GB1604416A - Vehicle suspension system - Google Patents

Description

(54) VEHICLE SUSPENSION SYSTEM (71) We, LUCAS INDUSTRIES LIMITED, a British Company, of Great King Street, Birmingham B 19 2XF, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to vehicle suspension systems and is modification of the system disclosed and claimed in our British Patent No. 1,555,124 filed 7th June, 1975.

A system in accordance with one aspect of the present invention comprises a plurality of hydro-pneumatic suspension units, one for each of the respective wheels of the vehicle, each such unit including a cylinder and a piston slidable therein, one of the two parts comprising the piston and the cylinder being mounted on the vehicle body and the other being supportingly connected to the vehicle wheel, a dividing wall in said cylinder dividing a portion of the cylinder in which the piston is slidable from another portion thereof which is held under pressure by pneumatic pressurising means, a damping control valve connecting said one portion of the cylinder to said other portion thereof, said damping control valve being electrically controlled, a plurality of electrohydraulic pressure transducer means each arranged to sense the hydraulic pressure in said one portion of an associated one of the cylinders, a plurality of wheel velocity transducers associated with the respective suspension units and each producing an electrical output corresponding to the velocity of movement of the associated wheel axis relative to the body, and control means receiving input signals from the pressure transducer means and the velocity transducers and controlling said damping control valves to vary the damping effect of each damping control valve so as to establish a desired functional inter-relationship between the pressure and velocity signals.

In accordance with another aspect of the present invention there is provided a vehicle suspension system comprising a plurality of hydraulic suspension units, one for each of the respective wheels of the vehicle, electrohydraulic transducer means associated with each hydraulic suspension unit and producing an electrical output corresponding to the hydraulic pressure in the associated suspension unit, a plurality of velocity transducers associated respectively with the suspension units and each producing an output corresponding to the velocity of movement of the associated wheel axis relative to the vehicle body, a plurality of damping control valves associated respectively with the respective suspension units and control means for the damping control valves, said control means having inputs from the pressure transducer means and the velocity transducers and providing outputs to vary the damping effect of each damping valve so as to establish a desired functional inter-relationship between the pressure and velocity outputs, and said control means further including means sensitive to said pressure outputs for overridingly opening the damping control valve of any of the suspension units when the pressure in such suspension unit is above a predetermined upper limit or below a predetermined lower limit.

An example of the invention is shown in the accompanying drawings in which: Figure 1 is a diagrammatic representation of one of a plurality of hydropneumatic suspension units used in the system, Figure 2 is a block diagram of the electrical control arrangement used in the system and Figure 3 is a circuit diagram of a pressure control shown in Figure 2.

The unit shown in Figure 1 includes a cylinder 10 in one portion 11 of which a piston 12 is slidable. The cylinder 10 is mounted on the vehicle body and the piston 12 is mounted on a wheel carrier 13 so that the unit transmits the weight of the vehicle to the wheels 14. The cylinder 10 has another portion 15 separated from the portion 11 by a dividing wall 16 and closed off by a flexible diaphragm 17 separating the portion 15 from a pressurised gas chamber 18. the gas acting to provide resilience.

Communication between the portions 11 and 15 is via an electrically controlled damping control valve 19.

An hydraulic pressure transducer 20 is associated with the unit and is arranged to sense the hydraulic pressure in the first mentioned portion 11 of the cylinder, such pressure being indicative of the force being carried by the unit in question. Each unit also has associated with it a velocity transducer 21 which produces an electrical output signal corresponding to the vertical component of the velocity of the wheel carrier 13 relative to the vehicle body. Such transducer 21, may of course, be a position transducer associated withan electronic differentiating circuit.

The transducers 20a to 20dand 21a to 21d associated with the four wheels of the vehicle all provided input signals to a common electronic control circuit controlling the damping control valves 19a to l9d. The circuit is the same as that described in Patent No. 1,555,124, with the exception that a pressure control 60 for each channel is added.

The pressure control 60a, as shown in Figure 3, comprises two comparators 61a, 62a connected to detect when the pressure signal from the associated pressure transducer 20a is above an upper limit and below a lower limit respectively. The outputs of the comparators 61 a, 62a are combined by an OR gate 63a the output of which is applied to a trigger circuit 64a with hysteresis to prevent spurious triggering by interference pulses.

The output of the trigger circuit 64a is connected via an absolute value circuit 65a to the output amplifier of the associated channel.

The result of this added circuit in each channel is firstly to limit the pressure which can be reached in each hydro-pneumatic suspension unit to a level at which no damage is suffered by the unit by overridingly opening the damping control valve. In addition in the event of very low pressure being detected, indicating that the wheel in question has lost contact with the ground, the damping control valve is overridingly opened to allow the wheel to move rapidly back into contact with the ground. The lower limit can be set lower than the pressure which exists in the suspension unit when that unit is fully extended (even though the wheel is out of contact with the ground), so as to override the normal control only when the wheel is off the ground and travelling freely.

WHAT WE CLAIM IS:- 1. A vehicle suspension system comprises ing a plurality of hydro-pneumatic suspension units, one for each of the respective wheels of the vehicle, each such unit including a cylinder and a piston slidable therein, one of the two parts comprising the piston and the cylinder being mounted on the vehicle body and the other being supportingly connected to the vehicle wheel, a dividing wall in said cylinder dividing a portion of the cylinder in which the piston is slidable from another portion thereof which is held under pressure by pneumatic pressurising means, a damping control valve connecting said one portion of the cylinder to said other portion thereof, said damping control valve being electrically controlled, a plurality of electrohydraulic pressure transducer means each arranged to sense the hydraulic presure in said one portion of an associated one of the cylinders, a plurality of wheel velocity transducers associated with the respective suspension units and each producing an electrical output corresponding to the velocity of movement of the associated wheel axis relative to the body, and control means receiving input signals from the pressure transducer means and the velocity transducers and controlling said damping control valves to vary the damping effect of each damping control valve so as to establish a desired functional inter-relationship between the pressure and velocity signals.

