SPEED CONTROL ACTUATOR

Abstract: The speed control actuator can be used to modify a control linkage fitted between an accelerator pedal and a fuel regulators (3), such as a carburettor or fuel injection pump on a vehicle engine. The actuator includes a forked lever (5) which is mounted for rotation on the shaft of the fuel regulator (3), and a pulley (18) which is mounted for rotation relatives to the forked lever (5). The accelerator pedal is connected by means of a cable (2) to the forked lever (5). Another cable (25) passes over the pulley (18) and is connected to a microprocessor controlled cable drive. The cable (25) is advanced and retracted, in accordance with a vehicle speed related signal, to adjust the fuel regulator (3) independently of the accelerator pedal. A preferred form of drive means is also described which employs a microprocessor producing a speed-related output in the form of a pulsating current of one polarity or another, and having a variable mark-to-space ratio, for driving a dc motor coupled to the actuator.

Description: This invention relates to a speed control actuator. The actuator can be generally used in a control system where the speed of an output shaft, driven by an engine or motor, needs to be maintained at a substantially constant value whilst the load applied to the engine or motor varies. The actuator is particularly useful in the field of vehicle speed control where a control linkage which normally connects an acceleration control to a fuel regulator for regulating the speed of an engine, is shortened or lengthened to modify the effect of the normal acceleration control. In the latter case, the actuator may be part of a throttle linkage which connects an accelerator pedal to a fuel injection pump or carburettor, the actuator being driven by means responsive to vehicle speed whereby the vehicle speed can be prevented from exceeding a predetermined value. However, the invention can also be applied to static engines which are subjected to varying loads. In conventional vehicle speed control systems, the control linkage (i.e. throttle linkage) needs to be cut in order to insert the actuator. The actuator is driven by an output from the means responsive to vehicle speed so as to adjust the length of the control linkage. As long as the vehicle speed does not exceed a first predetermined value, the actuator remains inoperative. However, if the first predetermined value is exceeded, the actuator shortens the control linkage. This causes less fuel to be supplied to the engine of the vehicle and the vehicle speed starts to fall. When the vehicle speed falls below a second predetermined value, the actuator lengthens the control linkage. This again enables more fuel to be supplied to increase the vehicle speed. The first and second predetermined values are separated by an amount which determines a "dead band" in which the length of the control linkage is not adjusted. The aim is to reach a vehicle speed within the dead band so as to avoid making continued small adjustments to the fuel regulator in the proximity of a maximum or legal speed limit. The dead band may be narrow if the frequency and speed at which the adjustments are made is high. Alternatively, the dead band may be wide if the frequency and speed of adjustment is low. The choice of dead bandwidth and the frequency and speed of adjustment depends on the characteristics of the vehicle (which can differ from vehicle to vehicle) and on other factors such as the load carried by the vehicle, the terrain over which the vehicle is travelling, etc. The designer of a speed control system must take these factors into account in order to achieve optimum vehicle performance. Instead of shortening the control linkage to reduce the amount of fuel supplied to the engine and lengthening the control linkage to enable more fuel to be supplied to the engine, some systems may operate in the reverse manner. The control system can otherwise operate in the same manner. A particular disadvantage of the conventional system is that the throttle linkage must be cut in order to install the actuator. This problem is aggravated by the wide variety of ways in which commercial vehicle engines are mounted and in which throttle linkages are fitted. Such variations therefore necessitate the use of a multiplicity of different actuator installation kits. One of the objects of the invention is to provide an actuator which can be simply fitted to the fuel regulator without cutting the existing throttle linkage. DE-A-3l00628 discloses a system wherein a resilient linkage (cylinder, piston and spring) is located between an acceleration control and a throttle arm. A speed governor, having a magnetically operated pneumatic valve connected to a pneumatic actuator, is also connected to the throttle arm. The resilient linkage normally provides direct control but the spring absorbs the motion imparted by the speed control actuator when a preset speed is exceeded. The present invention is characterised by an actuator comprising an arm