GB2081933A

GB2081933A - Automatic speed control systems

Info

Publication number: GB2081933A
Application number: GB8025881A
Authority: GB
Original assignee: Associated Engineering Ltd
Current assignee: Associated Engineering Ltd
Priority date: 1980-08-08
Filing date: 1980-08-08
Publication date: 1982-02-24
Also published as: ZA814690B; DE3175408D1; DK148559B; DK148559C; AU7281781A; AU546506B2; ES8204670A1; GB2081933B; ES504620A0; EP0045847B1; DK353481A; EP0045847A1; JPS5762942A; IE811799L; IE51672B1; US4457392A

Description

1 GB 2 081933 A 1

SPECIFICATION

Automatic speed control systems The invention relates to speed-responsive electrical systems and circuit arrangements and more specific ally to such systems and circuit arrangements responsive to the speed of a Vehicle, such as a road vehicle, and, for example, for automatically controll ing the speed of the vehicle.

Various novel features of the invention will be apparentfrom the following description, given by way of example only, of an electrical system for automatically controlling a road vehicle to run at a set speed which may be selected by the driver, reference being made to the accompanying di agrammatic drawings in which:

Figure 1 is a block circuit diagram of the system; Figure 2 shows waveforms occurring in the system; Figure 3 shows one form of pneumatic and mechanical linkage by means of which the system can control the engine power of the vehicle; Figure 4 shows another form of the linkage, again of pneumatic and mechanical form; and Figure 5shows a furtherform of the linkage, this time of electromechanical form.

To be described below is an automatic vehicle speed control system, comprising means responsive to desired and actual vehicle speeds to produce a control signal dependent on any speed error, a member whose movement adjusts the power of the engine of the vehicle, a driver-operable engine power control, connecting means interconnecting the driver's control with the said member whereby to enable the driver to adjust the engine power, and control means incorporated in the said connecting means and operative to vary the engine power in dependence on the said control signal, the arrange ment being such that the control means is rendered substantially unresponsive to the said control signal when the driver-operable control is in the minimum power setting.

Advantageously, the control means is a piston cylinder assembly.

For example, the system may be such that the driver operable control comprises driver-operable pressure adjusting valve means in a pressure line applying positive or negative pressure to the piston-cylinder assembly and the connecting means includes means connecting the said piston to the said member, and in cluding a control-signal-responsive pressure-adjusting valve means in series with and upstream of the driver operable pressure-adjusting valve means and responsive to the said control signal, whereby setting of the driver-operable control to the minimum engine power setting closes the driver-operable pressure adjusting valve means and substantially prevents the other pressure-adjusting valve means from affecting the pressure in the piston-cylinder assembly.

Instead the driver-operable control may comprise means connected to move the piston-cylinder assembly as a unit and the connecting means may comprise means connecting the said piston to the said member, and including control-signal- 130 responsive pressure-adjusting valve means connected in a pressure line for supplying positive or negative pressure to the piston-cylinder assembly and responsive to the said control signal.

Preferably, the control-signal-responsive pressure-adjusting valve means is normally open.

For example, the control signal responsive pressure-adjusting valve means may comprise a normally open inlet valve connected in series in the said line and a normally closed exhaust valve for connecting the line to exhaust.

Advantageously, the pressure is pneumatic pressure.

The said member may be the injection pump control rack of a diesel engine.

In another embodiment, the control means may comprise a mechanical link whose length is electromechanically variable and an electric motor responsive to the control signal to vary the length of the said link.

In a more specific example, there will be described a vehicle speed control system, comprising a member whose movement controls the power of the engine of the vehicle, a piston-cylinder assembly, a linkage connecting the piston of the said assembly to the said member, a source of pressure, a driveroperable control valve connected in pressure line between the pressure source and the piston-cylinder assembly whereby opening of the valve increases the pressure in the piston-cylinder assembly and increases the engine power and vice versa, normally open control valve means connected in series in the said pressure line between the pressure source and the driver-operable valve source, and automatic speed control means for adjusting the normallyopen control valve means in dependence on the error (if any) between desired and actual vehicle speeds so as to tend to reduce the error to zero, whereby movement of the driver-operable valve into its setting corresponding to minimum engine power prevents the control valve means from increasing the engine power from the minimum.

