GB2080451A - Transmission control systems - Google Patents

Abstract

A control system for an automatic transmission for a motor vehicle comprises means for comparing electrical signals related to vehicle velocity and to engine air intake vacuum or throttle opening and for producing a transmission shift control signal. The velocity signals may be produced by a rotary magnet system causing opening and closing of a reed switch connected to a frequency-to-voltage converter. Engine intake vacuum may be detected by vacuum responsive switches and converted stepwise into voltage signals which, with the velocity signals, are fed to a comparator whose output controls a shift valve and also provides positive feedback to the vacuum-responsive signal-forming circuit to cause upshift/downshift hysteresis. <IMAGE>

Description

SPECIFICATION Transmission control systems The invention relates to a control system for an automatic transmission for a motor vehicle.

A system according to the invention comprises means for producing a first signal related to vehicle velocity, means for producing a second signal related to the vacuum in an engine air intake, and means for comparing the first and second signals and producing a transmission shift control signal.

The vacuum in the air intake is closely related to the engine output torque or speed of rotation, and so constitutes a good basis for transmission shift control.

Preferably the means for producing the second signal comprises a vacuum switch positioned near a throttle valve on an engine air intake. Such a vacuum switch may have one or more switching or change-over points at different pressures for effecting shifts between different transmission speeds or gear ratios.

Drawings Figure 1 is a block diagram of a system according to the invention; Figure 2 shows a system for sensing vacuum in an engine air intake system; Figure 3 is a graph of vacuum P0 in the engine air intake against throttle opening angle 6; Figure 4 shows a vacuum switch VSW in Figure 2; Figure 5 is a transmission shift graph of throttle opening angle 0 against vehicle velocity Vv according to the invention; Figures 6a and 6b show a control circuit for a system according to the invention; and Figures 7a and 7b show structure of a hysteresis circuit in Figure 6a.

Figure 2 shows an engine air intake 20 between a throttle valve 21 and an engine 22. A vacuum switch VSW in a casing 1 is connected by a pipe 4 to the intake 20. Figure 4 shows how the pipe 4 leads into a vacuum chamber 2 inside the switch VSW. The vacuum chamber 2 is separated from an atmospheric pressure chamber 3 by a diaphragm 6. The atmospheric pressure chamber 3 is connected to atmosphere through a pipe 5.

The diaphragm 6 flexes, and core 11 secured thereto is moved longitudinally inside the casing 1 according to the pressure difference between the vacuum chamber 2 and the atmospheric pressure chamber 3. The core 11 is urged to the right in Figure 4 by a coil spring 7 which bears on the inside of the casing 1 through an adjustment screw 10. The core 11 has integral therewith a magnet 9, the longitudinal position of which actuates a reed switch 8. The reed switch 8 supplies a (second) signal related to the vacuum in the engine intake 20 through terminals 9a and 9b.

The vacuum switch VSW is set so that a vacuum of -250 mmHg corresponds to a throttle opening of 2025%, and -200 mmHg to 2530% when it is positioned close to the throttle valve 21 as shown in Figure 2. If the vacuum in the intake decreases, the vacuum switch VSW will turn ON, and cause an electric signal Ee to be supplied to the control circuit as shown in Figure 6a.

A (first) signal related to vehicle velocity is produced by means indicated in Figure 6b: An output shaft revolution speed or velocity sensor 31 comprises a magnet MG rotated by a speedometer cable which transmits rotary motion from the output shaft to a speedometer. A reed switch RSW under the influence of the rotating magnet MG opens and closes at a frequency related to the velocity of the vehicle. The reed switch RSW has its positive terminal connected to the input of a frequency-to-voltage (FV) converter 32, and has its negative terminal grounded on a vehicle body.

The reed switch RSW is in parallel with resistors R2, R3 and R4 which in turn are in series with a resistor R1. The constant voltage pulse which is produced by the sensor 31 is transmitted from the input terminal of the converter 32 through a diode D1 to a terminal L. The remainder of the converter circuit comprises transistors Trl to Tr3, and diodes D2 to D4, resistors R5 to R10, and capacitors C1 to C4 connected to provide wave-shaping, differentiation, integration and buffer circuits in the order mentioned between the input and an output A. The output A is connected to the emitter of the transistor Tr3 which is a npn buffer having its collector grounded. The emitter is connected by the resistor R10 to a common positive side Vs2 of the circuit.The negative side of the converter circuit 32 is grounded to the vehicle body.

The common positive side Vs2 and the output A are also connected to the left side as it appears in Figure 6a. The output A is connected to an inverting input terminal (-) of a comparator IC1, and to the non-inverting input terminal (+) of the comparator through a capacitor C8. The positive input terminal of the comparator Cl 1 is in turn connected to the output terminal of an OR circuit (the diodes D7 to D9) of a circuit 33 for forming the signal E, (which corresponds to the output torque), and to ground through a resistor R29. The comparator IC1 compares the (first) signal Ev related to vehicle velocity with the (second) signal E > related to the vacuum in the engine air intake and degree of throttle opening.

