GB2177765A

GB2177765A - Improvements relating to automatic transmission systems

Info

Publication number: GB2177765A
Application number: GB08614588A
Authority: GB
Inventors: Robert Bishop
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-15
Filing date: 1986-06-16
Publication date: 1987-01-28
Also published as: GB8614588D0; GB2177765B

Abstract

An automatic transmissions system for a vehicle has an infinitely variable transmission (29) driven by an engine (30). This transmission may be an epicyclic gear train in parallel with a hydraulic pump/motor unit whose output can be clutched to different gears of the train to produce forward and reverse drive, or be disengaged for neutral. A computer (36) receives information from transducers (37, 38, 39, 40, 41, 42) for the braking, acceleration, engine speed, vehicle motion and oil situation, and also from a selector (21) on the chosen mode of operation (forward, reverse, neutral). Through a servo (15), the computer governs the pump/motor unit and thus the transmission. It is programmed so that smooth clutch engagement is achieved once the mode is selected and, at least in the forward mode, to maintain the engine in a predetermined efficiency band. A further forward more can be provided where more power is available at less efficiency. <IMAGE>

Description

SPECIFICATION Improvements relating to automatic transmission systems This invention relates to automatic transmission systems.

With ever-increasing fuel costs economy and efficiency from internal combustion engines becomes more and more important.

Generally there are two types of transmission, one using manual control and the other automatic. Skilled drivers can use a manual gearbox very efficiently, but not everyone has the competence or concentration to keep it up over long periods. Automatic transmissions take- much of the work out of driving, but they are generally acknowledged to be "thirsty" and less efficient.

For the best fuel economy, the engine should run at an optimum combination of load and speed to produce the necessary power.

The thermal efficiency of an engine is normally greatest at a point between half and full load and around the mid-point of its speed range.

These properties are not matched by most conventional gearboxes, and so one aim is to provide a transmission system which does take account of them.

However, while economy and efficiency are important, so too is safety and, on occasions, the ability to accelerate hard and drive at high speeds. Thus any system that seeks to optimise on efficiency should preferably have provision for setting it aside when necessary.

According to the present invention there is provided an automatic transmission system for a vehicle comprising an infinitely variable transmission, a computer and transducer means providing the computer with information on input and output speeds of the transmission, on the vehicle motion, and on driver controls such as accelerator and brakes, the computer being programmed to govern the transmission and thereby influence engine performance.

The computer may be programmed to govern the transmission in a manner to maintain the engine in a pre-determined efficiency band.

Generally, there will be selector means by which an operator can choose different modes of operation, the state of the selector means being another input to the computer. Such modes will normally be forward, neutral and reverse, and the forward modes may also select the efficiency band.

There can also be another selectable forward mode, making more power or performance available at less efficiency than in the first forward mode.

The infinitely variable transmission is preferably split, the drive being directed in parallei through an epicyclic gear train and to a hydraulic pump/motor unit. The latter may have an associated servo governed by the computer to vary the pump displacement and thus the motor speed. The output of the pump/motor unit can be clutched to different parts of the epicyclic gear train to produce forward and reverse motion. When unclutched, the transmission is in neutral. The position of the clutch will be another input to the computer.

As well as receiving information on the accelerator and brake conditions, the computer will also have a continuous input representing the engine speed, which can be drawn from the ignition coil pulses. It will also have information on oil pressures and levels.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram of a divided torque automatic transmission, Figure 2 is a hydraulic circuit diagram related to the transmission of Figure 1, Figure 3 is a block circuit diagram of a computer control system for such a transmission, and Figure 4 is a flow chart showing the sequence of events for forward drive.

In Figure 1 a rotary input shaft 1 drives the sun 2S of a first epicyclic gear 2 and also a hydraulic pump unit 3 via gears 4 and 5, thus splitting the drive. The annulus 2A of the gear 2 is part of or fixed to a member which provides an output shaft 6, and this member also carries the planets 7P and 8P of second and third co-axially arranged epicyclic gears 7 and 8. The sun 7S of the gear 7 is on a member carrying the planets 2P and the annulus 7A is on a member providing the sun 8S of the gear 8. The latter's annulus 8A can be clutched by a sliding dog 9 to one flange 10 of a co-axial member 11 driven by a hydraulic motor 12 energised by the pump unit 3, while another flange 13 at the opposite end can be united to the annulus 7A by a sliding dog 14.