intended to be supported for rotary movement with respect to a rotary shaft that is part of a fuel or energy regulator, the arm being provided for connection to an accelerator control linkage. The actuator also includes a rotary member intended to be supported by the shaft for rotary movement therewith and a cable which is slidably mounted with respect to the arm and drivably connected to the rotary member. The cable forms a substantially rigid link between the rotary member and the arm to enable the rotary member to move together with the arm whereby the shaft can be rotated by the linkage. However, the cable is also capable of slidable movement relative to the arm whereby the rotary member can be moved independently of the arm for adjusting the position of the shaft whereby the amount of fuel or energy supplied to the engine or motor can be regulated independently of the acceleration control. The invention may be applied to a stationary engine for simply controlling its speed, or it may be applied to an engine fitted to a vehicle, i.e. as part of a vehicle speed control system. The invention may also be applied to an electrical motor. When the invention is applied to a vehicle speed control system, the actuator may be coupled to a shaft in, for example, a carburettor where the shaft operates a butterfly valve. With such a regulator, a lever is normally fitted to the shaft and one end of the lever is coupled to the accelerator pedal of the vehicle by means of a Bowden cable or rod linkage. Such a control linkage can be modified by first removing the conventional lever and by fitting an actuator in accordance with a preferred embodiment of the invention. This preferred form of actuator comprises a forked lever, which is mounted for rotation with respect to the shaft of the regulator. The rotary member is a pulley which is fast with the shaft but mounted for rotation relative to the forked lever. The cable or rod linkage connected to the accelerator pedal is connected to the forked lever. The cable connected to the rotary member or pulley passes over part of the pulley. An outer cover of this second cable is anchored to the forked lever so that the second cable, the pulley and the forked lever rotate together, as a unit, in order to adjust the position of the shaft when the accelerator pedal is operated. However, the second cable can be moved relative to the forked lever, e.g. in response to a vehical speed control input, so that the pulley rotates independently of the lever for adjusting the position of the shaft independently of the accelerator pedal. This enables the speed of the vehicle to be limited to a predetermined value, e.g. within a given dead band. The preferred embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which:- Figure 1 is a side elevation showing an actuator fitted between a fuel regulator and one end of an accelerator control cable, Figure 2 is an end elevation of the same components, some of which are shown in section, Figure 3 illustrates means responsive to vehicle speed for driving the actuator, and Figure 4 illustrates a circuit for limiting rotation of a motor used in the drive means shown in Figure 3. Referring to Figures l and 2, a throttle control linkage comprises an outer cover 1 and an inner cable 2, the inner cable being connected to an acceleration control (not shown) such as an accelerator pedal. The cable 2 moves relative to the outer cover 1 when the accelerator pedal is operated. A fuel regulator 3, such as a fuel injection pump or carburettor, has a shaft 4 which is connected to means (not shown) within the regulator for controlling the amount of fuel supplied to a vehicle engine (not shown). The shaft 4 rotates in one direction to increase the fuel supply and it rotates in the other direction to decrease the fuel supply. A forked lever 5 is mounted on shaft 4 so that it is capable of rotating, together with shaft 4, about an axis 6. The forked lever 5 has an arm 7 which is fitted with a bearing at 8 for supporting shaft 4 for rotatable movement. It also has an arm 9 with an aperture l0. A nut l2 has a head l3 to retain arm 9 and it has a shouldered portion ll which passes freely through aperture l0. The forked lever 5 is thereby mounted for rotation with respect to shaft 4. The nut l2 is screwed onto the threaded portion l5 of shaft 4 to secure the pulley l8 onto the shaft 4 whereby rotational forces applied to the pulley l8 are transmitted to the shaft 4. A torsional coil spring l6 surrounds a spacer l4 and is connected between arm 9 and the pulley l8. The spring l6 applies a rotational force between arm 9 and pulley l8 to ensure that the Bowden cable 25 is held under tension at all times. Arm 7 is joined rigidly to arm 9 by a bridging member 2l. Member 2l has a counterbore 22 for receiving the end of an outer cover 23 of a Bowden cable 24. An inner cable 25 is slidably received in the outer cover 23 and its end portion is entrained about an arcuate section of the pulley l8 (as shown in Figure l). The end of cable 25 terminates in a