An output terminal G of the comparator IC1 is connected to the positive side Vs2 through a resistor R30, and the positive side Vs2 is in series with a further positive side Vs1 through a resistor R31. A diode Dl2 and resistor R32, in parallel with the resistor R30 and a resistor R31,also are connected to the positive side Vsl The positive side Vs2 is connected to an output terminal K of the resistor R3 1.The positive side Vsl is connected to a positive constant voltage source through a diode Dl 6. An npn transistorTr6 has its collector connected to the positive side Vs1 through series-connected resistors R33 and R34, its emitter connected to ground, and its base connected via a diode D13 to a terminal M between the resistor R32 and the diode D12. The base of the transistor Tr6 is connected also to ground through a resistor R35, and its collector is connected to the base of a pnp transistor Tr7 through the resistor R34. The emitter of the transistorTr7 is connected to the positive side Vsl The collector of the transistor Tr7 is connected to a diode D17 which is in parallel with the coil of a shifting solenoid valve SSV, the other terminals being grounded.

An output signal VG of the comparator IC1 is applied by the hysteresis circuit as positive feedback to the Eg signal forming circuit 33 through a resistor R17, R24 or R28. The output signal VG is converted into a signal Es for the shifting solenoid valve SSV which changes the gear speed ratio of the transmission.

The Ee signal forming circuit 33, also in Figure 6a, has its OR circuit on the output side for selectively supplying the comparator IC1 with signal voltages VB, Vc, and VD, corresponding to three degrees of throttle opening. These signal voltages VB, Vc, and VD appear respectively at potential divider terminals B, C and D owing to the potential dividing action of resistor pairs R25, R26; R21, R22; and R14, R1 5 between ground and the positive line Vs2.The potential dividers are connected to the output terminal G of the comparator IC1 through the resistors R17, R24 and R28 in a positive feedback configuration so that VB < VC < VD. The signal voltage which the OR circuit delivers to the comparator corresponds to a particular degree of throttle opening. The terminal B is grounded through the resistor R26. The terminal C, which corresponds to a second degree of throttle opening, is grounded through a switching circuit SW1 comprising a transistor Tr5 which shunts the terminal C to ground when the transistor conducts.The switching circuit SWl has a bias voltage input terminal C' which is grounded through the vacuum switch VSW, and which is also connected to the constant-voltage supply line Vs2 through a resistor R18. The terminal D likewise is grounded through a switching circuit SW2 comprising a transistor Tr4.

The switching circuit SW2 has a bias voltage input terminal D' which is grounded through another vacuum switch ASW, which may alternatively be an accelerator position sensing switch, and which is connected to the positive side Vs2 through a resistor Rl 1. A reverse connected Zener diode DZ connects the positive side Vs2 to ground and is itself in parallel with a capacitor C5.

The transistor Tr5, which is of the npn-type, has its emitter grounded and its collector connected to the potential divider terminal C. The base of the transistor Tr5 is grounded through a parallel circuit consisting of a reverse connected diode D6, a capacitor C7, a resistor R20, and is further connected to the positive side Vs 2 through a resistor R19, the terminal C' and the resistor R18.

The transistor Tr4 is similarly connected with a diode D5, a capacitor C6, and a resistor R13.

The vehicle velocity signal Ev is a pulse frequency signal supplied to the converter 32 which develops an output voltage VA corresponding to a velocity Vv at the terminal A.

The signal VA is input at the inverting terminal (-) of the comparator IC1. A voltage signal V+, which is output from the circuit 33 (for forming the signal E6 related to vacuum and engine output) is input at the non-inverting terminal (+) of the comparator IC1. The vacuum switch VSW which is controlled by the degree of throttle opening closes (ON) or opens (OFF) when the vacuum in the intake is larger or smaller than preset value and opens or closes respectively the switching circuit SW1.

The other vacuum switch ASW is closed for an accelerator opening of 900 and thereby opens the switching circuit SW2. The switching circuits SW1 and SW2 connect the positive constantvoltage line to ground through the resistors R2 1, R14 respectively when they are closed. When the switching circuit SW1 is open, the prescribed voltage Vc appears at terminal C. When the switching circuit SW2 is open, the prescribed voltage VD appears at terminal D. The voltage VB, on the other hand, appears at the terminal B owing to the potential dividing action of the resistors R25, R26.The voltages VB Vc, and VD correspond to successive degrees of throttle opening 6. VB may correspond to from 0--3096, Vc to from 30-90%, and VD to above 90% as indicated in Figure 5. The voltages VB, Vc, and VD are applied to the non-inverting input terminal (+) of the comparator IC1 through the OR circuit comprising the diodes D7, D8, D9.