These dogs are linked so that only one clutch is engaged at a time and so that there is an intermediate neutral position.

The hydraulic pump unit 3, shown in more detail in Figure 2, preferably includes two pumps, one to power a hydraulic pilot system and supply lubrication and being of fixed displacement, while the other one, which drives the motor 12, is of variable displacement under the control of a servo unit 15, conveniently embodying a stepper motor.

With the clutches 9 and 14 in neutral and the output shaft stationary due to the inertia or braked condition of the vehicle, it will be seen that the annulus 7A will rotate in the opposite direction to the input shaft 1 while the annulus 8A will rotate in the same direction.

For forward motion, the pump unit 3 is initially caused to drive the motor 12 so that the member 11 rotates synchronously with the annulus 7A, this being achieved through the computer control system described below.

The clutch 14 can then be engaged. Subsequently varying the speed of the motor 12 provides the gear 7 with a reaction member, its annulus 7A being coupled to that motor, so that the output shaft 6 will rotate. Meanwhile, the gear 8 is de-clutched and spinning idly.

For reverse motion, the clutch 9 is engaged once the member 11 has been brought into synchronous rotation in the opposite direction, and the annulus 8A then provides a reaction member of variable speed in manner similar to that described above. The gear 7 is idle.

The hydraulic system is shown in more detail in Figure 2, where the motor 12 and servo 15 are referenced as before while the fixed and variable displacement pumps of the unit 3 are indicated at 16 and 17. Between the pump 17 and the motor 12 there is an isolating valve 18, solenoid operated with a spring return, and a pilot operated directional valve 19. A regulator valve 20 is provided in the return.

A selector valve 21 is manually operable to choose forward, neutral and reverse and cooperates with a clutch engagement valve 22, solenoid operated with a spring return, to actuate forward and reverse clutch cylinders 23F and 23R. A check valve 24 is provided in this circuit, while the broken line 25 represents a mechanical interlock between the clutches.

The line 26 from the pump 16 indicates the lubrication circuit, and a pressure regulator 27 is provided in the pilot line to the selector valve 21.

The operation of this system will be evident from the Figure. The isolating valve 18 is provided in order to relieve the servo at times of clutch engagement and to remove the possibility of vehicle "creep".

Turning to Figure 3, the clutches are shown by the single block 28 and the split transmission, apart from the servo 15, by the unit 29.

The vehicle is powered by an internal combustion engine 30 with a starter 31 having an associated solenoid 32. Other standard components are a battery 33, an ignition switch 34, and an ignition coil 35, the electrical connections between these being shown in full lines.

In addition, there is a computer 36 which receives signals from various transducers and which controls the transmission in conjunction with the selector 21. This has a simple hand lever which, in addition to determining the three basic modes of operation "forward", "neutral" and "reverse", as indicated by the corresponding initials, has a fourth position P (for "power"). This is another forward mode but the computer creates a different response, as explained below.

Transducers 37 and 38 associated with the transmission 29 respectively monitor the oil level and pressure. There are switches 39 and 40 associated with the hand and foot brakes, and an accelerator monitor 41. This will keep the computer 36 informed of the position of the accelerator, any change of position, and the rate of such change. An inhibitor 42 determines whether or not the vehicle is stationary, this information being fed to the computer to prevent reverse engagement until forward motion is stopped and vice versa.

The broken lines represent the inputs to the computer 36 from the various information sources, and the control signals issued by the computer.

When the ignition switch 34 is turned on, this is signalled to the computer 36, which thereupon institutes a check that the selector 21 is in the neutral mode N, that the transmission fluid level is sufficient (from transducer 37) and that the engine is stationary, the latter being indicated by no signal from the ignition coil 35. If all is correct, then the computer will send a return signal to the ignition switch which allows the starter to be energised via its solenoid 32. The engine will then fire and run, with the clutch 28 in neutral between the gears.

Assuming the driver wishes to move off forwardly, he will move the selector 21 to position F, the hand brake at least still being on and the clutch disengaged. This movement of the selector lever will trigger further checks by the computer, namely on the transmission fluid pressure from the transducer 38 and that the vehicle is stationary from the inhibitor 43.