nipple 26 which is located in an aperture 27 passing through the sides of the pulley 4. A slot 28 enables the nipple 26 and cable 25 to be fitted into aperture 27. The inner cable 25 moves relative to the outer cover 23 in response to a drive provided by the means shown in Figure 3 (and described in detail below). When the inner cable 25 is not so driven, it forms a substantially rigid link together with the anchorage of outer cover 23 on the bridging member 2l, between the pulley l8 and forked lever 5. A tension spring 29 connects the forked lever 5 to a stationary part 30 on the vehicle engine. Spring 29 maintains the throttle cable 2 in a taut condition. Under normal operation, i.e. when a predetermined vehicle speed has not been exceeded the forked lever 5, pulley l8 and Bowden cable 24 rotate together as a solid linkage (due to the rigidity of the inner cable 25 and the anchorage of the outer cover 23 on the bridging member 2l). Thus, when the accelerator pedal is operated, the inner cable 2 moves and thereby causes the forked lever 5 to rotate shaft 4 in either a clockwise, or anticlockwise direction. Under these circumstances, the driver of the vehicle has direct control over the fuel regulator 3. When a first predetermined vehicle speed has been exceeded, the inner cable 25 moves relative to the outer cover 23 and thereby causes pulley l8 to rotate independently of the forked lever 5. The effect of this is to rotate shaft 4 in such a way as to reduce the amount of fuel supplied to the vehicle engine. Therefore, even if the driver further depresses the accelerator pedal, the vehicle speed will not increase above the first predetermined value. Normally, the vehicle speed starts to fall soon after the inner cable 25 has been extended relative to outer cover 23. When the vehicle speed falls below a second predetermined value, the inner cable is retracted relative to outer cover 23 and the pulley l8 rotates in the opposite direction to enable more fuel to be supplied to the vehicle engine. These first and second predetermined values determine the limits of the dead band in the control system. This will now be described in more detail with reference to Figs 3 and 4. Figure 3 schematically illustrates means for driving the cable 25 of the speed control actuator. The other end of the outer cover 23 of Bowden cable 24 is located in a spigot 3l on the side of a housing 32. The other end of the inner cable 25 is entrained about an arcuate section of a pulley 33 (similar in construction to pulley l8) and is similarly secured by means of a nipple 34. Pulley 33 is fast with a toothed quadrant 35 which meshes with a worm gear 36 which is supported in spaced bearings 37, 38. The pulley 33 and quadrant 35 are mounted for rotation on a shaft 39. Cam arms 40a and 40b are pivotally mounted on shaft 39 and their rotary positions, with respect to the shaft, can be adjusted and secured by means of a clamping screw (not shown). The remote end of each arm 40a,40b acts as a cam for operating respective push buttons 4l, 42 on normally closed microswitches 43, 44. These microswitches act as limiting switches for limiting operation of a motor 45 which drivably rotates worm gear 36. As shown in Figure 4, the microswitches are connected by oppositely poled diodes 46, 47 to motor 45. Terminals 48,49 are respectively provided with positive and negative direct current, or vice-versa, from a microprocessor 50. The microprocessor 50 is preferably located within the casing of a tachograph (not shown), for example, a tachograph of the kind described in our copending application No: 8530ll9l.4. Microprocessor 50 has an input 5l for receiving a signal from means (not shown) responsive to vehicle speed. Such means for providing a vehicle speed related signal are of conventional construction and require no detailed explanation. The microprocessor 50 is programmed so as to provide a speed-related output for driving cable 24. If the first predetermined vehicle speed value is exceeded, the microprocessor 50 provides current of one polarity (i.e. pulsating d.c, see below) to terminals 48, 49. When the vehicle speed drops below a second predetermined value, the microprocessor then supplies current of the reverse polarity (i.e. pulsating d.c. see below) to terminals 48, 49. In either case, the voltage of the speed related-related output of microprocessor 50 is proportional to an integrated value of vehicle speed. In other words, the voltage is proportional to vehicle acceleration (or deceleration). As the speed of the motor 45 is proportional to voltage the motor rotates faster when the vehicle accelerates (or decelerates) at a higher rate. This enables the speed control system to react more quickly to a rapid change of vehicle speed. Certain conventional control systems employ control signals where the voltage changes in an analogue fashion to control the speed of an electric motor for driving an actuator. However, this form of control is not readily adapted for use with a microprocessor. This problem is solved, in the