GB2339746A

GB2339746A - Vacuum pump drive for vehicle braking system

Info

Publication number: GB2339746A
Application number: GB9815829A
Authority: GB
Inventors: Simon Peter Gilling
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-07-22
Filing date: 1998-07-22
Publication date: 2000-02-09
Also published as: GB9815829D0

Description

2339746 A Vehicle This invention relates to vehicles and in particular to

a vehicle including a cruise control system.

Recent proposals for cruise control systems include a collision avoidance feature which has at least a degree of control over the acceleration and 5 braking systems. One such intelligent cruise control system is disclosed in EP 0 605 104 in which the control of the throttle or brakes of the equipped vehicle may be through suitable brake servo means or through the engine and brake management control systems. Some such systems can suffer from reduced efficiency if there is insufficient vacuum assistance to aid the 10 braking operation during, for example, a collision avoidance sequence. During normal braking it is further possible for variations in manifold depression to occur which can result in an unacceptable variation in the braking pressure available, in particular at lower levels of braking pressure (for example in the region of 5 Bar).

In US 5,332,056 an automatic braking system for a vehicle is disclosed in which a device is provided to increase available negative pressure for a vacuum brake booster when the vehicle is in danger of colliding with an obstacle. Vacuum is tapped off from the downstream side of a throttle valve and into a vacuum chamber. Manifold depression is increased by forcing 20 the throttle valve towards a closed position or through increasing the engine speed by shifting down ratios of the transmission. A disadvantage of this system is that it relies on manifold depression in each embodiment to provide the increased vacuum and efficiency might be decreased if the throttle valve were to be open through, for example, a fault in the throttle valve motor or by being forced open by incorrect downshifts caused by a fault in the transmission controller.

It is an object of this invention to provide a vehicle including an improved cruise control system.

According to the invention there is provided a vehicle including an engine having a throttle valve and a cruise control system comprising a vacuum unit arranged in use to provide vacuum assistance for a brake servo of a braking system, wherein the vacuum unit comprises a vacuum pump arranged in use to provide said vacuum assistance independently of the position of said throttle valve.

The vacuum pump may comprise a mechanically driven vacuum pump which may be driven by an engine of the vehicle. The vacuum pump may comprise a clutch arranged to selectively engage and disengage the pump. The clutch may comprise an electrically operated clutch or may, in the alternative, comprise a vacuum operated clutch which is arranged to disengage the pump when the level of vacuum available to the brake servo is above a predetermined level and to engage the pump when the level of vacuum available to the brake servo falls below said predetermined level.

The vacuum pump may be arranged to produce vacuum at least during a collision avoidance sequence of the cruise control system.

The vehicle may further comprise a vacuum source which is arranged to supply vacuum assistance for the brake servo from manifold depression.

The level of vacuum assistance from the vacuum pump may be regulated to take account of the amount of vacuum assistance produced by the vacuum source.

The vehicle may further comprise means to vary the level of vacuum assistance provided to the brake servo between vacuum assistance provided by the vacuum pump and vacuum assistance provided by the vacuum source. The varying means may comprise, for example, a flap or a valve arranged to selectively cut off one of the vacuum pump and the vacuum source from the brake servo.

The vehicle may further comprise a vacuum sensor arranged to provide feedback indicative of the amount of vacuum assistance available to the brake servo to a vacuum controller and wherein the controller is arranged to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

The vehicle may further comprise a brake pressure sensor arranged to provide feedback indicative of available braking pressure to a vacuum controller and wherein the controller is arranged to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

The vehicle may further comprise a wheel speed sensor arranged to provide feedback indicative of braking efficiency to a vacuum controller and wherein the controller is arranged to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

The vacuum pump may be arranged to provide vacuum assistance for the brake servo such that braking pressure can be maintained at a substantially constant level for substantially any level of braking pressure within a predetermined range of braking pressures, whereby variation in braking pressure caused by a variation in vacuum assistance can be compensated for so as to improve driving refinement.

The vehicle may further comprise a vacuum reservoir arranged to damp out a variation in vacuum available to the brake servo. The vacuum reservoir may be arranged to damp out variations in the vacuum assistance during a variation in the level of vacuum assistance provided by the vacuum pump and may be arranged, in addition or in the alternative, to damp out variations in the vacuum assistance during at least part of the period during which the flap moves to cut off one of the vacuum pump and the 5 vacuum source from the brake servo.