2. A vehicle suspension system comprising a plurality of hydraulic suspension units, one for each of the respective wheels of the vehicle, electro-hydraulic transducer means associated with each hydraulic suspension unit and producing an electrical output corresponding to the hydraulic pressure in the associated suspension unit, a plurality of velocity transducers associated respectively with the suspension units and each producing an output corresponding to the velocity of movement of the associated wheel axis relative to the vehicle body, a plurality of damping control valves associated respectively with the respective suspension units and control means for the damping control valves, said control means having inputs from the pressure transducer means and the velocity transducers and providing outputs to vary the damping effect of each damping valve so as to establish a desired functional inter-relationship between the pressure and velocity outputs, and said control means further including means sensitive to said pressure outputs for overridingly opening the damping control valve of any of the suspension units when the pressure in such suspension unit is above a predetermined upper

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. mounted on the vehicle body and the piston 12 is mounted on a wheel carrier 13 so that the unit transmits the weight of the vehicle to the wheels 14. The cylinder 10 has another portion 15 separated from the portion 11 by a dividing wall 16 and closed off by a flexible diaphragm 17 separating the portion 15 from a pressurised gas chamber 18. the gas acting to provide resilience. Communication between the portions 11 and 15 is via an electrically controlled damping control valve 19. An hydraulic pressure transducer 20 is associated with the unit and is arranged to sense the hydraulic pressure in the first mentioned portion 11 of the cylinder, such pressure being indicative of the force being carried by the unit in question. Each unit also has associated with it a velocity transducer 21 which produces an electrical output signal corresponding to the vertical component of the velocity of the wheel carrier 13 relative to the vehicle body. Such transducer 21, may of course, be a position transducer associated withan electronic differentiating circuit. The transducers 20a to 20dand 21a to 21d associated with the four wheels of the vehicle all provided input signals to a common electronic control circuit controlling the damping control valves 19a to l9d. The circuit is the same as that described in Patent No. 1,555,124, with the exception that a pressure control 60 for each channel is added. The pressure control 60a, as shown in Figure 3, comprises two comparators 61a, 62a connected to detect when the pressure signal from the associated pressure transducer 20a is above an upper limit and below a lower limit respectively. The outputs of the comparators 61 a, 62a are combined by an OR gate 63a the output of which is applied to a trigger circuit 64a with hysteresis to prevent spurious triggering by interference pulses. The output of the trigger circuit 64a is connected via an absolute value circuit 65a to the output amplifier of the associated channel. The result of this added circuit in each channel is firstly to limit the pressure which can be reached in each hydro-pneumatic suspension unit to a level at which no damage is suffered by the unit by overridingly opening the damping control valve. In addition in the event of very low pressure being detected, indicating that the wheel in question has lost contact with the ground, the damping control valve is overridingly opened to allow the wheel to move rapidly back into contact with the ground. The lower limit can be set lower than the pressure which exists in the suspension unit when that unit is fully extended (even though the wheel is out of contact with the ground), so as to override the normal control only when the wheel is off the ground and travelling freely. WHAT WE CLAIM IS:-

1. A vehicle suspension system comprises ing a plurality of hydro-pneumatic suspension units, one for each of the respective wheels of the vehicle, each such unit including a cylinder and a piston slidable therein, one of the two parts comprising the piston and the cylinder being mounted on the vehicle body and the other being supportingly connected to the vehicle wheel, a dividing wall in said cylinder dividing a portion of the cylinder in which the piston is slidable from another portion thereof which is held under pressure by pneumatic pressurising means, a damping control valve connecting said one portion of the cylinder to said other portion thereof, said damping control valve being electrically controlled, a plurality of electrohydraulic pressure transducer means each arranged to sense the hydraulic presure in said one portion of an associated one of the cylinders, a plurality of wheel velocity transducers associated with the respective suspension units and each producing an electrical output corresponding to the velocity of movement of the associated wheel axis relative to the body, and control means receiving input signals from the pressure transducer means and the velocity transducers and controlling said damping control valves to vary the damping effect of each damping control valve so as to establish a desired functional inter-relationship between the pressure and velocity signals.

2. A vehicle suspension system comprising a plurality of hydraulic suspension units, one for each of the respective wheels of the vehicle, electro-hydraulic transducer means associated with each hydraulic suspension unit and producing an electrical output corresponding to the hydraulic pressure in the associated suspension unit, a plurality of velocity transducers associated respectively with the suspension units and each producing an output corresponding to the velocity of movement of the associated wheel axis relative to the vehicle body, a plurality of damping control valves associated respectively with the respective suspension units and control means for the damping control valves, said control means having inputs from the pressure transducer means and the velocity transducers and providing outputs to vary the damping effect of each damping valve so as to establish a desired functional inter-relationship between the pressure and velocity outputs, and said control means further including means sensitive to said pressure outputs for overridingly opening the damping control valve of any of the suspension units when the pressure in such suspension unit is above a predetermined upper

limit or below a predetermined lower limit.

3. A vehicle suspension system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.