preferred embodiment of the invention, by using a digital speed related signal to vary the mark-space ratio of a pulsating output that is supplied to the means (see Fig.3) for driving the actuator. For example, a sensor onboard the vehicle senses vehicle speed and provides a digital speed related signal. The sensor can be of conventional construction and hence requires no detailed description. The microprocessor 50 is programmed so as to determine vehicle speed and acceleration (or deceleration), on the basis of the digital output of the vehicle speed sensor, and to provide a pulsating output of positive or negative polarity as explained above) where the pulse width is proportional to vehicle acceleration (or deceleration). For example, the pulse width increases the faster the vehicle accelerates (or decelerates), and vice versa, and hence the mean voltage level is proportional to acceleration (or deceleration). The object is to produce an output for driving the actuator such that the vehicle speed smoothly approaches and enters the dead band under normal driving conditions and such that continuous adjustments of the fuel regulator are minimised as far as possible. The operation of the preferred embodiment of the invention will be clearer from the following example. Assuming that the vehicle is accelerating and has exceeded the first predetermined speed value, direct current is supplied to terminals 48,49 with the polarity shown in Fig.4. This current is supplied to motor 45 via normally closed microswitch 43 and diode 47. The motor thereby drives worm gear 36 so that quadrant 35 rotates in a clockwise direction. This causes inner cable 25 to advance with respect to its outer cover 23 so as to cause pulley l8 to rotate in a clockwise direction (see Fig.l). This in turn causes a reduction in the amount of fuel supplied to the engine of the vehicle and its rate of acceleration decreases. The voltage of the direct current supplied to terminals 48,49 thereby drops causing a reduction in the speed of motor 45. When the vehicle stops accelerating, the voltage applied to terminals 48,49 falls to a value at which the motor 45 stops rotating whereby no further speed regulation is applied between the normal throttle control linkage and the fuel regulator 3. However, in the case of a particularly high overshoot of the predetermined maximum vehicle speed (e.g. which can happen when the vehicle descends a hill), the cam arm 40a rotates sufficiently to contact the push button of normal closed microswitch 43, whereupon the switch opens and cuts off the supply of current to motor 45, thereby avoiding any damage. Normally, the vehicle speed starts to fall soon after cable 25 has been advanced due to rotation of motor 45 in the clockwise direction. As the vehicle speed falls below a second predetermined maximum value, direct current of the opposite polarity is supplied to terminals 47,48. The voltage applied to terminals 48,49 depends on the rate of vehicle deceleration. The motor 45 receives the current via normally closed microswitch 44 and diode 46. Motor 45 is thereby driven in the opposite direction to cause cable 25 to be retracted and hence pulley l8 to be rotated in the anticlockwise direction. This process will continue, as long as the vehicle speed is below the second predetermined value, until the cam arm 40b contacts the push button of normally closed microswitch 44. The switch then opens and cuts off the supply of current to motor 45. The system will always return to this "starting position" whenever the vehicle speed remains below the second predetermined value. Under normal operation, when the vehicle is driven at a speed in the proximity of the predetermined maximum value, the speed control system will settle on a mean balance point within the dead band whereby the average vehicle speed is at or just below a predetermined maximum value. In general, the system provides a proportional type of speed control which depends on both vehicle speed and acceleration (or deceleration). The concept of deriving a pulsating output having a mark-to-space ratio which is varied to provide a variable mean voltage for controlling the speed of an electric motor, the motor being driven in one direction or the other to modify the control linkage which normally connects an acceleration control to a fuel or energy regulating member, can be applied to a speed control actuator other than the preferred form of actuator described herein. This concept may employ direct pulsating current of one polarity, or another (as described above), or some alternative means for driving an electric motor in forward and reverse directions to achieve the same end. However, the concept preferably employs a digital speed-related input signal. Instead of using a microprocessor, the speed control system could be controlled by analogue circuitry. Whilst a preferred embodiment of the invention has been described in detail, modifications and changes are possible within the scope of the invention as defined by the appended claims.