The invention also provides: a cruise control system for a vehicle according to the invention; a vacuum pump for such a cruise control system; a controller for such a cruise control system; and a vacuum reservoir for such a cruise control system.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure I is a schematic diagram of a vehicle including a cruise control system according to one embodiment of the invention, Figure 2 is a schematic diagram of a vehicle including a cruise control 15 system according to a second embodiment of the invention; and Figure 3 is a schematic diagram of part of the cruise control system of Figure 2 in accordance with a modification to the invention.

6- Referring to Figure 1, a vehicle 10 comprises a set of wheels 12 each of which has an associated wheel brake 14. The brakes 14 are operated by hydraulic lines 16 which are selectively supplied with pressure by a brake servo 18.

The brake servo 18 is provided with vacuum assistance from a vacuum tapping 20 which is positioned downstream of a throttle valve 22 included in an inlet manifold 24 of an engine 26. A mechanical vacuum pump 28 is driven by the engine 26 and provides a source of vacuum for the brake servo 18 which is independent of the tapping 20. The vacuum pump 28 could be driven by a different source of mechanical power separate from the engine 26, such as by -a transmission shaft or by a driveshaft (neither shown).

An electronic brake controller (EBQ 32 regulates level of vacuum in the brake servo 18 to control the level of braking pressure produced. To ensure that the level of vacuum assistance is sufficient to provide the control required under substantially all braking conditions within the limits of the available spread in braking pressures, the EBC 32 monitors the vacuum assistance provided by the manifold tapping 20 and the vacuum pump 28. A pressure sensor 30 is included in the brake servo 18 and supplies a feedback signal, indicative of the vacuum available to the brake servo 18, to the EBC 32 for this purpose.

The vacuum assistance provided by the pump 28 to the brake servo 18 is in response to a braking demand signal from a cruise control system 34. The braking demand signal indicates, for example, the beginning of an automatic collision avoidance sequence which requires the use of the brakes 14 and, for example, indicates to the EBC that a predetermined deceleration in the order of 7 MS-2 is required.

When a braking demand signal is received by the EBC 32, it regulates the pump 28 to ensure that sufficient vacuum assistance is available for the I brake servo 18 to perform the necessary braking.

Referring now to Figure 2, a vehicle 100 comprises a set of wheels 120 each of which has an associated wheel brake 140. The brakes 140 are operated by hydraulic lines 160 which are selectively supplied with pressure by a brake servo 180.

The brake servo 180 is provided with vacuum assistance from a vacuum 15tapping 200 which is positioned downstream of a throttle valve 220 included in an inlet manifold 240 of an engine 260. An electrically driven vacuum pump 280 provides a source of vacuum for the brake servo 180 which is independent of the tapping 200.

An electronic brake controller (EBQ 320 regulates level of vacuum in the brake servo 180 to control the level of braking pressure produced. To ensure that the level of vacuum assistance is sufficient to provide the control required under substantially all braking conditions within the limits of the available spread in braking pressures, the EBC 320 monitors the vacuum assistance provided by the manifold tapping 200 and the vacuum pump 280. A pressure sensor 300 is included in the brake servo 180 and supplies a feedback signal, indicative of the vacuum available to the brake servo 180, to the EBC 320 for this purpose.

The vacuum assistance provided by the pump 280 to the brake servo is in response to a braking demand signal from a cruise control system 340. The braking demand signal indicates, for example, the beginning of an automatic collision avoidance sequence which re,quires the use of the brakes 140 and, for example, indicates to the EBC that a predetermined 15 deceleration in the order of 7 MS-2 is required.

When a collision avoidance signal is received by the EBC 320, it regulates the pump 280 to ensure that sufficient vacuum assistance is available for the brake servo 180 to perform the necessary braking.

The advantage of the separate vacuum pump 28, 280 is that it provides 20 a source of vacuum which is independent of the position of the throttle valve 22, 220 so that if it 22, 220 is open, thereby reducing manifold depression, vacuum assistance for the brakes 14, 140 through the brake servo 18, 180 is not reduced.