The voltage VA responsive to velocity is fed to the inverting input signal (-) of the comparator It1, while the voltage V+ is applied to its positive input terminal. Depending upon the sizes of these inputs, the output voltage is S high level (VA > V+) of low level (Va < V+). The transistor Tr6 acting as a switch is open when the voltage VG is high and closed when it is low. When the transistor Tr6 is conducting, the transistorTr7 is turned ON to connect the solenoid valve SSV to the constantvoltage line (battery) and energise the solenoid.

When the transistor Tr6 is not conducting, the transistor Tr7 is cut off, and disconnects the solenoid valve SSV from the constant-voltage line, de-energising the solenoid. Thus the solenoid valve SSV which controls the shifting of the gears in the transmission is supplied with a prescribed voltage according to the state, conductive or nonconductive, of the transistor Tr7. The transmission is shifted, ordinarily by hydraulic pressure, into a first speed ratio (low velocity range) when the solenoid valve SSV is energised, and into a second speed ratio (high velocity range) when the solenoid valve SSV is deenergised. The voltages VB, Vc, and V,, which correspond to the three ranges of throttle opening, determine the point at which the shift from the first to the second ratio is executed as only one of these voltages if passed by the OR circuit at any time. When the voltage VA is greater than the passed signal voltage (V8, Vc, or VD) at the positive input terminal of the comparator (that is when the voltage indicative of vehicle velocity is greater than that required for a gear shift corresponding to a particular throttle opening) an up-shift operation is executed from first to second gear speed ratio.In other words, each of the velocities VVB, VVC, and VVD at the shift points corresponding to the voltages VB, Vc, VD is as shown in Figure 5.

Once the voltage VA has exceeded the particular input voltage, say VB, at the noninverting terminal of the comparator ICl (i.e. the solenoid valve SSV is deenergised and the vehicle is operating in the second gear speed ratio) the output voltage VG at the output terminal G of the comparator drops to the low level. The voltage VB has up till this time (i.e. during high level at G) been the result of the potential dividing action of the resistors R25 and R28, and the resistor R26.

On the change to the low level at terminal G, terminal B is grounded through the resistors R26, R28, and there appears at terminal B a potential VBI which is less than VB. A similar relation holds at terminal C and D. Whenever the voltage VA exceeds VB, VC or VD (up-shift from first to second gear), VB falls to VBT, VC to Vc or VD to VD, so that the shift point from second back to first gear ratio occurs at a lower vehicle velocity than the shift from first to second gear.A difference in vehicle velocity (in the form of hysteresis) at the two shift points for up-shifting and down-shifting is determined by electrical hysteresis owing to the voltages VB, Vc, VD or the differences between VB and VBI, VC and Vc,, or VD and VDI. The width of such hysteresis is determined in accordance with the characteristics of the transmission, the type of vehicle, and/or the desired speed change characteristics. It is effected by a suitable combination of resistors R25, R26, and R28 in the case of VB, and should be large enough to preclude chattering.

'The vehicle is in first gear when the shift solenoid is energised, and is shifted into second gear when the solenoid is deenergised for safety reasons so that the solenoid is deenergised when the vehicle is travelling at a constant high speed.

The shift pattern is adaptable to a greater number of stepwise changes on the same principle.

In an alternative arrangement, the hysteresis may be established by changing the gradient of the converter 32 to increase VA to VA,. A potentiometer linked to the throttle valve may serve as the circuit 33 for forming the signals Eo corresponding to the engine output torque. The velocity responsive signal Ev also may be produced by other means.

Claims (8)

1. A control system for an automatic transmission for a vehicle comprising means for producing a first signal related to vehicle velocity, means for producing a second signal related to the vacuum in an engine air intake and means for comparing the first and second signals and producing a transmission shift control signal.

2. A control system according to claim 1 in which the means for producing the second signal comprises a vacuum switch positioned near the throttle valve on an engine air intake.

3. A control system according to claim 1 or claim 1 in which the comparing circuit includes a hysteresis circuit.

4. A control system according to any preceding claim in which the comparing circuit includes a number of potential divides.

5. A control system according to any preceding claim in which the comparing circuit includes positive feed back for its output signal through a resistor to the circuit for producing the input.

6. A control circuit according to any preceding claim including hysteresis circuit having means for changing the gradient of the first signal.

7. A control circuit according to any preceding claim including positive feed back of the output signal of the comparing circuit to a number of potential divider terminals through resistors.

8. A control system for an automatic transmission for a vehicle substantially as herein described with reference to the drawings.