WO1989009703A1

WO1989009703A1 - Height regulating system for a vehicle with air suspension

Info

Publication number: WO1989009703A1
Application number: PCT/EP1988/000315
Authority: WO
Inventors: Jürgen PISCHKE
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-04-14
Filing date: 1988-04-14
Publication date: 1989-10-19
Anticipated expiration: 1990-10-14

Abstract

In a height regulating system for a vehicle having an air spring suspension system with height regulation by comparator arrangements (52, 53) with delay in filters (50, 51), unfiltered variations in height (h and hr) at opposite ends of the axle (12) are compared with the desired height (ho) in further comparator arrangements (54, 55). The automatic height regulation is disabled on cornering in that the increase in measured height at one side of the vehicle simultaneously with a decrease at the other side produces an inhibit signal via gates (60, 61, 62). This inhibit signal is fed to the control computer (44) which also further delays re-establishment of height regulation after disappearance of the inhibit signal.

Description

HEIGHT REGULATING SYSTEM FOR A VEHICLE WITH AIR SUSPENSION

STATE OF THE ART

The present invention relates to a height regulating system of the kind described in the pre-characterizing clause of claim 1. Such a system is known from EP-A-0091 017 wherein compressed air is admitted to the air spring when a distance sensor senses that the height of the vehicle body is below a threshold and air is released from the air spring when the distance sensor senses that the body height is above the threshold.

It is desirable to render the height regulation inoperative when cornering and to re-establish the height regulation after the end of the cornering manoeuvre. Otherwise there is an unnecessary compressed air and energy consumption and unsafe driving conditions can arise. It has been proposed to arrange a mercury switch so as to respond to transverse acceleration. Such a switch must be arranged to open a contact responsively to acceleration forces transversely in either direction, opening of such contact acting to prevent the control device from opening the solenoid valve arrangement. Mercury switches have several disadvantages. They are difficult to mount accurately and fracture of their glass envelope releases mercury which is poisonous and damaging to the environment.

It is an object of the present invention to provide improved measures for rendering the height regulation in an air spring suspension system inoperative when cornering. ADVANTAGES OF THE INVENTION

The above disadvantages can be avoided by adopting the features set forth in the characterizing clause of claim 1. No additional mechanical components are required and all that are needed are a few extra simple electronic components. By adopting the feature of claim 2, it can be ensured that the height regulation is not re-established until well after completion of most cornering operations. DRAWINGS

The invention is further described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a diagram of an air spring suspension system for a vehicle fitted with height regulation; and

Fig. 2 is a block diagram of the height regulating system which can be disabled on cornering in accordance with the invention. DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Fig. 1 shows diagrammatically a part of a vehicle body 10 attached to an axle 12 by an air spring suspension system. The air spring suspension system comprises at each end of the axle 12 an air spring bellows 16,17, and a height measuring sensor 20,21, each arranged between the respective side of the vehicle body 10 and the respective end of the axle 12. Each height measuring sensor 20,21 can be a simple potentiometer or variable resistor or an inductive transducer. The air spring bellows 16,17 are filled and emptied as required by a compressed air reservoir 22 and respective solenoid valve arrangements 24,25. The reservoir 22 is charged from a compressor (not shown) via a line 26 containing a non-return valve 28. Each valve arrangement 24,25 comprises a 3-port, 2- position valve 30,31 and a 2-port, 2-position valve 32,33 in a line 34,35 between the reservoir 22 and the respective suspension bellows 16,17. The valves are spring-biased to their positions shown and are operated by solenoids 36,38 or 37,39. Actuation of both valves 30,32 or 31,33 of a valve arrangement 24 or 25 connects the air spring bellows 16 or 17 to the reservoir 22 in order to feed compressed air to the bellows 14 or 15 and thereby increase the height h_e or h_r of the vehicle body 10 relative to the axle 12 at the left-hand or right-hand side of the vehicle, respectively. Actuation of the valve 32 or 33 alone connects the air spring bellows 16 or 17 via the unactuated valve 30 or 31 to exhaust and thereby decrease the height _e or h_r of the vehicle body 10 at the respective side.