In both the embodiments described above, the vacuum pump 28, 280 is used to supplement the vacuum produced by the tapping 20, 200 so as to ensure consistent braking under varying conditions of manifold depression in a vehicle 10, 100 equipped with an engine 26, 260 including a throttle valve 22, 220, such as a petrol engine. It would also be possible to eliminate the vacuum tapping 20, 200 and to rely solely on the vacuum pump 28, 280 for all vacuum assistance, in similar fashion to that known for mechanical vacuum pumps on diesel engined vehicles. In that way, a petrol engined vehicle would not suffer reduced vacuum assistance under braking while its throttle valve was partly or fully open.

The vacuum assistance from the vacuum pump 28, 280 could also be used during normal cruise control conditions to refine and improve the regulation of braking under conditions not limited to collision avoidance. Examples of such further uses of the invention are described in more detail below.

Referring now to Figure 3, a close up view of part of the cruise control system of the vehicle 100 of Figure 2 is shown in the region of the brake servo 180 and is in a modified form. The vacuum line from the manifold tapping 200 and the vacuum line from the pump 280 meet at a "Y' piece connection 360, at which point they are united into a combined vacuum line and which then enters the brake servo 180. A motor 380 is under the control of the EBC 320 and selectively drives a flap 400 to close off one or the other of the vacuum lines from the manifold tapping 200 and the pump 280. The vacuum sensor 300 of the modified system is moved from the brake servo 180 to the manifold side of the flap 400 and is arranged to provide feedback to the EBC 320 of the vacuum in the line from the manifold tapping 200 to the "Y' piece 360. The EBC 320 determines the vacuum assistance available for the brake servo 180 from the manifold tapping 200 and if it falls below a sufficient level, in particular during a collision avoidance sequence, the EBC 320 drives the motor 380 to close off the vacuum line from the manifold tapping 200 and at the same time operates the pump 280 to provide an increase in negative pressure available to the brake servo 180.

This modification to the basic principle of the invention helps reduce the likelihood of vacuum being lost through interaction between the brake servo 180 and a manifold 240 in which there is reduced vacuum, e.g. when the butterfly 220 is open there may be interaction between the vacuum line from the pump 280 and the vacuum line from the manifold tapping 200 through the brake servo 180 as the vacuum tries to equalise across the system.

This modification could be applied to the embodiment which employs a mechanically driven vacuum pump by, for example, including an electrically 5 actuated clutch to the pump drive and controlling that clutch using the EBC. The clutch could also be vacuum operated by, for example, being connected to the brake servo so as to disengage the pump when the level of vacuum assistance available to the servo is above a predetermined level and further arranged in use to engage the pump when the level of vacuum assistance available to the brake servo falls below that predetermined level. In similar fashion, it is not essential to use an electrical motor to drive the flap 400, which could easily be driven instead by, for example, an electrical solenoid or a vacuum solenoid connected to the manifold 240 and arranged to close off the vacuum line from the tapping 200 if manifold depression was to fall below a predetermined level.

The invention is not limited to providing improved vacuum assistance only during a collision avoidance sequence. The modification to the invention by which an electrical or vacuum operated clutch is provided allows the mechanically driven pump to have the same level of flexibility as the electrically driven version and either could also be used to boost vacuum in the event of a vacuum leak or so as to provide a substantially consistent level of vacuum to improve refinement in braking operations across substantially the whole range of available braking pressures, but in particular at low brake pressures. For example, at levels of braking pressure in the region of 20 Bar, a variation in braking pressure of plus or minus 2 Bar is often unnoticeable to a user. At lower braking pressures, for example in the region of 5 Bar, a variation in vacuum assistance becomes significantly noticeable and the invention could be used to engage the vacuum pump so as to make vacuum assistance available so that braking pressure can be substantially stabilised and effects of the variation in braking pressure at those lower levels can thereby be reduced. The effect is to make the vehicle appear to the driver to be more refined under braking at lower levels of braking pressure.

The invention should not be considered as limited to the use of a vacuum sensor as means for determining the need for increased vacuum. It would also be possible, for example, to use a brake pressure sensor or a measure of vehicle wheel speed to.determine braking efficiency and from that measurement to derive the need for increased vacuum.

