Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2000-02-04
2001-08-07
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S070000, C701S073000, C701S080000, C303S121000, C303S122060, C303S122090, C477S182000
Reexamination Certificate
active
06272417
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a vehicle braking system having at least two wheels which are braked by fluid brake pressure. The braking system may comprise at least one brake control channel. The or each brakes channel may comprise a controller responsive to wheel skid signals from at least two wheel speed sensors, for sensing speed conditions of at least two wheels and for generating skid control instructions, a plurality of wheel brakes responsive to fluid brake pressure, supplied thereto, a supply means, comprising a common supply valve, for supplying brake pressure to said brakes from a fluid pressure supply in accordance with a brake operating signal and a skid control means controlled by said skid control instructions for controlling the brake pressure in a plurality of cycles each of which comprises a pressure reduction phase and a pressure increase phase and may also comprise a pressure hold phase between the pressure reduction and increase phases.
For example, the or each channel may comprise two wheels at opposite ends of a common axle or may comprise two wheels at the same end of different axles. The wheels may be of any type, e.g. driven, steered or load carrying.
When a “split co-efficient of friction situation” arises, i.e. when one wheel of a channel is engaged with a surface having a co-efficient of friction which is higher (higher friction surface) than the co-efficient of friction of a surface with which another wheel is engaged (lower friction surface), it has been known to select one of the wheels as the wheel which controls the operation of the skid control means. If the wheel engaged with the or a lower friction surface is selected (known as “low mode”) then, when the brakes are applied, the skid control means is operated, in dependence on the controller detecting a skid condition of the wheel engaged with the lower friction surface, to cause the common supply valve to control brake pressure to reduce the braking effect on all the wheels of the channel. Where the channel comprises more than two wheels normally the skid control means is controlled by the wheel engaged with the lowest friction surface, i.e. the first wheel to skid. However, if desired, any surface other than the highest friction surface may be selected if desired and such surface is referred to herein as the lower friction surface.
In a low mode the controller controls the brake pressure of the wheels in accordance with skid conditions of the wheel engaged with the lower friction surface. This causes a reduction in the braking effect of the wheel(s) engaged with the or each higher friction surface so that overall braking effect is reduced and the retardation is approximately equivalent to the wheels being engaged with the lower friction surface.
Alternatively, if the wheel engaged with a higher friction surface is selected (known as “high mode”), then when the brakes are applied the skid control means is operated in dependence on the controller detecting a skid condition of the wheel engaged with the higher friction surface, to cause the common supply valve to control brake pressure to reduce the braking effect of the wheels.
When the channel comprises more than two wheels normally tie skid control means is controlled by the wheel engaged with the highest friction surface, i.e. when all the wheels have skidded. However, if desired, any surface other than the highest friction surface may be selected if desired and such surface is referred to herein as the higher friction surface.
In a high mode the controller controls the brake pressure of the wheels in accordance with skid conditions of the wheel engaged with the higher friction surface. This causes the wheel(s) on the or each lower friction surface to continue to skid. In these circumstances, the wheel(s) engaged with the or each lower friction surface provides little stability, although by providing skid control to the wheel(s) engaged with the higher friction surface(s) retardation is maximised from the wheel(s) engaged with the higher friction surface(s) and overall stability is maintained.
A control system which is able to change from a select low mode to a high mode depending upon prevailing surface conditions would have the benefits of low mode on homogeneous low and narrow split friction surfaces and the benefit of high mode on wider split friction surfaces.
The principal of changing control mode requires a plurality of problems to be overcome. For example, at least one of:
the ability to recognise different road surface friction;
the ability to establish a relationship between the reaction of a wheel of the vehicle to low friction and high friction surfaces;
provision of adequate brake pressure, which is load and road surface dependant, available at the brake to enable the adhesion to be utilised before changing logic;
the effect of load on wheel reaction,
the ability to react to changes in driver demand during a stop.
The ability to react to changes in road surface, for example, homogeneous to split friction and split friction to homogeneous friction during a stop.
The only information available to make the above decisions is wheel speed of which there are three parameters that can be utilised, namely:
rate of wheel deceleration
rate of wheel acceleration
speed differences between an actual wheel speed and a notional wheel speed if there were no wheel slip relative to the road i.e. equivalent to vehicle speed.
An object of the invention is to provide a new and improved vehicle braking system whereby the above mentioned problems are overcome or reduced.
According to one aspect of the present invention we provide vehicle braking system comprising;
means, in an initial anti-skid cycle, to perform a first determination to select a high or a low control mode in accordance with wheel speed parameters;
means in a second, or subsequent anti-skid cycle, to perform a second determination to determine whether a near &mgr; test is to be performed in accordance with wheel speed parameters,
means, consequent upon selection of low control mode to perform the near &mgr; test comprising performing a rise in the brake pressure and then selecting a high or low mode in accordance with the speed of the wheels resulting from said rise in brake pressure in the near &mgr; test.
Said rise in brake pressure may be a controlled rise.
Said selection of mode as a result of the near &mgr; test may comprise performing said first determination.
Said selection of mode may be performed in the first cycle following the near test and said second determination may be performed in a following cycle or cycles.
In said first determination at least one of the following steps may be performed;
determine which wheel first achieves a pre-determined detection threshold, and nominate it the low wheel,
determine the deceleration of low wheel,
determine the acceleration of low wheel,
determine the slip of the other, high, wheel,
determine the acceleration of the other, high, wheel,
determine the ratio of accelerations of said low and high wheel and select a high/modified select high or a low control mode in accordance therewith.
Where said first determination results in a low mode, in a subsequent anti-skid cycle, said second determination may be performed.
In said second determination the following steps may be performed;
ascertain whether slip of said high wheel is below a threshold,
determine the slip of the low wheel,
determine the acceleration of the low wheel,
determine the acceleration of the high wheel,
determine the ratio of accelerations of the low and high wheels,
determine whether or not a near &mgr; test is to be performed in accordance therewith.
In an anti-skid cycle in which brake pressure in increased in steps by means comprising a solenoid which is intermittently de-energized the system may comprise means to,
determine a time T
1
for which the solenoid is de-energised in a first step of the anti-skid cycle,
and means to perform said near &mgr; test by de-energising said solenoid for a time T=T
1
+T
c
, where Tc is a constant.
A
Harrison Dudley J.
Ross Colin F.
Augustyn John M.
Beaulieu Yonel
Cuchlinski Jr. William A.
Haldex Brake Products Limited
Leydig , Voit & Mayer, Ltd.
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