A method of operating a vehicle, said method comprising the steps of:
- (a) providing an engine mounted in said vehicle and coupled to at least one vehicle wheel for its propulsion and braking, said engine including:
- (1) at least two cylinders and a cylinder chamber within each of said at least two cylinders, said at least two cylinders including at least one primary cylinder and at least one secondary cylinder,
- (2) a head mounted to said at least two cylinders, and
- (3) a piston in each of said at least two cylinders, with the piston to head and cylinder relationship being such that the volume of said cylinder chamber shrinks during a volume-decreasing stroke when said piston moves towards said head, and expands during a volume-increasing stroke, when said piston moves away from said head,
- (b) providing a control means for controlling the operation of said engine and said vehicle in response to driver's demands and in accordance with a control program incorporated in said control means,
- (c) providing a gas-transfer means for transferring gas between said at least one primary cylinder and said at least one secondary cylinder,
- (d) providing a gas exchange controlling means for selectively, variably, and alternatively connecting said at least two cylinders to outside atmosphere and to said gas-transfer means, in timed relation to said engine operation,
- (e) responding to a demand for a vehicle propulsion force by operating said engine in a mode selected from a set of propulsion modes in accordance with said control program, said set of propulsion modes comprising a two-stage gas-expansion mode, said two-stage gas-expansion mode including the steps of:
- (1) repeatedly performing a four-stroke internal combustion cycle in said at least one primary cylinder, said four-stroke internal combustion cycle including the steps of:
- (A) receiving air and fuel into said at least one primary cylinder during a first volume-increasing stroke,
- (B) compression of said air inside said at least one primary cylinder during a first volume-decreasing stroke,
- (C) combustion of air and fuel mixture inside said at least one primary cylinder, whereby said air and fuel mixture is converted into a combustion gas inside said at least one primary cylinder,
- (D) expansion of said combustion gas inside said at least one primary cylinder during a second volume-increasing stroke, said expansion being terminated without a gas blow-down at the end of said second volume-increasing stroke, whereby said combustion gas performs useful mechanical work on a piston and still remains pressurized at the end of said second volume-increasing stroke, and
- (E) expulsion of pressurized combustion gas from said at least one primary cylinder into said gas-transfer means during a second volume-decreasing stroke, said expulsion being performed without a reduction in said pressurized combustion gas pressure, whereby said pressurized combustion gas still retains a substantial amount of internal energy that was not dissipated during a blowdown,
- (2) using said gas-transfer means for transferring said pressurized combustion gas from said at least one primary cylinder into said at least one secondary cylinder, said transferring being performed without any increase in said pressurized combustion gas pressure and temperature and without adding additional air and fuel, and
- (3) repeatedly performing a two-stroke gas-expansion cycle in said at least one secondary cylinder, said two-stroke gas-expansion cycle taking place during one engine revolution and two said two-stroke gas-expansion cycles taking place in said secondary cylinder during time it takes for one four-stroke internal-combustion cycle in said primary cylinder, said two-stroke gas-expansion cycle including the steps of:
- (A) receiving said pressurized combustion gas from said transfer means into said at least one secondary cylinder during a first part of a volume-increasing stroke, volume of said pressurized combustion gas received into said secondary cylinder during two two-stroke cycles being not greater than volume displaced from said primary cylinder during each four-stroke cycle,
- whereby only a first part of the piston stroke is needed to receive said pressurized combustion gas into said secondary cylinder and a second part of said piston stroke is available to perform further gas expansion, and
- whereby said at least one secondary cylinder becomes filled with combustion gas only and no additional air and fuel are added to its content,
- (B) performing a further expansion of said pressurized combustion gas in said at least one secondary cylinder during a second part of said volume-increasing stroke, said further expansion being performed without being preceded by gas compression and combustion in said secondary cylinder, whereby there is no combustion in said at least one secondary cylinder, and whereby useful mechanical work performed on a piston in said at least one secondary cylinder uses only internal energy still retained in said pressurized combustion gas after its expulsion from said at least one primary cylinder, and
- (C) expelling said combustion gas from said at least one secondary cylinder during a volume-decreasing stroke,
- whereby said further expansion of said combustion gas in said at least one secondary cylinder extracts additional useful energy from said combustion gas without using additional fuel energy, and
- whereby said engine fuel consumption is reduced.