The computer will also determine the engine speed from the coil 35, which will be pulsing in direct relationship to that speed, and the speeds of the components of the clutch to be engaged (7A and 13 in Figure 1). From the latter, it will signal to the servo 15 to vary the transmission so that the clutch component speeds are equalised. Once this is achieved, the computer causes the solenoid valve 22 to operate to engage the clutch 28 for forward motion. A signal from another transducer informs the computer when that engagement occurs, whereupon the computer signals the solenoid valve to de-energise.

The two modes of operation for forward motion comprise the normal forward mode F where economy is imposed, and the power mode P in which economy is discarded and power or performance ratios are selected.

Initially, as mentioned above, the driver will select the normal forward mode F. Having done this, and with the clutch engaged, the hand and foot brakes will then be released, both sending signals to the computer. The driver will accelerate the engine from idling speed, and this will also be indicated to the computer from the distributer coil 35.

The flow chart of Figure 4 diagrammatically illustrates this sequence.

The brake release will cause the computer to adjust the servo 15 and thus the transmis sion 29 into-forward motion. The amount of acceleration will determine the gear ratio. For example, hard acceleration will delay changing up, thus allowing relatively greater power out put from the engine, as is normal with auto matic transmissions, than with slight accelera tion. As the vehicle moves, so the computer checks the engine speed from the coil 35 and maintains suitable ratios through the servo 15 which will keep that engine speed within lim its.

The driver will of course be varying the ac celeration to control the vehicle's speed, and the position of the accelerator is indicated by the monitor 41. The signals to the computer, which modifies the gear ratios accordingly through the servo 15, but still within the limits of the economy program.

Should the driver want to transfer to the power mode, he simply shifts the selector lever to position P, and this can be done when the vehicle is either stationary or mov ing forward. Transfer to this mode is signalled to the computer, which substitutes a power mode program for the economy program. This will allow the engine revolution range to be extended by holding relatively lower transmis sion ratios and removing the performance inhi biting effects of the economy program.

For reversing, the selector lever is moved to position R and the sequence is the same as for the normal forward mode F with the sole noid valve reversing the clutch engagement and the flow reversal valve 19 reversing the hydraulic motor rotation.

It will be understood that there could be more than two programs for forward motion, graduated between maximum economy and maximum performance.

These programs, depending upon the details therein, dedicating the transmission to sustain ing performance or economy from the engine, will result in vehicle performance better than that obtainable from a conventional manual gearbox.

Claims

1. An automatic transmission system for a vehicle comprising an infinitely variable transmission, a computer and transducer means providing the computer with informa tion on input and output speeds of the transmission, on the vehicle motion, and on driver controls such as accelerator and brakes, -the computer being programmed to govern the transmission and thereby influence engine performance.

2. A system as claimed in Claim 1, wherein the computer is programmed to govern the transmission in a manner to maintain the en gine in a pre-determined efficiency band.

3. A system as claimed in Claim 1 or 2, wherein selector means are provided by which an operator can choose different modes of operation, the state of the selector means being another input to the computer.

4. A system as claimed in Claim 3, wherein the modes of operation include forward, neutral and reverse.

5. A system as claimed in Claim 4 as appendent to Claim 2, wherein the forward mode also selects said efficiency band.

6. A system as claimed in Claim 5, wherein another selectable forward mode makes more power available at less efficiency than in the first forward mode.

7. A system as claimed in any preceding claim, wherein the infinitely variable transmission is split, the drive being directed in parallel through an epicyclic gear train and to a hydraulic pump/motor unit.

8. A system as claimed in Claim 7, wherein the hydraulic pump/motor unit has an associated servo governed by the computer to vary the pump displacement and thus the motor speed.

9. A system as claimed in Claim 7 or 8 as appendent to Claim 4, wherein the output of the pump/motor unit is clutchable to different parts of the epicyclic gear train to produce forward and reverse motion, and when unclutched keeps the transmission in neutral.

10. A system as claimed in Claim 9, wherein the clutch position is another input to the computer.

11. A system as claimed in any preceding claim, wherein the transmission input speed information for the computer is derived from ignition coil pulses for an internal combustion engine driving said transmission.

12. A system as claimed in any preceding claim, wherein information on oil pressure and levels is also provided for the computer.

13. An automatic transmission system substantially as hereinbefore described with reference to the accompanying drawings.