GB2234779A - A drive system for a fuel control device of a vehicle - Google Patents

Abstract

A control lever 13 of a fuel injection pump 10 is operable by an electric motor 15 having an output shaft 16 movable through an angle in response to a signal from a potentiometer 33 operable by an accelerator cable 36. A resilient element 26 tensioned by the cable operated lever 30 applies a torque to the motor output shaft in response to operation of the accelerator to assist the motor 15 in driving the lever 13. An accelerator cable 14 provides for direct operator control of the lever 13. <IMAGE>

Description

A DRIVE SYSTEM FOR A FUEL CONTROL DEVICE OF A VEHICLE The invention relates to a drive system for a fuel control device of a vehicle.

It has been proposed to provide semi-automatic change of ratios in a vehicle by permitting a driver to maintain control over gear selection whilst automatically operating a clutch and accelerator to eliminate the tediousness and awkwardness of declutching and controlling the accelerator when changing ratio.

An object of the present invention is to provide an improved drive system for a fuel control device and which is particularly suitable for use in a vehicle where the selection of ratios is under the control of the driver and the clutch and accelerator are operated automatically.

According to the invention there is provided a drive system for a fuel control device of a vehicle comprising a motor arranged to drive a shaft movable through an angle to drive the fuel control device, a manually operable accelerator and a resilient element arranged to apply a torque to the shaft in response to operation of the accelerator to assist the motor in driving the fuel control device.

By utilising a drive system in accordance with the invention, the resilient element, which may be a spring, applies a torque to the shaft in addition to that applied thereto by the motor itself to provide assistance.

The resilient element may be connected to an arm drivably connected to the shaft. The arm means provides a convenient way of converting, for example, a tensile load applied by the resilient element to a torsional load applied to the shaft.

The shaft is preferably an output shaft of the motor.

The resilient element may be connected to a lever which is movable by operation of the accelerator.

The lever may be drivably connected to a position sensing means, such as a potentiometer, by which the position of the accelerator can be sensed. In such a case, the position sensing means may sense the rotational position of a shaft to which the lever is drivably connected, the shaft being rotated by the lever during operation of the accelerator. The lever may comprise a first part connected to the accelerator and a second part connected to the resilient element. The said parts are preferably of equal length so that the movement applied to one part by the accelerator is equal to movement of the other part to which the resilient element is connected.

Preferably, the lever turns about an axis between the two parts.

Preferably the motor is arranged to operate a second position sensing means such as a second potentiometer. In such a case the first said position sensing means may provide a signal for a control means arranged to operate the motor and the second position sensing means may be arranged to provide a feedback signal for the control means. In that way the control means can operate so as to hold the motor, and hence the shaft, in a given position when the signal and feedback signal interrelate in a particular manner.

To provide a compact arrangement, the resilient element may extend between the lever and the arm so as to extend across an imaginary line passing through the axis of the shaft and an axis about which the lever pivots. In that way, rotation of the lever in one sense will be opposite to the direction in which torque is applied by the resilient element to the shaft.

Preferably, the shaft rotates between first and second limits. The first limit may be a normal rest position of the motor shaft and the resilient element is preferably held in tension so as to apply a load to the lever means when the shaft occupies that position.

The shaft may carry a further arm which is connected to the fuel control device by means of a suitable link e.g., an operating rod.

A drive system in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.1 shows a drive system in accordance with the invention for a fuel injector pump, Fig.2 is a diagrammatic representation of a control circuit, and Fig.3 is a graph illustrating the way in which assistance is provided for the motor.

A fuel injector pump 10 has a mounting flange 12 and a control lever 13 which can be operated either manually by means of a cable 14 or automatically by means of an electric motor 15.

The motor 15 is of a type which drives an output shaft 16 through an angle which, in the present case, is around 90 degrees. The output shaft 16 has an arm 17 rotatably mounted thereon and also drives a potentiometer 15a. The arm 17 has an outer end pivotally connected to a screw threaded mounting 19 for one end of an operating rod 20. The other end of the operating rod is screwed to a screw threaded further mounting 22 pivotally connected to the control lever 13. The operating rod 20 is axially adjustable in the screw threaded mountings and lockable in position by means of locking nuts 23.

The output shaft 16 is drivably connected to a drive block 18a having an arm 18. The drive block 18a is bolted to the shaft 16 and includes a finger 18b which abuts a shoulder 17b formed on the arm 17.