Optionally, a vacuum reservoir 410, shown by way of example in Figure 3 but equally applicable to each embodiment, could be provided to damp out any variations in the vacuum assistance. Such a reservoir would, for example, be particularly useful for damping out any variation in vacuum assistance during the change-over period of a flap as it moves to cut off one or the other of the vacuum pump or the manifold tapping or during a transient period as the vacuum pump was being started.

Claims

- 14CLAIMS

1. A vehicle including an engine having a throttle valve and a cruise control system comprising a vacuum unit arranged in use to provide vacuum assistance for a brake servo of a braking system, wherein the vacuum unit comprises a vacuum pump arranged in use to provide said vacuum assistance independently of the position of said throttle valve.

2. A vehicle according to Claim 1, the vacuum pump comprising a mechanically driven vacuum pump.

3. A vehicle according to Claim 2, wherein the vacuum pump is driven by an engine of the vehicle.

4. A vehicle according to Claim 2 or Claim 3, the vacuum pump comprising a clutch arranged to selectively engage and disengage the pump.

5. A vehicle according to Claim 4, the clutch comprising an electrically operated clutch.

6. A vehicle according to Claim 4, the clutch comprising a vacuum operated clutch which is arranged to disengage the pump when the level of vacuum available to the brake servo is above a predetermined level and to engage the pump when the level of vacuum available to the brake servo falls below said predetermined level.

7. A vehicle according to Claim 1, the vacuum pump comprising an electrically driven vacuum pump.

8. A vehicle according to any preceding claim, wherein the vacuum pump is arranged to produce vacuum at least during a collision avoidance sequence of the cruise control system.

9. A vehicle according to any preceding claim, further comprising a vacuum source which is arranged to supply vacuum assistance for the brake servo from manifold depression.

10. A vehicle according to Claim 9, wherein the level of vacuum assistance from the vacuum pump is regulated to take account of the amount of vacuum assistance produced by the vacuum source.

11. A vehicle according to Claim 9 or Claim 10, further comprising means to vary the level of vacuum assistance provided to the brake servo between vacuum assistance provided by the vacuum pump and vacuum assistance provided by the vacuum source.

16-

12. A vehicle according to Claim 11, the varying means comprising a flap arranged to selectively cut off one of the vacuum pump and the vacuum source from the brake servo.

13. A vehicle according to Claim 11, the varying means comprising a valve arranged to selectively cut off one of the vacuum pump and the vacuum source from the brake servo.

14. A vehicle according to any preceding claim, further comprising a vacuum sensor arranged to provide feedback indicative of the amount of vacuum assistance available to the brake servo to a vacuum controller and wherein the controller is arranged to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

15. A vehicle according to any preceding claim, further comprising a brake pressure sensor arranged to provide feedback indicative of available braking pressure to a vacuum controller and wherein the controller is arranged to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

16. A vehicle according to any preceding claim, further comprising a wheel speed sensor arranged to provide feedback indicative of braking efficiency to a vacuum controller and wherein the controller is arranged 17- to regulate the vacuum assistance produced by the vacuum pump in response to said feedback.

17. A vehicle according to any preceding claim, wherein the vacuum pump is arranged to provide vacuum assistance for the brake servo such that braking pressure can be maintained at a substantially constant level for substantially any level of braking pressure within a predetermined range of braking pressures, whereby variation in braking pressure caused by a variation in vacuum assistance can be compensated for so as to improve driving refinement.

18. A vehicle according to any preceding claim, further comprising a vacuum reservoir arranged to damp out a variation in vacuum available to the brake servo.

19. A vehicle according to Claim 18 when dependent on Claim 11, wherein the vacuum reservoir is arranged to damp out variations in the vacuum assistance during a variation in the level of vacuum assistance provided by the vacuum pump.

20. A vehicle according to Claim 18 when dependent on Claim 12 or Claim 13, wherein the vacuum reservoir is arranged to damp out variations in the vacuum assistance during at least part of the period during which the varying means moves to cut off one of the vacuum pump and the vacuum source from the brake servo.

21. A vehicle substantially as described herein with reference to Figure I or Figure 2 or Figures 2 and 3 of the accompanying drawings.

22. A cruise control system for a vehicle according to any preceding claim.

23. A vacuum pump for a cruise control system according to Claim 22.

24. A controller for a cruise control system according to Claim 22.

25. A vacuum reservoir for a cruise control system according to Claim 22.