Also to be more specifically described below is a vehicle speed control system, comprising a member whose movement controls the power of the engine of the vehicle, a piston- cylinder assembly, a linkage connecting the piston of the assembly to the said member, a driver-operable engine power control connected to move the cylinder, a source of press- ure, normally open control valve means connected in series between the pressure source and the interior of the piston-cylinder assembly, and automatic speed control means for adjusting the control valve means in dependence on the error (if any) between desired and actual vehicle speeds so as to tend to reduce the error to zero, whereby movement of the driver-operable control moves the pistoncylinder assembly as a unit to adjust the engine power and its movement to the position corresponding to minimum engine power prevents the said valve means from increasing the engine power above the minimum.

The foregoing are exemplary of, and not exhaustive of, the various features of the system now to be more specifically described.

GB 2 081 933 A 2 As shown in Figure 1, a signal representing the speed of the vehicle is derived by means of a pick-up 10 which may be in the form of a transducer, such as a magnetic transducer, sensing rotation of the propeller shaft of the vehicle. The pick-up 10 produces pulses at a frequency dependent on the road speed of the vehicle and these are shaped into a square wave in a shaping circuit 12 and used to control a monostable 14 which therefore produces constant width pulses at a frequency dependent on the road speed. A smoothing circuit 16 smoothes the pulses into a unidirectional voltage having a value which is dependent on road speed (in this example, it is arranged to be inversely dependent on road speed). A filter 18 removes most of the ripple on this voltage to produce an output signal which is fed to the first input of a comparator 20 and also to a differentiating circuit 22 which feeds the same input of the comparator. The effect of the differentiating circuit 22 is to augment the signal applied to the comparator 20 from the filter 18 when a sudden change occurs in the filter output. The purpose of this is to tend to stabilise the control system.

The signal applied to the first input of the compa- rator 20 is referred to below as Vs and is inversely dependent on the road speed of the vehicle.

In order to be able to select the desired road speed for the vehicle, the driver has a control 23 by means of which he can adjust a setting circuit 24 (a potential divider network, for example) to produce a desired speed signal Vr on a line 26. Signal Vr is fed to the second input of the comparator 20. The output of the comparator 20 is therefore an error signal Ve whose sign and magnitude are dependent on the sign and magnitude of the difference between the desired speed Vr and the actual speed Vs. The signal Ve is fed to an output control unit 30 to adjust the power output of the vehicle's engine in a direction and by an amount so as to bring the vehicle speed to a desired value Vr.

The output control circuit 30 may take any convenient form. In the example being considered, it comprises a ramp generator 32 generating an electrical waveform of triangular shape which ramps between fixed limits and which is added to the error signal Ve. The resultant signal Vc is fed to two comparators 34 and 36 whose second inputs receive respective fixed reference levels. The second input of the comparator 34 receives a relatively high fixed reference level Vh on a line 38 and the second input of comparator 36 receives a relatively low reference signal V1 on a line 40.

Figure 2 explains the operation of the comparators 34 and 36 and shows the upper and lower fixed references Vh and VL At Figure 2A is shown the signal Vc in circumstances in which the vehicle speed is above the desired value, this therefore being a situation in which Ve is significantly above its datum value. As shown, the effect of this is that the peaks of Vc rise above Vh causing the comparator 34 to produce a succession of output pulses, Figure 21), at the ramp frequency, and these pulses drive an output unit 42 whose operation tends to decrease the output power of the vehicle engine.

During this time comparator 36 produces a con- tinuous output which holds an output unit 44 in a setting in which it does not tend to increase the engine power.

At Figure 2B, the signal Vc is shown when the vehicle speed is below the desired value, this being a situation in which Ve is significantly below the datum value. Therefore, the troughs of Vc fall below the reference V] and comparator 36 produces output pulses which drive the output unit 44 and cause it to increase the power of the engine. Comparator 34 produces no output and output unit 42 is therefore held in a setting in which it does not tend to decrease the engine power.

At Figure 2C, the vehicle speed is assumed to be at the correct value and the signal Vc lies wholly between the upper and lower references Vh and VI. Therefore, comparator 34 produces no output and comparator 36 produces the continuous output mentioned above, and the engine power is main- tained constant.