Rotation of the drive block in a clockwise direction as shown in Fig.1 causes the finger 18b and shoulder 17b to interengage thereby causing the drive block to turn the arm 17 clockwise from the full line rest position towards the broken line position. The rest position of the arm 17 is dictated by a stop (not shown) on the pump 10 which positions the arm 13 for idling of the engine. In order to ensure that the arm 17 can take up that position, the rest position of the drive block 18a is such that a clearance C is defined between the finger 18b and shoulder 17b.

The outer end of arm 18 carries a pin 24 formed with a groove which locates a hook 25 formed at one end of a tension spring 26. The other end of the tension spring 26 is formed with a further hook 27 which locates in a groove formed on a pin 28 carried by one end 29 of a lever 30.

The lever 30 is drivably connected to a spindle 32 of a potentiometer 33 having electrical connections 34 which connect the potentiometer to a control module forming part of an overall control system for effecting control of the engine and clutch of the vehicle during a ratio change. The lever 30 has a further part 34 connected to a mounting pin 35 formed with a diametral bore through which passes an accelerator cable 36. The cable 36 has a nipple 37 crimped thereto to prevent withdrawal of the cable 36 from the diametral bore. The cable 36 is attached to an accelerator pedal (not shown) in a vehicle in which the drive system is installed. The lever 30 is normally biassed into the position shown (the rest position) by means of a torsion spring 38. The torsion spring 38 maintains the accelerator cable 36 in tension when the driver's foot is removed from the accelerator pedal.

The drive system is used to control the injector pump 10 in a system in which engine speed is to be controlled automatically during change of ratio. As the accelerator pedal is depressed, the cable 36 will move in the direction of arrow A thereby rotating the lever 30, turning potentiometer shaft 32. Such turning of the potentiometer shaft 32 causes a signal S to be transmitted from the potentiometer 33 to the control module 31. and applying tension to the spring 26. Normally, in the rest position of the lever 30, the spring 26 will have a certain amount of initial tension. Therefore, movement of the accelerator cable in the direction of arrow A will cause the tension to increase. The motor 15 is connected to the control module which switches on the motor 15 so as to turn the output shaft 16, drive block 18a and arm 17 clockwise as viewed in Fig.1, the tension in spring 26 will apply an additional torque through arm 18 to the output shaft 16 thereby providing a degree of assistance to the motor dependent on the position of the accelerator pedal. The rotation of the output shaft 16 causes the potentiometer 15a to transmit a feedback signal F to the control module 31. When the feedback signal F and signal S interrelate in a predetermined manner the control module 31 holds the motor 15 in the desired position. Obviously, the further the accelerator pedal is pressed, the greater will be the tension in spring 26 and, therefore, the greater the assistance given to the motor 15.In that way, it is possible to use a motor which would normally have only limited torque capacity in an application which demands a more powerful motor.

Therefore, commercially available low power motors can be used without modification to internal workings thereof.

The length of the arm 29 is greater than the length of the arm 18. Therefore, If the motor 15 rotates the arm 17 at a speed which matches the position of the accelerator pedal then the tension spring 26 will gradually stretch thereby giving more assistance to the drive motor the further the pedal is depressed.

If, however, the pedal is heldin a fixed position by the user and the motor 15 is rotated during a gear change, then a different degree of spring assistance will result.

Reference is made to the graph shown in Fig.2 to illustrate the effect of holding the pedal at different positions. In the graph, the angle of movement of shaft 16 in degrees is shown on the horizontal axis and the torque in NM required to effect such movement against a return spring (not shown) for the control lever 13 of the injector pump 10 is shown on the vertical axis. The torque available from the motor 15 is dependent upon the current supplied to the motor.

With the motor 15 unassisted by spring 26 (curve A) high torque and hence high current are required to rotate the shaft 16 which can cause the motor to overheat.

Where the rotation of the shaft 16 of motor 15 follows the movement of the accelerator pedal exactly, curve B results and it will be noted that the motor 15 is required to apply substantially less torque to rotate the shaft 16 when compared to curve A.

Where the user maintains the accelerator pedal constantly at 50% of the full throttle position, curve C results and it will be noted that even less torque is applied by the motor up to the point where graphs B and C intersect and only thereafter is the motor is required to apply a greater torque than when the motor and accelerator positions are matched.

