GB2170155A

GB2170155A - Suspension control system

Info

Publication number: GB2170155A
Application number: GB08600909A
Authority: GB
Inventors: Alan Peter Ogburn; John Howard Moore
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1985-01-29
Filing date: 1986-01-15
Publication date: 1986-07-30
Also published as: GB8600909D0; GB8502135D0; GB2170155B

Abstract

A control system for a vehicle suspension system of the so-called self levelling type includes height sensors responsive to the height of the vehicle from the ground in the vicinity of the vehicle wheels and electromagnetic devices operable to adjust said heights. The system includes means responsive to the rate of height adjustment and means for providing a signal indicative of rapid wheel movement, for assessing the condition of the shock absorbers of the vehicle.

Description

SPECIFICATION Control system This invention relates to a control system for a vehicle suspension system of the so-called self levelling type which includes a plurality of height sensors positioned so as to be responsive to the heights of the vehicle from the ground in the vicinity of the vehicle wheels and a plurality of electromagnetic devices which are operable to enable the actual heights to be varied. The height of the vehicle can be made to be substantially independent of the loading of the vehicle and in particular, uneven loading of the vehicle.

Each wheel suspension unit may include a fluid pressure responsive device such as an air spring the pressure in which can be varied by actuation of electromagnetic valves. Each suspension unit will also include a shock absorber which may be of the hydraulic type, the purpose of which is to damp the relative movement of the wheel associated with the suspension unit and the vehicle chassis.

The essential requirement of the control system is to maintain the vehicle height irrespective of the loading and this requirement is best achieved electronically using a microprocessor. It is possible to build into the system certain features such for example as the ability of the driver of the vehicle to select maximum height for the purpose of ensuring that the vehicle will clear an obstacle, and adjustable height so that the driver can trim the vehicle height to correspond to that of a loading bay.

With all these features it is necessary to provide a warning to the driver which indicates when a special feature is selected and it is also necessary to provide some warning to the driver in the event of a fault developing in the sytem which may not be immediately apparent. Such a fault could for example be a faulty shock absorber.

According to the invention a control system for a vehicle suspension system of the so-called self levelling type and which includes a plurality of height sensors positioned so as to be responsive to the heights of the vehicle from the ground in the vicinity of the vehicle wheels and a plurality of electromagnetic devices associated with wheel suspension units respectively for the vehicle wheels, the suspension units incorporating shock absorbers respectively, the control system in response to the signals from the sensors, acting to control the electromagnetic devices so that the.vehicle height is maintained at a substantially constant level, said control system including means for monitoring the rate of wheel movement and for providing a signal indicative of rapid wheel movement whereby the condition of the shock absorbers can be assessed.

The accompanying block diagram illustrates an example of a control system and with reference to the diagram there is provided a mircoprocessor 20 associated with which is a memory unit 21 and a programmable interface unit 22. The memory unit is of the EPROM type in which is stored the operating program for the mircoprocessor and the application data.

The interface unit 22 has outputs connected to a solenoid interface unit 23 which has outputs 24 connectd to solenoid controlled ON/OFF valves controlling the flow of air into and out of the air springs. Two further valves are provided and are connected to outputs 25, 26 which control air flow into and out of the springs by way of the first mentioned valves. There are four outputs 24 corresponding to four suspension units in the particular example. It will thus be seen that the air pressure in the suspension units can be altered to vary the height of the vehicle so that it corresponds to a set value contained in the memory unit 21.

In the example the interface unit 22 is connected to another interface unit 27 associated with which are digital optical sensors. The sensors produce a digital signal when interrogated by a signal at an output 28 the digital signal being returned to the interface unit 27 through an input 29. The selection of which sensor is interrogated is achieved using selection signals at outputs 30.

As an alternative to using digital optical sensors, potentiometer type sensors may be utilised in which case the interface unit 27 and an associated power supply 31 need not be provided. Instead an analogue/digital converter 32 is provided which receives the signals from the sensors through an interface unit 33. The analogue signals provided by the sensors are converted by the converter 32 and are used in the same way as the signals provided by the optical sensors.

Various other inputs to the control system are effected through the interface unit 33. For example input 35 is from a switch which can be operated to lift the vehicle to its maximum height this facility being brought into operation when for example, it is desired to drive the vehicle over an obstacle such as a ferry ramp. Input 36 is from a three posi tion switch which can be used by the driver to trim the height of the vehicle to the height of a loading bay. If the system is maintained in operation while loading or unloading takes place, the vehicle height will automatically adjust to compensate for lod variation.

When the system is operated in other than its normal mode a warning lamp 37 in the cab of the vehicle is illuminated. The lamp signal is supplied through the interface 22 and in the lamp circuit is a feedback device 38 which provides a feedback signal indicative of lamp operation by way of the interface 33.

Forming part of the system is a watchdog timer 39 of conventional type which receives pulses from the interface 22 when the processor is functioning correctly. In the event that these pulses cease due to some malfunction the timer will reset the processor 20.

The system can be used to check the function of the shock absorbers. A sound shock absorber will limit the rate at which height adjustment can take place whereas a failed shock absorber will provide a much reduced damping action. If therefore a check is made as to the extent of height variation within a predetermined time an assessment can be made as to the condition of the shock absorbers.

The test can take place during normal suspension movement, the sensors being interrogated many times per second to provide detection of rapid height variation or wheel movement indicative of a faulty shock absorber.

If a fault is detected of whatever nature the warning lamp will flash. However, since there are many types of fault it is important that the driver should be capable of being informed as to the nature and location of the fault. For this purpose a switch is provided which is connected to an input 40 of the interface unit 33, and which when operated causes the lamp to flash a number of times.

By counting the flashes and by reference to a manual the driver can determine the location of the fault.

The system is provided with a fault storage facility which can be interrogated to determine what faults if any have taken place during the use of the system. The interrogation may be achieved using a further interface unit 41. In this connection the interface units 23 and 27 have fault feedback connections to the interface 22.

Claims

1. A control system for a vehicle suspension system of the so-called self levelling type and which includes a plurality of height sensors positioned so as to be responsive to the heights of the vehicle from the ground in the vicinity of the vehicle wheels and a plurality of electromagnetic devices associated with wheel suspension units respectively for the vehicle wheels, the suspension units incorporating shock absorbers, the control system in response to the signals from the sensors, acting to control the electromagnetic devices so that the vehicle height is maintained at a substantially constant level, said control system including means for monitoring the rate of wheel movement and for providing a signal indicative of rapid wheel movement whereby the condition of the shock absorbers can be assessed.

2. A control system according to Claim 1 in which the monitoring of the rate of wheel movement for the purpose of determining the condition of the shock absorbers takes place during height adjustment

3. A control system according to Claim 1 or Claim 2 including means for providing a warning signal in the event that the rate of movement exceeds a predetermined value.

4. A control system according to Claim 1 or Claim 2 including means operable by the driver of the vehicle to cause adjustment of the height of the vehicle.

5. A control system according to Claim 3 in which the warning signal is provided by a warning lamp.

6. A control system according to Claim 5 including means for monitoring the operation of the sensors and electromagnetic devices and in the event of malfunction causing operation of said warning lamp.

7. A control system according to any one of the preceding claims including means for storing a record of system faults and further means through which said record can be interrogated.

8. A control system for a vehicle suspension system substantially as hereinbefore described with reference to the accompanying drawings.