When there is a speed error, the mark-space ratio at which the appropriate output unit 42 or 44 (depending on whether the vehicle speed is above or below the desired speed) is operated will depend on the magnitude of the speed error.

The output units 42 and 44 can control the engine power in any suitable way such as by controlling the engine throttle, or the injection pump rack in the case of a diesel engine, by a suitable electrical, mechanical or pneumatic or other linkage.

Three possible arrangements are shown by way of example in Figures 3,4 and 5, each being intended primarily for use with a diesel engine and thus controlling the output power by adjusting the posi- tion of the injection pump rack.

In the system shown in Figure 3, the position of the injection pump rack 60 is controlled by means of a pneumatic piston-cylinder assembly 62 through the intermediary of linkage 64. Pneumatic pressure for driving the piston-cylinder 62 is supplied by a reservoir 66 which may be fed by an engine-driven pump. The pressure is applied to the cylinder of the assembly 62 through a valve unit 68 and a variable pressure valve 70 operated by the driver's normal accelerator pedal 72.

The valve unit 68 has a normally open solenoidoperated inlet valve 74 and a normally closed solenoid operated exhaust valve 76. The solenoid of the inlet valve 74 is energised under control of the output unit 44 (Figure 1), and the solenoid of the exhaust valve 76 is energised under control of the output unit 42.

When the automatic speed control system is not in operation, the solenoids of the valves 74 and 76 are held de-energised and therefore the inlet valve 74 is held fully open and the exhaust valve 76 is held fully closed. Under these conditions, therefore, the pressure in the cylinder of the assembly 62 is controlled solely by the position of the driver's pedal 72 and he alone therefore controls the engine power and thus the speed of the vehicle.

When the driver wishes to bring the automatic speed control system into operation, he sets the desired speed by means of the control 23 (Figure 1) so as to set the value of the signal Vr appropriately.

3 GB 2 081 933 A 3 1 45 At the same time, he fu I ly depresses his pedal 72 (Figure 3). Because the pedal 72 is fully depressed, the pressure in the assembly 62 is now controlled by the states of the valves 74 and 76.

If the vehicle speed is too low, then the output unit 44 will be operated by the comparator 36. If the vehicle speed is sufficiently low below the desired level, the output unit 44 will continuously hold the solenoid valve 74 de-energised and the valve will be held fully open. Under these conditions, the compa rator 34 will be producing no output and therefore the output unit 42 will hold de-energised the sole noid of the exhaust valve 76. Therefore, full pressure will be applied to the assembly 62 and the engine power will be at a maximum so as to bring the vehicle up towards the desired speed.

As the vehicle approaches the desired speed, the mean value of the signal Vc (Figures 1 and 2) will start to rise and the comparator 3 now starts to produce a pulsed output. These pulses will have an increasing mark-space ratio as the speed increases and the solenoid of the inlet valve 74 will therefore be energised with an increasing mark-space ratio.

Therefore, the supply of air to the piston-cylinder assembly 62 will be gradually shut off. This will not in itself alter the engine power, because the air pressure previously applied to the assembly 62 will be held supplied (as the exhaust valve 76 is still closed). However, as the speed continues to in crease, the peaks of Vc now rise above the reference value Vh (Figure 2A) and comparator 34 now produces a pulsed output which energises valve 76 to connect the assembly 62 to exhaust and this therefore results in a decrease in engine power to tend to hold the vehicle at the desired speed.

If the vehicle speed is too high, and well above the desired value Vr, then comparator 36 will produce its continuous output and output unit 44 will therefore hold the solenoid of the inlet valve 74 (Figure 3) continuously energised and therefore closed. This will stop air entering the piston-cylinder assembly 62. At the same time, comparator 34 will produce an output which will cause the output unit 42 to open the exhaust valve 76 (either continuously or in a pulsed manner, depending on the magnitude of the error). Therefore, the air in the assembly 62 will leakaway and the engine power will reduce. As the vehicle speed falls, comparator 34 will close the exhaust valve 76 for proportionately longer and comparator 36 will start to produce a pulsed output which will allow air to begin to enter piston-cylinder 62 via inlet valve 74.

In this way, therefore, the output unit 30 (Figure 1) controls the valve unit 68 (Figure 3) in such a manner as to tend to hold the vehicle at the desired speed.