Where the user holds the accelerator pedal at full throttle position, curve D results and it will be noted that the output shaft 16 can be rotated fully with the minimum of torque applied by the motor.

Once the arm 17 has been moved to its fully displaced position as shown in broken lines in Fig.1, the torques applied by the motor 15 to return the arm 17 to its initial position are illustrated by curves AA, BB, CC and DD in Fig.2. When considering graphs CC and DD, it will be appreciated that a certain amount of back driving will be necessary by the motor 15 to drive the arm 17 anti-clockwise against the tension of spring 26. The backdriving will take place around 57 degrees where the throttle is held fully open as at curve DD and around 29 degrees where the pedal is held at 50t full throttle as at curve CC.

In the majority ratio changes in change speed gearing of the vehicle, no backdriving would be necessary.

However, but the system will need to cope with situations where, for example, a driver accelerates hard in second gear and then moves directly into fifth gear once the required road speed has been reached. In such a situation, the driver may not release the accelerator pedal until part way through or after the change of ratio but the motor 15 will need to rotate the arm 17 anticlockwise to reduce engine RPM.

If the accelerator pedal is held in the rest position so that the lever 30 occupies the full line rest position shown in Fig.1, the tensioned spring 26 will very rapidly run out of tension and travel once the motor 15 begins to turn the shaft 16 clockwise. The motor 15 will then revert to the unassisted characteristic shown in curve A.

If the spring 26 were to break, the driver would feel a reduction in accelerator pedal load and the motor 15 would try to follow the demands placed on it without assistance.

If the motor 15 were to fail, the torque generated by the spring 26 would be capable of moving the lever 17 by an amount sufficient to enable the vehicle to be driven thereby providing a fail safe limp-home capability.

The positioning of the potentiometer 33 adjacent the motor 15 enables a fairly compact assembly of parts to be produced which can be convenient from packaging and installation points of view.

Claims (5)

1. A drive system for a fuel control device of a vehicle comprising a motor arranged to drive a shaft movable through an angle to drive the fuel control device, a manually operable accelerator and a resilient element arranged to apply a torque to the shaft in response to operation of the accelerator to assist the motor in driving the fuel control device.

2. A drive system according to Claim 1 in which the resilient element is connected to an arm drivably connected to the a shift.

3. A drive system according to Claim 1 or 2 in which the resilient element is connected to a lever which is moved by operation of the accelerator.

4. A drive system according to Claim 3 in which the lever is drivably connected to a position sensing means by which the position of the accelerator can be sensed.

5. A drive system according to Claim 3 or 4 in which the lever has a first part connected to the accelerator and a second part connected to the resilient element.

5. A drive system according to Claim 3 or 4 in which the lever has a first part connected to the accelerator and a second part connected to the resilient element.

6. A drive system according to Claim 5 in which the lever parts are of equal length.

7. A drive system according to 5 or 6 in which the lever turns about an axis between the parts 8. A drive system according to Claim 4, 5 or 6 in which the motor is arranged to operate a second position sensing means.

9. A drive system according to Claim 8 in which the sensing means provides a signal for a control means arranged to operate the motor.

10. A drive system according to Claim 9 in which the second position sensing means is arranged to provide a feedback signal for the control means.

11. A drive system according to any of Claims 3 to 10 and where the resilient element is connected to an arm on the shaft, in which the resilient element extends between the lever and the arm so as to extend across an imaginary line passing through the axis of the motor output shaft and an axis about which the lever pivots.

12. A drive system according to any preceding Claim in which the shaft rotates between first and second limits and the resilient element is in tension at least at one of said limits.

13. A drive system according to any preceding Claim in which the shaft is an output shaft of the motor.

14. A drive system for a fuel control device of a vehicle constructed and arranged substantially as described herein with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A drive system for a fuel control device of a vehicle comprising a motor arranged to drive a shaft movable through an angle to drive the fuel control device, a manually operable accelerator and a resilient element arranged to apply a torque to the shaft in response to operation of the accelerator to assist the motor in driving the fuel control device.

2. A drive system according to Claim 1 in which the resilient element is connected to an arm drivably connected to the shaft.

3. A drive system according to Claim 1 or 2 in which the resilient element is connected to a lever which is moved by operation of the accelerator.

4. A drive system according to Claim 3 in which the lever is drivably connected to a position sensing means by which the position of the accelerator can be sensed.