston (9) is arranged in a cylinder housing (6) and displaceable between two path limiting devices (7, 8), which has a first end face (13) and a first cylinder space (14) and with a second, opposite end face (15) in the direction of the olpu mpe (3) delimits a second cylinder space (16), which has a smaller cross section than the first cylinder space (14).

2. Automatic transmission according to claim 1, characterized in that the stepped piston (3) in the bypass line (5) is arranged such that the first cylinder chamber (14) with the pressure line (4) downward of the switching valve (2) forms a spatial unit.

3. Automatic transmission according to claim 1 or 2, characterized in that by means of the switching valve (2) the pressure line (4) for guiding the oil from the oil pump. pe (3) on the secondary disc set (10), the primary disc set (12) and a control unit (11) can be shut off.

4. Automatic transmission according to one of claims 1 to 3, characterized in that a connection is provided between the first cylinder chamber (14) and the second cylinder chamber (16), which in the region of an end position of the stepped piston on the path limiting device (7) in the direction of first end face (13) is open and is closed in a position of the stepped piston (9) which differs from this.

5. Automatic transmission according to claim 4, characterized in that the stepped piston (9) for forming the connection has at least one of its first end face (13) and at least approximately coaxially arranged to its central axis (20) arranged channel (21) which up to a section (19) of the stepped piston (9) with a diameter that corresponds at least approximately to the diameter of the second end face (16), and in the area of this section (19) at least one bore (21) connected to the channel (21) 22), which extends radially outward into the circumferential area of the stepped piston (9).

6. Automatic transmission according to claim 5, characterized in that to form the connection in the cylinder housing (6) corresponding to the position of the bore (22) in the stepped piston (9) at its end position on the path limiting device (7) in the direction of the first end face ( 13) a connection (23) with a connecting line (24) opening into the bypass line (5) is arranged.

7. Automatic transmission according to claim 6, characterized g e k e n n z e i c h n e t that the connection is designed as an annular groove (23).

8. Automatic transmission according to one of claims 1 to 7, characterized in that a bypass line (5) in the bypass line (5) in front of the second cylinder chamber (16) of the stepped piston (9) is arranged a pump-effective throttle device (25).

9. Automatic transmission according to claim 8, characterized in that the throttle device (25) in the bypass line (5) is arranged in the region between its branch from the pressure line (4) and the junction of the connecting line (24).

10. Automatic transmission according to claim 9, characterized in that the throttle device is designed as an aperture (25).

11. Automatic transmission according to one of claims 1 to 10, characterized in that the volume of the first cylinder chamber (14) is dimensioned such that the first cylinder chamber (14) in an end position of the stepped piston (9) on the path limiting device (8) in the direction of the second cylinder chamber (16) serves as an absorber.