The operation of the system requires the driver to maintain the pedal 72 fully depressed. If he releases the pedal, then the valve unit 68 can no longer control the pressure in the piston-cylinder assembly 62 and the speed control system is therefore effec tively put out of operation and the engine power is reduced to a minimum.

Figure 4 shows a modified form of the system of Figure 3, and parts in Figure 4 corresponding to parts in Figure 3 are correspondingly referenced. 130 As shown in Figure 4, the driver's pedal 72 is now connected directly to the cylinder of the pistoncylinder assembly 62 via a mechanical linkage 80. As before, the piston of the assembly 62 is connected to control the position of the rack 60 via linkage 64, and the pneumatic pressure in the piston-cylinder assembly 62 is controllable by the valve unit 68. When the automatic speed control system is not in operation, the inlet valve 74 is fully opened and the exhaust valve 76 is fully closed, as for the system in Figure 3. In this situation, there is full air pressure in the piston-cylinder assembly 62 and the piston is held fully extended. In this condition, the position of the rack 60 and thus the power of the engine, are controlled solely by the position of the pedal 72 which moves the piston- cylinder assembly 62 bodily.

When the driver wishes to bring the automatic speed control system into operation, he sets the signal Vr (Figure 1) by means of the control 23 as before, and fully depresses the pedal 72 and holds it depressed.

In the same manner as described above with reference to Figure 3, the output units 42 and 44 of Figure 1 now control the valves 74 and 76 so as to adjust the pressure in the piston-cylinder assembly 62 in a sense and by an amount to tend to hold the vehicle at the required speed. As before, release of the pedal 72 puts the automatic speed control system effectively out of action.

The pressure source 66 need not be a source of pneumatic pressure but can be some other pressure source, and can also be a source of negative (i.e. partial vacuum) instead of positive pressure.

Figure 5 shows an electromechanical system and parts in Figure 5 corresponding to parts-in Figures 3 and 4 are correspondingly referenced.

As shown in Figure 5, the driver's pedal 72 is connected to the linkage 64 by a mechanical link 90 so that depression of the pedal 72 pushes on the link 90 and moves the rack 60 to the right so as to increase the engine power.

The link 90 is of adjustable length. It may for example comprise a tube internally coupled to a rod by means of a screw thread with the tube rotatably coupled to the linkage 80 and the rod coupled to the linkage 64. Therefore, rotation of the tube has the effect of changing the length of the link 90 and thus of adjusting the position of the rack 60 (and the power of the engine) even though the position of the pedal 72 is unchanged.

The link 90 is connected by a flexible drive 92 to an electric motor 94through a gearbox 96. Rotation of the shaft of the motor 94 therefore causes the flexible drive 92 to adjustthe link 90 (as by rotating the tube mentioned above) so as to increase or decrease its effective length, depending on the direction of rotation of the motor. The motor itself is energised under control of the output units 42 and 44 (Figure 1).

When the automatic speed control system is not in operation, the output units 42 and 44 set the electric motor 94 so that the link 90 has maximum length. In this condition, the position of the rack 60, and thus the power of the engine, are controlled solely by the 4 GB 2 081933 A 4 position of the pedal 72. The allowable movement of the pedal 72 is such that when fully released the rack 60 is in its minimum power setting.

The output units 42 and 44 of Figure 1 now control the motor 94 so as to adjust the length of the link 90 in a sense and by an amount to tend to hold the vehicle at the required speed. As before, release of the pedal 72 puts the automatic speed control system effectively out of action.

Claims

CLAIMS (Filed 22 June 1981)

1. An automatic vehicle speed control system, comprising means responsive to desired and actual vehicle speeds to produce a control signal dependent on any speed error, a member whose movement adjusts the power of the engine of the vehicle, a driver-operable engine power control, connecting means interconnecting the driver-operable control with the said member whereby to enable the driver to adjust the engine power, and control means incorporated in the said connecting means and operative to vary the engine power in dependence on the said control signal, the arrangement being such that the control means is rendered substantially unresponsive to the said control signal when the driver-operable control is in the minimum power setting.

_2. A system according to claim 1, in which the control means is a piston-cylinder assembly.