Claims: A speed control actuator for modifying a control linkage (1, 2) which normally connects an acceleration control to a rotary shaft (4) that is part of a regulator (3) provided for regulating the amount of fuel or energy supplied to an engine or motor, characterised in that said actuator comprises an arm (9) intended to be supported for rotary movement with respect to said shaft (4) and provided for connection to said control linkage (1, 2), a rotary member (18) intended to be supported by said shaft (4) for rotary movement therewith, and a cable (25) which is slidably mounted (21, 22) with respect to said arm (9) and which is drivably connected to said rotary member (18), said cable (25) forming a substantially rigid link between said rotary member (18) and said arm (9) to enable said rotary member (18) to move together with said arm (9) whereby said shaft (4) can be rotated by said linkage (1, 2), but said cable (25) also being capable of slidable movement relative to said arm (9) whereby said rotary member (18) can be moved independently of said arm (9) for adjusting the rotary position of said shaft (4) whereby the amount of fuel or energy supplied to the engine or motor can be regulated independently of said acceleration control. An actuator according to Claim 1 wherein said arm (9) is a first arm (9) which is connected to a second arm (7) by a bridging member (21), and wherein said second arm (7) is intended to be supported for rotary movement with respect to said shaft (4), said rotary member (18) being located between the first and second arms (7, 9). An actuator according to Claim 2, wherein said rotary member (18) is a pulley, said cable (25) being supported for slidable movement on said bridging member (21) and being at least partly entrained about said pulley (18). An actuator according to Claim 3 wherein said linkage (1, 2) includes a second cable (2) and wherein a spring (16) is interposed between the first arm (7) and the rotary member (18) to ensure that said first cable (25) is tensioned. An actuator according to Claim 4 wherein a hollow member (13) is secured to said shaft (4) and retains said first arm (9), said first arm (9) being rotatably supported by said hollow member (13). A vehicle speed control system including the actuator according to any one of the preceding Claims and further including drive means (41-50) responsive to vehicle speed for thereby driving said actuator. A vehicle speed control system according to Claim 6 wherein said drive means (41-50) includes circuitry (50) adapted or programmed to provide a vehicle speed-related output for limiting the vehicle speed to a predetermined value, and a motor (45) which responds to the vehicle speed-related output for adjusting the position of said fuel or energy regulating member whereby the vehicle speed is controlled independently of the accelerator control. A vehicle speed control system according to Claim 7 wherein said circuitry (50) comprises means for producing a pulsating output having a mark-to-space ratio which is varied to provide a variable mean voltage for controlling the speed of the motor (45). A vehicle speed control system according to Claim 8 wherein said circuitry comprises a microprocessor (50) which is programmed so as to determine vehicle speed and acceleration on the basis of a digital speed-related input (51) and to provide a vehicle speed-related output for deiving the motor (45). A vehicle speed control system according to any one of Claims 6-9 wherein the speed-related output is a direct current of one polarity or the other for driving the motor (45) in respective forward and reverse directions when the vehicle respectively accelerates or decelerates. A vehicle speed control system according to any one of Claims 6-10 wherein the motor (45) is driven when the vehicle speed exceeds a first predetermined value, or falls below a second predetermined value, said first and second values defining limits of a dead band in which no adjustments of the actuator are made.

Inventors: MICHELL, DAVID VIVIAN
Applicants: VEEDER-ROOT LIMITED
Application year: 1986
Main classification: B60K31
IPC codes: B60K31