Referring to Fig. 2, each height sensor 20,21 is connected via a respective filter 50,51 to a respective comparator arrangement 52,53. Each comparator arrangement 52 comprises two comparators of which one responds when the smoothed height NIV_e or NIV_r rises above a threshold h and the other responds when the smoothed height NIV_e or NIV_r is below a threshold h 2 - The desired height of h₀ lies in the "dead" range between hi and h2 and this "dead" range is no more than is necessary to provide a response hysteresis and so avoid an excessive number of opening and closing operations of the valves.

The outputs of the four comparators are connected to a control computer 44 which controls the energisation of the valve solenoids 36,38 and 37,39 via respective end stage amplifiers 46,48 and 47,49.

Upon an increase in load at, say, the left-hand end of the axle 10, the measured height h_e temporarily decreases to a value below t^**2 and the control computer 44 responds to open both of the solenoid valves 30 and 32 to admit compressed air to the left-hand air spring bellows 16 and so raise the vehicle body back to the desired height h₀ at that side.

The filters 50,51 having a time constant t serve to smooth the signals h_e and h_r to prevent response to oscillations which can be generated when driving on a rough road or over a pothole.

When driving at speed around a relatively sharp bend, the vehicle tends to tilt outwards, thereby decreasing the height at one side and increasing it at the other. That is to say, for a right-hand bend h_e < h₂ and h_r > h_j . But for the measures to be described, this would result in compensatory height regulation at both sides of the vehicle. However,

- 4 compensation in an opposite sense is then necessary after coming out of the bend. This would lead to an unnecessary consumption of compressed air and may cause a dangerous swaying motion of the vehicle.

To avoid these problems, the height regulation is disabled when cornering. For this purpose, the height sensors 20 and 21 are connected directly to further comparator arrangements 54,55 respectively. That is to say, there is no interposed filter or delay circuit. Each comparator arrangement 54,55 receives the reference height signals hχ,h2 and comprises two comparators 56,58 or 57,59 respectively. The comparators 56, 57, 58 and 59 respond respectively when h_e > hi, h_r > hi, h_e < h2 and h_r < h2 . The outputs of the comparators 56,58,57,59 are connected respectively to a first input of an AND gate 60, a first input of an AND gate 61, a second input of the AND gate 61 and a second input of the AND gate 60. The outputs of the AND gates 60 and 61 are connected via an OR gate to the control computer 44. Thus, when h_e < 2 and simultaneously hr > hi, as when taking a right-hand bend, the comparators 58 and 57 supply signals to both inputs of the AND gate 61 which signals the control device 44 via the OR gate 62 to inhibit height regulation. Because of the filters 50 and 51, such inhibit signal acts on the control computer 44 before the correction signals h2 - NIV_e and NIV_r - h i reach the control computer from the comparator arrangements 52 and 53.

So long as an inhibit signal is present at the output of the OR gate 62, the inhibition of the height regulation is continued. When the driver comes out of the bend, the vehicle levels out and the inhibit signal disappears from the output of the OR gate 62. However, the control computer 44 contains a delay device to prevent re-establishment of height regulation until a predetermined time interval after removal of the inhibit signal has elapsed. This allows time for any swaying motion of the vehicle as it comes out of the bend to die away before the height regulation again becomes operative.

Claims

1. Height regulating system for a vehicle with air suspension comprising solenoid valve arrangements (24,25) for admitting compressed air to and releasing air from the air springs (16,17), sensors (20,21) for measuring the height (h_e,h_r) between a respective wheel axle (12) and the vehicle body (10) at opposite ends of the axle, a control device (44) for operating the valve arrangements (24,25) responsively to the differences (h_e - h₀, h_r - h₀) between the measured heights and a desired height (h₀), filter circuits (40,41) for delaying the response of the control device (44) and an inhibiting device for rendering the height regulation inoperative when cornering, characterized in that the inhibiting device ascertains the differences (h _e- h₀, h_r - h₀) between the measured heights and the desired height, but without any filtering, and responds when differences are produced at both ends of the axle (12) and these differences are opposite in sense.

2. Height regulating system according to claim 1, in which the control device (44) is programmed to delay the re- establishment of height regulation for a predetermined time after termination of its inhibition by the inhibiting device.