3. A system according to claim 2, in which the driver-operable control comprises driver-operable pressure-adjusting valve means in a pressure line applying positive or negative pressure to the piston- cylinder assembly and the connecting means includes means connecting the said piston to the said member, and including a control-signal-responsive pressure-adjusting valve means in series with and upstream of the driveroperable pressure-adjusting valve means and responsive to the said control signal, whereby setting of the driver-operable control to the minimum engine power setting closes the driver-operable pressure-adjusting valve means and substantially prevents the other pressure-adjusting valve means from affecting the pressure in the piston-cylinder assembly.

4. A system according to claim 2, in which the driver-operable control comprises means connected to move the piston-cylinder assembly as a unit and the connecting means comprises means connecting the said piston to the said member, and including control-signal-responsive pressure-adjusting valve means connected in a pressure line for supplying positive or negative pressure to the piston-cylinder assembly and responsive to the said control signal.

5. A system according to claim 4, in which the control-signal-responsive pressure-adjusting valve means is normally open.

6. A system according to claim 5, in which the control-signal-responsive pressure-adjusting valve means comprises a normally open inlet valve connected in series in the said line and a normally closed exhaust valve for connecting the line to exhaust.

7. Asystem according to anyone of claims3to 6, in which the pressure is pneumatic pressure.

8. A system according to any preceding claim, in which the said member is the injection pump control rack of a diesel engine.

9. A system according to claim 1, in which the control means comprises a mechanical link whose length is electromechanically variable and an electric motor responsive to the control signal to vary the length of the said link.

10. A system according to claim 9, in which the mechanical link comprises two parts screwthreadedly coupled together whereby relative rotation of the two parts alters their length, one said part being rotatably coupled to the connecting means and the other said part being non-rotatably coupled to the connecting means, and in which the electric motor is coupled to rotate the said one part.

11. A system according to claim 10, in which the said one part is a hollow internally threaded tube and the said other part is a screw-threaded rod threadedly engaging the tube.

12. A vehicle speed control system, comprising a member whose movement controls the power of the engine of the vehicle, a piston-cylinder assembly, a linkage connecting the piston of the said assembly to the said member, a source of pressure, a driveroperable control valve connected in pressure line between the pressure source and the piston-cylinder assembly whereby opening of the valve increases the pressure in the piston-cylinder assembly and increases the engine power and vice versa, normally open control valve means connected in series in the said pressure line between the pressure source and the driver-operable valve source, and automatic speed control means for adjusting the normallyopen control valve means in dependence on the error (if any) between desired and actual vehicle speeds so as to tend to reduce the error to zero, whereby movement of the driver-operable valve into its setting corresponding to minimum engine power prevents the control valve means from increasing the engine power from the minimum.

13. A vehicle speed control system, comprising a member whose movement controls the power of the engine of the vehicle, a piston-cylinder assembly, a linkage connecting the piston of the assembly to the said member, a driver-operable engine power control connected to move the cylinder, a source of pressure, normally open control valve means connected in series between the pressure source and the interior of the piston-cylinder assembly, and automatic speed control means for adjusting the control valve means in dependence on the error (if any) between desired and actual vehicle speeds so as to tend to reduce the error to zero, whereby movement of the driver- operable control moves the piston-cylinver assembly as a unit to adjust the engine power and its movement to the position corresponding to minimum engine power prevents the said valve means from increasing the engine GB 2 081933 A 5 power above the minimum.

14. A vehicle speed control system, comprising a member whose movement controls the power of the engine of the vehicle, a driver-operable engine power control, a linkage comprising two parts screw-threaded together with one part rotatably connected to the driver-operable control and the other part non-rotatably connected to the said member, an electric motor connected to rotate the said one part relative to the other, and automatic speed control means for adjusting the electrical energisation of the electric motor in dependence on the error (if any) between desired and actual vehicle speeds so as to tend to reduce the error to zero, whereby movement of the driver-operable control moves the linkage as a unit to adjust the engine power and its movement to the position corresponding to minimum engine power prevents the electric motor from increasing the engine power above the minimum.

15. A vehicle speed control system substantially as described with reference to Figures 1, 2 and 3 of the accompanying drawings.

16. A vehicle speed control system substantially as described with reference to Figures 1, 2 and 4 of the accompanying drawings.

17. A vehicle speed control system substantially as described with reference to Figures 1, 2 and 5 of the accompanying drawings.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1982. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.